JP2018119171A - Polycrystal group iii nitride target and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group III nitride polycrystal target having a high bulk density (a relative density), a high film deposition rate and high in-plane uniformity of raw material discharge.SOLUTION: A group III nitride polycrystal target 100 is formed of a group III nitride polycrystal and has a relative density of 98% or more to the theoretical density of group III nitride. The polycrystal preferably has a columnar structure 120, an orientation rate of 40% or more and an orientation [11-20] or [0002] as a crystal orientation having the highest peak intensity obtained by the 2θ/θ measurement of X ray diffraction. A method for manufacturing the group III nitride polycrystal target 100 comprises the steps of: preparing a base substrate and growing a group III nitride polycrystal right on the base substrate by hydride vapor phase deposition.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polycrystalline group III nitride target and a method for manufacturing the same.

  Group III nitride semiconductors such as gallium nitride (GaN) are useful as materials for semiconductor devices such as optical devices and electronic devices. A technique for forming a film by depositing group III nitride by sputtering or the like has been studied, and a target for this purpose has been proposed.

  For example, Patent Document 1 proposes a sputtering target obtained by sintering GaN powder. However, it is difficult to increase the bulk density (relative density) of the sintered target because there are gaps between the sintered particles.

JP 2012-144424 A

  One object of the present invention is to provide a polycrystalline group III nitride target having a high bulk density (relative density).

According to one aspect of the invention,
There is provided a polycrystalline group III nitride target composed of polycrystalline group III nitride and having a relative density of 98% or more with respect to the theoretical density of the group III nitride.

According to another aspect of the invention,
Preparing a base substrate;
Growing polycrystalline III-nitride by hydride vapor deposition directly on the underlying substrate;
A method for producing a polycrystalline group III-nitride target having the following is provided:

  A polycrystalline III-nitride target with high bulk density (relative density) is provided.

FIG. 1 is a schematic cross-sectional view illustrating a polycrystalline group III nitride target according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a film formation state using the polycrystalline group III nitride target according to the embodiment. FIG. 3A to FIG. 3C are schematic cross-sectional views illustrating the manufacturing process of the polycrystalline group III nitride target according to the embodiment. FIGS. 4A and 4B are EBSD images of a top surface and a cross section of a polycrystalline GaN sample according to the first experiment of the experimental example, respectively. FIGS. 5A to 5C show X-ray diffraction 2θ / θ measurement results for the sample on PG, the sample on flexible graphite, and the sample on -c plane GaN, respectively, in the second experiment of the experimental example. It is a graph to show.

  A polycrystalline group III nitride target 100 (hereinafter, target 100) according to an embodiment of the present invention will be described.

  First, the features of the target 100 will be exemplarily described. As a comparison object, description will be given while illustrating a polycrystalline group III nitride target (hereinafter, sintered target) manufactured by sintering. FIG. 1 is a schematic cross-sectional view showing the target 100.

The target 100 is made of polycrystalline group III nitride. The group III nitride constituting the target 100 is, for example, gallium nitride (GaN), but is not limited to GaN. For example, aluminum nitride (AlN), aluminum gallium nitride (AlGaN), indium nitride (InN), indium nitride Group III nitrides such as gallium (InGaN) and aluminum indium gallium nitride (AlInGaN), that is, group III nitrides represented by a composition formula of Al _x In _y Ga _1-xy N (0 ≦ x + y ≦ 1) It may be.

  The target 100 is used as a member that releases a raw material for forming a group III nitride film. The film forming method performed using the target 100 is, for example, sputtering, but other film forming methods, for example, pulse laser deposition (PLD) may be used.

  The target 100 has a target surface. The target surface is a surface from which the material is released (scattered) when energy is applied. For example, when the film forming method is sputtering, the target surface is a surface on which ions of the sputtering gas collide. A target 100 illustrated in FIG. 1 has a flat plate shape and includes a pair of main surfaces 101 and 102. At least one main surface 101 is used as a target surface. In the following description of “target 100” and “use mode of target 100”, one main surface 101 is referred to as “target surface 101” as an example. FIG. 1 shows a cross section orthogonal to the target surface 101.

  The target 100 is composed of polycrystals grown integrally by hydride vapor phase deposition (HVPD). The direction in which polycrystals are deposited in the growth by HVPD, that is, the thickness direction of the polycrystals may be simply referred to as the growth direction.

  Since the target 100 is formed of HVPD, the polycrystalline structure does not have a gap (gap between sintered particles) as seen in the polycrystalline structure of the sintered target. Compared with a higher bulk density.

