Gallium trioxide single crystal substrate, method for producing gallium trioxide single crystal, and method for producing gallium trioxide single crystal substrate

Abstract

This gallium trioxide single crystal substrate has a circular main surface, the diameter of the gallium trioxide single crystal substrate is 100 mm or more, the thickness of the gallium trioxide single crystal substrate is 600 [mu] m or more, the gallium trioxide single crystal substrate contains boron, and the concentration of the boron is 4-200 ppm by mass (inclusive) in glow discharge mass spectrometry.

Description

TECHNICAL FIELD

[0001] The present application relates to a gallium sesquioxide single crystal substrate, a method for manufacturing a gallium sesquioxide single crystal, and a method for manufacturing a gallium sesquioxide single crystal substrate. BACKGROUND

[0002] Japanese Patent Application Publication No. 2016-079080 (Patent Literature 1), Japanese Patent Application Publication No. 2017-193466 (Patent Literature 2), Japanese Patent Application Publication No. 2020-105069 (Patent Literature 3), Japanese Patent Application Publication No. 2020-011899 (Patent Literature 4), and Japanese Patent Application Publication No. 2020-059633 (Patent Literature 5) disclose that a gallium sesquioxide single crystal (hereinafter also referred to as “Ga2O3 single crystal”) is grown in an atmospheric atmosphere by a vertical crystal boat method or an EFG method (Edge-defined Film-fed Growth method) or the like using a crucible composed of a platinum-rhodium alloy (hereinafter also referred to as “Pt-Rh alloy”) or a crucible or a mold composed of a platinum-iridium alloy (hereinafter also referred to as “Pt-Ir alloy”). D. Sajuti et al. Mater. Trans., JIM, 34 (1993), pp. 1195-1199 (Non-Patent Literature 1) discloses the feasibility of a method in which gallium sesquioxide (hereinafter also referred to as “Ga2O3”) is dissolved in liquid boron oxide (hereinafter also referred to as “B2O3”), and then it is cooled, thereby causing Ga2O3 single crystals to precipitate using the difference in solubility between the above-described B2O3 and Ga2O3.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2016-079080;

[0006] Patent Literature 2: Japanese Patent Application Publication No. 2017-193466;

[0007] Patent Literature 3: Japanese Patent Application Publication No. 2020-105069;

[0008] Patent Literature 4: Japanese Patent Application Publication No. 2020-011899;

[0009] Patent Literature 5: Japanese Patent Application Publication No. 2020-059633.

[0010] NON-PATENT LITERATURE

[0011] Non-Patent Literature 1: D. Sajuti et al. Mater. Trans., JIM, 34 (1993), pp. 1195-1199. SUMMARY

[0012] The gallium oxide single crystal substrate of the present application has a main surface in a circular shape. The gallium oxide single crystal substrate has a diameter of 100 mm or more. The gallium oxide single crystal substrate has a thickness of 600 μm or more. The gallium oxide single crystal substrate contains boron. The concentration of the boron is 4 mass ppm or more and 200 mass ppm or less in a glow discharge mass spectrometry. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is an explanatory diagram for explaining a main surface of the gallium oxide single crystal substrate of the present embodiment.

[0014] Figure 2 is an explanatory diagram for explaining measurement points of five positions set on the main surface of the gallium oxide single crystal substrate of Figure 1 for the purpose of obtaining nanoindentation hardness.

[0015] Figure 3 is an explanatory diagram for explaining a sample for Hall test produced using a central portion of the gallium oxide single crystal substrate of the present embodiment for the purpose of measuring each characteristic of resistivity, carrier concentration, and electron mobility of the gallium oxide single crystal substrate.

[0016] Figure 4 is a flowchart showing one example of a manufacturing method of a gallium oxide single crystal substrate including a manufacturing method of a gallium oxide single crystal of the present embodiment.

[0017] Figure 5 is a schematic diagram for explaining a manufacturing apparatus used in the manufacturing method of the gallium oxide single crystal of the present embodiment.

[0018] Figure 6 is a graph showing a relationship between nanoindentation hardness and crack load of the gallium oxide single crystal substrate produced in the example. DETAILED DESCRIPTION

[0019] [PROBLEMS TO BE SOLVED BY THE INVENTION]

[0020] Ga2O3 single crystals are crystals having strong cleavage and are easily cracked in a specific direction. Therefore, in a process of obtaining a gallium sesquioxide single crystal substrate (hereinafter also referred to as "Ga2O3 single crystal substrate") from a Ga2O3 single crystal, there is a concern that a large part of the substrate will be cracked in cases such as at the time of cutting the Ga2O3 single crystal and at the time of peripheral processing, and at the time of transportation after the above-mentioned substrate is obtained. Therefore, for the above-mentioned Ga2O3 single crystal substrate, it is required to suppress cracking. On the other hand, it is known that the strength of a gallium arsenide single crystal to which boron (B) is added as an impurity is improved. In the case where a Ga2O3 single crystal is obtained using a crucible or the like disclosed in the above-mentioned Patent Documents 1 to 5, there is a very small possibility that B is mixed as an impurity in the above-mentioned Ga2O3 single crystal. The above-mentioned Non-Patent Document 1 merely mentions the feasibility of causing a Ga2O3 single crystal to precipitate by using a difference in solubility between B2O3 and Ga2O3, and does not at all teach the effect of improving the strength of the above-mentioned Ga2O3 single crystal substrate and the effect of suppressing cracking of the above-mentioned Ga2O3 single crystal substrate due to the inclusion of B.

[0021] In view of the above, an object of the present application is to provide a gallium sesquioxide single crystal substrate capable of suppressing cracking, a method of manufacturing a gallium sesquioxide single crystal, and a method of manufacturing a gallium sesquioxide single crystal substrate.

[0022] [Effects of the Invention]

[0023] According to the present application, it is possible to provide a gallium sesquioxide single crystal substrate capable of suppressing cracking, a method of manufacturing a gallium sesquioxide single crystal, and a method of manufacturing a gallium sesquioxide single crystal substrate.

[0024] [Summary of Embodiments]

[0025] Hereinafter, a summary of an embodiment of the present application will be described. The present inventors have repeatedly conducted intensive research in order to solve the above-mentioned problems, and thereby completed the present application. The present inventors and the like have found that, in the case where a Ga2O3 single crystal substrate is obtained from a Ga2O3 single crystal to which a trace amount of B is added, cracking can be suppressed, and a concentration of B that can suppress cracking of the above-mentioned substrate. In particular, it has also been found that B and gallium (Ga) are in the same group, and therefore do not adversely affect the electrical characteristics of the above-mentioned substrate, and thereby completed the present application.

[0026] Next, an embodiment of the present application will be described.

