Sintered body of gallium nitride

Abstract

The present invention provides at least one of a sintered body of gallium nitride or a method for producing same, wherein the sintered body has high flexural strength despite containing 1.0 mass% or more of a dopant element, and is capable of directly forming a P-type gallium nitride film. The sintered body of gallium nitride contains an alloy containing at least one dopant element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), and cadmium (Cd), wherein the content of the dopant element is 1.0 mass% or more, and the content of oxygen is 0.6 at% or less.

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) films are used as materials for LEDs and power semiconductors, and p-type GaN films are required for semiconductor device fabrication.

[0003] 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.

[0004] Japanese Patent Publication No. 2008-091470 Japanese Patent Publication No. 2020-059644

[0005] However, the sputtering target for p-type gallium nitride thin films of Patent Document 2 has a significantly reduced bending strength as the content of the additive components increases, making it difficult to process into a sputtering target and prone to defects during handling, such as transportation.

[0006] An object of the present disclosure is to provide at least one of a gallium nitride sintered body and a method for producing the same, which has high flexural strength despite containing 1.0 mass % or more of a dopant element and is capable of directly forming a p-type gallium nitride film.

[0007] In this disclosure, we have investigated sputtering targets capable of directly depositing p-type gallium nitride films, focusing on the state of the dopant element and the sinterability of the sintered body. As a result, we have found that by using a specific raw material as a dopant source, we can obtain a gallium nitride sintered body containing a dopant element that has a higher flexural strength than conventional sputtering targets capable of directly depositing p-type gallium nitride films and that can directly deposit p-type gallium nitride films.

[0008] That is, the present invention is as defined in the claims, and the gist of the present disclosure is as follows.

[0009] [1] A gallium nitride sintered body comprising an alloy containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn) and cadmium (Cd), wherein the content of the dopant element is 1.0 mass% or more and the oxygen content is 0.6 atm% or less.

[0010] [2] The sintered body according to the above [1], wherein the alloy is an alloy of the dopant element and aluminum.

[0011] [3] The sintered body according to the above [1] or [2], wherein the total content of silicon, germanium, tin and lead is 10 mass ppm or less.

[0012] [4] The measured density is 3.50 g / cm ３ The sintered body according to any one of the above [1] to [3].

[0013] [5] The sintered body according to any one of [1] to [4] above, having a bending strength of 55 MPa or more.

[0014] [6] A method for producing a sintered body according to any one of the above [1] to [5], comprising: a sintering step of hot pressing a raw material powder containing a gallium nitride source and a dopant source made of an alloy containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), and cadmium (Cd), the raw material powder having a dopant source content of 1.0 mass% or more calculated as the dopant element, at a holding temperature of 400°C or higher and a holding pressure of 30 MPa or higher.

[0015] [7] The method according to the above [6], wherein the oxygen content of the gallium nitride source is less than 0.4 atm %.

[0016] [8] A sputtering target comprising the sintered body according to any one of [1] to [5] above.

[0017] [9] A method for producing a sputtered film using the sputtering target according to [8] above.

[0018] The present disclosure can provide at least one of a gallium nitride sintered body, a sputtering target, and a method for producing the same, which have high flexural strength despite containing 1.0 mass % or more of a dopant element and are capable of directly forming a p-type gallium nitride film.

[0019] SEM observation image of the sintered body of Example 1 (scale in the figure is 50 μm) Elemental mapping of gallium (Ga) of the sintered body of Example 1 (scale in the figure is 50 μm) Elemental mapping of magnesium (Mg) of the sintered body of Example 1 (scale in the figure is 50 μm) Elemental mapping of aluminum (Al) of the sintered body of Example 1 (scale in the figure is 50 μm) Secondary ion mass spectrometry (SIMS) results for the sputtered film obtained in Example 5

[0020] 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.

