Gallium nitride sintered body and method for producing the same

Abstract

The gallium nitride sintered body is a plate-shaped gallium nitride sintered body having a main surface, the ratio of the diameter of the main surface to the thickness of the gallium nitride sintered body is 20 or more, the thickness is 2 mm or less, and the SORI value of the gallium nitride sintered body is 0.3 mm or less.

Description

[Technical Field]

[0001] The present disclosure relates to a gallium nitride sintered body and a method for producing the same. [Background technology]

[0002] Gallium nitride has attracted attention as a material for realizing next-generation power devices. Gallium nitride films have traditionally been formed by epitaxial growth on silicon substrates via insulating buffer layers or the like. However, in this case, cracks may occur in the gallium nitride film due to differences in thermal expansion coefficients between the silicon substrate and the gallium nitride film. For this reason, QST (registered trademark) substrates have been used in recent years in place of silicon substrates (see, for example, Non-Patent Document 1 below). Because the QST substrate has a thermal expansion coefficient equivalent to that of a gallium nitride film, cracks are less likely to occur in the gallium nitride film even when it is formed on a QST substrate.

[0003] However, in the QST substrate, layers made of different materials such as a Si layer and a buffer layer are interposed between the gallium nitride film and the QST substrate, which may cause impurities to be mixed into the gallium nitride film. Therefore, from the viewpoint of suppressing impurities from being mixed into the gallium nitride film, it is preferable to use a gallium nitride substrate instead of a QST substrate.

[0004] It is known to use single-crystal gallium nitride as a gallium nitride substrate (see, for example, Patent Document 1). However, it is difficult to produce large single-crystal gallium nitride bulk bodies without defects when produced by the Na flux method or the HVPE method, making it difficult to increase the size of the substrate. Furthermore, both methods require time for gallium nitride crystal growth, making production time time-consuming. For this reason, when using a gallium nitride substrate, it is preferable to use a gallium nitride sintered body as the gallium nitride substrate from the viewpoints of increasing size and mass productivity. In particular, since gallium nitride is expensive, a thin plate-shaped sintered body is desired for use as a substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7044161 [Non-patent literature]

[0006] [Non-Patent Document 1] JH Leach et al., "Towards Manufacturing Large-Area GaN Substrates from QST® Seeds," [online], May 7-10, 2018, Proceedings of the 2018 Compd. Semicond. Manuf. Technol, [Retrieved March 12, 2024], Internet<https: / / csmantech.org / digests / ?digest=2018&thesession=4320> Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the gallium nitride substrate is composed of a thin plate-shaped gallium nitride sintered body, the sintered body is easily deformed during manufacturing, and for example, when the main surface of the gallium nitride sintered body is mirror-polished to form a gallium nitride film on the gallium nitride sintered body, cracks may occur in the gallium nitride sintered body. In other words, when the gallium nitride sintered body is simply formed into a thin plate shape using a conventional manufacturing method for a gallium nitride sintered body, cracks are likely to occur in the gallium nitride sintered body when the main surface of the gallium nitride sintered body is mirror-polished.

[0008] An object of the present disclosure is to provide at least one of a gallium nitride sintered body that can suppress the occurrence of cracks even after mirror polishing and a method for manufacturing the same. In particular, an object of the present disclosure is to provide at least one of a thin plate-shaped gallium nitride sintered body that can suppress the occurrence of cracks even after mirror polishing and a method for manufacturing the same. [Means for solving the problem]

[0009] The inventors of the present disclosure have investigated the causes of the above-mentioned problems. As a result, they have concluded that large waviness may occur in thin-plate gallium nitride sintered bodies, and that in such cases, mirror polishing the main surface of the gallium nitride sintered body may cause cracks. As a result of further intensive research, the inventors of the present disclosure have found that the above-mentioned problems can be solved by setting the SORI value, which is an indicator of waviness, in thin-plate gallium nitride sintered bodies to a specific value or less, and have arrived at the present disclosure.

[0010] That is, the contents of the present invention are as set forth in the claims, and the gist of the present disclosure is as follows.

[0011] (1) A plate-shaped gallium nitride sintered body having a main surface, wherein the aspect ratio, which is the ratio of the diameter of the main surface to the thickness of the gallium nitride sintered body, is 20 or more, the thickness is 2 mm or less, and the SORI value of the gallium nitride sintered body is 0.3 mm or less. (2) 4.2 g / cm 3 The gallium nitride sintered body according to (1), having an absolute density of at least 1000 kJ / cm. (3) The gallium nitride sintered body according to (1) or (2), wherein the surface roughness Ra of at least the main surface is 2 μm or less. (4) A gallium nitride sintered body according to any one of (1) to (3), in which the atomic ratio of gallium to the total of gallium and nitrogen is 0.55 or less. (5) The gallium nitride sintered body according to any one of (1) to (4), which is a substrate for epitaxial growth of a gallium nitride film. (6) A method for producing a gallium nitride sintered body according to any one of (1) to (5), comprising: a preparation step of preparing a raw material powder containing gallium nitride powder; a molding step of molding the raw material powder by uniaxial pressing to obtain a green body; a sintering step of sintering the compact; A method for producing a gallium nitride sintered body, comprising: (7) The method for producing a gallium nitride sintered body according to (6), wherein the pressure applied by the uniaxial press in the compacting step is 400 MPa or more. (8) The method for producing a gallium nitride sintered body according to (6) or (7), wherein after the molding step, the sintering step is carried out without subjecting the molded body to cold isostatic pressing. (9) The method for producing a gallium nitride sintered body according to any one of (6) to (8), wherein, in the sintering step, a warpage suppression treatment is performed on the green body to suppress warpage. (10) The method for producing a gallium nitride sintered body according to any one of (6) to (9), wherein the raw material powder further contains metallic gallium. [Effects of the Invention]

