Gallium nitride structure and method for producing same

Abstract

The purpose of the present invention is to provide: a gallium nitride structure which has a smoother surface than conventional gallium nitride sintered bodies, thereby enabling epitaxial growth of a gallium nitride film; and / or a method for producing the gallium nitride structure. A gallium nitride structure 10 according to the present disclosure comprises a gallium nitride sintered body layer 2 and a high-density gallium nitride layer 1 that is disposed on the surface of the gallium nitride sintered body layer 2, and the area density of the high-density gallium nitride layer 1 is 95.0 area% or more.

Description

Gallium nitride structure and method for manufacturing the same

[0001] This disclosure relates to gallium nitride structures and methods for manufacturing the same.

[0002] Gallium nitride is attracting attention as a material for realizing next-generation power devices. Conventionally, gallium nitride films were formed by epitaxial growth on a silicon substrate via an insulating buffer layer or the like. However, in this case, cracks sometimes occurred in the gallium nitride film because the thermal expansion coefficients of the silicon substrate and the gallium nitride film were different. For this reason, in recent years, QST™ substrates have been used instead of silicon substrates (see, for example, Non-Patent Document 1 below). Since the thermal expansion coefficient of QST™ substrates is equivalent to that of gallium nitride films, gallium nitride films formed on QST™ substrates are less likely to crack.

[0003] Furthermore, Patent Document 1 discloses a Group III nitride-based epitaxial growth substrate used for the epitaxial growth of gallium nitride films, comprising: a support substrate having a structure in which a core made of nitride ceramics is encased in a sealing layer with a thickness of 0.05 μm to 1.5 μm; a planarization layer provided on the upper surface of the support substrate and having a thickness of 0.5 μm to 3.0 μm; and a single-crystal seed crystal layer provided on the upper surface of the planarization layer and having a thickness of 0.04 μm to less than 0.1 μm.

[0004] However, since the substrates described above are composed of compounds with a different composition from gallium nitride, there is a risk of impurities being introduced into the gallium nitride film, for example, by diffusing yttrium additives contained in the aluminum nitride core layer into the gallium nitride film. Therefore, from the viewpoint of suppressing the introduction of impurities into the gallium nitride film, it is preferable to use a gallium nitride substrate instead of the above-mentioned substrates.

[0005] As a gallium nitride substrate, it is known to use single-crystalline gallium nitride. However, since it is difficult to produce a large single-crystalline gallium nitride bulk body without defects by the Na flux method or the HVPE method, it is difficult to increase its size. Furthermore, since both methods require time for the crystal growth of gallium nitride, the production takes a long time. Therefore, when using a gallium nitride substrate, from the viewpoints of increasing size and mass productivity, it is preferable to use a gallium nitride sintered body as the gallium nitride substrate.

[0006] Patent Document 2 discloses a high-density sintered body suitable as a sputtering target as a sintered body of gallium nitride.

[0007] International Publication No. 2023 / 127249, International Publication No. 2023 / 243566

[0008] J. h. Leach et al., "Towards Manufacturing Large Area GaN Substrates from QST (registered trademark) Seeds", [online], May 7 - 10, 2018, Proceedings Compd. Semicond. Manuf. Technol, [searched on November 11, 2024], Internet <https: / / csmantech.org / digests / ?digest=2018&thesession=4320>

[0009] However, the single-layer gallium nitride sintered body disclosed in Patent Document 2 does not have sufficient surface smoothness, and when applied as a substrate for epitaxial growth of a gallium nitride film, a gallium nitride film with a sufficiently smooth surface could not be obtained.

[0010] An object of the present disclosure is to provide at least one of a gallium nitride structure having a smoother surface compared to a conventional gallium nitride sintered body, thereby enabling epitaxial growth of a gallium nitride film, and a manufacturing method thereof.

[0011] In the present disclosure, attention is paid to a structure composed of a gallium nitride sintered body and a gallium nitride layer. It has been found that by providing a gallium nitride layer with a controlled surface state on the gallium nitride sintered body, the smoothness of the surface of the gallium nitride structure can be improved. Furthermore, it has been found that such a gallium nitride structure can be applied to a substrate for epitaxial growth of a gallium nitride film. That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows.

[0012] [1] A gallium nitride structure having a gallium nitride sintered body layer and a high-density gallium nitride layer on the surface of the gallium nitride sintered body layer, wherein the area density of the high-density gallium nitride layer is 95.0 area% or more. [2] The structure according to [1], wherein the Ga / (Ga+N) ratio, which is the atomic ratio of gallium to the sum of gallium and nitrogen, is 0.55 or less. [3] The structure according to [1] or [2], wherein the average surface roughness of the high-density gallium nitride layer as measured by a laser microscope is 2.30 μm or less. [4] The structure according to any one of [1] to [3], which is plate-shaped. [5] The structure according to [4], wherein the gallium nitride sintered body layer forms one main surface and the high-density gallium nitride layer forms the other main surface. [6] The structure according to any one of [1] to [5], wherein the average thickness of the gallium nitride structure is 0.50 mm or more and 3.0 mm or less. [7] The structure according to any one of [1] to [6] above, wherein the average thickness of the high-density gallium nitride layer is 1.0 μm or more and 30.0 μm or less. [8] The structure according to any one of [1] to [7] above, wherein the average thickness of the gallium nitride sintered body layer is 0.45 mm or more and 2.9 mm or less. [9] The structure according to any one of [1] to [8] above, wherein the surface roughness Ra of the high-density gallium nitride layer by AFM is 150 nm or less.

[10] The structure according to any one of [1] to [9] above, which is a substrate for epitaxial growth of a gallium nitride film.

[11] A method for manufacturing a gallium nitride structure according to any one of [1] to

[10] above, comprising forming the high-density gallium nitride layer on the gallium nitride sintered body layer.

[12] The method according to

[11] above, wherein the average surface roughness of the gallium nitride sintered body layer is 5.00 μm or less.

[13] The method according to

[11] or

[12] , wherein the high-density gallium nitride layer is formed by sputtering.

[0013] According to this disclosure, it is possible to provide at least one of the following: a gallium nitride structure having a smoother surface compared to conventional gallium nitride sintered bodies, thereby enabling the epitaxial growth of a gallium nitride film; and a method for manufacturing the same.

[0014] Figure 1 is a conceptual diagram showing the high-density gallium nitride layer and gallium nitride sintered body layer of the gallium nitride structure of this embodiment. Figure 2 is an SEM observation view (magnification: 1000x) of the cross-section of the gallium nitride structure of Example 1. Figure 3 is a schematic diagram showing the measurement points in the measurement of average surface roughness.

[0015] <Gallium Nitride Structure> The gallium nitride structure of this embodiment has a gallium nitride sintered body layer and a high-density gallium nitride layer on the surface of the gallium nitride sintered body layer, and the area density of the high-density gallium nitride layer is 95.0 area % or more.

[0016] This embodiment relates to a gallium nitride structure. The gallium nitride (GaN) structure is a structure whose main component (matrix, host phase) is gallium nitride, and in particular, it may be a structure that is mainly composed of gallium nitride. In this embodiment, having gallium nitride as the main component means that the mass ratio of gallium and nitrogen in the gallium nitride structure is 95% (95 mass%) or more. Preferably, the mass ratio of gallium and nitrogen in the gallium nitride structure is 98 mass% or more, more preferably 99 mass% or more, and also 100 mass% or less, or less than 100 mass%. The mass ratio of gallium and nitrogen in the gallium nitride structure may be the mass ratio calculated from formula (1) described later. The gallium nitride structure of this embodiment may contain components other than gallium nitride, such as metallic gallium.

[0017] Specifically, for example, as shown in Figure 1, the gallium nitride structure 10 of this embodiment may be in the form of a plate having a high-density gallium nitride layer 1 and a gallium nitride sintered body layer 2.

[0018] According to the gallium nitride structure of this embodiment, the area density of the high-density gallium nitride layer is sufficiently high that large voids on the surface do not affect its smoothness. Therefore, it is possible to make the surface smoother compared to conventional gallium nitride sintered bodies. Such a smooth surface is preferable for applying the gallium nitride structure of this embodiment to a substrate for epitaxial growth of gallium nitride. Furthermore, according to the gallium nitride structure of this embodiment, by having a high-density gallium nitride layer and a gallium nitride sintered body layer, the gallium nitride sintered body layer can function as a support layer for the high-density gallium nitride layer. This makes it possible to reduce the thickness of the high-density gallium nitride layer. In addition, the gallium nitride sintered body of this embodiment, which has a high-density layer and a low-density layer, can uniformly nitride the high-density layer compared to a gallium nitride sintered body in which the entire body is a high-density layer. As a result, a higher density high-density layer can be obtained, and the surface, i.e., the polished surface, is easier to smooth. Furthermore, by using the low-density layer as a support, the amount of Ga used can be reduced, and raw material costs can be reduced.