  A high bulk density of the target 100 is preferable, for example, from the viewpoint of increasing the film formation speed in film formation using the target 100. For example, the in-plane uniformity of the material discharge is increased by reducing the voids in the target surface 101. It is preferable from the viewpoint.

  The target 100 preferably has a relative density with respect to the theoretical density of the group III nitride constituting the target 100 of 98% or more, and more preferably 99% or more. The upper limit value of the relative density is not particularly limited, and may be 100% which is the maximum value. The relative density is a value expressed as a percentage by dividing the bulk density of the target 100 measured by the Archimedes method by the theoretical density of the group III nitride constituting the target 100.

For example, the target 100 made of GaN preferably has a bulk density of 5.97 g / cm ³ or more (relative density of 98% or more) with respect to a theoretical density of GaN of 6.09 g / cm ³ . It is more preferable to have a bulk density of 03 g / cm ³ or more (relative density of 99% or more). The inventor of the present application has confirmed that, for example, a polycrystalline GaN grown by HVPD has a bulk density of 6.04 g / cm ³ (relative density 99.2%).

  The polycrystal of the target 100 has a columnar structure 120. The columnar structure 120 has columnar crystal grains 121. In HVPD, since a grain boundary is hardly generated in the growth direction, columnar crystal grains 121 that are long in the growth direction are formed. On the other hand, the polycrystal of the sintered target is configured as an aggregate of powders and therefore does not have a columnar structure.

  In the target 100 illustrated in FIG. 1, the target surface 101 is configured as a surface orthogonal to the growth direction. “A plane perpendicular to the growth direction” refers to a plane in which the angle between the normal direction of the plane and the growth direction is close to 0 °, for example, within ± 10 °. The dimension in the growth direction of the columnar crystal grains 121 (hereinafter referred to as length) is, for example, 70% or more of the thickness of the target 100. The length of the columnar crystal grains 121 may be 100% of the thickness of the target 100. That is, the columnar crystal grains 121 may penetrate from one main surface 101 of the target 100 to the other main surface 102.

  The polycrystal of the target 100 has hexagonal crystal grains, and the crystal grains distributed in a plane perpendicular to the growth direction are non-oriented polycrystals, that is, powder-like polycrystals with the crystal orientation facing the growth direction. Compared to, there are more in a specific orientation. That is, the orientation is generally uniform in a plane orthogonal to the growth direction. For this reason, when it is preferable to form a film using the target 100 having a uniform orientation in the target surface 101, the target surface 101 may be configured as a surface orthogonal to the growth direction. On the other hand, the polycrystal of the sintered target can be regarded as non-oriented because it can be regarded as having the same orientation as that of the powdery polycrystal.

  The degree of orientation of the polycrystal in a specific crystal orientation can be expressed by an orientation rate as will be described in detail later. The orientation ratio of non-oriented polycrystal composed of hexagonal group III nitride is estimated to be about 33% at most. The orientation ratio of the polycrystal that constitutes the target 100 is higher than the orientation ratio of the non-oriented polycrystal and is 40% or more (for example). That is, the polycrystal constituting the target 100 has a specific crystal orientation in which the orientation rate is (for example) 40% or more.

  Such a specific crystal orientation is referred to as a highly oriented crystal orientation. The highly oriented crystal orientation can be controlled by the manufacturing conditions of the target 100, and can be, for example, [11-20] orientation, and can be, for example, [0002] orientation. The highly oriented crystal orientation is represented by arrow 122.

  The target surface 101 is preferably configured as a surface with high surface smoothness having an arithmetic average surface roughness Ra of, for example, 5 μm or less. Examples of the processing method for obtaining the surface smoothness include grinding, polishing, and electric discharge machining. The surface smoothness of the target surface 101 can be appropriately adjusted as necessary, and the target surface 101 may be mirror-finished.

  The planar shape of the target 100 is, for example, a circular shape, but is not limited to a circular shape, and may be another shape, for example, a rectangular shape. The size (dimension in plan view) of the target 100 is not particularly limited and can be adjusted as necessary. The thickness of the target 100 is not particularly limited and can be appropriately adjusted as necessary. However, it is preferably not too thin from the viewpoint of being repeatedly used for film formation, and is preferably 1 mm or more, for example, 2 mm or more. Is more preferable. An example of the size, thickness, and shape of the target 100 is a disk shape having a diameter of 102 mm (4 inches) and a thickness of 2 mm. Note that the shape of the target 100 is not necessarily a flat plate shape, and may be other shapes as necessary.

  Next, an example of how the target 100 is used will be described. FIG. 2 is a schematic diagram showing the state of film formation using the target 100.

