JP2002356398A - Gallium nitride wafer - Google Patents

Abstract

(57) [Problem] To provide, for the first time, a circular wafer of gallium nitride, which has not existed before, in a practical form. SOLUTION: This is a transparent and independent circular wafer made of a gallium nitride single crystal having a hexagonal system and {0001} plane orientation doped with oxygen at a concentration of 10 ¹⁶ cm ⁻³ to 10 ²⁰ cm ^−3. The outer circumference is 5mm ~ from front side and back side
Chamfering at an inclination angle of 30 °, 0.1-0.5mm
R chamfer of radius is performed. Attach one or two OFs specifying the direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gallium nitride single crystal circular wafer. Gallium nitride semiconductor (Ga
N) is important as a blue light emitting device because of its wide band gap. The crystal system belongs to the hexagonal system (Hexagonal).
The crystal structure is wurtzite (ZnO) type. GaN-based devices have already been sold and used in large quantities as blue light emitting diodes (LEDs).

[0002] GaN single crystals do not naturally occur. Ga
N directly sublimates when heated at normal pressure. It does not turn into a melt unless heated to a very high pressure. Therefore, the crystal cannot be grown by the Czochralski method (pulling method) or the Bridgman method (boat method) which are well known as the crystal growth method.

[0003]

2. Description of the Related Art Since the present invention is a GaN wafer, there are both conventional wafer technology and conventional GaN technology as conventional technologies. Both need to be described as prior art.

As described above, a GaN single crystal cannot be grown by a normal crystal growth method. Therefore, a GaN-based light-emitting element is manufactured by growing a thin film on a sapphire substrate. That is, it has a laminated structure such as GaN / sapphire. On the GaN thin film serving as such a buffer layer, n-type, p-type GaN, GaI
A thin film such as nN or AlGaInN is formed. Hetero-epitaxial growth. The thin film is formed by a vapor phase growth method or a sublimation method. There are three prominent methods for vapor phase growth. Metal organic chemical vapor deposition (MOCVD), chloride vapor deposition (MOC), hydride vapor deposition (HV)
PE method).

[0005] These are techniques for forming a thin film on a substrate. Therefore, a substrate is required, but a GaN substrate cannot be made. Therefore, a large number of LEDs using sapphire as a substrate are manufactured. Sapphire has a trigonal crystal structure. There is no six-fold symmetry or six-fold inversion symmetry. The crystal system is different from GaN which is a hexagonal system. Moreover, the lattice constant and the coefficient of thermal expansion are quite different.

However, a sapphire c-plane single crystal substrate (00
It has been found that the c-plane (0001) of GaN grows favorably on the (01) plane. Sapphire is a hard material, and GaN is also a hard and strong material. The sapphire remains stuck to the LED device because it cannot be removed.

Since sapphire has no cleavage, it is mechanically cut (diced) to separate individual GaN from the sapphire wafer.
-LED chips are cut out. Also, sapphire is an insulator and does not pass current. Therefore, the n-GaN layer is partially exposed, and an n-type electrode is provided thereon. In other words, the structure is such that both electrodes (p electrode and n electrode) are exposed on the upper surface. There is a disadvantage that the light emitting area is reduced due to the n-electrode.

Since the lattice constant and the coefficient of thermal expansion are different, GaN,
Many defects occur in the GaInN film. However, despite many defects, LEDs emit light and have a long life. Blue light-emitting GaN-LEDs fabricated on heterogeneous substrates have already been extensively used. The lack of cleavage, being an insulator, and having many defects did not reduce the value of the GaN / sapphire-LED. Sapphire substrate LEDs are extremely useful as small blue light-emitting elements and have a great deal of production and use results. The GaN / sapphire type LED has a proven track record of use and is a completed device.

However, in such a device, the substrate is a sapphire wafer. There is no GaN substrate. GaN is only a thin film formed thinly on a sapphire substrate. There, GaN is only a thin layer that relies on sapphire, both geometrically and mechanically. It is not an independent GaN substrate.

The above is the case of a blue LED (light emitting diode). The situation is a little different for a blue laser (LD). This is because an LD requires a resonator and is not easily made with a sapphire substrate. A GaN-LD on a sapphire substrate has been prototyped. Also in that case, GaN is a thin film and does not exist as a substrate. The difficulty with sapphire is that there is no cleavage plane.

FIG. 12 shows a hexagonal closest Pa.
cked; HCP) lattice structure. The transition metal alone may take this structure. It is a grid that forms a hexagonal prism. Equivalent six atoms are present at the bottom six corners and the top six corners. There is one atom at the bottom and top center. At half height, there are three atoms at the center of the three partial equilateral triangles. This is a lattice containing 6 atoms. There are six-fold inversion symmetry, three-fold symmetry, and reflection. From this structure, it can be easily understood that (0001) would be a cleavage plane for a single atom. If it contains two kinds of atoms, besides (0001), $ 1
You can see that it is possible that -100｝ could be a cleavage plane.

