HK1088715B - Single crystal gallium nitride substrate, method of growing the same and method of producing the same - Google Patents

Description

Single crystal gallium nitride substrate, method for growing same, and method for manufacturing same

Technical Field

The present invention relates to a single crystal gallium nitride (GaN) substrate that can be used as a substrate for blue light emitting devices such as blue Light Emitting Diodes (LEDs) and blue semiconductor Laser Diodes (LDs) made of group III-V nitride-based semiconductors, a method for growing a single crystal gallium nitride substrate (GaN), and a method for producing a single crystal gallium nitride substrate (GaN).

Background

A light emitting element using a nitride semiconductor (InGaN, GaN) has been put to practical use as a blue LED. However, since a GaN substrate having a large area cannot be obtained, insulating sapphire (. alpha. -Al) is almost used₂O₃) As a substrate. LED constructions were fabricated by heteroepitaxial growth of GAN and INGAN thin films on the cubic symmetry plane of sapphire. Further, GAN-based LEDs using SIC substrates have been proposed and partially put into practical use. GAINN-like blue LED fabricated on sapphire substrate despite displacement density of 10⁹-10¹⁰cm^-2But emits light without deterioration and has a long life.

Sapphire is convenient to manufacture, easy to obtain, and inexpensive, and is chemically stable and physically strong crystal, and thus is most suitable as a substrate for a light-emitting element. Sapphire substrates have been practically used as blue LED substrates, but continue to be used in the future.

However, the light emitting element of the sapphire substrate also has some disadvantages. Namely, the cleavage property is lost and the insulation property is exhibited. Without cleaving, problems arise in chip dicing. When a plurality of LED cut chips are manufactured on a sapphire wafer through a wafer manufacturing process, the chips cannot be naturally split, and only the chips are cut (dicing) by a cutter, so that the yield is low and the cost is high.

On the other hand, since the substrate is insulating, current cannot pass through the substrate, that is, an n-type electrode (negative electrode) cannot be attached to the bottom surface of the substrate. On the other hand, a thick N-type GaN layer is formed on a sapphire substrate, an InGa-based LED structure is formed thereon by epitaxial growth, and then a portion from the topmost p-GaN thin film to the bottommost N-GaN is removed by etching to expose the N-type portion, thereby attaching an N-type electrode (negative electrode) thereto and a p-type electrode to the topmost p-GaN in the remaining portion. n-GaN must be relatively thick and highly conductive. In addition, both electrodes are on top and must be wire bonded twice. For these reasons, the number of steps increases and the manufacturing time increases. Further, the light emitting area is reduced by the presence of the n-electrode, and thus the light emitting area is narrowed. Conversely, in order to obtain a given light emitting area, the chip area becomes large. This will result in increased costs.

These are disadvantages when used as an LED substrate, and in the case of a semiconductor Laser (LD), there is a problem that the end face of the laser resonator cannot be formed by cleaving because of lack of cleaving property. The resonator end face is formed by polishing, etching, or the like, which takes time. Yet another disadvantage is that: the defect density is high. GaN on sapphire substrates has a thickness of up to 10⁹cm^-2The left and right defects are more. This is not a problem with LEDs, and light can be emitted efficiently. However, in the case of an LD, since the current density is particularly high, deterioration may start due to a defect. Therefore, although a sapphire substrate has been used as a substrate for a blue InGaN light-emitting device, it cannot be said to be an optimal substrate.

The most suitable substrate for the nitride-based light-emitting device is a GaN single crystal substrate. Heretofore, since the technology for producing high-quality GaN single crystal substrates has not been mature, GaN substrates having a large area have not been realized. If a high quality GaN substrate can be produced, it is the best substrate for a nitride light emitting device. Since GaN single crystal has a natural cleavage property, chip division becomes simple and accurate, and resonator end faces of LDs can be formed by cleavage. Since GaN has conductivity as an n-type substrate, and an n-electrode can be added to the bottom surface of the n-type substrate, the device structure can be simplified and the light-emitting area can be increased. Moreover, the problem of lattice constant mismatch between the oriented film and the oriented film does not exist. These are all foreseeable advantages.

However, the GaN polycrystalline raw material sublimates when heated, and thus cannot be made into a GaN melt. Therefore, it is impossible to use a general heat-balanced large-size crystal production technique such as the bridgecksky method, the brinell (bridgmen) method, or the like, which produces solid crystals by cooling and heating a melt. It is said that the application of high pressure makes it possible to grow a single crystal while maintaining a thermal equilibrium state. If at all, only small crystals are obtained, and it is not desirable to produce large wafers that can be commercially viable.

In view of this, there has been proposed a method for manufacturing a GaN substrate, comprising: a GaN single crystal self-supporting film was obtained by growing a thick GaN crystal on a suitable single crystal substrate by a vapor phase growth method and removing the substrate. This can be said to be a method of extending the thin film growth method. However, since the sapphire substrate is chemically stable and physically hard, it cannot be removed after GaN growth, and thus it is not suitable for use as a substrate. Recently, a method of separating a sapphire substrate using a laser has been attempted, but it is estimated that the yield is low when a large-sized substrate is manufactured.

A substrate which is easy to remove after crystal growth and has good matching with GaN should be selected. For example, a thick GaN having a C-plane is produced by vapor-phase synthesizing GaN on a plane (111) having cubic symmetry of GaAs in the C-axis direction. Since the substrate and GaN are different in lattice constant and thermal expansion coefficient, GaN does not grow very smoothly on the substrate. For example, even if crystal growth occurs, the internal stress is large, and a high-quality single crystal substrate cannot be obtained. Therefore, further attack is needed.

On the other hand, the present inventors have created a so-called transverse growth method (Lateral Overgrowth) in which: a mask having a plurality of windows is placed on a GaAs substrate, and GaN is vapor-grown from above the mask, thereby producing a GaN crystal having low internal stress and few defects. The contents of this process are described in the following japanese patent.

(1) Japanese patent application No. 9-298300

(2) Japanese patent application No. 10-9008

(3) Japanese patent application No. 10-102546

(4) Japanese patent application No. 10-171276

(5) Japanese patent application No. 10-183446

For example, on a GaAs substrate with a cubic symmetry plane (111), a SiN mask (e.g., 100nm thick) with stripes (stripes) and circular windows is distributed over the mask. The rectangular, circular window of the mask has 6-fold symmetry when installed, and is aligned with the regular triangle vertex position of the pattern to be repeated with the regular triangle. So, looking at one window, there are 6 nearest windows at a central angle of 60 °.

The sides of the regular triangle are, for example, parallel to the [ -110] or [11-2] direction of GaAs in the pattern. The mask has a function of excluding GaN, which grows from the GaAs surface of the GaN window, and is not attached to the mask. The buffer layer, which is thinner (e.g., 80nm thick) than the mask, is initially formed at a low temperature (500 ℃ @and600 ℃), and is a layer that can only be formed inside the mask because it is lower than the mask. It grows independently in isolated windows of the core of free-standing GaN.

Then, GaN vapor phase growth is performed at a high temperature, and then GaN is deposited on the buffer layer until as high as the mask. Although GaN is not attached to the mask, GaN grows upward from the inside of the window, and thereafter GaN grows upward on the mask in both the longitudinal and lateral directions. As a result, the GaN thin film grows in a regular hexagonal truncated pyramid shape centered on the center of the window. Although a large amount of dislocation occurs in the GaN crystal, it continues parallel to the growth direction. Since the direction of edge growth of the mask is once toward the lateral direction, the direction of continuation of the displacement is also temporarily changed toward the lateral direction. Since GaN is a crystal with one side maintaining a regular hexagonal frustum shape, the transition points of displacement are arranged on an outwardly inclined surface drawn from the edge of the mask.

The laterally grown film eventually meets the laterally grown film from the adjacent window. Since the films are grown in the lateral direction (horizontal direction) at a constant rate because of the windows being equal in all of the 6 directions, the films are simultaneously integrated on a line connecting the windows, i.e., a vertical bisector. In this case, since the displacements extend in the lateral direction, they are antiparallel to each other and collide with each other, and the displacements are concentrated by the collisions. Some of the displacement may be eliminated. When the displacement is concentrated on a local portion, the other portion becomes low displacement, and it is sufficient to use the substrate as a substrate of a light emitting element.

The GaN thin film grown from the neighboring window becomes grown upward after the bisectors meet, and then grows along the c-axis. This is called maintaining the growth of the C-plane. It takes time for the vapor phase growth to obtain a relatively thick (hundreds of μm) GaN/mask/GaAs ingot. By removing the mask and GaAs to form a free-standing film of single remaining GaN, a substrate crystal of GaN is obtained. Here, GaAs can be removed by dissolution with aqua regia, and the mask can be simply removed.

The lateral growth method has the advantages that the extension direction of the dislocation is changed twice, and the dislocation density is reduced. Accordingly, a GaN single crystal of considerable size can be grown for the first time. It has a sufficient thickness (100 μm or more) and is free standing, and is a GaN single crystal substrate which has been obtained for the first time by the present inventors.

However, if the quality of the gallium nitride substrate itself is not high, it is impossible to fabricate a good semiconductor device thereon. In particular, as a substrate for mass production, excellent crystal quality, that is, low dislocation density over a wide range is required.

Even by the lateral growth method using vapor phase growth with a multi-window mask, the dislocation density reaches 1-2X 10⁷cm^-2On the left and right sides, low dislocation is not achieved, and it is not practical as a substrate for InGaN-based LD.

In view of the above, the present inventors have studied a novel method for growing a gallium nitride single crystal with high quality and low dislocation density, and the method is described in the following publications.

(6) Japanese patent laid-open No. 2000-102307 (Japanese patent application No. 11-273882)

The method comprises the following steps: when performing lateral growth on GaAs using a mask, instead of performing vapor phase growth while maintaining a flat C-plane, crystal growth is performed while maintaining an uneven rough surface (facet surface); instead of C-plane growth in the C-axis direction, a plane inclined to the C-plane is grown while being exposed on the surface. This method is referred to as a textured growth method.

This method of growing the irregularities will be described with reference to FIGS. 1 to 3. GaN crystal 2 is C-grown so that flat surface 7C-plane. The surface 6 inclined to the C-surface 7 is referred to as a concave-convex surface. The growth is performed without burying the uneven surface 6 but with the uneven surface 6 exposed. Since the crystals are accumulated upward, they are concentrated on the concave-convex surface 6 to form the reverse tapered pit 4. The pits 4 look like circles, actually hexagonal pyramids ({11-2m } or {1-10m }) or dodeca pyramids ({11-2m } and {1-10m }) (here, m is an integer, and the crystal orientation is described later). Fig. 1-2 show the pits 4 as inverted cones for ease of drawing, but in practice twelve pyramids appear more frequently.

This continuous growth without burying the pit 4 is a trick of the embossing method. Since the concave-convex surface 6 rises as the growth proceeds, the displacement advancing parallel to the growth direction advances inward with respect to the concave-convex surface, and converges on the boundary line (ridge line 8) of the concave-convex surfaces in different orientations. The dislocation reaching the ridge line advances inwards along with the growth, reaches the pit bottom and gathers at the composite point D. At the edge portion where the angle between each other is 60 DEG, there are many displacements in the way of aggregation, and the linear displacement aggregation defect portion 11 is constituted by aggregation at the composite point D. The displacements in the middle of the set are contained in a vertical plane from below the boundary line to the bottom surface. These 3 surfaces with the concentrated displacements forming an angle of 60 ° with each other are called planar defects 10. In particular, when many displacements are concentrated here, they tend to reach a fairly steady state.

The above-described uneven growth method has the following effects: the concave-convex surface is gathered and displaced to gather the surface-shaped defect and the center, namely the compound point. The grown crystal advances upward (toward the c-axis) as a whole, but the displacement beam is concentrated toward 3 boundary planes (planar defects 10). Since the growth direction is always in the direction of the inwardly inclined surface, a certain portion of the displaced beam is concentrated to form the linear defect beam 11.

Since the planar defect and the linear defect, which are beams in which the displacement is concentrated on the bottom of the pit formed by the uneven surface, are generated, the remaining portion constitutes low displacement. After the GaN/GaAs blank is grown to a proper thickness, the GaN/GaAs blank is taken out, and the GaAs substrate and the mask are removed. Thus, a free-standing film of single remaining GaN can be obtained. It is transparent and becomes a flat substrate after grinding. Is a material which looks like flat and smooth glass to the naked eye and is not seen with displacement. The displacement is only visible by microscopic observation after pits appear by etching with a special etching liquid. In addition, the difference in material can also be seen with a fluorescence microscope.

When observing the displacement density of the low displacement region on the substrate with a microscope, you surprisingly found that: is lowered to 10 at a time⁶cm^-2The following. The dislocation density is 1-2 × 10 during transverse growth⁷cm^-2Left and right, by one digit in comparison. This is really a clever and useful invention.

However, even in the above-described delicate inventions, a problem has been found to exist in the production of GaN single crystals that can be used as LD substrates.

Since the crystal is grown without burying the pit formed by the uneven surface, the displacement is concentrated on the bottom of the pit, and the displacement is concentrated in a narrow space. But has such problems: not just completely concentrated in one point, but rather somewhat dispersed. For example, it is assumed that a pit having a diameter of 100 μm is formed, and the displacement is concentrated in a narrow range of several μm at the center of the pit when viewed from the concentrated portion, but some displacement is sparsely dispersed in a range of about 30 μm in other portions.

This is because the displacements concentrated at the beginning are scattered randomly. The concentrated dislocation may be cracked. It has been found that randomly spread-out runout ribs contain a considerable amount of runout. That is, the displacement beam at a certain position may spread out around the center of the pit like a cloud. This disorder can be directly observed by fluorescence microscopy. Fig. 3 shows a case where the displacement cluster 15 at the bottom of the pit is scattered and the displacements spread around the pit.

It is found that when the pit diameter is enlarged to expand the low displacement region, the random displacement ribs tend to increase further. As the diameter of the pit increases, the number of displacements concentrated toward the center core increases, and therefore the number and area of the displacements which bloom into a cloud shape also increase.

Why will the displacement once condensed again fan out from the core? Exactly what is the reason why blooming occurs? The present inventors studied these matters, and found that the cause thereof is a repulsive force acting between displacements.

The displacement extends along the growth direction along with the growth, and although the displacement is separated and gathered, the displacement cannot be easily eliminated, but is concentrated instead of being eliminated. Since dislocations are a disorder of the crystal, they will cause the crystal to not be compressed integrally as soon as they are close to parallel, resulting in an increase in lattice energy. The increase in lattice energy brings about a repulsive force. The displacements can extend all over in one dimension, but as soon as they approach each other, they can cause the crystal structure to be disorganized and concentrated, increasing the energy and thus producing a repulsive force. This activity begins to appear after the displacement has been caused to agglutinate by a factor of a thousand or even ten thousand, but this has not been known so far.

When 1000 or 10000 transposition lines are concentrated in a narrow range, the repulsive force therebetween starts to be significant. Therefore, a part of the displacement that is originally coagulated is dissipated again. This produces a random star-like configuration that looks like a wave about the core.

The displacement density on the random displacement line was about 10⁷cm^-2order, average displacement density of other parts (10)⁶cm^-2order) is more than 10 times larger. The displacement density of the random displacement line is not sufficient for the LD substrate. From the viewpoint of being applicable to an LD substrate, it is desirable that the displacement density is less than 10⁶cm^-2order. Here, random displacement caused by blooming is the first problem.

The second problem is that: and a planar defect 10 formed by forming an angle of 60 degrees between the central parts of the pits when the displacement is concentrated on the bottom of the pit 4 formed by the uneven surface 6. When the pit is maintained and grown, the displacement is concentrated on the boundary between the uneven surfaces and accumulated there, and the displacement is concentrated in a planar shape to form a planar defect 10. It can be considered that: the planar defect 10, which is contained on the axis of the pit and forms an angle of 60 degrees with each other and has 6-order symmetry, is a displacement block in which displacements are arranged in parallel in a planar manner. The planar defects also have crystal defects, as well as the random displacements described above. The planar defect and the pit core form an angle of 60 degrees in a radial shape. Sometimes, crystal plane dislocation may occur on both sides of the planar defect. When an LD element is manufactured on a substrate, it is expected that the quality is deteriorated and the laser lifetime is shortened due to the existence of these planar defects. It is necessary to reduce the planar defects.

The last problem is the more fundamental one. It is the unpredictable contingency and probability of pit distribution. That is, the defect distribution is random. According to the above-described pit and projection growth method in which the pit and projection are grown without burying the pit and projection to reduce the displacement, it is impossible to specify or know in advance where the pit is located. The pits formed by the concave and convex surfaces are only formed at a certain place by chance, and the displacement is concentrated at the place by chance. Therefore, the probability and contingency of the distribution of the displacement beam constitute a problem.

When a GaN wafer is used and a wafer process is performed to manufacture a plurality of GaN-LD chips, stripes (stripes, i.e., active layers) of the LD often encounter a displacement beam. If a defect beam is present in the light-emitting layer, the LD life becomes short. This results in a reduced laser manufacturing yield due to the fact that the LD where the fringes hit the displacement beam has to be removed.

The size of the LD chip fabricated on the GaN substrate is not necessarily constant, and here, a rectangular LD of 400 μm × 600 μm is fabricated on a wafer, assuming that the width is 400 μm and the length is 600 μm, and the light-emitting layer (stripe) formed in the center longitudinal direction is 2 to 3 μm wide × 600 μm. Then, of the entire width of 400 μm, only 3 μm is a stripe. Therefore, it is possible that the phenomenon that the displacement core and the random displacement overlap the streak is not so small. The width of the stripe is really narrow, but its length is the same as the length of the chip and is certainly a straight line. Therefore, the phenomenon that the displacement core (displacement concentration point) touches the stripe frequently occurs.

In order to manufacture a substrate for an LD, a displacement core and a substrate in which random displacements do not collide with streaks are required. It is difficult to know where the deflection beam (deflection core) is. It is therefore desirable to actively control the position of the displacement core. Although the presence of the displacement core is not a matter of course, it is sufficient if the displacement core can be appropriately arranged at the time of manufacturing the LD and the arrangement can be known in advance. Therefore, a crystal growth method capable of controlling the position of a displaced core (beam) is desired.

The above three points are the subject of the present invention. Namely, the invention aims to solve the following three problems:

(1) the random distribution of the displacement collection part from the center of the pit formed by the concave-convex surface is reduced.

(2) The planar defect of the central displacement collection part of the pit formed by the concave-convex surface is eliminated.

(3) The position of the displacement collection part at the center of the pit formed by the uneven surface is controlled.

Before describing the present invention, a little bit is explained. First, as a vapor phase growth method, a vapor phase growth method is used as a GaN thin film formation method, and among them, there are an HVPE method, an MOCVD method, an MOC method, and a sublimation method. The method is also used in substrate manufacturing.

I concerning the HVPE method (Hydride Vapor Phase Epitaxy, Hydride Vapor Phase growth method)

Metal Ga is taken as Ga raw material, nitrogen raw material is ammonia NH₃The substrate was placed on a susceptor below the hot wall reactor, and GaN metal was placed on the upper plate and heated, and hydrogen gas and HCL gas were blown into the heated substrate to produce GaCL. This carrier is floated downward on the hydrogen gas and attached to the heated substrate. Hydrogen gas and ammonia gas are supplied near the substrate, and GaCL and ammonia are reacted to synthesize GaN, which is deposited on the heated substrate. Since GaCL is produced using metal Ga as a raw material, there is an advantage that carbon is not mixed in the GaN thin film.

II on MOCVD Process (Metal organic Chemical Vapor Deposition, Metal organic CVD)

It is the most commonly used GaN thin film growth method. In a cold wall type reactor, an organometallic raw material of Ga such as TMG (trimethylgallium) and ammonia NH are introduced₃With hydrogen (H)₂) Blown together onto the heated substrate. The use of an organometallic as a gallium source is often employed for forming a thin film of a gallium compound other than GaN. On the heated substrate, TMG reacts with ammonia to synthesize GaN, which is deposited to form a thin film. This method is useful as a thin film forming method. However, there is a problem in producing a thick substrate crystal rather than a thin film. Since this method uses a large amount of gas, the yield of the raw material gas is low. This does not pose a problem in the case of thin films, but the low yield is a disadvantage in the case of forming substrates. Yet another problem is: since the raw material contains organic matter and carbon, carbon is mixed in the GaN. Carbon may become a deep donor, which lowers electron mobility and deteriorates electrical characteristics.

III on MOC Process (Metalloorganic Chloride vapor phase growth)

Using organic metal compound of TNG, etc. as Ga raw material and nitrogen raw material as ammonia NH₃. Unlike the MOCVD process, it is not straightforward to combine TMG with ammonia. In a hot wall type reactor, GaCL is synthesized by reacting TMG and HCL gas. This is flowed onto the heated substrate in a gaseous state. Since ammonia is supplied near the substrate, ammonia and GaCL react near the substrate to synthesize GaN, and GaN gradually accumulates. This method also has a disadvantage that carbon is mixed in the film because an organic metal is used. But the raw material yield is higher than that of the MOCVD method.

IV sublimation method

Here, not gas but polycrystalline GaN is used as a raw material. The solid GaN and the substrate are respectively arranged at different positions in a reaction furnace, a temperature gradient is set, the solid GaN is heated and gasified, and the solid GaN moves to the position of the substrate with lower temperature, so that a GaN film is deposited on the substrate.

The crystal orientation will be described below. This is considered common sense in the industry, but not necessarily everyone knows that there are situations where the concept is confusing, and where the interpretation of the spatial geometry cannot be understood by the reader. Since the structure of the present invention will be described later by way of crystal orientation, the definition of orientation should be made clear. GaN belongs to the hexagonal system, and indices of display planes and orientations are 3 or 4. Here, 4 are used. The following expressions are described.

There are certain conventions regarding the behavior of crystal planes and crystal orientations, respectively. The total expression of the orientation of the planes is given by a parenthesis { }, such as { hkmn }, where h, k, m, n are called plane indices (or specular indices), and are not necessarily integers. The expression of individual face orientation is in circle brackets (), as expressed in (hkmn). The overall expression of the crystal orientation is by mid bracket < >, as expressed by < hkmn >. The individual expression of the crystal orientation is in brackets, as expressed in [ hkmn ]. The crystal planes and crystal orientations having the same crystal plane index are orthogonal, i.e. the direction orthogonal to (hkmn) is < hkmn >.

The allowable symmetry is determined by the symmetry group to which the crystal belongs, and when it is restored by the symmetry transformation operation, the crystal planes and the orientation are expressed in the same general expression. In the case of the hexagonal system, since the operation is allowed 3 times for the first 3 indexes, the symmetric operations in which h, k, and m are substituted with each other are equivalent. However, the index n of the c-axis is special and cannot be interchanged with these three indexes. The total crystal plane expressed in total expression as { hkmn } comprises all individual planes which, starting from one individual plane (hkmn), can be reached by allowing symmetrical operation. Even if they are hexagonal, the allowable symmetry operations are varied depending on the crystal, and it cannot be said that one is included in the overall expression.