[0027] [1] A gallium sesquioxide single crystal substrate of one embodiment of the present application has a main surface that is circular. The diameter of the gallium sesquioxide single crystal substrate is 100 mm or more. The thickness of the gallium sesquioxide single crystal substrate is 600 μm or more. The gallium sesquioxide single crystal substrate contains boron. The concentration of the boron is 4 mass ppm or more and 200 mass ppm or less in glow discharge mass spectrometry. The gallium sesquioxide single crystal substrate having such a feature can suppress generation of cracks.

[0028] [2] The concentration of the boron is preferably 5 mass ppm or more and 100 mass ppm or less in glow discharge mass spectrometry. Thus, the gallium sesquioxide single crystal substrate can be further suppressed from generation of cracks.

[0029] [3] The main surface is preferably a (001) plane of the gallium sesquioxide single crystal. The main surface preferably has a central portion including a center and a peripheral portion surrounding the central portion. The peripheral portion is preferably a region where chamfer processing is performed. In the gallium sesquioxide single crystal substrate, the nanoindentation hardnesses measured at five positions on the main surface under conditions where a load is applied at a maximum load of 10 mN and a direction in which a

[100] direction of the gallium sesquioxide single crystal is projected to the main surface and one side of an indentation form an intersection angle of 0° or more and 10° or less, in a nanoindentation method using a Berkovich indenter, are preferably 14.8 GPa or more and 22.0 GPa or less. When the length from the center of the main surface to the boundary between the central portion and the peripheral portion is r, two axes passing through the center and orthogonal to each other on the main surface are an X axis and a Y axis, and the Y axis is a b axis of the gallium sesquioxide single crystal, the coordinates (X, Y) of the five positions defined by the X axis and the Y axis are preferably (0, 0), (r - 5, 0), (0, r - 5), (-(r - 5), 0), and (0, -(r - 5)). The units of r and X and Y in the coordinates (X, Y) are preferably mm. Thus, the gallium sesquioxide single crystal substrate can be further suppressed from generation of cracks.

[0030] [4] The gallium sesquioxide single crystal substrate sometimes contains both or either of rhodium and iridium. In that case, the concentration of the rhodium and the concentration of the iridium are each preferably 0.1 mass ppm or less in glow discharge mass spectrometry. Thus, in the gallium sesquioxide single crystal substrate, an adverse effect on electrical characteristics can be prevented.

[0031] [5] The resistivity of the gallium sesquioxide single crystal substrate measured at 25 °C in a Hall test using a Van der Pauw method is preferably 1.0 x 10 -3Ω·cm or more and 2.0 Ω·cm or less. The carrier concentration of the above gallium oxide single crystal substrate measured at 25°C in a Hall test using the Van der Pauw method is preferably 4.0 x 10 17 cm -3 or more and 1.4 x 10 19 cm -3 or less. The electron mobility of the above gallium oxide single crystal substrate measured at 25°C in a Hall test using the Van der Pauw method is preferably 0.2 cm 2 / V·s or more and 15,000 cm 2 / V·s or less. Thus, in the above gallium oxide single crystal substrate, good electrical characteristics can be obtained.

[0032] [6] A gallium oxide single crystal production method of one embodiment of the present application is performed in an atmosphere. The above production method includes the following steps: a step of preparing a single crystal growth apparatus having at least a crucible that is cylindrical and a heating device that is disposed so as to surround the outer periphery of the crucible; a step of housing a seed crystal composed of the above gallium oxide single crystal at the bottom of the crucible, and housing a gallium oxide polycrystal, an n-type dopant, and boron oxide in a block shape or a powder shape at a position in the crucible that is higher than the seed crystal; a step of heating the crucible with the above heating device, thereby melting a part of the seed crystal, and obtaining a solution in which gallium oxide from the part of the seed crystal and the gallium oxide polycrystal is dissolved at a first concentration, the n-type dopant is dissolved at a second concentration, and the solution is in contact with the remaining part of the seed crystal; and a step of growing a crystal from the solution on the remaining part of the seed crystal, thereby obtaining a gallium oxide single crystal. The above crucible is composed of platinum. The concentration of boron in the above gallium oxide single crystal is 4 mass ppm or more and 200 mass ppm or less in glow discharge mass spectrometry. With the gallium oxide single crystal production method having such a feature, a gallium oxide single crystal for producing a gallium oxide single crystal substrate in which cracks are less likely to occur can be obtained.

[0033] [7] A method for producing a gallium sesquioxide single crystal according to one embodiment of the present application is performed in a nitrogen atmosphere. The above production method includes the following steps: a step of preparing a single crystal growth apparatus having at least a crucible having a cylindrical shape and a heating device disposed so as to surround the outer periphery of the crucible; a step of housing a seed crystal composed of the gallium sesquioxide single crystal in the bottom of the crucible, and housing a gallium sesquioxide polycrystal, an n-type dopant, and boron oxide in the crucible in a position higher than the seed crystal; a step of heating the crucible with the heating device, thereby melting a part of the seed crystal, and obtaining a solution in which gallium sesquioxide from the part of the seed crystal and the gallium sesquioxide polycrystal is dissolved at a first concentration, the n-type dopant is dissolved at a second concentration, and the solution is in contact with the remaining part of the seed crystal; and a step of growing a crystal from the solution on the remaining part of the seed crystal, thereby obtaining a gallium sesquioxide single crystal. The crucible is composed of pyrolytic boron nitride. The concentration of boron in the gallium sesquioxide single crystal is 4 mass ppm or more and 200 mass ppm or less in glow discharge mass spectrometry. According to the production method of the gallium sesquioxide single crystal having the above features, a gallium sesquioxide single crystal for producing a gallium sesquioxide single crystal substrate capable of suppressing generation of cracks can be obtained.

[0034] [8] The single crystal growth apparatus preferably has a nozzle for feeding the gallium sesquioxide polycrystal and the n-type dopant into the crucible, and a lid for sealing the crucible. The lid preferably has a hole into which the nozzle is inserted. The step of obtaining the gallium sesquioxide single crystal preferably includes the following steps: a step of sampling the solution in the crucible sealed by the lid through the nozzle, thereby analyzing the concentration of gallium sesquioxide from the part of the seed crystal and the gallium sesquioxide polycrystal and the concentration of the n-type dopant in the solution; a step of feeding the gallium sesquioxide polycrystal into the solution in the crucible through the nozzle in such a manner that the concentration becomes within 5% of the first concentration, based on the analysis result relating to the concentration of gallium sesquioxide; and a step of feeding the n-type dopant into the solution in the crucible through the nozzle in such a manner that the concentration becomes within 5% of the second concentration, based on the analysis result relating to the concentration of the n-type dopant. Thus, a gallium sesquioxide single crystal for producing a gallium sesquioxide single crystal substrate capable of suppressing generation of cracks can be obtained at a high yield.