[0021] [Sintered body] The sintered body of this embodiment is a gallium nitride sintered body containing an alloy containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), and cadmium (Cd), characterized in that the content of the dopant elements is 1.0 mass% or more. The sintered body of this embodiment has mechanical strength that makes it less likely to develop defects even during handling such as transportation, and can be used as a sputtering target for directly depositing a p-type gallium nitride film (hereinafter also referred to as a "p-type GaN film").

[0022] The sintered body of this embodiment relates to a gallium nitride (GaN) sintered body. The gallium nitride sintered body of this embodiment is a sintered body whose main component is gallium nitride, a so-called gallium nitride sintered body. The sintered body of this embodiment includes an alloy containing, in addition to gallium nitride, one or more dopant elements selected from the group consisting of beryllium, magnesium, calcium, strontium, vanadium, zinc, and cadmium (hereinafter also referred to as "p-type dopant elements"). Furthermore, in addition to the alloy of gallium nitride and p-type dopant elements, metallic gallium may also be included.

[0023] The dopant element is one or more selected from the group consisting of beryllium, magnesium, calcium, strontium, vanadium, zinc, and cadmium. For ease of industrial application, the dopant element is preferably at least one of magnesium and zinc, and more preferably magnesium.

[0024] The content of the dopant element is 1.0 mass% or more, and preferably 4.0 mass% or more, 4.5 mass% or more, or 6.0 mass% or more. Because the sintered body of this embodiment contains a dopant alloy, a stable sintered body can be obtained even if it contains such an amount of dopant element. The more dopant element, the easier it is to obtain a film exhibiting p-type characteristics. The upper limit of the dopant element content of the sintered body of this embodiment is 20.0 mass% or less, 16.0 mass% or less, or 12.0 mass% or less. The content of the dopant element of the sintered body of this embodiment is 1.0 mass% or more to 20.0 mass% or less, 4.0 mass% or more to 20.0 mass% or less, 4.5 mass% or more to 16.0 mass% or less, or 6.0 mass% or more to 12.0 mass% or less.

[0025] The sintered body of this embodiment includes an alloy containing a p-type dopant element (hereinafter also referred to as a "dopant alloy"). By including the p-type dopant element as an alloy, the stability of the dopant element is improved, and volatilization of the dopant element during the production of the sintered body is substantially suppressed. As a result, the sintered body of this embodiment has a high content of the dopant element. The dopant alloy may be an alloy consisting of a p-type dopant element and a metal element that forms an alloy with the p-type dopant. Examples of metal elements that form an alloy with the p-type dopant element include Group III metal elements, and are preferably at least one selected from the group consisting of aluminum, indium, and thallium, and further preferably at least one of aluminum and indium, or even aluminum.

[0026] The dopant alloy contained in the sintered body of this embodiment is preferably, for example, an aluminum alloy of a p-type dopant element, and more preferably an aluminum alloy of one or more elements selected from the group consisting of zinc and magnesium, and more preferably a magnesium-aluminum alloy.

[0027] The content of the dopant alloy may be any amount that allows the content of the dopant element in the sintered body of this embodiment to be the above-mentioned amount, and is, for example, preferably 7.5 mass% or more, 8.0 mass% or more, or 10.0 mass% or more, and preferably 35.0 mass% or less, 30.0 mass% or less, or 25.0 mass% or less. The content of the dopant element in the sintered body of this embodiment may be 7.5 mass% or more and 35.0 mass% or less, 8.0 mass% or more and 30.0 mass% or less, or 10.0 mass% or more and 25.0 mass% or less.

[0028] The sintered body of this embodiment preferably does not contain any elements that may reduce the p-type characteristics of the film obtained therefrom (0 mass ppm), preferably does not contain silicon (Si), 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"), and even more preferably does not contain any Group IV metal elements. The total content of silicon, germanium, tin, and lead in the sintered body of this embodiment is preferably, for example, 10 mass ppm or less, more preferably 5 mass ppm or less. On the other hand, the sintered body of this embodiment may contain an n-type dopant element as an inevitable impurity, for example, the content of the n-type dopant element may be 0 mass ppm or more or more than 0 mass ppm.