[0019] Furthermore, the presence of a high-density gallium nitride layer and a gallium nitride sintered body layer in the gallium nitride structure of this embodiment can be confirmed by scanning electron microscope (SEM) observation of the cross-section of the gallium nitride structure. Specifically, for example, by observing the region near one surface (hereinafter also referred to as the "first region") and the region on the other surface side (hereinafter also referred to as the "second region") in the direction from one surface of the gallium nitride structure toward the opposite surface (hereinafter also referred to as the "thickness direction") using SEM, it can be confirmed that the structure has a high-density gallium nitride layer and a gallium nitride sintered body layer of this embodiment if the area density in the first region is 95.0 area% or more and a gallium nitride sintered body is observed in the second region.

[0020] In this embodiment, it can be confirmed that the gallium nitride sintered body is composed of multiple crystal grains, and that the average crystal grain size of the crystal grains constituting the gallium nitride sintered body (hereinafter also referred to as "average crystal grain size") is 1.0 μm or more. The average crystal grain size may be 200 μm or less, 100 μm or less, or 50 μm or less, and may also be 2.0 μm or more, or 3.0 μm or more. Examples of average crystal grain sizes include 1.0 μm or more and 200 μm or less, or 2.0 μm or more and 100 μm or less.

[0021] In this embodiment, the gallium nitride sintered body is a sintered body whose main component (matrix, host phase) is gallium nitride, and may be a polycrystalline gallium nitride, or a sintered body mainly composed of gallium nitride.

[0022] In this embodiment, the gallium nitride sintered body is composed of multiple crystal grains, and the average crystal grain size can be determined by scanning electron microscopy-electron backscatter diffraction (hereinafter also referred to as "SEM-EBSD") of the cross-section of the gallium nitride structure. SEM-EBSD observation can be performed using a general EBSD (e.g., Symmetry, Oxford Instruments) to obtain an SEM observation map in a similar manner to the area density described below. The conditions for EBSD observation are as follows: Acceleration voltage: 15 kV Sample tilt: 70 degrees Tilt correction: 0° Magnification: 500x Step size: 0.2 μm

[0023] A position where the crystal orientation is tilted by 5° or more is considered a grain boundary, and the region enclosed by such grain boundaries is considered a crystal grain. The diameter of the circle corresponding to the area of ​​each crystal grain is calculated and is defined as the crystal grain size. SEM-EBSD observation is performed on the crystal grains observed in three fields of view, and the average crystal grain size in each field of view is calculated by image analysis. The average of these averages is then defined as the average crystal grain size.

[0024] In this embodiment, the high-density gallium nitride layer has an average grain size of less than 1.0 μm and may be a polycrystalline or single crystal, but it is preferable that it is a polycrystalline material with an average grain size of less than 1.0 μm. Examples of average grain sizes of the polycrystalline material constituting the high-density gallium nitride layer include 0.90 μm or less, 0.80 μm or less, or 0.60 μm or less, and also 0.01 μm or more, 0.02 μm or more, or 0.03 μm or more. Examples of average grain sizes of the polycrystalline material constituting the high-density gallium nitride layer include 0.01 μm or more and less than 1.0 μm, 0.02 μm or more and 0.90 μm or less, or 0.03 μm or more and 0.80 μm or less.

[0025] As an example, Figure 2 shows SEM observation images of the high-density gallium nitride layer and gallium nitride sintered body layer of Example 1. As shown in Figure 2, the first region shown in the upper part of the figure is gallium nitride with an area density of 95.0 area% or more, and the second region shown in the lower part of the figure is a gallium nitride sintered body. Therefore, it can be confirmed that the gallium nitride structure of Example 1 is the gallium nitride structure of this embodiment. The fact that the second region is a gallium nitride sintered body was confirmed by the fact that it consists of multiple crystal grains and has an average crystal grain size of 3.85 μm.

[0026] The average grain size of a high-density gallium nitride layer may be calculated using a SEM or AFM (atomic force microscope) observation of the surface of the high-density gallium nitride layer. When measuring the average grain size by AFM, the grain boundaries of the crystal particles can be identified from the surface topography profile. The region enclosed by such grain boundaries is considered a crystal particle. The surface of the high-density gallium nitride layer is observed using a grain size scanning probe microscope SPM-9600 (manufactured by Shimadzu Corporation) under the following conditions. For all crystal particles in the observation field, the diameter of the circle corresponding to the area of ​​each crystal particle is calculated by image analysis, and the average of these is taken as the average grain size. The average grain size is calculated for three fields of view, and their average value is taken as the average grain size obtained by AFM. Scanning speed: 1 Hz Scanning range: 10 μm × 10 μm Number of pixels: 512 × 512 Measurement temperature: 25 ± 5°C

[0027] (Area density of the high-density gallium nitride layer) In the gallium nitride structure of this embodiment, the area density of the high-density gallium nitride layer may be 95.0 area% or more, 96.0 area% or more, 97.0 area% or more, 98.0 area% or more, or 99.0 area% or more, and may also be 99.9 area% or less, 99.7 area% or less, 99.5 area% or less, 99.3 area% or less, or 99.2 area% or less. Furthermore, the area density of the high-density gallium nitride layer may be 95.0 area% or more and 99.9 area% or less, 96.0 area% or more and 99.7 area% or less, 97.0 area% or more and 99.5 area% or less, 98.0 area% or more and 99.3 area% or less, or 99.0 area% or more and 99.2 area% or less.

[0028] With respect to the gallium nitride structure of this embodiment, the area density can be measured as follows.

[0029] Prior to measurement, the gallium nitride structure is processed and polished as a pretreatment. Specifically, a cross-section is obtained by cutting the gallium nitride structure, and this cross-section is polished with sandpaper (in the order of #600, #1000, and #1500). Then, the measurement surface is obtained by polishing it at room temperature under the following conditions using a general polishing device (e.g., LaboForce-100, manufactured by Strürs): Rotation speed: 300 rpm Polishing compound: POLIPLA304M (manufactured by Fujimi Incorporated) Processing time: 10 minutes

[0030] The area density is determined by SEM observation of the region corresponding to the high-density gallium nitride layer and the region corresponding to the gallium nitride sintered body layer on the measurement surface obtained by pretreatment, obtaining SEM observation maps, and then analyzing the images of the obtained SEM observation maps. The observation is performed using a general SEM (e.g., VE-9800, manufactured by KEYENCE) under the following conditions: Acceleration voltage: 10kV Observation magnification: 500x Observation field of view: 3 fields of view

[0031] Next, using general image analysis software (for example, Image-Pro 10, manufactured by Hakuto Co., Ltd.), the obtained SEM observation image is binarized, and the vacancies are detected by distinguishing between non-vacancies (i.e., the gallium nitride portion constituting the gallium nitride structure) and vacancies, and their area [μm²] is determined. ２ The following formula is used to determine the area [μm²] of the SEM observation image. For binarization, the SEM observation image is imported into image analysis software as a grayscale image with 256 levels of black and white, and discriminant analysis is used. After detecting voids, the observation area [μm²] of the SEM observation image is calculated using the following formula. ２ Area of ​​the region excluding the voids [μm²] ２ From this, calculate the area density [area %]: Area density [area %] = {(area of ​​the part excluding voids) / (observed area of ​​the SEM observation map)} × 100 The area density is calculated by finding the area density in three fields of view and taking the average of these values.

[0032] (Surface orientation of the high-density gallium nitride layer) In the gallium nitride structure of this embodiment, it is preferable that the surface orientation of the high-density gallium nitride layer (hereinafter also referred to as "orientation degree") is 50% or more, 60% or more, or 70% or more. When the orientation degree is of the above value, when a seed crystal layer is placed on the surface of the high-density gallium nitride layer, the orientation degree of the seed crystal layer tends to be high. A higher orientation degree is preferable, but upper limits include 90% or less, 85% or less, or 80% or less. The orientation degree may also be 50% or more and 90% or less, 60% or more and 85% or less, or 70% or more and 80% or less.

[0033] Here, the degree of orientation can be determined by performing X-ray diffraction (hereinafter also referred to as "XRD") measurements on the surface of the gallium nitride structure and obtaining diffraction peaks corresponding to the 002 and 004 planes of the resulting XRD pattern. XRD measurement only requires measuring the surface of the high-density gallium nitride layer, and no pretreatment is necessary prior to the measurement.