  The target 100 is disposed in the film forming apparatus 200. The holding member 210 holds the target 100 with the target surface 101 exposed. A structure in which the target 100 is held by the holding member 210 may be called a target structure 211. The material release device 220 applies energy to the target surface 101 to release (scatter) the material 130 for forming the group III nitride film 240 from the target surface 101. For example, when the film forming method is sputtering, the holding member 210 is a backing plate, and the raw material discharge device 220 applies a high voltage to the sputtering gas and collides the ionized sputtering gas with the target surface 101. including.

  The source material 130 released from the target surface 101 is deposited on the base substrate 230 for film formation, and a group III nitride film 240 is formed. In addition to the raw material 130 emitted from the target 100, other raw materials may be used in combination as a raw material for forming the group III nitride film 240. Note that the conductivity determining impurity element may be supplied from the target 100 by using the target 100 to which the conductivity determining impurity element is added in the crystal grains.

  Next, an exemplary method for manufacturing the target 100 will be described. FIG. 3A to FIG. 3C are schematic cross-sectional views showing the manufacturing process of the target 100.

  Reference is made to FIG. First, a base substrate 10 (hereinafter referred to as substrate 10) for growing polycrystalline group III nitride 20 (hereinafter referred to as polycrystalline 20) is prepared. Examples of the material of the substrate 10 include pyrolytic graphite (PG), flexible graphite, metal, group III nitride, and mullite.

  When these materials are cooled after the growth of the polycrystal 20 on the substrate 10, the stress (the substrate 10) generated in the polycrystal 20 due to a difference in linear expansion coefficient (difference in thermal shrinkage) between the substrate 10 and the polycrystal 20. From the viewpoint of suppressing the polycrystal 20 from cracking due to the stress applied to the polycrystal 20.

  When PG is used, before the polycrystal 20 is cracked due to excessive stress, the outermost surface layer of PG is peeled off as a sacrificial layer. That is, the polycrystal 20 is peeled from the substrate 10 together with the outermost surface layer of PG. As a result, no stress is applied from the substrate 10 to the polycrystal 20. In addition to PG, pyrolytic boron nitride (PBN), mica, or the like may be used as the material of the base material 10.

  Flexible graphite is a material formed using expanded graphite, has flexibility, softness, compression recovery, etc., and is used, for example, in the form of a flexible graphite sheet having a thickness of 1 mm or less. The Examples of the flexible graphite include Permafoil (registered trademark) manufactured by Toyo Tanso Co., Ltd., Grafoil (registered trademark) manufactured by Graphtec International Holdings, Inc., and the like. In addition, compared with flexible graphite, PG is a material that does not have flexibility. In the case of using flexible graphite, the stress applied to the polycrystal 20 from the substrate 10 is reduced by the elasticity of the flexible graphite.

  Examples of the metal include tungsten (W) and molybdenum (Mo), which have a high melting point and can withstand the growth environment of HVPD. When a metal is used, the stress applied to the polycrystal 20 from the substrate 10 is reduced due to the elasticity of the metal.

  Examples of the group III nitride include a single crystal group III nitride. In order to suppress the difference in thermal shrinkage between the substrate 10 and the polycrystal 20, the same composition as that of the polycrystal 20 is preferable. When the group III nitride is used, the stress applied from the substrate 10 to the polycrystal 20 is suppressed because the linear expansion coefficients of the substrate 10 and the polycrystal 20 are close.

  When mullite is used, the stress applied from the substrate 10 to the polycrystal 20 is suppressed because the linear expansion coefficients of the substrate 10 and the polycrystal 20 are close.

  The substrate 10 using the material as described above is aligned in the main surface 11 according to the crystallinity of the material.

  Reference is made to FIG. The substrate 10 is carried into the HVPD device. By supplying a group III source gas and a nitrogen source gas on the substrate 10, the polycrystal 20 is grown.

As the group III source gas and the nitrogen source gas, source gases used in HVPD can be appropriately used. Among group III source gases, for example, aluminum trichloride (AlCl ₃ ) gas is used as the aluminum (Al) source gas, and gallium chloride (GaCl) gas is used as the gallium (Ga) source gas, for example, indium. As the (In) source gas, for example, indium trichloride (InCl ₃ ) gas is used. As the nitrogen source gas, for example, ammonia (NH ₃ ) gas is used. By appropriately adjusting the supply ratios of the Al source gas, the Ga source gas, and the In source gas, the group III element composition of the target 100 can be set to a desired composition. As the carrier gas, for example, nitrogen gas (N ₂ gas) is used. The growth conditions are, for example, a pressure of 500 Torr (about 66661 Pa) to 760 Torr (about 101325 Pa, normal pressure), a V / III ratio of 10 or less, and a growth temperature of 900 ° C. to 1200 ° C. In the present embodiment, since it is sufficient to grow a polycrystal, the allowable range of growth conditions is wider than that in the case of growing a single crystal, and the growth conditions may be appropriately selected as necessary.

