Gallium nitride sintered compact and method for producing same

Abstract

Provided are: a gallium nitride sintered compact which is capable of forming a sputtering film at a faster film-forming speed than conventional gallium nitride sintered compacts created by hot pressing; an industrial method for producing the same; a sputtering target provided with this sintered compact; and at least one film-forming method using this sputtering target. This gallium nitride sintered compact has a void ratio standard deviation of 1.0% or less as found from a cross sectional scanning electron micrograph.

Description

Gallium nitride sintered body and method for producing same

[0001] The present disclosure relates to a gallium nitride sintered body, and further to a gallium nitride sintered body suitable as a sputtering target.

[0002] Because gallium nitride sintered bodies, i.e., polycrystalline gallium nitride bodies, are less expensive than single-crystal gallium nitride, they have been considered as sputtering targets for forming gallium nitride films. However, compared to single-crystal gallium nitride, gallium nitride sintered bodies require improvements such as a high oxygen content, low strength, and low density, and various studies have been conducted to date to address these issues. In particular, gallium nitride has poor formability. Therefore, industrially, gallium nitride sintered bodies are produced by a hot press process in which gallium nitride powder filled into a carbon (C) mold is pressed, and molding and sintering proceed simultaneously (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 2020-75851

[0004] Hot pressing can introduce trace amounts of carbon below the detection limit into the sintered compact, resulting in sputtered films made from gallium nitride sintered compacts produced by hot pressing that tend to have high carbon contents.

[0005] The present disclosure aims to provide at least one of a gallium nitride sintered body that can form a sputtering film at a faster film formation rate than a gallium nitride sintered body produced by hot pressing, an industrial production method thereof, a sputtering target including the sintered body, and a film formation method using the sputtering target.

[0006] The present inventors have investigated sintering gallium nitride after molding, focusing on the moldability of gallium nitride. As a result, they have found that by controlling the composition of gallium nitride within a specific range, moldability is significantly improved, thereby making it possible to obtain a gallium nitride molded body without a heated atmosphere, and that such a molded body can be sintered by a sintering method other than hot pressing. Furthermore, they have found that sintered bodies obtained by sintering methods other than hot pressing have a structure different from conventional ones, and that this is suitable as a sputtering target.

[0007] That is, the present invention is as set forth in the claims, and the gist of the present disclosure is as follows. [1] A gallium nitride sintered body having a standard deviation of porosity of 1.0% or less as determined from a cross-sectional scanning electron microscope image. [2] The sintered body according to the above item [1], having an average porosity of 25% or less. [3] The sintered body according to the above item [1] or [2], having an oxygen content of 0.4 atm% or less. [4] The sintered body according to any one of the above items [1] to [3], having an atomic weight ratio of gallium to the total of gallium and nitrogen of 0.5 or less. [5] A sintered body having a bulk density of 4.0 g / cm ３ The sintered body according to any one of [1] to [4] above, wherein the sintered body has a Ga / (Ga+N) ratio exceeding 0.5 and includes the steps of: forming a powder containing gallium nitride and metallic gallium to obtain a molded body; and sintering the molded body in a nitriding atmosphere. [7] The manufacturing method according to [6] above, wherein the step of obtaining the molded body comprises uniaxially pressing the powder to obtain a primary molded body and subjecting the primary molded body to CIP molding. [8] The manufacturing method according to [6] or [7] above, wherein the nitriding atmosphere contains one or more gases selected from the group consisting of a nitrogen and hydrogen mixed gas, ammonia gas, hydrazine gas, and alkylamine gas. [9] A gallium nitride molded body having a Ga / (Ga+N) ratio exceeding 0.5.

[10] A sputtering target comprising the sintered body according to any one of [1] to [5] above.

[11] A method for manufacturing a sputtered film using the sputtering target according to

[10] above.

[0008] The present disclosure makes it possible to provide at least one of a gallium nitride sintered body that can form a sputtering film at a faster film formation rate than a gallium nitride sintered body produced by hot pressing, an industrial production method thereof, a sputtering target including the sintered body, and a film formation method that uses the sputtering target.

[0009] Schematic diagram showing the observation field for measuring the average porosity and SDρ.

[0010] Hereinafter, the present disclosure will be described with reference to an example embodiment.

[0011] [Gallium Nitride Sintered Body] The sintered body of this embodiment is a gallium nitride sintered body having a standard deviation of porosity of 1.0% or less as determined from a cross-sectional scanning electron microscope image.

[0012] This embodiment relates to a gallium nitride sintered body. A gallium nitride (GaN) sintered body is a sintered body containing gallium nitride as the main component (matrix, parent phase), and further a polycrystalline body of gallium nitride, a sintered body mainly composed of gallium nitride, so-called a gallium nitride sintered body. However, the sintered body of this embodiment may contain components other than gallium nitride, such as metallic gallium.