GaN has 3-fold symmetry, so (hkmn), (kmhn), (mhkn), (hmkn), (khmn), (mkhn) are 6 planes contained in the total expression { hkmn }. Conversely, the 6 total expressions { hkmn }, { kmhn }, { mhkn }, { hmkn }, { khmn }, { mkhn } are equivalent expressions. The plane index is an index, and is conventionally attached to a line when it is a negative number, but since there is no way to attach a line in the specification, the negative sign is attached to the former. Since no comma is added between the plane indices, it is possible to easily distinguish between the plane indices and the coordinates.

GaN belongs to the hexagonal system, with 3 axes with 3-fold symmetry. Two of these axes are called the a-axis and the b-axis, and the 3 rd axis is not named, and is called the d-axis for convenience 1. Then, the three axes abd are set at a central angle of 120 degrees. Orthogonal to the plane containing these three axes is the c-axis. The c-axis is a specific axis in the hexagonal system, and does not have symmetry between the abd-axes. The crystal plane is a set of numerous planes parallel to each other and oriented in the same direction. The crystal plane orientation is: the length of the slice obtained by cutting the 1 st facet into each axis is the reciprocal of the quotient obtained by dividing the axis length. For example, when the a-axis is cut by a/h, the b-axis is cut by b/k, the d-axis is cut by d/m, and the c-axis is cut by c/n, the index of the crystal plane is expressed as (hkmn).

It is seen that the smaller the crystal plane index is, the more elementary planes are formed, and the smaller the number of planes is. The crystal orientation [ hkmn ] is defined as the direction orthogonal to the plane (hkmn). The first three indices h, k, m among the 4 indices are dependent. Because of the two-dimensional nature, it can be expressed by two indices, and in fact, it can be expressed by two indices. However, for the sake of symmetry, 4 indices are used here. Therefore, although h, k, m are subordinate once, there is always a thumb rule that is easily recognized among them: h + k + m is 0.

Taking GaN, there are three representative planes, one of which is the C-plane, which can be expressed as the (0001) plane, i.e., it is the plane orthogonal to the C-axis. The plane and the axis are orthogonal to each other, and in the following description, the plane is indicated by capital letters and the axis is indicated by lowercase letters for distinction. GaN has 3-fold symmetry around the c-axis, i.e., symmetry that can be returned to the original position by 120 degrees of rotation. When GaN is grown on a different substrate, GaN is grown in the c-axis direction. In the case of heteroepitaxial growth on a GaAs substrate or a sapphire substrate, the growth is always carried out in the c-axis direction. GaN has no inverted symmetry, so the (0001) plane and (000-1) are not the same plane.

The 2 nd representative plane is called an M-plane, which is a cleavage plane and is a plane passing through the front end of one of the 3 symmetrical axes (a, b, c) and parallel to one of the other two axes and the c-axis, and can be expressed by general expressions {1-100}, {01-10}, { -1010}, { -1100}, {0-110}, {10-10}, and individual expressions (1-100), (01-10), (-1010), (-1100), (0-110), (10-10), and the like. The total expression is equivalent, but the individual expressions express different planes. The different faces are at an angle of 60 degrees to each other. It should be noted that: not 90 degrees but 60 degrees. The M-plane is a generic term and is convenient in expressing the representative orientation of GaN.

The 3 rd representative plane is called the A plane, which is a plane connecting the front ends of two axes of the symmetrical 3 axes (a, b, c) and parallel to the c axis, and can be expressed by the general expressions {2-1-10}, { -12-10}, { -1-120}, { -2110}, {1-210}, { 11-20 } and the individual expressions (2-1-10), (-12-10), (-1-120), (-2110), (1-210), (11-20). The total expression is equivalent, but individual expressions express different facets.

Since GaN has no 6-fold symmetry, the individual faces show two planes. The individual faces are at an angle of 60 degrees to each other. It should be noted that: not 90 degrees but 60 degrees. The A face is a generic term and is very convenient to express. Should be distinguished from the a-axis. Orientation <2-1-10> having the same crystal plane index as the A plane is an orientation orthogonal to the A plane, which is parallel to one of the M planes and seems to be called a orientation, but not to say it. Orientation <1-100> having the same crystal plane index as the M plane is an orientation orthogonal to the M plane, which is parallel to the A plane, and seems to be called M orientation, but not to say that. As can be seen, GaM has 3 representative faces, namely, face C, face A, and face M.

The uneven surface described later is formed by slightly inclining the a-surface and the M-surface in the c-axis direction. Examples thereof include irregularities {2-1-11} and {2-1-12} derived from the A plane, and irregularities {1-101} and {1-102} derived from the M plane. Equivalent 6 planes are grouped to form a pit. The hexagonal pyramid-shaped pits are constituted by irregularities {2-1-11} and {2-1-12} derived from the A-plane, or by irregularities {1-101} and {1-102} derived from the M-plane. The A face also had 6 faces with an angle of 60 degrees with each other like the M face, and when holes were formed, hexagonal pyramid-shaped pits were formed. Further, a dodecagonal pit may be formed by combining the A-surface irregularities {2-1-11}, {2-1-12} and the M-surface irregularities {1-101}, {1-102}, which form a dodecagonal shape. When the shape is a dodecagon, the surfaces are sometimes seen to be somewhat misaligned.

The 4 th exponent n is 1 or 2 in the case of the above unevenness. Since such a low surface index is common, it will be described below. For example, the A-plane {2-1-10} is slightly tilted with respect to the c-axis to become a {2-1-11} plane, and further tilted to become a {2-1-12} plane. The larger the value of the 4 th exponent n, the larger the tilt to the c-axis, i.e. close to horizontal. Although asperities with higher n indices have also appeared, generally n is 1 or 2.

In the following, the concept of two-stage overlapping concavities and convexities is described, and two kinds of concavities and convexities constituting pits and concavities shallower than the pits appear. In order not to obscure the present invention, the description is given in advance. The term shallow means: the plane index n horizontally closer to the C-plane, i.e., the C-axis direction, is large.

As described later, the irregularities appearing around the pits are typically {11-22} and {1-101}, which will be described later. When a represents the length of the a-axis and C represents the length of the C-axis, the inclination angle of the {1-101} plane with respect to the C-plane is tan^-1(3^1/2a/2C) and an inclination of {11-22} plane to C plane of tan^-1(a/c)。

In the case of the concavo-convex pattern, n is relatively large, such as {11-23}, {1-102}, {11-24}, and {1-103 }. The angle of inclination of {1-10n } (n.gtoreq.2) plane to C plane is tan^-1(3^1/2a/2cn), when n is greater than 2, the value is smaller than that in the case where n is 1. The angle of inclination of the {11-2n } (n.gtoreq.3) plane with respect to the C plane is tan^-1(2a/nc), and when n is greater than 3, the value is smaller than that in the case where n is 2. Therefore, the case with a large n is called a shallow unevenness.

GaN belongs to hexagonal system, wurtzite, and has the following: there are Ga atoms present at the bottom surface of 6 vertexes and the center of the regular hexagon, Ga atoms present at the upper surface of 6 vertexes and the center of the regular hexagon, N atoms present at the lower intermediate surface of 6 vertexes and the center of the regular hexagon between the bottom surface and the upper surface but slightly below, an intermediate surface having 3 Ga atoms present slightly above, and an upper intermediate surface having 3N atoms present further above. It has 3-fold symmetry, but no inversion symmetry, nor 6-fold symmetry.

Sapphire, Si, GaAs, etc. are used as the substrate. Sapphire (alpha-Al)₂O₃) Belongs to trigonal system, but has poor symmetry, no 3-degree symmetry and no inversion symmetry. The poor symmetry makes cleavage impossible.

Si is not a hexagonal crystal system but a cubic crystal system, and has a diamond structure. The crystal plane index is 3. The face orientation (khm) can be fully described by 3 indices. The 3 indices are independent, the thumb rule described above is not applicable, and k + h + m ≠ 0. The 3 rd order symmetry axis is in the diagonal direction and intersects the (111) plane. In general, a (001) plane is used for a Si semiconductor device, but it does not have 3 rd order symmetry. Since 3-fold symmetry is required, the (111) plane is used for Si.

GaAs is not a hexagonal crystal system but a cubic crystal system, and has a Zinc Blende (ZnS) structure. The crystal plane index is 3. The surface orientation can be described completely by 3 indices. The 3 rd order symmetry axis is in the diagonal direction and intersects the (111) plane. In general, in the fabrication of GaAs semiconductor devices, the (001) plane is used from the viewpoint of cleavage. But the face does not have 3-fold symmetry. Since 3-fold symmetry is required, the (111) plane is also used in GaAs. GaAs has no inversion symmetry, and there are only two kinds of (111) planes, that is, a (111) plane where As protrudes to the outside and a (111) plane where Ga protrudes to the outside. If necessary, the (111) As face and the (111) Ga face are referred to for distinction.

Disclosure of Invention

The method invented by the present inventors, in which GaN is grown while holding the uneven surface, instead of maintaining a flat C-plane, so that the displacement is concentrated at the pit bottom and the remaining displacement is reduced, is excellent, but as described above, there still remains a problem, and it is necessary to solve the following three problems:

(1) the random distribution of the displacement collection part from the center of the pit formed by the concave-convex surface is reduced.

(2) The planar defect of the central displacement collection part of the pit formed by the concave-convex surface is eliminated.

(3) The position of the displacement collection part at the center of the pit formed by the uneven surface is controlled.

These difficulties are further explained below.

The problem of the prior application of the present inventors in forming and maintaining the pits and pits on one side with a side of crystal is considered to be the aggregate state of displacement. Fig. 3(1) and (2) illustrate the set of shifts at the pit of the previous application. Pits 14 consisting of irregularities 14 are generated in a certain portion of the GaN crystal 12. The generation position of pit 14 cannot be specified, and there is a chance. When the flat surface 17 grows in the C-plane direction, the uneven surface 10 also rises, and the displacement 15 is accumulated at the bottom of the pit 14. As shown in fig. 3(2), the displacement group 15 may exist only at the bottom of the pit, and then the displacement itself may be dispersed, opened, and expanded.

In the pit portion formed by the uneven surface, when a large amount of displacement is concentrated in the center of the pit by utilizing anisotropy of the propagation direction of the displacement of the uneven surface, the collective state of the displacement becomes a problem. Although the displacement can be concentrated in the center of the pit, the displacement is concentrated at a high density, and the displacement does not disappear, and the pit is opened, which causes various problems.

The method of the present inventors has focused a large amount of displacement on the center of a pit by using a single-sided crystal while maintaining the pit shape in which the pits and projections grow, but a high-density displacement set poses a new problem.

It may sometimes be that shifts with the inverse-direction baker's spectrum collide and die. However, the displacements collected by one uneven surface are relatively many in the same sign. Therefore, it can be said that the displacements of the sets almost do not cancel each other due to the difference in sign. When the displacements of the same sign are collected, the displacements are not eliminated and remain. But has the advantage of reducing the displacement of the remaining part after concentration.

However, it is also possible that the displacements of the same sign are concentrated on the line and the plane stably, and this is not the case in practice. As described above, the spread of the random displacements can be seen from the displacement concentrated portion. Why then? The reason for this is considered to be that repulsive force is generated as soon as displacements of the same sign are concentrated between the displacements.

The continuous dislocation of the crystal lattice is dislocation, and the dislocation direction is doubled as soon as the same dislocation is concentrated on the dislocation direction, so that the mechanical energy of the crystal lattice is increased. For this purpose, the energy is reduced, and a repulsive force is formed. Due to the repulsive force acting between displacements, the displacements are released from a part of the displacement collector, and the random displacements are spread. The head is not easy to be concentrated, and part of the head is displaced, separated and spread, which causes brain injury.

Further, the pit combination and the displacement group are disturbed, and the displacement is concentrated by the confluence of the displacement group, and the displacement density is further increased. For this reason, the random displacement may be extended. This is the problem of the random distribution of the displacements described above.

In addition, when the displacement is collected toward the center of the pit formed by the concave-convex portions, a collection of radial displacements having an angle of 60 ° with respect to each other may be formed. This is the planar defect 10 of fig. 1 (b). This is due to the fact that the displacements are collected at 60 degrees. When displacements of the same sign are collected, the displacements may be concentrated on the radial planar defect 10, instead of being concentrated on the center, due to repulsive force acting between the displacements. This will further strengthen the planar defect.

When the size of the pit is increased by the combination of the plural pits, the number of displacements of the assembly toward the center of the pit is also increased, and the area of the planar defect is increased.

Further, since the generation of the unevenness is not a natural development, there is no rule. The pit locations are occasional, unpredictable and uncontrollable. Since the pit positions are random, unlimited, and random, the increase in the area of the random displacement group hinders the fabrication of a semiconductor device on the substrate, and the quality and yield of the semiconductor device are reduced.

To solve these problems, the present inventors considered the problems to be critical: when crystal growth is performed while maintaining pits formed by the uneven surface and displacement is concentrated in the center of the pits, the displacement is retained only in the collection portion and is not converged. (see FIG. 3 and 2) group 15)

The inventor takes the following steps: if the displacement eliminating means or the accumulating means is provided in the displaced collecting unit, the group of displacements in the collecting unit is fixed and does not spread, which is effective.

The inventor takes the following steps: if the crystal group has a displacement eliminating mechanism or a displacement accumulating mechanism, the displacement can be eliminated or accumulated even if the displacement is concentrated in a narrow region. Therefore, the displacement is not scattered and a planar defect is not formed.

What is used to make the displacement eliminating mechanism and the accumulating mechanism? The inventors do this: defects such as grain boundaries are intentionally formed in a single crystal, and dislocations are eliminated or accumulated by the defect surfaces. That is, defects such as grain boundaries are actively generated, and displacement is stably accumulated or eliminated. This is the first novel concept of the present invention.

The present invention is to newly form a grain boundary and to effectively utilize it. This is illustrated in fig. 4. Pits 24 having concave and convex surfaces 26 are formed on the GaN crystal 22. The displacement moves parallel to the C-plane between the concave and convex surfaces 26 while growing crystals, and reaches the bottom 29 of the pit 24. Thereafter, the direction of extension of the dislocations was parallel to the growth direction (c-axis direction). The junction 29 is formed as a closed defect pool 25. The closed defect condensed region 25 absorbs the above displacement. The displacement or annihilation or accumulation is in the closed defect cluster area 25.

Once accumulated, it is difficult to escape to the outside. In this sense, therefore, the meaning of so-called "closed" can also be seen. The confinement is performed at the grain boundary K surrounding the region 25 where the defect is confined. Since the closed defect pool 25 is blocked, the dislocation is trapped and hardly re-diffused.

How is it done to block the grain boundary K of the closed defect pool 25? As described above, when the concave-convex growth is performed while maintaining the concave-convex, the displacement is concentrated on the central bottom portion of the pit formed by the concave-convex. In the central portion, a crystal grain boundary K can be formed at the boundary by forming a crystal different from the surrounding single crystal. Since it is sufficient to form a crystal different from the surrounding single crystal, the crystal may be a single crystal having a different orientation or a polycrystal whose orientation cannot be uniquely defined. In any case, since the surrounding single crystals have the same orientation and remain as a single crystal as a whole, if a crystal different from the surrounding single crystal is formed in the central portion of the pit, a crystal grain boundary K should be formed between the heterogeneous crystals. The case where a polycrystal is formed in the central portion will be described.

Specifically, a polycrystalline region is formed in the central portion. Thus, a grain boundary K is generated between the peripheral single-crystal region and the polycrystalline region formed at the narrow region of the pit bottom. The grain boundary K is used as the location for erasing and accumulating the dislocation. This reduction in dislocation, however, newly produces a grain boundary K containing many dislocations, which effectively reverses the grain boundary K. Of course, not only the grain boundaries K but also the internal region surrounded by the grain boundaries K can be used as the accumulation of the displacement. This is a very unexpected idea and is new.

The invention can prevent the scattered distribution from growing and part from being eliminated by forming the displaced collecting groove (suction), and can promote the reduction and elimination of the planar defect spreading from the central part of the pit.

Further research shows that: the region that can function to eliminate and accumulate the dislocation is not limited to the polycrystal. If a single-crystal region is grown next to the pit bottom, a crystal grain boundary K is generated therebetween as long as it is oriented differently from other single-crystal crystals, and the crystal grain boundary K can be eliminated and accumulated as a result of displacement. For example, the c-axis may be inverted, that is, an inversion layer in which the Ga face and the nitrogen face are inverted may be formed. The inversion layer means: in a given region of the GaN crystal, only the <0001> direction of the GaN crystal is reversed by 180 degrees, with polarity (polarity) reversed, compared to the other regions. The (0001) plane of the GaN crystal is a Ga atom plane, while the (000-1) plane is a nitrogen atom plane.

It is further known that: even if a single crystal is oriented in the same manner as the other regions, when the crystal is surrounded by the surface defect and surrounded by the small-inclination-angle crystal grain boundary, the small-inclination crystal grain boundary K can constitute the extinction and accumulation of the dislocation. That is, as long as the following regions are formed next to the bottom of the central portion of the pit, the crystal grain boundary K can be generated between these regions and the respective peripheral regions.

A. Polycrystalline region

B. Single crystal region oriented differently from the surrounding single crystal

C. Single crystal region of the same orientation as the surrounding single crystal but surrounded by small tilt angle grain boundaries

Therefore, the crystal grain boundary K has the function of eliminating and accumulating the dislocation. Although it is effective to cancel the displacement, it is also effective to accumulate the displacement and not release the accumulated displacement. Such a portion constituting the crystal core contains crystal defects and is surrounded by the crystal grain boundary K, and hence can be referred to as a "closed defect cluster region". This part of the construction is novel in itself.

The term enclosed defect pool is too lengthy, and is simply referred to as enclosed defect pool H. It means the area that is: having a core S, which is grown in the bottom of a concave-convex surface collection, i.e., a pit, in concave-convex growth and has a certain crystal property different from that of the surrounding single crystal, the surface of which is surrounded by a crystal grain boundary K. That is, the core S is either A, B or C, and the closed defect aggregation region H is composed of the core S and the grain boundary K. If expressed visually, the following can be written:

H＝S+K

k ═ S, B or C

K is a crystal grain boundary and can eliminate and accumulate dislocations. The core S is located inside K, has a certain crystal property different from that of the surrounding single crystal, and is grown at the bottom of the pit in the concave-convex growth. These two components are collectively referred to as a closed defect pool area H. The deepest part of the pit is in the closed defect aggregation region H, and a displaced aggregation part is generated. In the above description, it seems that it is felt that only the crystal grain boundary K has the action of eliminating and accumulating the dislocation, and not only does it have the action of eliminating and accumulating the dislocation in the core S which closes the inside of the defect aggregation region H. Both K and S have the effect of destroying and accumulating dislocations.

In the prior application of the present inventors (japanese patent laid-open No. 2001-102307), it has not been possible to specify in advance where pits are generated. In that case, it is not possible to determine in advance where the closed defect aggregation region H generated following the pit is generated. However, it is meaningful to know the correlation that the closed defect pool area H is generated in the center of the pit. The inventor makes further research and finds that: the closed defect aggregate area H may be predetermined.

In other words, if the position of the closed defect aggregation area H can be determined in advance by some means, the place where the pit occurs can be determined. It should be noted that these views will bring about a leap.

The means for determining the closed defect aggregate area H will be described later. In short, a so-called "seed" is regularly arranged at a position of the substrate base where it is desired to produce the closed defect integrated region H. Upon growth of GaN thereon, pits are generated next to the seeds, and closed defect assembly regions H are generated next to the pits.

When the closed defect cluster region H is determined, the region grows at a slower rate than the other C-planes, and a depression (pit) appears in the grown portion compared with the other C-planes. When the depressions are formed, the periphery of the depressions is surrounded by a stable uneven surface having a low isosurface index. As the crystal grows, the concave-convex surface grows largely, resulting in formation of pits. Since the pit is not annihilated but maintained during the concave-convex growth, the closed defect aggregation region H is continuously grown next to the pit. Since the growth is in the longitudinal direction, the closed defect integrated regions are all located upward from the initially determined position of the closed defect integrated region H. According to this method, the pit position can be controlled, and the closed defect aggregation region H can be formed at an arbitrary position. This is also one of the salient features of the present invention.

There is another closed defect pool H generation mechanism. Although the pits are constituted by the concave-convex surface, other concave-convex surfaces (see (3) of fig. 5 (b)) having a shallow inclination (large c-axis surface index n) are easily formed at the bottom thereof, and the concave-convex surface having a shallow angle is formed at the bottom of the pits, thus constituting a dual concave-convex structure. This fixes the pit center. The closed defect concentration region H is generated by the shallow concavo-convex surface. As will be described later in detail, this phenomenon clearly occurs when the closed defect aggregation region H is constituted by an inversion layer with respect to the surrounding c-axis direction which is inverted only 180 degrees in the <0001) direction of the GaN crystal.

The closed defect collection area H has the following points. When a polycrystal is formed over the seed, the closed defect aggregation region H becomes a polycrystal, which is significantly different from other single crystal portions, and a grain boundary K is generated at the boundary.

However, the closed defect aggregation region H may be not only polycrystalline but also single-crystalline. The single crystal is not oriented in the same direction as the surrounding single crystal. Different directions and diversity, as will be described in detail later. Why do the crystal orientations differ? This is because the pit bottom is formed with a small inclined uneven surface (n is large) and the closed defect aggregation region H is formed with this surface as one surface, and therefore even if the closed defect aggregation region H is a single crystal, the crystal orientation thereof is different from that of other single crystal portions. The boundary between the closed defect pool region H and other single crystal portions must generate a grain boundary K due to the difference in crystal orientation. By the grain boundary K, the core S of the closed defect aggregation region H is completely sealed and oriented to form a closed defect aggregation. This is the closed defect pool area H.

In this method, the three problems can be completely solved by performing the GaN crystal growth in a closed defect cluster region where H ═ S + K is formed. The random displacements diffused from the center of the pit are absorbed and accumulated by the crystal grain boundary K and are not released, so that they do not escape to the outside. The planar defect at an angle of 60 degrees generated from the bottom of the center of the pit is sucked and accumulated by the grain boundary K and does not escape to the outside.

The accidental problem that the active layer (stripe) overlaps the pit when the LD is manufactured because the pit center position is not determined is solved by positively determining the closed defect aggregation region H, that is, the position where the pit is generated. It can also be said that it is the most useful advantage of the invention that the pit location can be determined.

The principle of the present invention has been described above, and the three problems (random displacement at the center of a pit, planar defect, difficulty in position control) can be solved according to the present invention. Specific embodiments of the present invention are described in more detail below.

