Sintered body of gallium nitride

Abstract

The present invention provides at least one of a sintered body of gallium nitride and a method for producing the same, the sintered body having a bending strength in which defects hardly occur even though the sintered body contains a dopant element amount of 15 mass ppm or more, and being capable of directly forming a p-type gallium nitride film.　The sintered body of gallium nitride is characterized by containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), vanadium (V), zinc (Zn) and cadmium (Cd), wherein the content of the dopant element is 15 mass ppm or more, and the atomic ratio of gallium to the total of nitrogen and gallium is less than 0.55.

Description

Gallium nitride sintered body

[0001] The present disclosure relates to a sintered body of gallium nitride from which a p-type gallium nitride film can be obtained.

[0002] Gallium nitride (GaN) is used as a material for LEDs and power semiconductors, and p-type gallium nitride films are required for manufacturing semiconductor devices. As a method for forming a p-type gallium nitride film, a method has been disclosed in which a gallium nitride film is formed by MOCVD and then doped with a p-type dopant element by pulse sputtering (e.g., Patent Document 1). However, the method of Patent Document 1 is a multi-step film formation method that requires a step of adding a dopant element to the gallium nitride film in addition to the step of forming the gallium nitride film. In contrast, Patent Document 2 reports a sputtering target for p-type gallium nitride thin films. By using such a target, a p-type gallium nitride film can be directly formed.

[0003] Japanese Patent Publication No. 2008-091470 Japanese Patent Publication No. 2020-059644

[0004] However, in the sputtering target for p-type gallium nitride thin films of Patent Document 2, increasing the content of dopant elements significantly reduces the flexural strength, making it difficult to process into sputtering targets, and also prone to defects during handling such as transportation. The present disclosure aims to provide at least one of a gallium nitride sintered body and a method for producing the same, which has a flexural strength that is less prone to defects despite containing 15 mass ppm or more of dopant elements, and which can be used to directly form a p-type gallium nitride film.

[0005] In the present disclosure, sputtering targets capable of directly depositing p-type gallium nitride films were investigated, focusing on the dopant element and gallium nitride composition and their formability. As a result, it was found that by using a raw material of a specific composition, a molded body with high shape retention can be obtained, and that, despite containing 15 mass ppm or more of a dopant element, a gallium nitride sintered body containing a dopant element that has higher flexural strength than conventional sputtering targets capable of directly depositing p-type gallium nitride films and can directly deposit p-type gallium nitride films can be obtained. That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows.

[0006] [1] A gallium nitride sintered body containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), vanadium (V), zinc (Zn), and cadmium (Cd), wherein the content of the dopant element is 15 mass ppm or more, and the atomic ratio of gallium to the total of nitrogen and gallium is less than 0.55. [2] The sintered body according to [1] above, having an oxygen content of 0 atm% or more and 0.4 atm% or less. [3] A bulk density of 4.00 g / cm ３The sintered body according to [1] or [2] above, wherein the total content of silicon, germanium, tin, and lead is 10 ppm by mass or less. [4] The sintered body according to any one of [1] to [3] above, wherein the total content of silicon, germanium, tin, and lead is 10 ppm by mass or less. [5] The sintered body according to any one of [1] to [4] above, wherein the degree of dispersion of the dopant element is 500 or less. [6] A method for producing a sintered body according to any one of [1] to [5] above, comprising a sintering step of sintering a molded body containing a gallium nitride source and a dopant source, wherein the atomic ratio of gallium to the total of nitrogen and gallium is less than 0.55, in an atmospheric pressure nitriding atmosphere. [7] The method for producing a sintered body according to [6] above, wherein the gallium nitride source is one or more selected from the group consisting of gallium oxide, metallic gallium, and gallium chloride, and gallium nitride. [8] The method for producing a sintered body according to [6] or [7] above, wherein the atmospheric pressure nitriding atmosphere is an atmosphere containing at least one of nitrogen and a nitrogen compound under atmospheric pressure. [9] A sputtering target comprising the sintered body according to any one of [1] to [5] above.

[10] A film formation method using the sputtering target according to [9] above.

[0007] The present disclosure makes it possible to provide at least one of a gallium nitride sintered body and a method for producing the same, which has a flexural strength that is less prone to defects despite containing a dopant element in an amount of 15 ppm by mass or more, and which is capable of directly forming a p-type gallium nitride film.

[0008] Graph showing SIMS measurement results of the magnesium-containing gallium nitride film of Example 7

[0009] The present disclosure will be described in detail with reference to one embodiment. However, the present disclosure is not limited to the following embodiment. Furthermore, the present disclosure includes any combination of the configurations and parameters disclosed in this specification, and also includes any combination of the upper and lower limits of the values ​​disclosed in this specification.

[0010] [Gallium nitride sintered body] This embodiment is a gallium nitride sintered body containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), vanadium (V), zinc (Zn), and cadmium (Cd), wherein the content of the dopant element is 15 mass ppm or more, and the atomic ratio of gallium to the total of nitrogen and gallium is less than 0.55. By using the sintered body of this embodiment, a p-type gallium nitride film (hereinafter also referred to as a "p-type GaN film") can be directly formed.

[0011] The sintered body of this embodiment is a gallium nitride (GaN) sintered body, particularly a gallium nitride sintered body containing one or more dopant elements (hereinafter simply referred to as "dopant elements") selected from the group consisting of beryllium, magnesium, calcium, strontium, vanadium, zinc, and cadmium. The sintered body of this embodiment may be a sintered body containing a dopant element and essentially consisting of gallium nitride, or a sintered body containing a dopant element and mainly composed of gallium nitride, but may also be a sintered body consisting of a dopant element and gallium nitride. In this embodiment, gallium nitride is the main component, meaning 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, less than 99.2% by mass, 99.1% by mass or less, or less than 99.1% by mass. The mass proportion of gallium and nitrogen in the sintered body may be a mass proportion calculated from the formula (1) described below. Examples of the mass proportion of gallium and nitrogen in the sintered body include 95% by mass to less than 100% by mass, 95% by mass to less than 99.2% by mass, 99% by mass to less than 99.2% by mass, and 99% by mass to 99.1% by mass.