[0013] The sintered body of this embodiment may contain a dopant element. Examples of dopant elements for forming an n-type semiconductor include one or more selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). Examples of dopant elements for forming a p-type semiconductor include one or more selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), vanadium (Ba), zinc (Zn), and cadmium (Cd). Examples of dopant elements for forming an LED with any color include at least one of aluminum (Al) and indium (In). Examples of the main dopant elements contained in the sintered body of this embodiment include one or more selected from the group consisting of silicon, magnesium, aluminum, and indium.

[0014] The content of the dopant element may be a sufficiently small amount relative to the amount of gallium nitride, and may vary depending on the type of dopant element. For example, the content of the dopant element may be 0 atomic % or more or more than 0 atomic %, and 25 atomic % or less, 15 atomic % or less, 1 atomic % or less, or 0.1 atomic % or less.

[0015] An ideal sintered body has no voids and therefore has a porosity of 0%. However, realistic sintered bodies contain voids. The porosity of the sintered body of this embodiment is greater than 0%. The sintered body is preferably dense, and the average porosity may be 1% or more or 10% or more. In order to exhibit mechanical properties that are applicable as a sputtering target, the average porosity of the sintered body of this embodiment may be 25% or less or 20% or less.

[0016] The sintered body of this embodiment has a standard deviation of porosity (hereinafter also referred to as "SDρ") determined from a scanning electron microscope image of the cross section of 1.0% or less, preferably 0.8% or less. If SDρ exceeds this value, the structure of the sintered body, particularly the structure inside the sintered body, becomes non-uniform. When sputtering is performed using such a sintered body, particles are likely to be generated and the film formation rate becomes slow. Ideally, SDρ is preferably 0%. However, realistic sintered bodies have voids, and the distribution of the voids and the porosity vary. The SDρ of the sintered body of this embodiment can be, for example, greater than 0%, 0.1% or more, or 0.3% or more.

[0017] Furthermore, one of the reasons why the sintered body of this embodiment has such an SDρ is thought to be the low amount of carbon mixed in as an impurity. That is, carbon is difficult to sinter, and even if it is below the detection limit, the presence of carbon inhibits the sintering of gallium nitride. In contrast, the sintered body of this embodiment has a lower carbon content than conventional sintered bodies, making sintering more likely to proceed. As a result, it is thought to have a uniform texture. This can also be confirmed by the fact that the sputtered film (sputtered film) obtained using the sintered body of this embodiment has a lower carbon content.

[0018] In this embodiment, the average porosity and SDρ may be determined by observing the cross section of the sintered body with a scanning electron microscope (hereinafter also referred to as "SEM"). SEM observation may be performed using a general SEM (e.g., 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 or even cryo-ion milling to obtain the observation surface. As shown in FIG. 1, the observation fields may be a total of three fields: the center of the cut surface (observation field 1; FIG. 1 (101)), a point 150 μm away from the end of observation field 1 on a line (line segment A-A' in FIG. 1) passing through observation field 1 (observation field 2; FIG. 1 (102)), and a point 150 μm away from observation field 1 on the line (line segment A-A' in FIG. 1) on the line (observation field 3; FIG. 1 (103)) on the line 150 μm away from observation field 1 in the opposite direction from observation field 1 to observation field 2. The observation field is a rectangular area of ​​250 μm × 180 μm. That is, Figure 1 shows three rectangular observation fields of 250 μm × 180 μm arranged in a straight line with an interval of 150 μm. The conditions for SEM observation are as follows: Acceleration voltage: 5 kV Observation magnification: 500x

[0019] Next, the obtained SEM observation image is subjected to image analysis using a general image analysis software (for example, Image-Pro 10, manufactured by Hakuto Co., Ltd.) to detect the voids and their areas. ２ ] can be detected from the binarized image of the SEM observation image. The porosity of each SEM observation image can be calculated using the following formula: Porosity [%] = {void area [μm ２ ] / SEM observation area [μm ２ ]×100

[0020] The average porosity can be calculated by measuring the porosity at three measurement points, for example, the observation field 1, the observation field 2, and the observation field 3, and then calculating the average value. ２ This refers to the above surface area.

[0021] SDρ can be calculated from the standard deviation of the porosity at each measurement point.

[0022] The bulk density of the sintered body of this embodiment is 4.0 g / cm ３or more than 4.2 g / cm ３ By having such a bulk density, the sintered body of the present embodiment is likely to have sufficient strength when used as a sputtering target. The higher the bulk density, the more preferable it is. ３ Below, 4.8g / cm ３ or less than 4.7 g / cm ３ The following points can be mentioned.

[0023] In this embodiment, the "density" refers to a bulk density measured by a method in accordance with JIS R 1634, and the pretreatment may be carried out by a vacuum method using distilled water.

[0024] The average crystal grain size of the sintered body of this embodiment is optional, and may be 0.1 μm or more or 0.2 μm or more, and may be 0.5 μm or less or 0.3 μm or less, for example.