[0029] The sintered body of this embodiment may contain elements other than the dopant alloy and gallium nitride, such as unavoidable impurities, as long as the effects of the sintered body are not impaired.

[0030] On the other hand, in order to enhance the p-type characteristics of the film obtained from the sintered body of this embodiment, the oxygen content of the sintered body of this embodiment is 0.6 atm% or less. With such an oxygen content, leakage current is less likely to occur when the gallium nitride film obtained from the sintered body of this embodiment is used in applications such as light-emitting diodes and power devices. An ideal gallium nitride sintered body does not contain 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 of the oxygen content include 0 atm% or more, more than 0 atm%, or 0.1 atm% or more. The oxygen content of the sintered body of this embodiment tends to decrease with an increase in the dopant alloy, but examples include 0.4 atm% or less, 0.35 atm% or less, or 0.3 atm% or less. The oxygen content of the sintered body of this embodiment may be 0 atm % or more and 0.6 atm % or less, more than 0 atm % and 0.6 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.

[0031] In this embodiment, the composition of the sintered body may be determined from the following formula.

[0032] 100 [mass%] = W Ｇａ +W Ｏ +W Ｎ +W Ａｌｌｏｙ (1) In the above equation, W Ｇａ , W Ｏ , W Ｎ and W Ａｌｌｏｙ are the mass percentages [mass %] of gallium, oxygen, nitrogen, and the dopant alloy in the sintered body, respectively.

[0033] In addition, W 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 (for example, LECO ON736, manufactured by Leco Corporation), respectively.

[0034] When the sintered body of the present embodiment contains elements such as inevitable impurities, the content thereof is a value [mass%] measured by glow discharge mass spectrometry. Due to differences in measurement methods, when the sintered body of the present embodiment contains elements such as inevitable impurities, the composition may apparently exceed 100 mass%.

[0035] In this embodiment, the oxygen content of the sintered body is measured by a method in accordance with JIS H 1695 and is a value calculated from the following formula.

[0036] Oxygen content [atm%] = (W Ｏ / M Ｏ ) / {(W Ｇａ / M Ｇａ ) + (W Ｎ / M Ｎ ) + (W Ｏ / M Ｏ ) + (W Ａｌｌｏｙ / M Ａｌｌｏｙ )} × 100 (2) In the above formula, W Ｇａ , W Ｏ , W Ｎ and W Ａｌｌｏｙ is the same as equation (1), and 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 Ｎ is the atomic weight of nitrogen: 14.01 [g / mol]. Ａｌｌｏｙ is the atomic weight of the dopant alloy. The atomic weights of the dopant elements contained in the dopant alloy 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. Furthermore, examples of metal elements that form an alloy with the p-type dopant contained in the dopant alloy include 26.98 g / mol for aluminum, 114.82 g / mol for indium, and 204.38 g / mol for thallium.

[0037] 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") [mol / mol] is preferably less than 0.55 or 0.50 or less. If the gallium ratio is 0.55 or more, handling properties are reduced. The gallium ratio is preferably 0 or more, more than 0, 0.10 or more, or 0.30 or more, and is preferably 0 or more but less than 0.55, more 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.

[0038] In this embodiment, the gallium ratio is a value calculated from the following formula.

[0039] Ga / (Ga+N) ratio = (W Ｇａ / M Ｇａ ) / {(W Ｇａ / M Ｇａ ) + (W Ｎ / M Ｎ )} (3) In the above formula, 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 is the mass ratio of gallium and nitrogen [mass%], 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].

[0040] The shape of the sintered body of this embodiment may be any shape depending on the purpose, and may be, for example, one or more selected from the group consisting of plate, disk, cylinder, cube, rectangular parallelepiped, polyhedron, column, pillar, and cone, or any shape that can be used as a sputtering target. In addition, the sintered body of this embodiment is preferably a sintered body in a state sintered by hot pressing, i.e., a so-called hot-pressed body.