[0012] The sintered body of this embodiment may contain elements other than the dopant element and gallium nitride, such as inevitable impurities. Examples of inevitable impurities contained in the sintered body of this embodiment include oxygen (O). Furthermore, the 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 indium (In) and aluminum (Al). However, the sintered body of this embodiment preferably does not contain elements that may reduce the p-type characteristics of the film obtained therefrom (0 mass ppm), preferably does not contain silicon (Si), and more preferably does not contain one or more elements selected from the group consisting of silicon, germanium (Ge), tin (Sn), and lead (Pb) (hereinafter also referred to as "n-type dopant elements"). The total content of silicon, germanium, tin, and lead is preferably 10 mass ppm or less, and even more preferably 5 mass ppm or less. On the other hand, an n-type dopant element may be contained to the extent of an unavoidable impurity, and for example, the content of the n-type dopant element may be 0 ppm by mass or more or more than 0 ppm by mass. Examples of the content of the n-type dopant element include 0 ppm by mass or more and 10 ppm by mass or less, more than 0 ppm by mass and 10 ppm by mass or less, or more than 0 ppm by mass and 5 ppm by mass or less.

[0013] In this embodiment, the composition of the sintered body can be determined from the following formula (1): 100 = W Ｇａ +W Ｏ +W Ｎ +W Ｄｏｐｅ (1) In equation (1), W Ｇａ , W Ｏ , W Ｎ and W Ｄｏｐｅ are the mass percentages (mass%) of gallium, oxygen, nitrogen, and the dopant element in the sintered body. Ｏ and W Ｎ are the values ​​of oxygen and nitrogen [mass %] measured by a pyrolysis method in which the sintered body is pyrolyzed using a general oxygen and nitrogen analyzer (e.g., LECO ON736, manufactured by Leco Corporation), and W Ｄｏｐｅ are the values ​​of the dopant elements [mass %] measured by glow discharge mass spectrometry.

[0014] Furthermore, when elements such as unavoidable impurities are contained, the content is the value [mass%] measured by glow discharge mass spectrometry. Due to differences in measurement methods, when the sintered body of this embodiment contains elements such as unavoidable impurities, its composition appears to exceed 100 mass%. The atomic ratio of gallium to the total of gallium and nitrogen in the sintered body of this embodiment (hereinafter also referred to as the "gallium ratio") is preferably less than 0.55 and 0.50 or less. This allows the sintered body of this embodiment to be produced even by sintering in a normal pressure atmosphere. If the gallium ratio is 0.55 or more, the shape retention of the precursor (molded body) of the sintered body of this embodiment is significantly reduced, making it prone to defects during handling. As a result, a molded body suitable for sintering in a normal pressure atmosphere cannot be obtained. The gallium ratio is preferably 0 or more, greater than 0, 0.10 or more, or 0.30 or more, and examples thereof include 0 or more but less than 0.55, greater than 0 but less than 0.55, 0.10 or more but 0.50 or less, or 0.30 or more but 0.50 or less.

[0015] In this embodiment, the gallium ratio is a value calculated from the following formula (2): Ga / (Ga+N) ratio = (W Ｇａ / M Ｇａ ) / {(W Ｇａ / M Ｇａ ) + (W Ｎ / M Ｎ )} (2) In formula (2), the Ga / (Ga+N) ratio is the gallium ratio, and W Ｇａ and W Ｎ is the mass ratio [mass%] of gallium and nitrogen in the sintered body, and M Ｇａ and M Ｎ are the atomic weights of gallium and nitrogen, and 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].

[0016] The dopant element may be one or more selected from the group consisting of beryllium, magnesium, calcium, strontium, vanadium, zinc, and cadmium, more preferably at least one of magnesium and zinc, and even more preferably magnesium. The content of the dopant element is 15 mass ppm or more, more preferably 20 mass ppm or more, 50 mass ppm or more, 90 mass ppm or more, 0.05 mass% or more (500 mass ppm or more), or 0.15 mass% or more (1500 mass ppm or more). By having such a value of the dopant element content, a p-type gallium nitride film with higher p-type characteristics can be obtained. Furthermore, if the content of the dopant element is 0.8 mass% or less, the shape retention of the precursor (molded body) used in sintering the sintered body is high, making it easier to obtain a molded body with a stable shape. The content of the dopant element may be 0.55% by mass or less, 0.35% by mass or less, or 0.25% by mass or less, and examples thereof include 15 ppm by mass or more and 0.8% by mass or less, 20 ppm by mass or more and 0.8% by mass or less, 20 ppm by mass or more and 0.55% by mass or less, 90 ppm by mass or more and 0.55% by mass or less, or 0.15 ppm by mass or more and 0.25% by mass or less.

[0017] In the sintered body of this embodiment, the degree of dispersion of the dopant element (hereinafter also simply referred to as "degree of dispersion") is preferably 500 or less or 400 or less, and may be 200 or more, or even 300 or more. The degree of dispersion is one of the indicators showing the degree of dispersion of the dopant element obtained from element mapping, and the higher the degree of dispersion of the dopant element, the smaller the value of the degree of dispersion. In this embodiment, the degree of dispersion is the standard deviation [Count] of the element intensity of the dopant element obtained by analyzing element mapping obtained using a general FE-EPMA (for example, JXA-iHP200F, manufactured by JEOL Ltd.) under the following conditions using general analysis software (for example, PC-EPMA Ver. 2.7.0).