[0035] [9] A method for manufacturing a gallium trioxide single crystal substrate of one embodiment of the present application includes a step of processing the gallium trioxide single crystal obtained by the method for manufacturing a gallium trioxide single crystal, and thereby obtaining a gallium trioxide single crystal substrate having a circular main surface. With the method for manufacturing a gallium trioxide single crystal substrate having such a feature, a gallium trioxide single crystal substrate in which generation of cracks is suppressed can be obtained.

[0036]

[10] In the gallium trioxide single crystal substrate described in [2] above, the main surface is preferably a (001) plane of the gallium trioxide single crystal. The main surface preferably has a central portion including a center thereof and a peripheral portion surrounding the central portion. The peripheral portion is preferably a region subjected to chamfer processing. In the gallium trioxide single crystal substrate, the nanoindentation hardness measured at five positions on the main surface under conditions where a Berkovich indenter is used, the maximum load is 10 mN, and the load is applied in such a manner that the direction in which the

[100] direction of the gallium trioxide single crystal is projected on the main surface and one side of the indentation intersect at an angle of greater than or equal to 0° and less than or equal to 10° is preferably greater than or equal to 14.8 GPa and less than or equal to 22.0 GPa. When the length from the center of the main surface to the boundary between the central portion and the peripheral portion is r, two axes that pass through the center and are orthogonal to each other on the main surface are an X axis and a Y axis, and the Y axis is a b axis of the gallium trioxide single crystal, the coordinates (X, Y) of the five positions defined by the X axis and the Y axis are preferably (0, 0), (r - 5, 0), (0, r - 5), (-(r - 5), 0), and (0, -(r - 5)). The units of r and X and Y in the coordinates (X, Y) are preferably mm. The gallium trioxide single crystal substrate preferably contains both or either of rhodium and iridium. The concentration of the rhodium and the concentration of the iridium are each preferably less than or equal to 0.1 mass ppm in a glow discharge mass spectrometry. The resistivity of the gallium trioxide single crystal substrate measured at 25 °C in Hall measurement by the Van der Pauw method is preferably greater than or equal to 1.0 x 10 -3 Ω・cm and less than or equal to 2.0 Ω・cm. The carrier concentration of the gallium trioxide single crystal substrate measured at 25 °C in Hall measurement by the Van der Pauw method is preferably greater than or equal to 4.0 x 10 17 cm -3 and less than or equal to 1.4 x 10 19 cm -3 . The electron mobility of the gallium trioxide single crystal substrate measured at 25 °C in Hall measurement by the Van der Pauw method is preferably greater than or equal to 0.2 cm 2 / V・s and less than or equal to 15000 cm 2 / V・s. Thus, in the gallium trioxide single crystal substrate, generation of cracks can be further suppressed, and good electrical characteristics can be obtained.

[0037] [Details of the implementation method]

[0038] Hereinafter, one embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described in more detail, but the present invention is not limited thereto. Hereinafter, reference will sometimes be made to the accompanying drawings. Figure 1 In this specification and accompanying drawings, identical or corresponding elements are labeled with the same reference numerals, and their descriptions are not repeated. Furthermore, in the accompanying drawings, the scale is appropriately adjusted for ease of understanding of each component element; the scale of each component element shown in the drawings may not be consistent with the actual scale of the component elements.

[0039] In this specification, expressions such as "A~B" refer to the upper and lower limits of a range (i.e., above A and below B). Where no unit is specified in A but only in B, the unit of A is the same as the unit of B. Furthermore, in this specification, when compounds are represented by chemical formulas, all conventionally known atomic ratios are included unless otherwise specified, and are not necessarily limited to atomic ratios within stoichiometric ranges.

[0040] In this specification, the "main surface" of a gallium oxide single crystal substrate refers to both of the two circular surfaces of the aforementioned gallium oxide single crystal substrate. If at least one of these two surfaces satisfies the claims of this invention, it falls within the scope of this invention. Furthermore, in this specification, the term "surface" used in the term "in-plane" refers to the "main surface." Moreover, when the diameter of the gallium oxide single crystal substrate is described as "100 mm," it means a diameter of approximately 100 mm (approximately 95 to 105 mm), or 4 inches. When the diameter is described as "150 mm," it means a diameter of approximately 150 mm (approximately 145 to 155 mm), or 6 inches. Additionally, the aforementioned diameter can be measured using conventionally known outer diameter measuring instruments such as vernier calipers.

[0041] In this specification, "nanoindentation hardness" refers to the indentation hardness obtained by an instrumented indentation test according to the international standard ISO 14577, which includes the nanoindentation method (Ryo Nikenya, "Method for evaluating mechanical properties using a nanoindentation instrument", Analysis, 561 (2021), pp. 457-461). Specifically, it refers to the following hardness: according to the nanoindentation method, an indentation test is performed on a specified position on the main surface of a gallium oxide single crystal substrate using a Burkevich indenter, thereby obtaining a load-displacement curve, and the hardness is obtained by analyzing the load-displacement curve. The above-mentioned "nanoindentation hardness" is obtained by dividing the maximum load (mN) applied to the gallium oxide single crystal substrate by the Burkevich indenter by the area (mm²) of the contact between the Burkevich indenter and the gallium oxide single crystal substrate when the maximum load is applied. 2 The unit for the above "nanoindentation hardness" is Pascal (Pa).

[0042] In the crystallographic descriptions in this specification, [] represents individual orientations, <> represents aggregate orientations, () represents individual planes, and {} represents aggregate planes. Furthermore, while negative crystallographic indices are typically indicated by placing a "-" (hyphen) above the number, in this specification, a negative sign is placed before the number.

[0043] [Gallium trioxide single crystal substrate]

[0044] The gallium trioxide single crystal substrate (Ga2O3 single crystal substrate) of this embodiment is a Ga2O3 single crystal substrate with a circular main surface. The diameter of the Ga2O3 single crystal substrate is 100 mm or more. The thickness of the Ga2O3 single crystal substrate is 600 μm or more. The Ga2O3 single crystal substrate contains boron. The concentration of boron, in glow discharge mass spectrometry analysis, is 4 ppm or more and 200 ppm or less. A Ga2O3 single crystal substrate with these characteristics can suppress crack formation.

[0045] <Diameter and Thickness>

[0046] The diameter of the aforementioned Ga₂O₃ single crystal substrate is 100 mm or more, as described above. In particular, the diameter of the Ga₂O₃ single crystal substrate is preferably 99.5 mm or more and 152.5 mm or less. Specifically, a Ga₂O₃ single crystal substrate with a diameter of 100 mm or 150 mm is preferred; in other words, a Ga₂O₃ single crystal substrate with a diameter of 4 inches or 6 inches is preferred. This allows for a crack-resistant feature in large-size Ga₂O₃ single crystal substrates.