[0012] According to the present disclosure, there is provided at least one of a gallium nitride sintered body capable of suppressing the occurrence of cracks even after mirror polishing and a method for manufacturing the same. In particular, according to the present disclosure, there is provided at least one of a thin plate-shaped gallium nitride sintered body capable of suppressing the occurrence of cracks even after mirror polishing and a method for manufacturing the same. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing one embodiment of a gallium nitride sintered body according to the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing measurement points in measuring surface roughness Ra obtained by AFM. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present disclosure will be described in detail using an example. However, the present disclosure is not limited to the following embodiment. In addition, the present disclosure includes any combination of the configurations and parameters disclosed herein, and also includes any combination of upper and lower limits of the values disclosed herein.

[0015] <Gallium nitride sintered body> First, one embodiment of the gallium nitride sintered body of the present disclosure will be described with reference to FIG.

[0016] The gallium nitride (hereinafter also referred to as "GaN") sintered body 10 is a plate-like body having a main surface 11. In this embodiment, the "main surface" is the surface of the sintered body 10 that has the largest area. The aspect ratio (D / T) of the GaN sintered body 10, which is the ratio of the diameter D of the main surface 11 to the thickness T, is 20 or more, the thickness T is 2 mm or less, and the SORI value of the GaN sintered body 10 is 0.3 mm or less. This GaN sintered body 10 can suppress the occurrence of cracks even when mirror polished. The reason for this is thought to be as follows. First, the SORI value of the GaN sintered compact 10 is the sum of the heights of the highest and lowest points on the surface of the GaN sintered compact 10, with the least-squares plane of the GaN sintered compact 10 as the reference plane. Here, the smaller the SORI value, the smaller the waviness of the GaN sintered compact 10. When the main surface 11 of the GaN sintered compact 10 is mirror-polished with the flat polishing surface of a polishing pad, the polishing surface first contacts the highest point on the surface of the GaN sintered compact 10. Therefore, in the early stages of mirror polishing, stress from the polishing surface is concentrated near the highest point on the surface of the GaN sintered compact 10. However, as the mirror polishing progresses, the polishing surface reaches the lowest point on the surface of the GaN sintered compact 10 in a relatively short time. Therefore, the stress from the polishing surface is dispersed in a relatively short time. As a result, excessive stress is prevented from being applied to the GaN sintered compact 10 for a long period of time. This is thought to make the GaN sintered compact 10 less susceptible to cracks.

[0017] The GaN sintered body 10 of this embodiment will be described in detail below. This embodiment relates to a gallium nitride sintered body. A gallium nitride (GaN) sintered body is a sintered body whose main component (matrix, parent phase) is gallium nitride, and may be a polycrystalline gallium nitride or a sintered body mainly composed of gallium nitride. In this embodiment, having gallium nitride as the main component means that the total mass percentage of gallium and nitrogen in the sintered body is 95% (95 mass%) or more. The total mass percentage of gallium and nitrogen in the sintered body is preferably 98 mass% or more, or even 99 mass% or more, and may also be less than 100 mass%, 99.9 mass% or less, or 99.5 mass% or less. The mass percentages of gallium and nitrogen in the sintered body may be calculated using the formula (1) described below. The mass percentages of gallium and nitrogen in the sintered body may be 95 mass% or more but less than 100 mass%, 98 mass% or more but less than 99.9 mass%, or 99 mass% or more but less than 99.5 mass%. The gallium nitride sintered body of this embodiment may contain components other than gallium nitride, such as metallic gallium.

[0018] (Main surface) The diameter D of the main surface 11 of the GaN sintered body 10 refers to the equivalent circle diameter of the main surface 11. In other words, the diameter D of the main surface of the GaN sintered body 10 refers to the diameter of a circle having the same area as the area of the main surface 11 of the GaN sintered body 10. In this embodiment, the diameter D of the main surface of the GaN sintered compact 10 may be measured using a general three-dimensional shape measuring instrument (for example, a one-shot 3D shape measuring instrument VR-6000, manufactured by Keyence Corporation). The diameter D of the main surface of the GaN sintered compact 10 may be calculated as a circle-equivalent diameter, and specifically, the diameter D of the main surface is calculated by multiplying the area S (mm 2 ) and calculate based on the following formula: D = 2 × (S / π) 1 / 2 The shape of the main surface 11 is not particularly limited, and examples of the shape of the main surface 11 include a circle and a polygon such as a rectangle, and include at least one of a circle and a rectangle, with a circle being preferred.

[0019] The surface roughness Ra of the main surface 11 represents the arithmetic mean roughness. There are no particular limitations on the surface roughness Ra, but it is preferably 2 μm or less. If the surface roughness Ra is 2 μm or less, the irregularities on the main surface 11 will be small, making it easier to flatten the main surface 11 by mirror polishing. The surface roughness Ra is preferably 2 μm or less, more preferably 1.5 μm or less, even more preferably 1.3 μm or less, and particularly preferably 1.0 μm or less. The surface roughness Ra may be 0 μm or more, 0.20 μm or more, or 0.40 μm or more. The upper and lower limits of the surface roughness Ra may be any combination of the above. Examples of the surface roughness Ra include 0 μm to 2 μm, 0.20 μm to 1.5 μm, and 0.40 μm to 1.3 μm. The surface roughness Ra of the main surface opposite to main surface 11 is not particularly limited, and may be the same as or different from the surface roughness Ra of main surface 11, or may be the same. In this embodiment, the surface roughness Ra can be determined for the main surface of the unpolished (e.g., not mirror-polished) GaN sintered body 10 using a general tactile surface roughness meter (e.g., HANDYSURF, manufactured by Tokyo Seimitsu Co., Ltd.) under the following measurement conditions: Cutoff value: 0.80mm Evaluation length: 4.0 mm