Drawings

Fig. 1 is a perspective view illustrating that in the uneven growth method of GaN crystal growth performed while forming pits formed of uneven surfaces on the surface and maintaining them, which was proposed by the present inventors in jp 2001-102307, the unevenness grows into the pits in a direction other than the average growth direction and shifts and converges on the uneven ridge line. Wherein (a) is a perspective view illustrating the in-growth of the concave-convex surface, the concentration of displacement on the ridge line, and the low retention of the displacement in the pit, and (b) is a perspective view illustrating the formation of the planar defect spreading around in a radial shape due to the strong repulsive force generated between the displacements retained in the low retention of the pit.

Fig. 2 is a plan view illustrating that in the uneven growth method of GaN crystal growth performed while forming pits formed by uneven surfaces on the surface and maintaining them, proposed in kokai 2001-102307, the present inventors grown the unevenness outward in the average growth direction and inward in the pits, and shifted and converged in the uneven ridge line and further concentrated at the pit bottom junction while growing.

Fig. 3 is a cross-sectional view of a pit, which is a view for explaining the following situation: in the uneven growth method of GaN crystal growth while forming and maintaining pits formed by uneven surfaces on the surface, proposed in jp 2001-102307, the present inventors grown the unevenness outward in the average growth direction toward the inside of the pits, shifted and converged on the uneven ridge line and further concentrated on the pit bottom junction while growing, and then formed a shifted cluster in the vertical direction. Wherein (1) is a cross-sectional view illustrating the growth with displacement concentrated toward the pit bottom to form a longitudinally extending displacement beam; (2) is a sectional view illustrating the case: the displacement is concentrated to the bottom of the pit during growth, so that a longitudinally extending displacement beam is formed, but a uncovered displacement set is opened, and strong repulsive force is generated between the displacements, so that once the displacement set is gathered, the displacement is dispersed again and expanded to the periphery, and disordered displacement diffusion occurs.

FIG. 4 is a schematic cross-sectional view showing the growth method of a single crystal gallium nitride substrate according to the present invention, in which the growth of GaN crystal is carried out while forming and maintaining pits formed on the surface of the substrate, and the pits and pits grow inward from the average growth direction, and the dislocations converge on the ridge lines of the pits and further converge on the junction point of the pit bottoms while growing, and then the dislocation cluster H is formed in the longitudinal direction of the bottom, i.e., the closed defect cluster region H, so that the dislocations are concentrated in the closed space and do not spread. Wherein, (1) is a cross-sectional view illustrating that the dislocation is concentrated toward the bottom of the pit while the growth is being performed, so that the dislocation clusters are concentrated in a closed defect concentration region H extending in the longitudinal direction; (2) the cross-sectional view is a view illustrating that the dislocation rises toward the pit bottom while growing, but the closed defect aggregation region H always absorbs the dislocation as it goes to the bottom.

FIG. 5 is a view for explaining a method of growing a single crystal gallium nitride substrate according to the present invention, according to which a seed is disposed on a base substrate, GaN is grown on the seed, a closed defect aggregation region H is formed at the pit bottom, a single crystal low displacement accompanying region Z is formed around the closed defect aggregation region H, and a single crystal low displacement remaining region Y is formed around the closed defect aggregation region Z.

FIG. 6 is a plan view showing a method of growing a single crystal gallium nitride substrate according to the present invention, in which a seed is disposed on a base substrate, GaN is grown on the seed, a closed defect aggregation region H is formed at the pit bottom, a single crystal low displacement accompanying region Z is formed around the closed defect aggregation region H, and a single crystal low displacement remaining region Y is formed around the closed defect aggregation region H. As can be seen, the seed is regularly arranged geometrically on the substrate base plate.

FIG. 7 is a perspective view illustrating a single-crystal gallium nitride substrate of the present invention, which is formed by: a seed is arranged on a substrate, GaN is grown on the seed, a closed defect region H is formed in the bottom of the pit, a single crystal low displacement accompanying region Z is formed around the closed defect region H, a single crystal low displacement remaining region Y is formed around the closed defect region Z, and after the growth of the seed, the substrate is removed and planarized.

FIG. 8 is a top view of a single-crystal GaN substrate of the present invention in which seeds are arranged on a substrate in a 6-fold symmetrical pattern to grow crystals.

FIG. 9 is a top view of a single-crystal GaN substrate of the present invention in which seeds are arranged on a base substrate in a 4-order symmetrical pattern to grow crystals.

FIG. 10 is a top view of a single-crystal GaN substrate of the present invention in which seeds are arranged in a 2-fold symmetrical pattern on a base substrate to grow crystals.

Fig. 11 is a schematic view of a method for growing a single-crystal gallium nitride substrate according to embodiment 1 of the present invention, the substrate being formed by: a GaN oriented growth layer is grown on a base substrate, a seed is placed on the GaN oriented growth layer to carry out concave-convex growth of GaN, a closed defect aggregation region H is formed in the pit bottom, a single crystal low displacement accompanying region Z is formed around the closed defect aggregation region H, a single crystal low displacement remaining region Y is formed around the closed defect aggregation region Z, and after the growth of the crystal, the base substrate and the GaN oriented growth layer are removed and planarized.

Fig. 12 is a schematic view of a method for growing a single-crystal gallium nitride substrate according to embodiment 2 of the present invention, the substrate being formed by: a seed is arranged on a substrate, GaN is grown on the seed, a closed defect region H is formed in the bottom of the pit, a single crystal low displacement accompanying region Z is formed around the closed defect region H, a single crystal low displacement remaining region Y is formed around the closed defect region Z, and after the growth of the seed, the substrate is removed and planarized.

Fig. 13 is a schematic view of a method for growing a single-crystal gallium nitride substrate according to embodiment 4 of the present invention, the substrate being formed by: after a GaN epitaxial layer is grown on a different substrate such as sapphire, GaN grains, that is, seeds, are arranged thereon to grow a GaN uneven surface, a closed defect aggregation region H is formed at the bottom of the pit, a single crystal low displacement accompanying region Z is formed around the closed defect aggregation region, and a single crystal low displacement remaining region Y is formed around the closed defect aggregation region.

Fig. 14 is a schematic view of a method for growing a single-crystal gallium nitride substrate according to embodiment 5 of the present invention, the substrate being formed by: after such crystal growth, the sapphire substrate and the GaN epitaxial layer are removed and planarized.

Fig. 15 is a schematic view of a process for producing a single crystal gallium nitride substrate according to example 6 of the present invention, in which a GaN substrate formed using pattern a of example 1 of the present invention is used as a base substrate, a GaN epitaxial growth layer is grown thereon without disposing a seed, a closed defect aggregation region H is formed above the closed defect aggregation region H, one of a single crystal low displacement accompanying region Z and a single crystal low displacement remaining region Y is formed above the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y, and the obtained thick GaN crystal is sliced and polished to obtain a plurality of GaN substrates.

Detailed Description

The following describes embodiments of the present invention. The principle of the invention is as follows.

Gallium nitride is grown while ensuring that pits formed by concave and convex surfaces are always present on the surface and a closed defect aggregation region H, which is a defect aggregation, is present inside, and the crystal grain boundary K, which is the interface between the closed defect aggregation region H and a single crystal low displacement accompanying region Z around the closed defect aggregation region H, is regarded as a site for annihilation and accumulation of displacement, thereby reducing the displacement of the single crystal low displacement accompanying region Z around the closed defect aggregation region H and a single crystal low displacement remaining region Y, and obtaining a low displacement GaN crystal substrate.

Alternatively, the low dislocation crystal substrate can be obtained by growing gallium nitride while ensuring that pits formed of concave and convex surfaces are always present on the surface and that a closed defect aggregation region H, which is a defect aggregation, is present inside, and reducing the dislocations of the single crystal low dislocation co-occurrence region Z around the closed defect aggregation region H and the single crystal low dislocation remaining region Y by using a crystal grain boundary K, which is the interface between the closed defect aggregation region H and the single crystal low dislocation co-occurrence region Z around the closed defect aggregation region H, and the core S inside the closed defect aggregation region H, as the site for annihilation and accumulation of dislocations.

The practical realization method is as follows: on the growth surface at the time of crystal growth, pits formed of uneven surfaces are formed, the closed defect aggregation region H is always held at the bottom of the pits and crystal growth is performed, and displacement is trapped in the closed defect aggregation region H, whereby displacement of the peripheral single crystal portion (the single crystal low displacement residual region Y and the single crystal low displacement accompanying region Z) is reduced.

This is the basic idea of the invention. It is not sufficient to form pits consisting of a concave-convex surface only on the crystal surface, and it is necessary to form a closed defect cluster region H on the bottom of the pits. The closed defect cluster region H is composed of an inner portion (referred to as a core S) and a surface (referred to as a grain boundary K), but is a defect cluster and is a space completely closed by the grain boundary K. This is important. Thus, the crystal grain boundary K and the core S are responsible for accumulating and eliminating the displacement, so that the displacement of other parts is reduced.

The "other portion" includes a portion located outside the pit and connected to the lower portion of the pit. The portion covered with the pit is referred to as a single crystal low dislocation accompanying region Z. The portion outside the pit is referred to as a single crystal low dislocation remaining region Y. Both are low dislocation and are single crystals.

The closed defect concentration region H serves to make the single crystal low dislocation remaining region Y and the single crystal low dislocation accompanying region Z into a low dislocation single crystal. This is because the crystal grain boundary K and the core S absorb displacement and are destroyed or accumulated so as not to be detached. The most important part of the present invention is to enclose the defect collection area H. The closed defect cluster region H has the most fundamental importance of the present invention.

Why is the pits in the surface necessary? It has two functions. First, the closed defect aggregation region H is to be kept at the pit bottom. The closed defect aggregation region H is formed next to the pit bottom, and the closed defect aggregation region H cannot be formed without a pit and is a closed defect aggregation region H next to a pit. From this point of view, pits must be generated. But not necessarily the reverse. Sometimes, the defect aggregation region H is not closed even if there is a pit. At this time, it is called a blank pit. Empty pits are not allowed.

The prior application (Japanese patent laid-open No. 2001-103207) of the present inventors is to use pits as a requirement, but that means empty pits not accompanied by a closed defect aggregation region H, and therefore accumulated dislocation cannot be eliminated. The planar defect and the linear defect with an angle of 60 degrees can be generated at the bottom of the hollow pit, but the displacement cannot be closed.

The invention forms a closed defect gathering area H at the bottom of the pit. Such pits having a closed defect aggregation region H at the bottom are referred to as "solid pits". Therefore, the present invention is to generate a real pit and provide a closed defect cluster region H to permanently eliminate and accumulate the displacement in the closed defect cluster region H.

The pit has another function of: the crystal is grown while being tilted inward, and the displacement of the periphery (the single crystal low displacement accompanying region and the single crystal low displacement remaining region) is pulled inward and converged into the closed defect cluster region H. Without pit tilt, the dislocations extend only straight upward (parallel to the growth direction) and do not cluster in the closed defect pool H. The dislocation is reduced without agglomeration. Therefore, the pits have the function of holding the closed defect aggregation region H and the function of introducing the pits into the closed defect aggregation region H by concentrating the displacement.

How is the closed defect set region H formed? For this purpose, the seeds are distributed on the substrate surface at the initial stage of crystal growth. The closed defect aggregation regions H and pits can be formed thereon by letting the seeds exist on the substrate surface. By positively disposing the seed on the substrate surface, the positions of the closed defect aggregation region H and the pit can be accurately specified. In fact, the new and inventive concept of the present invention is the sowing of seeds. By geometrically regularly arranging the seed, the closed defect pool areas H and pits can be geometrically regularly generated.

If the closed defect cluster region H is a defect cluster and cannot be used, the remaining single crystal low dislocation co-region Z and the single crystal low dislocation remaining region Y can be used. If the position of the closed defect concentrated region H can be specified precisely in advance by seeding, the single crystal low dislocation residual region Y and the single crystal low dislocation accompanying region Z can also be specified in advance. This spatial control arises from seeding. The present invention is valuable in that the controllability of the space where the low dislocation residual region of the single crystal and the low dislocation accompanying region of the single crystal can be specified by seeding is high.

Fundamentally, enclosing the defect pool H is important to the present invention. It is necessary to describe the closed defect collection area H in detail. The closed defect cluster region H may have not only one structure but also various structures such as a polycrystalline structure and a single crystal structure. There are also various types of single crystals. The kind of the closed defect pool area is described below. The closed defect cluster region H of either configuration can achieve the effect of reducing the dislocation according to the basic principle of the present invention.

(1) Polycrystalline closed defect collection region H

This means that the closed defect aggregation regions H are polycrystalline GaN with different orientations. In this case, only the closed defect aggregation region H is polycrystalline, and the single crystal low displacement accompanying region Z accompanying the pit below the closed defect aggregation region H and the single crystal low displacement remaining region Y outside the single crystal low displacement accompanying region Z are single crystals. If the closed defect aggregation region H is polycrystalline, it is an aggregation of grain boundaries. The grain boundary K at the outer periphery of the closed defect aggregation region H means a continuum of the outermost grain boundary.

(2) Single crystal closed defect assembly region H with different orientation

This means that the closed defect aggregation region H is an aggregation of one or more single crystal GaN of a certain orientation different from the surrounding single crystal. In the case of crystal growth in the C direction, the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y are single crystals having a (0001) plane parallel to the surface. The closed defect aggregation region H is an aggregation of crystals having a certain orientation, but the c-axis and the b-axis do not coincide with the c-axis, the b-axis, and the like of a single crystal.

(3) Single crystal closed defect region H with only <0001> uniform orientation

This means that the closed defect aggregation region H is an aggregation of one or more single crystal GaN having a certain orientation that is common to the surrounding single crystal but different from the surrounding single crystal by <0001 >. In the case of crystal growth in the C direction, the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y are single crystals having a (0001) plane parallel to the surface. The c-axis of the closed defect pool H is parallel to the c-axis (<0001>) of the single crystal portion, and the a-axis and the b-axis are different from the a-axis and the b-axis of the single crystal. I.e. about the c-axis. If the closed defect cluster region H is reversely rotated about the c-axis, the orientation becomes the same as that of the single crystal portion.

(4) Polarity reversed single crystal closed defect assembly H

This means that the c-axis of the closed defect pool region H is antiparallel to the c-axis of the single crystal portion. That is, in the closed defect cluster region H, the orientation is reversed by 180 degrees with respect to the periphery thereof, and the crystal becomes a single crystal with reversed polarity. If the c-axis of the closed defect aggregation region H is rotated by 180 degrees, the orientation becomes the same as that of the single crystal portion. Although the GaN crystal has polarity, the surface of the (0001) plane is the Ga atom plane, and the (000-1) plane is the nitrogen atom plane. Therefore, when the <0001> direction is reversed by 180 degrees and the polarity is reversed, a grain boundary exists at the region boundary. The closed defect cluster region H may be a single crystal or a polycrystal having one or more crystal grains whose <0001> orientation is inverted by 180 degrees.

(5) Closed defect collection area H separated by planar defect

The closed defect cluster region H is one or more crystal grains separated from the surrounding single crystal portion by the planar defect.

(6) Closed defect collection region H separated by linear defects

The closed defect assembly region H is one or more crystal grains separated from the surrounding single crystal portion by linear defects.

(7) Closed defect assembly area H separated by planar defect and in same orientation

The closed defect pool H has the same crystal orientation as the surrounding single crystal portion, but is one or more crystal grains separated by planar defects.

(8) Closed defect assembly region H of same orientation separated by linear defects

The closed defect pool H has the same crystal orientation as the surrounding single crystal portion, but is one or more crystal grains separated by linear defects.

(9) Slightly inclined closed defect concentrated region H

The closed defect integrated region H is almost in the same crystal orientation as the surrounding single crystal portion, but slightly inclined.

Described above is the diversity of crystal orientations of the closed defect aggregation regions H. Then the crystal orientation says the defect. The closed defect aggregation region H has a large number of crystal defects therein, and when the closed defect aggregation region H is polycrystalline (1), there is a grain boundary. However, when the closed defect cluster region H is a single crystal, the number of defects is also increased. The bottom of the pit formed by the concave-convex surface is located inside the closed defect aggregation region H. In some cases, a dislocation cluster portion is formed in the closed defect cluster region H to form a defect. Therefore, the closed defect cluster region H may contain defects and be separated from the surrounding single crystal portion by planar defects.

(10) Closed defect collection region H containing defects and separated by planar defects

The closed defect concentration region H contains crystal defects and is separated from the surrounding single junction portion by surface defects.

(11) Closed defect collection regions H containing defects and separated by linear defects

The closed defect concentration region H contains crystal defects and is separated from the surrounding single junction portion by linear defects.

(12) Closed defect assembly area H containing planar defect and linear defect

The closed defect aggregate region H contains crystal defects, which are often planar defects or linear defects.

Various closed defect collection areas H are described above. Then the crystal growth orientation is said again below. Generally, the crystal growth direction is the c-axis direction. Since hexagonal gallium nitride is grown on the hetero substrate, the symmetry of the crystal orientations of the hetero substrate and GaN can be made uniform when crystals are grown in the c-axis direction having 3-order symmetry. Therefore, the growth tends to be in the c-axis direction. If GaN itself can be used as a substrate, growth in a direction other than the c-axis direction is also possible, but since it is a heterogeneous substrate, growth is mainly in the c-axis direction.

In this case, the pits formed by the uneven surface are inverted hexagonal pyramids or inverted dodecagonal pyramids. This is because GaN is a hexagonal system, has 6 equal tilted surfaces, and can form hexagonal pyramid pits. Fig. 1 shows pits generated in the C-plane. The inverted hexagonal pyramid shaped pit has six inclined planes. The average growth direction is the c-axis direction, i.e., the upper direction in the figure. However, the inclined surface (uneven surface) grows inward as indicated by the arrow in the figure. If there are two sets of equal inclined surfaces, a dodecapyramid is formed. That is, since the first three indices h, k, and m of (hkmn) are the same when exchanged, there are 6 equivalent planes.

The surface index of the concave-convex surface can be generally expressed as { kk-2kn } (k, n are integers) and { k-k0n }. The two faces are respectively arranged at intervals of 60 degrees, and the angles of the two groups of faces are 30 degrees, so that 30-degree facets can be formed. A dodecapyramid can thus be produced. When only one of the groups is superior, an inverted hexagonal pyramid is formed.

Among them, the most common uneven surfaces are {11-22} surfaces and {1-101} surfaces. The reverse hexagonal pyramid can be generated only by one party, and the reverse dodecapyramid can be formed when the two parties coexist. Sometimes {11-21} planes also appear.

Further, the pit formed by the uneven surface may be an inverted hexagonal pyramid or an inverted dodecapyramid having two overlapping segments with different inclination angles. This is the case when the c-axis index is different, such as 11-22, 11-21, or 1-101, 1-102. Run to the center with shallow slope (n is large); the inclination is large and goes to the outer periphery (n is small), but follows the single crystal low displacement accompanying region Z.

The relationship between the closed defect region H and the irregularities upon crystal growth will be described. It is known that: the closed defect set region H has a certain relation with the surface index of the concave-convex surface.

The closed defect aggregation region H is located at the bottom of a pit formed by the concave-convex surface. The closed defect integrated region H has a face slightly different in face index from the concave-convex face of the pit. As described above, the surface indexes of the most concave-convex surfaces constituting the pits are {11-22} and {1-101 }.

However, the top (pit bottom) of the closed defect aggregation region H is inclined shallower than the inclined surface of the unevenness. For example, the two-step inclined surface shown in FIG. 5(b) and (3) has a large index of the c-axis, and therefore {11-24}, {11-25}, {11-26}, {1-102}, and {1-104} appear, and constitute the inclined surface of the pit bottom. Then, in the closed defect aggregation region H at the bottom of the pit formed by the uneven surface, the <0001> direction is inverted by 180 degrees with respect to the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y, and when the polarity is inverted, the surface is grown with the crystal plane orientation having a significantly small inclination angle. In this case, the crystal plane orientation having a small tilt angle includes: {11-2-4}, {11-2-5}, {11-2-6}, {1-10-2}, {1-10-3}, {1-10-4 }. Since it is buried with growth to constitute the closed defect aggregation region H, the closed defect aggregation region H has such a large area index of n. The boundary of the closed defect aggregation region H at the bottom of the pit constituting the uneven surface is formed at a boundary portion having a shallower angle than the uneven surface constituting the pit. This phenomenon is clearly evident especially in this case: the enclosed defect assembly region H is reversed in the <0001> direction by 180 degrees and reversed in polarity with respect to the surrounding single crystal region. The shallow angle of the inclined plane of the pit bottom is an important concept.

The closed defect aggregation regions H at the bottoms of the pits formed by the concave and convex surfaces exist in a concentrated manner. Here, the dot shape does not mean a linear shape or a circular shape, but means that the point is concentrated at one point. For example, the black portion at the center of the concentric circles of fig. 7 is a closed defect aggregation region H, concentrated in a dot shape. The point-shaped concentration has the advantages that: even if the GaN substrate is cleaved in any direction, the probability that the closed defect aggregation region H appears on the fracture surface is low.

Since the closed defect integrated region H is hardly exposed to the cleavage plane, the cleavage plane can be effectively used. Thus, the advantage of easy splitting is also brought. This is because cleaving is hampered if a defect occurs on the plane to be cleaved.

The closed defect aggregation regions H formed at the bottom of the pits can be grown while maintaining a diameter of 1 μm to 200 μm. Although growth conditions are also concerned, in any case, by growing while keeping the diameter of the closed defect aggregation region H at 1 μm to 200 μm, it is possible to concentrate dislocation in the closed defect aggregation region H in the center of the pit.

Preferably, when the diameter of the concave-convex shaped pit is small, the diameter of the closed defect aggregation region H is also small; when the diameter of the concave-convex shaped pit is large, the diameter of the closed defect aggregation region H is also large. In practice, when the diameter of the closed defect aggregation region H is 1 μm in small hours, the effect (reduction in displacement) is obtained, and when the diameter is large, it is appropriate that the diameter is not more than 200 μm at maximum in consideration of economic factors.

The closed defect cluster region H at the bottom of the pit formed by the concave-convex surface is generally amorphous in shape (cross section). This is because the energy becomes unstable as the closed defect aggregation region H grows, and for this reason, the closed defect aggregation region H deforms in accordance with the shape of the irregularities based on the relationship of the isomorphous orientation.

Sometimes, the shape (cross section) of the closed defect aggregation region H may also be circular. A circular cross section is often seen when the number of polycrystalline grains in the closed defect aggregation region H is large or when the diameter of the closed defect aggregation region H is large.

On the other hand, when the number of polycrystalline grains in the closed defect aggregation region H at the bottom of the pit having the uneven surface is small or the diameter of the closed defect aggregation region H is small, the shape of the closed defect aggregation region H may be angular.

When the average crystal growth direction is the c-axis direction, polycrystalline regions at the bottoms of pits formed by the uneven surfaces on the outermost surface of the actual crystal growth are formed following the pit bottom as the crystal grows, and as a result, the polycrystalline regions exist in a crystal in a columnar shape parallel to the c-axis and in a stretched form.