[0034] XRD measurements can be performed using a general-purpose X-ray diffractometer (e.g., RINT Ultima III, Rigaku Corporation) under the following conditions: Source: CuKα rays (λ = 1.5405 Å) Measurement mode: Continuous scan Step width: 0.02° Scan speed: 2° / min Measurement range: 2θ = 20° to 80°

[0035] From the diffraction peaks corresponding to the 002 and 004 planes, which have peak tops at 2θ = 34.56 ± 0.08° and 72.90 ± 0.08° in the obtained XRD pattern, the Rottgering factor F(002,004) can be determined using the following formula, and this can be used as the degree of orientation: F(002,004) = (ρ - ρ ０ ) / (1-ρ) ０ )

[0036] Here, ρ and ρ ０ The following is true: ρ: The ratio of the peak heights of diffraction peaks with peak tops at 2θ = 34.56 ± 0.08° and 72.90 ± 0.08° to the total peak height of diffraction peaks in the XRD pattern of the gallium nitride structure. ０ The ratio of the peak heights of diffraction peaks with peak tops at 2θ = 34.56 ± 0.08° and 72.90 ± 0.08° to the total peak height of diffraction peaks in the XRD pattern of gallium nitride shown in PDF card No. 01-073-7289.

[0037] (Composition) Furthermore, according to the gallium nitride structure of this embodiment, the Ga / (Ga+N) ratio is 0.55 or less, that is, the degree of nitriding of gallium is high, so when applied to a substrate for epitaxial growth of gallium nitride, it can have a coefficient of thermal expansion similar to that of gallium nitride that is epitaxially grown.

[0038] The Ga / (Ga+N) ratio of the gallium nitride structure in this embodiment is preferably 0.50 or less. With such a Ga / (Ga+N) ratio, the gallium nitride structure in this embodiment is substantially composed of gallium nitride alone.

[0039] The Ga / (Ga+N) ratio of the gallium nitride structure in this embodiment may be 0.55 or less, 0.53 or less, 0.50 or less, less than 0.50, or 0.49 or less, and may also be 0.45 or more, 0.46 or more, or 0.47 or more. Furthermore, this Ga / (Ga+N) ratio may be 0.45 or more and 0.53 or less, 0.45 or more and 0.50 or less, 0.46 or more and less than 0.50, or 0.47 or more and 0.49 or less.

[0040] When the gallium nitride structure of this embodiment is applied to a substrate for epitaxial growth of gallium nitride, it is preferable that the gallium nitride structure of this embodiment has a low content of elements other than nitrogen and gallium in order to prevent contamination of the gallium nitride with impurities to be epitaxially grown. Examples of impurities contained in the gallium nitride structure of this embodiment include oxygen. Furthermore, the gallium nitride structure of this embodiment may contain metallic impurities as long as its effectiveness is not impaired. Examples of metallic impurities include at least one of aluminum (Al) and indium (In). Metallic impurities may be contained as metals or as metallic compounds. It is preferable that the structure contains substantially no metallic impurities. Therefore, the content of metallic impurities may be 50 ppm by mass or less, 10 ppm by mass or less, or 5 ppm by mass or less as the mass ratio of metallic impurities [mass ppm] of the total mass of elements determined by glow discharge mass spectrometry to the total mass of elements determined by glow discharge mass spectrometry. The lower limit of the metal impurity content is 0 ppm or more by mass, greater than 0 ppm by mass, or 1 ppm or more by mass. Furthermore, the metal impurity content is 0 ppm or more and 50 ppm or less by mass, or greater than 0 ppm and 10 ppm or less by mass.

[0041] In the gallium nitride structure of this embodiment, the oxygen content may be 5.00 atm% or less, 4.00 atm% or less, 3.00 atm% or less, 2.00 atm% or less, 1.50 atm% or less, 1.00 atm% or less, 0.50 atm% or less, 0.40 atm% or less, or 0.30 atm% or less, and may also be 0.01 atm% or more, 0.02 atm% or more, 0.05 atm% or more, 0.10 atm% or more, 0.15 atm% or more, 0.18 atm% or more, or 0.20 atm% or more. Further, the oxygen content may be 0.01 atm% or more and 5.00 atm% or less, 0.01 atm% or more and 4.00 atm% or less, 0.02 atm% or more and 3.00 atm% or less, 0.02 atm% or more and 2.00 atm% or less, 0.05 atm% or more and 1.50 atm% or less, 0.10 atm% or more and 1.00 atm% or less, 0.15 atm% or more and 0.50 atm% or less, 0.18 atm% or more and 0.40 atm% or less, or 0.20 atm% or more and 0.30 atm% or less.

[0042] The composition of the gallium nitride structure of this embodiment can be substantially represented by the following formula (1): 100 [mass%] = W Ｇａ [mass%] + W Ｏ [mass%] + W Ｎ [mass%]... (1) Here, W Ｇａ 、W Ｏ and W Ｎ are the mass ratios of gallium, oxygen, and nitrogen in the gallium nitride structure, respectively.

[0043] W Ｏ and W Ｎ are values measured by a thermal decomposition method (inert gas fusion-infrared absorption method) in which the gallium nitride structure is thermally decomposed using a general oxygen and nitrogen analyzer (for example, LECO ON736, manufactured by LECO Corporation). W Ｇａ is a value obtained from the measured values of W Ｏ and W Ｎ according to formula (1).

[0044] If the material contains elements such as metallic impurities, the content is the mass ratio [mass ppm] of the metallic elements to the total mass of the elements determined by glow discharge mass spectrometry. Due to differences in measurement methods, if the sintered body of this embodiment contains elements such as metallic impurities, its composition may appear to exceed 100% by mass.

[0045] Furthermore, the oxygen content [atm%] is measured according to the method in accordance with JIS H 1695 and is a value obtained from the following formula (2): Oxygen content [atm%] = (W Ｏ / M Ｏ ) / {(W Ｇａ / M Ｇａ ) + (W Ｎ / M Ｎ ) + (W Ｏ / M Ｏ )} × 100 … (2) Here, M Ｏ The atomic weight of oxygen is 16.00 [g / mol], M Ｇａ The atomic weight of gallium is 69.72 [g / mol], and M Ｎ The atomic weight of nitrogen is 14.01 [g / mol].

[0046] The Ga / (Ga+N) ratio is a value that can be obtained from the following equation (3): Ga / (Ga+N) ratio = (W Ｇａ / M Ｇａ ) / {(W Ｇａ / M Ｇａ ) + (W Ｎ / M Ｎ )} ... (3)

[0047] (Area density of gallium nitride sintered layer) In the gallium nitride structure of this embodiment, the area density of the cross-section of the gallium nitride sintered layer may be 65 area % or more.

[0048] According to the gallium nitride structure of this embodiment, the strength of the gallium nitride sintered body layer tends to be higher because the area density of the gallium nitride sintered body layer is 65 area% or more. Furthermore, this reduces the difference in thermal expansion coefficient between the gallium nitride sintered body layer and the high-density gallium nitride layer, making it easier to suppress distortion of the sintered body shape due to the difference in thermal expansion coefficients, such as warping of the sintered body.

[0049] In particular, according to the gallium nitride structure of this embodiment, the area density of the gallium nitride sintered body layer near the surface on which the high-density gallium nitride layer is laminated is 65 area % or more, which makes it easier for the surface of the high-density gallium nitride layer laminated thereon to become smoother.

[0050] For example, in the gallium nitride structure of this embodiment, the area density of the gallium nitride sintered body layer may be 65.0 area% or more, 70.0 area% or more, 75.0 area% or more, or 80.0 area% or more, and may also be 90.0 area% or less, 88.0 area% or less, 86.0 area% or less, or 84.0 area% or less. Furthermore, the area density of the cross-section of the gallium nitride sintered body layer may be 65.0 area% or more and 90.0 area% or less, 70.0 area% or more and 88.0 area% or less, 75.0 area% or more and 86.0 area% or less, or 80.0 area% or more and 84.0 area% or less.

[0051] (Average surface roughness of the high-density gallium nitride layer as measured by laser microscope) In the gallium nitride structure of this embodiment, the average surface roughness of the high-density gallium nitride layer as measured by laser microscope may be 2.30 μm or less. The surface of the high-density gallium nitride layer of the gallium nitride structure of this embodiment may be polished.

[0052] According to the gallium nitride structure of this embodiment, the average surface roughness of the high-density gallium nitride layer as measured by a laser microscope is small, making it possible to suitably apply the gallium nitride structure of this embodiment to a substrate for epitaxial growth of gallium nitride.