[0047] The thickness of the Ga2O3 single crystal substrate is 600 μm or more, as described above. In particular, the thickness of the Ga2O3 single crystal substrate is preferably 650 μm or more and 700 μm or less. Therefore, a Ga2O3 single crystal substrate with a generally acceptable thickness can be characterized by being less prone to cracking. Regarding the diameter of the Ga2O3 single crystal substrate, even if the main surface is not geometrically circular due to the influence of the positioning edge (hereinafter also referred to as "OF"), indicator edge (hereinafter also referred to as "IF"), etc., the diameter can be determined based on the circular shape before the formation of the OF, IF, etc. Furthermore, as described above, the diameter of the Ga2O3 single crystal substrate can be measured using conventionally known outer diameter measuring instruments such as vernier calipers. The thickness of the Ga2O3 single crystal substrate can be measured using a non-contact thickness measuring instrument (trade name (model): "TAP-2H-200XY", manufactured by COMS Corporation). The positioning accuracy of this measuring instrument is 25 μm. The display resolution of this measuring instrument is 0.01 μm. The repeatability of this measuring instrument is 0.01 μm. Regarding the measuring instrument used for measuring the thickness of Ga2O3 single crystal substrates, as long as the positioning accuracy, display resolution, and repeatability are equal or higher, it is not limited to the above-mentioned measuring instrument; other measuring instruments can also be used. In this specification, "thickness of Ga2O3 single crystal substrate" refers to the thickness at the center of the main surface of the Ga2O3 single crystal substrate.

[0048] <Main Surface>

[0049] (Circular shape)

[0050] The Ga2O3 single-crystal substrate described above has a circular main surface as described. In this specification, the term "circular shape" to refer to the shape of this main surface includes not only a geometrically circular shape, but also the shape where, as described above, the main surface does not have a geometrically circular shape due to the formation of at least one of a groove, OF, or IF on its outer periphery. Here, "the shape where the main surface does not have a geometrically circular shape" refers to a shape where, among the line segments extending from any point on the outer periphery of the main surface to the center of the main surface, the length of the line segment extending from any point on the groove, OF, or IF to the center of the main surface is shorter. Furthermore, "the shape where the main surface does not have a geometrically circular shape" also includes a shape where, due to the shape of the Ga2O3 single crystal used as the raw material for the Ga2O3 single-crystal substrate, the lengths of all line segments extending from any point on the outer periphery of the main surface to the center of the main surface are not necessarily the same. In this case, the center of the main surface refers to the location of the center of gravity, and the diameter of the Ga2O3 single crystal substrate refers to the length of the longest line segment that starts from any point on the outer periphery of the Ga2O3 single crystal substrate, passes through the center of the main surface, and extends to other points on the outer periphery.

[0051] (001 facet of Ga2O3 single crystal)

[0052] The aforementioned main surface is preferably the (001) plane of a Ga2O3 single crystal. It is known that Ga2O3 single crystal substrates with the (001) plane as the main surface are prone to cracking due to external stress because the (001) plane typically has strong cleavage. Therefore, in this embodiment, cracking can be suppressed in Ga2O3 single crystal substrates with the (001) plane as the main surface.

[0053] In this invention, the crystal plane of the main surface has an accuracy error of ±0.5°. For example, the case where the main surface is the "(001) plane" of a Ga2O3 single crystal means that the main surface may be the (001)just plane, or the main surface may be a plane with an angle of -0.5 to +0.5° relative to the (001) plane. The angle of the (001) plane relative to the main surface of the Ga2O3 single crystal substrate can be measured using a conventionally known crystal orientation measuring device (e.g., trade name (model): "2991G2", Rigaku Corporation).

[0054] (Central part and outer perimeter)

[0055] The aforementioned main surface preferably has a central portion containing its center and an outer peripheral portion surrounding the central portion. The outer peripheral portion is preferably a region that has undergone chamfering. Figure 1 This is an explanatory diagram illustrating the main surface of the gallium oxide single-crystal substrate of this embodiment. For example, in Figure 1 In the Ga2O3 single crystal substrate 100 shown, the main surface 10 has a central portion 11 including its center and an outer peripheral portion 12 surrounding the outer periphery of the central portion 11. The central portion 11 is a region in the Ga2O3 single crystal substrate 100 where an epitaxial layer for forming an electronic device is stacked, for example. The outer peripheral portion 12 is a region where a chamfering process has been performed. By performing a chamfering process on the outer peripheral portion 12, when processing the Ga2O3 single crystal substrate 100, the occurrence of cracks and defects at the outer edge of the outer peripheral portion 12 can be reduced. The chamfering process on the outer peripheral portion 12 can be performed using conventionally known methods.

[0056] The central portion 11 preferably has a circular shape. Therefore, the length from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer periphery 12 can be represented by the predetermined value "r," as described later. Here, the "circular shape" representing the shape of the central portion 11 includes not only a geometrically circular shape but also shapes that do not form a geometrically circular shape, such as those resulting from chamfering of the outer periphery 12. In this case, the length r from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer periphery 12 refers to the length of the shortest line segment extending from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer periphery 12. The shape of the central portion 11 can also be a polygon such as a triangle, quadrilateral, or hexagon.

[0057] The width of the outer peripheral portion 12, i.e., the length from the outer edge of the outer peripheral portion 12 to the boundary 13 between the center portion 11 and the outer peripheral portion 12, is preferably 2 to 5 mm. This is because: the area of ​​the width of the outer peripheral portion 12 of the Ga2O3 single crystal substrate 100 is known to have large variations in the number of dislocations and poor flatness in each substrate, in addition to the possibility of residual processing strain from chamfering. It is generally not used as a material for semiconductor devices.

[0058] The central portion 11 and the outer peripheral portion 12 can be distinguished based on the difference in the thickness of the Ga2O3 single crystal substrate 100 in these portions. The thickness of the Ga2O3 single crystal substrate 100 in the outer peripheral portion 12 is less than 99% compared to the thickness of the Ga2O3 single crystal substrate 100 in the central portion 11. That is, the outer peripheral portion 12 refers to the region that has undergone chamfering as described above, and the thickness of this region is less than 99% compared to the thickness of the central portion 11. For example, if the thickness of the central portion 11 is 675 μm, the thickness of the outer peripheral portion 12 is 668 μm or less. The thicknesses of the central portion 11 and the outer peripheral portion 12 can be measured separately using the non-contact thickness measuring instrument described above. For the measuring instrument used to measure the thickness of the central portion 11 and the outer peripheral portion 12, as long as the positioning accuracy, display resolution, and repeatability are equal or higher, it is not limited to the measuring instrument described above, and other measuring instruments can also be used. In this specification, "thickness of the Ga2O3 single crystal substrate 100 of the central portion 11" refers to the thickness of the center O of the main surface 10 of the Ga2O3 single crystal substrate 100. Therefore, the length from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer peripheral portion 12, i.e., "r", can be calculated as a specific numerical value (in mm).