  By growing the group III nitride directly on the substrate 10, that is, on the main surface 11 of the substrate 10 (without a buffer layer), the polycrystal 20 (not a single crystal) is obtained. The growth direction is indicated by an arrow 21. In HVPD, since a grain boundary is hardly generated in the growth direction, columnar crystal grains that are long in the growth direction are grown, and a columnar structure is formed. Note that smaller crystal grains smaller than these may be formed in the gaps between the columnar crystal grains.

  By aligning the orientation within the main surface 11 of the substrate 10 to some extent, the orientation of the polycrystal 20 grown on the main surface 11 is aligned to some extent within the plane orthogonal to the growth direction, that is, a highly oriented crystal orientation. It is speculated that this may occur.

  As will be described in detail in an experimental example described later, the highly oriented crystal orientation can be controlled by selecting the material of the substrate 10. For example, by using PG for the substrate 10, the highly oriented crystal orientation can be set to [11-20] orientation, and for example, by using flexible graphite or group III nitride for the substrate 10, highly oriented The crystal orientation can be the [0002] orientation. Further, the orientation ratio of the highly oriented crystal orientation can be changed by selecting flexible graphite or group III nitride. Thus, the degree of freedom to change the orientation of the target 100 according to the required characteristics is increased by selecting the material of the substrate 10.

  Reference is made to FIG. The polycrystal 20 is grown until a desired thickness is obtained for obtaining one or more targets 100. The polycrystal 20 at the stage where the growth is completed is called an ingot 22. By using the above-described material as the material of the substrate 10, the ingot 22 is prevented from being cracked during the cooling after the growth.

  The thickness of the ingot 22 is not particularly limited, but is preferably thick from the viewpoint of obtaining a sufficiently thick target 100 or efficiently obtaining a plurality of targets 100, for example, at least 1 mm or more, preferably It is 2 mm or more, more preferably 5 mm or more. By using HVPD (for example, compared with MOCVD which is another vapor phase growth), even a thick ingot 22 of, for example, 10 mm or more can be grown in a short time. The upper limit of the thickness of the ingot 22 is not particularly limited, but is 20 mm, for example, from the viewpoint of suppressing an excessively long growth time.

  After cooling, the ingot 22 is separated from the substrate 10. When PG is used as the material of the substrate 10, the ingot 22 can be easily separated by peeling off the outermost surface layer of the substrate 10 as a sacrificial layer. When the substrate 10 made of other materials is used, the ingot 22 is cut from the substrate 10 using an appropriate slicer.

  Thereafter, surface smoothing is performed on the upper surface (surface on the tip side of growth) and the lower surface (surface on the root side of growth) of the ingot 22 (at least on the upper surface). If necessary, the side surface may be smoothed. When obtaining one target 100, the target 100 is obtained in this way. In the case of obtaining a plurality of targets 100, for example, the ingot 22 is cut in a direction orthogonal to the growth direction and the ingot 22 is divided to obtain a plurality of targets 100. The “direction perpendicular to the growth direction” refers to a direction in which an angle formed with the growth direction is close to 90 °, for example, within 90 ° ± 10 °. Each of the plurality of targets 100 is subjected to a surface smoothing process as necessary. In this way, the target 100 is manufactured.

  As the target surface, the main surface 101 on the ingot upper surface side (growth tip side) of the target 100 may be used according to the characteristics required for the target 100 or the like, and the ingot lower surface side (growth root side) may be used. The main surface 102 may be used.

  In addition, although the direction orthogonal to the growth direction is illustrated as the direction for cutting the ingot 22, the target surface (main surface 101 or main surface 102) obtained by cutting the ingot 22 is orthogonal to the growth direction. Although the case where it comprises as a surface is illustrated, the direction which cut | disconnects the ingot 22 is not limited to this, You may change suitably according to the characteristic etc. which are calculated | required by the target 100. FIG.

In addition to the group III source gas and the nitrogen source gas, a gas containing a conductivity-determining impurity element is supplied for growth to obtain the target 100 in which the conductivity-determining impurity element is added in the crystal grains. May be. For example, silicon (Si) is used as the n-type impurity element, and silane (SiH ₄ ) gas and dichlorosilane (SiH ₂ Cl ₂ ) gas are used as the gas containing the n-type impurity element, for example. For example, magnesium (Mg) is used as the p-type impurity element, and for example, biscyclopentadienyl magnesium (Cp ₂ Mg) gas is used as the gas containing the p-type impurity element.