[0053] For example, in the gallium nitride structure of this embodiment, the average surface roughness of the high-density gallium nitride layer as measured by laser microscopy may be 2.30 μm or less, 2.00 μm or less, 1.50 μm or less, 1.20 μm or less, 1.00 μm or less, or 0.50 μm or less, and may also be 0.10 μm or more, 0.15 μm or more, 0.20 μm or more, 0.25 μm or more, or 0.30 μm or more. Furthermore, the average surface roughness of the high-density gallium nitride layer as measured by laser microscopy may be 0.10 μm or more and 2.30 μm or less, 0.10 μm or more and 2.00 μm or less, 0.15 μm or more and 1.50 μm or less, 0.20 μm or more and 1.20 μm or less, 0.25 μm or more and 1.00 μm or less, or 0.30 μm or more and 0.50 μm or less.

[0054] Using a laser microscope (e.g., VK-X250 / 260, manufactured by Keyence Corporation), the surface roughness at five points is measured under the following conditions, and the average value of these measurements is taken as the average surface roughness measured by the laser microscope. Prior to measurement, the gallium nitride structure may or may not undergo pretreatment such as polishing. Measurement mode: Surface shape Objective lens magnification: 50x Measurement surface: Entire surface

[0055] The reference plane is the average plane of the entire surface, and this average plane is determined using the analysis tool attached to the laser microscope. The measurement points are the center of the circle corresponding to the area of ​​the outer circumference of the gallium nitride structure, and four points equidistant from that center, for a total of five points.

[0056] Specifically, as shown in Figure 3, the diameter of the area-equivalent circle on the outer circumference of the gallium nitride structure 300 is divided into four equal parts, and the length of the divided line segments is defined as the four-part length 300a. On this diameter, a point is set at a four-part length 300a from the center of the area-equivalent circle. Similarly, on the diameter of the area-equivalent circle perpendicular to this diameter, another measurement point is set at a four-part length 300a from the center of the area-equivalent circle. As shown in Figure 3, measurements are performed at five measurement points: the four measurement points determined in this way plus the center of the area-equivalent circle on the outer circumference of the gallium nitride structure.

[0057] (Average surface roughness by AFM) Furthermore, to measure the surface roughness of the high-density gallium nitride layer using AFM (atomic force microscopy), three fields of view were measured using a scanning probe microscope SPM-9600 (manufactured by Shimadzu Corporation) under the following measurement conditions, and the surface roughness in each field of view was measured. The average value of these measurements was defined as the average surface roughness Ra by AFM. Scanning speed: 1 Hz Scanning range: 10 μm × 10 μm Number of pixels: 512 × 512 Measurement temperature: 25 ± 5℃

[0058] The average surface roughness Ra of the high-density gallium nitride layer determined by AFM may be 150 nm or less, 100 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less, and may also be 0.10 nm or more, 1.00 nm or more, 2.00 nm or more, 3.00 nm or more, or 5.00 nm or more. Furthermore, the average surface roughness Ra of the high-density gallium nitride layer determined by AFM may be 1.00 nm or more and 150 nm or less, 2.00 nm or more and 100 nm or less, 3.00 nm or more and 50 nm or less, 3.00 nm or more and 40 nm or less, 5.00 nm or more and 30 nm or less, 5.00 nm or more and 20 nm or less, or 5.00 nm or more and 10 nm or less.

[0059] (Shape) The gallium nitride structure of this embodiment only needs to have a shape that can be used as an epitaxial growth substrate, and may be plate-shaped, particularly disc-shaped. Furthermore, if the gallium nitride structure of this embodiment is plate-shaped, a high-density gallium nitride layer may form one main surface, and a sintered gallium nitride layer may form the other main surface.

[0060] The gallium nitride structure of this embodiment, being plate-shaped, and especially disc-shaped, can be handled in the same way as silicon wafers and the like used in existing semiconductor manufacturing processes. Specifically, for example, the aspect ratio of the gallium nitride structure of this embodiment, i.e., the ratio of the diameter in the plane direction to the thickness, may be 25 or more, 50 or more, 100 or more, 200 or more, or 300 or more, and may also be 500 or less, 480 or less, 450 or less, or 400 or less. Furthermore, this aspect ratio may be 25 to 500, 50 to 480, 100 to 450, 200 to 400, or 300 to 400. In this embodiment, "diameter in the plane direction" means the diameter of a circle equivalent to the plane direction of the gallium nitride structure, i.e., the diameter of a circle having an area equal to the plane direction area of ​​the gallium nitride structure.

[0061] (Thickness) The average thickness of the gallium nitride structure in this embodiment may be 0.5 mm or more and 3.0 mm or less.

[0062] For example, the average thickness of the gallium nitride structure in this embodiment is preferably the thickness applicable as an epitaxial growth substrate, and may be 0.5 mm or more, 0.6 mm or more, 0.7 mm or more, 0.8 mm or more, or 0.9 mm or more, and may also be 3.0 mm or less, 2.8 mm or less, 2.5 mm or less, 2.0 mm or less, 1.5 mm or less, or 1.3 mm or less. Furthermore, the average thickness of the gallium nitride structure may be 0.5 mm or more and 2.8 mm or less, 0.6 mm or more and 2.5 mm or less, 0.7 mm or more and 2.0 mm or less, 0.8 mm or more and 1.5 mm or less, or 0.9 mm or more and 1.3 mm or less.

[0063] Here, the average thickness of the gallium nitride structure is measured using a micrometer. For example, the average thickness of the gallium nitride structure is calculated by taking measurements at four equally spaced points on the outer circumference of the gallium nitride structure, and at the centroid of the gallium nitride structure, determining the thickness at each point, and then taking the average of these five points.

[0064] The average thickness of the high-density gallium nitride layer of the gallium nitride structure in this embodiment (hereinafter also referred to as "average thickness of the high-density gallium nitride layer") may be 1.0 μm or more and 30.0 μm or less.

[0065] For example, the average thickness of this high-density gallium nitride layer may be 1.0 μm or more, greater than 1.0 μm, 3.0 μm or more, 5.0 μm or more, 8.0 μm or more, or 10.0 μm or more, and may also be 30.0 μm or less, 28.0 μm or less, 25.0 μm or less, or 20.0 μm or less. It is preferable that the average thickness of the high-density gallium nitride layer be 8.0 μm or more, or 10.0 μm or more, because this tends to result in a smaller average surface roughness and a higher degree of orientation. Furthermore, the average thickness of the high-density gallium nitride layer may be 1.0 μm or more and 30.0 μm or less, greater than 1.0 μm and 30.0 μm or less, 3.0 μm or more and 28.0 μm or less, 5.0 μm or more and 25.0 μm or less, 8.0 μm or more and 25.0 μm or less, or 10.0 μm or more and 20.0 μm or less.

[0066] The average thickness of the high-density gallium nitride layer is determined by measuring the thickness of the high-density gallium nitride layer at nine points using a laser microscope (product name: VK-X250 / 260, manufactured by Keyence Corporation) under the following conditions, and taking the average of these measurements. When measuring the thickness of the high-density gallium nitride layer at nine points, the laser microscope is observed in three fields, and the thickness of the high-density gallium nitride layer is measured at three points at 10 μm ± 1 μm intervals in one laser microscope observation image. Measurement mode: Surface shape Objective lens magnification: 50x

[0067] The average thickness of the gallium nitride sintered body layer of the gallium nitride structure in this embodiment (hereinafter also referred to as the "average thickness of the gallium nitride sintered body layer") may be 0.45 mm or more and 2.9 mm or less. The average thickness of the gallium nitride sintered body layer is determined from the difference between the average thickness of the gallium nitride structure and the average thickness of the high-density gallium nitride layer.

[0068] For example, the average thickness of this gallium nitride sintered body layer may be 0.45 mm or more, 0.5 mm or more, or 0.6 mm or more, and may also be 2.9 mm or less, 2.5 mm or less, 2.0 mm or less, 1.5 mm or less, or 1.2 mm or less. Furthermore, the average thickness of the gallium nitride sintered body layer may be 0.45 mm or more and 2.9 mm or less, 0.5 mm or more and 2.5 mm or less, or 0.6 mm or more and 2.0 mm or less.

[0069] The gallium nitride sintered layer may be thicker or thinner than the high-density gallium nitride layer, but in order for the gallium nitride sintered layer to function as a support layer for the high-density gallium nitride layer, it is preferable that the gallium nitride sintered layer be thicker than the high-density gallium nitride layer.

[0070] For example, the average thickness of the gallium nitride sintered body layer may be more than 1.0 times, 10.0 times or more, 30.0 times or more, 50.0 times or more, or 80.0 times or more than the average thickness of the high-density gallium nitride layer, and may also be 500.0 times or less, 400.0 times or less, 300.0 times or less, 200.0 times or less, or 100.0 times or less. Furthermore, the average thickness of the gallium nitride sintered body layer may be more than 1.0 times and 500.0 times or less, 10.0 times or more and 400.0 times or less, 30.0 times or more and 300.0 times or less, 50.0 times or more and 200.0 times or less, or 80.0 times or more and 100.0 times or less than the average thickness of the high-density gallium nitride layer.