[0041] The higher the measured density of the sintered body of this embodiment, the better, but this varies depending on the composition. For example, the measured density of the sintered body of this embodiment is 3.50 g / cm ３ Above, 4.00g / cm ３ or more than 4.20 g / cm ３or more, and 5.00 g / cm ３ Below, 4.80g / cm ３ or less than 4.60 g / cm ３ and 3.50 g / cm ３ 5.00g / cm or more ３ Below, 4.00g / cm ３ 4.80g / cm or more ３ or less, or 4.20 g / cm ３ 4.60g / cm or more ３ It is preferable that:

[0042] In this embodiment, the "measured density" refers to the density [g / cm 3 ] measured by a method according to JIS R 1634:1998. ３ Pretreatment can be carried out by a vacuum method using distilled water.

[0043] The sintered body of this embodiment preferably has higher mechanical strength and a flexural strength that is less likely to cause defects when used as a sputtering target compared to conventional sintered bodies containing the same amount of dopant element. Specifically, the flexural strength is preferably 55 MPa or more, more preferably 60 MPa or more or 80 MPa or more. While a high flexural strength is preferred, the upper limit can be, for example, 200 MPa or less, 150 MPa or less, or 130 MPa or less. Examples of the flexural strength of the sintered body of this embodiment include 55 MPa or more and 200 MPa or less, 60 MPa or more and 150 MPa or less, or 80 MPa or more and 130 MPa or less.

[0044] 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.

[0045] The sintered body of this 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 GaN film.

[0046] [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. A preferred method for manufacturing the sintered body of this embodiment includes a method for manufacturing a sintered body (hereinafter also referred to as the "manufacturing method of this embodiment"), which includes a sintering step of hot-pressing a raw material powder containing a gallium nitride source and a dopant source made of an alloy containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), and cadmium (Cd), and having a dopant source content of 1.0 mass % or more calculated as the dopant element, at a holding temperature of 400°C or higher and a holding pressure of 30 MPa or higher.

[0047] In the firing step, raw material powder containing a gallium nitride source and a dopant source is provided.

[0048] 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 nitride, gallium oxide, metallic gallium, and gallium chloride, and further preferably gallium nitride, and further preferably gallium nitride powder. Gallium nitride powder preferred as the gallium nitride source is not particularly limited, but examples include gallium nitride powder produced by known methods, such as the method described in JP 2021-059483 A.

[0049] To reduce the oxygen content of the resulting sintered body, the oxygen content of the gallium nitride source is preferably less than 0.4 atm%, less than 0.3 atm%, or 0.2 atm% or less. The gallium nitride source preferably does not contain oxygen (i.e., the oxygen content is 0 atm%), but the oxygen content of the gallium nitride source may be 0.005 atm% or more, 0.01 atm% or more, or 0.1 atm% or more. Examples of the oxygen content of the gallium nitride source include 0.005 atm% or more and less than 0.4 atm%, 0.01 atm% or more and less than 0.3 atm%, and 0.1 atm% or more and 0.2 atm% or less.

[0050] The oxygen content of the gallium nitride source is a value calculated from the above-mentioned method and formula (3).

[0051] The gallium nitride source has an atomic ratio of gallium to the total of nitrogen and gallium (gallium ratio) of less than 0.55 and preferably 0.50 or less, and more preferably 0 or more, more than 0, 0.10 or more, or 0.30 or more. The gallium ratio of the gallium nitride source may be 0 or more and less than 0.55, more than 0 but 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 production method of this embodiment, the gallium ratio of the gallium nitride source and the gallium ratio of the obtained sintered body are equivalent.

[0052] The dopant source may be at least one of an alloy containing one or more dopant elements selected from the group consisting of beryllium, magnesium, calcium, strontium, vanadium, zinc, and cadmium, and a precursor thereof, or may be powder of these.

[0053] The dopant source has a tendency that the oxygen content of the resulting sintered body decreases as the maximum particle size of the primary particles of the powder increases, but the maximum particle size is preferably 500 μm or less, 300 μm or less, or 200 μm or less, or 100 μm or more. The maximum particle size is preferably 100 μm or more and 500 μm or less, or 100 μm or more and 200 μm or less.

