Method for producing single-crystal beta-digallium trioxide, method for producing single-crystal beta-digallium trioxide substrate, and single-crystal beta-digallium trioxide substrate

Abstract

This method for producing single-crystal beta-digallium trioxide includes a step in which an opening of a crucible having the opening is closed with a lid and a step in which the crucible is heated to grow single-crystal beta-digallium trioxide. The inner peripheral surface of the crucible is coated with a first film comprising rhodium and / or platinum. The first film has a thickness of 100-500 μm. The step for growth is for growing the single-crystal beta-digallium trioxide in a closed space formed by closing the opening with the lid.

Description

Method for manufacturing beta-type digallium trioxide single crystal, method for manufacturing beta-type digallium trioxide single crystal substrate, and beta-type digallium trioxide single crystal substrate

[0001] The present disclosure relates to a method for producing a beta-type digallium trioxide single crystal, a method for producing a beta-type digallium trioxide single crystal substrate, and a beta-type digallium trioxide single crystal substrate. This application claims priority to Japanese Patent Application No. 2024-097334, filed on June 17, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] Japanese Patent Application Laid-Open No. 2016-079080 (Patent Document 1), Japanese Patent Application Laid-Open No. 2017-193466 (Patent Document 2), Japanese Patent Application Laid-Open No. 2021-031367 (Patent Document 3), Japanese Patent Application Laid-Open No. 2021-031379 (Patent Document 4), Japanese Patent Application Laid-Open No. 2020-059633 (Patent Document 5), and Hoshikawa et al., Journal of the Japanese Society for Crystal Growth, Vol. 44, No. 4 (2017), 44-4-03 (Non-Patent Document 1) discloses a method for growing a beta-type gallium trioxide single crystal (hereinafter also referred to as a "beta-type GaO single crystal") by a vertical boat method using a crucible made of a platinum-rhodium alloy (hereinafter also referred to as a "Pt-Rh alloy") or a crucible or die made of a platinum-iridium alloy (hereinafter also referred to as a "Pt-Ir alloy"), or an EFG (Edge-defined Film-fed Growth) method, or the like.

[0003] JP 2016-079080 A JP 2017-193466 A JP 2021-031367 A JP 2021-031379 A JP 2020-059633 A

[0004] Hoshikawa et al., Journal of the Japanese Society for Crystal Growth, Vol. 44, No. 4 (2017), 44-4-03 Mitsuru Kurita, Journal of the Japanese Society for Thermal Measurement, "Thermal Measurement", Vol. 12, No. 4 (1985), pp. 196-198

[0005] The method for producing a beta-type GaO single crystal according to the present disclosure includes the steps of: placing a crucible having an opening, closing the opening with a lid, and heating the crucible to grow a beta-type GaO single crystal. The inner peripheral surface of the crucible is coated with a first film containing both or either of rhodium and platinum. The thickness of the first film is 100 μm or more and 500 μm or less. The growing step is a step of growing the beta-type GaO single crystal in a closed space formed by closing the opening with the lid.

[0006] FIG. 1 is a flowchart illustrating an example of a method for manufacturing a beta-type GaO single crystal substrate according to this embodiment. FIG. 2 is a schematic diagram illustrating a single crystal growth apparatus of a first embodiment used in the method for manufacturing a beta-type GaO single crystal substrate according to this embodiment. FIG. 3 is an enlarged cross-sectional view of a main portion illustrating the shape of the inner peripheral surface of a crucible used in the single crystal growth apparatus of FIG. 2. FIG. 4 is a schematic diagram illustrating a single crystal growth apparatus of a second embodiment used in the method for manufacturing a beta-type GaO single crystal substrate according to this embodiment. FIG. 5 is a schematic diagram illustrating a single crystal growth apparatus of a third embodiment used in the method for manufacturing a beta-type GaO single crystal substrate according to this embodiment. FIG. 6 is a schematic diagram illustrating a beta-type GaO single crystal substrate according to this embodiment.

[0007] [Problem to be Solved by the Present Disclosure] The methods disclosed in Patent Documents 1 to 5, Non-Patent Document 1, etc., involve growing beta-type GaO single crystals at approximately 1800°C, which results in high temperatures in the single crystal manufacturing equipment, including the crucible. To address this, zirconia-based insulating materials containing zirconium or other elements are typically used in various parts of the single crystal manufacturing equipment. For example, Mitsuru Kurita, "Thermal Measurement," Journal of the Japan Society of Thermal Measurement, Vol. 12, No. 4 (1985), pp. 196-198 (Non-Patent Document 2), teaches the use of zirconia fiber as an insulating material that can be used in environments of approximately 1800°C. However, in such cases, contamination of the beta-type GaO single crystals due to trace amounts of zirconium being mixed in during manufacturing may occur. Zirconium is known to emit alpha rays due to its ore.

[0008] Alpha rays may cause malfunctions in electronic devices (hereinafter also referred to as "soft errors"). Therefore, when a beta-type GaO single crystal substrate is obtained from the beta-type GaO single crystal, it is desirable to minimize the amount of alpha rays emitted from the beta-type GaO single crystal substrate by reducing the zirconium contamination described above, for example.

[0009] In view of the above, an object of the present disclosure is to provide a method for manufacturing a beta-type GaO single crystal, a method for manufacturing a beta-type GaO single crystal substrate, and a beta-type GaO single crystal substrate that can reduce the amount of alpha-ray emission.

[0010] [Effects of the Present Disclosure] According to the present disclosure, a method for manufacturing a beta-type Ga2O3 single crystal, a method for manufacturing a beta-type Ga2O3 single crystal substrate, and a beta-type Ga2O3 single crystal substrate that can reduce the amount of alpha-ray emission are provided.

[0011] [Description of Embodiments of the Present Disclosure] An outline of an embodiment of the present disclosure will be described below. The present inventors have conducted extensive research to solve the above-mentioned problems and arrived at the present disclosure. The present inventors came up with the idea of ​​providing a new lid to close the opening of a crucible for growing beta-type GaO single crystals in the single crystal manufacturing equipment. As a result, they discovered that growing the beta-type GaO single crystal in a closed space formed by closing the opening with the lid reduces contamination by zirconium. This has resulted in the production of beta-type GaO single crystals with a low alpha-ray emission, leading to the completion of the present disclosure.

[0012] Next, embodiments of the present disclosure will be listed and described. [1] A method for producing a beta-type GaO single crystal according to one aspect of the present disclosure includes the steps of: closing an opening of a crucible with a lid; and heating the crucible to grow a beta-type GaO single crystal. The inner surface of the crucible is coated with a first film containing both or either of rhodium and platinum. The thickness of the first film is 100 μm or more and 500 μm or less. The growing step is a step of growing the beta-type GaO single crystal in a closed space formed by closing the opening with the lid. A beta-type GaO single crystal with a reduced amount of alpha-ray emission can be obtained by the method for producing a beta-type GaO single crystal having such characteristics.

[0013] [2] In the method for producing a beta-type GaO single crystal according to [1], the surface of the lid facing the opening may be coated with a second film containing both or either one of rhodium and platinum. The thickness of the second film may be 100 μm or more and 500 μm or less. In this case, beta-type GaO single crystals with reduced alpha-ray emission can be obtained with a high yield.

[0014] [3] In the method for producing a beta-type GaO single crystal according to [1] or [2], the lid may be made of sapphire. In this case, a beta-type GaO single crystal with a reduced amount of alpha-ray emission can be obtained with a high yield.

[0015] [4] In the method for producing a beta-type GaO single crystal according to any one of [1] to [3], the crucible may contain stabilized zirconia. In this case, a beta-type GaO single crystal with a reduced alpha-ray emission amount can be obtained while suppressing an increase in cost.

[0016] [5] In the method for producing a beta-type GaO single crystal according to [2], the lid may contain stabilized zirconia. In this case, a beta-type GaO single crystal with a reduced amount of alpha-ray emission can be obtained while suppressing an increase in cost.

[0017] [6] In the method for producing a beta-type GaO single crystal according to any one of [1] to [3], the crucible and the lid may be made of sapphire. The crucible may have a cylindrical shape with a disk-shaped bottom surface and a cylindrical side surface, and the side surface and the bottom surface are joined by sapphire diffusion bonding. In this case, beta-type GaO single crystals with reduced alpha-ray emission can be obtained with a high yield.

[0018] [7] In the method for producing a beta-type GaO single crystal according to any one of [1] to [6], the surface roughness Rz of the inner peripheral surface may be 300 μm or more and 500 μm or less. In this case, the occurrence of cracks, chips, etc. of the crucible during crystal growth is reduced.

[0019] [8] In the method for producing a beta-type GaO single crystal according to any one of [1] to [7], the crucible may have a thickness of 1 mm or more and 10 mm or less. The maximum inner diameter of the crucible may be 100 mm or more. In this case, the amount of alpha-ray emission can be reduced in a beta-type GaO single crystal having a large diameter.

[0020] [9] In the method for producing a beta-type GaO single crystal according to any one of [1] to [8], 99 mass % or more of the platinum is １９６ In this case, a beta type Ga2O3 single crystal with a reduced amount of alpha ray emission can be obtained with a good yield.

[0021]

[10] The method for producing a beta-type GaO single crystal according to any one of [1] to [9] may include a step of preparing an insulating material that prevents heat generated by heating the crucible from being transferred to the external environment. The insulating material may contain zirconium. In this case, in a beta-type GaO single crystal with a reduced alpha-ray emission, the amount of power consumed for production can be reduced, and production costs can be reduced.

[0022]

[11] A method for producing a beta-type GaO single crystal substrate according to one embodiment of the present disclosure includes a step of obtaining a beta-type GaO single crystal substrate having a circular main surface by processing the beta-type GaO single crystal obtained by the method for producing a beta-type GaO single crystal according to any one of [1] to

[10] . A production method having such characteristics can obtain a beta-type GaO single crystal substrate with a reduced amount of alpha-ray emission.