[0059] (Nano-indentation hardness)

[0060] In the aforementioned Ga2O3 single crystal substrate, using a Burkevich indenter nanoindentation method, under the condition that a maximum load of 10 mN is applied and the angle between the direction projected from the

[100] direction of the gallium oxide single crystal onto the main surface and one side of the indentation is 0° or more and 10° or less, the nanoindentation hardness measured at five positions on the main surface is preferably 14.8 GPa or more and 22.0 GPa or less. When the length from the center of the main surface to the boundary between the center and the outer periphery is r, and the two axes passing through the center and orthogonal to each other on the main surface are the X-axis and the Y-axis, and the Y-axis is the b-axis of the gallium oxide single crystal, the coordinates (X, Y) of the five positions defined by the X-axis and the Y-axis are preferably (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)). The units of r and X and Y in the coordinates (X, Y) mentioned above are preferably mm. The nanoindentation hardness measured at the five locations on the main surface is more preferably 15.0 GPa or more and 21.0 GPa or less.

[0061] Figure 2 In order to determine the hardness of nanoindentation Figure 1 An explanatory diagram illustrating the measurement points at five locations set on the main surface of a gallium oxide single-crystal substrate. The following explanation refers to... Figure 2 The method for measuring nanoindentation hardness at five locations on the main surface 10 using a Burkevich indenter is described. This method can be performed using, for example, a nanoindenter (trade name: "Bruker Hysitron TI980 TriboIndenter", manufactured by Bruker Japan Co., Ltd.).

[0062] 1) Prediction

[0063] First, the Ga2O3 single crystal substrate 100 is pre-defined. This pre-defined definition is to apply a load such that the angle between the direction projected onto the main surface from the

[100] direction of the Ga2O3 single crystal and one side of the indentation of the Burkevich indenter is 0° or more and 10° or less. First, the Ga2O3 single crystal substrate 100 is fixed on the sample stage of the nanoindenter. Next, the Ga2O3 single crystal substrate 100 on the sample stage is observed using the optical system of the nanoindenter, thereby designating, for example, any position of the center portion 11 on the main surface 10 as the measurement position. As this measurement position, in order to facilitate the formal measurement described later, it is preferable to designate a position on the main surface 10 other than the five positions mentioned above (i.e., other than the coordinates (X, Y), namely (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)) of the five positions). Next, the Burkovich indenter is moved to the aforementioned measurement position, and an indentation test is performed with a maximum load of 10 mN. Then, the Ga2O3 single crystal substrate 100 is removed from the sample stage. At this time, an indentation from the Burkovich indenter is formed at the aforementioned measurement position, and therefore the intersection angle between one side of this indentation and the

[100] direction of the Ga2O3 single crystal constituting the Ga2O3 single crystal substrate 100 can be determined. This intersection angle can be determined using conventionally known methods.

[0064] 2) Formal measurement

[0065] Next, a formal measurement of the nanoindentation hardness is performed. When the cross angle determined in the above-mentioned prediction is 0° or more and 10° or less, the Ga2O3 single crystal substrate 100 is fixed to the sample stage in the same direction as in the preliminary test. When the cross angle determined in the above-mentioned prediction is greater than 10°, the orientation of the Ga2O3 single crystal substrate 100 is adjusted so that the cross angle is 0° or more and 10° or less, and the Ga2O3 single crystal substrate 100 is fixed to the sample stage. Then, the optical system of the nanoindenter is used to observe the Ga2O3 single crystal substrate 100 on the sample stage, thereby designating one of the five coordinates (X, Y) of the main surface 10 (e.g., (0, 0)) as the measurement position. Next, the Burkovich indenter is moved to the measurement position (e.g., (0, 0)), and an indentation test is performed with a maximum load of 10 mN. Then, the Ga2O3 single crystal substrate 100 is removed from the sample stage. At this time, an indentation of the Burkovich indenter is formed at the measured location. Therefore, based on the indentation, the area (mm²) of the contact between the Burkovich indenter and the Ga₂O₃ single crystal substrate 100 when the maximum load of 10 mN is applied can be calculated. 2 ), and by dividing the maximum load of 10mN by the aforementioned area (mm²) 2This allows us to determine the nanoindentation hardness of the measured location (e.g., (0, 0)).

[0066] Next, as the measurement location, the remaining portions of the coordinates (X, Y) of the aforementioned five locations on the main surface 10 are specified (e.g., (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)). Then, an indentation test is performed at the same points as when (0, 0) is specified as the measurement location, and a prescribed calculation is performed, thereby determining the nano-indentation hardness of the remaining portions of the coordinates (X, Y) of the aforementioned five locations on the main surface 10.

[0067] Here, the aforementioned nanoindentation hardness is determined by an indentation test performed with a maximum load of 10 mN. Under this test, the Burkovich indenter is considered to have penetrated relatively into the interior of the Ga₂O₃ single-crystal substrate, forming an indentation. Therefore, it is possible to determine that the aforementioned nanoindentation hardness reflects the indentation hardness within the Ga₂O₃ single-crystal substrate.

[0068] <Boron (B)>

[0069] The Ga2O3 single-crystal substrate described above contains boron (B). The concentration of B, as determined by glow discharge mass spectrometry (GDMS), is 4 ppm to 200 ppm by mass. If the B concentration in GDMS is less than 4 ppm by mass, the strength improvement effect from the inclusion of B may be insufficient to resist external stresses applied during processing and handling. If the B concentration in GDMS is greater than 200 ppm by mass, B clustering may occur in the Ga2O3 single crystal, or the residual strain may become excessive due to the thermal history during crystal growth, thereby making the Ga2O3 single-crystal substrate prone to cracking. Preferably, the B concentration in GDMS is 5 ppm to 100 ppm by mass. More preferably, the B concentration in GDMS is 50 ppm to 100 ppm by mass.

[0070] The inventors hypothesize that when the Ga₂O₃ single crystal substrate contains boron at the aforementioned concentration, it exhibits appropriate hardness, thereby increasing strength and suppressing crack formation. Specifically, it can be assumed that when B is contained in the Ga₂O₃ single crystal at the aforementioned concentration, B can exist in an isolated, substituted manner at Ga sites within the lattice constituting the Ga₂O₃ single crystal. In this case, a solid solution strengthening effect of B can be expected. In particular, by setting the concentration of B to 4 ppm by mass or more, it can be inferred that, based on the aforementioned effect, sufficient strength can be obtained to resist external stresses applied during processing and handling. On the other hand, by setting the concentration of B to 200 ppm by mass or less, it can be inferred that B will not cluster in the Ga₂O₃ single crystal, or that excessive strength or excessive residual strain caused by the thermal process during crystal growth can be avoided, thus fully leveraging the role of B in mitigating the crack susceptibility of the Ga₂O₃ single crystal substrate.