[0025] 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 in the same manner as for the average porosity. 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

[0026] Positions where the crystal orientation is tilted by 5° or more are considered to be crystal grain boundaries, and the regions surrounded by these crystal grain boundaries are considered to be crystal grains. The diameter of a circle corresponding to the area of ​​each crystal grain is calculated and used as the crystal grain size. SEM-EBSD observation is performed on crystal grains observed in three fields of view (e.g., 10,000 to 30,000 crystal grains per field) obtained in a similar manner to the average porosity, and the average crystal grain size within each field of view is calculated by image analysis. The average of these values ​​is used as the average crystal grain size. The sintered body of this embodiment has an atomic weight ratio of gallium to the sum of gallium and nitrogen ([mol / mol]; hereinafter, also referred to as the "Ga / (Ga+N) ratio") of 0.5 or less. With such a Ga / (Ga+N) ratio, the gallium contained in the sintered body of this embodiment is substantially gallium nitride only. In other words, metallic Ga is completely nitrided, and the sintered body does not contain metallic Ga. Ga / (Ga+N) is preferably less than 0.5 or 0.49 or less, and may be 0.45 or more, or 0.47 or more.

[0027] The oxygen content of the sintered body of this embodiment is preferably 0.4 atm% or less or 0.2 atm% or less. The sintered body of this embodiment preferably does not contain oxygen (i.e., the oxygen content is 0 atm%), but examples of the oxygen content include 0 atm% or more, more than 0 atm%, 0.01 atm% or more, and 0.1 atm% or more. With such an oxygen content, a film obtained by using this as a sputtering target is more likely to exhibit characteristics more suitable for applications such as light-emitting diodes and power devices. Specific examples of the oxygen content include 0.1 atm% or more and 0.3 atm% or less, and even 0.13 atm% or more and 0.2 atm% or less.

[0028] The composition of the sintered body of this embodiment can be considered to be the composition represented by the following formula: 100 = W Ｇａ [Mass%] +W Ｏ [Mass%] +W Ｎ [Mass%] +W Ｘ [Mass%] (1)

[0029] In equation (1), W Ｇａ , WＯ , W Ｎ and W Ｘ are the mass proportions of gallium, oxygen, nitrogen and the dopant element in the sintered body, respectively. Ｏ and W Ｎ is a value measured by a pyrolysis method in which the sintered body is pyrolyzed using a general oxygen and nitrogen analyzer (for example, LECO ON736, manufactured by Leco Corporation), and W Ｘ is a value measured by glow discharge mass spectrometry. Ｇａ Is W Ｏ , W Ｎ and W Ｘ This is the value calculated from the measured values ​​using equation (1).

[0030] The oxygen content 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 Ｘ / M Ｘ ) (2)

[0031] In equation (2), M Ｏ is the atomic weight of oxygen: 16.00 [g / mol], M Ｇａ is the amount of gallium in oxygen: 69.72 [g / mol], and M Ｎ is the atomic weight of nitrogen: 14.01 [g / mol]. Ｘ is the atomic weight of the dopant element, and examples thereof include the atomic weight of silicon: 28.09 [g / mol], the atomic weight of magnesium: 24.31 [g / mol], the atomic weight of aluminum: 26.98 [g / mol], and the atomic weight of indium: 114.82 [g / mol].

[0032] 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)

[0033] In order to exhibit mechanical properties suitable for use as a sputtering target, the sintered body of this embodiment preferably has a Vickers hardness of 100 HV or more or 150 HV or more. A moderately high Vickers hardness is sufficient, and examples of the Vickers hardness include 1000 HV or less, 300 HV or less, or 250 HV or less.

[0034] 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 a sintered compact 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.

[0035] For the same reason, the flexural strength of the sintered body of this embodiment is preferably 20 MPa or more, more preferably 30 MPa or more, and even more preferably 50 MPa, and can be, for example, 150 MPa or less, 100 MPa or less, or 60 MPa or less.

[0036] In the sintered body of this embodiment, the upper and lower limits of parameters such as the average porosity, SDρ, bulk density, average crystal grain size, Ga / (Ga+N) ratio, oxygen content, dopant element content, Vickers hardness, and bending strength may be any combination as described above.

[0037] The sintered body of this embodiment can be used for known applications of gallium nitride sintered bodies, but is particularly preferably used as a sintered body for a sputtering target. [Method for producing a sintered body] The method for producing a sintered body of this embodiment is a method for producing a sintered body, which has a Ga / (Ga+N) ratio of more than 0.5 and includes a step of molding a powder containing gallium nitride and metallic gallium to obtain a molded body, and a step of sintering the molded body in a nitriding atmosphere. This allows for industrial production of sintered bodies of any shape without being limited by the shape of the mold for the sintering furnace.

[0038] The powder (hereinafter also referred to as "raw material powder") to be subjected to a step of forming a powder containing gallium nitride and metallic gallium into a formed body (hereinafter also referred to as "forming step"), which has a Ga / (Ga+N) ratio of more than 0.5, and which contains gallium nitride and metallic gallium, may contain gallium nitride and metallic gallium, for example, a mixed powder of gallium nitride and metallic gallium.