[0020] In the GaN sintered body 10 of this embodiment, the surface roughness Ra (hereinafter also referred to as "Ra(AFM)") measured by AFM is 100 nm or less for the polished primary surface 11. If Ra(AFM) is 100 nm or less, crystal defects are less likely to occur in the GaN film when the GaN film is formed on the surface of the polished primary surface 11. Examples of Ra(AFM) include 100 nm or less, 50 nm or less, 40 nm or less, 20 nm or less, and 10 nm or less. A smaller Ra(AFM) is preferable, but the lower limit may be 0.01 nm or more, 0.05 nm or more, 0.1 nm or more, 0.5 nm or more, or 1 nm or more. Examples of Ra(AFM) include 0.01 nm or more and 100 nm or less, 0.05 nm or more and 50 nm or less, 0.1 nm or more and 40 nm or less, 0.5 nm or more and 20 nm or less, and 1 nm or more and 10 nm or less. The Ra(AFM) of the principal surface opposite to the principal surface 11 is not particularly limited, and may be the same as or different from the Ra(AFM) of the principal surface 11, or may be the same. In this embodiment, Ra(AFM) is the arithmetic mean value of the surface roughness at three points measured under the following measurement conditions using a general scanning probe microscope (for example, SPM-9600, manufactured by Shimadzu Corporation). Scanning speed: 1Hz Scanning range: 10μm x 10μm Number of pixels: 512 x 512 Measurement temperature: 25±5℃ Specifically, the measurement of the surface roughness at each point can be performed as follows. First, as shown in FIG. 2, the diameter of an area-equivalent circle 200 on the inside of the outer periphery of the main surface 11 of the GaN sintered compact 10 is divided into four equal parts, and the lengths of the divided line segments are defined as quarter lengths 200a. On this diameter, two points A1 and A2, which are located at the quarter lengths 200a from the center O of the area-equivalent circle 200, are defined as measurement points. Then, as shown in FIG. 2, the surface roughness can be measured at three measurement points: the two measurement points A1 and A2 determined in this way, and the center O of the area-equivalent circle 200 on the inside of the outer periphery of the main surface 11 of the GaN sintered compact 10. Prior to measurement, the surface of the GaN sintered compact 10 is polished as a pretreatment. Specifically, the surface of the GaN sintered compact 10 is polished with sandpaper, and then polished at room temperature using a general polishing machine (for example, LaboForce-100, manufactured by Struers) under the following conditions. In this way, a measurement surface can be obtained. Rotation speed: 300 rpm Abrasive: POLIPLA304M (Fujimi Incorporated) Processing time: 10 minutes

[0021] (shape) The GaN sintered body 10 has a plate-like shape, and examples of the plate-like shape include a disk-like shape and a flat plate-like shape, and at least one of a disk-like shape and a flat plate-like shape is included, and the plate-like shape may particularly be a disk-like shape.

[0022] (aspect ratio) The aspect ratio (D / T) is 20 or more. In this embodiment, the term "thin plate-like" refers to a plate-like shape with an aspect ratio of 20 or more. The aspect ratio may be 25 or more, 50 or more, 75 or more, 100 or more, 120 or more, 150 or more, or 300 or more. The aspect ratio may be 450 or less, 300 or less, 200 or less, 180 or less, or 150 or less. The upper and lower limits of the aspect ratio may be any combination of the above. Examples of the aspect ratio include 20 to 450, 20 to 300, 50 to 450, 75 to 450, 100 to 300, 120 to 200, and 150 to 180. (Thickness) The thickness T of the GaN sintered body 10 is 2 mm or less. The thickness T is preferably a thickness suitable for use as an epitaxial growth substrate, and may be 1.8 mm or less, 1.5 mm or less, or 1.3 mm or less, or 0.3 mm or more, 0.5 mm or more, 0.8 mm or more, or 1.0 mm or more. Examples of the thickness T include 0.3 mm to 2 mm, 0.5 mm to 1.8 mm, 0.8 mm to 1.5 mm, and 1.0 mm to 1.3 mm. In this embodiment, the thickness T of the GaN sintered body 10 may be measured using a general three-dimensional shape measuring machine (for example, one-shot 3D shape measuring machine VR-6000, manufactured by Keyence Corporation). (diameter of main surface) The diameter D of the main surface 11 of the GaN sintered body 10 may be 30 mm or more, 50 mm or more, 100 mm or more, or 120 mm or more, or may be 300 mm or less, 250 mm or less, 200 mm or less, or 180 mm or less. The diameter D of the main surface 11 can be, for example, 30 mm or more and 300 mm or less, 50 mm or more and 250 mm or less, 100 mm or more and 200 mm or less, or 120 mm or more and 180 mm or less.