FIG. 13 shows a lattice structure of sapphire. Oxygen (O) atoms enter the atomic positions of the close-packed structure, and four Al atoms
The atom is at the center of a tetrahedron formed by four oxygen atoms. Two Al atoms overlap in the c-axis direction, and the other two Al atoms are at the center of an equilateral triangle two away from each other.
There is no triple symmetry or triple inversion symmetry. Therefore, it is not hexagonal but trigonal. The bonding force is Al-O
Localizes to binding. The O—O and Al—Al bonds are weak or antibonding. Due to the presence of Al, the upper and lower bonds are strengthened, but (0001) is no longer a cleavage plane. A
The {1-100} plane cannot be a cleavage plane because of the asymmetric existence of the 1 atom. That is why there is no cleavage in sapphire.

Therefore, in the case of the sapphire substrate LD, the resonator cannot be formed by natural cleavage. A flat mirror surface must be created by dicing, etching, polishing, etc., with much effort and time, resulting in high cost and low yield.
In a blue LD, a cleaved ZnSe-based LD is superior to a sapphire substrate GaN-based LD. It is Ga
This does not mean that N-based semiconductors are unsuitable for LD.

[0014] Instead, the use of a sapphire substrate without cleavage causes only such a disadvantage. If a single-crystal GaN substrate is present, a GaN-based LD comparable to a ZnSe-based LD will be produced.

GaN has a zinc blende type (ZnS;
zinc-blende). It is the same as GaAs and belongs to the cubic system (cubic), and has fourfold inversion, threefold symmetry, and reflection (−43 m). At higher temperatures, a mixture of cubic and hexagonal crystals results.

At higher temperatures, including room temperature, hexagonal (Hexago)
nal). It is called wurtzite (ZnO). FIG. 14 shows a lattice structure of hexagonal GaN. In the present invention, G
aN refers to a hexagonal crystal. A gallium atom exists at the atomic position of HCP. 3 of 6 vertical ridgelines of hexagonal prism
There are six nitrogen (N) atoms at a height of / 8. Three gallium atoms are present at the center of three equilateral triangles taken every other half height. Immediately above the Ga atom, 7 /
There are three N atoms at a height of eight. This is a structure containing 5Ga and 5N. Ga is at the center of the tetrahedron created by N. N is at the center of the tetrahedron created by Ga. Covalent bonds of GaN form crystals. Ga-Ga and NN do not have a bonding force. (0001) is not cleaved because the longitudinal coupling of GaN has a length of 3/8 and a total of three. {1-100}, which requires only two cuts, becomes the cleavage plane. As such, GaN also has the advantage of having a clear natural cleavage.

However, it has not been possible to form a single crystal of GaN for a long time. However, with the efforts of the present inventor, an independent crystal of GaN can be obtained by depositing a thick GaN film on a certain substrate and removing the substrate using a vapor phase growth method. It is a transparent thin plate-shaped crystal. Since it is an independent single crystal substrate, it can be called a wafer, but it is a rectangular substrate having a small size and about 10 to 18 mm square.

This is intended to be a circular wafer. Since the thin film is grown on the base substrate, the shape is determined by the shape of the base substrate. The shape is not exactly the same as the underlying substrate but slightly smaller. Since a mechanical force is applied when removing the base substrate, a thin amorphous GaN crystal is obtained when the base substrate is removed. In some cases, this was cut into an octagonal wafer. However, what has been obtained so far is a rectangular substrate having a size of about 10 mm to 18 mm as described above, which is several sheets per month.

They are used experimentally as GaN-LD substrates. A GaN substrate is more suitable as an LD substrate than a sapphire substrate. Thus, an LD in which a GaN-based layer is epitaxially grown on a GaN substrate has been experimentally manufactured. However, there is not yet a practical level of a circular GaN wafer having a diameter of 2 inches or more.

Now that we have an overview of sapphire and GaN, let's look back at the prior art on wafer grinding and OF. These all relate to a Si wafer or a GaAs wafer. Each of them is opaque, has a metallic luster, and is softer than GaN. Both are cubic, Si is diamond type and GaAs is zinc-blende type.

Japanese Unexamined Patent Publication No. Hei 2-144908 discloses a method of manufacturing a semiconductor device. In order to distinguish the front and back surfaces of an Si wafer, an OF (orientation flat) and a C
Although F (cartridge flat) is attached, it points out a problem that the alignment apparatus may erroneously detect OF and CF. Therefore, on the outer edge of the Si wafer,
It proposes that the front and back surfaces are chamfered at different angles. It says that after chamfering, both sides are polished to a mirror surface. This is to distinguish the front and back by changing the chamfer angle of the front and back. Although not visible to the naked eye, the alignment device detects the chamfer angle, so that the front and back are not mistaken.