At this time, there is also a mechanism to work: at the boundary between the closed defect aggregation region H at the bottom of the pit formed by the uneven surface and the surrounding single crystal part (the single crystal low displacement residual region Y and the single crystal low displacement accompanying region Z), displacement extending from the single crystal part to the plane parallel to C of the closed defect aggregation region H is concentrated, and the displacement is annihilated and accumulated at the crystal grain boundary K to reduce the displacement of the single crystal part.

This shift concentration mechanism is: in the pit formed from the concave-convex surface inclined to the C-plane, the pit extends parallel to the center of the pit with the concave-convex surface growth displacement and concentrates on the closed defect aggregation region H, whereby the penetrating displacement in the single crystal portions Z and Y can be reduced. For example, according to (a) and (b) of fig. 1, the concave-convex surface is laminated inward as indicated by an arrow, so that the displacement advances inward parallel to the C-plane as indicated by the arrow. That is, the displacement is concentrated toward the pit center and absorbed by the closed defect aggregation region H in the center. Fig. 2 is a schematic diagram of the displacement movement on the concave-convex surface. The inwardly-propelled deflection is converted to the direction of the ridge line as soon as the inwardly-propelled deflection touches the ridge line 8 of the hexagonal pyramid, and the inwardly-propelled deflection is horizontally propelled along the ridge line. It will concentrate on the central complex point D.

This is a deflection reduction mechanism also described in the prior application. However, in the prior application, the closed defect cluster region H does not exist at the recombination point, and as shown in fig. 1(b), the planar defect 10 is large and the displacement reduction is insufficient.

Fig. 3 illustrates the indexing motion of the prior application, without the pit bottom enclosing the defect pool H. Therefore, the displacement is concentrated but is open, and the displacement may be redeployed. Its concentration is also low. Open systems are not feasible.

In the present invention, as shown in fig. 4, there is a closed defect aggregation region H at the bottom of the pit, and the dislocation is absorbed by the closed defect aggregation region H. One of them is destroyed, and the other is accumulated. The parts are the periphery of the closed defect aggregation region H, namely a crystal grain boundary K and an internal core S. Sometimes only the grain boundary K, sometimes both K and S. In either case, the closed defect aggregation region H is a closed space closed by the grain boundary K. In principle, the displacements cannot escape once they enter the closed defect pool H. Therefore, the displacement reduction in the single crystal low displacement remaining region Y and the single crystal low displacement accompanying region Z is permanent. Fig. 3 and 4 show a clear contrast between the prior application and the present invention.

The following describes how the method of the present invention is applied in the actual fabrication of a gallium nitride substrate. Since a heterogeneous substrate is used, the c-axis direction having 3-order symmetry is the growth direction.

As a method for growing a crystal on an actual crystal substrate, pits having a concave-convex surface are formed on the surface of the substrate during crystal growth, and a closed defect cluster region H is formed in the central bottom of each pit.

That means that the pits, the closed defect aggregation areas H, are spatially regularly arranged. Fig. 6(b), fig. 7, fig. 8(a), (b), and the like show regular base structure arrangements. Preferably, all spaces are regularly buried in the same pattern. In this case, the possible patterns are naturally defined.

Here, when pits having a closed defect aggregation region H in the center of the concave-convex surface are regularly arranged, there are only three patterns of 6-fold symmetry (regular triangles arranged at the vertices), 4-fold symmetry (squares arranged at the vertices), and 2-fold symmetry (rectangles arranged at the vertices). If the condition of arranging the same pattern everywhere is abandoned, there may be more patterns.

(1)6 th order symmetry (FIGS. 8(a), (b)) (L55)

As shown in fig. 8, the pits are arranged in the most dense arrangement because they are nearly conical, and have a 12-angle shape and a 6-angle shape. The long pitch p of one side of the regular triangle, which is the pattern repetition period. If adjacent pits are in contact with each other, the pit diameter d is substantially equal to the pitch p (p ═ d). In FIG. 8(a), the direction of the pitch is parallel to the <11-20> direction of the GaN crystal. In FIG. 8(b), the direction of the pitch is parallel to the <1-100> direction of the GaN crystal.

In the figure, the black dot at the center of the concentric circle is the closed defect collection region H. The white circles around the pits show the extension of the pits and also show the range of the single crystal low displacement zone Z. The narrow triangular region formed by the gap between the adjoining concentric circles is the single crystal low dislocation residual region Y. The most dense arrangement means that the area occupied by the single crystal low dislocation accompanying region Z is the largest in a given area, while the area of the closed defect accumulating region H is also the largest, and the area of the single crystal low dislocation remaining region Y is the smallest. Since the resistivity of the region grown from the C-plane (the single crystal low displacement remaining region Y) tends to be high, it is desirable to use a 6-fold symmetrical pattern in which Y is narrow for the conductive substrate.

(2) 4-degree symmetry pattern (FIGS. 9(a), (b)) (L56)

As shown in fig. 9, the pits are arranged in a medium density because they are nearly circular, 12-cornered, and 6-cornered. The long dimension of one side of the square, referred to as the pitch p, is the pattern repeat period. If adjacent pits are in contact with each other, the pit diameter d is substantially equal to the pitch p (p ═ d). In FIG. 9(a), the direction of the spacing is parallel to the <11-20> and <1-100> directions of the GaN crystal. In FIG. 9(b), the direction of the spacing is at a 45 degree angle relative to the <11-20> and <1-100> directions of the GaN crystal. This orientation cannot be expressed by a low plane index.

In the figure, the black dot at the center of the concentric circle is the closed defect collection region H. The white circles around the pits show the extension of the pits and also show the range of the single crystal low displacement zone Z. The star-shaped region formed by the gap between the adjoining concentric circles is the single crystal low dislocation residual region Y. Here, the single crystal low dislocation residual region Y occupies a large area and the region grown from the C-plane (single crystal low dislocation residual region Y) has a high resistivity as compared with example 1, so that it is not suitable as a conductive substrate, but it is quite preferable if the GaN semiconductor device chip has a square shape. What can be practically utilized as a semiconductor device chip is the single crystal low dislocation residual region Y and the single crystal low dislocation accompanying region Z, which are sufficiently spread out regularly for the semiconductor device configuration. If the semiconductor device pitch and the pit pitch are made to coincide with each other, the semiconductor device can be manufactured under all the same conditions, and the cleaving is also facilitated.

(3) 2-degree symmetry pattern (FIGS. 10(a), (b)) (L57)

As shown in fig. 10, the pits are arranged in a moderately dense pattern because they are nearly circular, and have a 12-corner shape and a 6-corner shape. Substantially rectangular in arrangement. It is necessary to distinguish the short side pitch p from the long side pitch q, that is, the pattern repetition period has anisotropy. If adjacent pits are in contact with each other, the pit diameter d is substantially equal to the pitch p (p ═ d). In FIG. 10(a), the direction of the short pitch p is parallel to the <11-20> direction of the GaN crystal. In FIG. 10(b), the direction of the short pitch p is parallel to the <1-100> direction of the GaN crystal.

In the figure, the black dot at the center of the concentric circle is the closed defect collection region H. The white circles around the pits show the extension of the pits and also show the range of the single crystal low displacement zone Z. The wide band-like region formed by the gap between the adjoining concentric circles is the single crystal low dislocation remaining region Y. Here, as q is made larger than p, the area occupied by the single crystal low dislocation remaining region Y is larger as compared with the above two examples. What can be effectively utilized as a semiconductor device chip is the single crystal low dislocation residual region Y and the single crystal low dislocation accompanying region Z, which are sufficiently spread out regularly for semiconductor device configuration. Since the semiconductor device chip is rectangular in nature, it can be said that such a pattern is most suitable.

When pits composed of a large number of concave and convex surfaces having closed defect aggregation regions H at the bottoms are regularly arranged on the crystal surface at the time of crystal growth, it is desirable that the shortest center distance (pitch p) between the pits is 50 μm to 2000 μm.

Considering the actual case of manufacturing a semiconductor device thereon, it is difficult to use the semiconductor device if the pitch of pits is smaller than the chip size of the semiconductor device. Therefore, the pitch of the low-dislocation single crystal pits is as small as 50 μm, and it is difficult to manufacture a semiconductor device below the pitch.

On the other hand, the upper limit of the pit pitch is 2000 μm. If the pitch is too large, the pit depth becomes large. The pit portion is to be removed by grinding. If the pit is large, the depth is large and the polishing thickness is large, so that waste is increased. Since this is uneconomical, the pitch of pits is set to 2000 μm or less. However, this is a limitation for economic reasons, and the effect of reducing the displacement of the present invention can be achieved even if the actual pitch exceeds the limitation.

[ method for Forming closed defect aggregation region H ]

A method for forming a closed defect cluster region H formed in the central bottom of a pit having a concave-convex surface is described. FIGS. 5(a), (b) illustrate the growth of one pit. Fig. 6 is a schematic view of a substrate.

In the crystal growth of the present invention, a base substrate 21 as a substrate is used. Of course, gallium nitride may be used as the base substrate 21. However, since a large GaN single crystal substrate is not easy to manufacture, a different material is actually used as the substrate. In both the dissimilar substrate and the GaN substrate, the seed 23 for blocking the defect aggregation region H is disposed in a portion of the base substrate 21 to be the blocking defect aggregation region H. Only one set of pits, seeds and closed defect aggregation regions H is shown in the figure, and a large number of pits are actually formed on the surface.

The seeds 23 are geometrically regularly arranged on the substrate surface. As shown in fig. 6(a), the seed 23 is arranged at a position on the base substrate 21 that is symmetrical 6 times. The remainder 19 of the substrate 21 is exposed at the substrate surface. A GaN crystal 22 is grown over the base substrate 21 and the seed 23. GaN is difficult to grow on the seed 23 and is easy to grow on the substrate. It is this poor growth difficulty that is used to create pits. This is an elegant approach. As shown in (2) of FIGS. 5(a) and (b), a layer is thickly formed on the base surface of the GaN crystal 22, and a flat surface 27(C surface) is formed thereon. Since crystals are hard to adhere to the seed 23, a pit 24 (concave portion) is formed. The pits 24 are constituted by 6 or 12 asperities 26. It is important that pits 24 are formed on the seed 23.

When the GaN crystal 22 is further grown, the opposing concave-convex surfaces 26 meet on the seed 23. Then, a part of the GaN crystal is also deposited on the seed 23. This portion constitutes the bottom 29 of the pit 24. As growth pit 24 moves upward, crystal deposition also gradually occurs in bottom portion 29 of pit 24. This state is shown in (3) of FIGS. 5(a), (b).

The grown crystal 25 connected to the bottom 29 is heterogeneous to the other part of the crystal 22. The portion of crystal 25 opposite to seed 23 under bottom 29 is called closed defect pool H. The boundary 30 between the closed defect pool H and the other crystals 22 is the grain boundary K. In this regard, the interior is referred to as the core S. That is, the seed 23, the closed defect pool H, and the bottom 29 are arranged in this order from bottom to top. There must be a central pit bottom above the seed 23 with a closed defect pool H between the seed and the pit bottom.

The portion of the crystal immediately below the concave-convex surface 26 corresponds to the single-crystal low-dislocation accompanying region Z. The crystal immediately below the flat surface 27 corresponds to the single crystal low dislocation remaining region Y.

There are two cases of pit bottom portions 29, and in fig. 5(a), the inclination of pit bottom portions 29 is the same as that of concave-convex surface 26, and is a surface of the same crystal orientation; in contrast, in fig. 5(b), the inclination of pit bottom 29 is shallower than the inclination of concave-convex surface 26. The inclined shallow pit bottom 29 is a surface slightly different from the concave-convex surface 26, i.e., the surface index n in the c-axis direction is slightly larger. Assuming that the relief surface 26 is (11-22), then its base 29 can be expressed as (11-24).

[ possibility of multiple seeds ]

The seed 23 serving as the seed for closing the defect aggregation region H may be directly attached to the substrate, or may be attached to the substrate after a GaN layer is thinly coated on the substrate.

The seeds 23 should be spatially regularly arranged. Seed patterns of 6-fold symmetry, 4-fold symmetry and 2-fold symmetry have already been mentioned above.

The seed material may be any material that is difficult to grow GaN, such as a thin film, particles, a surface of a different substrate, or the like. For the film, both an amorphous film and a polycrystalline film can be used. The seed production method and the seed arrangement method are different depending on the form of the thin film, the particle, the substrate surface, and the like.

[ method 1 for preparing seed (in the case of thin film) ]

And placing a thin film seed on the part of the substrate base plate which is to form the closed defect assembly area H. The film has a two-dimensional shape and can be patterned in a desired shape and distribution. In the patterning, a photolithography method, a method of vapor deposition using a metal mask, a printing method using a mask, or the like can be used. The position precision of the closed defect assembly area H can be improved through high-precision patterning.

The shape of each seed may be circular, polygonal, etc. The polygon includes a triangle, a 4-corner, a 6-corner, and an 8-corner. It also affects the shape of the closed defect collection area H. Preferably, the amorphous, polycrystalline thin film patterned into circles and polygons has a diameter of 1 μm to 300. mu.m. The size of the seed may generally determine the size of the closed defect pool H grown thereon. This is true for the seed size, since the diameter of the closed defect pool H is preferably about 1 μm to 300. mu.m. But slightly smaller than the seed diameter to enclose the defect pool H.

[ kinds of thin film seed materials ]

The polycrystalline thin film and the amorphous thin film used as the seed may be either metal or oxide. Especially, the following effects are good:

a.SiO₂film (polycrystal or amorphous)

b.Si₃N₄Film (polycrystal or amorphous)

Pt (platinum) thin films (polycrystalline)

d.W tungsten film (polycrystal)

[ method 2 for producing seeds (in the case of particles) ]

The seeds are not necessarily limited to only thin films. The seed of the closed defect aggregation region H can be constituted by regularly arranging GaN polycrystalline particles on the base substrate. By disposing GaN single crystal grains on the base substrate, a polycrystal having a different orientation from that of the peripheral single crystal portion is grown thereon.

It seems surprising that the GaN particles, by nature, retard the formation of pits upon growth of GaN thereon. However, GaN, which is a common material, prevents crystal growth due to different particle orientations. Not limited to GaN, particles of any material may be used. However, GaN is preferred because it is not contaminated by diffusion.

The particles have a three-dimensional structure unlike the thin film, but have the effect of forming pits and closing the defect aggregation regions H as in the thin film. The particles are independent and can be freely placed on the base substrate 21.

[ method 3 for producing seeds (for different substrates) ]

The seed is not necessarily limited to a thin film or a particle, and the substrate itself of a different type may be used as the seed. Since the base substrate is different from GaN, a motive force for generating pits can be provided. This is also a method of choice.

The non-GaN substrate surface is periodically exposed from the GaN layer as a seed. Light is so difficult to understand, and this is true: the closed defect aggregation region H can be formed by thinly growing a GaN-oriented growth layer (GaN buffer layer) on the base substrate, removing the GaN-oriented growth layer at a portion where the closed defect aggregation region H should be formed to expose the base substrate, and then epitaxially growing GaN thereon to form pits due to slow growth of the crystal on the base substrate.

As for the method of forming the seed by exposing the base substrate, GaN is grown without a GaN buffer layer, and a closed defect aggregate region H tends to be generated thereon. The thin film seed can be formed by photolithography, but in the case of a substrate surface, it should be noted that the negative and positive are reversed. The substrate can be made of sapphire, spinel, SiC, GaAs, or the like.

[ seed production method 4 (in the case of providing a thin film on a GaN oriented growth layer) ]

The seed is not limited to the seed formed by directly providing the thin film on the base substrate. This approach is also feasible: a GaN oriented growth layer is grown on a base substrate, a polycrystalline or amorphous thin film mask made of a different material is deposited thereon, and after a part of the mask is removed by photolithography, the remaining mask is used as a seed. Namely, a substrate/GaN/thin film seed structure is constituted. The structure of substrate/thin film seed, described earlier without GaN, must be distinguished. The closed defect pool region H can also be grown from the grown pit by the thin film seed, and then grown from the bottom of the pit.

[ seed production method 5 (when a thin film is formed on a substrate) ]

A polycrystalline and amorphous thin film mask of a different material is directly stacked on a base substrate, and after a part of the mask is removed by photolithography, the remaining mask can be used as a seed. That is, a substrate/thin film seed structure is constituted.

[ Effect of seed (FIG. 15) ]

On the substrate provided with the seed, GaN is grown in an orientation except for the seed. Since the seed has a function of preventing GaN growth, GaN growth is delayed. Although delayed, the epitaxial layer on the surrounding base substrate grows high and further penetrates, and as a result, GaN is also deposited on the seed. It varies depending on the growth conditions. Sometimes, GaN grown on the seed is polycrystalline (a).

Sometimes, there is a pile of surrounding single crystals on the seed, and then there is a single crystal on the seed, which is in a different crystal orientation from the surrounding single crystal (B). Sometimes the crystal orientation is different but the polarity is reversed. In some cases, the <0001> axis is common and deflected to the surrounding single crystal. Or sometimes a single crystal with slightly different orientation. Since GaN generated on the seed is the closed defect aggregation region H, the structure of the closed defect aggregation region H varies depending on the conditions.

[ use of 1 (simultaneously) for both ELO mask and seed mask for blocking defect set region ]

The ELO (epithelial temporal evolution) means: a mask having regularly arranged small windows is attached to a substrate, a GaN layer trapped in the small windows is grown in an oriented manner, the direction of displacement becomes lateral as soon as the GaN layer exceeds the thickness of the mask, and the displacements collide and disappear when the GaN layers meet at bisectors between adjacent small windows. This is a delicate way to reduce displacement at the beginning. It is also mentioned in the prior application of the present inventors, Japanese patent application No. Hei 9-298300, Japanese patent application No. Hei 10-9008. Since the layer extends laterally across the mask and the dislocations run laterally, it is called a lateral line, and since it grows across the mask, it is also called a overgrowth.

The ELO mask is a female mask with large mask area, narrow opening area, and regularly small windows in small area (mask area greater than 50%). The small windows are often arranged at the vertices of regular triangles spread out and clustered together, and the mask pattern is 6 times symmetrical. This is also similar to the seed pattern of the closed defect pool H described so far.

But there are significant differences. The ELO mask has small windows and small arrangement intervals of the windows, and the aperture and the interval of the windows are about several micrometers. The mask is a female mask having a large mask area and a narrow opening area (mask area is more than 50%).

The seed pattern is a pattern in which large seeds (1 μm to 300 μm in diameter) are widely and loosely distributed (50 μm to 2000 μm). The mask is a male mask (mask area is less than 50%) with a small mask area and a large opening area. If so, the two are different in shape and size.

They are also different in action and not mixed. After all, ELO aims to eliminate the dislocation, and the seed of the closed defect pool H aims to form the closed defect pool H positively.

The blank portion (substrate-exposed portion) of the seed pattern, on which the ELO mask is placed, is wide. That is, the base substrate is masked by two different kinds of masks, the seed pattern and the ELO mask formed on the blank portion thereof. This is a rather complicated and scouring process. For example, as shown in fig. 6(a), the seed 23 is arranged 6 times symmetrically on the base substrate 21, leaving a wide margin 19. The ELO mask is placed over the blank 19. The same mask material is used. SiO can be used₂SiN, or metal mask. If the mask material is the same, the mask can be formed by evaporation, photolithography, or printing at one time.

Such composite masks do not function well. GaN grown under an ELO mask has the effect of allowing lateral dislocation and reducing dislocation at the beginning. And by the seed of the seed mask, pits and closed defect assembly regions H can be formed. Although these two effects are simply added, the displacement is reduced at the initial stage of growth, and the reduced displacement is absorbed by the closed defect pool region H to eliminate the accumulation, so that the displacement reduction in the single crystal low displacement associated region Z and the displacement reduction residual region Y can be further advanced.

[ use of ELO mask and closed defect pool seed mask in combination with 2 (different) ]

The above method of putting an ELO mask on the blank 19 (fig. 6(a)) of the seed has an advantage that the mask formation and GaN growth are completed at once. However, since the ELO mask is placed only on the blank 19 without the seed 23, the growth conditions vary depending on the place. When such is not desired, two-stage growth may be performed, i.e., ELO growth may be performed by attaching an ELO mask on the base substrate 21 to generate a thin low dislocation GaN layer; then, a seed mask is attached thereto to perform concave-convex growth. The ELO mask may be attached after the GaN thin buffer layer is grown on the substrate. In the same manner as in the subsequent steps, ELO growth is performed, and uneven growth is performed by attaching a seed mask.

According to the above method, an ELO mask is formed on a base substrate or a base substrate having a GaN buffer layer. This can be formed by: SiO is formed first₂SiN, etcThe thin film (100 and 200nm) was etched to remove small windows (circular, angular, rectangular) at the apex positions of regular triangles each having a side of several μm arranged throughout. On which a GaN buffer layer (80-130nm) is formed by low-temperature vapor phase growth. The buffer layer is a layer for adjusting lattice unconformity, on which a GaN orientation layer is formed by high-temperature phase growth. The GaN layer is reduced in dislocation by lateral overgrowth.

On which the above-mentioned seed pattern is set. It may be a film or a particle. The pattern size is large, so that the method can be distinguished from ELO. When GaN is grown on the GaN alignment layer having the seed pattern, a pit is formed next to the seed, and a closed defect assembly region H is generated at the bottom of the pit. The single crystal low displacement accompanying region Z can be formed under the pit slope. A C-plane is grown between the pits, and a single crystal low dislocation residual region Y is grown thereunder. Since the low-dislocation growth is performed in two different stages, the GaN crystal is further reduced in dislocation.

[ method for controlling pit position on uneven surface ]

When the seed pattern is arranged on the base substrate (the GaN buffer layer may be provided on the base substrate) and GaN is grown on the seed pattern in a concave-convex manner, pits are formed in the seed pattern in a one-to-one correspondence. This is the basis of the present invention and has been described several times so far. A comparison of the seed pattern of fig. 6(a) and the GaN thick film configuration of (b) is well understood.

According to the present invention, a seed for pit formation is arranged in advance on a base substrate, GaN is grown thereon, and a pit is preferably formed in the seed position.

This can be done in particular: amorphous, polycrystalline seeds, which have been patterned, are discretely and periodically arranged on a substrate, and GaN is grown thereon to preferentially form pits in the thin film seeds. This is because, when GaN is grown on a patterned amorphous or polycrystalline thin film seed, the growth conditions of the seed and the vacant part of the base substrate are different, and the growth of the seed part is slow, so that a pit with the seed as a bottom can be formed.

As for the substance constituting the seed, any substance such as a metal, an oxide, a nitride, or the like may be used, and the substance may be a thin film or a particle. The seed can also be formed by combining and matching the substrate base plate and the GaN buffer layer. This has already been described in detail. As amorphous polycrystalline thin films, SiO₂Films, SiN films, are particularly effective. As the seed, fine particles may be used. Fine particles are regularly arranged after a thin GaN buffer layer is directly provided on a substrate base plate or provided on the substrate base plate, and GaN is grown on the fine particles in a concave-convex manner. Thus, pits with bottoms are formed on the fine particles depending on the growth conditions of the fine particles and other portions.