[0071] (Bulk density) The bulk density of the gallium nitride structure in this embodiment is 4.5 g / cm³. ３ The above is sufficient. A high bulk density of the gallium nitride structure means that there are few voids contained within the gallium nitride structure. This bulk density is 4.5 g / cm³. ３ Above, 4.6g / cm ３ The above, or 4.7 g / cm³ ３ The above is sufficient, and also 6.0 g / cm³. ３ Below, 5.8g / cm ３ The following, or 5.6 g / cm³ ３ The following density may be used. Furthermore, this density is 4.5 g / cm³. ３ 6.0g / cm or more ３ Below, 4.6g / cm ３ 5.8g / cm or more ３ The following, or 4.7 g / cm³ ３ 5.6g / cm or more ３ The following is acceptable. The true density of gallium nitride is approximately 6.15 g / cm³. ３ That is the case.

[0072] The bulk density of the gallium nitride structure in this embodiment is measured by a method in accordance with JIS R 1634. Here, the pretreatment for bulk density measurement is performed using a vacuum method with distilled water.

[0073] (Lamination) The gallium nitride sintered layer and the high-density gallium nitride layer may each consist of a single layer or multiple layers. If the gallium nitride sintered layer or the high-density gallium nitride layer consists of multiple layers, the multiple layers constituting the gallium nitride sintered layer or the high-density gallium nitride layer as a whole can satisfy the above requirements for a gallium nitride sintered layer or a high-density gallium nitride layer.

[0074] (Applications) As described above, the gallium nitride structure of this embodiment is preferred for use as a substrate for epitaxial growth of gallium nitride. Therefore, the gallium nitride structure of this embodiment may be a substrate for epitaxial growth of gallium nitride films.

[0075] When the gallium nitride structure of this embodiment is a substrate for epitaxial growth of a gallium nitride film, the gallium nitride structure of this embodiment may have a seed crystal layer (orientation layer) on the surface of the high-density gallium nitride layer. The seed crystal layer may be a layer of Si<111>, SiC, sapphire, aluminum nitride, aluminum gallium nitride, or gallium nitride. With these seed crystal layers, there is little risk of impurity elements diffusing into the gallium nitride film. The thickness of the seed crystal layer may be 0.04 μm or more, or less than 0.10 μm. For details of the seed crystal layer, please refer to the description in Patent Document 1.

[0076] (Manufacturing Method) The gallium nitride structure of this embodiment can be manufactured by any method, for example, by the method of this embodiment shown below.

[0077] <Method for Manufacturing Gallium Nitride Structures> The method for manufacturing the gallium nitride structure of this embodiment includes forming a high-density gallium nitride layer on a gallium nitride sintered body layer. This makes it possible to form a high-density gallium nitride layer on the surface of the gallium nitride sintered body layer. The method of this embodiment preferably includes forming a high-density gallium nitride layer on a gallium nitride sintered body layer having an average surface roughness of 5.00 μm or less, and more preferably includes forming a high-density gallium nitride layer on a gallium nitride sintered body layer having an average surface roughness of 5.00 μm or less by sputtering.

[0078] In the method of this embodiment, the method for forming the high-density gallium nitride layer is not particularly limited, and can be one or more selected from the group consisting of sputtering, coating and nitriding of gallium solution, halide vapor deposition (HVPE method), metal-organic vapor deposition (MOCVD method), Na flux method, oxide vapor deposition (OVPE method), and amonothermal method, or one or more selected from the group consisting of sputtering, coating and nitriding of gallium solution, halide vapor deposition, and metal-organic vapor deposition, or even sputtering. Therefore, for example, the high-density gallium nitride layer can be a film formed by sputtering, a so-called sputtered film.

[0079] When forming a high-density gallium nitride layer by coating and nitriding with a gallium solution, a gallium solution such as a gallium nitrate solution can be applied to a gallium nitride sintered body layer, and then dried and fired in a nitriding atmosphere such as an ammonia atmosphere.

[0080] When depositing a high-density gallium nitride layer by halide vapor phase growth, gallium chloride (GaCl) is used. ３ ) and ammonia, which serves as a nitrogen source, can be reacted in the gas phase to epitaxially grow gallium nitride on a gallium nitride sintered body layer.

[0081] When depositing a high-density gallium nitride layer using metal-organic vapor deposition, trimethylgallium (CH4) is used as the raw material gas. ３ ) ３A high-density gallium nitride layer can be obtained by using Ga) and ammonia to decompose the raw materials on a heated gallium nitride sintered layer.

[0082] The following describes the preferred conditions for the sputtering method in this embodiment.

[0083] The sputtering method is one or more selected from the group consisting of DC sputtering, pulsed DC sputtering, RF sputtering, AC sputtering, DC magnetron sputtering, RF magnetron sputtering, ECR sputtering, pulsed laser deposition, and ion beam sputtering, preferably at least one of DC magnetron sputtering and RF magnetron sputtering, with RF magnetron sputtering being preferred.

[0084] The sputtering gas can be any gas used for sputtering, and may include inert gases, and more specifically, at least one of argon and nitrogen gases, with nitrogen gas being preferred. A nitrogen-containing gas is preferred for the sputtering gas because it makes it easier to obtain a smooth surface for the resulting sputtered film, and a mixture of argon and nitrogen is preferred. The mixture gas is preferably nitrogen-rich, and the nitrogen / (nitrogen + argon) partial pressure ratio [Pa / Pa] is preferably greater than 0.5, 0.7 or greater, or 0.9 or greater. If only nitrogen gas is used, the nitrogen / (nitrogen + argon) partial pressure ratio will be 1.0.

[0085] The flow rate of the sputtering gas can be 1 sccm or more or 5 sccm or more, and can also be 50 sccm or less or 30 sccm or less, with examples including 1 sccm to 50 sccm or 5 sccm to 30 sccm.

[0086] The sputtering gas pressure is 0.05 Pa or higher or 0.1 Pa or higher, and may also be 3 Pa or lower, 2 Pa or lower, or 1 Pa or lower, including 0.05 Pa to 3 Pa, 0.1 Pa to 2 Pa, or 0.1 Pa to 1 Pa.

[0087] To generate a stable plasma, the discharge power density in sputtering is 0.1 W / cm². ２Above or above, or 0.3 W / cm² ２ That's all, and also 5 W / cm ２ The following is acceptable: 0.1 W / cm² ２ More than 5W / cm ２ The following, or 0.3 W / cm² ２ More than 5W / cm ２ The following are listed:

[0088] The temperature of the gallium nitride sintered layer in sputtering deposition (hereinafter also referred to as the "deposition temperature") is arbitrary and may be 10°C or higher, 20°C or higher, or 800°C or lower, or 500°C or lower. When the deposition rate is increased, the deposition temperature may be 100°C or higher, 300°C or higher, or 800°C or lower, or 500°C or lower. Examples of deposition temperatures include 10°C to 800°C, or 20°C to 500°C.

[0089] The sputtering time (hereinafter also referred to as "deposition time") can be set appropriately depending on the sputtering conditions, the size of the gallium nitride structure, and the desired thickness of the sputtered film. For example, it can be 10 minutes or more, or 30 minutes or more, and it can also be 100 hours or less, 50 hours or less, or 30 hours or less. Examples of deposition times include 10 minutes to 100 hours, or 30 minutes to 50 hours.

[0090] In the method of this embodiment, the gallium nitride sintered body layer preferably has an area density of 65 area% or more, as described above with respect to the gallium nitride structure of this embodiment. Furthermore, it is preferable that this gallium nitride sintered body layer has a low average surface roughness.

[0091] The average surface roughness of the gallium nitride sintered layer may be 5.00 μm or less. By having an average surface roughness of 5.00 μm or less for the gallium nitride sintered layer, the flatness of the high-density gallium nitride layer laminated on top of it can be improved.

[0092] The surface of the gallium nitride sintered body layer may be processed. Therefore, the method of this embodiment may include a step of processing the surface of the gallium nitride sintered body layer. The processing can be any treatment that results in the average surface roughness of the sintered body layer being the value described above, and at least one of grinding and polishing can be exemplified. Specific grinding methods include one or more processing methods selected from the group consisting of surface grinding, rotary grinding, and cylindrical grinding. Specific polishing methods include polishing using an abrasive, and at least one of lapping and polishing.