  Next, experimental examples will be described. First, a first experiment in which a polycrystalline group III nitride is grown and the state of crystal grains is observed will be described.

  In the first experiment, a polycrystalline GaN sample (hereinafter referred to as a sample) was grown by HVPD on a substrate formed of PG, and observation by electron beam backscatter diffraction (EBSD) was performed.

  FIG. 4A is an EBSD image of the upper surface of the sample (surface on the tip side of growth). Within the upper surface of the sample, that is, within the plane orthogonal to the growth direction, the crystal grains are distributed approximately evenly in any region (compared to the state of crystal grains in the cross section described later). The average grain size of the crystal grains is 143 μm.

  FIG. 4B is an EBSD image of a sample cross section orthogonal to the upper surface of the sample, and shows a cross section of one columnar crystal grain 30. In the sample cross section, that is, in a plane parallel to the growth direction, columnar crystal grains 30 that grow thicker from the lower side (growth base side) to the upper side (growth tip side) are observed. Further, many fine crystal grains generated at the initial stage of growth are distributed at the lower end.

  From the EBSD image of the upper surface of the sample in FIG. 4A and the EBSD image of the cross section of the sample in FIG. 4B, the polycrystal of the sample has no gap between crystal grains and has a columnar structure. I understand. That is, the target manufactured using such a polycrystal does not have a gap as seen in the polycrystalline structure of the sintered target, has a higher bulk density than the sintered target, It can be seen that it has a columnar structure.

  The thickness of the sample shown in FIG. 4 (b) is 2.5 mm. In the cross section of the sample shown in FIG. 4B, the lower end 31 of the columnar crystal grain 30 is observed at a position 0.27 mm from the lower surface (the surface on the root side of growth), and the upper end 32 reaches the upper surface and reaches the lower surface. To 2.5 mm. That is, the length of the columnar crystal grain 30 is at least 2.2 mm or more and 88% or more of the total thickness of 2.5 mm of the sample. Note that the columnar crystal grains 30 are regions that do not appear in the sample cross section shown in FIG.

  Hereinafter, based on this, when a target is manufactured from this sample, it is estimated how much the length of the columnar crystal grains 30 is relative to the thickness of the target. In addition, in order to avoid the complicated explanation, the thickness that is reduced by the surface smoothing process is not considered (if the process of removing the portion on the lower surface side where the columnar crystal grains 30 are not generated is considered) , The ratio will increase further).

  For example, when the target is manufactured using the entire thickness of 2.5 mm, the length of the columnar crystal grains 30 of 2.2 mm is estimated to be 88% or more, at least 80% or more of the target thickness. For example, when the target is manufactured using a thickness of 1 mm from the lower surface, the length of the columnar crystal grains 30 is 0.73 mm, and is estimated to be 73% or more and at least 70% or more of the thickness of the target. For example, when the target is manufactured using a thickness of 1 mm from the upper surface, the length of the columnar crystal grain 30 is 1 mm, which is 100% of the thickness of the target. From the above, it is estimated that the length of the columnar crystal grains 30 observed in the target is at least 70% or more of the thickness of the target.

  Next, a second experiment for examining how the orientation of the growing polycrystalline group III-nitride changes when the substrate material is changed will be described.

  In the second experiment, a polycrystalline GaN sample (hereinafter referred to as a sample) was grown by HVPD on each of a substrate formed of PG, a substrate formed of flexible graphite, and a substrate formed of single crystal GaN. 2θ / θ measurement of X-ray diffraction was performed.

  Prior to the description of the measurement results for the sample, the definition of the orientation rate will be described first, and the orientation rate of non-oriented polycrystal will be considered. Since the orientation of the crystal orientation in the polycrystal is considered, in the following, the diffraction peak on the (hkmn) plane (where h, k, m, n is an integer) as the predetermined crystal plane is It is expressed as “peak of [hkmn] orientation” as a crystal orientation perpendicular to the crystal plane.

  Regarding the hexagonal group III nitride, the orientation ratio of a certain crystal orientation is defined by the ratio of the peak intensity of the crystal orientation to the sum of the peak intensities of each crystal orientation in the 2θ / θ measurement. Here, the range of the angle 2θ is 20 ° or more and 80 ° or less, and diffraction from a symmetrical plane is excluded. [10-10] orientation, [0002] orientation, [10-11] orientation, [10-12] orientation, [11-20] orientation, [10-13] orientation, [11-22] orientation, and , [20-21] orientation, and [20-20] orientation, [0004] orientation, etc. are excluded.