[0039] The Ga / (Ga+N) ratio of the raw material powder is preferably greater than 0.5 and greater than or equal to 0.51. Having such a composition for the raw material powder makes it easier to mold without a heated atmosphere. One of the reasons why the raw material powder can be molded in this embodiment without a heated atmosphere, particularly an atmosphere where molding and sintering are performed simultaneously, is thought to be that the presence of metallic gallium between gallium nitride particles increases the flowability of the particles and increases the bonding strength between the particles. This results in a molded body that is substantially free of metallic gallium and has higher shape stability than a molded body made only of gallium nitride. The Ga / (Ga+N) ratio may be 0.6 or less or 0.55 or less.

[0040] The raw material powder may be a powder made of gallium nitride and metallic gallium. It may contain a dopant element to impart properties such as semiconductor properties according to the application. The dopant element may be a compound containing one or more elements selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), lead (Pb), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), indium (In), and aluminum (Al), or a compound containing one or more elements selected from the group consisting of silicon, magnesium, indium, and aluminum.

[0041] To obtain a sintered body exhibiting n-type semiconductor properties, the raw material powder may contain one or more elements selected from the group consisting of silicon, germanium, tin, and lead. Furthermore, to obtain a sintered body exhibiting p-type semiconductor properties, the raw material powder may contain one or more elements selected from the group consisting of magnesium, calcium, strontium, barium, and zinc. To obtain a sintered body with a modified band gap, the raw material powder may contain at least one of indium and aluminum. The type of dopant element contained in the raw material powder may be appropriately selected depending on the desired sintered body, and its content may be the same as the content of the dopant element in the sintered body of this embodiment described above. In other words, the content of the dopant element does not change before and after sintering, and the content of the dopant element contained in the sintered body is equal to the content of the element in the raw material powder used for sintering.

[0042] In order to reduce the oxygen content of the resulting sintered body, the oxygen content of the raw material powder is preferably 1 atm% or less, 0.5 atm% or less, or 0.3 atm% or less. The raw material powder 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. Examples of the oxygen content of the raw material powder include 0.005 atm% or more, or 0.01 atm% or more.

[0043] The oxygen content of the raw material powder in this embodiment is a value measured by a method in accordance with JIS H 1695.

[0044] The oxygen content is easily reduced, so the specific surface area of ​​the raw powder is 0.01 m ２ / g or more, and 1.5m ２ / g or less or 0.8m ２ It is preferable that the solubility is less than 1 / g.

[0045] The specific surface area of ​​the raw material powder in this embodiment is a value measured by a method in accordance with JIS R 1626:1996.

[0046] Since the strength of the resulting sintered body tends to be high, the raw material powder has a loose bulk density of 1.0 g / cm ３ or more or 1.4 g / cm ３Since moldability is easily improved, the loose bulk density is preferably 3.0 g / cm or more. ３ Less than or 2.5 g / cm ３ That's fine.

[0047] The loose bulk density of the raw material powder in this embodiment is a value measured by a method in accordance with JIS Z 2504.

[0048] The average particle size of the raw material powder is preferably 1 μm or more, 5 μm or more, or 9 μm or more, and is preferably 150 μm or less, 100 μm or less, or 80 μm or less.

[0049] The average particle diameter of the raw material powder in this embodiment is the average value of the circle-equivalent diameters determined from the areas of 1200±400 primary particles in a scanning electron microscope (hereinafter also referred to as "SEM") observation image obtained under the following conditions: Acceleration voltage: 10 kV Observation magnification: 50 to 5000 times

[0050] SEM observation in measuring the average particle size may be performed using a general SEM (for example, VE-9800, manufactured by KEYENCE Corp.). Alternatively, only primary particles whose entire particles can be confirmed in the SEM observation image may be measured, and multiple SEM observation images may be used so as to obtain the above-mentioned particle number.

[0051] In the compacting step, the raw material powder is compacted to obtain a compact. The compacting method may be any method that can obtain a compact having the desired shape, and examples include at least one of uniaxial press compacting and cold isostatic pressing (hereinafter also referred to as "CIP") compacting. A compact (green compact) is obtained by these compacting methods. In the compacting step, the raw material powder is preferably compacted without heating, and the raw material powder is preferably compacted at room temperature (25±10°C). It is preferable that the Ga / (Ga+N) ratio does not change before and after compacting. In other words, it is preferable that the Ga / (Ga+N) ratio of the raw material powder and the Ga / (Ga+N) ratio of the compact are the same. A compacting method that does not change the Ga / (Ga+N) ratio before and after compacting has a high degree of freedom in the shape of the compact.

[0052] A particularly preferred molding method involves uniaxially pressing a raw material powder to obtain a primary compact, followed by CIP molding of the primary compact. The uniaxial pressing conditions may be any conditions that result in a primary compact having sufficient shape retention to prevent defects when subjected to CIP molding. Furthermore, such a molding method does not change the Ga / (Ga+N) ratio before and after molding. For example, the pressure of the uniaxial pressing may be 10 MPa or more or 25 MPa or more, and 200 MPa or less or 300 MPa or less. The CIP molding may be performed under any conditions that result in a molded body as described below, such as 100 MPa or more or 200 MPa or more, and 400 MPa or less or 500 MPa or less.