[0071] (Glow discharge mass spectrometry (GDMS))

[0072] The following describes a method for determining the concentration of boron (B) in the aforementioned Ga₂O₃ single-crystal substrate using glow discharge mass spectrometry (GDMS). GDMS involves generating glow discharge plasma by using the analytical sample as the cathode in a high-purity argon atmosphere, sputtering the surface of the analytical sample within this plasma, and then determining the constituent elements in the ionized analytical sample using a mass spectrometer. This allows for the qualitative and quantitative determination of impurity elements, represented by B, in the aforementioned Ga₂O₃ single-crystal substrate, excluding Ga and O. As the ion source for the GDMS, either a flat cell or a pin-shaped cell can be used. For the pin-shaped cell, it can be applied to analytical samples that can be shaped into an elongated strip approximately 2 mm square and 20 mm in length. Specifically, it can be used when analyzing Si single crystals, gallium arsenide (GaAs) single crystals, and indium phosphide (InP) single crystals, which can be formed into samples through cleavage. The planar element can be used to form an analytical sample in the shape of a disk with a diameter of about 10 mm, for example, in the analysis of polycrystalline materials. In summary, from the viewpoint of avoiding contamination of the analytical sample by external impurity elements, either the planar element or the needle-shaped element is preferred as the ion source of the aforementioned GDMS. When the Ga2O3 single crystal substrate has a (001) plane orientation on its main surface, the analytical sample can be fabricated by cleaving along one direction. Therefore, it is preferable to fabricate an analytical sample with a needle-shaped element having a cleavage plane along its length from the aforementioned Ga2O3 single crystal substrate and use it as the ion source of the GDMS.

[0073] The aforementioned GDMS can be performed by, for example, the following steps. First, a Ga2O3 single-crystal substrate is obtained using the manufacturing method described later. Then, the Ga2O3 single-crystal substrate is cleaved to produce a strip-shaped Ga2O3 analytical sample, 2 mm square and 20 mm in length. The uncleaved sections are cut using known methods such as a precision hand grinder. This sample is then placed in the sample preparation section of the apparatus described below. Here, the sample preparation section is preferably cleaned using conventional methods and pre-sputtered for 60 minutes to prevent and remove foreign matter.

[0074] Next, for the Ga2O3 analytical sample disposed on the aforementioned sample surface, GDMS can be performed under the following conditions. Furthermore, for B, which is an element other than Ga and O among the constituent elements of the Ga2O3 analytical sample, the ionic strength ratio of Ga to B can be corrected using the relative sensitivity factor (RSF), thereby calculating a semi-quantitative value. Additionally, the relative sensitivity factor can be obtained using a value built into the software accompanying the apparatus described below.

[0075] Apparatus: Glow discharge mass spectrometry analyzer (trade name (model): VG-9000, manufactured by VG Elemental)

[0076] Ion source: needle-shaped element (cooled by liquid nitrogen during analysis)

[0077] Discharge area: 10mm in diameter

[0078] Discharge gas: High-purity argon (6N grade)

[0079] Discharge conditions: 2mA, 1kV (constant current mode)

[0080] Detectors: Faraday cup and multiplier

[0081] Quality resolution: 4000 or higher m / Δm (high resolution mode).

[0082] By analyzing the Ga2O3 sample as described above, the qualitative and quantitative analysis of B contained in the Ga2O3 single crystal substrate can be performed. The preferred detection limit concentration for this GDMS is 0.01 ppm by mass.

[0083] <Rhodium (Rh) and Iridium (Ir)>

[0084] The aforementioned Ga2O3 single-crystal substrate sometimes contains rhodium (Rh) and iridium (Ir), or either one. In this case, the concentrations of both Rh and Ir in GDMS are preferably below 0.1 ppm by mass. More preferably, the concentrations of both Rh and Ir in GDMS are below 0.01 ppm by mass. The lower limit for the concentrations of both Rh and Ir is that they are undetectable in GDMS. If the concentrations of Rh and Ir are within the aforementioned ranges, adverse effects on electrical properties can be prevented.

[0085] It is known that Rh and Ir are elements that may be contained in the Ga2O3 single crystal substrate. On the other hand, when manufacturing the Ga2O3 single crystal substrate using the method described later, by using platinum or pyrolytic boron nitride as the crucible material, it is easy to make the concentrations of Rh and Ir in GDMS both below 0.1 ppm by mass. The Ga2O3 single crystal substrate can suppress crack formation and, based on the low concentrations of Rh and Ir, can exhibit good electrical properties.

[0086] (Resistivity)

[0087] In the Ga2O3 single-crystal substrate of this embodiment, the resistivity of the aforementioned gallium oxide single-crystal substrate, measured at 25°C using the van der Bauer method in a Hall test, is preferably 1.0 × 10⁻⁶. -3 The resistivity is above Ω·cm and below 2.0 Ω·cm. Specifically, taking the center of the aforementioned Ga2O3 single crystal substrate as the measurement object, the resistivity obtained at 25°C using the Van der Bauer method in a Hall test is preferably 1.0 × 10⁻⁶. -3 The resistivity is above 1.0 Ω·cm and below 2.0 Ω·cm. Therefore, as an n-type (electron-donating) Ga₂O₃ single crystal substrate, it can possess excellent electrical properties, thereby facilitating the formation of electronic devices. In the above-mentioned Ga₂O₃ single crystal substrate, the resistivity is less than 1.0 × 10⁻⁶. -3 When using the aforementioned Ga2O3 single-crystal substrate to fabricate Schottky barrier diodes with a resistivity of Ω·cm, the reverse current increases, the breakdown voltage deteriorates, and thermal runaway may occur. When the resistivity is greater than 2.0 Ω·cm, the forward voltage is high, which may reduce efficiency. The preferred resistivity is 5.0 × 10⁻⁶ Ω·cm. -3 Ω・cm or more and 1.0×10 -1 Below Ω・cm.

[0088] The following is a reference. Figure 1 and Figure 3 The steps for calculating the resistivity described above will be explained in detail below. Figure 3This is an explanatory diagram illustrating a Hall effect test sample fabricated using the central portion of the aforementioned substrate for measuring the resistivity, carrier concentration, and electron mobility of the gallium oxide single-crystal substrate of this embodiment. First, as... Figure 1 As shown, for example, for a Ga2O3 single crystal obtained based on the manufacturing method described later, a Ga2O3 single crystal substrate 100, which is the object of measurement, is obtained by applying a conventionally known processing method. A rectangular slice 11a (e.g., 600 μm thick), with dimensions of 10 mm x 10 mm and a center point (e.g., the center of the main surface 10) as its center O, is formed from the central portion of this Ga2O3 single crystal substrate 100. Next, as... Figure 3 As shown, gold electrodes 21 are formed at the four corners of the rectangular slice 11a (the surface to be measured), thereby obtaining a sample for Hall testing. Here, the shape of the electrodes 21 is not limited to the rectangle shown; it can also be fan-shaped or circular. For the rectangular slice 11a with such electrodes 21, the resistivity can be determined by applying a Hall test using the van der Bauer method in an atmosphere at 25°C. Furthermore, in this specification, the resistivity obtained based on the rectangular slice as the measurement object is defined as the resistivity of the Ga2O3 single-crystal substrate measured at 25°C using the van der Bauer method in a Hall test.