[0023]

[12] The beta-type GaO single crystal substrate according to one embodiment of the present disclosure has an alpha ray emission rate of 0.05 cph / cm ２ The beta type Ga2O3 single crystal substrate having these characteristics emits a small amount of alpha rays.

[0024]

[13] In the beta-type GaO single crystal substrate according to

[12] , the alpha ray emission rate is 0.03 cph / cm ２ In this case, a beta type Ga2O3 single crystal substrate with a smaller amount of alpha ray emission is provided.

[0025]

[14] In the beta-type GaO single crystal substrate according to

[12] or

[13] , the zirconium content may be 0.02 mass ppm or less. In this case, a beta-type GaO single crystal substrate with low alpha ray emission is provided.

[0026]

[15] In the beta-type GaO single crystal substrate according to any one of

[12] to

[14] , the tin content may be 0.01 mass ppm or more and 200 mass ppm or less. In this case, a beta-type GaO single crystal substrate containing a dopant is provided, which has a small amount of alpha-ray emission.

[0027]

[16] In the beta type GaO single crystal substrate according to any one of

[12] to

[15] , the alpha ray emission dose is 0.01 cph / cm ２The zirconium content may be 0.02 ppm by mass or less. The tin content may be 0.01 ppm by mass or more and 200 ppm by mass or less. In this case, a beta-type GaO single crystal substrate containing a dopant is provided that has a small amount of alpha-ray emission.

[0028]

[17] The beta-type GaO single crystal substrate according to any one of

[12] to

[16] may have a diameter of 100 mm or more and 300 mm or less. In this case, a large-diameter beta-type GaO single crystal substrate with a small amount of alpha-ray emission is provided.

[0029] [Details of the embodiment of the present disclosure] One embodiment according to the present disclosure (hereinafter also referred to as "the present embodiment") will be described in further detail below, but the present disclosure is not limited thereto. The following description may be made with reference to the drawings, and the same or corresponding elements in the present specification and drawings will be designated by the same reference numerals, and the same description will not be repeated. Furthermore, in the drawings, the scale of each component has been adjusted appropriately for ease of understanding, and the scale of each component shown in the drawings does not necessarily coincide with the scale of the actual component.

[0030] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and only a unit is specified for B, the units of A and B are the same. In this specification, when a compound or the like is expressed by a chemical formula, the chemical formula is intended to include any conventionally known atomic ratios if the atomic ratio is not particularly limited, and is not necessarily limited to only those within a stoichiometric range.

[0031] In this specification, the term "yield" refers to the rate at which a beta-type GaO single crystal having a minimum amount of alpha-ray emission can be grown to a desired thickness in a crucible without cracking or chipping occurring in the crucible. The term "yield" refers to the rate at which a beta-type GaO single crystal having a minimum amount of alpha-ray emission can be grown to a desired thickness in a crucible without cracking or chipping occurring in the crucible. The term "yield" refers to the rate at which a beta-type GaO single crystal substrate can be grown to a desired thickness in a crucible without cracking or chipping occurring in the crucible. ２ This means the rate at which beta-type Ga2O3 single crystal substrates can be obtained (which is hereinafter referred to as "Ga2O3 single crystal substrates").

[0032] In this specification, the "maximum inner diameter" of a crucible refers to the inner diameter of the crucible at the position where the inner diameter of the ring, which appears in a cross section perpendicular to the axial direction of the cylindrical crucible, is maximum when compared along the axial direction of the crucible. In the present disclosure, the crucible may have a structure including a cylindrical seed crystal accommodating section, an increasing diameter section connected to the seed crystal accommodating section, and a straight body section connected to the increasing diameter section, as described below. In such a crucible, the "maximum inner diameter" refers to the inner diameter of the straight body section. Furthermore, in the present disclosure, when the crucible is made of sapphire, it may have a cylindrical shape having a disk-shaped bottom surface and a cylindrical side surface, and the side surface and the bottom surface are joined by diffusion bonding of the sapphire, as described below. In such a crucible, the "maximum inner diameter" refers to the inner diameter of the side surface.

[0033] In this specification, the "main surface" of a beta-type GaO single crystal substrate refers to both of the two circular faces of the beta-type GaO single crystal substrate. The beta-type GaO single crystal substrate falls within the technical scope of the present disclosure if at least one of the two faces satisfies the scope of the claims of the present disclosure. Furthermore, in this specification, the "face" used in the term "in-plane" refers to the "main surface." Furthermore, when the diameter of a beta-type GaO single crystal substrate is described as "100 mm," this means that the diameter is approximately 100 mm (approximately 95 to 105 mm) or 4 inches. When the diameter is described as "150 mm," this means that the diameter is approximately 150 mm (approximately 145 to 155 mm) or 6 inches. When the diameter is described as "200 mm," this means that the diameter is approximately 200 mm (approximately 195 to 210 mm) or 8 inches. When the diameter is described as "300 mm," this means that the diameter is approximately 300 mm (approximately 285 to 315 mm), or 12 inches. The diameter is measured using a conventionally known outer diameter measuring device such as a vernier caliper.

[0034] In the crystallographic descriptions in this specification, individual directions are represented by [ ], collective directions by < >, individual planes by ( ), and collective planes by {}. In addition, negative indices in crystallography are usually represented by placing a "- (bar)" above the number, but in this specification they are represented by placing a minus sign before the number.

[0035] [Method for Manufacturing Beta-Type GaO Single Crystal] The method for manufacturing a beta-type GaO single crystal according to this embodiment includes the steps of: closing an opening of a crucible with a lid; and heating the crucible to grow a beta-type GaO single crystal. The inner surface of the crucible is coated with a first film containing both or either of rhodium and platinum. The thickness of the first film is 100 μm or more and 500 μm or less. The growing step is a step of growing the beta-type GaO single crystal in a closed space formed by closing the opening with the lid. The method for manufacturing a beta-type GaO single crystal having these characteristics allows the production of a beta-type GaO single crystal with a reduced amount of alpha-ray emission.

[0036] FIG. 1 is a flowchart showing an example of a method for manufacturing a beta-type GaO single crystal substrate according to this embodiment. The method for manufacturing the beta-type GaO single crystal substrate shown in FIG. 1 includes the steps included in the method for manufacturing a beta-type GaO single crystal according to this embodiment and a step of manufacturing a beta-type GaO single crystal substrate having a circular main surface by processing the beta-type GaO single crystal obtained by the manufacturing method. The beta-type GaO single crystal manufacturing step S100 shown in FIG. 1 is an example of a method for manufacturing a beta-type GaO single crystal according to this embodiment. The beta-type GaO single crystal manufacturing step S100 may include a step (preparation step S110) of preparing a single crystal growth apparatus including at least a cylindrical crucible having an opening, a lid for closing the opening, and a heating device arranged to surround the outer periphery of the crucible. In the preparation step S110, in addition to the single crystal growth apparatus including the crucible and the lid, a seed crystal consisting of a beta-type Ga2O3 single crystal, a massive gallium trioxide bulk body (Ga2O3 bulk body), etc. may also be prepared.

[0037] The beta-type GaO single crystal production process S100 may include a step (melting step S120) of placing the seed crystal and the GaO bulk in the crucible, melting the GaO bulk and a portion of the seed crystal to obtain a digallium trioxide melt (GaO melt), and contacting the GaO melt with the remainder of the seed crystal. In the melting step S120, the GaO bulk may be placed above the seed crystal in the crucible. The beta-type GaO single crystal production process S100 further includes a step (closing step S130) of closing the opening of the crucible with a lid. The crucible with an opening and the lid for closing the opening will be described in detail below. The beta-type GaO single crystal manufacturing process S100 includes a step of heating the crucible to grow a beta-type GaO single crystal (growing step S140). In the growing step S140, a crystal formed on the remaining portion of the seed crystal grows from the GaO melt. This results in a beta-type GaO single crystal with reduced alpha-ray emission.

[0038] The beta-type GaO single crystal substrate manufacturing process S200 shown in Fig. 1 may include a cutting process, a periphery grinding process, and a polishing process, which will be described later. In the beta-type GaO single crystal substrate manufacturing process S200, the above steps are performed in this order to obtain a beta-type GaO single crystal substrate with a reduced amount of alpha-ray emission. The beta-type GaO single crystal substrate manufacturing process S200, together with the beta-type GaO single crystal manufacturing process S100, is an example of a method for manufacturing a beta-type GaO single crystal substrate according to this embodiment.

[0039] <Beta-type GaO single crystal manufacturing process S100> Hereinafter, each step included in the beta-type GaO single crystal manufacturing method according to this embodiment will be described with reference to FIGS. 1 and 2, etc. FIG. 2 is a schematic diagram illustrating a single crystal growth apparatus of a first embodiment used in the beta-type GaO single crystal substrate manufacturing method according to this embodiment. In the beta-type GaO single crystal manufacturing process S100, for example, a lid 4 and a crucible 5 applied to the single crystal growth apparatus 100 shown in FIG. 2 are used, and a beta-type GaO single crystal may be grown by the vertical boat method. Hereinafter, the vertical boat method will be abbreviated as the VB method. The VB method includes the vertical Bridgman method and the vertical temperature gradient solidification method.