[0053] The manufacturing method of this embodiment includes a step of sintering a compact in a nitriding atmosphere (hereinafter also referred to as the "sintering step"). By providing a compact having a fixed shape as the object to be sintered, a sintered body having any size and shape derived from the size and shape of the compact can be obtained. Furthermore, compared to conventional sintering methods in which molding and sintering are performed in one step, such as hot pressing (hereinafter also referred to as "HP") processing, a larger sintered body can be obtained.

[0054] The compact to be subjected to the sintering step may be any compact having a composition similar to that of the raw material powder, and may include a compact having a Ga / (Ga + N) ratio of more than 0.5 and containing gallium nitride and metallic gallium. The Ga / (Ga + N) ratio of the compact is preferably 0.51 or more. The Ga / (Ga + N) ratio of the compact may be 0.6 or less or 0.55 or less.

[0055] The raw material powder of this embodiment does not require molding in a heated atmosphere, so that a gallium nitride molded body having a desired shape can be obtained. The shape of the molded body may be any desired shape, such as one or more selected from the group consisting of a disk, a columnar shape, a rectangular shape, a polyhedral shape, and a cone shape, or any other shape depending on the purpose or application.

[0056] The size of the compact is arbitrary, but since the raw material powder of this embodiment can be molded in an unheated atmosphere such as at room temperature, a large compact can also be obtained. For example, a plate-shaped or disk-shaped compact can be given as a compact suitable as a precursor of a sintered body used as a sputtering target. Because the raw material powder has high moldability, the compact can be made to have an area of ​​100 mm ２ or more or 1,000 mm ２ The surface area may be 100,000 mm or more. ２ Below, 20,000mm ２ Less than or equal to 5,000 mm ２ The following can be exemplified.

[0057] The specific shape of the molded body is 5 mm in diameter. ２ More than or equal to 10 mm ２ or more and 300 mm ２ Less than or equal to 150 mm ２ The following disk shapes can be exemplified:

[0058] The measured density of the molded body is 3.0 g / cm ３ or more than 3.6 g / cm ３ or more, and 5.8 g / cm ３ or less than 5.5 g / cm ３ The following points can be mentioned.

[0059] The measured density of the molded body in this embodiment is a value measured by a method in accordance with JIS Z 8807.

[0060] In the sintering process, the compact is sintered in a nitriding atmosphere. Sintering in a nitriding atmosphere nitrides the metallic gallium in the compact, converting it into gallium nitride. This results in a sintered compact having the Ga / (Ga+N) ratio of this embodiment. Conventionally, gallium nitride sintered compacts (polycrystalline compacts) have been sintered by simultaneously molding and sintering them using HP processing. In HP processing, raw material powder is filled into a mold and then pressurized, so the shape of the resulting compact is limited by the shape of the mold, and impurities from the mold are likely to be introduced. In contrast, in this embodiment, a pre-shaped compact is sintered without pressure, eliminating the need for a mold during sintering. In other words, the shape of the compact is independent of the mold installed in the HP apparatus. This allows for greater flexibility in the shape of the compact. Furthermore, carbon molds are primarily used in industrial HP processing. In contrast, the manufacturing method of this embodiment prevents the introduction of impurities, particularly carbon (C), from the mold. As a result, when a sputtering film is formed using a sputtering target including the sintered body of this embodiment, a sputtering film with a lower carbon content can be obtained. From the viewpoint of avoiding the inclusion of impurities, particularly carbon, it is preferable that the manufacturing method of this embodiment does not include HP treatment, particularly HP treatment using a carbon molding die.

[0061] In this embodiment, the nitriding atmosphere is an atmosphere in which the nitriding reaction proceeds, particularly an atmosphere in which the nitriding reaction proceeds but the oxidation reaction does not proceed. Therefore, the nitriding atmosphere includes not only a nitrogen atmosphere but also an atmosphere containing elements other than nitrogen. Examples of the nitriding atmosphere include an atmosphere containing at least one of nitrogen and a nitrogen compound, and preferably at least one selected from the group consisting of a nitrogen and hydrogen mixed gas, ammonia gas, hydrazine gas, and alkylamine gas, and further preferably at least one of ammonia gas and a nitrogen and hydrogen mixed gas, or even ammonia gas.

[0062] Particularly preferred nitriding atmospheres include a flow atmosphere, a nitrogen compound flow atmosphere, and even an ammonia flow atmosphere. A flow atmosphere, i.e., an atmosphere in which an atmospheric medium such as a nitrogen compound-containing gas flows, promotes the nitriding reaction of metallic gallium. This results in a more uniform composition of the resulting sintered body. The flow atmosphere may be one in which the atmospheric medium flows, and examples include a flow rate of 0.1 mL / min or more or 1 L / min or more. Meanwhile, 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 a flow rate of 20 L / min or less or 10 mL / min or less.

[0063] In the sintering step, it is preferable to sinter the compact (object to be sintered) without applying pressure, and it is more preferable to sinter the compact without applying molding pressure.

