Gallium nitride sintered body and production method therefor

Abstract

This gallium nitride sintered body has a plate-like shape and has a main surface. The ratio of the diameter of the main surface with respect to the thickness of the gallium nitride sintered body is 20 or more. The thickness of the gallium nitride sintered body is 2 mm or less. The SORI value in the gallium nitride sintered body is 0.3 mm or less.

Description

Gallium nitride sintered body and method for producing the same

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

[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 instead 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 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 the mixing of impurities 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, single-crystal gallium nitride bulk bodies produced by the Na flux method or the HVPE method are difficult to produce in large sizes without defects, making it difficult to increase the size. 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 size increase and mass productivity. In particular, since gallium nitride is expensive, a thin-plate sintered body is desired for use as a substrate.

[0005] Patent No. 7044161

[0006] JH Leach et al., "Towards Manufacturing Large-Area GaN Substrates from QST® Seeds," [online], May 7-10, 2018, Proceedings of Compd. Semicond. Manuf. Technol, [Retrieved March 12, 2024], Internet: <https: / / csmantech.org / digests / ?digest=2018&thesession=4320>

[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.

[0009] The inventors of the present disclosure have investigated the causes of the above-mentioned problems. As a result, they have considered 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. ３ (1) The gallium nitride sintered body according to (1), having an absolute density of 1000 MPa or more. (3) The gallium nitride sintered body according to (1) or (2), having a surface roughness Ra of 2 μm or less on at least the main surface. (4) The gallium nitride sintered body according to any one of (1) to (3), having an atomic ratio of gallium to the total of gallium and nitrogen of 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 the 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 molded body; and a sintering step of sintering the molded body. (7) A method for producing the gallium nitride sintered body according to (6), wherein the pressure applied by the uniaxial pressing in the molding step is 400 MPa or more. (8) A 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 performing cold isostatic pressing on the green body. (9) A 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) A 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.

[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.

[0013] 1 is a cross-sectional view showing an embodiment of a gallium nitride sintered body according to the present disclosure, and FIG. 2 is a schematic diagram showing measurement points in measuring surface roughness Ra obtained by AFM.

[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 a gallium nitride sintered body according to 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-shaped body having a main surface 11. In this embodiment, the "main surface" refers to the surface of the sintered body 10 having the largest area. The aspect ratio (D / T), which is the ratio of the diameter D of the main surface 11 to the thickness T of the GaN sintered body 10, 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 after mirror polishing. The reason for this is thought to be as follows. That is, first, the SORI value of the GaN sintered body 10 is the sum of the heights of the highest point and the lowest point on the surface of the GaN sintered body 10, with the least-squares plane of the GaN sintered body 10 as the reference plane. Here, the smaller the SORI value, the smaller the waviness of the GaN sintered body 10. At this time, when the main surface 11 of the GaN sintered body 10 is mirror-polished with the flat polishing surface of the polishing pad, the polishing surface first comes into contact with the highest point on the surface of the GaN sintered body 10, so that 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 body 10. However, as the mirror polishing progresses, the polishing surface reaches the lowest point on the surface of the GaN sintered body 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 body 10 for a long period of time. It is thought that this makes it less likely for cracks to occur in the GaN sintered body 10.

[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 having gallium nitride as the main component (matrix, parent phase), particularly a polycrystalline gallium nitride, or may be a sintered body mainly composed of gallium nitride. In this embodiment, having gallium nitride as the main component means that the total mass proportion of gallium and nitrogen in the sintered body is 95% (95% by mass) or more. The total mass proportion of gallium and nitrogen in the sintered body is preferably 98% by mass or more, or even 99% by mass or more, and may also be less than 100% by mass, 99.9% by mass or less, or 99.5% by mass or less. The mass proportion of gallium and nitrogen in the sintered body may be the mass proportion calculated from the formula (1) described below. The mass ratio of gallium and nitrogen in the sintered body may be 95 mass% or more and less than 100 mass%, 98 mass% or more and 99.9 mass% or less, or 99 mass% or more and 99.5 mass% or less. 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 circle-equivalent 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 an area equal to 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 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). The diameter D of the main surface of the GaN sintered body 10 may be found as the circle-equivalent diameter, and specifically, the diameter D of the main surface is calculated by multiplying the area S (mm ２ ) and calculate it 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 examples thereof 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. The surface roughness Ra is not particularly limited, but is preferably 2 μm or less. When the surface roughness Ra is 2 μm or less, the irregularities of the main surface 11 are reduced, 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 or more to 2 μm or less, 0.20 μm or more to 1.5 μm or less, or 0.40 μm or more to 1.3 μm or less. The surface roughness Ra of the main surface opposite to the main surface 11 is not particularly limited, and may be the same as or different from the surface roughness Ra of the main surface 11. In this embodiment, the surface roughness Ra may be determined for the unpolished (e.g., not mirror-polished) main surface of the 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: 0.80 mm Evaluation length: 4.0 mm