[0023] (SORI value) The SORI value of the GaN sintered body 10 is 0.3 mm or less. Here, the SORI value is the sum of the height of the highest point and the height of the lowest point on the surface of the GaN sintered body 10, with the least-squares plane as the reference plane. When the SORI value is 0.3 mm or less, the occurrence of cracks can be suppressed even when the GaN sintered body 10 is mirror-polished. From the viewpoint of suppressing the occurrence of cracks due to mirror polishing, the SORI value is preferably 0.28 mm or less, more preferably 0.24 mm or less, particularly preferably 0.20 mm or less, and even more preferably 0.10 mm or less. The SORI value may be 0.00 mm or greater, greater than 0.00 mm, 0.03 mm or greater, 0.05 mm or greater, or 0.10 mm or greater. The upper and lower limits of the SORI value may be any combination of the above. Examples of the SORI value include 0.00 mm or more and 0.3 mm or less, more than 0.00 mm and 0.28 mm or less, 0.05 mm or more and 0.24 mm or less, 0.05 mm or more and 0.20 mm or less, 0.10 mm or more and 0.20 mm or less, 0.03 mm or more and 0.10 mm or less, and 0.05 mm or more and 0.10 mm or less.

[0024] In this embodiment, the SORI value of the GaN sintered body 10 can be measured using a general three-dimensional shape measuring machine (for example, one-shot 3D shape measuring machine VR-6000, manufactured by Keyence Corporation). Specifically, the SORI value can be measured as follows. First, the GaN sintered body is placed on the stage of the microscope of the three-dimensional shape measuring machine. Next, a least-squares plane is set as a reference plane using analysis software attached to the three-dimensional shape measuring instrument. More specifically, using the analysis software attached to the three-dimensional shape measuring instrument, a reference plane is set by the least-squares method from the height data on the front and back surfaces of the GaN sintered body so that the height is 0, and then the entire height data is corrected so that the set reference plane is horizontal, and a least-squares plane is set. Next, the sum of the height of the highest point on the main surface of the GaN sintered compact 10 from the set least squares plane and the height of the lowest point on the main surface of the GaN sintered compact 10 from the least squares plane can be calculated as the SORI value.

[0025] (absolute density) The absolute density of the GaN sintered body 10 is not particularly limited, and is 4.2 g / cm 3 Even above 4.2g / cm 3 It may be less than 4.2 g / cm 3 The absolute density of the GaN sintered body 10 is 4.2 g / cm 3 As a result, it is possible to reduce voids in the GaN sintered body 10. As a result, even if the main surface 11 of the GaN sintered body 10 is mirror-polished, recesses due to voids are unlikely to be formed on the surface of the polished main surface 11, and when a GaN film is formed on the surface of the polished main surface 11, crystal defects in the GaN film are unlikely to occur. The absolute density of the GaN sintered body 10 is more preferably 4.3 g / cm 3 More preferably, it is 4.5 g / cm 3 More preferably, it is 4.8 g / cm 3 More preferably, 4.9 g / cm 3 That's all. The absolute density of the GaN sintered body 10 is 5.8 g / cm 3 Below, 5.5g / cm 3 or less, or 5.2 g / cm 3 The absolute density of the GaN sintered body 10 may be 4.2 g / cm or less. 3 More than 5.8g / cm 3 Below 4.5g / cm 3 More than 5.5g / cm 3 or less, or 4.8 g / cm 3More than 5.2g / cm 3 The following points can be mentioned. In this embodiment, the absolute density ρ is calculated by measuring the mass m (g) of the GaN sintered body, and multiplying this mass m by the area S (mm 2 ) and thickness T (mm) using the following formula: Absolute density ρ=1000×m / (S×T)

[0026] (dopant) The GaN sintered body 10 may contain a dopant. When the GaN sintered body 10 contains a dopant, the conductivity of the GaN sintered body 10 can be further improved, and a stack formed by forming a GaN film on the primary surface 11 of the GaN sintered body 10 can be used as a device. The dopant may be an n-type or a p-type dopant. Examples of n-type dopants include silicon, germanium, tin, etc. Examples of n-type dopants include one or more selected from the group consisting of silicon, germanium, and tin, and further include at least one of silicon and germanium. Examples of p-type dopants include magnesium, zinc, cadmium, etc. Examples of p-type dopants include one or more selected from the group consisting of magnesium, zinc, and cadmium, and further include at least one of magnesium and zinc. The GaN sintered body 10 may contain a single dopant element or may contain two or more kinds of dopant elements.

[0027] (composition) The atomic ratio of gallium to the sum of gallium and nitrogen in the gallium nitride sintered body of this embodiment (hereinafter also referred to as the "Ga / (Ga+N) ratio") may be 0.55 or less, 0.53 or less, 0.50 or less, less than 0.50, or 0.49 or less, or may 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. The Ga / (Ga+N) ratio of the gallium nitride sintered body of this embodiment is preferably 0.50 or less. With such a Ga / (Ga+N) ratio, the gallium nitride sintered body of this embodiment is composed substantially of gallium nitride only.

[0028] When the gallium nitride sintered body of this embodiment is applied to a film-forming substrate for forming a film by epitaxial growth of gallium nitride, the gallium nitride sintered body of this embodiment preferably has a low content of elements other than nitrogen and gallium in order to prevent impurities from being mixed into the gallium nitride to be epitaxially grown. Impurities contained in the gallium nitride sintered body of this embodiment include, for example, oxygen.

[0029] The gallium nitride sintered body of this embodiment may contain metal impurities as long as the effects are not impaired. Examples of metal impurities include at least one of aluminum (Al) and indium (In). The metal impurities may be contained as metals or as metal compounds. It is preferable that the metal impurities are substantially absent. Therefore, the content of metal impurities may be 50 mass ppm or less, 10 mass ppm or less, or 5 mass ppm or less, as a mass ratio [ppm by mass] of the metal impurities determined by glow discharge mass spectrometry relative to the total mass of the elements determined by glow discharge mass spectrometry. The lower limit of the content of metal impurities may be 0 mass ppm or more, more than 0 mass ppm, or 1 mass ppm or more. The content of metal impurities may be 0 mass ppm or more to 50 mass ppm or less, or more than 0 mass ppm to 10 mass ppm or less.