Japanese Unexamined Patent Publication No. 60-167426, "Semiconductor Crystal Wafer", shows a crystal orientation of an Si wafer by providing an OF on a cleavage plane in the past. He points out that defects are likely to occur. It is said that since the diameter of the Si wafer increases, material loss at the OF portion increases.
Therefore, it is stated that a laser beam is used to form a molten hole having a diameter of 1 mm and a depth of several hundred μm in a specific direction instead of the OF.
This is a wafer without OF. Although the element chips formed in the holes are wasted, the number is smaller than the number of element chips wasted by the OF. He also says that no slips will occur.

Japanese Unexamined Patent Publication No. 2000-331898 "Notched Semiconductor Wafer" discloses a conventional wafer in which an OF is provided at one position on the wafer, or a combination of an OF and an IF (index flat).
Since the weight of the conventional wafer provided at the location is reduced only by that portion, it is pointed out that the risk that the wafer is detached from the rotor due to an uneven load when spin coating the resist is pointed out. When the diameter of the wafer increases, such deviation of the center of gravity becomes a problem.

Therefore, a notch (notch) is provided on a peripheral edge of a specific direction of the wafer instead of being cut in an arc shape. Since the notch is small, the problem of unbalanced load does not occur.
However, the notch states that the crystal orientation is known but the front and back surfaces are unknown. When a GaAs wafer is polished on both sides, it is not clear just by looking at which is the front. Therefore, a proposal has been made in which the periphery of a circular wafer is rounded so that the width differs between the front and back sides. It is common to distinguish front and back by chamfer dimensions. The notch and the front and back unequal chamfer show the orientation and front and back of the wafer.

Japanese Unexamined Patent Publication No. 7-212603 discloses a method of processing a wafer. When an OF is provided on a Si wafer, the intersection between the circumferential portion and the linear portion is sharpened. (Chipping), it states that there is a problem that the chipping pieces adhere to the wafer surface and cause scratches or uneven film thickness. The problem is explained that the notch end is pointed and may be missing even in a wafer indicating the orientation by the notch instead of the OF. Therefore, a wafer in which the sharp portion is replaced with a smooth arc is proposed. It is stated that the OF end and the notch end are not sharp points but have a smooth curve, so that they are not easily damaged.

Japanese Patent Application Laid-Open No. 58-71616, "Method of Manufacturing Semiconductor Device", proposes that a Si wafer is machined asymmetrically by, for example, chamfering only one side to make it easy to see the front and back. . If only the front side is chamfered and the back side is left as it is, the front and back sides can be distinguished just by visual inspection.

Japanese Unexamined Patent Publication No. Hei 8-316112 "Notched Semiconductor Wafer" states that a wafer with an orientation flat or a laser mark is not desirable because the effective area is reduced correspondingly and the manufacturing cost is increased. Therefore, a small notch is attached to the periphery of the wafer to indicate the orientation, and the entire periphery is chamfered asymmetrically to give a distinction between the front and the back. This is similar to a wafer such as, for example, in that the front and back are shown by asymmetric chamfering.

US Pat. No. 6,177,292 "Metho
d For Forming GaN Semiconductor And GaN Diode With
The Substrate is an oxide substrate (eg sapphire)
GaN is heteroepitaxially grown by vapor phase epitaxy to form a thin film, removed from the furnace, sapphire substrate is shaved, and then put again in the furnace to grow a GaN thin film.
Then, a sample was taken out, the sapphire substrate was cut into a furnace, the GaN thin film was increased by 50 to 100 μm, and the GaN thin film was taken out and the sapphire substrate was cut off. ing. The purpose of shaving the sapphire substrate many times is to remove distortion due to differences in lattice constant and coefficient of thermal expansion. Ultimately GaN without sapphire substrate
Although a substrate can be obtained, it is an extremely complicated process and is not practical.

[0029]

SUMMARY OF THE INVENTION With the efforts of the present applicant, it has become possible to manufacture a 2-inch freestanding GaN single crystal substrate. Although a rectangular wafer may be used, a circular wafer may be more convenient in terms of transportation and thin film growth. Assuming that a 2-inch freestanding circular wafer of GaN has been made, the problem will be considered in advance. First, the front and back sides of the wafer must be distinguished. It is necessary to know the crystal orientation. Furthermore, it is also important that it is not easily chipped in the transfer process and the wafer process.