[0054] The content of the dopant source in the raw material powder, calculated as the dopant element, is 1.0 mass % or more, and may be the same content [mass %] as the content of the dopant element in the sintered body of the present embodiment described above. In the manufacturing method of the present embodiment, the contents of the dopant alloy and the dopant element contained in the dopant source in the raw material powder are equivalent to the contents of the dopant alloy and the dopant element contained in the obtained sintered body.

[0055] In the manufacturing method of this embodiment, the raw material powder is hot pressed at a holding temperature of 400° C. or higher and a holding pressure of 30 MPa or higher.

[0056] In the sintering process, the raw material powder is hot-pressed. By hot-pressing the raw material powder containing the dopant element as an alloy, volatilization of the dopant element is suppressed while densification proceeds and dispersion of the dopant element is promoted. This makes it easier to obtain a sintered body with a flexural strength of 55 MPa or more.

[0057] The holding temperature for the hot pressing treatment is 400°C or higher, and preferably 500°C or higher. If the holding temperature is lower than 400°C, densification does not proceed, and a sintered body having a dopant element content equivalent to that of the sintered body of this embodiment cannot be obtained. The holding temperature for the hot pressing treatment can be lower than 800°C or lower than 700°C. Furthermore, the holding temperature for the hot pressing treatment can be 400°C or higher but lower than 800°C, or 500°C or higher but lower than 700°C.

[0058] The holding pressure of the hot pressing treatment is 30 MPa or more, preferably 35 MPa or more. If the holding pressure is less than 30 MPa, side reactions occur during the hot pressing treatment, resulting in a high oxygen content. The holding pressure of the hot pressing treatment is 80 MPa or less or 60 MPa or less, and the processing pressure of the hot pressing treatment is 30 MPa or more and 80 MPa or less, or 35 MPa or more and 60 MPa or less, for example.

[0059] The processing atmosphere for the hot pressing treatment is preferably a vacuum atmosphere. This suppresses the incorporation of impurities resulting from the hot pressing treatment. Specific examples of the vacuum atmosphere include a reduced-pressure atmosphere with a degree of vacuum of 0.01 Pa or less, or 0.005 Pa or less. The degree of vacuum is preferably 0 Pa, but may be 0 Pa or more, more than 0 Pa, or 0.0001 Pa or more. Furthermore, the degree of vacuum may be 0 Pa or more and 0.01 Pa or less, or 0 Pa or more and 0.005 Pa or less.

[0060] The holding time for the hot pressing treatment may be adjusted as appropriate depending on the size of the hot pressing treatment device, the amount of raw material powder to be subjected to the hot pressing treatment, etc., and may be, for example, from 0.5 hours to 5.0 hours, or from 0.5 hours to 3.0 hours.

[0061] A specific example of the hot pressing treatment is to create a vacuum atmosphere, then raise the temperature to a holding temperature, and then hold the temperature at a holding pressure.

[0062] [Sputtering target] The sintered body of this embodiment can be used as a sputtering target provided with the sintered body (hereinafter also referred to as "the target of this embodiment"). The target of this embodiment may be the sintered body of this embodiment, that is, the sintered body of this embodiment may be used as a sputtering target as it is, but it is preferable that the sintered body of this embodiment is a sputtering target bonded to a support via a bonding layer.

[0063] 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.

[0064] The target of this embodiment preferably has a structure in which 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. The bonding layer is preferably composed of a solder containing indium, as this tends to increase the electrical conductivity and thermal conductivity of the target. 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 has high wettability to indium, and is preferably at least one of nickel and chromium.

[0065] 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.

[0066] 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 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.

[0067] [Film formation method] The sintered body of this embodiment and the target of this embodiment can be used in a method for forming a sputtered film using them. A p-type gallium nitride sputtered film can be directly formed using the sintered body of this embodiment. The sputtered film is a so-called laminated film that is formed by sputtering using the target of this embodiment and is laminated on a substrate.

[0068] 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.