[0020] The GaN sintered body 10 of this embodiment has a surface roughness Ra (hereinafter also referred to as "Ra (AFM)") measured by AFM on the polished main surface 11 of 100 nm or less. If Ra (AFM) is 100 nm or less, crystal defects in the GaN film are less likely to occur when a GaN film is formed on the surface of the polished main surface 11. Examples of Ra (AFM) include 100 nm or less, 50 nm or less, 40 nm or less, 20 nm or less, or 10 nm or less. Although a smaller Ra (AFM) is preferable, 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 to 100 nm or less, 0.05 nm or more to 50 nm or less, 0.1 nm or more to 40 nm or less, 0.5 nm or more to 20 nm or less, or 1 nm or more to 10 nm or less. The Ra (AFM) of the principal surface opposite 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. In this embodiment, Ra (AFM) is the arithmetic mean value of the surface roughness at three points measured using a general scanning probe microscope (e.g., SPM-9600, manufactured by Shimadzu Corporation) under the following measurement conditions: Scanning speed: 1 Hz, Scanning range: 10 μm × 10 μm, Number of pixels: 512 × 512, Measurement temperature: 25 ± 5°C. Specifically, the surface roughness at each point can be measured as follows. First, as shown in FIG. 2 , the diameter of an area-equivalent circle 200 on the inner periphery of the principal surface 11 of the GaN sintered body 10 is divided into four equal parts, and the length of the divided line segment is defined as the quarter length 200a. On this diameter, two points A1 and A2, located at the quarter length 200a from the center O of the area-equivalent circle 200, are used as measurement points. 2, the surface roughness can be measured at three measurement points: the two measurement points A1 and A2 determined in this way, plus the center O of a circle 200 corresponding to the area inside the outer periphery of the main surface 11 of the GaN sintered body 10. Prior to the measurement, the surface of the GaN sintered body 10 is polished as a pretreatment. Specifically, the surface of the GaN sintered body 10 is polished with sandpaper, and then polished at room temperature under the following conditions using a general polishing device (for example, LaboForce-100, manufactured by Struers).In this way, a measurement surface can be obtained. Rotation speed: 300 rpm Abrasive: POLIPLA304M (manufactured by Fujimi Inc.) Treatment 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 in particular, the plate-like shape may be a disk-like shape.

[0022] (Aspect Ratio) The aspect ratio (D / T) is 20 or more. In this embodiment, "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 or more and 450 or less, 20 or more and 300 or less, 50 or more and 450 or less, 75 or more and 450 or less, 100 or more and 300 or less, 120 or more and 200 or less, or 150 or more and 180 or less. (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 may be 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 or more and 2 mm or less, 0.5 mm or more and 1.8 mm or less, 0.8 mm or more and 1.5 mm or more, or 1.0 mm or more and 1.3 mm or less. In this embodiment, the thickness T of the GaN sintered body 10 may be measured using a general three-dimensional shape measuring instrument (e.g., a one-shot 3D shape measuring instrument VR-6000 manufactured by Keyence Corporation). (Diameter of the 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 subjected to mirror polishing. 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 more, more than 0.00 mm, 0.03 mm or more, 0.05 mm or more, or 0.10 mm or more. The upper and lower limits of the SORI value may be any combination as described above. The SORI value 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, 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, or 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, a 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 microscope stage of the three-dimensional shape measuring machine. Next, a least-squares plane is set as a reference plane using analysis software provided with the three-dimensional shape measuring machine. More specifically, using the analysis software provided with the three-dimensional shape measuring machine, a reference plane is set using the least-squares method from 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 to set a least-squares plane. Next, the SORI value can be calculated by calculating the sum of the height of the highest point on the main surface of the GaN sintered body 10 from the set least-squares plane and the height of the lowest point on the main surface of the GaN sintered body 10 from the least-squares plane.