In the case of a Si wafer or a GaAs wafer, the front surface is often mirror-polished and the rear surface is not mirror-finished. In that case, the rough surface and the mirror surface can be easily recognized by the naked eye. Since it has a metallic luster, is opaque, and has strong reflection, it is easy to distinguish between a mirror surface and a non-mirror surface having different surface roughness. However, since GaN is thin and transparent, it is difficult to see itself. If the base is a white background, transparent, or the like, the existence of the wafer itself becomes difficult to understand. Even if the surface roughness of the front and back surfaces is different, it is difficult to visually distinguish the front and back surfaces. When placed on a dark-colored base, the presence of a transparent plate can be seen, but the front and back cannot be distinguished. This point is Si, GaAs
It is different from s wafer. Therefore, one object is to propose a GaN wafer in which the front and back of transparent GaN can be easily distinguished.

GaN has a feel closer to that of a ceramic than a metal or a semiconductor, has a higher rigidity than Si and GaAs, and is a hard material. Even if it is thin, it has high hardness and robustness, but is easily damaged by impact, so it is necessary to protect the circular wafer from damage. An object of the present invention is to provide a gallium nitride circular wafer, which has not existed before, in a practical form for the first time.

[0032]

Gallium nitride wafer of the present invention SUMMARY OF THE INVENTION ^may, at 10 ^{16 cm -3} ~10 20 cm at a concentration of ^-3 oxygen or silicon doped hexagonal {000
A transparent and independent circular wafer made of gallium nitride single crystal having a 1 ° plane orientation and having an outer peripheral portion chamfered (C-chamfered) at an inclination angle of 5 ° to 30 ° from the front side and the back side. . Alternatively, instead of the C-chamfering, the entire outer peripheral portion may be chamfered (R-chamfered) so as to have an arc cross section with a radius of 0.1 mm to 0.5 mm. GaN is transparent and hard to see, but if the edge is chamfered, the outline becomes clear due to diffuse reflection. It is easy to handle because it can be visualized.

Alternatively, a gallium nitride wafer 10 ¹⁶ cm
^A transparent and independent circular wafer made of a hexagonal gallium nitride single crystal having a {0001} plane orientation and doped with oxygen at a concentration of ⁻³ to 10 ²⁰ cm ^{−3 and having} an arcuate shape at a part of the outer peripheral portion A flat portion is provided for indicating a specific crystal orientation {hkm0} perpendicular to the cut surface.

As a specific crystal orientation, for example, cleavage plane # 1
-100 選 ぶ can be selected. Alternatively, the {11-20} plane orthogonal to the cleavage plane can be selected and displayed as a specific crystal orientation.

Alternatively, a specific crystal orientation {hkm0} perpendicular to the cut surface of the arcuate portion in a part of the outer peripheral portion of the wafer.
May be provided, and a second flat portion having a different azimuth length perpendicular to the first flat portion may be provided to distinguish between the front and back sides.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1. Circular GaN Wafer with Peripheral Edge Chamfered on Front and Back (FIG. 1)] This is a transparent and circular GaN wafer with its peripheral front and back sides chamfered by flat inclined surfaces. This is called C chamfering. GaN is GaA
It has higher rigidity and hardness than s and Si. It may be brittle to impact. When the sharp peripheral portion of the wafer collides with a transfer device or the like, the peripheral portion may be chipped. Therefore, the periphery is chamfered. FIG. 1 shows only the peripheral portion. The chamfer angle θ is 5 ° to 30 °. The thickness of the wafer is about 350 μm to 500 μm. The periphery of the GaN wafer is ground by a rotating grindstone 7 as shown in FIG.

Since it is harder than Si and GaAs, a whetstone having higher hardness is used. The grinding time also takes longer. Because it is transparent, the chamfered part can be easily understood by the naked eye. Since the wafer is transparent, if the base is white, transparent, gray, or the like, it is difficult to see the presence of the wafer as it is, but if chamfering, the outline shines white due to irregular reflection, so that the location can be clearly understood.

Further, GaN is doped with oxygen to provide n-type conductivity. When a substrate wafer for a GaN-based LD or LED is used, an n-electrode can be attached below the substrate to pull out the cathode. The oxygen doping amount is 10 ¹⁶ to 10
^{It is} about ²⁰ cm ⁻³ .

[2. Circular GaN wafer whose peripheral edge is chamfered so as to have an arc cross section over both sides (FIG. 2)] This is a transparent and circular GaN wafer chamfered by an arc-shaped curved surface from the peripheral surface to the rear surface. This is called R chamfering. GaN has higher hardness than GaAs or Si, and may have a lack of peripheral portion. Since the chamfer in FIG. 1 is chamfered on an inclined surface, a ridgeline remains. It needs to be ground twice. If it is not preferable that a ridge line is formed, the peripheral edge is chamfered by the R surface. FIG. 2 shows only the peripheral portion of the wafer that has been rounded. Chamfer radius R is 0.1mm ~
0.5 mm. The thickness of the wafer is 350 μm to 500
μm (0.5 mm).