  According to the International Diffraction Data Center (ICDD) card, the orientation ratios (three from the largest) of powdery, that is, non-oriented GaN, AlN, and InN are estimated as follows. The orientation ratio of non-oriented GaN is 32.1% in the [10-11] orientation, 17.9% in the [10-10] orientation, and 14.4% in the [0002] orientation. The orientation ratio of non-oriented AlN is 27.0% in the [10-10] orientation, 21.6% in the [10-11] orientation, and 16.2% in the [0002] orientation. The orientation ratio of non-oriented InN is 33.4% in the [10-11] orientation, 14.7% in the [10-10] orientation, and 13.7% in the [0002] orientation.

Among the orientation ratios of non-oriented GaN, AlN, and InN, the maximum is the orientation ratio of 33.4% in the [10-11] orientation of non-oriented InN. From this, in the non-oriented group III nitride having an arbitrary composition represented by the composition formula of Al _x In _y Ga _1-xy N (0 ≦ x + y ≦ 1), the orientation ratio of which crystal orientation Is estimated to be no more than 33.4%.

  As for non-oriented GaN, AlN, and InN, the orientation ratio in the [10-10] orientation is 17.9% for GaN, 27.0% for AlN, and 14.7% for InN, and 27.0 at most. The orientation ratio in the [0002] orientation is 14.4% for GaN, 16.2% for AlN, and 13.7% for InN, and is estimated to be 16.2% at most. The orientation ratio in the −20] orientation is estimated to be 11.4% at most, with 9.9% for GaN, 10.8% for AlN, and 11.4% for InN.

  From the above considerations, as a rough criterion, when the hexagonal polycrystalline group III nitride has a specific crystal orientation with an orientation ratio of more than 33.4%, for example 40% or more, for example 45% or more It can be said that it has higher orientation than non-oriented polycrystals.

  Further, regarding the individual orientations, when the orientation rate of the [10-10] orientation is more than 27.0%, for example, 30% or more, the orientation rate of the [0002] orientation is more than 16.2%, for example, When it is 20% or more, the orientation ratio of [11-20] orientation is higher than 11.4%, for example, when it is 20% or more, it has higher orientation than non-oriented polycrystal. it can.

  In non-oriented GaN and InN, the highest orientation ratio, that is, the direction with the highest peak intensity is the [10-11] orientation, and in non-oriented AlN, the highest orientation ratio, that is, the highest peak. The direction with high intensity is the [10-10] direction. Therefore, the orientation of the polycrystal having the crystal orientation with the highest peak intensity other than these, for example, the [11-20] orientation, the [0002] orientation, etc., is controlled as compared with the non-oriented polycrystal. It can be said that

  Next, a sample grown on a substrate formed of PG (hereinafter referred to as a sample on PG), a sample grown on a substrate formed of flexible graphite (hereinafter referred to as a sample on flexible graphite), and a single sample. The 2θ / θ measurement results of a sample grown on a substrate formed of crystalline GaN (hereinafter, a sample on the −c plane GaN) will be described. 2θ / θ measurement was performed on the upper surface of the sample (the surface on the tip side of the growth).

  The polycrystalline GaN samples on the PG, the flexible graphite, and the -c-plane GaN were each grown to a thickness of 2.7 mm. In the sample on the flexible graphite, as the flexible graphite, Permafoil (registered trademark) manufactured by Toyo Tanso Co., Ltd., having a thickness of 20 μm was used. Permafoil clearly shows a peak in the [0002] orientation (around 27 °) and a peak in the [0004] orientation (around 54 °) of hexagonal graphite by X-ray diffraction 2θ / θ measurement. In the -c plane GaN sample, a polycrystal was grown on the single crystal GaN -c plane.

  FIG. 5A to FIG. 5C are graphs showing 2θ / θ measurement results of the sample on PG, the sample on flexible graphite, and the sample on -c-plane GaN, respectively. In each graph, the horizontal axis indicates 2θ expressed in ° units, and the vertical axis indicates the diffraction intensity expressed in cps units.

  As shown in FIG. 5A, the sample on PG has the highest peak intensity in the [11-20] orientation (57.95 °), and the orientation rate is 82.1%. The orientation ratio next to that of the sample on PG is 9.4% in the [0002] orientation (34.75 °) and 3.1% in the [10-13] orientation (63.45 °).

  As shown in FIG. 5 (b), the sample on flexible graphite has the highest peak intensity in the [0002] orientation (34.29 °), and its orientation rate is 45.8%. The orientation rate next to that of the sample on flexible graphite is 25.1% in the [10-13] orientation (63.25 °) and 7.5% in the [10-11] orientation (36.63 °). .

  As shown in FIG. 5C, the sample on the −c-plane GaN has the highest peak intensity in the [0002] orientation (34.57 °), and its orientation rate is 69.3%. The orientation ratio next to that of the sample on the -c-plane GaN is 11% of the [11-20] orientation (57.47 °) and 5.8% of the [10-10] orientation (32.27 °).