[0040] (Preparation Step S110) As shown in FIGS. 1 and 2, the beta-type GaO single crystal production step S100 first involves preparing a single crystal growth apparatus 100 (preparation step S110) including at least a cylindrical crucible 5 having an opening, a lid 4 for closing the opening, and a heating device 7 arranged to surround the outer periphery of the crucible 5. In the preparation step S110, in addition to the single crystal growth apparatus 100 described above for producing a beta-type GaO single crystal 81, a seed crystal 8a and a GaO bulk mass may also be prepared. The seed crystal 8a is made of a beta-type GaO single crystal. The GaO bulk mass may be made of polycrystalline GaO. The seed crystal 8a and the GaO bulk mass may be prepared by a conventionally known method or by purchasing commercially available products.

[0041] 1) Single Crystal Growth Apparatus of First Embodiment In the preparation step S110, a single crystal growth apparatus 100 of the first embodiment, for example, as shown in Fig. 2, is prepared. As shown in Fig. 2, the single crystal growth apparatus 100 includes a lid 4, a crucible 5, a crucible holder 6 that holds the crucible 5, and a heating device 7. The single crystal growth apparatus 100 may further include a sealed container 9 in which the single crystal growth apparatus 100 itself is housed.

[0042] (a) Crucible The crucible 5 is a cylindrical crucible with an opening for growing beta-type GaO single crystals. The crucible 5 may have a thickness of 1 mm or more and 10 mm or less. The maximum inner diameter of the crucible 5 may be 100 mm or more. In the single crystal growth apparatus 100 of the first embodiment, the crucible 5 may contain stabilized zirconia. More specifically, the composition of the crucible 5 may be stabilized zirconia containing, for example, both or either yttrium oxide and calcium oxide. The stabilized zirconia may contain at least 12.0 mass% to 15.5 mass% of the yttrium oxide, or 10.2 mass% to 11.4 mass% of the calcium oxide. These features may reduce the occurrence of cracks, chips, etc. in the crucible 5 itself during crystal growth.

[0043] The crucible 5 may include a cylindrical seed crystal accommodation portion 51, an increasing diameter portion 52 connected to the seed crystal accommodation portion 51, and a straight body portion 53 connected to the increasing diameter portion 52. The seed crystal accommodation portion 51 is cylindrical and has a hollow portion that opens at a position connected to the increasing diameter portion 52 and has a bottom wall formed at a position opposite the increasing diameter portion 52. The seed crystal accommodation portion 51 can accommodate and hold a seed crystal 8a in the hollow portion. The increasing diameter portion 52 has a truncated cone shape that expands upward in the axial direction of the crucible 5 and is connected to the seed crystal accommodation portion 51 at a position where the increasing diameter portion 52 has a small diameter. The straight body portion 53 has a hollow cylindrical shape and is connected to the increasing diameter portion 52 at a position where the increasing diameter portion 52 has a large diameter. The increasing diameter portion 52 and the straight body portion 53 function to hold a massive GaO bulk body therein. The diameter increasing portion 52 and the body portion 53 have the function of solidifying the Ga2O3 bulk melt to grow a beta type Ga2O3 single crystal as a crystal, as will be described later.

[0044] As described above, the crucible 5 may have a thickness of 1 mm or more and 10 mm or less. More specifically, the sidewalls of the seed crystal accommodating portion 51, the increased diameter portion 52, and the straight body portion 53 of the crucible 5 may all have a thickness of 1 mm or more and 10 mm or less. This reduces cracking and chipping of the crucible 5 during crystal growth. The possibility of deformation of the crucible 5 is also eliminated. Note that if the thickness of the crucible 5 exceeds 10 mm, the cost reduction and other benefits obtained by reducing cracking and chipping of the crucible 5 during crystal growth may be offset by the increased cost of the crucible 5 itself. The sidewalls of the seed crystal accommodating portion 51, the increased diameter portion 52, and the straight body portion 53 of the crucible 5 may all have a thickness of 5 mm or more and 10 mm or less. Furthermore, the maximum inner diameter of the crucible 5 may be 100 mm or more. More specifically, the inner diameter of the body portion 53 of the crucible 5 may be 100 mm or more. The inner diameter of the body portion 53 of the crucible 5 may be 150 mm or more, 200 mm or more, or 300 mm or more. The upper limit of the maximum inner diameter of the crucible 5 is not particularly limited, but is, for example, 330 mm. By making the maximum inner diameter of the crucible 5 100 mm or more, a beta-type GaO single crystal substrate having a large diameter, such as 4 inches, 6 inches, 8 inches, or 12 inches, with a reduced amount of alpha ray emission can be obtained from the beta-type GaO single crystal produced in this crucible 5.

[0045] The composition of the crucible 5 may be stabilized zirconia (hereinafter also referred to as "stabilized ZrO") containing both or either yttrium oxide (yttria: YO) and calcium oxide (calcia: CaO), as described above. The composition of the crucible 5 may be stabilized ZrO containing either YO or CaO. Specifically, the stabilized ZrO may contain at least 12.0 mass% to 15.5 mass% YO or 10.2 mass% to 11.4 mass% CaO. By using stabilized ZrO with low thermal conductivity as described above for the crucible 5, crystal defects occurring during crystal growth are more likely to be repelled to the periphery of the crystal. This prevents polycrystallization of the beta-type GaO single crystal during crystal growth. "Stabilized ZrO" refers to a mixture of ZrO and YO. 3、This refers to ZrO2 in which the high-temperature phase (typically a cubic or tetragonal solid solution) can be stably present down to room temperature by adding CaO, magnesium oxide (MgO), aluminum oxide (alumina: Al2O3), etc. The oxides that form a solid solution in stabilized ZrO2 are YO 3、 It is not limited to only CaO, MgO and Al2O3.

[0046] The inner peripheral surface 5a of the crucible 5 is coated with a first film 5b containing both or either one of rhodium (Rh) and platinum (Pt). For example, in the crucible 5 shown in FIG. 2, the first film 5b may be made of a platinum-rhodium alloy (Pt—Rh alloy) containing 10% by mass to 30% by mass of Rh. Furthermore, for example, the first film 5b may be formed by thermally spraying a Pt—Rh alloy containing 10% by mass to 30% by mass of Rh toward the inner peripheral surface 5a. This reduces the possibility of zirconium, contained in the composition of the crucible 5, being mixed in trace amounts into the beta-type GaO single crystal during crystal growth, thereby reducing the contamination of the single crystal with zirconium. The Pt—Rh alloy forming the first film 5b has an Rh content of 10% by mass or more and 30% by mass or less, which can reduce contamination of the beta-type GaO single crystal with zirconium during crystal growth while mitigating an increase in the cost of the crucible 5. The first film 5b may be made of a Pt—Rh alloy containing 20% ​​by mass or more and 30% by mass or less of Rh.

[0047] The thickness of the first film 5b is 100 μm or more and 500 μm or less. If the thickness of the first film 5b is less than 100 μm, the first film 5b may peel off from the inner peripheral surface 5a. In this case, the beta-type GaO single crystal obtained in the growth step S140 described below may be contaminated with zirconium contained in the composition of the crucible 5. If the thickness of the first film 5b exceeds 500 μm, the adverse effect of increased cost of the crucible 5 may outweigh the effect of reducing contamination. The thickness of the first film 5b may be 200 μm or more and 500 μm or less. The first film 5b may cover the entire inner peripheral surface 5a of the crucible 5. However, as long as the above-described effect is obtained, it does not deviate from the scope of the present disclosure even if a portion of the inner surface 5a is not covered with the first film 5b or if the composition of the first film 5b is partially different.

[0048] The thickness of the first film 5b is measured in accordance with JIS H 8401:1999 (Testing Method for Thickness of Thermal Sprayed Products). Specifically, the thickness of the first film 5b is measured by a direct method using a micrometer (for example, a product name (product number) of "U-shaped micrometer PMU100-25" manufactured by Mitutoyo Corporation, or a product name (product number) of "laser digital micrometer LSM-501S" manufactured by Mitutoyo Corporation) by determining the difference between the thickness of the crucible 5 before and after thermal spraying. The concentration of Rh in the Pt—Rh alloy can be determined when preparing the thermal spray material.

[0049] 99% by mass or more of the platinum (Pt) １９６ The isotope nuclide of Pt may be Pt. Pt undergoes alpha decay, which is a type of radioactive decay. １９０ It is known that Pt isotopes exist at a natural abundance of 0.014% by mass. １９６ Since Pt isotopes are relatively easy to concentrate, more than 99 mass% of Pt can be enriched. １９６ By using an isotope nuclide of Pt and forming the first film 5b containing this, it is possible to reduce the amount of alpha rays emitted from the crucible 5. In this case, beta-type GaO single crystals with reduced alpha ray emission can be obtained with good yield.

[0050] The first film 5b may have pores. The porosity, which is the volume ratio of pores in the first film 5b, may be 30% by volume or more and 50% by volume or less. This makes it possible to reduce the occurrence of cracks, chips, etc. in the crucible 5 during crystal growth. Figure 3 is an enlarged cross-sectional view of a main part illustrating the shape of the inner peripheral surface of the crucible used in the single crystal growth apparatus of Figure 2. The first film 5b covering the inner peripheral surface 5a shown in Figure 3 has pores 5c. The porosity, which is the volume ratio of pores 5c in the first film 5b, may be 30% by volume or more and 50% by volume or less.

[0051] The porosity is measured in accordance with JIS K 7112:1999 Method A (underwater displacement method). Specifically, the density of the crucible 5 is measured before and after coating to calculate the actual density of the first film 5b. The composition of the first film is determined using an energy dispersive X-ray device (SEM-EDX: Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) attached to a transmission electron microscope, and the ideal density is calculated from the composition. The porosity is calculated by dividing the actual density by the ideal density x 100.