[0069] The sputtering gas may be any gas used in sputtering, including at least one of an inert gas, argon gas, and nitrogen gas. When sputtering 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] (hereinafter also simply referred to as "nitrogen partial pressure ratio") is preferably greater than 0.5, 0.7 or greater, or 0.9 or greater. The nitrogen partial pressure ratio may be 1.0 or less, or less than 1.0, and may further be greater than 0.5 and 1.0 or less, 0.7 or greater but less than 1.0, or 0.9 or greater but less than 1.0.

[0070] 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 or more and 100 ml / min or less, or 10 ml / min or more and 70 ml / min or less.

[0071] 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. The gas pressure of the sputtering gas may be 0.05 Pa or more and 3 Pa or less, or 0.1 Pa or more and 2 Pa or less.

[0072] 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 is 0.1 W / cm or less. ２More than 5W / cm ２ or less or 0.1 Pa or more 5 W / cm ２ The following points can be mentioned.

[0073] The substrate may be appropriately selected depending on the desired laminate of the film and the substrate (hereinafter simply 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.

[0074] The sputtering method and conditions can be appropriately selected depending on the desired sputtered film.

[0075] 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.

[0076] 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 more or 10 minutes or more and 5 hours or less or 1 hour or less. The film formation time may be 1 minute or more and 5 hours or less, or 10 minutes or more and 1 hour or less.

[0077] 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 conforming to JIS H 1695. (Measured Density of Sintered Body) The measured density of the sintered body was measured in accordance with the method for measuring actual density in JIS R 1634. The mass was determined by weighing the mass of the sintered body pretreated by a vacuum method using distilled water, and the volume was calculated from the shape measured using a micrometer. (Flexural Strength) The three-point bending strength of the sintered body was measured in accordance with JIS R 1601. The measurement was performed twice, and the average value was used as the flexural strength. (Textural Observation) The texture of the sintered body was observed by observing the cross section using a SEM equipped with EDS (product name: JSM-IT800, manufactured by JEOL Ltd.). Further, mapping images of the elements Ga, Mg, and Al were obtained for the cross section where the structure was observed. Observation: Secondary electron image, backscattered electron image, element mapping Acceleration voltage: 15 kV Probe current: 50 nA Analysis area: 100 × 150 μm Number of fields: 1 field per sample

[0078] Example 1 Gallium nitride powder having a gallium ratio of 0.5 and an oxygen content of 0.12 atm % and aluminum-magnesium alloy powder (manufactured by Kanto Metals Co., Ltd.) having a maximum particle size of less than 150 μm were mixed together so that the aluminum-magnesium alloy content was 8.8 mass % (5.0 mass % as magnesium), to obtain a raw material powder.

[0079] 15 g of the obtained raw material powder was filled into a carbon mold measuring 17 mm in length and 45 mm in width, and this was placed in a hot press device. After placement, the pressure was reduced to a vacuum degree of 0.004 Pa, and then the temperature was increased and maintained under the following conditions, whereby hot press processing was performed.

[0080] Heating rate: 200°C / hour Holding temperature: 600°C Holding pressure: 40 MPa Holding time: 1 hour After the hot press treatment, the temperature was lowered to 500°C, at which time a cooling gas (argon) was introduced, and after the temperature was further lowered to 50°C, the sintered body was recovered from the hot press apparatus, yielding a gallium nitride sintered body containing an aluminum-magnesium alloy and having a magnesium content of 5.0 mass%.

[0081] 1 to 4 show SEM observation images of the sintered body of this example, as well as elemental mapping of Ga, Mg, and Al. From Figures 1 and 2, it was confirmed that the crystal grains of the sintered body of this embodiment have irregular shapes and that gallium (gallium nitride) is the matrix. Furthermore, since Mg and Al are distributed similarly, it was confirmed that magnesium and aluminum are contained in the sintered body as an alloy.

[0082] Example 2 A gallium nitride sintered body containing an aluminum-magnesium alloy and having a magnesium content of 7.0 mass% was obtained in the same manner as in Example 1, except that gallium nitride powder and aluminum-magnesium alloy powder were mixed so that the aluminum-magnesium alloy content was 12.3 mass% (7.0 mass% as magnesium).