[0030] The gallium nitride sintered body of this embodiment may have an oxygen content of 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, or may have an oxygen content of 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. 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.

[0031] The composition of the gallium nitride sintered body of this embodiment can be expressed by the following formula (1): 100[mass%] = W Ga [Mass%]+W O [Mass%]+W N [mass%] +W Dope [Mass%] …(1) where W Ga , W O , W N and W Dope are the mass proportions of gallium, oxygen, nitrogen, and the dopant element in the gallium nitride sintered body, respectively. W O and W N is a value measured by a pyrolysis method (inert gas fusion-infrared absorption method) in which a gallium nitride sintered body is thermally decomposed using a general oxygen and nitrogen analyzer (e.g., LECO ON736, manufactured by Leco). Dope is the value measured by glow discharge mass spectrometry. Ga is W O , W N and W DopeThis is the value calculated from the measured values using formula (1). When the gallium nitride sintered body of this embodiment contains metal impurities, the content is the mass ratio [mass ppm] of the metal element determined by glow discharge mass spectrometry to the total mass of the elements determined by glow discharge mass spectrometry. Due to differences in measurement methods, when the gallium nitride sintered body of this embodiment contains metal impurities, the composition may appear to exceed 100 mass%. The oxygen content [atm%] is measured by a method in accordance with JIS H 1695 and is a value calculated from the following formula (2): Oxygen content [atm%] =[(W O / M O ) / {(W Ga / M Ga )+(W N / M N )+(W O / M O ) +(W Dope / M Dope )}]×100 …(2) where: M O is the atomic weight of oxygen: 16.00 [g / mol], M Ga is the atomic weight of gallium: 69.72 [g / mol], and M N is the atomic weight of nitrogen: 14.01 [g / mol]. Also, M Dope is the atomic weight of the dopant element. The Ga / (Ga+N) ratio is calculated from the following formula (3): Ga / (Ga+N) ratio = (W Ga / M Ga ) / {(W Ga / M Ga )+(W N / M N )} …(3)

[0032] (Application) As applications of the GaN sintered body 10, there may be mentioned a sputtering target, a substrate for film formation for forming a GaN film by CVD, epitaxial growth, etc., that is, a substrate for epitaxial growth of a gallium nitride film.

[0033] <Manufacturing method of GaN sintered body> The GaN sintered body of the present disclosure can be manufactured by any method, but the manufacturing method of the GaN sintered body of the present disclosure includes a preparation step of preparing a raw material powder containing GaN powder, a molding step of molding the raw material powder by uniaxial pressing to obtain a plate-shaped molded body, and a sintering step of sintering the molded body to obtain the above-described GaN sintered body 10. According to this manufacturing method, after preparing a raw material powder containing GaN powder, molding the raw material powder by uniaxial pressing to obtain a plate-shaped molded body, and then sintering the molded body, it is possible to obtain a GaN sintered body 10 in which the occurrence of cracks can be suppressed even when mirror polishing is performed. As a preferable manufacturing method of the GaN sintered body of the present disclosure, there may be mentioned a manufacturing method including a preparation step of preparing a raw material powder containing GaN powder, a molding step of molding the raw material powder by uniaxial pressing at a pressure of 400 MPa or more (hereinafter, also referred to as "uniaxial pressing pressure") by uniaxial pressing to obtain a plate-shaped molded body, and a sintering step of sintering the molded body. Further, there may be mentioned a manufacturing method including a preparation step of preparing a raw material powder containing GaN powder, a molding step of molding the raw material powder by uniaxial pressing at a uniaxial pressing pressure of 400 MPa or more to obtain a plate-shaped molded body, and a sintering step of sintering the molded body, and in the sintering step, performing a warpage suppression treatment for suppressing the warpage of the molded body.

[0034] (1) Preparation step In the preparation step, a raw material powder containing GaN powder is prepared. The raw material powder may be composed of only GaN powder, but in addition to GaN powder, it may further contain a powder of metallic gallium. In this case, the melting point of metallic gallium is about 30°C, and in the sintering step, since metallic gallium is liquefied by heating, it becomes easier to suppress the warpage of the molded body. Further, in the sintering step, by performing a warpage suppression treatment on the molded body, the warpage of the obtained GaN sintered body 10 can be more effectively suppressed. The raw material powder may further contain a powder containing a dopant element, if necessary. The raw material powder may be a raw material powder obtained by passing through a sieve, or may be a raw material powder obtained as is without passing through a sieve, but is preferably a raw material powder obtained by passing through a sieve, which makes it less likely that the particle size of the raw material powder will vary, and makes it easier to suppress local strain in the compact. The sieve diameter of the sieve is not particularly limited, but is preferably 150 μm or less, and even less than 150 μm. A sieve diameter of 150 μm or less, and even less than 150 μm, reduces the variation in particle size of the raw material powder, making it easier to effectively suppress local strain within the compact. As a result, warping of the GaN sintered body 10 is more easily suppressed. The sieve diameter is the mesh opening of the sieve. That is, the sieve diameter is the length of one side of the square if the sieve has square openings, the length of the short side of the rectangle if the sieve has rectangular openings, and the diameter of the circle if the sieve has circular openings. The sieve size is more preferably 130 μm or less, even more preferably 100 μm or less, and particularly preferably 75 μm or less. The sieve diameter is preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 30 μm or more. The sieve diameter may be 10 μm or more and 150 μm or less, 20 μm or more and 100 μm or less, or 30 μm or more and 75 μm or less.