[0052] When the crucible 5 is made of the above-mentioned stabilized ZrO2, it is unlikely to deform due to thermal contraction during crystal growth and cooling after crystal growth. However, even if the beta-type Ga2O3 single crystal present in the crucible 5 presses against the inner peripheral surface 5a due to some thermal contraction of the crucible 5, particularly during cooling after crystal growth, the pores 5c contained in the first film 5b are crushed, thereby reducing the occurrence of cracks, chips, etc. in the crucible 5. When the porosity is 30% by volume or more and 50% by volume or less, the occurrence of cracks, chips, etc. in the crucible 5 can be sufficiently reduced.

[0053] As shown in Fig. 3, the inner peripheral surface 5a of the crucible 5 may have a predetermined surface roughness. Specifically, the surface roughness Rz of the inner peripheral surface 5a may be 300 µm or more and 500 µm or less. The first film 5b having such a configuration may also have pores 5c. The surface roughness Rz of the inner peripheral surface 5a may be 300 µm or more and 400 µm or less.

[0054] The method for measuring the surface roughness Rz of the inner peripheral surface 5a is as follows. That is, the maximum height (Rz) of the inner peripheral surface 5a as defined in JIS B0601:2001 is determined, thereby measuring the surface roughness Rz. For example, a surface roughness measuring instrument (product name (product number): "Surface Roughness Measuring Instrument SV-2100M4" manufactured by Mitutoyo Corporation, or product name (product number): "Surface Roughness Measuring Instrument SURFCOM TOUCH 550" manufactured by Tokyo Seimitsu Co., Ltd.) is used to measure the surface roughness Rz. Specifically, a measuring unit is set on the inner peripheral surface 5a of the crucible 5, and the roughness is measured using a display / control unit, thereby measuring the surface roughness Rz.

[0055] When the surface roughness Rz of the inner peripheral surface 5a is 300 μm or more and 500 μm or less, even if the beta-type GaO single crystal present in the crucible 5 presses against the inner peripheral surface 5a due to some thermal contraction of the crucible 5 during cooling after crystal growth, the convex portions present on the inner peripheral surface 5a due to the surface roughness are crushed, thereby reducing the occurrence of cracks, chips, etc. of the crucible 5. As described above, the pores 5c contained in the first film 5b are crushed, thereby reducing the occurrence of cracks, chips, etc. of the crucible 5.

[0056] As described above, the first film 5b may be formed by spraying a Pt—Rh alloy containing 10% by mass or more and 30% by mass or less of Rh toward the inner peripheral surface 5a. The first film 5b may be sprayed by a conventionally known method, such as plasma spraying. For example, the spraying may be performed by heating the Pt—Rh alloy to form molten particles or particles similar to the molten particles (e.g., particle diameter: 45 to 300 μm), and supplying the spray material toward the inner peripheral surface 5a using a spray nozzle from a direction tilted at 30 to 45 degrees with respect to the axis of the crucible 5. In this case, the distance from the tip of the spray nozzle to the inner peripheral surface 5a of the crucible 5 may be 20 to 120 mm along the direction in which the tip of the nozzle faces.

[0057] Furthermore, the thickness of the first film 5b can be determined by controlling the supply rate of the thermal spray material. For example, the supply rate of the thermal spray material may be 50 to 75 g / min. The thickness of the first film 5b can be adjusted to 100 to 500 μm by controlling the supply rate of the thermal spray material. The porosity of the first film 5b can be determined by controlling the angle of the thermal spray nozzle and the supply rate of the thermal spray material. The porosity in the first film 5b can be adjusted to 10 to 50 volume % by controlling the angle of the thermal spray nozzle and the supply rate of the thermal spray material. Increasing the particle size of the thermal spray material tends to increase the surface roughness Rz.

[0058] (b) Lid The lid 4 functions to close the opening of the crucible 5 in a closing step S130, which will be described later. This makes it possible to grow the beta-type GaO single crystal in the closed space formed by closing the opening with the lid 4 in a growing step S140, which will be described later, and reduces contamination of the beta-type GaO single crystal with zirconium. Therefore, the beta-type GaO single crystal with a reduced amount of alpha-ray emission can be obtained.

[0059] In the single crystal growth apparatus 100 of the first embodiment, the lid 4 may contain stabilized zirconia. In this embodiment, the surface of the lid 4 facing the opening may be covered with a second film 4b containing both or either Rh and Pt. The thickness of the second film may be 100 μm or more and 500 μm or less. This allows a beta-type GaO single crystal with a reduced amount of alpha-ray emission to be obtained while suppressing an increase in cost.

[0060] 2, the lid 4 may have a convex portion that can fit into the opening of the crucible 5. This can prevent the lid 4 from coming off the crucible 5 when the beta-type GaO single crystal is grown while rotating the crucible 5 in the growth step S140 described below. The thickness of the lid 4 is not particularly limited, but may be 5 mm or more, or may be 10 mm or more, from the viewpoint of durability to withstand repeated use. The thickness of the lid 4 is not particularly limited, but may be 50 mm or less.

[0061] The composition of the stabilized zirconia contained in the lid 4 may be different from, or may be the same as, the composition of the stabilized zirconia contained in the crucible 5. In this case, the composition of the stabilized zirconia contained in the lid 4 is the same as that of the crucible 5, so a redundant description will not be repeated. Furthermore, the composition of the second film 4b covering the surface of the lid 4 facing the opening contains both or either Rh and Pt as described above, and the thickness of the second film 4b is 100 μm or more and 500 μm or less. The composition and thickness of this second film 4b may also be different from, or may be the same as, those of the first film 5b covering the inner peripheral surface 5a of the crucible 5 within the above-described ranges. In this case, the composition and thickness of the second film 4b are the same as those of the first film 5b, so a redundant description will not be repeated.

[0062] The surface of the lid 4 facing the opening may have a predetermined surface roughness Rz, or may be smooth. When the surface of the lid 4 facing the opening has a predetermined surface roughness Rz, the surface roughness Rz may be 300 μm or more and 500 μm or less. Furthermore, the second film 4b may have pores or may not have pores. When the second film 4b has pores, the porosity, which is the volume ratio of pores in the second film 4b, may be 10 vol% or more and less than 50 vol%.

[0063] (c) Heating Device The heating device 7 is installed for the purpose of heating the crucible 5. The heating device 7 may be, for example, a conventionally known electric heater (hereinafter simply referred to as "heater"). For example, two heaters are provided, and these two heaters are arranged to surround the outer periphery of the crucible 5. The output of each heater may be controlled independently. In particular, the heater may be divided into multiple sections with respect to the axis of the crucible 5, thereby forming a multi-stage structure. In this case, the output of each heater may be controlled independently for each of the multiple sections. This allows the temperature of the contents (beta-type GaO single crystal and GaO melt) in the crucible 5 to be precisely adjusted along the axis of the crucible 5. For example, by independently controlling the heater output for each of the multi-stage sections to heat the diameter increasing section 52 and the straight body section 53, the growth rates of the crystals growing in the diameter increasing section 52 and the straight body section 53 can be stabilized.

[0064] Although not shown, the single crystal growth apparatus 100 may include a thermocouple capable of measuring the temperature of the crucible 5 heated by the heater. A plurality of thermocouples may be arranged outside the crucible 5 and along the axis thereof. As the thermocouple, for example, a known temperature monitor may be employed.

[0065] (d) Crucible Holder As shown in FIG. 2 , the single crystal growth apparatus 100 includes a crucible holder 6 that holds the crucible 5. The crucible holder 6 contacts the bottom of the crucible 5 to hold the crucible 5. The crucible holder 6 may have a cylindrical appearance. The material of the crucible holder 6 is not particularly limited, but examples of materials that may be used include quartz, alumina, zirconia, and silicon carbide. The outer diameter of the crucible holder 6 depends on the diameter of the crucible 5 it supports, but is, for example, 75 mm or more and 350 mm or less.

[0066] 2, the single crystal growth apparatus 100 may include a sealed container 9 in which the apparatus itself is housed. The sealed container 9 has a heat insulating material 9a on the inner wall of the container. That is, the beta-type GaO single crystal production process S100 may include, as one of the preparation steps S110, a step of preparing a heat insulating material 9a that prevents heat generated by heating the crucible 5 from being transferred to the external environment.

[0067] The insulating material 9a may contain zirconium. The insulating material 9a may contain, for example, stabilized zirconia. This prevents heat generated by heating the crucible 5 from being transferred to the external environment in the beta-type GaO single crystal production step S100. On the other hand, even if the insulating material 9a contains zirconium, the beta-type GaO single crystal grows in the closed space of the crucible 5, the opening of which is closed with the lid 4, in the growth step S140 described below. Therefore, contamination of the beta-type GaO single crystal with the zirconium in the insulating material 9a is prevented. Specifically, the insulating material 9a may be a zirconia fiber insulating material (manufactured by Zircar Zirconia), porous zirconia ceramics (manufactured by TEP Corporation), ZN-1 (manufactured by Eight Ceramics Co., Ltd.), or the like.

[0068] The dimensions and material of the sealed container 9 are not particularly limited as long as it can accommodate the single crystal growth apparatus 100 and the like and has the function of preventing impurities from entering from the outside. The sealed container 9 can be made of alumina, for example.

[0069] 2) Second-Aspect Single Crystal Growth Apparatus FIG. 4 is a schematic diagram illustrating a second-spectrum single crystal growth apparatus used in the manufacturing method for a beta-type GaO single crystal substrate according to this embodiment. In the preparation step S110, for example, a second-spectrum single crystal growth apparatus 200 as shown in FIG. 4 may be prepared. The second-spectrum single crystal growth apparatus 200 shown in FIG. 4 differs from the first-spectrum single crystal growth apparatus 100 in that the lid 4 is made of sapphire. In this case, there is no need to consider the risk of the beta-type GaO single crystal being contaminated by zirconium derived from the lid 4. In other words, the lid 4 may be made of sapphire.