[0018] Observation: Secondary electron image, backscattered electron image, element mapping Measurement method: Wavelength dispersive (WDS) Acceleration voltage: 15 kV Probe current: 300 nA Analysis area: 1.0 mm x 5.0 mm Number of fields: 1 field per sample

[0019] An ideal gallium nitride sintered body contains no oxygen, so its oxygen content is 0 atm%. However, realistic gallium nitride sintered bodies contain oxygen. The sintered body of this embodiment preferably does not contain oxygen (i.e., the oxygen content is 0 atm%), but examples include 0 atm% or more, more than 0 atm%, or 0.1 atm% or more. Although the amount of oxygen tends to increase with an increase in dopant elements, the oxygen content of the sintered body of this embodiment is preferably 0.4 atm% or less, 0.35 atm% or less, or 0.3 atm% or less. With such an oxygen content, leakage current is less likely to occur when a gallium nitride film obtained from the sintered body of this embodiment is used in applications such as light-emitting diodes and power devices. The oxygen content of the sintered body of this embodiment may be 0 atm% or more and 0.4 atm% or less, more than 0 atm% and 0.4 atm% or less, 0.1 atm% or more and 0.4 atm% or less, or 0.1 atm% or more and 0.3 atm% or less.

[0020] In this embodiment, the oxygen content of the sintered body is measured by a method conforming to JIS H 1695 and is a value calculated from the following formula (3): Oxygen content [atm %] = [(W Ｏ / M Ｏ ) / {(W Ｇａ / M Ｇａ ) + (W Ｎ / M Ｎ ) + (W Ｏ / M Ｏ ) + (W Ｄｏｐｅ / M Ｄｏｐｅ ) ] × 100 (3)

[0021] In formula (3), M Ｏ is the atomic weight of oxygen: 16.00 [g / mol], M Ｇａ is the atomic weight of gallium: 69.72 [g / mol], M Ｎis the atomic weight of nitrogen: 14.01 [g / mol]. Ｄｏｐｅ is the atomic weight of the dopant element. The atomic weights of the dopant elements are 9.01 [g / mol] for beryllium, 24.31 [g / mol] for magnesium, 40.08 [g / mol] for calcium, 87.62 [g / mol] for strontium, 50.94 [g / mol] for vanadium, 65.39 [g / mol] for zinc, and 112.41 [g / mol] for cadmium.

[0022] The shape of the sintered body of this embodiment may be any shape depending on the purpose, for example, one or more selected from the group consisting of plate-like, disk-like, cylindrical, cubic, rectangular, polyhedral, columnar, cylindrical, and conical shapes, as well as any shape that can be used as a sputtering target. In particular, the sintered body of this embodiment can also be produced by the production method described below. Therefore, compared to sintered bodies obtained by the hot pressing method (hereinafter also referred to as the "HP method"), the sintered body of this embodiment can be produced in any shape and size.

[0023] The average crystal grain size of the sintered body of this embodiment is preferably 1.6 μm or more and 2.5 μm or less. In this embodiment, the average crystal grain size may be determined by scanning electron microscope-electron backscatter diffraction (hereinafter also referred to as "SEM-EBSD") of the cross section of the sintered body. SEM-EBSD observation may be performed by using a general EBSD (for example, Symmetry, manufactured by Oxford Instruments) on an SEM observation image obtained by the following measurement method. The conditions for EBSD observation are as follows: Acceleration voltage: 15 kV Sample tilt: 70 degrees Tilt correction: 0 degrees Measurement magnification: 500x Step size: 0.2 μm

[0024] The orientation where the crystal orientation is tilted by 5° or more is regarded as a grain boundary, and the area surrounded by the grain boundary is regarded as a crystal grain. The diameter of a circle corresponding to the area of ​​each crystal grain is calculated and used as the crystal grain size. EBSD observation is performed on crystal grains (e.g., 10,000 to 30,000 crystal grains) observed in three fields of view obtained by the following measurement method, and the average of the results is used as the average crystal grain size.

[0025] SEM observation is performed using a general SEM (for example, JSM-IT800, manufactured by JEOL Ltd.), and the cut surface obtained by cutting the sintered body may be used as the observation surface. Prior to SEM observation, the cut surface may be subjected to ion milling processing, and further cryo-ion milling processing, to provide the observation surface. The conditions for SEM observation are as follows: Acceleration voltage: 5 kV Observation magnification: 500x

[0026] Since the sintered body of this embodiment tends to have mechanical properties suitable for a sputtering target, the bulk density of the sintered body of this embodiment is 4.00 g / cm ３ or more than 4.20 g / cm ３ The higher the bulk density, the more preferable it is, and the bulk density of the sintered body of this embodiment is, for example, 5.00 g / cm ３ Below, 4.80g / cm ３ or less than 4.60 g / cm ３ Preferably, it is 4.00 g / cm or less. ３ 5.00g / cm or more ３ Below, 4.20g / cm ３ 4.80g / cm or more ３ or less, or 4.20 g / cm ３ 4.60g / cm or more ３ The following points can be mentioned.

[0027] In this embodiment, the "bulk density" refers to the density [g / cm 3 ] measured by a method according to JIS R 1634:1998. ３ ]. The pretreatment may be performed by a vacuum method using distilled water. Since defects are less likely to occur during handling, the flexural strength of the sintered body of this embodiment may be 10 MPa or more, and is preferably 15 MPa or more or 30 MPa or more. Furthermore, a high flexural strength is preferable, but examples include 60 MPa or less or 50 MPa or less. Examples of the flexural strength of the sintered body of this embodiment include 15 MPa or more and 60 MPa or less, or 30 MPa or more and 50 MPa or less.

[0028] In this embodiment, the bending strength is the three-point bending strength of the sintered body measured by a method in accordance with JIS R 1601. The measurement is carried out 3±1 times, and the average value is taken as the bending strength in this embodiment.