The fine particles for the above-mentioned applications may be different metal fine particles, oxide fine particles, or the like, or may be GaN polycrystalline fine particles or GaN single crystal fine particles. In this way, by arranging the seed in the regular space on the substrate base plate and growing GaN in the concave-convex manner, a pit bottom is formed at the seed position. The location of the pits can be predetermined. Since the closed defect concentration region H is present in the pit bottom, the single crystal low displacement accompanying region Z is present under the inclined surface (unevenness) of the pit, and the single crystal low displacement remaining region Y is present in the C-plane growth flat portion outside the pit, the three regions H, Y, Z can be precisely and accurately set by the seed arrangement.

[ production of Flat gallium nitride substrate ]

Conventionally, when growing gallium nitride on a substrate such as GaAs, flat C-plane crystal growth is adopted without exception. In the case of C-plane crystal growth, crystal growth can be carried out while maintaining a beautiful flat surface, and a large amount of displacement is uniformly distributed, and the surface becomes flat with high displacement. The ELO (epitaxial growth) crystal growth is also a flat C-plane crystal growth. In this way, the flat surface can be used as it is.

However, the concave-convex growth was proposed for the first time in the prior application of the present inventors (Japanese patent laid-open No. 2001-102307). The invention also proposes a growing method for generating the closed defect pool H by seeding seeds on top of the relief growth. Since this method also maintains the crystal side by side with the concave-convex surface, the crystal surface produced contains a large number of pits formed by the concave-convex surface, and the semiconductor device cannot be produced because of the presence of the concave-convex surface without any treatment because of the change of the concave-convex surface.

Therefore, the gallium nitride substrate manufactured according to the method of the present invention must be subjected to mechanical polishing. The gallium nitride substrate after mechanical polishing has a flat surface and can be used as a wafer for manufacturing a semiconductor device. The machining may be sheet machining, grinding, polishing, or the like. The substrate attached to the back surface is removed by etching, polishing, mechanical grinding, or the like. The back surface of the base substrate is also removed and polished to be planarized.

According to the present invention, in the GaN crystal growth, a closed defect aggregation region H is maintained while the crystal is grown, and the core S and the crystal grain boundary K of the closed defect aggregation region H are used as means for eliminating accumulated displacement, whereby the peripheral single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y are subjected to low displacement, and the GaN crystal thus obtained is machined and then used as a substrate having a flat surface.

Alternatively, according to the present invention, in GaN crystal growth, pits having an uneven surface are formed on the surface of the crystal growth, the crystal growth is performed while maintaining the closed defect aggregation region H at the bottom of the pits, the core S and the grain boundary K of the closed defect aggregation region H are used for eliminating accumulated displacement, the displacement of the peripheral single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y is reduced, and the GaN crystal thus obtained is machined and polished and then used as a substrate having a flat surface.

The mechanical processing may be one of thin-sheet processing, grinding processing, and polishing processing, or a combination of two or more thereof.

As the long crystal substrate of the present invention, single crystals of GaN, sapphire, SiC, spinel, GaAs, Si, or the like can be used.

In the above-described manufacturing method, when GaN is grown, a plurality of gallium nitride crystals can be obtained by sheet processing of thick GaN grown crystals as a material. Further, the GaN substrate that has been produced by the method of the present invention can be used as a seed crystal on which a thick crystal is grown. At this time, it is noted that: here, the closed defect aggregation region H is grown over the closed defect aggregation region H of the seed crystal, and the single crystal low displacement accompanying region Z or the single crystal low displacement remaining region Y is grown over the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y. In other words, a pit having a concave-convex surface is formed on the closed defect aggregation region H of the seed crystal, the closed defect aggregation region H is formed, and a slope and a horizontal concave-convex surface of the pit having a concave-convex surface are formed on the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y, thereby growing the single crystal low displacement accompanying region Z or the single crystal low displacement remaining region Y. As a result, when GaN is grown thick using the GaN crystal of the present invention as a seed crystal, a substantially identical ingot as the above-described ingot can be obtained. By processing these ingots, a plurality of gallium nitride crystals can be obtained.

[ gallium nitride substrate of the present invention ]

The gallium nitride substrate manufactured by the crystal growth method and the manufacturing method according to the invention is described. Since it is a substrate polished by machining, it is flat and the underlying substrate is also removed. FIG. 7 shows a GaN substrate of the present invention with the substrate removed and planarized. It illustrates in a simplified and easily understandable perspective view a CL (cathodoluminescence) observation image, which is neither a macroscopic image nor a microscopic image. To the naked eye, it is merely like a transparent glass.

The patterns are regularly arranged and are repeated to form a pattern of concentric circles. The central black portion is a closed defect aggregation region H, which is a portion grown next to the pit bottom, and is composed of a core S and a grain boundary K surrounding it. The grain boundary K and the core S or the grain boundary K constitute a means for eliminating accumulated dislocation. Pits are formed followed by seeds. Since the seed is regularly arranged on the substrate base, the closed defect regions H themselves are regularly arranged.

In this state, since the substrate is planarized by polishing, neither pits nor seeds are present, and only the closed defect aggregation regions H are left in the middle portions in the vertical direction. The white circle portion concentric with the closed defect cluster region H is the single crystal low displacement accompanying region Z, and is a portion grown as a sloped wall of a pit, that is, a sloped wall portion of a conventional pit. The pit is removed by mechanical grinding and does not exist, and the portion corresponding to the mark is the single crystal low dislocation accompanying region Z.

The single crystal low dislocation accompanying region Z is circular (dodecagonal, hexagonal) and has substantially the same size. The single crystal portion between the adjoining portions is the single crystal low dislocation remaining region Y. The single crystal low displacement remaining region Y is also a single crystal low displacement accompanying region Z, and is a single crystal having the C-plane as the surface. However, there was a significant difference in CL image, indicating a difference in brightness.

The gallium nitride substrate of the present invention has a closed defect aggregation region H in a part of the surface of the substrate and a single crystal low-level-shift region (Y, Z) in the periphery thereof.

This is simply a unit basic structure body composed of H + Y + Z. This is true for each piece cut in units. In some cases, the pit diameter is large, and one pit is formed over the entire substrate.

Alternatively, the gallium nitride substrate of the present invention is composed of a plurality of basic structures, and each (unit) basic structure (H + Y + Z) is composed of: the substrate has a closed defect cluster region H in a part of the surface thereof and a single crystal low dislocation region (Y, Z) in the periphery thereof. (L2)

The above is the basic structure of the single crystal gallium nitride substrate of the present invention.

[ type of closed defect pool H ]

It has been mentioned so far that the closed defect pool H has a diversity. Both monocrystalline and polycrystalline. Even single crystals, have a different crystal orientation than the surrounding single crystal (Y, Z). Even if the orientations are different, there is no case where the orientations are different, and there are single crystals that rotate around the axis in common with the <0001> axis of the surrounding single crystal, and there are cases where the <0001> axis is inverted, and there are some deviations from the crystal orientation of the surrounding single crystal.

A. In the case of polycrystals

The closed defect aggregation region H is polycrystalline, and the peripheral portion (Z, Y) is a low-dislocation single crystal. At this time, a grain boundary K is clearly present between the crystal grains and the surrounding portion due to the difference in orientation.

B. In the case of a single crystal having a different orientation from the surrounding single crystal portion

The closed defect aggregation region H may be a single crystal, but may be composed of one or more single crystals having different orientations from the surrounding single crystal.

Sometimes, the closed defect aggregation region H is composed of one or more crystal grains, which are all in such crystal orientations: only the <0001> axis coincides with the peripheral single crystal portion, and the remaining 3 axes are different.

The closed defect aggregation region H is effective when it is a single crystal region having a crystal orientation 180 degrees different from that of the surrounding single crystal portion in the <0001> axial direction and having a reversed polarity. The closed defect cluster region H may be composed of one or more crystal grains having a difference in crystal orientation of 180 degrees in the <0001> axial direction, instead of a single crystal.

At this time, the crystal grain boundary K is defined as the boundary between the inner and outer (0001) Ga faces and the (000-1) face. Since GaN has no inverted symmetry, the [0001] and [000-1] planes are different.

The closed defect concentrated region H may be composed of one or more crystal grains having a crystal orientation slightly inclined from the surrounding single crystal portion.

In some cases, the closed defect cluster region H and the peripheral single crystal portion are separated by a planar defect.

The closed defect aggregation region H and the surrounding single crystal portion may be separated by a linear defect.

C. The crystal orientation of the surrounding single crystal portion is the same

In some cases, the closed defect cluster region H is a single crystal having the same crystal orientation as the surrounding single crystal portion, but is separated from the surrounding single crystal portion by a planar defect.

In some cases, the closed defect aggregation region H is a single crystal having the same crystal orientation as the surrounding single crystal portion, but is separated from the surrounding single crystal portion by a linear defect.

[ internal Structure of closed defect Assembly region H ]

The closed defect concentration region H is particularly rich in crystal defects. A dislocation cluster, a planar defect, or the like may be formed. The boundary, that is, the crystal grain boundary K, may be a collection of planar defects and linear defects, and the inner core S may be a collection of planar defects and linear defects.

The closed defect cluster region H and the peripheral single crystal region (Z, Y) are separated by a planar defect at the boundary thereof, and become a crystal region containing a crystal defect therein.

Alternatively, the closed defect cluster region H and the peripheral single crystal region (Z, Y) are separated by a linear defect cluster at the boundary thereof, and become a crystal region containing crystal defects therein.

The crystal defects contained in the core S of the closed defect aggregation region H of the present invention tend to be linear defects or planar defects.

[ shape of closed defect pool H ]

The diameter of the closed defect assembly region H is 1 μm-200 μm. This can be controlled simply with the seed diameter.

The closed defect aggregation regions H may exist in the form of dots (dots) on the substrate surface, and have a diameter of 5 μm to 70 μm, preferably 20 μm to 70 μm. The term "point" is a word representing a situation where an individual point is in a group, and is not limited to a shape. As for the shape, see below.

Sometimes, the closed defect aggregation region H is amorphous on the substrate surface.

Sometimes, the closed defect aggregation region H is circular on the substrate surface.

Also, sometimes, the closed defect aggregation regions H are angular on the substrate surface.

The shape of the closed defect aggregation region H varies depending on the seed shape, the growth condition, the control condition, and the like.

[ Displacement Density distribution ]

The dislocation density of the gallium nitride substrate of the present invention was estimated. The average through dislocation density of the single crystal low dislocation accompanying region Z and the single crystal low dislocation remaining region Y was 5X 10⁶cm^-2The following.

Further, in more detail, it can also be observed that: in the region of 30 μm or less (single crystal low dislocation accompanying region Z) very close to the closed defect cluster region H, the through dislocation density is slightly increased, i.e., 1X 10⁷cm^-2-3×10⁷cm^-2The area of (a). However, when the sample is separated from the sample, the density of the through displacement is extremely low, i.e., less than 10⁵cm^-2The left and right regions. The lowest place, namely 5 multiplied by 10 can be seen⁴cm^-2The area of (a).

It can be seen that the average dislocation density has a tendency to decrease with increasing distance from the closed defect aggregation region H because the closure of the closed defect aggregation region H to the dislocations is incomplete and dislocation from H occurs.

These displacement densities can be estimated by measurement with a Transmission Electron Microscope (TEM), a Cathode Luminescence (CL), an Etch Pit Density (EPD), or the like.

[ orientation of substrate ]

The effect of reducing the dislocation by the present invention is particularly remarkable when the gallium nitride crystal growth direction is <0001 >. That is, when the average crystal growth surface is a (0001) plane and the C plane is used as the surface at the time of dicing, the displacement density of the surface is significantly reduced. At this time, the surface of the final gallium nitride substrate will be the C-plane.

[ extending direction of displacement ]

The single crystal gallium nitride substrate of the present invention is a single crystal having a large number of pits formed by a concave-convex surface formed on the surface and maintained when the average crystal growth direction is the c-axis direction. The pit bottom has a closed defect aggregation region H. Since the concave-convex surface grows in a direction perpendicular to the surface and the displacement surface moves parallel to the C-plane toward the center of the pit, the displacement is concentrated toward the center. Horizontal arrows 98 and 99 in fig. 4(1) indicate directions in which the displacements are parallel to the C-plane and toward the center. Pits formed by the concave and convex surfaces have a centering action (CentripetalFunction). It is this mechanism that concentrates the shift toward the central closed defect pool H. Therefore, in the peripheral single crystal low dislocation satellite zone Z, most dislocations are distributed centripetally parallel to the C-plane toward the closed defect pool H (central Distribution).

[ extending direction of closed defect concentration region H ]

In the single crystal GaN substrate of the present invention, when the average crystal growth direction is the c-axis direction, the closed defect aggregation region H is present in a form extending in the c-axis direction inside the crystal. That is, the closed defect concentrated region H crosses the substrate in the thickness direction. This is because the closed defect integrated regions H also extend parallel to the crystal growth direction at the time of crystal growth. Therefore, when the flat GaN substrate surface is the (0001) plane (C-plane), the closed defect aggregation region H extends perpendicular to the substrate surface.

The crystal growth according to the present invention is a crystal growth in which pits formed of a large number of uneven surfaces are formed and maintained on the surface, and therefore, pits occur. Therefore, it is necessary to perform mechanical grinding and polishing to process the substrate into a flat and smooth surface. When the average crystal growth direction is the c-axis direction, the planar substrate thus obtained is a gallium nitride substrate having the (0001) plane as the surface. Of course, when the closed defect aggregate region H is composed of polycrystals, only the portion is polycrystals. When the closed defect aggregation region H is inverted by 180 degrees in the c-axis direction with respect to the surrounding single-crystal region, only this portion becomes a (000-1) plane, i.e., a Ga plane. In this case, a height difference occurs in the closed defect aggregation region H after polishing, and the height difference becomes slightly lower. This is because the degree of abrasion resistance is different.

[ closed defect pool H pattern ]

Although the pattern of the closed defect regions H, which are periodically and regularly distributed, has been described, it is repeated here.

The GaN crystal of the present invention is a unit of a basic structure, and each basic structure is composed of a closed defect cluster region H extending perpendicularly to the surface and containing a plurality of defects, a single crystal low dislocation co-occurrence region Z concentric with and surrounding the closed defect cluster region H, and a single crystal low dislocation remaining region Y which is the remaining space outside. The GaN crystal may be composed of one unit basic structure or may be composed of a plurality of units arranged regularly.

There are 4 kinds of patterns regularly arranged in two dimensions: A. 6 times of symmetry (fig. 8), B, 4 times of symmetry (fig. 9), C, 2 times of symmetry (fig. 10), D, 3 times of symmetry. Where A-C have been repeatedly described, D is also a possible one. All possible arrangements are described herein.

A. 6 degree symmetrical pattern (fig. 8)

The basic structure body composed of the closed defect aggregation region H, the single crystal low displacement accompanying region Z around the closed defect aggregation region H and the single crystal low displacement remaining region Y is arranged symmetrically for 6 times as a unit, that is, the closed defect aggregation region H is arranged at the vertex of a regular triangle all over. This is the most dense arrangement. Strictly speaking, the pits are not circles but dodecagons, but for the convenience of description, adjacent pits are considered to circumscribe each other.

The side direction of the regular triangle, i.e., the shortest pitch p direction, may be<1-100>Direction (fig. 8 (b)). If the pit diameter is d, the pitch p is d. The spacing H of the closed defect pool H can be widened during cleaving. The cleavage plane of GaN is the M plane {1-100}, but the direction is<11-20>. Is arranged at<11-20>When the pit diameter is d in the direction cutting, the interval H of the closed defect aggregation region H is 3^1/2d. The repetition pitch q in the direction orthogonal to cleavage is narrow, q ═ d.

Regular triangleThe side direction of (i.e. the shortest pitch p direction) may be<11-20>Direction (fig. 8 (a)). The pitch p is d. Splitting (edge)<11-20>Directional cutting) is narrow. The spacing H of the closed defect set region H is d, and the repetition pitch q in the direction orthogonal to the cleavage can be increased by 3^1/2d。

Compare the cross-sectional area of H, Z, Y. As long as the pattern is determined, the ratio of the single crystal low displacement accompanying region Z to the single crystal low displacement remaining region Y is determined, but the ratio of Z and H, which are concentric, is not determined. If the ratio of the Z radius to the H radius is xi (xi > 1), the following formula holds:

Z∶H＝ξ²-1∶1

Y∶(H+Z)＝2×3^1/2-π∶π＝1∶10

is a pattern in which the single crystal low dislocation residual region Y becomes narrowest. The single crystal low dislocation remaining region Y is a portion where the C-plane is grown, and has low conductivity. Since the ratio of the single crystal low displacement residual region Y is low, it is suitable for use as a conductive substrate.

B. 4 degree symmetrical pattern (fig. 9)

The basic structure body composed of the closed defect aggregation region H, the single crystal low displacement accompanying region Z around the closed defect aggregation region H, and the single crystal low displacement remaining region Y is arranged in a 4-order symmetrical manner as a unit, that is, in a manner that the closed defect aggregation region H is located at the vertexes of a square extending all over.

The side direction of the square may be the <1-100> direction (fig. 9 (a)). If the pit diameter is d, the pitch p is d. The pitch H of the closed defect aggregation regions H at the time of cleavage (cutting in the <11-20> direction) is narrow (H ═ d). The repetition pitch q in the direction orthogonal to cleavage is also narrow (q ═ d).

The diagonal direction of the square may be<1-100>Direction (fig. 9 (b)). If the pit diameter is d, the pitch p is d. Splitting (edge)<11-20>Directional cutting) of the closed defect aggregation region H (H is 2) is wide^1/2d) The repetition pitch q in the direction orthogonal to cleavage is also wide (q is 2)^1/2d)。

Comparing the cross-sectional area of H, Z, Y, the following holds:

Z∶H＝ξ²-1∶1

Y∶(H+Z)＝4-π∶π＝1∶3.66

where ξ is the ratio of the Z and H radii.

The single crystal low displacement residual region Y is enlarged and the interval between the closed defect regions H is also enlarged, and this is suitable for manufacturing a semiconductor device having a square chip.

C. 2 degree symmetrical pattern (fig. 10)

The basic structure body composed of the closed defect aggregation region H, the single crystal low displacement accompanying region Z around the closed defect aggregation region H and the single crystal low displacement remaining region Y is arranged in a 2-order symmetrical manner as a unit, that is, in a manner that the closed defect aggregation region H is located at the vertex of a rectangle extending all over. Let xi be the ratio of the long side to the short side of the rectangle. (ξ > 1).

The shorter side direction of the rectangle may be the <11-20> direction (fig. 10 (a)). When the pit diameter is d, the pitch p in the short-side direction is d, and the pitch in the long-side direction is ξ d. The pitch H of the closed defect aggregation region H at the time of cleavage (cutting in the <11-20> direction) is wide (H ═ d). The repetition pitch q in the direction orthogonal to cleavage is narrow (q ═ ξ d).

The shorter side direction of the rectangle may be the <1-100> direction (fig. 10 (b)). When the pit diameter is d, the pitch p in the short-side direction is d, and the pitch in the long-side direction is ξ d. The pitch H of the closed defect aggregation region H is narrow (H ═ ξ d) by cleaving (cutting in the <11-20> direction). The repetition pitch q in the direction orthogonal to cleavage is wide (q ═ d).

Comparing the cross-sectional area of H, Z, Y, the following holds:

Z∶H＝ξ²-1∶1

Y∶(H+Z)＝4ξ-π∶π＝1+4.66(ξ-1)∶3.66

where ξ is the ratio of the Z and H radii.

The single crystal low displacement residual region Y becomes larger and the interval of the closed defect concentration region H also becomes larger, and this method is suitable for manufacturing semiconductor devices of square chips and rectangular chips.

D. 3-degree symmetrical pattern

The basic structure body composed of the closed defect aggregation region H, the single crystal low displacement accompanying region Z around the closed defect aggregation region H, and the single crystal low displacement remaining region Y is arranged symmetrically 3 times as a unit, that is, the closed defect aggregation region H is arranged in a form of extending vertices of a regular hexagon. It is formed by removing every other basic tissue from the configuration shown in fig. 8, and is therefore sparsely arranged.

The side direction of the regular hexagon, i.e., the direction of the shortest pitch p, may be the <1-100> direction. The side direction of the regular hexagon, i.e., the direction of the shortest pitch p, may also be the <11-20> direction.

Comparing the cross-sectional areas of H, Z, Y, the ratio of the region Z accompanied by low dislocation of single crystal to the remaining region Y accompanied by low dislocation of single crystal was determined as long as the pattern was determined, but the ratio of Z and H which are concentric was not determined. If the ratio of the Z radius to the H radius is xi (xi > 1), the following formula holds:

Z∶H＝ξ²-1∶1

Y∶(H+Z)＝3×3^1/2-π∶π＝1∶1.5

the pattern is larger than the single crystal low dislocation residual region Y, and is about 6 times of symmetry. Since the single crystal low dislocation remaining region Y is a low dislocation, single crystal, if large, it is more than sufficient for manufacturing a semiconductor device.

[ spacing between closed defect pools H ]

In the gallium nitride substrate of the present invention, the center distance between the closed defect aggregation regions H is 50 μm to 2000 μm. This is due to limitations on pit formation.

[ Enclosed defect aggregate region H is to penetrate through the substrate ]

In the gallium nitride substrate of the present invention, the closed defect aggregation region H extends in the c-axis direction. The closed defect aggregation region H is present in a form penetrating through the substrate.

On the occasion of long crystal in the c-axis direction, the closed defect gathering region H extends along the c-axis direction; in the case of a substrate having the surface of C, the closed defect aggregation region H penetrates the substrate in the thickness direction.

A semiconductor laser device can be produced using the single-crystal gallium nitride substrate. Since the conductive substrate has very low displacement, a laser device having a long life and excellent performance can be manufactured.

As described above, the gallium nitride growth method includes the HVPE method, MOCVD method, MBE method, MOC method, and sublimation method. The method of the present invention can be carried out by any manufacturing method.

Description of the embodiments

Example 1 (sapphire substrate, FIG. 11)

The method for manufacturing a GaN substrate of the present invention (example 1) will be described. The manufacturing steps are shown in fig. 11. A sapphire C-plane substrate 51 is used as a substrate. Fig. 11(1) shows a sapphire substrate 51. Sapphire is a trigonal system, and GaN belongs to a hexagonal system. A sapphire C-plane substrate is used exclusively for LEDs and LDs already put into practical use.

First, a GaN epitaxial layer 52 having a thickness of about 2 μm was formed on a sapphire substrate 51 by MOCVD (metal organic CVD). Accordingly, the surface becomes the C-plane of GaN.