[0070] The lid 4 may have a convex portion shaped to fit into the opening of the crucible 5, similar to that of the single crystal growth apparatus 100 of the first embodiment. Furthermore, the surface of the lid 4 facing the opening may be coated with a second film containing both or either Rh and Pt. In this case, the thickness of the second film may be 100 μm or more and 500 μm or less. The composition of the second film may also be different from or the same as that of the first film 5b within the above-mentioned range. The second film may or may not have pores. The surface of the lid 4 facing the opening may have a predetermined surface roughness Rz, or may be smooth.

[0071] In the single crystal growth apparatus 200 of the second embodiment, the components other than the lid 4, namely the crucible 5, the crucible holder 6, the heating device 7, and the sealed container 9, may be the same as those of the single crystal growth apparatus 100 of the first embodiment. In this case, since the crucible 5, the crucible holder 6, the heating device 7, and the sealed container 9 in the single crystal growth apparatus 200 of the second embodiment are the same as those in the single crystal growth apparatus 100 of the first embodiment, redundant description will not be repeated.

[0072] 3) Single Crystal Growth Apparatus of Third Aspect FIG. 5 is a schematic diagram illustrating a single crystal growth apparatus of a third aspect used in the manufacturing method of a beta-type GaO single crystal substrate according to this embodiment. In the preparation step S110, for example, a single crystal growth apparatus 300 of the third aspect as shown in FIG. 5 may be prepared. The single crystal growth apparatus 300 of the third aspect shown in FIG. 5 differs from the single crystal growth apparatus 100 of the first aspect and the single crystal growth apparatus 200 of the second aspect in that the crucible 5 and the lid 4 are made of sapphire. In this case, there is no need to consider the risk of the beta-type GaO single crystal being contaminated by zirconium derived from the crucible 5 and the lid 4. In other words, the crucible 5 and the lid 4 may be made of sapphire. The lid 4 in the single crystal growth apparatus 300 of the third aspect may be the same as that in the single crystal growth apparatus 200 of the second aspect. In this case, the lid 4 is the same as that of the single crystal growth apparatus 200 of the second embodiment, and therefore a duplicated description will not be repeated.

[0073] The crucible 5 may have a cylindrical shape. Specifically, the crucible 5 may have a disk-shaped bottom surface 54 and a cylindrical side surface 55, with the side surface 55 and the bottom surface 54 joined by sapphire diffusion bonding. In the crucible 5 of this type, the maximum inner diameter means the inner diameter of the side surface 55 as described above, and may be 100 mm or more. The upper limit of the inner diameter may be, for example, 330 mm.

[0074] The crucible 5 may be fabricated as follows. First, a cylindrical side wall 55 is prepared by hollowing out the center of the axis of a predetermined cylindrical sapphire single crystal. The thickness of the side wall 55 may be 1 mm or more and 10 mm or less. Meanwhile, a disk-shaped sapphire single crystal having the same diameter as the outer diameter of the cylindrical side wall 55 is prepared, which serves as the bottom wall 54. The thickness of the bottom wall 54 may also be 1 mm or more and 10 mm or less. Next, one end of the side wall 55 and the flat surface of the bottom wall 54 are joined together so that their central axes coincide, forming an integrated body. The integrated body is then heat-treated at 1500°C or more for 10 to 20 minutes, thereby performing diffusion bonding of the sapphire. This completes the fabrication of the crucible 5 for the single crystal growth apparatus 300 of the third embodiment.

[0075] The inner peripheral surface of the crucible 5 is coated with a first film 5b containing both or either Rh and Pt, similar to that of the single crystal growth apparatus 100 of the first embodiment. This first film 5b may be the same as that of the single crystal growth apparatus 100 of the first embodiment in terms of its composition, thickness, the fact that it is formed by thermal spraying toward the inner peripheral surface of the crucible 5, and the fact that it has pores. In this case, since the first film 5b is the same as that of the single crystal growth apparatus 100 of the first embodiment, a redundant description will not be repeated. The inner peripheral surface of the crucible 5 may have a surface roughness Rz of 300 μm or more and 500 μm or less. Since the characteristics of the inner peripheral surface of such a crucible 5 are also the same as those of the single crystal growth apparatus 100 of the first embodiment, a redundant description will not be repeated.

[0076] In the single crystal growth apparatus 300 of the third embodiment, the components other than the crucible 5 and the lid 4, namely the crucible holder 6, the heating device 7, and the sealed container 9, may be the same as those in the single crystal growth apparatus 100 of the first embodiment and the single crystal growth apparatus 200 of the second embodiment. Therefore, since the crucible holder 6, the heating device 7, and the sealed container 9 in the single crystal growth apparatus 300 of the third embodiment are the same as those in the single crystal growth apparatus 100 of the first embodiment and the single crystal growth apparatus 200 of the second embodiment, redundant description will not be repeated.

[0077] (Melting Step S120) As shown in Fig. 1, the beta-type GaO single crystal manufacturing process S100 may include a melting step S120. The melting step S120 is a step of placing a seed crystal 8a and the GaO bulk body in a crucible 5, melting the GaO bulk body and a portion of the seed crystal 8a to obtain a GaO melt, and bringing the GaO melt into contact with the remainder of the seed crystal 8a. In other words, the melting step S120 is a combination of the following raw material charging step and raw material melting step. The raw material charging step is a step of placing a seed crystal 8a at the bottom of the crucible 5 and placing a massive GaO bulk body above the seed crystal 8a in the crucible 5. The raw material melting step is a step of heating the crucible 5 with the heating device to melt the GaO bulk body and a portion of the seed crystal 8a to obtain a GaO melt, and bringing the GaO melt into contact with the remainder of the seed crystal 8a.

[0078] In the raw material charging step, solid B2O3 may be placed in the crucible 5 above the seed crystal 8a along with the Ga2O3 bulk mass. The purpose of the raw material charging step is to seal various raw materials for crystal growth in the crucible 5 using the single crystal growth apparatus. In the raw material charging step, a seed crystal 8a consisting of a beta-type Ga2O3 single crystal is first placed in the hollow portion of the seed crystal storage portion 51 of the crucible 5 in the single crystal production apparatus of the first and second embodiments, or in the bottom of the crucible 5 in the single crystal production apparatus of the third embodiment. Next, multiple Ga2O3 bulk masses are loaded and stacked in the increased diameter portion and straight body portion of the crucible 5 in the single crystal production apparatus of the first and second embodiments, or in the internal space of the crucible 5 in the single crystal production apparatus of the third embodiment. In the raw material charging step, when a plurality of GaO bulk bodies are charged into the crucible 5, a predetermined amount of tin (Sn) may be added. As a result, a beta-type GaO single crystal substrate containing the Sn as a dopant is obtained from the beta-type GaO single crystal obtained in the beta-type GaO single crystal manufacturing step. As for the Sn, a material with low alpha ray emission is commercially available, as will be described later. When the Sn is added, the concentration of the dopant in the beta-type GaO single crystal substrate is set to, for example, 1.0 × 10 18 cm -3 (5.0 x 10 17 cm -3 Above 4.0 x 10 19 cm -3 The amount added may be adjusted so that the

[0079] In the raw material melting step, the crucible 5 is heated by the heating device, melting the GaO bulk and a portion of the seed crystal 8a to form a GaO melt, and the GaO melt comes into contact with the remainder of the seed crystal 8a. The purpose of the raw material melting step is to melt the GaO bulk and a portion of the seed crystal 8a and bring the seed crystal 8a into contact with the GaO melt so that a beta-type GaO single crystal can grow on the remainder of the seed crystal 8a in the growth step S140 described below. Specifically, in the raw material melting step, the crucible 5 containing the seed crystal 8a and the GaO bulk is supported on a crucible holder. Then, current is supplied to the heating device to heat the crucible 5. This melts the GaO bulk and forms a GaO melt. Next, a part of the seed crystal 8a also melts, and the remainder of the seed crystal 8a comes into contact with the Ga2O3 melt at the interface.

[0080] (Closure Step S130) The beta-type GaO single crystal production process S100 includes a closure step S130. The closure step S130 is a step of closing the opening of the crucible 5 with a lid. The purpose of the closure step S130 is to form a closed space in which the beta-type GaO single crystal will grow in the growth step S140, which will be described later. Specifically, the closure step S130 involves closing the opening of the crucible 5 with a lid. This operation is performed manually or by machine. The closure step S130 may be performed after the crucible 5 containing the seed crystal 8a and the GaO bulk body is supported on the crucible holder in the melting step S120, but before current is supplied to the heating device.

[0081] (Growing Step S140) The beta-type GaO single crystal manufacturing process S100 includes a growing step S140. The growing step S140 is a step of heating the crucible 5 to grow a beta-type GaO single crystal. The purpose of growing step S140 is to obtain a beta-type GaO single crystal until it reaches a predetermined thickness in the closed space formed in the closing step S130. In growing step S140, for example, the crucible 5 is gradually lowered downward along its axis (toward the seed crystal 8a) relative to the heating device, thereby forming a temperature gradient in the crucible 5 such that the temperature at the position of the seed crystal 8a is low and the temperature at the position of the GaO melt is high. As a result, the GaO melt in contact with the seed crystal 8a solidifies, and a beta-type GaO single crystal is continuously produced (grown) from the GaO melt on the remaining portion of the seed crystal 8a. At this time, the temperature at the position of the GaO melt is, for example, 1800 to 1820°C. The temperature gradient at the interface between the GaO melt and the growing beta-type GaO single crystal is, for example, 3°C / cm or more and 8°C / cm or less. The speed at which the crucible is pulled downward along its axis is not particularly limited, but is, for example, 0.1 mm / hour or more and 2 mm / hour or less.