[0029] The Vickers hardness of the sintered body of this embodiment is preferably 50 HV or more, 100 HV or more, or 150 HV or more. The Vickers hardness may be moderately high, for example, 500 HV or less, 300 HV or less, or 250 HV or less, and is preferably 50 HV or more and 500 HV or less, or 80 HV or more and 300 HV or less. In this embodiment, the Vickers hardness may be a value measured by a method conforming to JIS B 7725. The Vickers hardness may be determined by pressing a pyramidal indenter against the sintered body with a force of 1 kgf, observing the formed indentation under a microscope, and calculating the surface area of ​​the indentation from the horizontal distance between the diagonals.

[0030] The sintered body of the present embodiment can be used in known applications of gallium nitride sintered bodies, and is preferably used as a sputtering target, more preferably as a sputtering target for forming a p-type gallium nitride film.

[0031] [Method for manufacturing sintered body] The sintered body of this embodiment can be manufactured by any method as long as it satisfies the above-mentioned configuration. However, since it is suitable for industrial production, it is preferably manufactured by a manufacturing method including a sintering step in an atmospheric pressure atmosphere. A preferred method for manufacturing the sintered body of this embodiment is a manufacturing method for a sintered body (hereinafter also referred to as the "manufacturing method of this embodiment") that includes a sintering step of sintering a molded body containing a gallium nitride source and a dopant source, in an atmospheric pressure nitriding atmosphere, where the atomic ratio of gallium to the total of nitrogen and gallium is less than 0.55. This not only allows the sintered body to be obtained by a simpler method than sintering by the HP method, but also increases the degree of freedom in the shape and size of the molded body to be subjected to the sintering step.

[0032] In the sintering step, a molded body containing a gallium nitride source and a dopant source is provided. The gallium nitride source may be at least one of gallium nitride and its precursor, in which the atomic ratio of gallium to the total of nitrogen and gallium (gallium ratio) is less than 0.55. Examples of gallium nitride precursors include one or more selected from the group consisting of gallium oxide, metallic gallium, and gallium chloride, and metallic gallium. The gallium nitride source is preferably one or more selected from the group consisting of gallium oxide, metallic gallium, and gallium chloride, and gallium nitride, and is preferably metallic gallium or gallium nitride.

[0033] The dopant source may be at least one of a dopant element and its compound, such as at least one selected from the group consisting of beryllium, magnesium, calcium, strontium, vanadium, zinc, cadmium, and aluminum, and at least one of their compounds. To reduce the inclusion of impurities, the dopant source is preferably at least one of a metal and a nitride. Examples of metals include the metal of the dopant element (single metal) and an alloy containing the same. Examples of alloys include alloys containing at least one of gallium and aluminum and the dopant element. Particularly preferred dopant sources include at least one selected from the group consisting of magnesium, zinc, and zinc nitride, and magnesium.

[0034] The content of the dopant source, converted into the dopant element, may be the same content [mass%] as the content of the dopant element in the sintered body of this embodiment described above. The gallium ratio (gallium ratio) of the molded body to the total of nitrogen and gallium is preferably less than 0.55 and less than 0.50, and more preferably 0 or more, more than 0, 0.10 or more, or 0.30 or more. The gallium ratio of the molded body may be 0 or more and less than 0.55, more than 0 and less than 0.55, 0.10 or more and 0.50 or less, or 0.30 or more and 0.50 or less. In the manufacturing method of this embodiment, the gallium ratio of the gallium nitride source, the gallium ratio of the molded body, and further the gallium ratio of the resulting sintered body are equivalent. By having the gallium ratio of the molded body be less than 0.55, a molded body with high shape retention can be obtained, and the molded body can be subjected to sintering in a normal pressure atmosphere.

[0035] To reduce the oxygen content of the resulting sintered body, the oxygen content of the compact is preferably less than 0.4 atm%, less than 0.35 atm%, or less than 0.3 atm%. The compact preferably does not contain oxygen (i.e., the oxygen content is 0 atm%), but may contain oxygen to the extent that it does not affect the properties of the resulting sintered body. The oxygen content of the compact can be, for example, 0.005 atm% or more or 0.01 atm% or more. The oxygen content of the compact can be 0.005 atm% or more but less than 0.4 atm%, or 0.01 atm% or more but less than 0.35 atm%.

[0036] The oxygen content of the compact in this embodiment is a value calculated from the above-mentioned method and formula (3). The measured density of the compact is 3.00 g / cm ３ or more than 3.60 g / cm ３ or more, and 5.80 g / cm ３ or less or 5.50 g / cm ３ Preferably, it is 3.00 g / cm or less. ３ 5.80g / cm or more ３ or less, or 3.60 g / cm ３ 5.50g / cm or more ３ The following points can be mentioned.

[0037] The measured density of the molded body in this embodiment is a value measured by a method conforming to JIS Z 8807. Note that air conforming to JIS Z 8807 may be used as a reference substance in measuring the measured density.

[0038] The shape of the molded body may be any shape that allows a sintered body of the desired shape to be obtained, such as one or more selected from the group consisting of plate, disk, cylinder, cube, rectangular parallelepiped, polyhedron, column, column, and cone, as well as any shape that can be used as a sputtering target. Examples of shapes that can be used as a sputtering target include plate and disk shapes. Taking into account the thermal shrinkage of the molded body due to sintering, the molded body may be larger than the desired size of the sintered body. Specific examples of the shape of the molded body include a rectangular parallelepiped (rectangle) with a length of 5 mm to 60 mm and a width of 30 mm to 60 mm, or a disk shape with a diameter of 5 mm or more or 10 mm or more and a length of 100 mm or less or 80 mm or less.

[0039] The molded body to be subjected to the sintering step may be produced by any method as long as it satisfies the above-mentioned requirements. For example, a method for producing a molded body that includes a molding step of molding a raw material powder that contains a gallium nitride source and a dopant source and has an atomic ratio of gallium to the total of nitrogen and gallium (gallium ratio) of less than 0.55 can be exemplified.