SiO with a thickness of about 100nm is uniformly formed on the GaN epitaxial growth layer 52₂And (3) a membrane. This is to regularly arrange the seeds 53 on the GaN orientation growing layer 52. The desired seed 53 is formed using photolithography. Sometimes the seed pattern is also called a mask. The seed pattern 52 is: leaving only right triangles all over and close together-all of the same size and all in one side direction<11-20>Number of vertices of regular triangle (a direction)A circular portion 53 and the remaining portion is removed. The rounded portion constitutes a seed 53. The regular triangular configuration, as shown in fig. 8 and 9, is a 6-fold symmetrical configuration, which corresponds to 6-fold symmetry of GaN on the C-plane. The state is shown in FIG. 11 (3).

Although the seed pattern is 6-fold symmetrical, the following 4 patterns a-D are provided by varying the diameter of the circular portion and the pitch between the circles. The diameters of the circular portions of the various patterns and the pitches between the circles (the sides of the regular triangles) are as follows.

Pattern a — round part caliber: 50 μm, side length of regular triangle: 400 μm

Pattern B — round part diameter: 200 μm, side length of regular triangle: 400 μm

Pattern C — diameter of circular portion: 2 μm, side length of regular triangle: 20 μm

Pattern D — round portion caliber: 300 μm, side length of regular triangle: 2000 μm

The blanks each having a seed pattern A, B, C, D were referred to as sample A, B, C, D.

(1) Growth of samples A and B

On sample a having the seed pattern a and sample B having the seed pattern B, GaN crystal growth was performed. The growth method adopts HVPE method. A vertically long reaction furnace is provided with a partition plate for accommodating Ga metal at the upper part inside the reaction furnace, and a base for supporting a substrate upward is arranged at the lower part. The substrate is placed on the susceptor. Here, samples a and B were placed on a susceptor, and Ga growth was performed under the same conditions.

Supplying hydrogen gas and HCL gas to the Ga plate from above the reaction furnace, and supplying ammonia gas (NH) to the vicinity of the substrate supported on the susceptor₃) And hydrogen gas. Hydrogen is the carrier gas.

In this example, the reactor heated the Ga plate to 800 ℃ or higher at normal pressure, and the sapphire substrate to 1050 ℃. Ga and HCL are synthesized as GaCL. The GaCL reacts with ammonia in the vicinity of the substrate, and GaN is deposited on the GaN epitaxial layer 52 and the seed 53.

The growth conditions of the oriented growth layer were as follows:

growth temperature 1050 deg.C

NH₃Partial pressure 0.3atm (30kPa)

HCL partial pressure 0.02atm (30kPa)

Growth time is 10 hours

As a result of the growth, samples A and B each having a 1200 μm thick GaN epitaxial layer were obtained on the patterns A and B. Fig. 11(4) shows the state thereof.

[ Observation (SEM, TEM, CL) of sample A ]

Sample a was first observed. Sample a had pits formed on one surface thereof by the concave-convex surface 56 of an inverted dodecagonal pyramid, and observed with a microscope: pits formed by the concave-convex surface 56 are regularly arranged on the substrate.

The regularity of pit arrangement is consistent with the original mask (seed pattern). The center 59 of the pit formed by the uneven surface 56 is accurately positioned at the position of the circular portion (seed) formed on the GaN layer. That is, directly above seed 53 is pit center 59. Pit centers 59 are arranged at the apexes of regular triangles in the above-described pattern. One side of the regular triangle is 400 μm.

The diameter of the pit appearing on the surface of sample A was about 400 μm, which was equivalent to the circle portion arrangement pitch (one side of a regular triangle). That is, pits are formed in the seed pattern 53 (SiO)₂) The upper part is grown in a conical shape. It is further known that pits grown adjacent to each other on the seed are in contact with each other.

That is, the pits formed by the concave-convex surface 56 grow with the seeds (rounded portions) 53 as the centers, which are overlapped with the apexes of the regular triangles that are spread over and close to each other. Referring to fig. 11(4), there are mortar-like pits above the seeds 53. The bottom 59 of the mortar-like pit constitutes the above-described closed defect aggregate region 55 (H). (the boundary line 60 around the closed defect aggregation region 55 constitutes the grain boundary K). A flat portion 57 is present at the junction between adjacent pits. The coupling portion flat portion (C-plane) 57 is a cross-shaped portion excluding a circular pit on the substrate surface.

To accelerate understanding, the relationship between the inside of the crystal and the pit is first concluded. Inside the crystal, including the portion grown on the seed 53 and other portions. The portion growing above the seed 53 is the closed defect pool area 55 and the pit bottom 59, which is the slowest growing portion. When the pit bottom 59 continues to grow after becoming the closed defect integrated area H55, it becomes the closed defect integrated area H on both sides. Due to the seed 53 (SiO)₂) Since the growth is not slow, the pit bottom 59 is formed therein. Since the pits grow while collecting defects, the defects are collected directly above the seeds that grow the slowest, and a closed defect collection region 55 is formed. That is, the pit bottom 59 on the surface of the crystal corresponds to the closed defect aggregation region H55 and the seed 53 one on top of the other.

The portion grown directly below the inclined surface of the pit corresponds to the single crystal low displacement accompanying region 54(Z), and this portion Z is a single crystal. The correspondence relationship between the seed periphery-single crystal low displacement accompanying region Z54-pit inclined wall 56 is in the vertical direction. Only a little flat portion 57 is left at the junction of the pit and the pit. Immediately below the flat portion 57, a single crystal low displacement remaining region 58 is formed. This portion is also monocrystalline. There is a correspondence of the seed gap-single crystal low displacement remaining region 58-flat portion 57 in the up-down direction.

According to the observation of a microscope, the following results are obtained: the flat portions 57 in the gaps between the dodecagonal pits are all mirror-like (0001) surfaces, the inclined surfaces (concave-convex surfaces) inside the pits are a set of {11-22} surfaces and {1-101} surfaces, and the concave-convex surfaces 59 having a slightly shallow angle are also present on the pit bottom.

The sample A was cleaved with a {1-101} cleavage plane, and the pit section on the cleavage plane was observed. The cross section was observed by a Scanning Electron Microscope (SEM) and a Cathode Luminescence (CL).

The observation results show that: one portion (hereinafter referred to as a closed defect cluster region) which is located below the pit bottom 59, has a certain width, and extends in the c-axis direction (growth direction) can be distinguished from the other portions. The distinguishable portion extending in the growth direction (closed defect pool region H) has a diameter of about 40 μm and is contrasted (dark) with other regions as observed by CL. This part can be clearly distinguished from other areas. Further, by cleaving in various ways it is known that: . The distinguishable portion extending in the c-axis direction is present in a three-dimensional prismatic form.

Further, the prismatic portion abutting the pit bottom 59 was analyzed in detail by CL and TEM. It is known that: the deflection is significantly different from the other parts. That is, there is a large amount of displacement in the portion (closed defect cluster region) surrounded by the dark line-shaped boundary line 60, where the displacement density is as high as 10⁸-10⁹cm^-2. The dark line boundary 60 (hereinafter referred to as a grain boundary K) is a displacement aggregate.

It is also known that: the portion 55 surrounded by the boundary line 60 (grain boundary K) is a crystal defect set (which corresponds to the homocore S). The region 55 extending in the crystallographic direction and having a three-dimensional structure has a large number of crystal defects, which are clearly surrounded by the boundary line 60. This portion 55 is then referred to as the core S. Then, a boundary line (grain boundary K) which is a defect aggregate surrounding the defect-containing core S is added to a region called a closed defect aggregate region H (H ═ K + S). The closed defect concentration region H has an extremely high defect density as compared with other portions, and has different crystal properties. It is important to be able to distinguish this from others.

Due to the seal H position. The feasibility of this control suggests that the invention will find wide application.

Then, the outside of the closed defect aggregation region H is viewed. In the region outside the dark boundary line (grain boundary K), the dislocation density is extremely low. I.e. a sharp asymmetry is shown bounded by the boundary lines. The outside of the boundary line has low displacement density, and the position very close to the boundary line has a displacement density centered at 10⁶-10⁷cm^-2Part (c) of (a). With the separationThe boundary line is opened, and the displacement density is also decreased. When 100 μm away from the cross-connect line, the dislocation density is as low as 10⁴-10⁵cm^-2. In some places, even if the distance from the boundary line is very close, the displacement density is 10⁴-10⁵cm^-2Part (c) of (a). It can be seen that outside the boundary line, the displacement density gradually decreases as it goes away from the pit center 59.

Although the displacement of this portion is small, the extending direction thereof is almost parallel to the C-plane, and tends to extend in the direction of the closed defect concentrated region H which is parallel to the C-plane and toward the center. In addition, it is also known that: the dislocation density outside the closed defect aggregation region is initially high, but becomes lower as the crystal grows. That is, outside the boundary line, the displacement density gradually decreases as compared with the initial stage and the latter stage of the lamination. It is also known that the outside of the boundary line is monocrystalline.

Namely, the above facts explain: since the defects outside the boundary line are gathered to the central portion (the closed defect aggregation region H) by the uneven surface while growing the crystal and accumulated in the boundary line, the displacement density at the outer portion is reduced, the displacement density at the boundary line is high, and the defects can further enter the core S inside from the boundary line. The details of the ratio of displacement defects existing in the boundary portion and the core S are not clear at present.

Since the outer part called the boundary line is troublesome, it is unexpectedly called a single crystal low-dislocation region because of its properties. It is said that outside the boundary there are two distinguishable regions, namely a portion 54 where the inclined wall 56 of the pit passes and a portion 58 where the flat 57 at the pit gap passes. The portion 54 immediately below the inclined wall 56 of the pit becomes low displacement as the unevenness grows, and is referred to as "single crystal low displacement accompanying region Z" herein, and is referred to as an accompanying region because it accompanies the unevenness. Since the portion is accompanied by the closed defect aggregate area, the portion is increased by the presence of the closed defect aggregate area at a high density (seed at a high density).

The portion 58 directly below the flat portion 57 (mirror portion parallel to the C-plane) is the most varied and is a beautiful crystal region. Here, although the uneven surface does not pass through, the displacement is low due to the influence of the uneven surface. Since the irregularities extend upward in a circular shape or a dodecagonal shape, an unnecessary portion remains anyway. The regular triangle shape can be distributed on the whole plane, and the regular hexagon shape can be distributed on the whole plane.

However, the shape of a regular dodecagon, a circle, or the like cannot be distributed over the entire plane, and a part is left in any case. Even if the adjacent circular portions with the same diameter are arranged, the cross-shaped portions remain. It is known that: this portion will become 58 below flat portion 57, but will still be a low dislocation, single crystal. Since the region is located outside the irregularities, it is referred to as "single crystal low dislocation residual region Y". The term "residual" refers to the residual portion of the asperity. The partial area decreases as the closed defect concentrated region H exists at a high density. This point is different from the single crystal low dislocation accompanying region Z just described, but the same point is true in that the crystal is a low dislocation single crystal.

That is, the entire GaN surface T is the sum of the closed defect aggregation region H, the single crystal low displacement accompanying region Z, and the single crystal low displacement remaining region Y, and the closed defect aggregation region H is the sum of the core S and the crystal grain boundary K. I.e. -%

T＝H+Z+Y

H＝S+K

As such, terms are defined to distinguish crystals. Accordingly, the GaN crystal structure of the present invention is more defined.

Further, the relationship between the closed defect aggregation region H and the concave-convex surface 56 of the pit will be discussed in detail. The pits and projections forming the pits are mainly {11-22} planes and {1-101} planes, and a pit bottom 59 has a slightly shallower angle of the pit and projection surface 59 with respect to the pit and projection surface 56. This has already been mentioned above. Then what is the dimple 59?

According to the survey, the following results are obtained: the portion grown with the shallower portion corresponds to the closed defect integrated region H. Next, the boundary between the shallow-angle concave-convex surface 59 and the deep-angle concave-convex surface 56 is a crystal grain boundary K (60) which is the boundary of the closed defect aggregation region H. It has been found that: in the case of sample A, the shallow-angled concave-convex surface formed the closed defect aggregation region H.

The concave-convex surface 59 having a shallow angle is formed from both sides of the pit bottom. In the peripheral part, the shallow-angle concave-convex surface extends along the c-axis direction to form a crystal grain boundary K, and in the central part, the shallow-angle concave-convex surface extends along the c-axis direction to form a core S; the two parts are combined to form a closed defect cluster region H. The core S has a high partial displacement density, and displacements concentrated in the center of the pit due to the uneven surfaces {11-22} and {1-101} are accumulated in the core S in the closed defect pool region H. Thus, the peripheral portion constitutes a single crystal low displacement accompanying region Z for bottom displacement and a single crystal low displacement remaining region Y.

To this end, it has been clear that: the present invention is to make a closed defect aggregation region H accompany the bottom of a recess and projection and make a defect converge on a crystal grain boundary K by always maintaining the recess and projection with one side of the crystal. A portion may still accumulate in the core S. Thus, according to the crystal growth method of the present invention, the displacement of the portion around the closed defect aggregation region H can be reduced by the uneven surface.

[ Observation (SEM, TEM, CL) of sample B ]

Sample a was also observed using SEM, TEM, CL with similar results. However, in sample B, the closed defect pool area H was enlarged to 180 μm. Whereas the closed defect pool H of sample A was only 40 μm in diameter. This indicates that sample B has a diameter of 4 times or more and an area of 20 times more than sample A. The shape of the closed defect concentrated region H is an indefinite shape in cross section and is three-dimensionally prismatic.

Further, it was found that the closed defect aggregation region H of the sample B was slightly inclined with respect to the surrounding single-crystal region Z, Y by examining the closed defect aggregation region H in detail, and that some partial regions having different crystal orientations were present in the closed defect aggregation region H. The crystal orientation of the partial regions is inclined. It is also known that: the closed defect cluster region H of sample B included slightly inclined crystal grains containing dislocation defects and planar defects.

(processing of sample A and sample B)

The substrates of sample a and sample B were ground. The sapphire substrate on the back side was removed by grinding. Thereafter, the surface is ground to have a flat plate shape. Subsequently, a grinding process was performed to produce a GaN substrate having a flat surface. Thus, a GaN substrate having a diameter of about 1 inch was obtained, and the shape thereof was as shown in FIG. 11 (5). The irregularities are absent, but there are a closed defect aggregation region H (55) directly below the central portion of the irregularities, a single crystal low displacement accompanying region Z (54) below the uneven wall, and a single crystal low displacement remaining region Y (58) directly below the flat portion (C-plane). The grain boundary K provides an interface 60. FIG. 11(5) is an enlarged sectional view, and can be illustrated differently. In fact, the glass plate is simply a transparent plate like a glass plate when viewed by the naked eye. Even with a microscope, such differences are not visible.

This GaN substrate is a substrate having a (0001) plane and a C plane as surfaces, and the substrate itself is transparent and flat, but when a CL image on the substrate surface is observed, crystal growth scars are observed as contrasts. When CL observation was performed with light having a wavelength of 360nm near the end of the optical band of GaN, it was found that the closed defect concentration regions H were regularly arranged at a pitch of 400 μm. This is the same as the pitch of the mask 53.

Although the closed defect regions H are often seen with a dark contrast, their properties do not always match when there is a bright contrast even at different locations. The light and shade is the same as the CL image, i.e., transparent and flat. Is transparent and flat even when observed with a microscope. The difference in brightness is seen only by the CL image.

The single crystal low dislocation accompanying region Z grown next to the pit wall 56 was seen with a twelve-sided contrast.

The single crystal low dislocation remaining region Y below the flat portion 57 is seen with dark contrast. This is the C-plane growth portion.

When observed by CL, the closed defect aggregation region H of a circle, the single crystal low displacement accompanying region Z of a circle concentric therewith, and the remaining single crystal low displacement remaining region Y can be easily distinguished by contrast.

The closed defect integrated region H extends in the c-axis direction. The closed defect aggregation region H is formed to penetrate the substrate crystal and to be vertical to the substrate surface. However, the base plate is not perforated, but is a uniform solid, and is a tissue that is visible only by CL. However, the closed defect aggregation region H sometimes has some level difference and is recessed. In particular, a height difference of about 0.3 μm was observed in sample A. This is said to be caused by a slight difference in polishing speed when polishing the closed defect aggregation region H.

When the substrate had reached a flat shape, the through displacement density was easily measured. Can be observed by a CL image, an etching pit, a TEM, or the like. But is most easily observed with CL images.

The through displacement appears as a dark spot when the CL image is observed. It is known that: in samples a and B, the through displacement was concentrated inside the closed defect aggregation region H. It is also known that: the dislocation is concentrated at the boundary of the closed defect concentration area H and is arranged linearly. This corresponds to a three-dimensional planar defect. The closed defect concentration region H can also be distinguished by CL with a dark closed curve (boundary line, grain boundary K).

The closed defect pool region H of sample A had a diameter of 40 μm (seed diameter of 50 μm), and a shape of an angular or irregular shape. And the closed defect concentrated region H of sample B had a diameter of 180 μm (seed diameter of 200 μm) and a shape of indeterminate form with rounded corners. Samples A and B differ only in the diameter of the closed defect pool H, which is formed by the Seed (SiO)₂) The size is determined.

In both of the samples A and B, the displacement was small outside the closed defect aggregation region H (the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y), and the displacement density gradually decreased as the sample gradually separated from the closed defect aggregation region H. In some places, the displacement density decreases sharply as soon as the closed defect aggregate area H is left. The average displacement density in the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y is 5X 10⁶cm^-2The following. In the single crystal low transformationThe bit remaining region Y and the single crystal low dislocation accompanying region Z are arranged such that most dislocations go parallel to the C plane toward the closed defect aggregation region H. Therefore, the dislocation can be absorbed and accumulated in the closed defect concentrated region H, and the dislocation in other regions (the single crystal low dislocation associated region Z and the single crystal low dislocation remaining region Y) is reduced.

The GaN substrates of samples a and B were etched by heating and using an aqueous KOH solution. Observing sample B reveals: in particular, a portion which is easily selectively etched exists in the closed defect aggregation region H, and the other single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y are hardly etched. The existence of portions in the closed defect aggregation region H that are easily and not easily selectively etched means that: the closed defect cluster region H has not only a (0001) plane (hard to etch) which is a Ga plane, but also a (000-1) plane which is an N (N) plane. The single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y are Ga surfaces and are difficult to etch, while the closed defect aggregation region H has a part of a nitrogen surface (000-1) due to polarity inversion, and therefore has a part which is easily etched by KOH. It can be seen that a partial polarity inversion portion exists in the closed defect aggregation region H.

On the other hand, careful examination of sample a revealed that: most of the closed defect pool H is etched and recessed. Further, analysis in combination with TEM (transmission electron microscope) observation results revealed that: the bulk of the closed defect collection region H of sample a was a single crystal whose orientation was reversed by 180 degrees relative to the <0001> direction of crystal orientation as compared to the surrounding single crystal region. Thus, the peripheral single-crystal region is a Ga-face and the closed defect pool region H is a nitrogen face, as viewed from the polished surface. Further, it is found from the detailed analysis result that: in the bulk of the closed defect aggregation region H of sample a, there was also a portion made up of a plurality of crystal grains reversed by 180 degrees with respect to the <0001> direction of crystal orientation.

From these results, it can be considered that: when the crystal grows in sample A, the indices of the facets corresponding to the small-dip irregularities in the closed defect pool areas H are {11-2-4}, {11-2-5}, {11-2-6}, {1-10-2}, {1-10-3}, and {1-10-4 }.

The GaN substrates of sample A (seed aperture 50 μm) and sample B (seed aperture 200 μm) were identical in basic properties, the largest difference being the size of the closed defect pool H (between 40 μm and 180 μm), which can be predetermined by the seed size. In order to utilize the substrate as efficiently as possible, it is preferable that the closed defect aggregation region H having a large displacement be made smaller, and the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y be made larger.

However, if the closed defect cluster region H is too small (the seed is reduced), the closed defect cluster region H may not be formed at all. Thus, defects cannot be collected by the uneven growth, the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y cannot be formed, and the displacement density cannot be reduced.

(2) Growth of sample C (seed caliber 2 μm, spacing 20 μm)

GaN crystal growth was carried out on sample C in which seeds having a diameter of 2 μm were distributed at the apexes of a 20 μm-side regular triangle. This is an example where the seed diameter and spacing are small. The HVPE method was also used for the growth as in the above-described samples A and B. However, even if a Seed (SiO) with a diameter of 2 μm is buried₂) However, the causal relationship of the formation of the concave-convex bottom from the seed is not obtained. Therefore, the concave-convex center cannot be defined by the seed 53. The distribution of the concave-convex is random, and the position of the pit cannot be controlled. There is a problem.

Then, instead of the NVPE method, the MOCVD method was used to grow GaN crystals at a slow growth rate. The speed is reduced by making the pits from the Seed (SiO)₂) Are produced.

In the MOCVD method, not metallic Ga but an organic metal containing Ga is used as a raw material. The gas raw material adopts trimethyl gallium (TMG, III group gas) and ammonia (NH)₃Group V gas) and hydrogen (H)₂A carrier gas).

Sample C was placed on the susceptor of the reaction furnace and heated to 1030 ℃, and a raw material gas was supplied at normal pressure in a ratio of group III to group V of 1: 2000 to perform GaN crystal growth. The growth rate was 4 μm/h and the growth time was 30 hours. Thus, a GaN layer having a thickness of about 120 μm is grown.

Thus, crystal growth having pit-like projections and depressions with the seeds 53 as bottoms was performed. Since the pit bottom coincides with the position of the seed 53, the pit position can be controlled. The closed defect collection region H follows the pit bottom.

In sample C, the diameter of the seed was only 2 μm and very small, and the closed defect pool H formed at the bottom of the pit was therefore small, and the diameter was only about 1 μm. This means that the seed 53 not only provides the location of the closed defect pool H but also its size.

The single crystal low dislocation-accompanying region Z, which is a small circle due to the narrow pitch, is grown next under the inclined surface 56 of the pit. It was confirmed to be a low dislocation single crystal by TEM observation. The single crystal low dislocation residual region Y, which is also a low dislocation single crystal here, is generated corresponding to the inter-pit flat surface (C surface) 57. These properties are consistent with those of samples A and B. Sample C is characterized by a very small closed defect pool H. Here, even if the HVPE method cannot be used, the distribution of the closed defect aggregation regions H can be obtained by the MOCVD method in accordance with the arrangement size of the small seeds.

(3) Growth of sample D (seed caliber 300 μm, spacing 2000 μm)

GaN crystal growth was carried out on sample D in which seeds having a diameter of 300 μm were distributed at the apexes of a regular triangle having sides of 2000 μm. This is an example where both the seed diameter and the spacing are large. The HVPE method was also used for the growth as in the above-described samples A and B. The growth conditions for HVPE are as follows:

the growth temperature is 1030 DEG C

NH₃Partial pressure 0.3atm (30kPa)

Partial pressure of HCL 2.5X 10^-2atm(2.5kPa)

The growth time is 30 hours

As a result, a GaN thick film crystal having a thickness of 4.3mm was obtained. On sample D, pits formed by concave and convex surfaces of an inverted 12-pyramid shape were observed. Closed defect collectionThe regions H are arranged regularly. The same position as the Seed (SiO) formed on the original GaN film₂Mask) 53 are positioned uniformly.