If it is 500 μm, a cross section of a semicircular arc is obtained at R = 250 μm. R is 100 μm to 250 μm
In the case of, the chamfer is separated into upper and lower edges. R is 250μ
If it is m to 500 μm, a ridge line intersecting the front and back surfaces is generated. The periphery of the GaN wafer is ground by a rotating grindstone as shown in FIG.

Since the grindstone is harder than Si and GaAs, a whetstone suitable for a hard material such as a hard bond material for fixing abrasive grains is used. The grinding time also takes longer. In the same manner as in the previous example, the wafer is difficult to see because it is transparent as it is, but the chamfered portion shines white so that it can be easily seen with the naked eye. The same ^applies to doping about 10 ¹⁶ to 10 ²⁰ cm ⁻³ of oxygen to obtain an n-type.

[3. GaN wafer having cleavage plane with OF (FIG. 4)] This is a transparent and circular GaN wafer having a c-plane as a surface, which is obtained by cutting an arc parallel to the {1-100} plane at the periphery of the GaN wafer. GaN is a hexagonal crystal and has a cleavage plane {1-100} at the periphery of a GaN wafer (0001) having the c-plane as the front and back surfaces. The cleavage plane has three planes at an angle of 60 ° to each other. There are three planes around one point, but there are six cleavage planes around the wafer.

This is a method in which EL is formed on a GaAs (111) substrate.
GaN is grown by a vapor phase epitaxy by the O method, the GaAs substrate is removed, and then ground into a circle. The crystal orientation is determined by X-rays to determine the cleavage direction. Then, an arcuate portion is cut out so that the cleavage surface of the circular wafer is exposed. Cleavage is (1-100), (01-10), (-1010)
And so on. If the GaN wafer has a diameter of 2 inches, the length of the chord is about 10 to 20 mm. For example, 16
mm.

When an LD substrate is used, oxygen is doped at 10 ¹⁶ to 10 ²⁰ cm ⁻³ to obtain n-type GaN.
Since the orientation is clear, it is convenient for alignment in the case of device manufacturing. This is also doped with oxygen to be n-type. L
D. The cathode can be pulled out from the lower side when the LED substrate is used. The same applies to the following examples.

[4. GaN wafer with an OF in the direction perpendicular to the cleavage plane (Fig. 5)] A transparent and circular GaN wafer with a c-plane as the surface, and an arc cut parallel to the {11-20} plane at the periphery of the GaN wafer and cut into an OF It is. GaN is a GaN wafer (000
There is a cleavage plane {1-100} at the periphery of 1). The direction perpendicular to the cleavage plane is {11-20}.

{11-20} also has three surfaces that are at an angle of 60 ° to each other. There are three planes around one point, but there are six cleavage orthogonal planes around the wafer. This is a cut of the bow so that the plane perpendicular to the cleavage is exposed. (11-20), (-2110), (1-210)
And so on. If the GaN wafer has a diameter of 2 inches, the length of the chord is about 10 to 20 mm. In the case of using as an LD substrate, oxygen is set to 10 ¹⁶ to form n-type GaN.
Doping is performed at 10 ²⁰ cm ⁻³ . Silicon is also used for doping. There is an auto-dope which cannot be controlled by oxygen from the raw material or the like. Since the orientation is clear, it is convenient for alignment in the case of device manufacturing.

[0047]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The GaN wafer of the present invention is provided with, for the first time, a practically dimensioned and marked bevel. (111) Ga
A mask with a window is attached on the As substrate (ELO method), and a GaN thin film is passed through the window by C-plane (000) by HVPE method.
1) Grow. If vapor deposition can be performed to the thickness of one sheet, H
Remove from VPE furnace. A two-layer structure in which GaN 2 is stacked on a GaAs substrate 1 as shown in FIG. 7 is obtained.

The GaAs substrate 1 is removed by etching with aqua regia. Then, a self-standing film of the GaN crystal 2 is obtained. This is because the peripheral surface 3 is jagged, so the rotating whetstone 4 as shown in FIG.
To grind the peripheral surface into a smooth peripheral surface. The result is a circular GaN wafer 5 as shown in FIG. These elemental technologies are made by the present inventors independently. The element technologies required for manufacturing the GaN wafer of the present invention will be described in order.

As a method of vapor-phase growing a GaN thin film on sapphire, there are HVPE (Hydride Vapor Phase Epitaxy), MOC (Metal Organic Chloride Vapor Growth).
Phase Epitaxy), MOCVD (Metalorganic Chemical Vapor Depositio)
n) and sublimation method. All of these are techniques developed for growing GaN having a thickness of several μm on a sapphire substrate. MO is most often used
This is a CVD method. However, this is undesirable because carbon is included as an impurity.