[0040] The raw material powder may be a powder containing a gallium nitride source and a dopant source, or may be a mixed powder of a gallium nitride source powder and a dopant source powder. The raw material powder may have a composition similar to that of the compact. Preferred raw material powders include raw material powders containing one or more selected from the group consisting of gallium oxide, metallic gallium, and gallium chloride, gallium nitride, and a dopant source, as well as raw material powders containing metallic gallium, gallium nitride, and a dopant source.

[0041] In the compacting step, the raw material powder is compacted. This produces a compacted body to be subjected to the sintering step. The compacting method may be any method that produces a compacted body having a desired shape, and examples thereof include at least one of uniaxial press compacting and cold isostatic pressing (hereinafter also referred to as "CIP") compacting, with uniaxial press compacting and CIP compacting being preferred. A compacted body (green compact) is obtained by these compacting methods. The compacting is preferably performed without heating the raw material powder, and is preferably performed at room temperature (25±10°C).

[0042] A particularly preferred molding method is one in which a raw material powder is subjected to primary molding to obtain a primary molded body, and then the primary molded body is subjected to secondary molding. Primary molding may be performed by any method that can obtain a primary molded body having sufficient shape retention to prevent defects when subjected to secondary molding, and uniaxial press molding is preferred. Preferred uniaxial press molding conditions include a molding pressure of 50 MPa or more or 75 MPa or more, and 200 MPa or less or 300 MPa or less. Examples of molding pressures include 50 MPa or more and 300 MPa or less, or 75 MPa or more and 200 MPa or less. Secondary molding may be performed by any molding method that can obtain a molded body as described below, and CIP molding is preferred. Preferred CIP molding conditions include a CIP pressure of 100 MPa or more and 200 MPa or more, and 400 MPa or less or 500 MPa or less. Examples of CIP pressures include 100 MPa or more and 500 MPa or less, or 200 MPa or more and 400 MPa or less.

[0043] The manufacturing method of this embodiment includes a step of sintering the compact in an atmospheric nitriding atmosphere (hereinafter also referred to as the "sintering step"). In the sintering step, the compact is sintered in an atmospheric nitriding atmosphere. This sintering not only promotes the densification of the compact, but also promotes the nitridation of the gallium nitride precursor in the compact to form gallium nitride, and promotes the dispersion of the dopant element.

[0044] In this embodiment, the atmospheric pressure nitriding atmosphere is an atmosphere under atmospheric pressure in which the nitriding reaction proceeds. The atmosphere in which the nitriding reaction proceeds (hereinafter also referred to as "nitriding atmosphere") includes not only a nitrogen atmosphere but also an atmosphere containing nitrogen and other elements. The atmospheric pressure nitriding atmosphere can be exemplified by an atmosphere containing at least one of nitrogen and a nitrogen compound under atmospheric pressure, and is preferably at least one selected from the group consisting of a nitrogen and hydrogen mixed atmosphere, an ammonia atmosphere, a hydrazine atmosphere, and an alkylamine atmosphere, and further preferably at least one of a nitrogen and hydrogen mixed atmosphere and an ammonia atmosphere, or even an ammonia atmosphere. Furthermore, as long as the nitriding of the gallium nitride precursor proceeds, the nitriding atmosphere may contain oxygen.

[0045] A preferred atmospheric pressure nitriding atmosphere is a flow atmosphere under atmospheric pressure, i.e., an atmosphere in which an atmospheric medium such as a nitrogen compound-containing gas flows. This further promotes the nitridation reaction of the gallium nitride precursor. In particular, a nitrogen compound-containing gas flow atmosphere, and even an ammonia flow atmosphere, are preferred. This makes the composition of the resulting sintered body more uniform. Furthermore, it further promotes the dispersion of the dopant element. The flow atmosphere may be in a state in which the atmospheric medium flows, for example, a flow rate of 0.1 mL / min or more or 1 L / min or more. On the other hand, the flow rate may be appropriately set depending on the molded body to be treated and the performance of the sintering furnace, and examples include 20 L / min or less or 10 mL / min or less. The flow rate may be 0.1 mL / min or more to 20 L / min or less, or 1 L / min or more to 10 mL / min or less.

[0046] The sintering atmosphere in the sintering step is an atmospheric nitriding atmosphere, which is an atmosphere in which nitriding proceeds at atmospheric pressure without pressurizing the compact (object to be sintered). Therefore, unlike a method in which a compact is sintered while applying a molding pressure to the compact, or a method in which molding and sintering are performed simultaneously, the manufacturing method of this embodiment does not require pressure sintering such as hot pressing, and a sintered body can be easily obtained.

[0047] The holding temperature in the sintering step may be any temperature at which sintering of gallium nitride progresses and the dopant element diffuses into the sintered body. Examples of holding temperatures include 1100°C or less, 1050°C or less, or 1000°C or less, and also 800°C or more or 850°C or more. Examples of preferred holding temperatures include 800°C or more and 1100°C or less, or 850°C or more and 1000°C or less. The holding time at the holding temperature varies depending on the holding temperature, the size of the molded body, the performance of the sintering furnace used, etc., but examples of the holding time at the holding temperature include 1 hour to 20 hours, and even 2 hours to 10 hours.

[0048] [Sputtering target] A sputtering target including the sintered body of this embodiment (hereinafter also referred to as "the target of this embodiment") may be the sintered body of this embodiment, but is preferably a sputtering target in which the sintered body of this embodiment is bonded to a support via a bonding layer. The shape of the target of this embodiment is arbitrary, and examples thereof include at least one of a flat shape and a cylindrical shape, as well as other shapes suitable for the application.

[0049] The target of this embodiment preferably has a structure in which the sintered body of this embodiment is bonded (i.e., bonded) to a support by a bonding layer. The bonding layer may be composed of a solder containing one or more selected from the group consisting of tin, indium, and zinc, and may further comprise a solder containing indium. Since the electrical conductivity and thermal conductivity of the target are likely to be high, the bonding layer is preferably composed of a solder containing indium. When the bonding layer is a solder containing indium, the target of this embodiment may have a layer for improving wettability (hereinafter also referred to as a "barrier layer") between the gallium nitride sintered body and the bonding layer. This improves the wettability of the sintered body to indium, resulting in a stronger bond between the sintered body and the bonding layer. The barrier layer may be composed of a component that is highly wettable to indium, and is preferably at least one of nickel and chromium. On the other hand, due to increased costs, the target of this embodiment preferably does not have a layer containing tungsten (W), and it is particularly preferable not to have a layer containing tungsten as a barrier layer.