[0025] (Absolute Density) The absolute density of the GaN sintered body 10 is not particularly limited, and is 4.2 g / cm ３ Even at 4.2 g / 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 This makes it 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 main surface 11 after polishing, and when a GaN film is formed on the surface of the main surface 11 after polishing, 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 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 5.8g / cm or more ３ Below, 4.5g / cm ３ 5.5g / cm or more ３ or less, or 4.8 g / cm ３ 5.2g / cm or more ３ In this embodiment, the absolute density ρ is calculated by measuring the mass m (g) of the GaN sintered body, 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. By containing a dopant in the GaN sintered body 10, the conductivity of the GaN sintered body 10 can be further improved, and a stack formed by forming a GaN film on the main surface 11 of the GaN sintered body 10 can be used as a device. The dopant may be an n-type dopant 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 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 at least one of magnesium and zinc. The GaN sintered body 10 may contain a single dopant element, or may contain two or more dopant elements.

[0027] (Composition) The atomic ratio of gallium to the total 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 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 substantially composed of only gallium nitride.

[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] Furthermore, the gallium nitride sintered body of this embodiment may contain metal impurities as long as the effect is not impaired. Examples of metal impurities include at least one of aluminum (Al) and indium (In). Metal impurities may be contained as metals or as metal compounds. It is preferable that metal impurities are substantially not contained. 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 the mass ratio [ppm by mass] of metal impurities determined by glow discharge mass spectrometry relative to the total mass of 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. Furthermore, the content of metal impurities may be 0 mass ppm or more and 50 mass ppm or less, or more than 0 mass ppm and 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%] +WＮ [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. 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 (for example, LECO ON736, manufactured by Leco Corporation). Ｄｏｐｅ is a value measured by glow discharge mass spectrometry. Ｇａ Is W Ｏ , W Ｎ and W Ｄｏｐｅ is a value calculated from the measured values ​​of the oxygen content by 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 elements determined by glow discharge mass spectrometry relative to the total mass of the elements determined by glow discharge mass spectrometry. When the gallium nitride sintered body of this embodiment contains metal impurities, the composition may appear to exceed 100 mass % due to differences in measurement methods. Furthermore, 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]. Ｄｏｐｅis the atomic weight of the dopant element. The Ga / (Ga+N) ratio is a value calculated from the following formula (3): Ga / (Ga+N) ratio = (W Ｇａ / M Ｇａ ) / {(W Ｇａ / M Ｇａ ) + (W Ｎ / M Ｎ ) …(3)

[0032] (Uses) Uses of the GaN sintered body 10 include a sputtering target, a film-forming substrate for forming a GaN film by CVD, epitaxial growth, or the like, that is, a substrate for epitaxial growth of a gallium nitride film.

[0033] <Method for manufacturing GaN sintered body> The GaN sintered body of the present disclosure can be manufactured by any method, but the method for manufacturing the GaN sintered body of the present disclosure may include 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 compact, and a sintering step of sintering the compact to obtain the above-mentioned GaN sintered body 10. According to this manufacturing method, a raw material powder containing GaN powder is prepared, the raw material powder is molded by uniaxial pressing to obtain a plate-shaped compact, and then the compact is sintered, thereby obtaining a GaN sintered body 10 that can suppress the occurrence of cracks even when mirror polishing is performed. Preferred methods for producing the GaN sintered body of the present disclosure include a production method including a preparation step of preparing a raw material powder containing GaN powder, a molding step of uniaxially pressing the raw material powder at a pressure of 400 MPa or more (hereinafter also referred to as "uniaxial press pressure") to obtain a plate-shaped molded body, and a sintering step of sintering the molded body, as well as a production method including a preparation step of preparing a raw material powder containing GaN powder, a molding step of uniaxially pressing the raw material powder at a uniaxial press pressure of 400 MPa or more to obtain a plate-shaped molded body, and a sintering step of sintering the molded body, in which a warpage suppression treatment is performed on the molded body in the sintering step to suppress warpage.