We choose the HVPE method. The HVPE method is used not for growing a thin film but for forming a single crystal. [HVPE method] G containing Ga melt in the upper part of a vertically long furnace
Provide a boat. A susceptor indicated by a rotating shaft is provided directly below the Ga boat in the furnace. Place a (111) GaAs single crystal wafer about 2 inches in diameter on the susceptor.
From the gas supply pipe above the furnace, supply hydrogen + hydrogen chloride gas to Ga
Spray towards the boat. 2Ga + 2HCl → 2Ga
Reaction of Cl + _{H 2} takes place. Gallium chloride falls in gaseous form. Hydrogen + ammonia gas is blown from another gas supply pipe to the vicinity of the susceptor. NH ₃ +
The reaction of GaCl → GaN + HCl + H ₂ occurs, and G
GaN molecules are adsorbed on the aAs substrate.

This is disclosed, for example, in Japanese Patent Application No. 10-78333 by the present inventors (Japanese Patent Application Laid-Open No. 2000-222).
12) (10) Japanese Patent Application No. 10-171276 (JP-A-2000-12)
900).

[ELO (Epitaxial Lateral Overgrowth)
th)] Growing on a GaAs substrate is unique to the present inventors. As mentioned frequently, sapphire is used exclusively for the substrate for GaN thin film growth.
Experiments for growing GaN on GaAs substrates were repeated many times thirty years ago and were unsuccessful.

The fact that a GaN thin film can be grown on a GaAs substrate is actually achieved by attaching a mask (SiN, SiO ₂ ) having many windows to a GaAs substrate and then independently growing GaN crystals through the windows. ELO
The law was invented. The details of the ELO method are described in the above-mentioned (10) application of the present inventors.

Alternatively, the present invention is described in (11) Japanese Patent Application No. 9-298300 and (12) Japanese Patent Application No. 10-9008.

Since GaN is hexagonal, it has a mask structure in which windows are arranged in accordance with the windows. That is, the window (circle, polygon, rectangle) is arranged at the vertex position, assuming that the surface is filled with equivalent equilateral triangles. The mask thickness is, for example, 1
00 nm (0.1 μm). GaN does not deposit on the mask. GaN crystal grains whose orientation is defined by GaAs grow from the isolated window.

It grows at a relatively low temperature. Dislocations extend in the growth direction. The temperature is increased to continue GaN growth. When the GaN layer exceeds the mask thickness, it grows so as to crawl on the mask in the lateral direction. Lateral growth is important, which causes dislocations to be lateral. GaN grown laterally in a regular hexagonal shape meets that grown from the adjacent window. Dislocations accumulate on the meeting surface. Thereafter, vertical growth occurs, but since dislocations are not dragged, GaN with low dislocations grows. The ELO method has an effect of reducing such dislocations and strains, and for the first time, GaN can be grown on a GaAs substrate.

However, only the present inventors use the GaAs substrate. Other researchers are still growing GaN on sapphire. Even if the dislocations are reduced by the ELO method, it is only for a while for a while that the GaN grown from the adjacent window is associated, and only for a short time. If the thickness is further increased, dislocations increase again. A method to prevent this is given by the present inventors. (13) Japanese Patent Application No. 11-273882 (JP-A-2001-10)
2307).

[Oxygen doping (for use as an n-type substrate)]
Although an n-type substrate GaN has not existed until now, an n-type dopant must be added to make it n-type. GaN-LED on sapphire n
Type GaN-based thin films have been widely used.
The one adopted as the type dopant was Si. Silane gas (hydride gas of Si) is introduced to impart n-type conductivity to the GaN thin film (thickness of about 0.01 μm to several μm).

Since silane gas is highly dangerous, oxygen may be used as the n-type dopant instead. Oxygen can be conducted into the furnace as water and oxygen gas, but these are safe substances.

(14) Japanese Patent Application No. 11-144151 (JP-A-2
000-44400) Oxygen is introduced into the furnace in the form of water or oxygen gas to dope GaN with oxygen. But that's not easy. There is a reason that oxygen could not be used as an n-type dopant. GaN on sapphire substrate
When growing a thin film, the sapphire substrate is a c-plane substrate, so that the GaN thin film also grows flat and smooth on the c-plane. Since the thin film is grown to a thickness of 1 μm or less, the surface is naturally flat.

As has been found by the study of the present inventors, there is a property that oxygen does not enter the c-plane. This means that oxygen doping has surface selectivity. Until now, oxygen was not doped because c-plane growth was performed on sapphire without exception. Therefore, there was no room for using oxygen as an n-type dopant. However, planes other than c-plane, for example, A-plane {11-20}, M-plane {1-100},
Alternatively, oxygen is taken into the A-plane {11-2m} or M-plane {1-10m} (m is an integer) inclined from this point. Therefore, oxygen can be doped by performing a rough growth having a zigzag surface without performing mirror growth while maintaining the c-plane.