[0050] The support in the target of this embodiment is preferably one or more selected from the group consisting of copper, stainless steel, and titanium, and more preferably copper. The shape of the support may be any desired shape depending on the shape of the sintered body of this embodiment, and examples thereof include at least one of a flat plate shape and a cylindrical shape, as well as other shapes suitable for the application.

[0051] [Film formation method] The sintered body of this embodiment can be used as a sputtering target, which can form a gallium nitride sputtered film, more specifically a p-type gallium nitride sputtered film. The sputtered film is a so-called laminated film formed on a substrate by sputtering using the sputtering target of this embodiment, and a laminated substrate having a sputtered film can be obtained by sputtering using the sputtering target of this embodiment. Preferred conditions for the film formation method (sputtering method) using the sputtering target of this embodiment are shown below.

[0052] The sputtering method is one or more selected from the group consisting of DC sputtering, pulsed DC sputtering, RF sputtering, AC sputtering, DC magnetron sputtering, RF magnetron sputtering, and ion beam sputtering, and preferably at least one of DC magnetron sputtering and RF magnetron sputtering, with RF magnetron sputtering being preferred.

[0053] The sputtering gas may be any gas used in sputtering, including an inert gas, and at least one of argon gas and nitrogen gas, with nitrogen gas being preferred. When sputtering is performed using the target of this embodiment, the surface of the resulting sputtered film is likely to be smooth, so the sputtering gas is preferably a nitrogen-containing gas, and preferably a mixed gas of argon and nitrogen. The mixed gas preferably contains an excess of nitrogen, and the nitrogen / (nitrogen + argon) partial pressure ratio [Pa / Pa] is preferably greater than 0.5, 0.7 or greater, or 0.9 or greater. When nitrogen gas alone is used, the nitrogen / (nitrogen + argon) partial pressure ratio is 1.0.

[0054] The flow rate of the sputtering gas is 5 ml / min or more, or 10 ml / min or more, and 100 ml / min or less, or 70 ml / min or less. The flow rate of the sputtering gas is 5 ml / min to 100 ml / min or less, or 10 ml / min to 70 ml / min. The gas pressure of the sputtering gas is 0.05 Pa or more, or 0.1 Pa or more, and may be 3 Pa or less, 2 Pa or less, or 1 Pa or less, and examples thereof include 0.05 Pa to 3 Pa or 0.1 Pa to 2 Pa or 0.1 Pa to 1 Pa.

[0055] In order to generate plasma stably, the discharge power density in sputtering is set to 0.1 W / cm ２ or more than 0.3 W / cm ２ or more, and 5 W / cm ２ The discharge power density in sputtering is 0.1 W / cm or less. ２ More than 5W / cm ２ or less, or 0.3 W / cm ２More than 5W / cm ２ The following are included:

[0056] The substrate may be appropriately selected depending on the desired film and substrate stack (hereinafter simply referred to as "stack"), and may be, for example, one or more selected from the group consisting of a glass substrate, an alumina substrate, a silicon substrate, a gallium nitride substrate, an aluminum nitride substrate, and a silicon carbide substrate, or one or more selected from the group consisting of an alumina substrate, a silicon substrate, and a gallium nitride substrate. The sputtering method and conditions may be appropriately selected depending on the desired sputtered film.

[0057] The substrate temperature during film formation by sputtering (hereinafter also referred to as "film formation temperature") is optional and may be 10°C or higher or 20°C or higher, or 800°C or lower. When the film formation rate is to be increased, the film formation temperature may be 100°C or higher or 300°C or higher, and 800°C or lower or 500°C or lower. Examples of film formation temperatures include 10°C or higher and 800°C or lower, 20°C or higher and 800°C or lower, 100°C or higher and 800°C or lower, or 300°C or higher and 500°C or lower. The sputtering time (hereinafter also referred to as "film formation time") may be appropriately set depending on the sputtering conditions, the size of the substrate, and the desired thickness of the sputtered film, and may be, for example, 1 minute or higher or 10 minutes or higher, and 5 hours or lower or 1 hour or lower. Examples of film formation times include 1 minute to 5 hours or lower, or 10 minutes to 1 hour.

[0058] By such sputtering, a gallium nitride film, a gallium nitride film containing a dopant element, or a gallium nitride sputtered film containing a dopant element can be obtained, i.e., a laminated substrate having a gallium nitride film, a laminated substrate having a gallium nitride film containing a dopant element, or a laminated substrate having a gallium nitride sputtered film containing a dopant element can be obtained.

[0059] The thickness of the gallium nitride film may be any thickness depending on the purpose, for example, 10 nm or more or 50 nm or more, and 200 nm or less or 150 nm or less, and preferably 10 nm or more and 200 nm or less, or 50 nm or more and 150 nm or less. The content of the dopant element in these gallium nitride films is equivalent to the content of the dopant element in the sintered body of this embodiment, for example, 15 mass ppm or more, 20 mass ppm or more, 50 mass ppm or more, 90 mass ppm or more, 0.05 mass% or more, 0.15 mass% or more, and 0.8 mass% or less, 0.55 mass% or less, 0.35 mass% or less, or 0.25 mass% or less. The content of the dopant element in the gallium nitride film may be, for example, 15 mass ppm or more and 0.8 mass% or less, 20 mass ppm or more and 0.8 mass% or less, 20 mass ppm or more and 0.55 mass% or less, 90 mass ppm or more and 0.55 mass% or less, or 0.15 mass ppm or more and 0.25 mass% or less.