[0035] (2) Molding process In this embodiment, the molding step may involve obtaining a molded body by molding in which pressure is applied only from a direction perpendicular to the main surface, or may involve obtaining a molded body by molding in which pressure is applied only from a direction perpendicular to the main surface. Examples of molding in which pressure is applied only from a direction perpendicular to the main surface include at least one of uniaxial pressing and hot pressing, and further include uniaxial pressing. In the compacting step, the raw material powder is compacted by uniaxial pressing to obtain a plate-shaped compact. The uniaxial pressing pressure is not particularly limited, but is preferably 350 MPa or higher. In this case, by setting the uniaxial pressing pressure to 350 MPa or higher, it is possible to sufficiently reduce the voids in the compact, and to sufficiently increase the density of the GaN sintered compact 10. In addition, since the density variation in the compact is easily suppressed, the SORI value of the resulting GaN sintered compact is likely to be small. From the viewpoint of further increasing the density of the GaN sintered body 10, the uniaxial pressing pressure is preferably 400 MPa or more, and particularly preferably 450 MPa or more. The uniaxial pressing pressure may be 1000 MPa or less, 800 MPa or less, 600 MPa or less, or 500 MPa or less. The SORI value of the compact obtained by the compacting step is preferably 0.3 mm or less. This makes it easier for the SORI value of the GaN sintered body obtained by the sintering step to be small. The SORI value of the compact may be 0.28 mm or less, 0.24 mm or less, or 0.22 mm or less, or may be 0.00 mm or more, more than 0.00 mm, 0.05 mm or more, or 0.10 mm or more. The SORI value of the compact may be 0.00 mm or more and 0.3 mm or less, more than 0.00 mm and 0.28 mm or less, 0.05 mm or more and 0.24 mm or less, or 0.10 mm or more and 0.22 mm or less.

[0036] (3) Sintering process The sintering step is a step of sintering the green body to obtain a GaN sintered body. In the sintering step, the green body may be sintered without being placed in a mold to obtain a GaN sintered body.

[0037] The sintering step may be carried out without cold isostatic pressing (CIP) on the compact after the compacting step, or may be carried out after cold isostatic pressing (CIP). The sintering step is preferably performed after the molding step without subjecting the molded body to cold isostatic pressing (CIP). In this case, it is easier to prevent the molded body from waviness due to CIP. In particular, when molding into a thin plate, it is thought that the difference between the shrinkage rate in the direction parallel to the main surface and the shrinkage rate in the direction perpendicular to the main surface can be made smaller when isostatic pressing, specifically, when cold isostatic pressing (CIP), is not performed compared to when isostatic pressing is performed, and therefore the SORI value of the resulting sintered body is more likely to be smaller.

[0038] (atmosphere) The above atmosphere is preferably a nitriding atmosphere from the viewpoint of reducing the amount of impurities such as oxygen in the GaN sintered body 10. A nitriding atmosphere is an atmosphere in which a nitriding reaction proceeds, particularly an atmosphere in which a nitriding reaction proceeds but an oxidation reaction does not proceed. Therefore, the nitriding atmosphere includes not only a nitrogen atmosphere but also an atmosphere containing elements other than nitrogen. An example of a nitriding atmosphere is an atmosphere containing at least one of nitrogen and a nitrogen compound. The gas constituting the nitriding atmosphere is preferably at least one selected from the group consisting of a mixed gas of nitrogen and hydrogen, ammonia gas, hydrazine gas, and alkylamine gas, further preferably ammonia gas, and / or a mixed gas of nitrogen and hydrogen, or further preferably ammonia gas. The gas constituting the nitriding atmosphere is particularly preferably ammonia gas from the viewpoint of nitriding metal Ga and improving the purity of GaN.

[0039] (temperature) The temperature in the sintering step (sintering temperature) may be any temperature that allows the compact to be sintered, but the sintering temperature is preferably 1100°C or lower, more preferably 1050°C or lower, and particularly preferably 1000°C or lower. The sintering temperature is preferably 800° C. or higher, more preferably 900° C. or higher, and particularly preferably 950° C. or higher. Examples of the sintering temperature include 800° C. or higher and 1100° C. or lower, 900° C. or higher and 1050° C. or lower, and 950° C. or higher and 1000° C. or lower.

[0040] (warp suppression treatment) In the sintering step, the compact may or may not be subjected to a warpage suppression treatment for suppressing warpage, but it is preferable to perform such a treatment. In this case, warping of the compact is suppressed, so that a GaN sintered body 10 that can generate cracks even when the main surface 11 is mirror-polished can be obtained. The warpage suppression treatment may be, for example, a treatment in which the molded body is sandwiched between a pair of plate-like members, and a treatment in which the molded body is sandwiched between a pair of plate-like members is preferred. The plate-like member is preferably an air-permeable member having air permeability, such as a mesh plate.

[0041] (sintering time) The sintering time is preferably 0.5 hours or more, more preferably 1 hour or more, and particularly preferably 2 hours or more. The sintering time may be 20 hours or less, 10 hours or less, or 5 hours or less. The sintering time may be 0.5 hours or more and 20 hours or less, 1 hour or more and 10 hours or less, or 2 hours or more and 5 hours or less.

[0042] <Mirror polished body> Next, one embodiment of the mirror-polished body of the present disclosure will be described. The mirror-polished body of the present disclosure is obtained by mirror-polishing the main surface 11 of the GaN sintered body 10. The GaN sintered body 10 can suppress the occurrence of cracks even when mirror-polished. Therefore, when a GaN film is formed on the mirror surface of the mirror-polished body of the present disclosure, crystal defects in the GaN film can be reduced. [Example]

[0043] The present disclosure will be described in more detail below using examples, but the present disclosure is not limited to the following examples.