  Thus, all of the sample on PG, the sample on flexible graphite, and the sample on -c-plane GaN faced the growth direction of crystal grains distributed in the upper surface of the sample, that is, in a plane orthogonal to the growth direction. It can be seen that the crystal orientation increases in a specific orientation as compared with non-oriented polycrystals, that is, powdery polycrystals. That is, it can be seen that the orientation is generally aligned within a plane orthogonal to the growth direction. More specifically, all the polycrystals of the sample on PG, the sample on flexible graphite, and the sample on -c-plane GaN have a crystal orientation (highly oriented crystal orientation) with an orientation rate of 40% or more. I understand that.

  It can also be seen that the orientation of the growing polycrystal is controlled by the difference in the material of the base substrate on which the polycrystal is grown. The sample on PG has a strong tendency to be oriented in the [11-20] orientation, and the orientation ratio in the orientation is 82.1%, which indicates 80% or more. That is, it can be seen that by using PG for the substrate, the highly oriented crystal orientation can be changed to the [11-20] orientation.

  The sample on flexible graphite and the sample on -c-plane GaN tend to be oriented in the [0002] direction. The orientation ratio in this direction is 45.8% for the sample on flexible graphite, showing 40% or more, 69.3% for the sample on -c-plane GaN, and showing 60% or more. That is, it can be seen that the highly oriented crystal orientation can be changed to the [0002] orientation by using flexible graphite or group III nitride for the substrate.

  In addition, the sample (henceforth a sapphire sample) which grew polycrystalline GaN by HVPD on the board | substrate (on the c surface of sapphire) formed with sapphire was also measured. In the sample on sapphire, although an extremely high value of 99.8% was obtained as the orientation rate in the [0002] orientation, the polycrystal was broken during cooling after growth. Therefore, it can be said that sapphire is not suitable as a material for the substrate from the viewpoint of suppressing polycrystalline cracks.

  As described above, according to the present embodiment, by using hydride vapor phase growth, a polycrystalline group III nitride target having a high bulk density (relative density) can be obtained more easily than, for example, sintering. . Such a polycrystal of the group III nitride target has a columnar structure and a crystal orientation with an orientation rate of, for example, 40% or more. The orientation of the polycrystalline group III nitride target can be controlled by selecting the material of the underlying substrate used for growth.

  As mentioned above, although this invention was demonstrated along embodiment, this invention is not restrict | limited to these. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

<Preferred embodiment of the present invention>
Hereinafter, preferred embodiments of the present invention will be additionally described.

(Appendix 1)
A polycrystalline group III nitride target composed of polycrystalline group III nitride and having a relative density to the theoretical density of group III nitride of preferably 98% or more, more preferably 99% or more.

(Appendix 2)
The polycrystalline group III nitride target according to appendix 1, wherein the polycrystal is an integrally grown polycrystal.

(Appendix 3)
The polycrystalline group III nitride target according to appendix 1 or 2, wherein the polycrystal is a polycrystal grown by hydride vapor phase epitaxy.

(Appendix 4)
The polycrystalline group III nitride target according to any one of supplementary notes 1 to 3, wherein the polycrystal has a columnar structure.

(Appendix 5)
The polycrystalline group III nitride target according to supplementary note 4, wherein a length of columnar crystal grains of the columnar structure is 70% or more of a thickness of the polycrystalline group III nitride target.

(Appendix 6)
6. The polycrystalline group III nitride target according to appendix 4 or 5, wherein the columnar crystal grains of the columnar structure penetrate from one main surface to the other main surface of the polycrystalline group III nitride target.

(Appendix 7)
The polycrystalline group III nitride target according to any one of supplementary notes 1 to 6, wherein the polycrystal has a crystal orientation in which an orientation ratio is preferably 40% or more, and more preferably 45% or more.

(Appendix 8)
The polycrystalline group III nitride according to any one of appendices 1 to 6, wherein the polycrystal has a [11-20] orientation as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction. Object target.

(Appendix 9)
The polycrystalline group III nitride according to any one of supplementary notes 1 to 6, wherein the polycrystal has an orientation ratio of [11-20] orientation of preferably 20% or more, more preferably 80% or more. target.

(Appendix 10)
The polycrystalline group III nitride target according to any one of supplementary notes 1 to 6, wherein the polycrystal has a [0002] orientation as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction. .

(Appendix 11)
The polycrystal has an orientation rate of [0002] orientation of preferably 20% or more, more preferably 40% or more, and further preferably 60% or more, according to any one of Supplementary notes 1 to 6. Polycrystalline III-nitride target.