[0082] In the growth step S140, the crucible 5 is pulled downward along its axis relative to the heating device, thereby raising the interface between the beta-type GaO single crystal and the GaO melt, and solidifying the GaO melt as a beta-type GaO single crystal. As a result, the crystal growth of the beta-type GaO single crystal continues until solidification of the GaO melt remaining in the crucible 5 is completed. In this manner, an ingot of a beta-type GaO single crystal is obtained.

[0083] [Method for Manufacturing Beta-Type GaO Single Crystal Substrate] <Beta-Type GaO Single Crystal Substrate Manufacturing Step S200> The method for manufacturing the beta-type GaO single crystal substrate includes a step (beta-type GaO single crystal substrate manufacturing step S200) of obtaining a beta-type GaO single crystal substrate having a circular main surface by processing the beta-type GaO single crystal obtained through the growth step S140, as shown in Fig. 1. The beta-type GaO single crystal substrate manufacturing step S200 includes the following cutting step, outer periphery grinding step, and polishing step, and the beta-type GaO single crystal substrate is obtained by performing these steps in this order.

[0084] The cutting step is a step of slicing the ingot made of a beta-type GaO single crystal removed from the crucible 5 into wafers having a predetermined thickness to obtain beta-type GaO single crystal substrates. The periphery grinding step is a step of grinding the periphery of the wafer to obtain beta-type GaO single crystal substrates having circular main surfaces. The periphery grinding step may include, for example, a chamfering step. The cutting step and the periphery grinding step may use conventionally known cutting and periphery grinding methods. The polishing step is a step of mirror-finishing the main surfaces. Conventionally known polishing methods may be used for the polishing step. The polishing step may result in the main surfaces of the beta-type GaO single crystal substrate having a surface roughness Ra of 10 nm or less as specified in JIS B 0681-2:2018, for example.

[0085] <Effects> By performing the above steps, a beta-type GaO single crystal substrate according to this embodiment is manufactured. In the method for manufacturing a beta-type GaO single crystal substrate, the beta-type GaO single crystal is manufactured using the single crystal manufacturing apparatus according to any one of the first to third aspects described above, so that the beta-type GaO single crystal is prevented from being mixed with zirconium during crystal growth, and the beta-type GaO single crystal is prevented from being contaminated by zirconium. As a result, the amount of alpha-ray emission can be reduced in the beta-type GaO single crystal substrate obtained from the beta-type GaO single crystal.

[0086] [Beta-type GaO single crystal substrate] The beta-type GaO single crystal substrate according to this embodiment has an alpha ray emission rate of 0.05 cph / cm 2 This provides a beta-type GaO single crystal substrate with a low alpha ray emission rate. The inventors have found that the beta-type GaO single crystal substrate obtained by the above-described method for producing a beta-type GaO single crystal substrate has an alpha ray emission rate of 0.05 cph / cm or less. 2 We have discovered the following and have reached the point where we can contribute to preventing soft errors in electronic devices.

[0087] <Major Surface> Figure 6 is a schematic diagram illustrating a beta-type GaO single crystal substrate according to this embodiment. As shown in Figure 6, the beta-type GaO single crystal substrate 1 according to this embodiment has a circular major surface 10. In this specification, the term "circular shape" used to describe the shape of the major surface includes not only a geometric circular shape but also a shape in which the major surface does not form a geometric circular shape due to the formation of at least one of a notch, OF, or IF on the periphery of the major surface 10. Here, the term "a shape in which the major surface does not form a geometric circular shape" refers to a shape in which, among line segments extending from any point on the periphery of the major surface 10 to the center of the main surface 10, the length of a line segment extending from any point on the notch, OF, or IF to the center of the main surface is shorter. Furthermore, the "shape in which the main surface does not form a geometrically circular shape" also includes a shape in which the lengths of all line segments extending from any point on the periphery of the main surface 10 to the center of the main surface 10 are not necessarily the same due to the shape of the beta-type GaO single crystal that is the raw material for the beta-type GaO single crystal substrate 1. In this case, the center of the main surface 10 refers to the position of the center of gravity, and the diameter of the beta-type GaO single crystal substrate 1 refers to the length of the longest line segment among the line segments that extend from any point on the periphery of the beta-type GaO single crystal substrate 1, passing through the center of the main surface 10, to another point on the periphery.

[0088] (The (001) plane of the beta-type GaO single crystal) The main surface 10 is the (001) plane of the beta-type GaO single crystal. Alternatively, the main surface 10 is a plane having an off-angle of more than 0° and not more than 10° from the (001) plane of the beta-type GaO single crystal, and an off-direction that is the

[010] direction of the beta-type GaO single crystal or a direction perpendicular to the

[010] direction. This makes it possible to provide a beta-type GaO single crystal substrate 1 whose main surface 10 is the (001) plane of a beta-type GaO single crystal that is widely used for forming optical devices, electronic devices, etc.

[0089] In this specification, the crystal plane of the main surface 10 is assumed to have an accuracy error of ±0.5°. For example, when the main surface 10 is referred to as the "(001) plane" of a beta-type GaO single crystal, the main surface 10 may be a (001) just plane, or the main surface 10 may be a plane having an off-angle of -0.5 to +0.5° from the (001) plane. The off-angle and off-direction from the (001) plane at the main surface 10 of the beta-type GaO single crystal substrate 1 are measured using a conventionally known crystal orientation measuring device (for example, the product name (product number) "FSASIII" manufactured by Rigaku Corporation).

[0090] <Diameter> The diameter of the beta-type GaO single crystal substrate may be 100 mm or more and 300 mm or less. In this case, a large-diameter beta-type GaO single crystal substrate with a small amount of alpha-ray emission is provided. In particular, the diameter of the beta-type GaO single crystal substrate 1 may be 100 mm or more and 155 mm or less. The beta-type GaO single crystal substrate 1 having a diameter of 100 mm or more and 155 mm or less may specifically have a diameter of 101.6 mm or 152.4 mm, in other words, a diameter of 4 inches or 6 inches. Even if the main surface has a shape that is not geometrically circular due to the influence of an orientation flat (hereinafter also referred to as "OF"), an index flat (hereinafter also referred to as "IF"), etc., the diameter of the beta-type GaO single crystal substrate is determined based on the circular shape before the formation of the OF, IF, etc. The diameter of the beta type Ga2O3 single crystal substrate is measured using a conventionally known outer diameter measuring device such as a vernier caliper.

[0091] <Alpha ray emission yield> The alpha ray emission yield of the beta type GaO single crystal substrate is 0.05 cph / cm 2 The alpha ray emission rate is 0.03 cph / cm 2 The alpha ray emission rate may be 0.01 cph / cm or less. 2 In this specification, the unit of the amount of alpha-ray emission, "cph," means counts per hour, and may be, for example, counts per hour and cm as measured using a nuclide fission type α (alpha) counter (product name (product number): "KS-1000" manufactured by Hitachi, Ltd.). 2 The amount of alpha rays emitted from the beta type Ga2O3 single crystal substrate is specifically measured as follows.

[0092] The beta-type GaO single crystal substrate to be used as the measurement sample is packed with nitrogen until immediately before measurement. For example, if the beta-type GaO single crystal substrate has a diameter of 150 mm, it is prepared as a square plate sample with a side length of 130 mm and centered at the center of its main surface. The counter is used for the plate sample, and the decay energy in the range of 2 to 9 MeV (megaelectronvolts) is measured. The resolution of the counter is 200 keV. The lower measurement limit of the counter is 0.005 cph / cm. 2 The measurement time was 200 hours. Therefore, the alpha ray emission rate of the beta type GaO single crystal substrate was 0.005 cph / cm 2 If it is less than this, it may not be detected by the counter.

[0093] <Zirconium Content> The zirconium (Zr) content of the beta-type GaO single crystal substrate may be 0.02 mass ppm or less. In this case, beta-type GaO single crystal substrates with low alpha ray emission are provided with a high yield. The lower limit of the Zr content may be 0 mass ppm as an ideal value (or Zr may not be detected in measurements using glow discharge mass spectrometry (GDMS), which will be described later). The Zr content of the beta-type GaO single crystal substrate is measured using glow discharge mass spectrometry (GDMS).

[0094] (Glow Discharge Mass Spectrometry (GDMS)) A method for measuring the Zr content in the beta-type GaO single crystal substrate using the GDMS is described below. GDMS is a technique in which glow discharge plasma is generated using the analytical sample as the cathode in a high-purity argon atmosphere, the surface of the analytical sample is sputtered in the plasma, and the ionized constituent elements of the analytical sample are measured using a mass spectrometer. This allows for qualitative and quantitative determination of impurity elements, including Zr, other than Ga and O contained in the beta-type GaO single crystal substrate. Either a flat cell or a pin-shaped cell is used as the ion source for the GDMS. The pin-shaped cell is used for analytical samples that can be formed into strips approximately 2 mm square and 20 mm long. Specifically, it is used when analyzing Si single crystals, gallium arsenide (GaAs) single crystals, indium phosphide (InP) single crystals, and the like, which can be prepared by cleavage. The flat cell is applied to analytical samples that can be formed into a disk shape with a diameter of about 10 mm, for example, when analyzing polycrystalline bodies. In either case, from the viewpoint of avoiding contamination of the analytical sample with external impurity elements, either a flat cell or a pin-shaped cell may be selected as the GDMS ion source. Since the beta-type GaO single crystal substrate can be cleaved longitudinally to produce a pin-shaped analytical sample, an analytical sample formed into a pin-shaped cell from the beta-type GaO single crystal substrate can be used as the GDMS ion source.