[0093] The average surface roughness of the gallium nitride sintered body layer may be 5.00 μm or less, 4.00 μm or less, 3.00 μm or less, 2.50 μm or less, 2.00 μm or less, or 1.50 μm or less, and may also be 0.80 μm or more, 0.90 μm or more, or 1.00 μm or more. Furthermore, the average surface roughness of the gallium nitride sintered body layer may be 0.80 μm or more and 5.00 μm or less, 0.80 μm or more and 4.00 μm or less, 0.90 μm or more and 3.00 μm or less, 1.00 μm or more and 2.50 μm or less, 1.00 μm or more and 2.00 μm or less, or 1.00 μm or more and 1.50 μm or less.

[0094] Examples of average surface roughness of the gallium nitride sintered body layer after lapping include 3.00 μm or less, 2.50 μm or less, 2.00 μm or less, or 1.50 μm or less, and also 0.80 μm or more, 0.90 μm or more, or 1.00 μm or more. Furthermore, examples of average surface roughness of the gallium nitride sintered body layer after lapping include 0.80 μm or more and 3.00 μm or less, 0.90 μm or more and 2.50 μm or less, 0.90 μm or more and 2.00 μm or less, 0.90 μm or more and 1.50 μm or less, or 1.00 μm or more and 1.50 μm or less.

[0095] The gallium nitride sintered body layer used in the manufacturing method of this embodiment can be obtained by any method, for example, by the method described in Patent Document 2.

[0096] Furthermore, for example, a gallium nitride sintered body layer can be manufactured by a method including the following steps: molding a powder containing gallium nitride and metallic gallium, wherein the Ga / (Ga+N) ratio, which is the atomic ratio of gallium to the total amount of gallium and nitrogen, is greater than 0.50 and less than or equal to 0.65, to obtain a molded body, and sintering the molded body in a nitriding atmosphere.

[0097] According to the method of this embodiment, by forming a molded body from a powder containing gallium nitride and metallic gallium (hereinafter also referred to as "raw material powder"), metallic gallium is interposed between the gallium nitride powder particles, which is thought to increase the bonding strength between the powder particles, and the density of the molded body increases due to the inclusion of metallic gallium. Therefore, according to the method of this embodiment for producing a gallium nitride sintered body layer, a gallium nitride sintered body layer with a relatively high area density can be formed from a powder layer with a Ga / (Ga+N) ratio greater than 0.50 and less than or equal to 0.65.

[0098] The method of this embodiment includes a step of molding the raw material powder to obtain a molded body (hereinafter also referred to as the "molding step").

[0099] (Average particle size) The average particle size of the raw material powder in this embodiment is 0.1 μm or more or 0.2 μm or more, and can also be 150 μm or less, 50 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. Preferred average particle sizes include 0.1 μm or more and 150 μm or less, 0.2 μm or more and 50 μm or less, 0.2 μm or more and 20 μm or less, or 0.2 μm or more and 10 μm or less.

[0100] In this embodiment, the average particle diameter is determined from the area of ​​primary particles observed in an SEM observation map obtained using a general scanning electron microscope (e.g., VE-9800, manufactured by KEYENCE) under the following conditions: Acceleration voltage: 10 kV; Magnification: 50 to 5000x.

[0101] The obtained SEM observation image is binarized and analyzed using general image analysis software (e.g., Image-Pro 10, manufactured by Hakuto Co., Ltd.). 1200 ± 400 primary particles whose contours are observed without interruption in the SEM observation image are extracted, and the longest diameter of each primary particle is measured and defined as the particle diameter of each primary particle. The average particle diameter can then be calculated by taking the average of the particle diameters of each primary particle.

[0102] The raw material powder may be powder obtained by passing it through a sieve, or it may be powder in its original state without passing it through a sieve, but it is preferable that the powder be obtained by passing it through a sieve. In this case, variations in the particle size of the raw material powder are less likely to occur, and local strain within the molded body is more easily suppressed.

[0103] The sieve diameter is not particularly limited, but it is preferably 500 μm or less. A sufficiently small sieve diameter makes it particularly difficult for variations in the particle size of the raw material powder to occur, and it becomes easier to effectively suppress local strain within the molded body. Note that the sieve diameter is the opening of the sieve. That is, if the sieve mesh is square, the sieve diameter is the length of one side of the square; if the sieve mesh is rectangular, it is the length of the shorter side of the rectangle; and if the sieve mesh is circular, it is the diameter of the circle.

[0104] The sieve diameter may be 500 μm or less, 300 μm or less, 250 μm or less, or 200 μm or less, and may also be 20 μm or more, 50 μm or more, 80 μm or more, or 100 μm or more. Furthermore, the sieve diameter may be 20 μm or more and 500 μm or less, 50 μm or more and 300 μm or less, 80 μm or more and 250 μm or less, or 100 μm or more and 200 μm or less.

[0105] (Composition) In the method of this embodiment, the Ga / (Ga+N) ratio of the powder containing gallium nitride and metallic gallium may be greater than 0.50 and less than or equal to 0.65. Alternatively, this ratio may be 0.53 or more, 0.55 or more, or 0.59 or more, and may also be 0.64 or less, 0.63 or less, or 0.62 or less. Alternatively, this ratio may be 0.53 or more and less

[0106] In the method of this embodiment, the oxygen content of the raw material powder is preferably less than 0.4 atm%, less than 0.35 atm%, or less than 0.3 atm% in order to reduce the oxygen content of the resulting gallium nitride sintered body layer. It is preferable that the molded body does not contain oxygen (i.e., the oxygen content is 0 atm%), but it may contain oxygen to an extent that does not affect the properties of the resulting gallium nitride sintered body layer, and examples of oxygen content in the molded body include 0.005 atm% or more or 0.01 atm% or more.

[0107] In the method of this embodiment, the oxygen content of the raw material powder is the value calculated from the method and formula (2) described above.

[0108] (Filling) The raw material powder can be filled into the mold by any method. For example, the raw material powder can be filled into the mold and the top surface can be leveled. Alternatively, the mold may be vibrated after filling it with the raw material powder; for example, tapping can be used.

[0109] (Pressing) The raw material powder can be pressed by any method. Examples of pressing methods include uniaxial press molding and cold isostatic pressing (hereinafter also referred to as "CIP") molding, with uniaxial press molding being preferred. A molded body (compacted powder) can be obtained by these molding methods. It is preferable to perform the molding without heating the raw material powder, and it is preferable to perform uniaxial press molding at room temperature (25 ± 10°C).

[0110] The molding pressure is not particularly limited, but is preferably 300 MPa or higher. By applying sufficient molding pressure, the voids in the molded body can be sufficiently reduced, and the density of the gallium nitride structure can be sufficiently increased. From the viewpoint of further increasing the density of the gallium nitride structure, the molding pressure is preferably 400 MPa or higher, and particularly preferably 450 MPa or higher. Alternatively, the molding pressure may be 1000 MPa or less, 800 MPa or less, or 600 MPa or less.

[0111] A preferred forming method is uniaxial press forming, and preferred conditions for uniaxial press forming include a forming pressure of 350 MPa to 1000 MPa, and 400 MPa to 800 MPa.

[0112] (Measured density) The measured density of the molded body is 3.00 g / cm³. ３ or more, or 3.60 g / cm³ ３ That is all, and also 5.80 g / cm³ ３ The following or 5.50 g / cm³ ３ The following is a possible explanation, and the measured density of the molded body is 3.00 g / cm³. ３ 5.50g / cm or more ３ The following, or 3.60 g / cm³ ３ 5.80g / cm or more ３ The following can be given as examples.

[0113] The measured density of the molded body in this embodiment is a value measured by a method compliant with JIS Z 8807. Air compliant with JIS Z 8807 may be used as the reference substance for measuring the measured density.

[0114] (Shape) The shape of the molded body may be any desired shape, and may be one or more selected from the group consisting of disc-shaped, cylindrical, rectangular, polyhedral, and conical shapes, or any other shape depending on the purpose and application. Specific examples of molded body shapes include disc-shaped bodies with aspect ratios of 25 to 800, 50 to 700, 100 to 600, 200 to 500, or 300 to 400.

[0115] (Sintering) The method of this embodiment includes sintering the molded body obtained from the raw material powder in a nitriding atmosphere (hereinafter also referred to as the "sintering step").

[0116] The sintering process involves sintering the molded body to obtain a gallium nitride sintered layer. This process densifies the molded body. In the sintering process, the gallium nitride sintered layer may be obtained by sintering the molded body without placing it in a mold.