[0064] The holding temperature in the sintering step may be any temperature at which sintering of gallium nitride proceeds. Furthermore, unlike HP processing and the like, the molded body subjected to the sintering step has a fixed shape. Therefore, compared to sintering methods in which molding and sintering proceed simultaneously, such as HP processing, a sintered body with high density can be obtained even at a lower holding temperature. Therefore, examples of the sintering temperature include 1100°C or less, 1050°C or less, and 1000°C or less. On the other hand, examples of the holding temperature include 800°C or more, 900°C or more, and 950°C or more.

[0065] 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 at the above holding temperature, the holding time can be, for example, 1 hour or more and 20 hours or less, or even 2 hours or more and 10 hours or less.

[0066] In the manufacturing method of this embodiment, the upper and lower limits of parameters such as the Ga / (Ga+N) ratio, the surface area of ​​the compact, the measured density of the compact, the flow rate of the atmospheric medium, the holding temperature and the holding time may be any combination as described above. [Sputtering Target] Next, a sputtering target including the sintered body of this embodiment will be described.

[0067] A sputtering target including the sintered body of this embodiment (hereinafter also referred to as "the target of this embodiment") is a sputtering target in which the sintered body of this embodiment is bonded to a support via a bonding layer.

[0068] The shape of the target in this embodiment is arbitrary, and examples thereof include at least one of a flat plate shape and a cylindrical shape, as well as other shapes suitable for the intended use.

[0069] In the target of this embodiment, the sintered body of this embodiment is joined (i.e., bonded) to a support by a bonding layer. The bonding layer may be composed of a solder containing one or more elements selected from the group consisting of tin, indium, and zinc. 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 (hereinafter also referred to as a "barrier layer") that improves wettability between the gallium nitride sintered body and the bonding layer. This improves the indium wettability of the sintered body, 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.

[0070] On the other hand, since this increases costs, it is preferable that the target of this embodiment does not have a layer containing tungsten (W), and it is particularly preferable that the target does not have a layer containing tungsten as a barrier layer.

[0071] The support in the target of this embodiment is preferably one or more selected from the group consisting of copper, stainless steel, and titanium. The shape of the support may be any desired shape according to 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. [Film Formation Method] Next, a method for producing a sputtered film (film formation method) using the target of this embodiment will be described.

[0072] A sputtered film is formed on a substrate by sputtering using the target of this embodiment, thereby forming a sputtered film, further a gallium nitride film, and further a gallium nitride thin film.

[0073] For example, the sputtering method may be 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.

[0074] The sputtering gas may be any gas used in sputtering, including an inert gas, argon gas, or at least one of nitrogen gas. When sputtering using the target of this embodiment, the sputtering gas is preferably a nitrogen-containing gas, and more preferably a mixed gas of argon and nitrogen, because the surface of the resulting sputtered film is likely to be smooth. The mixed gas preferably contains excess 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.

[0075] The flow rate of the sputtering gas is, for example, 5 ml / min or more, or 10 ml / min or more, and 100 ml / min or less, or 70 ml / min or less.

[0076] The gas pressure of the sputtering gas may be 0.05 Pa or more, or 0.1 Pa or more, and 3 Pa or less, or 2 Pa or less.

[0077] 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 following is fine.

[0078] The substrate may be appropriately selected depending on the desired laminate of the film and substrate (hereinafter also referred to as "laminate"), and examples thereof include 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, and further at least one of an alumina substrate, a silicon substrate, and a gallium nitride substrate.

[0079] The sputtering method and conditions can be appropriately selected depending on the desired sputtered film.

[0080] The temperature of the substrate during film formation by sputtering (hereinafter also referred to as "film formation temperature") is arbitrary and may be 10° C. or higher or 20° C. or higher, and may be 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 may be 800° C. or lower or 500° C. or lower, for example.

[0081] The sputtering time (hereinafter also referred to as "film formation time") may be set appropriately 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 more or 10 minutes or more, and 5 hours or less or 1 hour or less.

[0082] The present disclosure will be described below with reference to examples, but the present disclosure is not limited thereto.

[0083] (Average porosity and SDρ) The sintered body was cut to expose the cut surface at the center of the sintered body, and then a measurement surface was prepared by cryo-Ar ion milling the cut surface. Observation fields 1, 2, and 3 of the cut surface were observed using an SEM as shown in Figure 1. SEM observation was performed using a general SEM (device name: JSM-IT800, manufactured by JEOL Ltd.) under the following conditions: Acceleration voltage: 5 kV Observation magnification: 500x Next, the obtained SEM observation image was binarized using general image analysis software (Image-Pro 10, manufactured by Hakutosha), and then image analysis was performed to detect voids and their area. The porosity of the SEM observation image corresponding to each observation field was calculated using the following formula: Porosity [%] = {void area [μm ２ ] / SEM observation area [μm ２]} × 100 The average porosity was calculated by determining the porosity for each of three observation fields and then calculating the average value. SDρ was calculated from the standard deviation of the porosity for each observation field.