[0095] The GDMS is performed, for example, as follows. First, a beta-type GaO single crystal substrate is obtained by the manufacturing method described below. A GaO analysis sample, 2 mm square and 20 mm long, is then prepared from the beta-type GaO single crystal substrate by processing it so that the longitudinal direction is the cleavage direction. This GaO analysis sample is then placed on the sample placement section of the apparatus described below. The sample placement section is cleaned in advance by a conventional method to prevent and remove foreign matter, and pre-sputtering is performed for 60 minutes. The analysis value during pre-sputtering serves as the background.

[0096] Next, GDMS is performed on the GaO analysis sample placed on the sample placement surface under the following conditions. For Zr, an element other than Ga and O in the GaO analysis sample, a semi-quantitative value is calculated by correcting the ion intensity ratio of Ga to Zr using the relative sensitivity factor (RSF). The relative sensitivity factor is a value stored in the software provided with the following instrument: Instrument: Glow discharge mass spectrometer (product name (product number): VG-9000, manufactured by VG Elemental); Ion source: Pin cell (cooled with liquid nitrogen during analysis); Discharge area: 10 mm diameter; Discharge gas: High-purity argon (6N grade); Discharge conditions: 2 mA, 1 kV (constant current mode); Detector: Faraday cup and multiplier; Mass resolution: 4000 m / Δm or higher (high resolution mode).

[0097] By analyzing the Ga2O3 analysis sample in the above manner, the Zr contained in the beta type Ga2O3 single crystal substrate can be qualitatively and quantitatively determined.

[0098] <Tin Content> The Sn content of the beta-type GaO single crystal substrate may be 0.01 mass ppm or more and 200 mass ppm or less. In particular, the beta-type GaO single crystal substrate may be doped with Sn. In such a case, the Sn content of the beta-type GaO single crystal substrate may be 1 mass ppm or more and 200 mass ppm or less. In this case, the alpha ray emission amount can be reduced in a beta-type GaO single crystal substrate containing Sn as a dopant. This is because Sn is commercially available as a solder material for semiconductor applications, etc., with reduced alpha ray emission. Therefore, commercially available Sn with reduced alpha ray emission can be used as a dopant for the beta-type GaO single crystal substrate.

[0099] The Sn content may be 10 ppm by mass or more and 200 ppm by mass or less. The Sn content can also be measured by the above-mentioned GDMS.

[0100] <Applications> The beta-type GaO single crystal substrate according to this embodiment has an extremely low alpha ray emission rate and can therefore be used as a substrate for forming optical devices and electronic devices. In particular, the beta-type GaO single crystal substrate can be used as a substrate that contributes to reducing soft errors when fabricating electronic devices.

[0101] [Additional Notes] The above description includes the following additional notes.

[0102] <Supplementary Note 1> An apparatus for growing beta-type GaO single crystals, comprising at least a cylindrical crucible having an opening, and a lid for closing the opening, wherein an inner peripheral surface of the crucible is coated with a first film containing both or either one of rhodium and platinum, and a thickness of the first film is 100 μm or more and 500 μm or less.

[0103] <Supplementary Note 2> The single-crystal growth apparatus for growing beta-type GaO single crystals according to Supplementary Note 1, wherein a surface of the lid facing the opening is coated with a second film containing both or either one of rhodium and platinum, and the second film has a thickness of 100 μm or more and 500 μm or less.

[0104] <Supplementary Note 3> The single crystal growth apparatus for growing beta-type Ga2O3 single crystals according to Supplementary Note 1 or Supplementary Note 2, wherein the lid is made of sapphire.

[0105] <Supplementary Note 4> The single crystal growth apparatus for growing a beta-type Ga2O3 single crystal according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the crucible contains stabilized zirconia.

[0106] <Appendix 5> The apparatus for growing a beta-type Ga2O3 single crystal according to appendix 2, wherein the lid contains stabilized zirconia.

[0107] <Supplementary Note 6> The single crystal growth apparatus for growing beta-type GaO single crystals according to Supplementary Note 1, wherein the crucible and the lid are made of sapphire, and the crucible has a disk-shaped bottom surface and a cylindrical side surface, and the side surface and the bottom surface are joined by sapphire diffusion bonding to form a cylindrical shape.

[0108] <Supplementary Note 7> The single-crystal growth apparatus for growing beta-type Ga2O3 single crystals according to any one of Supplementary Note 1 to Supplementary Note 6, wherein the surface roughness Rz of the inner peripheral surface is 300 μm or more and 500 μm or less.

[0109] <Supplementary Note 8> The single-crystal growth apparatus for growing a beta-type Ga2O3 single crystal according to any one of Supplementary Note 1 to Supplementary Note 7, wherein the crucible has a thickness of 1 mm or more and 10 mm or less, and the maximum inner diameter of the crucible is 100 mm or more.

[0110] <Supplementary Note 9> 99% by mass or more of the platinum is １９６ 9. A single crystal growth apparatus for growing beta-type Ga2O3 single crystals according to any one of appendices 1 to 8, which comprises an isotope nuclide of Pt.

[0111] <Supplementary Note 10> The single-crystal growth apparatus for growing a beta-type GaO single crystal according to any one of Supplementary Note 1 to Supplementary Note 9, further comprising a heat insulating material that prevents heat generated by heating the crucible from being transferred to an external environment, the heat insulating material containing zirconia.

[0112] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. In these examples, a beta-type GaO single crystal substrate with a diameter of 150 mm was manufactured according to the flowchart shown in FIG. 1. In the following description, Samples 1 to 8 are examples. Samples 101 and 102 are comparative examples.

[0113] [Manufacturing of beta-type GaO single crystal substrate] <Sample 1> (beta-type GaO single crystal manufacturing step S100, preparation step S110) First, a single crystal growth apparatus 100 of the first embodiment as shown in Fig. 2 was prepared. Specifically, a crucible 5 was prepared, which was made of stabilized ZrO with a purity of 89.2 mass% containing 10.8 mass% CaO, had a thickness of 3 mm, and was provided with a first film 5b having a thickness of 200 µm on its inner circumferential surface 5a. The first film 5b was formed by spraying a first spray material onto the inner circumferential surface 5a to form a first sprayed film made of Rh, having a porosity of 30%, and having a thickness of 50 µm. The first film 5b was formed by spraying a second spray material onto the first sprayed film to form a second sprayed film made of Pt, having a porosity of 30%, and having a thickness of 150 µm. The maximum inner diameter of the crucible 5 was 150 mm. The surface roughness Rz of the inner peripheral surface 5a was 20 μm.

[0114] Furthermore, a lid 4 was prepared, which was made of stabilized ZrO2 with a purity of 89.2% by mass and containing 10.8% by mass of CaO, and had a thickness of 3 mm. The second film 4b was a Pt-Rh alloy containing 30% by mass of Rh. A seed crystal 8a consisting of a beta-type Ga2O3 single crystal and a bulk Ga2O3 polycrystal were prepared by a conventionally known method or by purchasing commercially available products.

[0115] (Melting step S120) Next, by a conventionally known method, a seed crystal 8a was placed in the seed crystal accommodation portion 51 of the crucible 5, and a chunk of GaO polycrystal was placed above the seed crystal 8a. Specifically, a plurality of chunks of GaO polycrystal were placed and stacked in the increased diameter portion 52 and the straight body portion 53. Next, the crucible 5 containing the seed crystal 8a and the chunk of GaO polycrystal was supported by the crucible holder 6. Thereafter, an electric current was supplied to the heating device 7 to heat the crucible 5, and the GaO polycrystal and a portion of the seed crystal 8a were melted, thereby preparing a GaO melt 82. Next, the remaining portion of the seed crystal 8a and the GaO melt 82 came into contact at their interface.

[0116] (Closure step S130) The crucible 5 was closed with the lid 4. This operation was performed using a predetermined machine. The closing step S130 was performed after the crucible 5 containing the seed crystal 8a and the GaO bulk body in the melting step S120 was supported on the crucible holder 6 and before a current was supplied to the heating device 7.

[0117] (Growth Step S140) The crucible 5 was gradually pulled downward along its axis (from the lid 4 toward the seed crystal 8a) relative to the heating device 7, thereby forming a temperature gradient in the crucible 5 such that the temperature at the position of the seed crystal 8a was low and the temperature at the position of the GaO melt 82 was high. As a result, a crystal grew from the GaO melt 82 onto the remaining portion on the seed crystal 8a side, with the growth direction being the

[001] direction, thereby obtaining a beta-type GaO single crystal 81. This operation was further continued until the pulling-down distance reached 100 mm. The temperature at the interface between the growing beta-type GaO single crystal 81 and the GaO melt 82 was 1800 to 1820°C. The temperature gradient at the interface was 5°C / cm. The speed at which the crucible 5 was pulled downward along its axis was 1 mm / hour. In this way, an ingot of beta-type Ga2O3 single crystal was obtained. The outer diameter of the beta-type Ga2O3 single crystal was 153 mm.

[0118] (Beta-type GaO single crystal substrate manufacturing process S200) The beta-type GaO single crystal ingot obtained in the growing process S140 was processed in each of the processes of a cutting process, a periphery grinding process, and a polishing process, thereby obtaining a beta-type GaO single crystal substrate. First, in the cutting process, a conventionally known method was used to slice the ingot into wafers having a thickness of 700 μm. In the periphery grinding process, a conventionally known method was used to grind the periphery of the wafer so as to chamfer it, thereby obtaining wafers having main surfaces consisting of a central portion and an outer periphery surrounding the periphery of the central portion. Furthermore, in the polishing process, a conventionally known polishing method was used to polish the central portion, so that the surface roughness Ra of the central portion, as specified in JIS B 0681-2:2018, was 8 nm, for example.

[0119] In this way, a beta-type Ga2O3 single crystal substrate was produced as Sample 1. The diameter of the beta-type Ga2O3 single crystal substrate as Sample 1 was 152.4 mm, and the thickness was 650 μm.