[0117] In this embodiment, the nitriding atmosphere is an atmosphere in which the nitriding reaction proceeds, and more particularly, an atmosphere in which the nitriding reaction proceeds but the oxidation reaction does not. Therefore, the nitriding atmosphere includes not only a nitrogen atmosphere but also atmospheres containing substances other than nitrogen. An example of a nitriding atmosphere is an atmosphere containing at least one of nitrogen and nitrogen compounds. The gas constituting the nitriding atmosphere is preferably one or more selected from the group consisting of a mixture of nitrogen and hydrogen, ammonia gas, hydrazine gas, and alkylamine gas, and more preferably at least one of ammonia gas and a mixture of nitrogen and hydrogen, and even more preferably ammonia gas. From the viewpoint of nitriding metallic gallium and improving the purity of the gallium nitride structure, the gas constituting the nitriding atmosphere is particularly preferably ammonia gas.

[0118] Particularly preferred nitriding atmospheres include flow atmospheres, nitrogen compound flow atmospheres, and ammonia flow atmospheres. A flow atmosphere, i.e., an atmosphere in which an atmospheric medium such as a nitrogen compound-containing gas flows, promotes the nitriding reaction of metallic gallium. This results in a more uniform composition of the resulting sintered body. A flow atmosphere is one in which the atmospheric medium is flowing, for example, with a flow rate of 0.1 mL / min or more or 1 L / min or more. On the other hand, the flow rate can be appropriately set according to the performance of the molded body to be processed and the sintering furnace, and examples include 20 L / min or less or 10 L / min or less.

[0119] In the sintering process, it is preferable to sinter the molded body (the material to be sintered) without applying pressure, and it is preferable to sinter the molded body without applying molding pressure.

[0120] The holding temperature in the sintering process can be any temperature at which the sintering of gallium nitride progresses, but the holding temperature is preferably 1100°C or lower, more preferably 1050°C or lower, and particularly preferably 1000°C or lower. The holding temperature is preferably 800°C or higher, more preferably 850°C or higher, and particularly preferably 900°C or higher.

[0121] In the sintering process, the molded body may be sintered without performing a warp suppression treatment to suppress warping, but it is preferable to perform such a treatment before sintering. Examples of warp suppression treatments include sintering while holding the molded body, specifically, by sandwiching the molded body between a pair of plate-like members. The plate-like members are preferably breathable members that allow for airflow. Examples of breathable members include mesh plates.

[0122] The holding time at the holding temperature is preferably 0.5 hours or more, more preferably 1 hour or more, and particularly preferably 2 hours or more. Examples of holding times include 20 hours or less, 10 hours or less, or 5 hours or less.

[0123] (Other) For further details of the method of this embodiment, please refer to the description in Patent Document 2.

[0124] The present disclosure will be described below with reference to examples and comparative examples. However, the present disclosure is not limited to these examples.

[0125] (Area Density) Prior to measurement, the gallium nitride structure was processed and polished as a pretreatment. Specifically, a diamond cutter was used to process the gallium nitride structure into a rectangular parallelepiped shape with a width of 5 ± 1 mm, a length of 5 ± 1 mm, and a thickness of 1 ± 0.1 mm. After polishing the cross-section of the gallium nitride structure with sandpaper (in the order of #600, #1000, and #1500), the measurement surface was obtained by polishing it at room temperature under the following conditions using a polishing device (device name: LaboForce-100, manufactured by Strürs). Rotation speed: 300 rpm Polishing agent: POLIPLA304M (manufactured by Fujimi Incorporated) Processing time: 10 minutes

[0126] The area density was determined by SEM observation of the region corresponding to the high-density gallium nitride layer and the region corresponding to the gallium nitride sintered body layer on the measurement surface obtained by pretreatment, obtaining SEM observation maps, and then analyzing the images of the obtained SEM observation maps. SEM observation was performed using an SEM (device name: VE-9800, manufactured by KEYENCE) under the following conditions: Acceleration voltage: 10kV Observation magnification: 500x Observation field of view: 3 fields of view

[0127] Next, using image analysis software (software name: Image-Pro 10, manufactured by Hakuto Co., Ltd.), the obtained SEM observation image is binarized, and the vacancies are detected by distinguishing between non-vacancies (i.e., the gallium nitride portion constituting the gallium nitride structure) and vacancies, and their area [μm²] is determined. ２ The area [μm²] of the SEM observation was calculated. For the binarization process, the SEM observation image was imported into image analysis software as a grayscale image representing the shades of black and white in 256 levels, and discriminant analysis was used. After detecting voids, the observation area [μm²] of the SEM observation image was calculated using the following formula. ２ Area of ​​the region excluding the voids [μm²] ２ The area density [area %] was calculated from the following: Area density [area %] = {(area excluding voids) / (observed area of ​​the SEM observation map)} × 100 The area density was calculated by determining the area density in three fields of view and taking the average of these values.

[0128] (Bulk Density) The bulk density of the sintered body was measured according to the method in accordance with JIS R 1634. Pretreatment was performed using a vacuum method with distilled water.

[0129] (Composition) The mass percentages of oxygen [mass%] and nitrogen [mass%] in the sintered body were measured using an oxygen / nitrogen analyzer (instrument name: LECO ON736, manufactured by Leco) by inert gas fusion-infrared absorption method. From the obtained mass percentages of oxygen and nitrogen, the mass percentage of gallium was determined from equation (1) above, the oxygen content [atm%] from equation (2) above, and the Ga / (Ga+N) ratio from equation (3) above.

[0130] (Average grain size) The average grain size was determined by scanning electron microscopy-electron backscatter diffraction of the cross-section of the sintered body. SEM-EBSD observation was performed using an EBSD (device surface: Symmetry, Oxford Instruments) to obtain SEM observation images in the same way as area density. The conditions for EBSD observation are as follows: Acceleration voltage: 15 kV Sample tilt: 70 degrees Tilt correction: 0° Magnification: 500x Step size: 0.2 μm

[0131] Positions where the crystal orientation is tilted by 5° or more were considered grain boundaries, and the regions enclosed by these grain boundaries were defined as crystal grains. The diameter of the circle corresponding to the area of ​​each crystal grain was calculated and defined as the crystal grain size. SEM-EBSD observation was performed on the crystal grains observed in three fields of view, and the average crystal grain size within each field of view was calculated by image analysis. The average of these averages was defined as the average crystal grain size.

[0132] The average grain size of the high-density gallium nitride layer was calculated using an AFM observation map of the surface of the high-density gallium nitride layer. The grain boundaries of the crystal particles were identified from the surface topography, and the regions enclosed by these grain boundaries were considered as crystal particles. The surface of the high-density gallium nitride layer was observed using a grain size scanning probe microscope SPM-9600 (Shimadzu Corporation) under the following conditions. For all crystal particles within the observation field, the diameter of the circle corresponding to the area of ​​each crystal particle was calculated by image analysis, and the average of these was used as the average grain size. The average grain size was calculated for three fields of view, and their average value was used as the average grain size determined by AFM. Scanning speed: 1 Hz; Scanning range: 10 μm × 10 μm; Number of pixels: 512 × 512; Measurement temperature: 25 ± 5°C

[0133] (Average thickness of gallium nitride structure) The average thickness of the gallium nitride structure was measured using a micrometer. The average thickness of the gallium nitride structure was calculated by taking measurements at four equally spaced points on the outer circumference of the gallium nitride structure, and at the centroid of the gallium nitride structure, determining the thickness at each measurement point, and then taking the average of these values.

[0134] (Orientation) The degree of orientation was determined by irradiating the surface of the high-density gallium nitride layer with X-rays and performing X-ray diffraction measurements, and obtaining the diffraction peaks corresponding to the 002 and 004 planes. For Comparative Example 1, which does not have a high-density gallium nitride layer, X-ray diffraction measurements were performed by irradiating the surface of the gallium nitride sintered body layer with X-rays. XRD measurements were performed using an X-ray diffractometer (device name: RINT Ultima III, manufactured by Rigaku Corporation) under the following conditions: Radiation source: CuKα rays (λ = 1.5405 Å) Measurement mode: Continuous scan Step width: 0.02° Scan speed: 2° / min Measurement range: 2θ = 20° to 80°

[0135] The Rottgering factor F(002,004) was determined from the diffraction peaks corresponding to the 002 and 004 planes, which have peak tops at 2θ = 34.56 ± 0.08° and 72.90 ± 0.08° of the obtained XRD pattern, using the following formula, and this was taken as the degree of orientation. F(002,004) = (ρ - ρ ０ ) / (1-ρ) ０ )

[0136] ρ is the ratio of the intensity of the diffraction peaks with peak tops at 2θ = 34.56 ± 0.08° and 72.90 ± 0.08° to the total intensity of the diffraction peaks in the XRD pattern of the gallium nitride sintered body. ０ This is the ratio of the intensity of diffraction peaks with peak tops at 2θ = 34.56 ± 0.08° and 72.90 ± 0.08° to the total intensity of diffraction peaks in the XRD pattern of gallium nitride shown in PDF card No. 01-073-7289.