However, there were many pits damaged in shape. In addition, small pits are formed in addition to pits regularly arranged corresponding to the mask. The pit position controllability is not yet satisfactory.

The closed defect aggregate regions H exist at a pitch of 2000 μm, which is equal to the pitch of the initial mask (seed) 53. Some pits in regular positions have a diameter of about 2000 μm and are in the shape of beautiful dodecapyramids. However, although there are pits at a given position at a pitch of about 2000 μm, the shape is deteriorated and the pits are connected to adjacent pits. The pits (although correctly positioned) with such shape breakage have a diameter of only about 200 μm and are small. The shift of the closed defect aggregation area H is high.

However, a single crystal low dislocation residual region Y and a single crystal low dislocation accompanying region Z are formed around a closed defect aggregation region H which is located at a predetermined position in spite of the breakage of the shape of the closed defect aggregation region, and the average dislocation density of the region is 5X 10⁶cm or less, low displacement.

In some cases, the generation of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y is not clear and is not sufficiently low in the periphery of the closed defect aggregation region H generated at a position shifted from the regular position (not corresponding to the seed position).

The experiments with samples a-D show that: the effect of the invention can be fully achieved under the following conditions:

diameter of closed defect cluster region H: 1-200 μm

Diameter of seed (mask, circle) providing closed defect collection region H: 2-300 mu m

Pitch of closed defect integrated area H: 20-2000 mu m

Example 2(GaAs, Si, sapphire substrate, Pattern A, H (A + ELO), FIG. 12)

Three substrates of dissimilar materials were prepared:

A. (111) plane GaAs substrate

B. C-plane (0001) sapphire substrate

C. (111) plane Si substrate

Si is a diamond-structure cubic system. GaAs is a cubic system of sphalerite (Zinc blend) structure. GaN belongs to the hexagonal system. The C face has 3-times rotational symmetry. Only the (111) face of the cubic system has 3-fold symmetry. Therefore, a (111) plane substrate with 3-order symmetry is used as the GaAs and Si substrate. Sapphire belongs to trigonal system, and is a single crystal having C-plane (0001) as a substrate in order to grow crystal in C-axis direction.

Fig. 12(1) - (3) show a GaN growth method. In samples A to D, a 2 μm thick GaN layer was formed on a dissimilar substrate and then covered with a mask (SiO)₂) The material forming the seed 53. However, in example 2, a seed 53 is formed by first covering a different-type substrate 51 with a mask material. SiO was formed directly on the hetero substrate 51 to a thickness of 0.1 μm₂The layer is formed by photolithography to form a seed 53, which is a pattern having 6-fold symmetry formed by leaving a circular portion at the apex of a regularly-arranged regular triangle.

The arrangement pattern of the seed 53 used in example 2 includes two patterns, pattern a and pattern H. Pattern a is the same as that of example 1, and pattern H is a hybrid type in which an ELO (lateral growth) mask is superimposed on pattern a.

As for pattern A, the same configuration as that of pattern A (diameter 50 μm, pitch 400 μm) of example 1, that is, a set of regular triangles with side length 400 μm is imagined, and a circular part with diameter 50 μm is formed at the vertex, and nothing is added to the rest (blank 19, see FIG. 16 (a)).

Regarding pattern H-a hybrid mask with ELO mask superimposed over pattern A (diameter 50 μm, pitch 400 μm). Here, the configuration of pattern a is: a set of regular triangles with a side length of 400 μm was conceived, and a circular part with a diameter of 50 μm was provided at the apex. It is a pattern having a large area occupied by the opening. An ELO mask is attached to a portion (blank portion 19) where the circular portion is not present. The ELO mask is a pattern for lateral overtaking, and has a small number of openings and a large mask area. It is assumed here that a dot-shaped opening (window) having a diameter of 2 μm is disposed at the apex of a regular triangle in a pattern in which regular triangles having a side length of 4 μm are spread over and close to each other. One side of the regular triangle as a reference is parallel to the direction of one side of the regular triangle of the pattern a. For the reason of being too fine, the ELO pattern is omitted in fig. 12(1), but actually a thin film layer having many windows is provided between the seeds 53.

Since the mask pattern is directly placed on the dissimilar substrate, the orientation thereof cannot be defined by the GaN crystal orientation, and is defined by the orientation of the dissimilar substrate. In the case of the pattern a, the direction of the regular triangle side is set as a reference direction. In the case of GaAs substrate, the <1-10> direction is used as the reference direction. In the case of a sapphire substrate, the orientation is <1-100 >. In the case of an Si substrate, the orientation is <1-10 >. Thus, 4 samples E to H were produced with different substrates and different patterns. Each sample is described in detail below.

Sample E: a pattern A (diameter 50 μm, pitch 400 μm) was directly arranged as a seed on a GaAs substrate (111).

Sample F: the pattern A (diameter 50 μm, pitch 400 μm) was directly arranged as a seed on the sapphire substrate (111).

Sample G: a seed pattern of a pattern A is directly formed on a Si substrate (111).

Sample H: the pattern H (pattern a + ELO) is directly formed on the GaAs substrate.

The state of these sample samples with the mask attached is shown in FIG. 12 (1). The difference from the embodiment 1 is that: a mask pattern is formed directly on a substrate without attaching a GaN layer on a dissimilar substrate. As in example 1, a GaN layer was formed on samples E to H by the HVPE method. The HVPE process is carried out as follows: a metal Ga partition plate is arranged above the reaction furnace, and a base for bearing the substrate is arranged below the reaction furnace. The Ga plate is supplied with hydrogen gas and HCL gas from above the reactor to generate GaCL, which flows downward, and ammonia gas is supplied to a portion in contact with the heated substrate to react with the GaCL to synthesize GaN. After the GaN buffer layer grows on the mask at low temperature, a GaN oriented growth layer grows thickly at high temperature. Namely, GaN is allowed to grow in two stages.

(1, growth of GaN buffer layer)

A GaN buffer layer was grown on a GaAs, Si, sapphire substrate or the like under the following conditions by HVPE method. Usually with a GaN buffer layer.

Ammonia partial pressure 0.2atm (20kPa)

Partial pressure of HCL 2X 10^-3atm(200Pa)

The growth temperature is 490 DEG C

Growth time 15 minutes

The thickness of the buffer layer is 50nm

(2, growth of GaN orientation growth layer)

A GaN oriented growth layer is formed on the GaN buffer layer grown at a low temperature by an HVPE method at a high temperature.

Ammonia partial pressure 0.2atm (20kPa)

Partial pressure of HCL 2.5X 10^-2atm(2500Pa)

The growth temperature is 1010 DEG C

Growth time is 11 hours

The thickness of the oriented growth layer was about 1300 μm (1.3mm)

Methods such as growing buffer layers at low temperatures and growing epitaxial layers at high temperatures are common. The transparent GaN substrates obtained in sample E H were all 1.3mm thick, and were transparent and glassy in appearance in the same manner as in example 1. The differences among the closed defect aggregation region H, the single crystal low displacement accompanying region Z, the single crystal low displacement remaining region Y, and the like can be known only by CL observation, but since the growth is uneven, unevenness (pits) on the surface can be seen by microscopic observation.

Fig. 12(2) shows a sectional view. On the surface of each of the 4 samples, there were a plurality of pits formed by the concave-convex surface 56. Pit center (bottom) 59 is used as a Seed (SiO) at the beginning₂) The mask positions at 53 are identical. That is, as in example 1, the most densely arranged pits having a diameter of 400 μm were present on the surface side by side, and it was also confirmed that the pits had an inverted dodecagonal pyramid shape and had irregularities having a small angle at the center portion thereof.

A defect pool area (H)55 is then enclosed over the seed 53, and a pit bottom 59 is over it. A single crystal low displacement accompanying region Z is located below the inclined surface 56 of the pit, and a single crystal low displacement remaining region (Y)58 is located below the flat surface 57 of the C-plane. The single crystal low dislocation remaining region Y and the single crystal low dislocation accompanying region Z are both low dislocation, single crystals.

(grinding processing)

Samples E-H were ground. First, the back surface is ground to remove the GaAs substrate, Si substrate, sapphire substrate, which are the different substrate 51. Subsequently, the seeds 53 are also removed. Further, the surface was also ground to remove the pits and flatten the surface. Thus, a substrate having a flat surface and a back surface is produced. Thus, a flat, smooth and transparent substrate having a diameter of about 2 inches was obtained, and the shape thereof was as shown in FIG. 12 (3). These substrates are all transparent substrates having a GaN (0001) plane (C plane) as a surface. On the substrate surface, 6-fold symmetric closed defect regions (H)55 are arranged, the center of which coincides with the seed 53. Each closed defect concentrated region H is amorphous. The diameter of the closed defect aggregation region H is about 40 μm, which corresponds to the seed pattern (diameter 50 μm, pitch 400 μm). Considering that in SiO with 6-fold symmetry₂This result is acceptable if a closed defect pool H is grown on the seed 53.

The displacement density is high inside the closed defect aggregation area H, but decreases as it goes away from the closed defect aggregation area H. Outside the closed defect cluster region HThe displacement density in the remaining region (Y)58 and the accompanying region Z for low displacement of the single crystal was low, and was 5X 10 for all samples⁶cm^-2The following low displacement. More specifically, the average displacement density of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y is as follows:

sample E (GaAs substrate) 2X 10⁶cm^-2

Sample F (sapphire substrate) 1X 10⁶cm^-2

Sample G (Si substrate) 3X 10⁶cm^-2

Sample H (GaAs substrate) 9X 10⁵cm^-2

It is seen that both are low dislocation densities. As if there is a dependence on the substrate. In sample E, F, G, the lowest displacement density was the sapphire substrate (F), and the next lowest was the GaAs substrate (E), and the displacement reduction effect of the Si substrate (G) was the worst.

The sample H using the ELO method was most excellent in the low displacement, and the average displacement density was reduced by about half as compared with the sample E using only the seed mask. So, it can be deduced that: the effect of seed mask reduction (closing of the defect pool H) and ELO mask reduction (direction change and collision-induced displacement reduction) is substantially the same.

The state of the closed defect integrated area H is also the same as that of embodiment 1. Pits formed of the uneven surface grow on the initial seed 53, and are displaced and concentrated at the pit bottom to form a closed defect cluster region H. Since the dislocation is concentrated in the closed defect concentrated region, the dislocation is reduced in the other single crystal low dislocation accompanying region Z and the single crystal low dislocation remaining region Y.

(sample E's objection)

Two samples were prepared for sample E (GaAs substrate, pattern a). It is not surprising that the two samples did not grow crystalline. In one of the samples E, as in example 1 and example 2, the closed defect aggregation region H, the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y were clearly distinguished from each other, and displacement was low at Z + Y, as described above. However, in the other sample E, although the pits formed by the concave and convex surfaces were correctly grown at the 6-fold symmetrical positions on the seed 53, the closed defect aggregation region H was not present in the center of the pits. This is known by looking at the CL image. The same recipe generates different things and is actually not surprising.

(sample E lacking the closure defect pooling region H)

Further more careful study of this sample E revealed that: the displacement beam to be collected by the unevenness, which does not exist in the closed defect aggregation region H of the succeeding pit bottom 59, is spread over a wide area. Average deflection density of 6X 10⁶cm^-2. Therefore, the displacement density is higher than that of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y of the other samples. In some pits of this sample E, displacements were linearly arranged from the pit center 59, and a planar defect was present around the linear defect. The planar defects are planar defects that form an angle of 60 degrees with each other as shown in fig. 1(b), and the linear defects extend just below the pit bottom, which is the intersection of the planar defects. Some of the planar defects extend from the center of the pit by 100 μm or more. This is believed to be due to the seven-to-eight dispersion once the concentrated displacements are concentrated.

If the closed defect aggregation region H disappears, the sample E cannot be displaced well and accumulated in the pit formed by the unevenness, and the displacement is scattered, and the planar defect appears at the bottom of the pit. Of course, even in this case, the arrangement of pits is still the arrangement in which the seeds are correctly copied, but the closed defect aggregation regions H (empty pits) cannot be formed at the bottoms of the pits. Therefore, no low displacement is achieved, and no empty pit is available.

That is, in order to make the present invention of low dislocation GaN crystal effective, the following two conditions are required: first, pits are grown so as to faithfully replicate the alignment of seeds; second, a closed defect cluster region H is to be generated at the bottom of the pit. : it is not enough to make pits regularly formed, but it is also necessary to generate a closed defect aggregation region H at the bottom of the pits. Then, it can be understood that the importance of the closed defect aggregation region H to the GaN substrate of the present invention is high.

Example 3 (mask type)

A plurality of GaAs substrates having a plane-oriented (111) As plane were prepared As base substrates, and different thin film seed patterns were formed on the substrates in order to confirm what effect would be brought about by a difference in a lower mask (seed pattern).

The preparation method comprises the following steps: forming Si with a thickness of 0.15 μm directly on a (111) As-GaAs substrate₃N₄The thin film was formed to obtain a product (I), the thin film was formed to obtain a Pt thin film having a thickness of 0.2 μm to obtain a product (J), the thin film was formed to obtain a W thin film having a thickness of 0.2 μm to obtain a product (K), and the thin film was formed to obtain a SiO thin film having a thickness of 0.1 μm₂The product obtained after film formation (L, M).

By applying a resist and then performing photolithography and etching, a part of the thin film is removed, thereby producing a seed pattern.

The seed pattern was defined as 6-fold symmetrical pattern a described in example 1 for SiN film (I), Pt film (J), and W film (fig. 6 (a)). Pattern a is such that: a seed having a diameter of 50 μm was arranged at each vertex of a regularly repeating 400 μm-sided regular triangle. One side (pitch) direction of the regular triangle is parallel to the <1-10> direction of the GaAs substrate.

For SiO₂A thin film substrate was fabricated with 4-order symmetric patterns L and 2-order symmetric patterns M. The pattern L is such that: circular seeds with a diameter of 50 μm were arranged at the respective vertices of a square with a side of 400 μm that appeared repeatedly, 4 times symmetrical. And the pattern M is such that: circular seeds with a diameter of 50 μm were arranged at each vertex of a rectangle with a side length of 400 μm × 600 μm, which appeared repeatedly, and were symmetric 2 times. The direction of one side of the repeated squares of the pattern L is parallel to the GaAs substrate<1-10>And (4) direction. And the direction of the shorter side of the repeated rectangles of the pattern M is parallel to the GaAs substrate<1-10>And (4) direction.

These 4 films were examined by X-ray refraction。Si₃N₄The film (I) is amorphous, the Pt film (J) is polycrystalline, the W film (K) is polycrystalline, SiO₂The film is amorphous.

The sample having these 5 kinds of masks was designated as sample I, J, K, L, M.

Sample I: directly form Si₃N₄GaAs substrate of thin film pattern A

Sample J: GaAs substrate directly formed with Pt thin film pattern A

Sample K: GaAs substrate having W thin film pattern A directly formed thereon

Sample L: directly form SiO₂GaAs substrate of thin film pattern L

Sample M: directly form SiO₂GaAs substrate of thin film pattern M

Then, GaN growth was performed on these sample substrates by HVPE method. The HVPE process of example 3 was performed as in examples 1 and 2.

A Ga plate is arranged above the hot wall type reaction furnace, and a base for bearing a substrate is arranged below the hot wall type reaction furnace. Ga is heated to 800 ℃ or higher to become a Ga molten liquid. The substrate is also heated to the following temperature. The Ga sheet is supplied with hydrogen gas and HCL gas from above to be synthesized into GaCL. NH introduced from below to near the substrate by GaCL₃(+ hydrogen) reaction to produce GaN. GaN is deposited on the substrate to form a GaN layer.

The GaN buffer layer is first grown thinly at a low temperature, and then an orientation growth layer is grown thickly thereon at a high temperature. The growth conditions were as follows:

(growth conditions of buffer layer, HVPE method)

The growth temperature is 490 DEG C

NH₃Partial pressure 0.2atm (20kPa)

Partial pressure of HCL 2X 10^-3atm(200Pa)

Growth time 20 minutes

Film thickness of 60nm

(growth conditions of alignment-growth layer, HVPE method)

The growth temperature is 1030 DEG C

NH₃Partial pressure 0.25atm (25kPa)

Partial pressure of HCL 2.5X 10^-2atm(2.5kPa)

Growth time is 13 hours

Film thickness 1800 μm

The surface on which the sample having an average film thickness of 1.8mm was deposited had many pits. Sample I, J, K had almost the same surface morphology in appearance, had many pits formed by concave-convex surfaces on an inverted dodecagonal pyramid, and was positioned at the same position as the circular dot-like seeds provided on the original substrate, and was arranged symmetrically at regular 6 times. That is, the configuration is as shown in fig. 6 (a). Is the two-dimensional densest arrangement with a pitch of about 400 μm, a pit diameter of about 400 μm, and a circumscribed contiguous pit. The appearance was identical to that of sample A of example 1. That is, the seed position coincides with the pit center position.

Sample L, M also showed many pits formed by the depressions of the inverted dodecagonal pyramid. However, the arrangement was different, and the sample L was 4-fold symmetrical with a square pattern having a pitch of 400 μm. The sample M was 2-fold symmetric and formed of a rectangular pattern having a short side of 400 μ M and a long side of 600 μ M. Both of these are also the seed position and the pit center position.

In sample M, a large gap (single crystal low dislocation remaining region Y) was generated between the pit and the rectangular long side. In the single crystal low dislocation remaining region Y, scattered pits which were not formed corresponding to the seed were observed. But generally the pits and seeds correspond up and down.

The bottom shape of the pit formed by the uneven surface was observed. In sample I, J, K, L, M, it was confirmed that a concave-convex surface (c-axis index n is large) having a shallower angle than the concave-convex surface forming the inclined surface of the pit existed at the pit bottom. However, in sample J, the concave and convex portions with pimples were observed at the pit bottoms.

Thereafter, these 5 samples I to M were subjected to grinding. That is, the GaAs substrate on the back surface was removed by grinding, and then the surface was ground to have a flat plate shape. Subsequently, a grinding process is performed to produce a substrate having a flat and smooth surface. Thus, a substrate having a diameter of about 2 inches was obtained.

The substrate of sample I, J, K was a substrate having a (0001) plane, i.e., a C plane, as a surface. The substrate itself is flat and transparent. The closed defect assembly regions H are regularly arranged on the surface. The closed defect pool areas H of samples I-K were arranged symmetrically 6 times. As to the shape of the closed defect pool H, sample I, K, L, M was an amorphous shape containing corners with a diameter of about 40 μm. However, the closed defect cluster region H of sample J was not uniform in diameter and was mostly circular and irregular with rounded corners in a diameter range of 50 to 80 μm.

In any of the samples, the displacement outside the closed defect aggregation region H was small, and the displacement density tended to decrease as the sample was separated from the closed defect aggregation region H. It was also confirmed that: in some places, the dislocation density sharply decreases as soon as the boundary of the closed defect aggregation region H is left.

The average displacement density of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y outside the closed defect aggregation region H was 5X 10⁶cm^-2The following are specific:

sample I: 1X 10⁶cm^-2

Sample J: 4X 10⁶cm^-2

Sample K: 2X 10⁶cm^-2

Sample L: 2X 10⁶cm^-2

Sample M: 4X 10⁶cm^-2

The closed defect pool H of sample I, K, L, M was the same as that of sample A of example 1. Firstly, pits formed by concave-convex surfaces are formed by taking a circular mask (seed) as a center, a defect gathering area H is sealed on the circular mask (seed), and then the pits grow at the bottom; the second is that the shift is concentrated in the closed defect pool area H.

By taking CL images of the substrate surface, it was found that: the case of sample J seeded with Pt is somewhat different. It is found that the closed defect aggregation region H is polycrystalline.

The structure of the closed defect assembly region H was analyzed by CL image and TEM to find: the closed defect aggregation region H has various shapes.

That is, there are various closed defect pool areas H: there were both polycrystals made up of several grains like sample J, and there were only one grain (monocrystalline) but with a different crystal orientation than its surrounding monocrystalline region (Z, Y), and there were also regions that were only coincident with the surrounding monocrystalline region along the <0001> axis and with a different crystal orientation.

Even sample J seeded with Pt is the same as the other samples in the following respects: the pit formed by the concave-convex surface is formed with a circular mask as the center, the closed defect aggregation region H is formed on the circular mask, and the closed defect aggregation region H grows next to the pit bottom, whereby the displacement is concentrated in the closed defect aggregation region H.

The polycrystalline closed defect pool H, which is highlighted in sample J, is also seen in sample a or sample E, and is particularly clearly seen in sample J. The generation of the polycrystalline closed defect cluster region H is considered to be caused because the polycrystalline structure of GaN formed on the initial circular mask of crystal growth extends first and extends sufficiently before being buried in the shallow-angle concave-convex surface.

The closed defect pool H of the sample L was generated at 4-fold symmetrical positions at the vertices of a 400 μm square. The closed defect pool H of the sample M was generated at the 2-fold symmetrical position at the vertex of a rectangle having a side length of 400. mu. m.times.600. mu.m. The closest direction (pitch direction) adjacent to the closed defect aggregation region H is the <11-20> direction of the GaAs substrate. With the arrangement as in sample L, M, the positions of the closed defect aggregation regions H and pits can be arranged in an orthogonal relationship. When manufacturing square or rectangular semiconductor devices, the displacement distribution and the crystal properties can be made uniform. In sample L, M, the pattern arrangement direction (pitch direction) was <11-20> but could be <1-100> as well.

Example 4 (GaN particle as seed, FIG. 13)

GaN single crystal and GaN polycrystal were pulverized to produce GaN fine particles. The particles are GaN single crystal or polycrystalline particles with different diameters of 10-50 μm.

A metal plate was also produced with fine holes perforated at the vertices of an imaginary regular triangle having a side length of 500 μm all over and close to each other. Since photolithography cannot be used, a metal plate is used as a template in order to seed fine particles regularly.

A sapphire substrate 61 having a C-plane as a surface is prepared as a substrate (fig. 13 (1)). A GaN epitaxial layer 62 having a thickness of about 3 μm was grown in advance on the entire surface of the sapphire substrate 61 by HVPE. (FIG. 13 (2)).

A metal plate is placed on a GaN layer of a sapphire substrate such that the side direction of a regular triangle is parallel to the <11-20> direction of GaN, and then GaN fine particles are scattered from above. The fine particles are embedded in the fine holes and attached to the GaN layer. When the metal plate is removed, fine particles as seeds are arranged at 6-th order symmetrical positions of the GaN layer. The state is shown in FIG. 13 (3).

Two substrates were prepared, in which single crystal GaN fine particles and polycrystalline GaN fine particles were respectively scattered on a GaN layer through a metal plate, and the samples were regarded as N and O, respectively.