[0034] (1) Preparation Step In the preparation step, raw material powder containing GaN powder is prepared. The raw material powder may consist solely of GaN powder, but may also contain metallic gallium powder in addition to the GaN powder. In this case, the melting point of metallic gallium is approximately 30°C, and metallic gallium is liquefied by heating during the sintering step, making it easier to suppress warpage of the compact. Furthermore, by performing a warpage suppression treatment on the compact during the sintering step, warpage of the resulting GaN sintered body 10 can be more effectively suppressed. The raw material powder may further contain a powder containing a dopant element, as necessary. The raw material powder may be raw material powder obtained by passing through a sieve, or raw material powder obtained as is without passing through a sieve, but raw material powder obtained by passing through a sieve is preferable. In this case, variation in particle size of the raw material powder is less likely to occur, making it easier to suppress local strain within the compact. The sieve mesh size is not particularly limited, but is preferably 150 μm or less, and even more preferably less than 150 μm. By having a sieve diameter of 150 μm or less, or even less than 150 μm, variation in the particle size of the raw material powder is particularly unlikely to occur, 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 size of the sieve. That is, the sieve diameter refers to the length of one side of a square if the sieve has square openings, the length of the short side of a rectangle if the sieve has rectangular openings, and the diameter of a circle if the sieve has circular openings. The sieve diameter 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 Step In this embodiment, the molding step may involve obtaining a molded body by applying pressure only in a direction perpendicular to the main surface, or even by applying pressure only in a direction perpendicular to the main surface. Examples of molding in which pressure is applied only in a direction perpendicular to the main surface include uniaxial pressing and hot pressing, and even uniaxial pressing. In the molding step, the raw material powder is molded by uniaxial pressing to obtain a plate-shaped molded body. The uniaxial pressing pressure is not particularly limited, but is preferably 350 MPa or higher. In this case, by applying a uniaxial pressing pressure of 350 MPa or higher, the voids in the molded body can be sufficiently reduced, thereby sufficiently increasing the density of the GaN sintered body 10. Furthermore, since density variation in the molded body is easily suppressed, the SORI value of the resulting GaN sintered body 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 higher, and particularly preferably 450 MPa or higher. 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 molded body obtained by the molding 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 molded body 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 molded body 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 Step The sintering step is a step of sintering the compact to obtain a GaN sintered body. In the sintering step, the compact may be sintered without being placed in a mold to obtain a GaN sintered body.

[0037] The sintering step may be performed without cold isostatic pressing (CIP) on the compact after the molding step, or may be performed after cold isostatic pressing (CIP). The sintering step is preferably performed without cold isostatic pressing (CIP) on the compact after the molding step. In this case, waviness of the compact due to CIP can be easily suppressed. Particularly when molding into a thin plate, when isostatic pressing, specifically, when cold isostatic pressing (CIP) is not performed, 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 reduced compared to when isostatic pressing is performed, which is thought to result in a smaller SORI value for the resulting sintered body.

[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 at least one mixed gas of nitrogen and hydrogen, or further preferably ammonia gas. The gas constituting the nitriding atmosphere is preferably ammonia gas, particularly 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 at which the molded body can 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, warp suppression treatment for suppressing warpage of the compact may or may not be performed, but is preferably performed. In this case, warpage of the compact is suppressed, so that a GaN sintered body 10 that can generate cracks even when mirror polishing is performed on the main surface 11 can be obtained. An example of the warp suppression treatment is a treatment in which the compact is sandwiched between a pair of plate-like members, and a treatment in which the compact is sandwiched between a pair of plate-like members is preferred. The plate-like members are preferably breathable members that have breathability. An example of the breathable member is 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. Examples of the sintering time include 20 hours or less, 10 hours or less, and 5 hours or less. Examples of the sintering time include 0.5 hours or more and 20 hours or less, 1 hour or more and 10 hours or less, and 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 a 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.

[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 having 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 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 compacts were placed in a sintering furnace and sintered under the sintering conditions shown in Table 1. Note that, for Examples 2 and 4, a warpage suppression treatment was performed on the compacts. The warpage suppression treatment was performed by placing the compacts between a pair of alumina (Al ２ O ３ The GaN sintered body was then sandwiched between mesh plates made of aluminum. Thus, a GaN sintered body having the configuration 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) The GaN sintered body of this example was obtained in the same manner as in Example 2, except that the uniaxial pressing pressure was 200 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.

[0045] Comparative Example 1 A 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 using a uniaxial press cylinder at the uniaxial press pressure shown in Table 1 to form a plate-shaped primary compact having a thickness of 1.31 mm and a diameter of 150 mm. Next, the primary compact was pressed using a CIP at the CIP pressure shown in Table 1 to form a plate-shaped secondary compact having a thickness of 1.06 mm and a diameter of 150 mm. The SORI value of the secondary compact was measured using a three-dimensional shape measuring device, and the SORI value was as shown in Table 1. Next, the secondary compact was placed in a sintering furnace and sintered under the sintering conditions shown in Table 1. For Comparative Example 1, the secondary compact was also subjected to warpage suppression treatment in the same manner as in Example 2. In this manner, 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 Main Surface) The thickness T (mm) and diameter D (mm) of the main surface of the GaN sintered body were measured using a three-dimensional shape measuring instrument (product name: One-shot 3D Shape Measuring Instrument VR-6000, manufactured by Keyence Corporation). The diameter D of the main surface was calculated as the equivalent circle diameter. Specifically, the diameter D of the main surface was calculated by multiplying the area S (mm ２ ) was obtained and calculated based on the following formula: D = 2 × (S / π) １／２