(15) Japanese Patent Application No. 2001-113872 proposes such a method.

In this manner, the transparent (00
A hexagonal GaN wafer having a (01) plane is obtained. Polished on both sides or one side to make a circular wafer. Thereafter, as described above, the peripheral surface is smoothed by the rotating grindstone of FIG. In the apparatus shown in FIG. 10, the front and back surfaces of the wafer are C-chamfered. Alternatively, R chamfering is performed using the apparatus shown in FIG.

Further, O was added to the cleavage plane (M plane) {1-100}.
Insert F. Or, a plane orthogonal to it (A plane) # 11
Insert OF at -20 °. Further, a first OF and a second OF can be provided as shown in FIG. 6 to distinguish between the front surface and the back surface. In FIG. 6, the length of the first flat portion is made longer than the length of the second flat portion, so that the front and back surfaces can be easily identified.

[0065]

Conventionally, sapphire has been used as a substrate for a GaN-LED. A GaN-LD using sapphire as a substrate has also been developed. The present invention provides for the first time a GaN circular wafer that is more useful than a sapphire substrate as a substrate for a GaN-LD. GaN single crystal substrate is GaN-based L
We knew that it would be optimal as a substrate for D, but there was no suitable manufacturing method so far, so 10 mm
A rectangular wafer of about １８18 mm square was merely made in a laboratory. It was impossible to make a large circular GaN wafer.

However, due to the efforts of the present inventors, HV
Circular GaN of about 2 inches (52 mm) is obtained by combining the PE method and the ELO method and growing over time.
Wafers can now be manufactured. GaAs (11
1) Growing GaN on a substrate by vapor phase epitaxy
By removing aAs, GaN wafers are manufactured one by one as independent films. The GaN wafer is transparent, has high rigidity and is robust, but the peripheral portion may be damaged due to contact with objects. When the peripheral surface is chamfered as in the present invention, the risk of breakage is reduced. However, since it is harder than GaAs or Si, it is necessary to use a special whetstone, which requires extra processing time.

Since the substrate is a thin plate and is transparent, the location of the GaN wafer may be difficult to recognize with the naked eye when the base is white, light color, or transparent. However, when the peripheral edge portion is chamfered as in the present invention, light is irregularly reflected at that portion, so that the outline is easy to understand and the location is clear. Chamfering a transparent wafer that is difficult to see has such a visual effect. Such an effect is unique to Si and GaAs.

Since oxygen is doped, an n-type GaN substrate can be obtained. Since the substrate is an n-type substrate, a GaN-LED or GaN-LD can be formed thereon and an n-type electrode (cathode) can be provided below the substrate. The area for the n-electrode can be saved. LED on sapphire substrate
Unlike this, the area for the n-electrode is not required. Small LD, L
ED can be used and the use is expanded.

The {1-100} plane of the GaN substrate shows a clear cleavage. The nitride semiconductor thin film (AlGaN, InGaN, AlInGaN, etc.) grown on the GaN substrate has the same plane orientation as the substrate. The orientation of the cleavage plane of the GaN single crystal substrate and the cleavage plane of the nitride-based semiconductor grown thereon are exactly the same.

Since the homoepitaxial growth satisfies not only the same orientation but also the lattice matching condition, the internal stress at the interface between the substrate and the thin film is small. When the substrate is naturally cleaved at the cleavage plane of the substrate, the thin film is also cut at the cleavage plane. It is a beautiful mirror surface because it is cut at the cleavage plane. In the case of LD, the resonators at both end faces can be formed by natural cleavage of the substrate. It is much easier to manufacture than a sapphire substrate LD that is mechanically diced and mirror-polished.

[Brief description of the drawings]

FIG. 1 shows a C-chamfered on the front side and the back side of a peripheral portion of a hexagonal GaN (gallium nitride) wafer grown on a transparent c-plane.
FIG. 4 is a cross-sectional view of only a peripheral portion of a chamfered wafer.

FIG. 2 is a cross-sectional view of only the periphery of an R-chamfered wafer in which the periphery of a transparent c-plane grown hexagonal GaN wafer is chamfered so that the cross-sectional shape becomes an arc.

FIG. 3 is a plan view of a GaN wafer having a transparent c-plane grown hexagonal GaN wafer having a specified plane orientation (klm0) in which an arcuate portion at a peripheral edge is cut to form a flat plane having a specified orientation.

FIG. 4 is a plan view of a GaN wafer having a cleaved plane (1-100) of a hexagonal GaN wafer grown on a transparent c-plane, in which a bowed portion at a peripheral edge is cut to form a flat plane that is a cleavage plane.