[0084] (Average Crystal Grain Size) SEM observations of three fields obtained in the same manner as in the measurement of the average porosity and SDρ were observed using a general EBSD device (device name: Symmetry, manufactured by Oxford Instruments). EBSD observations were performed under the following conditions: Acceleration voltage: 15 kV, Sample tilt: 70 degrees, Tilt correction: 0 degrees, Measurement magnification: 500x, Step size: 0.2 μm. Positions where the crystal orientation was tilted by 5° or more were considered to be grain boundaries, and the areas surrounded by the grain boundaries were considered to be crystal grains. The diameter of a circle corresponding to the area of ​​each crystal grain was calculated to determine the crystal grain size. The average of the crystal grains observed in the three fields obtained in the same manner as in the measurement of the average porosity was used as the average crystal grain size.

[0085] (Bulk Density) The bulk density of the sintered body was measured according to JIS R 1634. Pretreatment was performed using a vacuum method using distilled water. (Composition) The oxygen [mass %] and nitrogen mass percentage [mass %] of the sintered body were measured by inert gas fusion-infrared absorption using an oxygen / nitrogen analyzer (device name: LECO ON736, manufactured by Leco Corporation). From the obtained oxygen and nitrogen mass percentages, the mass percentage of gallium was calculated using the above formula (1), the oxygen content [atm %] using the above formula (2), and the Ga / (Ga+N) ratio using the above formula (3). (Vickers Hardness) The Vickers hardness of the sintered body was measured according to JIS Z 2244. Five measurements were taken for each measurement sample, and the average value was used as the Vickers hardness. (Measurement of flexural strength) The three-point bending strength of the sintered body was measured according to JIS R 1601. The measurement was performed twice, and the average value was taken as the flexural strength. (Carbon content) The carbon content of the sputtered film was measured using secondary ion mass spectrometry (SIMS). The measurement was performed at a depth of 50 nm from the thin film surface.

[0086] Example 1: 8 g of a mixed powder of metallic gallium and gallium nitride with a Ga / (Ga+N) ratio of 0.52 was prepared and filled into a rectangular mold measuring 10 mm in length and 40 mm in width. After filling, the mixture was 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.

[0087] The CIP-treated body was placed on an alumina setter and sintered in an atmosphere furnace under the following conditions to obtain a sintered body of this example: Heat treatment atmosphere: Ammonia flow atmosphere (ammonia gas flow rate: 6000 mL / min) Holding temperature: 980°C Holding time: 5 hours

[0088] Example 2 A sintered body of this example was obtained in the same manner as in Example 1, except that 8 g of a mixed powder of metallic gallium and gallium nitride with a Ga / (Ga+N) ratio of 0.51 was used.

[0089] Example 3 A sintered body of this example was obtained in the same manner as in Example 1, except that 8 g of a mixed powder of metallic gallium and gallium nitride with a Ga / (Ga+N) ratio of 0.53 was used.

[0090] Example 4 A sintered body of this example was obtained in the same manner as in Example 1, except that 8 g of a mixed powder of metallic gallium and gallium nitride with a Ga / (Ga+N) ratio of 0.54 was used.

[0091] Comparative Example 1: 8 g of a mixed powder of metallic gallium and gallium nitride with a Ga / (Ga+N) ratio of 0.48 was filled into a rectangular mold measuring 10 mm in length and 40 mm in width. After filling, the mixture was subjected to uniaxial press molding at a pressure of 100 MPa for 180 seconds. However, defects such as chipping and cracking occurred upon removal from the mold, and a primary compact could not be obtained.

[0092] From the examples and comparative examples, it was confirmed that, compared with gallium nitride-rich powders, metallic gallium-rich mixed powders having a Ga / (Ga+N) ratio of 0.5 or more have high moldability and can be molded even without high temperatures.

[0093] Comparative Example 2 300 g of a gallium nitride mixed powder having a Ga / (Ga+N) ratio of 0.48 was filled into a carbon press mold having a diameter of 130 mm, and this was subjected to a hot press treatment under the following conditions.

[0094] Heat treatment atmosphere: vacuum Heating rate: 200°C / hour Holding temperature: 1060°C Holding time: 3 hours Press pressure: 40 MPa Heating rate: 200°C / hour After the HP treatment, a gallium nitride sintered body was obtained from the carbon press mold, and this was used as the sintered body of this comparative example.

[0095] The results of the examples and comparative examples are shown in the table below.

[0096]

[0097] The sintered bodies of the Examples had an SDρ of 1.0% or less, and it was confirmed that the structures of the sintered bodies were more uniform than the sintered body of Comparative Example 2. The average crystal grain sizes were 2.5 μm for Example 1, 2.1 μm for Example 3, 1.6 μm for Example 4, and 2.4 μm for Comparative Example 2.

[0098] Example 5 A sintered body of this example was obtained in the same manner as in Example 1, except that the heat treatment atmosphere was an ammonia flow atmosphere (ammonia gas flow rate: 2000 mL / min). The sintered body of this example had a Ga / (Ga+N) ratio of 0.48 and an oxygen content of 0.23 atm %.

[0099] Example 6 A sintered body of this example was obtained in the same manner as in Example 2, except that the holding temperature was 930°C and the holding time was 1 hour. The sintered body of this example had a Ga / (Ga+N) ratio of 0.49 and an oxygen content of 0.29 atm%.