[0044] (Examples 1 to 5) First, metallic gallium (Ga) powder and GaN powder were mixed in a ratio (mass ratio) of 1:9, and the resulting mixed powder was passed through a sieve (JIS) having openings with the sieve diameters shown in Table 1 to obtain raw material powders. The masses of the raw material powders were 106 g for Example 1, 95 g for Example 2, 86 g for Example 3, 90 g for Example 4, and 57 g for Example 5, respectively. Next, the raw material powder was filled into a cylindrical mold with an inner diameter of 150 mm, and the raw material powder was pressed using a uniaxial press cylinder at the uniaxial press pressure shown in Table 1 to obtain a plate-shaped compact having a thickness of 1.20 mm and a diameter of 150 mm for Example 1, a plate-shaped compact having a thickness of 0.95 mm and a diameter of 150 mm for Example 2, a plate-shaped compact having a thickness of 0.90 mm and a diameter of 150 mm for Example 3, a plate-shaped compact having a thickness of 0.90 mm and a diameter of 150 mm for Example 4, and a plate-shaped compact having a thickness of 0.55 mm and a diameter of 150 mm for Example 5. The SORI values of the compacts were measured using a three-dimensional shape measuring machine in the same manner as for the SORI value of the GaN sintered body described below, and the SORI values of the compacts were as shown in Table 1. Next, the above-mentioned compacts were placed in a sintering furnace and sintered under the sintering conditions shown in Table 1. Note that for Examples 2 and 4, warpage suppression treatment was performed on the compacts, which was performed by sandwiching the compacts between a pair of alumina (Al2O3) mesh plates. In this way, a GaN sintered body having the structure shown in Table 2 was obtained. Example 6 The GaN sintered body of this example was obtained in the same manner as in Example 2, except that a cylindrical mold with an inner diameter of 50 mm was used and the mass of the raw material powder was 19 g. The obtained compact was a plate-like compact with a thickness of 1.90 mm and a diameter of 50 mm. Example 7 The GaN sintered body of this example was obtained in the same manner as in Example 2, except that the uniaxial pressing pressure was 400 MPa and the mass of the raw material powder was 90 g. The obtained compact was a plate-like compact with a thickness of 1.00 mm and a diameter of 150 mm. Example 8 A GaN sintered body of this example was obtained in the same manner as in Example 2, except that the uniaxial press pressure was 200 MPa and the mass of the raw material powder was 90 g. The obtained molded body was a plate-shaped molded body with a thickness of 1.00 mm and a diameter of 150 mm.

[0045] (Comparative Example 1) Raw material powder was obtained in the same manner as in Example 1. The mass of the raw material powder was 90 g. Next, the raw material powder was filled into a cylindrical mold with an inner diameter of 150 mm, and the raw material powder was pressed with a uniaxial press cylinder at the uniaxial press pressure shown in Table 1 to perform molding, and a plate-shaped primary molded body with a thickness of 1.31 mm and a diameter of 150 mm was obtained. Subsequently, the primary molded body was pressed with a CIP at the CIP pressure shown in Table 1 to perform molding, and a plate-shaped secondary molded body with a thickness of 1.06 mm and a diameter of 150 mm was obtained. When the SORI value of the above secondary molded body was measured with a three-dimensional shape measuring machine, the SORI value was as shown in Table 1. Next, the above secondary molded body was put into a sintering furnace and sintered under the sintering conditions shown in Table 1. For Comparative Example 1, the warpage suppression treatment was also performed on the secondary molded body in the same manner as in Example 2. Thus, a GaN sintered body having the configuration shown in Table 2 was obtained.

[0046] <Configuration of GaN Sintered Body> (Thickness T and diameter D of the main surface) The thickness T (mm) and the diameter D (mm) of the main surface of the GaN sintered body were measured using a three-dimensional shape measuring machine (product name: One Shot 3D Shape Measuring Machine VR-6000, manufactured by Keyence Corporation). The diameter D of the main surface was obtained as the equivalent diameter of a circle. Specifically, the diameter D of the main surface was obtained by obtaining the area S (mm 2 ) of the main surface and calculating it based on the following formula. D = 2 × (S / π) 1 / 2

[0047] (Aspect ratio) The aspect ratio (D / T) was calculated using the values of the above thickness T and the diameter D of the main surface.

[0048] (Absolute density) The absolute density ρ was calculated by measuring the mass m (g) of the GaN sintered body and dividing the mass m by the area S (mm 2 ) and thickness T (mm) using the following formula. ρ=1000×m / (S×T)

[0049] (surface roughness Ra) The surface roughness Ra was measured on the main surface of the GaN sintered body that was not mirror-polished using a tactile surface roughness meter (device name: HANDYSURF, manufactured by Tokyo Seimitsu Co., Ltd.) under the following measurement conditions. Cutoff value: 0.80mm Evaluation length: 4.0 mm