[0089] (Carrier concentration and electron mobility)

[0090] In this embodiment, the carrier concentration of the Ga2O3 single crystal substrate measured at 25°C using the van der Bauer method is preferably 4.0 × 10⁻⁶. 17 cm -3 Above and 1.4×10 19 cm -3 The electron mobility of the aforementioned Ga2O3 single crystal substrate, measured at 25°C using the Van der Bauer method in a Hall effect test, is preferably 0.2 cm⁻¹. 2 / V・s or higher and 15000cm 2 / V・s or less. Meanwhile, the above-mentioned Ga2O3 single crystal substrate exhibits a carrier concentration of less than 4.0 × 10⁻⁶. 17 cm -3 In cases where the aforementioned Ga2O3 single-crystal substrate is used to fabricate a Schottky barrier diode, the loss may increase. This is especially true when the carrier concentration is greater than 1.4 × 10⁻⁶. 19 cm -3 In cases where a Schottky barrier diode is fabricated from the aforementioned Ga2O3 single-crystal substrate, the reverse current increases, the breakdown voltage deteriorates, and thermal runaway may occur. In the aforementioned Ga2O3 single-crystal substrate, by controlling the carrier concentration and electron mobility within the aforementioned ranges, a preferred resistivity within these ranges can be obtained.

[0091] In particular, the aforementioned carrier concentration is more preferably 4.5 × 10⁻⁶. 17 cm -3 Above and 4.0×10 18 cm -3 The electron mobility described above is more preferably 10 cm⁻¹. 2 / V・s or higher and 1500cm 2 / V・s or less. Therefore, the aforementioned n-type Ga2O3 single-crystal substrate can possess excellent electrical properties suitable for use in various electronic devices. The aforementioned carrier concentration and electron mobility can both be determined using the same method as the aforementioned resistivity measurement method.

[0092] <Uses>

[0093] The Ga2O3 single-crystal substrate of this embodiment possesses the aforementioned characteristics, and therefore can be used as a substrate for forming optical and electronic devices. In particular, the Ga2O3 single-crystal substrate is preferably used as a substrate for forming electronic devices due to its excellent electrical properties.

[0094] [Manufacturing method of gallium trioxide single crystal]

[0095] The method for manufacturing gallium trioxide (Ga2O3) single crystal in this embodiment is preferably, for example, a method for manufacturing a Ga2O3 single crystal that constitutes the Ga2O3 single crystal substrate having the aforementioned circular main surface. For example, the method for manufacturing the Ga2O3 single crystal is carried out in an atmospheric atmosphere and can include the following steps. That is, the above manufacturing method includes: a step of preparing a single crystal growth apparatus (hereinafter also referred to as "Ga2O3 single crystal growth apparatus") having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; a step of placing a seed crystal composed of the Ga2O3 single crystal at the bottom of the crucible, and placing in the crucible in a bulk or powdered form of gallium trioxide polycrystalline (Ga2O3 polycrystalline), an n-type dopant, and boron oxide (B2O3) at a position above the seed crystal; a step of heating the crucible with the heating device, thereby melting a portion of the seed crystal and obtaining a solution in which Ga2O3 from a portion of the seed crystal and the Ga2O3 polycrystalline at a first concentration and the n-type dopant at a second concentration are dissolved in the B2O3, while contacting the solution with the remaining portion of the seed crystal; and a step of growing a crystal from the solution on the remaining portion of the seed crystal, thereby obtaining a Ga2O3 single crystal. The crucible is made of platinum. The boron concentration in the aforementioned gallium oxide single crystal is between 4 ppm and 200 ppm by mass in GDMS. Using a method for manufacturing Ga2O3 single crystals with these characteristics, it is possible to obtain Ga2O3 single crystals for fabricating Ga2O3 single crystal substrates capable of suppressing crack formation.

[0096] Furthermore, the above-described method for manufacturing Ga2O3 single crystals can also be performed in a nitrogen atmosphere. That is, the above-described method for manufacturing Ga2O3 single crystals is performed in a nitrogen atmosphere and can include the following steps. The manufacturing method described above includes the following steps: preparing a single crystal growth apparatus (hereinafter also referred to as "Ga2O3 single crystal growth apparatus") having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; placing a seed crystal composed of the Ga2O3 single crystal at the bottom of the crucible, and placing a block or powdered Ga2O3 polycrystal, an n-type dopant, and B2O3 at a position above the seed crystal within the crucible; heating the crucible with the heating device, thereby melting a portion of the seed crystal and obtaining a solution in which a portion of the seed crystal and the Ga2O3 polycrystal are dissolved in the B2O3 at a first concentration and the n-type dopant at a second concentration, respectively, while contacting the solution with the remaining portion of the seed crystal; and growing a crystal from the solution on the remaining portion of the seed crystal, thereby obtaining a Ga2O3 single crystal. The crucible in this method is made of pyrolytic boron nitride (pBN). The boron concentration in the aforementioned gallium oxide single crystal is 4 ppm by mass and 200 ppm by mass in GDMS. In the manufacturing method of Ga2O3 single crystals with these characteristics, it is also possible to obtain Ga2O3 single crystals for manufacturing Ga2O3 single crystal substrates capable of suppressing crack formation.

[0097] Figure 4 This is a flowchart illustrating an example of a method for manufacturing a gallium oxide single crystal substrate, including the method for manufacturing a gallium oxide single crystal according to this embodiment. The method for manufacturing a Ga₂O₃ single crystal according to this embodiment is preferably, for example, as... Figure 4 The flowchart shows the Ga2O3 single crystal manufacturing process S100, which is included in the manufacturing method of the Ga2O3 single crystal substrate. Figure 4The method for manufacturing a Ga2O3 single crystal substrate according to this embodiment includes a Ga2O3 single crystal manufacturing step S100 and a Ga2O3 single crystal substrate manufacturing step S200. The Ga2O3 single crystal manufacturing step S100 includes a step of preparing a Ga2O3 single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible (first step: preparation step S110). In the preparation step S110, preferably, in addition to the Ga2O3 single crystal growth apparatus, a seed crystal composed of the Ga2O3 single crystal, a bulk or powdered Ga2O3 polycrystalline material, an n-type dopant, and solid B2O3 are also prepared. The Ga2O3 single crystal manufacturing step S100 includes a step of receiving the seed crystal at the bottom of the crucible and receiving the Ga2O3 polycrystalline material, the n-type dopant, and the B2O3 at a position higher than the seed crystal within the crucible (second step: raw material receiving step S120). The Ga2O3 single crystal manufacturing process S100 includes heating the crucible with the aforementioned heating device, thereby melting a portion of the seed crystal and obtaining a solution from the portion of the seed crystal and the Ga2O3 polycrystalline material dissolved in the B2O3 at a first concentration and the n-type dopant at a second concentration, respectively, while simultaneously contacting the solution with the remaining portion of the seed crystal (third step: raw material melting process S130). Furthermore, the Ga2O3 single crystal manufacturing process S100 includes growing a crystal from the solution on the remaining portion of the seed crystal, thereby obtaining a Ga2O3 single crystal (fourth step: Ga2O3 single crystal growth process S140). The atmosphere for performing the Ga2O3 single crystal growth process S140 is either a nitrogen atmosphere or an atmospheric atmosphere, depending on the material of the crucible.