[0100] Example 7 A sintered body of this example was obtained in the same manner as in Example 3, except that the holding temperature was 1030°C and the holding time was 1 hour. The sintered body of this example had a Ga / (Ga+N) ratio of 0.49 and an oxygen content of 0.10 atm%.

[0101] The oxygen content of the sintered body of Example 1 was 0.17 atm%, while the oxygen content of the sintered body of Example 5 was 0.23 atm%, confirming that the reduction proceeded more easily as the ammonia flow rate increased, resulting in a decrease in the oxygen content. The oxygen content of the sintered body of Example 2 was 0.16 atm%, while the oxygen content of the sintered body of Example 6 was 0.29 atm%, confirming that the oxygen content decreased as the sintering temperature increased. The oxygen content of the sintered body of Example 3 was 0.15 atm%, while the oxygen content of the sintered body of Example 7 was 0.10 atm%, confirming that the oxygen content decreased as the sintering temperature increased, regardless of the ammonia flow rate (6000 mL / min or 2000 mL / min). It is believed that the decrease in oxygen content due to the increase in the holding temperature had a greater impact than the increase in oxygen content due to the decrease in ammonia flow rate.

[0102] Example 8 A sintered body of this example was obtained in the same manner as in Example 1, except that 95 g of a mixed powder of metallic gallium and gallium nitride having a Ga / (Ga+N) ratio of 0.52 was used and that it was filled into a rectangular mold of 60 mm x 60 mm.

[0103] Example 9 A sintered body of this example was obtained in the same manner as in Example 1, except that 380 g of a mixed powder of metallic gallium and gallium nitride having a Ga / (Ga+N) ratio of 0.52 was used and that it was filled into a circular mold having a diameter of 135 mm.

[0104] The evaluation results of the sintered bodies obtained in these examples are shown in the table below.

[0105]

[0106] From the above table, it can be seen that in the examples, not only circular but also rectangular sintered bodies can be produced. ２ More than 10,000 mm ２It was confirmed that large sintered bodies as described above could be obtained. [Evaluation of Film Formation] The sintered bodies obtained in Example 8 and Comparative Example 2 were each machined into a disk shape with a diameter of 101 mm. An indium-based solder material was applied to the machined sintered body, and a copper backing plate was joined to this to form a sputtering target.

[0107] Using the obtained sputtering target, sputtering was carried out under the following conditions to form a gallium nitride film (sputtered film).

[0108] Discharge method: RF sputtering Substrate: Al ２ O ３ Sputtering gas: nitrogen gas Sputtering gas flow rate: 50 sccm Sputtering gas pressure: 0.5 Pa Discharge power density: 2.5 W / cm ２ Film formation temperature: 25° C. Film formation time: 60 minutes The results of the film formation evaluation are shown in the table below. However, the carbon content of Example 9 was not measured and is indicated by "-".

[0109]

[0110] The sintered body of Example 8 is equivalent to the sintered body of Example 1 except for the sintered body size, and has a smaller SDρ than the sintered body of Comparative Example 2. It was confirmed that the target of the Example had a film formation rate 1.9 times or more faster than the target of Comparative Example 2, and exhibited a faster film formation rate. Furthermore, the carbon content of the gallium nitride film obtained from the target of the Example was ⅓ or less of the gallium nitride film obtained from Comparative Example 2, and it was confirmed that a sputtered film with a low carbon content could be obtained.

[0111] This application is based on a Japanese patent application (Patent Application No. 2022-095341) filed on June 13, 2022, the entire contents of which are incorporated by reference. In addition, all references cited herein are incorporated in their entirety.

[0112] 100 Sintered body 101 Observation field 1 102 Observation field 2 103 Observation field 3

Claims

1. A gallium nitride sintered body having a standard deviation of porosity of 1.0% or less as determined from a cross-sectional scanning electron microscope image.

2. 2. The sintered body according to claim 1, having an average porosity of 25% or less.

3. 3. The sintered body according to claim 1, having an oxygen content of 0.4 atm % or less.

4. 3. The sintered body according to claim 1, wherein the atomic ratio of gallium to the total of gallium and nitrogen is 0.5 or less.

5. Bulk density is 4.0 g / cm ３ The sintered body according to claim 1 or 2.

6. 2. A method for producing a sintered body according to claim 1, comprising the steps of: forming a powder having a Ga / (Ga+N) ratio of more than 0.5 and containing gallium nitride and metallic gallium to obtain a molded body; and sintering the molded body in a nitriding atmosphere.

7. The method according to claim 6, wherein the step of obtaining the green body comprises a step of obtaining a primary green body by uniaxial press molding of the powder, and subjecting the primary green body to CIP molding.

8. 8. The method according to claim 6, wherein the nitriding atmosphere contains one or more gases selected from the group consisting of a mixed gas of nitrogen and hydrogen, ammonia gas, hydrazine gas, and an alkylamine gas.

9. A gallium nitride body having a Ga / (Ga+N) ratio of more than 0.

5.

10. A sputtering target comprising the sintered body according to claim 1 or 2.

11. A method for producing a sputtered film, using the sputtering target according to claim 10.