[0083] Example 3 A gallium nitride sintered body containing an aluminum-magnesium alloy and having a magnesium content of 9.6 mass% was obtained in the same manner as in Example 1, except that gallium nitride powder and aluminum-magnesium alloy powder were mixed so that the aluminum-magnesium alloy content was 16.6 mass% (9.6 mass% as magnesium).

[0084] Example 4 A gallium nitride sintered body containing an aluminum-magnesium alloy with a magnesium content of 15.1 mass% was obtained in the same manner as in Example 1, except that gallium nitride powder and aluminum-magnesium alloy powder were mixed so that the aluminum-magnesium alloy content was 26.3 mass% (15.1 mass% as magnesium). Example 5 A gallium nitride sintered body containing an aluminum-magnesium alloy with a magnesium content of 5.0 mass% was obtained in the same manner as in Example 1, except that aluminum-magnesium alloy powder with a maximum particle size of less than 300 μm was mixed to obtain a raw material powder.

[0085] Comparative Example 1 A gallium nitride sintered body containing an aluminum-magnesium alloy and having a magnesium content of 3.0 mass% was obtained in the same manner as in Example 1, except that gallium nitride powder and aluminum-magnesium alloy powder were mixed so that the aluminum-magnesium alloy content was 5.2 mass% (3.0 mass% as magnesium).

[0086] Comparative Example 2 A gallium nitride sintered body containing 5.0 mass % magnesium and containing an aluminum-magnesium alloy was obtained in the same manner as in Example 1, except that the holding pressure in the hot press treatment was 20 MPa.

[0087] Comparative Example 3: Hot pressing was carried out in the same manner as in Comparative Example 1, except that the holding temperature in the hot pressing was set to 300° C. and the holding pressure was set to 20 MPa. However, cracks occurred during the hot pressing, and a sintered body could not be obtained.

[0088] Comparative Example 4 A magnesium-containing gallium nitride sintered body having a magnesium content of 16.4 mass% was obtained in the same manner as in Example 1, except that magnesium powder (manufactured by Kanto Metal Co., Ltd.) having a particle size of 500 μm was used instead of the aluminum-magnesium alloy powder, that the gallium nitride powder and magnesium powder were mixed so that the magnesium powder content was 16.4 mass%, and that the processing temperature for the hot press treatment was 800°C.

[0089] Comparative Example 5 A sintered body was produced by the method of Example 6 of Patent Document 2. That is, magnesium nitride (Mg ３ N ２ The magnesium nitride was added to 100 g of gallium nitride powder at a concentration of 14,000 wtppm using a hot press mixer, and the resulting mixture was mixed uniformly to obtain a raw material powder. The resulting raw material powder was filled into a carbon mold with a diameter of 78 mm, which was then placed in a hot press apparatus and subjected to hot press processing under the following conditions:

[0090] Heating rate: 200°C / hour Holding temperature: 1090°C Holding pressure: 50 MPa Holding time: 2 hours After the hot press treatment, the temperature was lowered to 50°C, and then the sintered body was recovered from the hot press apparatus, yielding a gallium nitride sintered body containing magnesium nitride and having a magnesium content of 1.4 mass%.

[0091] The results of the examples and comparative examples are shown in the table below.

[0092]

[0093] From the above table, it was confirmed that the sintered bodies of the Examples all contain magnesium, and therefore are gallium nitride sintered bodies that can be used to directly form p-type gallium nitride films. Furthermore, from Examples 1 to 4 and Comparative Example 1, it was confirmed that the sintered bodies of the Examples have a flexural strength of 60 MPa or more and an oxygen content of 0.5 atmt% or less, despite the magnesium content being 1.0 mass% or more, and even 4.0 mass% or more. From Examples 3 and 5, it was confirmed that increasing the particle size of the dopant alloy (aluminum-magnesium alloy) reduces the oxygen content, while the effect on flexural strength and density is small. In addition, the sintered bodies of all Examples had a total content of silicon, germanium, tin, and lead of 10 mass ppm or less.