[0060] The present disclosure will be described below with reference to examples. However, the present disclosure is not limited thereto. (Oxygen Content) The oxygen content of the sintered body was measured using an oxygen / nitrogen analyzer (device name: LECO ON736, manufactured by LECO Corporation) in accordance with a method in accordance with JIS H 1695. (Bulk Density of Sintered Body) The bulk density of the sintered body was measured in accordance with the bulk density measurement method in JIS R 1634. The mass was determined by weighing the mass of the sintered body that had been pretreated by a vacuum method using distilled water, and the volume was calculated from the shape measured using a micrometer.

[0061] (Dispersion Degree) The dispersion degree was determined by obtaining elemental mapping under the following conditions using an FE-EPMA (apparatus name: JXA-iHP200F, manufactured by JEOL Ltd.), and analyzing this with analysis software (software name: PC-EPMA Ver. 2.7.0, manufactured by JEOL Ltd.) to determine the standard deviation [Count] of the intensity of the dopant element. Observation: secondary electron image, backscattered electron image, elemental mapping Measurement method: wavelength dispersive (WDS) Acceleration voltage: 15 kV Probe current: 300 nA Analysis area: 1.0 × 5.0 mm Number of fields of view: 1 field of view per sample

[0062] (Dopant Content) The content of the dopant element was measured by GDMS (Glow Discharge Mass Spectrometry). (Flexural Strength) The three-point bending strength of the sintered body was measured by a method according to JIS R 1601. The measurement was performed twice, and the average value was taken as the flexural strength. (SIMS Measurement) The magnesium content in the sputtered film was measured using secondary ion mass spectrometry (SIMS). The measurement device used was a SIMS device (device name: Model 6600 Quadruple SIMS instrument, manufactured by Physical Electronics PHI).

[0063] Example 1: A mixed powder of gallium nitride and metallic gallium with a gallium ratio of 0.48 was mixed with magnesium powder to obtain a raw material powder so that the magnesium content was 100 mass ppm (0.01 mass%). 8 g of the raw material powder was filled into a rectangular mold measuring 10 mm in length and 40 mm in width, and then uniaxially pressed at a pressure of 100 MPa to obtain a primary compact. The primary compact was then cold isostatically pressed at a pressure of 300 MPa to obtain a CIP-treated body. The density of the obtained CIP-treated body (molded body, green compact) was 4.94 g / cm. ３ It was.

[0064] The CIP-treated body was placed on an alumina setter and then placed in a tubular furnace. After placement, it was sintered under the following conditions to obtain a rectangular magnesium-containing gallium nitride sintered body measuring 10 mm long x 40 mm wide and having a magnesium content of 100 ppm by mass, which was designated as the sintered body of this example. The dispersion of magnesium in the sintered body of this example was 347 counts. Ｇａ and W Ｎ were 83.18 and 16.72, respectively. Heat treatment atmosphere: ammonia flow atmosphere (ammonia gas flow rate 1000 mL / min) Holding temperature: 900°C Holding time: 3 hours

[0065] Example 2 A magnesium-containing gallium nitride sintered body having a rectangular shape of 10 mm length x 40 mm width and a magnesium content of 120 ppm by mass was obtained in the same manner as in Example 1, except that a mixed powder of gallium nitride and metallic gallium having a gallium ratio of 0.49 was mixed with magnesium powder to obtain a raw material powder so that the magnesium content was 1200 ppm by mass (0.12% by mass). The density of the obtained CIP-treated body was 4.93 g / cm ３ The dispersion degree of magnesium in the sintered body of this example was 359 counts. Ｇａ and W Ｎ were 83.08 and 16.70, respectively.

[0066] Example 3 A magnesium-containing gallium nitride sintered body having a rectangular shape of 10 mm length x 40 mm width and a magnesium content of 2100 ppm by mass was obtained in the same manner as in Example 1, except that a mixed powder of gallium nitride and metallic gallium having a gallium ratio of 0.49 was mixed with magnesium powder to obtain a raw material powder so that the magnesium content was 2100 ppm by mass (0.21% by mass). The density of the obtained CIP-treated body was 4.81 g / cm ３ The dispersion degree of magnesium in the sintered body of this example was 329 counts. Ｇａ and W Ｎwere 82.99 and 16.68, respectively.

[0067] Example 4 A magnesium-containing gallium nitride sintered body having a rectangular shape of 10 mm length x 40 mm width and a magnesium content of 3100 ppm by mass was obtained in the same manner as in Example 1, except that a mixed powder of gallium nitride and metallic gallium having a gallium ratio of 0.49 was mixed with magnesium powder to obtain a raw material powder so that the magnesium content was 3100 ppm by mass (0.31% by mass). The density of the obtained CIP-treated body was 4.80 g / cm ３ The dispersion degree of magnesium in the sintered body of this example was 341 counts. Ｇａ and W Ｎ were 82.91 and 16.66, respectively.

[0068] Example 5 A magnesium-containing gallium nitride sintered body having a rectangular shape of 10 mm length x 40 mm width and a magnesium content of 5100 ppm by mass was obtained in the same manner as in Example 1, except that a mixed powder of gallium nitride and metallic gallium having a gallium ratio of 0.49 was mixed with magnesium powder to obtain a raw material powder so that the magnesium content was 5100 ppm by mass (0.51% by mass). The density of the obtained CIP-treated body was 4.62 g / cm ３ The dispersion degree of magnesium in the sintered body of this example was 367 counts. Ｇａ and W Ｎ were 82.73 and 16.62, respectively.

[0069] Example 6 A magnesium-containing gallium nitride sintered body having a rectangular shape of 10 mm length x 40 mm width and a magnesium content of 20 ppm by mass was obtained in the same manner as in Example 1, except that a mixed powder of gallium nitride and metallic gallium having a gallium ratio of 0.49 was mixed with magnesium powder to obtain a raw material powder so that the magnesium content was 20 ppm by mass (0.02% by mass). The density of the obtained CIP-treated body was 4.95 g / cm ３The dispersion degree of magnesium in the sintered body of this example was 311 counts.