(Appendix 12)
The polycrystalline group III nitride target according to any one of appendices 1 to 11, having a target surface with an arithmetic average surface roughness Ra of 5 μm or less.

(Appendix 13)
The polycrystalline group III nitride target according to any one of supplementary notes 1 to 12, wherein the thickness is preferably 1 mm or more, more preferably 2 mm or more.

(Appendix 14)
The polycrystalline group III nitride target according to any one of appendices 1 to 13, wherein a conductivity determining impurity element is added in the crystal grain.

(Appendix 15)
Preparing a base substrate;
Growing polycrystalline III-nitride by hydride vapor deposition directly on the underlying substrate;
A method for producing a polycrystalline group III-nitride target having

(Appendix 16)
Separating the polycrystalline III-nitride from the underlying substrate;
The method for producing a polycrystalline group III nitride target according to supplementary note 15, further comprising:

(Appendix 17)
Cutting the polycrystalline III-nitride;
The method for producing a polycrystalline group III nitride target according to supplementary note 15 or 16, further comprising:

(Appendix 18)
Any of Supplementary Notes 15 to 17, wherein a material that has crystallinity and that does not cause cracks in the polycrystalline III-nitride when cooling after the growth of the polycrystalline III-nitride is used as the material of the base substrate A method for producing a polycrystalline group III nitride target according to claim 1.

(Appendix 19)
The polycrystalline according to any one of appendices 15 to 18, wherein one of a pyrolytic graphite, a flexible graphite, a metal, a (single crystal) group III nitride, and a mullite is used as the material of the base substrate. A method for producing a group III nitride target.

(Appendix 20)
Pyrolytic graphite is used as the material of the base substrate,
The crystal group III nitride having the [11-20] orientation as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction grows as described in any one of appendices 15 to 19 A method for producing a polycrystalline group III nitride target.

(Appendix 21)
As a material for the base substrate, flexible graphite is used,
The polycrystalline according to any one of supplementary notes 15 to 19, wherein the polycrystalline group III nitride having a [0002] orientation is grown as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction. A method for producing a group III nitride target.

(Appendix 22)
As the material of the base substrate, a (single crystal) group III nitride is used,
The polycrystalline according to any one of supplementary notes 15 to 19, wherein the polycrystalline group III nitride having a [0002] orientation is grown as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction. A method for producing a group III nitride target.

10 Underlying substrate 20 (for polycrystal growth) Polycrystalline group III nitride 21 Growth direction 22 Ingot 30 Columnar crystal grain 31 Lower end 32 (columnar crystal grain) Upper end 100 (columnar crystal grain) Upper end 100 Group III nitride target 101 , 102 Main surface 120 Columnar structure 121 Columnar crystal grain 122 Highly oriented crystal orientation 200 Film formation device 210 Holding member 220 Raw material release device 230 Base substrate 240 (for film formation) Group III nitride film

Claims (10)

  A polycrystalline group III nitride target composed of polycrystalline group III nitride and having a relative density of 98% or more with respect to the theoretical density of the group III nitride.   The polycrystalline group III nitride target according to claim 1, wherein the polycrystal has a columnar structure.   The polycrystalline group III nitride target according to claim 1, wherein the polycrystal has a crystal orientation with an orientation ratio of 40% or more.   The polycrystal group III according to any one of claims 1 to 3, wherein the polycrystal has a [11-20] orientation as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction. Nitride target.   The polycrystalline group III nitride according to any one of claims 1 to 3, wherein the polycrystal has a [0002] orientation as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction. target. Preparing a base substrate;
Growing polycrystalline III-nitride by hydride vapor deposition directly on the underlying substrate;
A method for producing a polycrystalline group III-nitride target having   The method for producing a polycrystalline group III nitride target according to claim 6, wherein one of a pyrolytic graphite, a flexible graphite, a metal, a group III nitride, and a mullite is used as a material for the base substrate. Pyrolytic graphite is used as the material of the base substrate,
The polycrystalline group III according to claim 6 or 7, wherein the polycrystalline group III nitride having a [11-20] orientation grows as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction. A method for manufacturing a nitride target. As a material for the base substrate, flexible graphite is used,
The polycrystalline group III nitride according to claim 6 or 7, wherein the polycrystalline group III nitride having a [0002] orientation as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction grows. Target manufacturing method. Group III nitride is used as the material of the base substrate,
The polycrystalline group III nitride according to claim 6 or 7, wherein the polycrystalline group III nitride having a [0002] orientation as a crystal orientation having the highest peak intensity obtained by 2θ / θ measurement of X-ray diffraction grows. Target manufacturing method.