[0094] Furthermore, it was confirmed from Comparative Example 2 that the oxygen content increases when the holding pressure in the hot press treatment is less than 30 MPa, and from Comparative Example 3 that a sintered body cannot be obtained when the holding temperature in the hot press treatment is 300°C or less. Furthermore, it was confirmed from Example 5 and Comparative Example 4 that in the example in which magnesium was added instead of a magnesium-aluminum alloy, the oxygen content increased and the bending strength was low despite the particle size being large. Furthermore, the sintered body disclosed in Patent Document 2 was a sintered body that contained magnesium and had a low oxygen content, but had low bending strength.

[0095] Example 6: A sintered body was obtained in the same manner as in Example 5, except that 50 g of the raw material powder was filled into a circular mold having a diameter of 53 mm, and then ground into a disk-shaped sintered body having a diameter of 50.8 mm and a thickness of 3 mm. A circular sputtering target with a backing plate was produced using the obtained sintered body, indium solder as a bonding layer, and a backing plate made of oxygen-free copper as a support.

[0096] Using the obtained sputtering target, a film was formed on a substrate by sputtering under the following conditions to obtain a laminated substrate having a magnesium-containing gallium nitride film (sputtered film). The sputtering device used was a CMS-6400 (manufactured by Comet Co.). Sputtering method: RF magnetron sputtering. Substrate: sapphire substrate. Film formation temperature: 500°C. Sputtering gas: nitrogen (i.e., nitrogen partial pressure ratio: 1.0). Gas pressure: 0.3 Pa. Output: 3.8 W / cm. ２

[0097] (Analysis of sputtered film) Secondary ion mass spectrometry (SIMS) was performed on the laminate substrate having the obtained sputtered film. The analytical device used was a Model 6600 Quadruple SIMS instrument manufactured by Physical Electronics PHI. Figure 5 shows the measurement results of the magnesium concentration, aluminum concentration, and gallium concentration of the obtained laminate substrate by SIMS, with the magnesium concentration shown as a solid line, the aluminum concentration shown as a dotted line, and the gallium concentration shown as a dashed line. Figure 5 shows that magnesium is continuously and uniformly present along the depth direction from the surface (depth = 0 mm), and that its content is 7.8 × 10 ２１ It was confirmed that the aluminum content was 52,000 mass ppm (= 5.2 mass %). In addition, since the aluminum content increased at a depth of 90 nm or more, it was confirmed that the thickness of the magnesium-containing gallium nitride film was 90 nm.

[0098] The entire contents of the specification, claims, abstract and drawings of Japanese Patent Application No. 2024-155023, filed on September 9, 2024, are hereby incorporated by reference as the disclosure of the specification of the present disclosure.

Claims

1. A gallium nitride sintered body comprising an alloy containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn) and cadmium (Cd), wherein the content of the dopant element is 1.0 mass% or more and the oxygen content is 0.6 atm% or less.

2. The sintered body according to claim 1, wherein the alloy is an alloy of the dopant element and aluminum.

3. The sintered body according to claim 1 or 2, wherein the total content of silicon, germanium, tin and lead is 10 mass ppm or less.

4. The measured density is 3.50 g / cm ３ The sintered body according to any one of claims 1 to 3.

5. The sintered body according to any one of claims 1 to 4, having a bending strength of 55 MPa or more.

6. A method for producing a sintered body according to any one of claims 1 to 5, comprising a sintering step of hot pressing a raw material powder containing a gallium nitride source and a dopant source made of an alloy containing one or more dopant elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn) and cadmium (Cd), the dopant source content calculated as the dopant element being 1.0 mass % or more, at a holding temperature of 400°C or more and a holding pressure of 30 MPa or more.

7. The method of claim 6, wherein the oxygen content of the gallium nitride source is less than 0.4 atm %.

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

9. A method for producing a sputtered film using the sputtering target according to claim 8.

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