[0137] (Average surface roughness measured by laser microscope) Using a laser microscope (product name: VK-X250 / 260, manufactured by Keyence Corporation), surface roughness was measured at five points under the following measurement conditions, and the average value of these measurements was taken as the average surface roughness measured by the laser microscope. Measurement mode: Surface shape Objective lens magnification: 50x Measurement surface: Entire surface

[0138] The reference plane was defined as the average plane of the entire surface, and this average plane was determined using the analysis tool attached to the laser microscope.

[0139] As shown in Figure 3, the measurement points were determined by dividing the diameter of the area-equivalent circle on the outer circumference of the gallium nitride structure 300 into four equal parts, and the length of each divided line segment was defined as the four-part length 300a. On this diameter, a point was set at a four-part length 300a from the center of the area-equivalent circle. Similarly, on the diameter of the area-equivalent circle perpendicular to this diameter, another measurement point was set at a four-part length 300a from the center of the area-equivalent circle. As shown in Figure 3, measurements were performed at five measurement points: the four measurement points determined in this way plus the center of the area-equivalent circle on the outer circumference of the gallium nitride structure.

[0140] (Average surface roughness by AFM) Furthermore, to measure the surface roughness of the high-density gallium nitride layer using AFM (atomic force microscopy), three fields of view were measured using a scanning probe microscope SPM-9600 (manufactured by Shimadzu Corporation) under the following measurement conditions, and the surface roughness in each field of view was measured. The average value of these measurements was defined as the average surface roughness Ra by AFM. Scanning speed: 1 Hz Scanning range: 10 μm × 10 μm Number of pixels: 512 × 512 Measurement temperature: 25 ± 5℃

[0141] (Average thickness of the high-density gallium nitride layer) The average thickness of the high-density gallium nitride layer was determined by measuring the thickness of the high-density gallium nitride layer at nine points using a laser microscope (product name: VK-X250 / 260, manufactured by Keyence Corporation) and taking the average of these measurements. Three fields of view were observed with the laser microscope, and the thickness of the high-density gallium nitride layer was measured at three points every 10 ± 1 μm in one laser microscope observation image. Measurement mode: Surface shape Objective lens magnification: 50x

[0142] <Example 1> (Gallium Nitride Sintered Body Layer) A gallium nitride sintered body was obtained using the method described in Patent Document 2. Specifically, a gallium nitride sintered body was obtained as described below.

[0143] Ten g of a mixed powder of metallic gallium and gallium nitride with a Ga / (Ga+N) ratio of 0.56 was prepared and filled into a cylindrical mold with a diameter of 50 mm. Then, a molded body was obtained by uniaxial press molding at a pressure of 300 MPa.

[0144] A molded body was placed on an alumina setter and sintered in an atmospheric furnace under the following heat treatment conditions to obtain a gallium nitride sintered body. In the obtained gallium nitride sintered body, the Ga / (Ga+N) ratio was 0.48 and the average crystal grain size was 3.85 μm. Heat treatment atmosphere: Ammonia flow atmosphere (ammonia gas flow rate 6000 mL / min) Holding temperature: 950°C Holding time: 2 hours

[0145] Using a polishing apparatus (apparatus name: LaboForce-100, manufactured by Strürs), the obtained gallium nitride sintered body was lap-polished at room temperature under the following conditions to obtain the gallium nitride sintered body layer of Example 1. The average surface roughness of the obtained gallium nitride sintered body layer was 1.04 μm. Rotation speed: 300 rpm Polishing agent: POLIPLA304M (manufactured by Fujimi Incorporated) Processing time: 10 minutes

[0146] (High-Density Gallium Nitride Layer) Using a sputtering apparatus (apparatus name: MPS-3000-MC1C1LTS1, manufactured by ULVAC, Inc.) equipped with a gallium nitride sputtering target (purity: 5N), a sputtered film was deposited on the surface of the gallium nitride sintered body layer obtained above by sputtering under the following conditions to obtain the gallium nitride structure of Example 1 having a gallium nitride sintered body layer and a high-density gallium nitride layer obtained by sputtering on the surface of the gallium nitride sintered body layer. Sputtering method: RF magnetron sputtering Deposition temperature: 25°C Sputtering gas: Nitrogen (partial pressure ratio of nitrogen / (nitrogen + argon) = 1 [Pa / Pa]) Sputtering gas flow rate: 12 sccm Sputtering gas pressure: 0.15 Pa Discharge power density: 1.8 W / cm ２ Deposition time: 2100 minutes

[0147] In the gallium nitride structure of this embodiment, the average thickness of the high-density gallium nitride layer was 11.7 μm.

[0148] Figure 2 shows a cross-sectional SEM view of the gallium nitride structure of this embodiment. As can be seen from Figure 2, it was confirmed that the gallium nitride structure of this embodiment has a layer of dense microstructure on its surface (dashed line in Figure 2).

[0149] <Examples 2 to 4> Gallium nitride structures were obtained in the same manner as in Example 1, except that sputtering was performed under the conditions shown in Table 2.

[0150] <Comparative Example 1> The gallium nitride sintered body obtained by the same method as in Example 1 was used as the gallium nitride structure in this comparative example.

[0151] Table 1 shows the evaluation results for the examples and comparative examples. Table 2 shows the sputtering conditions for the examples.

[0152]

[0153]

[0154] In Table 1, the "surface" of the "gallium nitride structure" refers to the surface of the high-density gallium nitride layer for the gallium nitride structure of Example 1, and to the surface of the gallium nitride sintered body layer for the gallium nitride structure of Comparative Example 1. In Table 1, the average grain size of the high-density gallium nitride layer was measured by AFM, and the average grain size of the gallium nitride sintered body layer was measured by SEM.

[0155] In the gallium nitride structure of Example 1, which had a high-density gallium nitride layer with an area density of 99.1 area%, the average surface roughness measured by laser microscopy was 0.36 μm, and the average surface roughness Ra measured by AFM was 9.81 nm, thus confirming that the surface was smooth. Because of the high surface smoothness, it was confirmed that such a gallium nitride structure can be applied as a substrate for epitaxial growth of gallium nitride. On the other hand, the gallium nitride structure of Comparative Example 1, which did not have a high-density gallium nitride layer, had a large average surface roughness (average surface roughness of 2.43 μm).

[0156] The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2024-227639, filed on December 24, 2024, are incorporated herein by reference as part of the disclosure of this specification.

[0157] 1 High-density gallium nitride layer 2 Sintered gallium nitride layer 10 Gallium nitride structure 300 Gallium nitride structure 300a Length of line segments obtained by dividing the diameter of the circle equivalent to the area of ​​the outer circumference of the gallium nitride structure into four parts

Claims

1. A gallium nitride structure having a gallium nitride sintered layer and a high-density gallium nitride layer on the surface of the gallium nitride sintered layer, wherein the area density of the high-density gallium nitride layer is 95.0 area % or more.

2. The structure according to claim 1, wherein the Ga / (Ga+N) ratio, which is the atomic ratio of gallium to the total amount of gallium and nitrogen, is 0.55 or less.

3. The structure according to claim 1, wherein the average surface roughness of the high-density gallium nitride layer as measured by a laser microscope is 2.30 μm or less.

4. The structure according to claim 1, which is plate-shaped.

5. The structure according to claim 4, wherein the gallium nitride sintered layer forms one main surface and the high-density gallium nitride layer forms the other main surface.

6. The structure according to claim 1, wherein the average thickness of the gallium nitride structure is 0.50 mm or more and 3.0 mm or less.

7. The structure according to claim 1, wherein the average thickness of the high-density gallium nitride layer is 1.0 μm or more and 30.0 μm or less.

8. The structure according to claim 1, wherein the average thickness of the gallium nitride sintered layer is 0.45 mm or more and 2.9 mm or less.

9. The structure according to claim 1, wherein the surface roughness Ra of the high-density gallium nitride layer determined by AFM is 150 nm or less.

10. The structure according to claim 1, which is a substrate for epitaxial growth of a gallium nitride film.

11. A method for manufacturing a gallium nitride structure according to any one of claims 1 to 10, comprising forming the high-density gallium nitride layer on the gallium nitride sintered layer.

12. The method according to claim 11, wherein the average surface roughness of the gallium nitride sintered layer is 5.00 μm or less.

13. The method according to claim 11, wherein the high-density gallium nitride layer is formed by sputtering.

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