FIG. 5 is a plan view of a GaN wafer in which a flat surface which is a cleavage orthogonal plane is formed by cutting off an arcuate portion of a peripheral portion on one plane (11-20) orthogonal to the cleavage plane of a transparent c-plane grown hexagonal GaN wafer. Plan view.

FIG. 6 (1) is a plan view of a transparent c-plane grown hexagonal GaN wafer in which a first flat portion is formed by cutting an arc-shaped portion at a specified plane orientation (klm0), and an arc-shaped portion is formed at an orientation (stu0) orthogonal to the first flat portion. FIG. 4 is a plan view of a GaN wafer in which a second flat portion is formed by cutting a part. (2) is an example, and GaN in which a first flat portion is formed on a cleavage plane (1-100) and a second flat portion is formed on (11-20).
The top view of a wafer.

FIG. 7 is a cross-sectional view showing a state in which a circular GaN single crystal is stacked on a circular (111) GaAs substrate by a vapor phase growth method. The peripheral surface of the GaN crystal is jagged.

FIG. 8 is a plan view showing a step of polishing a peripheral portion of a GaN crystal having a jagged peripheral surface with a rotating grindstone to smooth the peripheral portion.

FIG. 9 shows a G in which the peripheral portion is smoothed because the peripheral portion is ground.
aN wafer sectional view.

FIG. 10 is a cross-sectional view showing a step of grinding and C-chamfering the front side and the back side of the peripheral portion of a circular GaN wafer with a rotating grindstone having an inclined surface.

FIG. 11 is a cross-sectional view showing a step of grinding and rounding the periphery of a circular GaN wafer with a rotary grindstone having a concave curved surface.

FIG. 12 is a perspective view showing a lattice structure of a hexagonal close-packed structure.

FIG. 13 is a perspective view showing a lattice structure of sapphire.

FIG. 14 is a perspective view showing a lattice structure of gallium nitride (GaN).

[Explanation of symbols]

 Reference Signs List 1 GaAs substrate 2 GaN crystal 3 peripheral surface 4 grindstone 5 GaN wafer 6 GaN wafer 7 grindstone 8 rotation axis 9 GaN wafer 10 grindstone 11 rotation axis

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G077 AA02 AA03 BE15 DB04 EB01 ED06 EE07 FJ03 HA02 TB02 TK11

Claims (8)

[Claims] 1. A transparent and independent circular wafer made of a hexagonal gallium nitride single crystal having a {0001} plane orientation and having an outer peripheral portion inclined at 5 ° to 30 ° from the front side and the back side. A gallium nitride wafer characterized by being chamfered at a corner. 2. A transparent and independent circular wafer made of a hexagonal gallium nitride single crystal having a {0001} plane orientation and having a whole outer peripheral portion having a radius of 0.1 mm to 0.5 mm.
A gallium nitride wafer, which is chamfered so as to have an arc cross section. 3. A specific, transparent, independent circular wafer made of hexagonal gallium nitride single crystal having a {0001} plane orientation and having an arcuate portion cut at a part of an outer peripheral portion and orthogonal to the plane. A gallium nitride wafer provided with a flat portion for indicating a crystal orientation {hkm0}. 4. A transparent and independent circular wafer made of a hexagonal gallium nitride single crystal having a {0001} plane orientation, and a part of an outer peripheral portion is cut off at an arcuate portion having a cleavage plane as a chord. A gallium nitride wafer having a flat portion that is a cleavage plane {1-100} perpendicular to the plane. 5. A transparent and independent circular wafer made of a hexagonal gallium nitride single crystal with a {0001} plane orientation, and a plane perpendicular to the cleavage plane in a part of an outer peripheral portion is defined as a chord. # 11-2 perpendicular to the cut surface
A gallium nitride wafer having a flat portion that is a 0 ° plane. 6. A specific, transparent and independent circular wafer made of a hexagonal gallium nitride single crystal having a {0001} plane orientation and having an arcuate portion cut at a part of an outer peripheral portion and orthogonal to the plane. A gallium nitride, comprising: a first flat portion for indicating a crystal orientation {hkm0}; and a second flat portion having a different direction length perpendicular to the first flat portion for distinguishing front and back surfaces. Wafer. 7. The ^{semiconductor device according} to claim 1, wherein silicon is doped at a concentration of 10 ¹⁶ cm ⁻³ to 10 ²⁰ cm ^−3.
7. The gallium nitride wafer according to any one of items 1 to 6. 8. claim 1, wherein 10 ¹⁶ cm ^-3 ~10 ²⁰ cm at a concentration of ^-3 having been oxygen doping
The gallium nitride wafer according to any one of the above.