[0070] Comparative Example 1 A magnesium-containing gallium nitride molded body having a rectangular shape of 10 mm length x 40 mm width and a magnesium content of 5100 ppm by mass was produced in the same manner as in Example 1, except that the dopant source to be added was changed to magnesium nitride, and a mixed powder of gallium nitride and metallic gallium having a gallium ratio of 0.49 was mixed with magnesium nitride powder to obtain a raw material powder so that the magnesium content was 5100 ppm by mass (0.51% by mass). However, the molded body collapsed when removed from the mold, and it was not possible to obtain a molded body.

[0071] Comparative Example 2 A magnesium-containing gallium nitride sintered body was prepared using a method similar to Example 5 of Patent Document 2. Specifically, the dopant source was changed to magnesium nitride, and gallium nitride powder and magnesium nitride powder were mixed to obtain a raw material powder with a magnesium content of 140 ppm by mass (0.014% by mass). The obtained raw material powder was placed in a rectangular carbon mold measuring 17 mm long x 45 mm wide and then placed in a hot press. After the vacuum reached 0.004 Pa, sintering began. The temperature was increased to a holding temperature of 1100°C at a rate of 200°C / h while applying pressure. The compact was sintered by hot pressing for 3 hours at the holding temperature (1100°C) and a holding pressure of 50 MPa. After sintering, the temperature was lowered to approximately 50°C, and the sintered body was recovered to obtain a magnesium-containing gallium nitride sintered body with a magnesium content of 140 ppm by mass. This was designated the sintered body of this comparative example.

[0072] The results of the examples and comparative examples are shown in the table below.

[0073] All of the gallium nitride sintered bodies of the examples containing magnesium as a dopant element had a flexural strength of 10 MPa or more, no cracks after sintering, and no defects occurred during handling. In contrast, the sintered body of Comparative Example 2 had a flexural strength of less than 0.5 MPa despite having a dopant element content similar to that of Example 1, and it was confirmed that it had low mechanical strength. Furthermore, while Comparative Example 1, which used magnesium nitride as the dopant source, did not produce a sintered body, Example 5, by using magnesium as the dopant source, was able to produce a sintered body without defects even when the dopant element content was 100 mass ppm or more, or even 1000 mass ppm or more.

[0074] Example 7 (Preparation of Sputtered Film) A sintered body was obtained in the same manner as in Example 3, except that 50 g of raw material powder was filled into a cylindrical mold with an inner diameter of 50.8 mm, and this was ground into a disk-shaped sintered body with a diameter of 50.8 mm and a thickness of 3.0 mm. A circular sputtering target with a backing plate was prepared using the obtained sintered body, indium solder as a bonding layer, and a backing plate made of oxygen-free copper as a support. Using the obtained sputtering target, a film was formed on a substrate by sputtering under the following conditions, obtaining a laminated substrate having a magnesium-containing gallium nitride film (sputtered film). A sputtering apparatus (apparatus name: CMS-6400, manufactured by Comet Co., Ltd.) was used for sputtering. Sputtering method: RF magnetron sputtering Substrate: Sapphire substrate Film formation temperature: 25°C Sputtering gas: Nitrogen (nitrogen / (nitrogen + argon) partial pressure ratio = 1 [Pa / Pa]) Gas pressure: 0.3 Pa Output: 3.8 W / cm ２

[0075] 1 shows the results of measuring the magnesium concentration of the magnesium-containing gallium nitride film of the obtained laminated substrate (substrate with magnesium-containing gallium nitride film) by SIMS. From FIG. 1, it can be seen that magnesium is present continuously and uniformly along the depth direction from the surface (depth = 0 mm), and that the content is 3.3 × 10 ２０ It was confirmed that the aluminum content was 1500 mass ppm. In addition, since the aluminum content increased at a depth of 100 nm or more, it was confirmed that the thickness of the magnesium-containing gallium nitride film was 100 nm.

[0076] The entire contents of the specifications, claims, abstracts and drawings of Japanese Patent Application No. 2024-067760 filed on April 18, 2024, Japanese Patent Application No. 2024-154359 filed on September 6, 2024, and Japanese Patent Application No. 2025-011168 filed on January 27, 2025 are hereby incorporated by reference as the disclosure of the specification of the present disclosure.

Claims

1. A gallium nitride sintered body containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), vanadium (V), zinc (Zn) and cadmium (Cd), wherein the content of the dopant elements is 15 mass ppm or more, and the atomic ratio of gallium to the total of nitrogen and gallium is less than 0.

55.

2. The sintered body according to claim 1, having an oxygen content of 0 atm % or more and 0.4 atm % or less.

3. Bulk density of 4.00 g / cm ３ The sintered body according to claim 1 or 2.

4. A sintered body according to any one of claims 1 to 3, wherein the total content of silicon, germanium, tin and lead is 10 mass ppm or less.

5. A sintered body according to any one of claims 1 to 4, wherein the degree of dispersion of the dopant element is 500 or less.

6. A method for producing a sintered body according to any one of claims 1 to 5, comprising a sintering step of sintering, in a normal pressure nitriding atmosphere, a molded body containing a gallium nitride source and a dopant source, the atomic ratio of gallium to the total of nitrogen and gallium being less than 0.

55.

7. The method according to claim 6, wherein the gallium nitride source is at least one selected from the group consisting of gallium oxide, metallic gallium, and gallium chloride, and gallium nitride.

8. The manufacturing method according to claim 6 or 7, wherein the atmospheric pressure nitriding atmosphere is an atmosphere containing at least one of nitrogen and a nitrogen compound under atmospheric pressure.

9. A sputtering target comprising the sintered body according to any one of claims 1 to 5.

10. A film forming method using the sputtering target according to claim 9.

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