Sample N: sapphire substrate with GaN layer and arranged by taking GaN single crystal microparticles as seeds

Sample O: sapphire substrate with GaN layer and arranged by taking GaN polycrystalline microparticles as seeds

A thick GaN layer was formed on these substrates using the HCPE method. The procedure was as in examples 1, 2 and 3. The substrate was supported on a susceptor of a reaction furnace having a Ga partition plate at the top and a susceptor at the bottom, and the Ga plate was heated to 800 ℃, hydrogen gas and HCL gas were supplied to the Ga plate, and ammonia gas and hydrogen gas were introduced into the susceptor to react with the ammonia gas after the synthesis of GaCL, thereby depositing a GaN layer on the substrate.

(conditions for orientation growth)

Growth temperature 1050 deg.C

NH₃Partial pressure 0.3atm (30kPa)

Partial pressure of HCL 2.5X 10^-2atm(2.5kPa)

Growth time is 10 hours

The thickness of the grown film is about 1400 mu m

The GaN thick film layer with the thickness of about 1400 mu m is obtained through long crystal. Samples N and 0 had almost the same surface morphology in appearance, and the cross-sectional shape is shown in fig. 13 (4). Pits formed by the concave-convex surface 66 of the reverse dodecagonal pyramid are regularly arranged on the surface. The pits are arranged in the surface substantially in the two-dimensional densest manner, with pits of 500 μm in diameter circumscribing each other. Between the pits, there is a flat portion 67 (C-plane). When the pit bottom 69 is observed, another uneven surface (c-axis surface index n is large) shallower than the inclination angle of the uneven surface 66 is observed.

The portion next to the base 69 is the closed defect collection region (H)65, separated by the grain boundary (K) 70. Directly below the uneven surface 66 and outside the crystal grain boundary K70, a single crystal low displacement accompanying region Z (64) is formed. Directly below the flat surface 67 is a single crystal low displacement remaining region Y (68). That is, the pit bottom 69, the closed defect accumulating region (H)65, and the seed 63 are arranged vertically, and the uneven surface 66, the single crystal low displacement accompanying region Z, and the flat portion 67, and the single crystal low displacement remaining region (Y)68 are arranged vertically.

Sample N, O was ground because of the irregularities on the substrate. First, the sapphire substrate 61 and the seed (fine particle) 63 are removed from the back surface by grinding. Thereafter, the surface is ground to remove the pits and to obtain a flat surface. Subsequently, a grinding process is performed to produce a flat substrate having a flat and smooth surface. Thus, a GaN substrate having a diameter of about 2 inches was obtained.

Fig. 13(5) shows a flat smooth substrate. The closed defect aggregation region H, the single crystal low displacement accompanying region Z at both ends thereof, and the single crystal low displacement remaining region Y at the separated portion are seen in cross section. The substrate N, O is a substrate having a (0001) plane, i.e., a C plane, as a surface. The substrate itself is transparent and simply looks like a uniform transparency to the naked eye. When CL and TEM are observed, the closed defect aggregation region H, the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y can be distinguished. The closed defect set regions H are regularly (like the seeds) arranged at 6 symmetrical positions. Its (cross-sectional) shape is amorphous. The diameter of the closed defect aggregation region H varies from 10-70 μm, which reflects the variation in the diameter of the seed or micro-particle.

There is a high density of defects inside the closed defect aggregation region H. The displacement is small in the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y, and the displacement density tends to decrease as the distance from the closed defect aggregation region H increases. In some places, the dislocation density decreases sharply as soon as it leaves the grain boundary K (70). In any of the samples, the average displacement density of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y was 5X 10⁶cm^-2The following are specific:

sample N: 1X 10⁶cm^-2

Sample O: 2X 10⁶cm^-2

The case of blocking the defect aggregation regions H is the same as in sample A of example 1.

In example 4, since the fine particles were positioned by the metal plate, the diameters and the scattering of the fine particles were not uniform, and the positional accuracy was not as high as in examples 1 and 2 using photolithography. In this way, it was confirmed that the microparticles can also be used as seeds for blocking the defect pool region H. In addition, it is also known that: there was no difference between using GaN single crystal fine particles (sample N) and using GaN polycrystalline fine particles (sample O).

Here, although GaN itself is regarded as fine particles in order to avoid impurities, fine particles of other semiconductor materials, metal materials, and insulating materials may be similarly used as seeds for the closed defect aggregation regions H. At this time, since the substrate base plate 61 and the seed 63 are also removed by grinding the back surface, the internal structure of the final flat base plate is not changed.

Example 5 (seeded by a part of the exposed part of the substrate base plate, FIG. 14)

A sapphire substrate 71 having a C-plane as a surface is prepared as a substrate (fig. 14 (1)). A GaN epitaxial layer 72 having a thickness of about 2 μm was grown on the entire surface of the sapphire substrate 71 by MOCVD. (FIG. 14 (2)).

Such a seed pattern is assumed on a sapphire substrate: regular triangles with 400 μm sides are spread all over and close together, and the directions of the sides of the regular triangles are parallel to the <11-20> direction of GaN 72. Circular holes having a diameter of 70 μm were formed in portions of the GaN layer 72 facing the apexes of the regular triangles of the seed pattern. Then, the shape becomes the one shown in FIG. 14 (3). The growth of GaN on the substrate base plate 73 at the substrate base plate surface, i.e., at the circular hole, is slower than that on the GaN layer 72, so the substrate base plate exposed portion 73 at the circular hole can function as a seed. In example 5, the substrate exposed portion is used as the seed 73. Because other materials are not used, the GaN film has the advantages of high GaN purity and accurate positioning by utilizing photoetching. The seed pattern was also a 6-fold symmetrical pattern with a pitch of 400 μm and a seed diameter of 70 μm. Let it be a pattern P, and use the substrate with the pattern P as a sample P.

Sample P: a sapphire substrate with a GaN layer having a substrate exposed portion of a different material as a seed.

A thick layer of GaN was formed on the substrate P by the HCPE method. The procedure was as in examples 1, 2, 3 and 4. A substrate is placed on a susceptor of a reaction furnace having a Ga barrier provided on the upper side and a susceptor provided on the lower side, the Ga plate is heated to 800 ℃ or higher, hydrogen gas and HCL gas are supplied to the Ga plate, and ammonia gas and hydrogen gas are introduced into the susceptor to react with the ammonia gas after GaCL is synthesized, thereby depositing a GaN layer on the substrate.

(conditions for orientation growth)

The growth temperature is 1030 DEG C

NH₃Partial pressure 0.25atm (25kPa)

Partial pressure of HCL 2.0X 10^-2atm(2kPa)

Growth time is 12 hours

The thickness of the growth film is about 1500 μm

The GaN thick film layer with the thickness of about 1500 mu m is obtained through long crystal. The cross-sectional shape of the sample P is shown in fig. 14 (4). Pits formed by the concave-convex surface 76 of the reverse dodecagonal pyramid are regularly arranged on the surface. The pits are arranged in the surface substantially in the two-dimensional densest manner, with pits of 400 μm in diameter circumscribing each other. Between the pits, there is a flat portion 77 (C-plane). When the pit bottom 79 is observed, another uneven surface (c-axis surface index n is large) shallower than the inclination angle of the uneven surface 76 is observed.

The portion next to the base 79 is the closed defect collection area (H)75, separated by the grain boundary (K) 80. Directly below the concave-convex surface 76 and outside the crystal grain boundary (K)80, a single crystal low displacement accompanying region Z is formed. Directly below the flat surface 77 is a single crystal low displacement residual region Y (78). That is, the pit bottom 79, the closed defect aggregation region (H)75, the seed 73, the uneven surface 76, the single crystal low displacement accompanying region (Z)74, and the flat portion 77, the single crystal low displacement remaining region (Y)78 are arranged vertically.

The substrate of sample P was polished because of the unevenness. First, the sapphire substrate 71 and the GaN layer 72 (portions sandwiching the seed 73) are ground off at the back surface. Thereafter, the surface is ground to remove the pits and to obtain a flat surface. Subsequently, a grinding process is performed to produce a flat substrate having a flat and smooth surface. Thus, a GaN substrate having a diameter of about 2 inches was obtained. Fig. 14(5) shows a flat smooth substrate. The closed defect aggregation region H, the single crystal low displacement accompanying region Z at both ends thereof, and the single crystal low displacement remaining region Y at the separated portion are seen in cross section.

The substrate N, O is a substrate having a (0001) plane, i.e., a C plane, as a surface. The substrate itself is transparent and simply looks like a uniform transparency to the naked eye. When observed by CL or TEM, the closed defect aggregation region H, the single crystal low dislocation accompanying region Z and the single crystal low dislocation remaining region Y can be distinguished. The closed defect set regions H are regularly (like the seeds) arranged at 6 symmetrical positions. Its (cross-sectional) shape is amorphous. The diameter of the closed defect aggregation region H is substantially about 50 μm. Since the substrate exposed portion 73 is formed accurately by photolithography, the degree of variation in diameter is low and positional deviation is small. This is a highly accurate method.

There is a high density of defects inside the closed defect aggregation region H. The displacement is small in the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y, and the displacement tends to decrease as the crystal moves away from the closed defect aggregation region H. In some places, the K (80) dislocation is dramatically reduced as soon as it leaves the grain boundary. The average displacement density of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y of the sample P was 1X 10⁶cm^-2Hereinafter, the case of blocking the defect aggregation regions H is the same as in sample a of example 1.

In this way, it was confirmed that the exposed surface 73 of the base substrate exposed by removing a part of the GaN layer can be used as a seed for blocking the defect cluster region H. Here, since GaN itself is used as a seed root, there is no problem of impurity contamination. Since the GaN of the seed portion is always removed, there is no problem of unevenness in the thickness direction of the GaN crystal.

Example 6(GaN substrate, Pattern A, FIG. 15)

Two samples were prepared in example 6. One is a GaN substrate (fig. 15(1)) produced using pattern a (seed pattern circular portion diameter 50 μm, circular portion pitch 400 μm) used in example 1, from which the underlying substrate has been removed, surface processing and polishing have also been performed, and epitaxial growth has been possible on the substrate. Let sample Q be this sample.

The other is that SiO is formed on a sapphire substrate₂Samples of the film. It is formed by: growing a GaN epitaxial layer with a thickness of 2 μm on a sapphire substrate by MOCVD method, and forming SiO with a thickness of 0.1 μm on the epitaxial layer₂The film is then patterned using photolithography. The procedure was the same as in example 1, using pattern A. This sample is referred to as sample R.

A GaN epitaxial layer was thickly formed on both of samples Q and R (FIGS. 15(2), (3)). Here, as in the above examples, the HVPE method was used as the growth method. After the substrate is placed in a reaction furnace, the temperature is raised by using hydrogen as carrier gas, and a GaN oriented growth layer grows at a high temperature of 1030 ℃. The growth conditions of the GaN oriented growth layer were as follows, in which the substrate calibers of sample Q and sample R were each 30 mm.

(conditions for orientation growth)

The growth temperature is 1030 DEG C

NH₃Partial pressure 0.25atm (25kPa)

Partial pressure of HCL 2X 10^-2atm(2kPa)

The growth time is 80 hours

The thickness of the grown film is about 10mm

As a result, GaN crystal ingots (ingot) having a thickness of about 10mm were obtained for both sample Q and sample R. These two billets are called Q billet and R billet, respectively. The two billets were grown under the same surface morphology. That is, the pattern had a shape in which pits formed by irregularities having a diameter of 400 μm were arranged substantially two-dimensionally at the highest density in accordance with the original pattern. It should be noted that, in particular, the Q ingot is not patterned but is grown on a GaN substrate already fabricated, but the surface morphology after growth is equivalent to that when patterned.

Further, the Q-stock and the R-stock were observed in cross section after cutting the end portions longitudinally. The section of the Q billet is shown in fig. 15 (3). The results show that: the closed defect concentrated region (H)85 is grown next to the closed defect concentrated region (H)55 of the Q ingot, and the single crystal low displacement accompanying region (Z)54 is not necessarily the same as the single crystal low displacement remaining region (Y)58, but either the single crystal low displacement accompanying region (Z)84 or the single crystal low displacement remaining region (Y)88 is grown. Of course, the closed defect collection region H85 is located at the bottom 89 of the pit formed by the concave-convex surface 86.

These two kinds of blanks were sliced to cut out a plurality of GaN substrates, and then subjected to surface grinding and polishing. The slicing process is performed by using a wire saw. As a result, 9 GaN substrates were obtained from each of the blanks (see fig. 15 (4)).

Among these substrates, foreign matter defects were found in 2 to 3 sheets at the final growth stage, while 6 to 7 sheets at the initial growth stage were good. These substrates are substrates having a (0001) plane, i.e., a C plane, as a surface, and the substrates themselves are transparent. The closed defect regions H on the substrate surface are arranged symmetrically for 6 times, and have an indefinite shape with a diameter of about 50 μm. The displacement is small outside the closed defect aggregation region H, and the displacement density tends to decrease as the closed defect aggregation region H is separated. In some places, the boundary displacement upon leaving the closed defect aggregation region H sharply decreases. The average displacement density outside the closed defect cluster region H is 5 × 10⁶cm^-2Hereinafter, it is sufficient as a practical GaN substrate.

This method is considered to be an effective production method for improving the productivity of crystal growth.

The invention concentrates the displacement on the bottom of the pit by concave-convex growth to make the other parts low in displacement, and a closed defect gathering area H is formed at the bottom of the pit, so that the phenomenon that the displacement is scattered after being closed can not occur. Because of the closed defect assembly area H, the invention can solve the 3 big problems mentioned above at one stroke

(1) The random distribution of the displacement collection part from the center of the pit formed by the concave-convex surface is reduced.

(2) The planar defect of the central displacement collection part of the pit formed by the concave-convex surface is eliminated.

(3) The position of the displacement collection part at the center of the pit formed by the uneven surface is controlled.

According to the method of the invention, the position of the closed defect aggregation region H of the dislocation aggregation can be accurately controlled, and the gallium nitride substrate with low dislocation can be manufactured. In the GaN substrate of the present invention, the displacement is regularly concentrated in a specific narrow portion, and the portion (the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y) used in an important portion of the semiconductor device is a low displacement single crystal. A substrate suitable for a low-displacement GaN substrate such as an InGaN blue-violet Laser Diode (LD) is provided.

Claims (32)

1. A single-crystal gallium nitride substrate characterized by comprising, on the surface of a gallium nitride substrate:

a closed defect cluster region H extending through the surface of the substrate and having a core S in which a plurality of defects are clustered, a closed region separated by a grain boundary K, and

a single-crystal low-dislocation accompanying region Z which is a region formed around the defect concentration region H as a result of being enclosed, and

the single crystal low dislocation remaining region Y is a region having the same crystal orientation and existing outside the single crystal low dislocation accompanying region Z.

2. A single-crystal gallium nitride substrate characterized by being composed of a plurality of basic structures, wherein a unit basic structure is composed of the following regions on the surface of a gallium nitride J substrate:

a closed defect cluster region H extending through the surface of the substrate and having a core S in which a plurality of defects are clustered, a closed region separated by a grain boundary K, and

a single-crystal low-dislocation accompanying region Z which is a region formed around the defect concentration region H as a result of being enclosed, and

the single crystal low dislocation remaining region Y is a region having the same crystal orientation and existing outside the single crystal low dislocation accompanying region Z.

3. A single crystal gallium nitride substrate according to claim 2, wherein: the closed defect aggregation region H is polycrystalline, and the peripheral single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y are both single crystals.

4. A single crystal gallium nitride substrate according to any one of claims 1 to 3, wherein: the closed defect concentrated region H is composed of one or more crystal grains having a crystal orientation different from that of the peripheral single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y.

5. A single crystal gallium nitride substrate according to any one of claims 1 to 3, wherein: the closed defect concentrated region H is composed of one or more crystal grains, and the crystal grains are all aligned with the surrounding single crystal low dislocation accompanying region Z and the single crystal low dislocation remaining region Y in the <0001> direction, and have different crystal orientations.

6. A single crystal gallium nitride substrate according to claim 1 or 2, wherein: the closed defect concentration region H is composed of a single crystal, and the single crystal, the surrounding low displacement accompanying region Z of the single crystal, and the remaining low displacement region Y of the single crystal are inverted by 180 degrees and reversed in polarity only in the <0001> direction in the crystal orientation.

7. A single crystal gallium nitride substrate according to any one of claims 1 to 3, wherein: the closed defect aggregation region H is composed of one or more crystal grains, and the crystal grains and the surrounding single crystal low dislocation accompanying region Z and the single crystal low dislocation remaining region Y are reversed in crystal orientation by 180 degrees only in the <0001> direction and reversed in polarity.

8. A single crystal gallium nitride substrate according to any one of claims 1 to 3, wherein: the closed defect concentrated region H is composed of one or more crystal grains, and the crystal orientation of these crystal grains is slightly inclined with respect to the crystal orientation of both the peripheral single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y.

9. A single crystal gallium nitride substrate according to any one of claims 1 to 3, wherein: the closed defect cluster region H is a single crystal region separated from the surrounding single crystal low displacement accompanying region by a planar defect or a linear defect and having the same crystal orientation as the surrounding single crystal low displacement accompanying region Z, or a crystal region composed of one or more crystal grains separated from the surrounding single crystal low displacement accompanying region by a planar defect or a linear defect and containing a crystal defect therein.

10. A single crystal gallium nitride substrate according to any one of claims 1 to 3, wherein: the crystal defects contained in the closed defect aggregation region H are linear defects or planar defects.

11. A single crystal gallium nitride substrate according to claim 1 or 2, wherein: the substrate surface is a (0001) plane.

12. A single crystal gallium nitride substrate according to any one of claims 1 to 3, wherein: the surface of the region other than the closed defect collective region H is a Ga surface, and the surface of only the closed defect collective region H is a nitrogen surface having a different polarity.

13. A single crystal gallium nitride substrate according to claim 12, wherein: the surface of the closed defect aggregation area H is slightly lower than the surface of the closed defect aggregation area H by a height difference relative to the area outside the closed defect aggregation area H.

14. A single crystal gallium nitride substrate according to claim 1 or 2, wherein: in the single crystal low dislocation-accompanying region Z, most of the dislocations extend parallel to the C-plane.

15. A single crystal gallium nitride substrate according to claim 1 or 2, wherein: inside the substrate crystal, a closed defect aggregation region H extends parallel to the c-axis direction.

16. A single crystal gallium nitride substrate according to claim 1 or 2, wherein: a basic structure body Q consisting of a closed defect region H, a single crystal low displacement accompanying region Z surrounding the closed defect region H, and a single crystal low displacement remaining region Y surrounding the closed defect region H is periodically and regularly arranged on the surface of a substrate.

17. A method for growing a single crystal gallium nitride substrate is characterized in that: the displacement of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y is reduced by forming pits formed of an uneven surface on the surface of the grown crystal, growing a closed defect aggregation region H at the bottom of the pits, and absorbing and eliminating or accumulating the displacement of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y around the closed defect aggregation region H.

18. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the closed defect aggregation region H formed after the rise of the pit formed by the grown-up uneven surface is polycrystalline, and the peripheral single crystal low displacement associated region Z is a single crystal having the same orientation as the single crystal low displacement remaining region Y located outside the region.

19. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y located outside the single crystal low displacement accompanying region Z are single crystals having the same orientation, and the closed defect aggregation region H is composed of one or more crystal grains having a crystal orientation different from that of the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y.

20. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the single crystal low displacement accompanying region Z is a single crystal having the same orientation as the single crystal low displacement remaining region Y located outside the single crystal low displacement accompanying region Z, and the closed defect aggregation region H is composed of one or more crystal grains having a crystal orientation different from that of the single crystal low displacement remaining region Y except that the crystal grains and the single crystal low displacement accompanying region Z are aligned only along the <0001> axis.

21. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y lying outside the region Z are single crystals having the same orientation, and the closed defect aggregation region H is composed of a single crystal, and the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y have 180-degree inversion and polarity inversion in the crystal orientation direction only in the <0001> direction.

22. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y located outside the region are single crystals having the same orientation, and the closed defect aggregation region H is composed of one or more crystal grains, and these crystal grains are inverted by 180 degrees and reversed in polarity only in the <0001> direction with respect to the crystal orientation of the surrounding single crystal low displacement accompanying region Z and single crystal low displacement remaining region Y.

23. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y located outside the single crystal low displacement accompanying region Z are single crystals having the same orientation, and the closed defect aggregation region H is composed of one or more crystal grains having crystal orientations that are slightly inclined with respect to the crystal orientations of both the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y.

24. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the single crystal low displacement accompanying region Z is a single crystal having the same orientation as the single crystal low displacement remaining region Y located outside the region Z, the core S enclosing the defect aggregation region H contains crystal defects and is composed of one or more crystal grains, and the crystal grain boundary K surrounding the core S is a planar defect or a linear defect.

25. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the single crystal low displacement accompanying region Z is a single crystal having the same orientation as the single crystal low displacement remaining region Y located outside the single crystal low displacement accompanying region Z, the core S enclosing the defect aggregation region H contains a crystal defect and is a single crystal having the same orientation as the single crystal low displacement accompanying region Z and the single crystal low displacement remaining region Y, and the crystal grain boundary K surrounding the core S is a planar defect or a linear defect.

26. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: the pit formed by the concave-convex surface is a hexagonal pyramid or an inverted dodecagonal pyramid, or is an inverted hexagonal pyramid with two overlapped sections with different side angles or an inverted dodecagonal pyramid with two overlapped sections with different side angles.

27. A method of growing a single crystal gallium nitride substrate according to claim 26, wherein: the surface index of the concave-convex surface constituting the pit is { kk-2kn } surface and { k-k0n } surface, where k and n are integers.

28. A method of growing a single crystal gallium nitride substrate according to claim 27, wherein: the surface indexes of the concave and convex surfaces constituting the pits are {11-22} plane and {1-101} plane.

29. A method of growing a single crystal gallium nitride substrate according to claim 17, wherein: a polycrystalline or amorphous thin film is disposed on a substrate as a seed for closing the defect cluster region H.

30. A method of growing a single crystal gallium nitride substrate according to claim 29, wherein: polycrystalline or amorphous thin films patterned in a circular or polygonal shape or other given shapes are disposed on the base substrate as seeds for enclosing the defect cluster regions H.

31. A method of growing a single crystal gallium nitride substrate according to claim 30, wherein: a polycrystalline or amorphous thin film patterned into a predetermined shape is disposed on a substrate as a seed for a closed defect cluster region H, an ELO pattern for epitaxial lateral overgrowth is disposed on the surface of the substrate where the seed is not present, and GaN is grown on the substrate having the seed pattern and the ELO pattern.

32. A method of growing a single crystal gallium nitride substrate according to claim 30, wherein: an ELO pattern is arranged on a substrate, a low-dislocation GaN thin film is grown by an orientation transverse transcendental method, and a polycrystalline or amorphous thin film layer which is made of a dissimilar material other than GaN and has been patterned into a given shape is formed on the low-dislocation GaN thin film to be used as a seed for the closed defect cluster region H.