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

[0048] (Absolute Density) The absolute density ρ is calculated by measuring the mass m (g) of the GaN sintered body and multiplying the mass m by the area S (mm ２ The thickness T (mm) was calculated 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 had not been mirror-polished using a tactile surface roughness meter (device name: HANDYSURF, manufactured by Tokyo Seimitsu Co., Ltd.) under the following measurement conditions: Cutoff value: 0.80 mm Evaluation length: 4.0 mm

[0050] (Ra (AFM)) Ra (AFM) was the arithmetic average value of the surface roughness at three points measured under the following measurement conditions using a scanning probe microscope (product name: SPM-9600, manufactured by Shimadzu Corporation). Scanning speed: 1 Hz Scanning range: 10 μm × 10 μm Number of pixels: 512 × 512 Measurement temperature: 25±5°C Specifically, the measurement of the surface roughness at each point was performed as follows. First, as shown in FIG. 2, the diameter of an area-equivalent circle 200 on the inner 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, surface roughness was measured at three measurement points: the two measurement points A1 and A2 determined in this way, plus the center O of a circle 200 equivalent to the area of ​​the outer periphery of the main surface of the GaN sintered compact. Prior to the measurement, the surface of the GaN sintered compact was polished as a pretreatment. Specifically, the surface of the gallium nitride sintered compact was polished with sandpaper, and then polished at room temperature using a polishing device (device name: LaboForce-100, manufactured by Struers) under the following conditions. In this way, the measurement surface was obtained. Rotation speed: 300 rpm Abrasive: POLIPLA304M (manufactured by Fujimi Incorporated) Processing time: 10 minutes

[0051] (SORI Value) The SORI value was measured using a three-dimensional shape measuring machine (product name: One-Shot 3D Shape Measuring Machine VR-6000, manufactured by Keyence Corporation). Specifically, first, the GaN sintered body was placed on the microscope stage 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 machine. More specifically, using the analysis software attached to the three-dimensional shape measuring machine, 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 to set a least-squares plane. Next, the total value of the height of the highest point of the main surface of the GaN sintered body from the set least-squares plane and the height of the lowest point of the main surface of the GaN sintered body from the least-squares plane was calculated as the SORI value.

[0052] (Composition) The oxygen [mass %] and nitrogen mass proportions [mass %] of the GaN sintered body were measured by inert gas fusion-infrared absorption using an oxygen and nitrogen analyzer (device name: LECO ON736, manufactured by Leco Corporation). The mass proportions of dopant elements were measured by glow discharge mass spectrometry. The obtained mass proportions of oxygen, nitrogen, and dopant elements, as well as the mass proportion of gallium 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), were each calculated.

[0053] <Evaluation> While holding the GaN sintered body with a holder, the main surface was brought into contact with the flat polishing surface of a polishing pad with the main surface facing downward, and mirror polishing was performed. The mirror polishing was performed by CMP polishing. The GaN sintered body was then visually observed for the presence or absence of cracks. The results are shown in Table 2.

[0054]

[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. From a comparison of Examples 2, 7, and 8, it was 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 all of the GaN sintered bodies of the examples had a surface roughness Ra of 1.14 μm or less, which was smaller than the surface roughness Ra of the comparative examples. Furthermore, the GaN sintered bodies of the examples had an Ra (AFM) of 6.71 nm or less, confirming that the surface of the GaN sintered body after polishing was smooth. The entire contents of the specifications, claims, abstracts 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.

[0056] 10... GaN sintered body, 11... main surface, T... thickness of GaN sintered body, D... diameter of 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 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 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 claim 1 , having an absolute density of at least 1000 kJ / cm 2 .

3. A gallium nitride sintered body according to claim 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 claims 1 to 3, wherein 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 claims 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 claims 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 plate-shaped compact; and a sintering step of sintering the compact to obtain the gallium nitride sintered body.

7. The method for producing a gallium nitride sintered body according to claim 6, wherein the pressure applied by the uniaxial press in the molding step is 400 MPa or more.

8. A method for producing a gallium nitride sintered body according to claim 6 or 7, wherein after the molding step, the sintering step is carried out without subjecting the compact to cold isostatic pressing.

9. A method for producing a gallium nitride sintered body according to any one of claims 6 to 8, wherein warpage suppression treatment is performed on the green body in the sintering step to suppress warpage.

10. The method for producing a gallium nitride sintered body according to any one of claims 6 to 9, wherein the raw material powder further contains metallic gallium.

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