[0050] (Ra(AFM)) Ra (AFM) was the arithmetic mean value of the surface roughness measured at three points under the following measurement conditions using a scanning probe microscope (product name: SPM-9600, manufactured by Shimadzu Corporation). Scanning speed: 1Hz Scanning range: 10μm x 10μm Number of pixels: 512 x 512 Measurement temperature: 25±5℃ Specifically, the surface roughness at each point was measured as follows. First, as shown in Figure 2, the diameter of a circle 200 corresponding to the area inside the outer periphery of the main surface of the GaN sintered compact was divided into four equal parts, and the length of the divided line segment was defined as the quarter length 200a. On this diameter, two points A1 and A2, which are located at the quarter length 200a from the center O of the area-equivalent circle 200, were defined as measurement points. Then, as shown in Figure 2, the surface roughness was measured at three measurement points: the two measurement points A1 and A2 determined in this way, and the center O of the area-equivalent circle 200 on the outer periphery of the main surface of the GaN sintered compact. Prior to the measurement, the surface of the GaN sintered body was polished as a pretreatment. Specifically, the surface of the gallium nitride sintered body was polished with sandpaper, and then polished at room temperature using a polishing machine (machine name: LaboForce-100, manufactured by Struers) under the following conditions. In this way, the measurement surface was obtained. Rotation speed: 300 rpm Abrasive: POLIPLA304M (Fujimi Incorporated) Processing time: 10 minutes

[0051] (SORI value) The SORI value was measured using a three-dimensional shape measuring instrument (product name: One-shot 3D shape measuring instrument VR-6000, manufactured by Keyence Corporation). Specifically, first, the GaN sintered body was placed on the stage of the microscope of the three-dimensional shape measuring machine. Next, a least-squares plane was set as a reference plane using analysis software attached to the three-dimensional shape measuring instrument. More specifically, using the analysis software attached to the three-dimensional shape measuring instrument, a reference plane was set by the least-squares method from the height data on the front and back surfaces of the GaN sintered body so that the height was 0, and then the entire height data was corrected so that the set reference plane was horizontal, and a least-squares plane was set. Next, the sum of the height of the highest point on the main surface of the GaN sintered compact from the set least squares plane and the height of the lowest point on the main surface of the GaN sintered compact from the least squares plane was calculated as the SORI value.

[0052] (composition) The oxygen (mass%) and nitrogen (mass%) content of the GaN sintered body were measured by inert gas fusion-infrared absorption using an oxygen and nitrogen analyzer (LECO ON736, manufactured by Leco). The mass percentages of the dopant elements were measured by glow discharge mass spectrometry. The mass percentages of the oxygen, nitrogen, and dopant elements obtained were used to calculate the gallium mass percentage from the above formula (1), the oxygen content (atm%) from the above formula (2), and the Ga / (Ga+N) ratio from the above formula (3).

[0053] <Evaluation> While holding the GaN sintered compact with a holder, the main surface was placed face down on the flat polishing surface of a polishing pad and subjected to mirror polishing. The mirror polishing was performed by CMP polishing. The GaN sintered compact was then visually inspected for the presence or absence of cracks. The results are shown in Table 2.

[0054] [Table 1] [Table 2]

[0055] From the results shown in Table 2, in Examples 1 to 8 in which the SORI value of the gallium nitride sintered body was 0.3 mm or less, no cracks occurred even after mirror polishing, whereas in Comparative Example 1 in which the SORI value of the gallium nitride sintered body was greater than 0.3 mm, cracks occurred when mirror polishing was performed. Comparison of Examples 2, 7 and 8 confirmed that the greater the uniaxial pressing pressure, the greater the absolute density ρ of the gallium nitride sintered body and the smaller the SORI value. From the above, it was confirmed that the GaN sintered body of the present disclosure can suppress the occurrence of cracks even when mirror polishing is performed. From the results shown in Table 2, it was confirmed that the surface roughness Ra of all the GaN sintered bodies of the examples was 1.14 μm or less, which was smaller than the surface roughness Ra of the comparative example. Furthermore, it was confirmed that the GaN sintered bodies of the examples had Ra (AFM) of 6.71 nm or less, which confirmed that the surfaces of the GaN sintered bodies after polishing were smooth. The entire contents of the specification, claims, abstract and drawings of Japanese Patent Application No. 2024-058836 filed on April 1, 2024, and Japanese Patent Application No. 2025-003684 filed on January 9, 2025 are hereby incorporated by reference as the disclosure of the specification of the present disclosure. [Explanation of symbols]

[0056] 10...GaN sintered body, 11...main surface, T...thickness of the GaN sintered body, D...diameter of the main surface, 200...circle equivalent to the area inside the outer periphery of the main surface of the gallium nitride sintered body, 200a...length of the line segment obtained by dividing the diameter of the circle equivalent to the area of the outer periphery of the gallium nitride sintered body into four.

Claims

1. A method for producing a gallium nitride sintered body, comprising: a preparation step of preparing a raw material powder containing gallium nitride powder; a molding step of molding the raw material powder by uniaxial pressing to obtain a plate-shaped compact; a sintering step of sintering the green body to obtain the gallium nitride sintered body; Including, In the molding step, the pressure applied by the uniaxial press is 400 MPa or more, The gallium nitride sintered body, A plate-shaped gallium nitride sintered body having a main surface, an aspect ratio, which is the ratio of the diameter of the main surface to the thickness of the gallium nitride sintered body, of 20 or more; The thickness is 2 mm or less, The method for producing a gallium nitride sintered body, wherein the SORI value of the gallium nitride sintered body is 0.3 mm or less.

2. The method for producing a gallium nitride sintered body according to claim 1 , wherein after the molding step, the sintering step is carried out without performing cold isostatic pressing on the compact.

3. The method for producing a gallium nitride sintered body according to claim 1 or 2, wherein a warpage suppression treatment is performed on the compact in the sintering step to suppress warpage of the compact.

4. The method for producing a gallium nitride sintered body according to claim 1 or 2, wherein the raw material powder further contains metallic gallium.