[0120] <Sample 2> In the preparation step S110, a single crystal growth apparatus 200 of the second embodiment as shown in Fig. 4 was prepared. A beta-type GaO single crystal ingot was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of Sample 1, and the beta-type GaO single crystal substrate of Sample 2 was obtained from the beta-type GaO single crystal ingot. That is, for Sample 2, the beta-type GaO single crystal ingot was produced by using a sapphire lid 4. No second film was formed on the surface of the sapphire lid 4 facing the opening of the crucible 5. The diameter of the beta-type GaO single crystal substrate of Sample 2 was 152.4 mm and its thickness was 650 µm.

[0121] <Sample 3> In the preparation step S110, a single crystal growth apparatus 300 of the third embodiment as shown in Fig. 5 was prepared. A beta-type GaO single crystal ingot was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of Sample 1, and the beta-type GaO single crystal substrate of Sample 3 was obtained from the beta-type GaO single crystal ingot. That is, for Sample 3, the beta-type GaO single crystal ingot was manufactured by using a sapphire lid 4 and crucible 5. No second film was formed on the surface of the sapphire lid 4 facing the opening of the crucible 5.

[0122] The sapphire crucible 5 had a disk-shaped bottom surface 54 and a cylindrical side surface 55, and the side surface 55 and the bottom surface 54 were joined by sapphire diffusion bonding to form a cylindrical shape. The maximum inner diameter of the sapphire crucible 5 was the inner diameter of the side surface 55, which was 150 mm. The diameter of the beta-type GaO single crystal substrate of Sample 3 was 152.4 mm, and the thickness was 650 μm.

[0123] <Sample 4> In the preparation step S110, a single crystal growth apparatus 300 according to the third embodiment as shown in FIG. 5 is prepared, and Pt contained in the first film 5b covering the inner peripheral surface of the crucible 5 of the single crystal growth apparatus 300 is １９６ Apart from that, a beta-type GaO single crystal ingot was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of sample 3, and the beta-type GaO single crystal substrate of sample 4 was obtained from the beta-type GaO single crystal ingot. The beta-type GaO single crystal substrate of sample 4 had a diameter of 152.4 mm and a thickness of 650 μm.

[0124] <Samples 5 to 8> When the seed crystal 8a and the GaO polycrystal were placed in the crucible 5 in the melting step S120, Sn, which functions as a dopant in the substrate, was added. A beta-type GaO single crystal ingot was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of Sample 1, and the beta-type GaO single crystal substrate of Sample 5 was obtained from the beta-type GaO single crystal ingot. Similarly, a beta-type GaO single crystal substrate of Sample 6 was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of Sample 2, except for the addition of Sn, which functions as a dopant in the substrate. A beta-type GaO single crystal substrate of Sample 7 was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of Sample 3, and a beta-type GaO single crystal substrate of Sample 8 was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of Sample 4. The amount of alpha-ray emission from the Sn was measured by the method using the above-mentioned nuclide fission type α (alpha) counter, and was below the lower limit of detection (0.005 cph / cm 2 The diameter of the beta-type Ga2O3 single crystal substrates of Samples 5 to 8 was 152.4 mm, and the thickness was 650 μm.

[0125] <Sample 101> In the preparation step S110, the single crystal growth apparatus 100 of the first embodiment was prepared as shown in Fig. 2, excluding the lid 4. A beta-type GaO single crystal ingot was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of Sample 1, and the beta-type GaO single crystal substrate of Sample 101 was obtained from the beta-type GaO single crystal ingot. The beta-type GaO single crystal substrate of Sample 101 had a diameter of 152.4 mm and a thickness of 650 µm.

[0126] <Sample 102> When the seed crystal 8a and GaO polycrystal were placed in the crucible 5 in the melting step S120, Sn, which functions as a dopant in the substrate, was added. Apart from that, a beta-type GaO single crystal ingot was obtained in the same manner as the method for obtaining the beta-type GaO single crystal substrate of sample 101, and the beta-type GaO single crystal substrate of sample 102 was obtained from the beta-type GaO single crystal ingot. The beta-type GaO single crystal substrate of sample 102 had a diameter of 152.4 mm and a thickness of 650 μm.

[0127] [Evaluation] <Alpha ray emission amount> The alpha ray emission amount (unit: cph / cm) of the beta type GaO single crystal substrates of Samples 1 to 8 and Samples 101 to 102 was measured by the method using the above-mentioned nuclide fission type α (alpha) counter. 2 The results are shown in Table 1. In Table 1, "<0.01" in the zirconium content column means that the content is below the lower limit of detection.

[0128] <Zirconium Content and Tin Content> Using the above-described method using GMDS, the zirconium content and tin content (unit: ppm by mass) of the beta-type GaO single crystal substrates of Samples 1 to 8 and Samples 101 and 102 were measured. The results are shown in Table 1.

[0129]

[0130] [Discussion] According to Table 1, the beta type GaO single crystal substrates of Samples 1 to 8, which were manufactured using a single crystal growth apparatus equipped with the lid 4, had an alpha ray emission rate of 0.05 cph / cm 2 The beta type GaO single crystal substrates of samples 1 to 8 had a zirconium content of 0.02 mass ppm or less and a tin content of 0.01 mass ppm or more and 200 mass ppm or less. From the above, the beta type GaO single crystal substrates of samples 1 to 8 are evaluated as having a small amount of alpha ray emission.

[0131] Although the embodiments and examples of the present disclosure have been described above, it is also intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined.

[0132] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0133] S100 Beta-type GaO single crystal manufacturing process, S110 Preparation process, S120 Melting process, S130 Closing process, S140 Growing process, S200 Beta-type GaO single crystal substrate manufacturing process, 100, 200, 300 Single crystal growing apparatus, 4 Lid, 4b Second film, 5 Crucible, 51 Seed crystal accommodating section, 52 Diameter increasing section, 53 Straight body section, 54 Bottom surface section, 55 Side surface section, 5a Inner peripheral surface, 5b First film, 5c Hole, 6 Crucible holding stand, 7 Heating device, 8a Seed crystal, 81 Beta-type GaO single crystal, 82 GaO melt, 9 Sealed container, 9a Heat insulating material, 1 Beta-type Ga2O3 single crystal substrate, 10 main surface, OF orientation flat.

Claims

1. A method for producing a beta-type digallium trioxide single crystal, comprising: a step of closing an opening of a crucible with a lid; and a step of growing a beta-type digallium trioxide single crystal by heating the crucible, wherein the inner peripheral surface of the crucible is coated with a first film containing both or either of rhodium and platinum, and the thickness of the first film is 100 μm or more and 500 μm or less, and the growing step is a step of growing the beta-type digallium trioxide single crystal in a closed space formed by closing the opening with the lid.

2. The method for producing beta-type gallium trioxide single crystals according to claim 1, wherein the surface of the lid facing the opening is coated with a second film containing rhodium and / or platinum, and the thickness of the second film is 100 μm or more and 500 μm or less.

3. A method for producing beta-type gallium trioxide single crystals according to claim 1 or claim 2, wherein the lid is made of sapphire.

4. A method for producing a beta-type gallium trioxide single crystal according to any one of claims 1 to 3, wherein the crucible contains stabilized zirconia.

5. The method for producing a beta-type gallium trioxide single crystal according to claim 2, wherein the lid contains stabilized zirconia.

6. A method for producing beta-type gallium trioxide single crystals according to any one of claims 1 to 3, wherein the crucible and the lid are made of sapphire, and the crucible has a disk-shaped bottom surface and a cylindrical side surface, and the side surface and the bottom surface are joined by diffusion bonding of the sapphire to form a cylindrical shape.

7. A method for producing beta-type gallium trioxide single crystals according to any one of claims 1 to 6, wherein the surface roughness Rz of the inner peripheral surface is 300 μm or more and 500 μm or less.

8. A method for producing beta-type gallium trioxide single crystals according to any one of claims 1 to 7, wherein the crucible has a thickness of 1 mm or more and 10 mm or less, and the maximum inner diameter of the crucible is 100 mm or more.

9. 99% by mass or more of the platinum is １９６ The method for producing a beta-type digallium trioxide single crystal according to any one of claims 1 to 8, comprising an isotope nuclide of Pt.

10. A method for producing a beta-type gallium trioxide single crystal according to any one of claims 1 to 9, comprising a step of preparing an insulating material that prevents heat generated by heating the crucible from being transferred to the external environment, the insulating material containing zirconium.

11. A method for producing a beta-type digallium trioxide single crystal substrate, comprising a step of processing a beta-type digallium trioxide single crystal obtained by the method for producing a beta-type digallium trioxide single crystal according to any one of claims 1 to 10, to obtain a beta-type digallium trioxide single crystal substrate having a circular main surface.

12. Alpha radiation emission rate is 0.05 cph / cm ２ The following is a beta-type gallium sesquioxide single crystal substrate.

13. The alpha ray emission rate is 0.03 cph / cm ２ The beta-type gallium trioxide single crystal substrate according to claim 12, wherein:

14. A beta-type gallium trioxide single crystal substrate according to claim 12 or 13, having a zirconium content of 0.02 mass ppm or less.

15. A beta-type digallium trioxide single crystal substrate according to any one of claims 12 to 14, wherein the tin content is 0.01 ppm by mass or more and 200 ppm by mass or less.

16. The alpha ray emission rate is 0.01 cph / cm ２ The beta-type digallium trioxide single crystal substrate according to any one of claims 12 to 15, wherein the zirconium content is 0.02 ppm by mass or less, and the tin content is 0.01 ppm by mass or more and 200 ppm by mass or less.

17. A beta-type gallium trioxide single crystal substrate according to any one of claims 12 to 16, having a diameter of 100 mm or more and 300 mm or less.

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