[0098] Regarding the method for growing a Ga2O3 single crystal that constitutes a Ga2O3 single crystal substrate having the above-mentioned properties, the inventors focused on dissolving Ga2O3 in liquid B2O3 in a crucible, cooling it, and thereby precipitating and obtaining a Ga2O3 single crystal by utilizing the solubility difference between B2O3 and Ga2O3. It was found that in this case, a slight amount of B2O3 was introduced into the precipitated Ga2O3 single crystal. Furthermore, it was found that when a Ga2O3 single crystal substrate is obtained from a Ga2O3 single crystal containing B at a predetermined concentration, the generation of cracks in the Ga2O3 single crystal substrate is suppressed, thus completing the method for manufacturing a Ga2O3 single crystal according to this embodiment.

[0099] In this specification, "n-type dopant" refers to an oxide of an element that, when incorporated as a dopant into a Ga2O3 single-crystal substrate, imparts n-type (electron-donating) electrical properties to the Ga2O3 single-crystal substrate. Examples of elements that impart n-type (electron-donating) properties to the aforementioned Ga2O3 single-crystal substrate include tin (Sn), silicon (Si), and germanium (Ge).

[0100] The following is based on reference Figure 4 and Figure 5 The overview of the Ga2O3 single crystal growth apparatus and the Ga2O3 single crystal manufacturing process S100 are described respectively. Figure 5 This is a schematic diagram illustrating the manufacturing apparatus used in the method for manufacturing gallium oxide single crystals according to this embodiment. In the method for manufacturing Ga₂O₃ single crystals (Ga₂O₃ single crystal manufacturing step S100) of this embodiment, for example... Figure 5 The Ga2O3 single crystal growth apparatus shown.

[0101] <Ga2O3 Single Crystal Growth Device>

[0102] like Figure 5 As shown, the Ga2O3 single crystal growth apparatus includes the aforementioned crucible 2, a crucible holding platform 8 for holding the crucible 2, a lower shaft 9 supporting the crucible 2 and the crucible holding platform 8, and a heating device 1 for heating the crucible 2. Furthermore, the Ga2O3 single crystal growth apparatus includes a cover 3 for sealing the crucible 2. The cover 3 functions to prevent the B2O3 solution 52 (hereinafter also referred to as "B2O3-Ga2O3 solution 52") containing dissolved Ga2O3 and n-type dopant from evaporating to the outside during the Ga2O3 single crystal growth process S140 due to heating. The Ga2O3 single crystal growth apparatus includes nozzles for introducing Ga2O3 polycrystals and n-type dopant into the crucible 2. These nozzles consist of a first nozzle 41 and a second nozzle 42, each penetrating the cover 3 from the outside with its tip positioned inside the crucible 2. The first nozzle 41 functions as a supply path for supplying Ga2O3 polycrystals into the crucible 2 from the outside. The second nozzle 42 functions as a supply channel for supplying n-type dopant from the outside into the crucible 2.

[0103] In the Ga2O3 single crystal manufacturing method of this embodiment, although the illustrations are omitted, in addition to the Ga2O3 single crystal growth apparatus described above, for the purpose of setting the atmosphere for the Ga2O3 single crystal growth step S140 to a nitrogen atmosphere, a chamber capable of housing the crucible 2, cover 3, first nozzle 41 and second nozzle 42, crucible holding platform 8, lower shaft 9, and heating device 1 is sometimes prepared. The size and material of the chamber are not particularly limited as long as they are large enough to house the Ga2O3 single crystal growth apparatus and allow for a nitrogen atmosphere inside. Furthermore, if the heat transmittance of the chamber's sidewalls is good, the heating device from the Ga2O3 single crystal growth apparatus can also be positioned outside the chamber.

[0104] (Heating device)

[0105] like Figure 5As shown, in a Ga2O3 single crystal growth apparatus, a heating device 1 is arranged to surround the outer periphery of the crucible 2 for the purpose of heating the crucible 2. The heating device 1 can be, for example, a conventionally known electric heater (hereinafter simply referred to as a "heater"). For example, there are two heaters arranged to surround the outer periphery of the crucible 2. Sometimes the output power of each heater can be controlled independently. In particular, each heater sometimes... Figure 5 As shown, the crucible 2 is constructed in multiple segments by dividing it into several parts in a direction perpendicular to the axis of crucible 2. In this case, it is preferable to control the output power of the heater independently for each segment. This allows for precise adjustment of the temperature of the contents inside the crucible 2 along its axial direction. For example, by controlling the output power of the heater independently for each segment, the growth rate of the Ga2O3 single crystal grown inside the crucible 2 can be stabilized.

[0106] (crucible)

[0107] like Figure 5 As shown, in the Ga2O3 single crystal growth apparatus, the crucible 2 is cylindrical. A seed crystal 51 composed of Ga2O3 single crystals is housed at the bottom of the crucible 2. Furthermore, bulk or powdered Ga2O3 polycrystalline material, an n-type dopant, and solid B2O3 are placed on the seed crystal 51. That is, the crucible 2 functions to hold the seed crystal 51, the Ga2O3 polycrystalline material, the n-type dopant, and B2O3. In addition, the crucible 2 functions to allow the Ga2O3 single crystal to precipitate from the B2O3-Ga2O3 solution 52 within its interior, as described later, thereby growing the Ga2O3 single crystal on the seed crystal 51.

[0108] As the crucible 2, various materials capable of withstanding the temperature of the B2O3-Ga2O3 solution 52 can be used. For example, platinum alloys containing platinum, rhodium, or iridium, pBN, etc., can be used as the material of the crucible 2. In particular, when the atmosphere for the Ga2O3 single crystal growth process S140 is atmospheric, the crucible 2 is made of platinum. As a result, in the Ga2O3 single crystal obtained by the above manufacturing method, the concentrations of rhodium and iridium can be zero or extremely low (e.g., less than 0.1 ppm by mass). Furthermore, when the atmosphere for the Ga2O3 single crystal growth process S140 is nitrogen atmosphere, the crucible 2 is made of pBN. In this case, the manufacturing cost of the Ga2O3 single crystal growth apparatus can be reduced. In the Ga2O3 single crystal obtained by the above manufacturing method, the concentrations of rhodium and iridium can also be zero or extremely low (e.g., less than 0.1 ppm by mass). The inner diameter of the crucible 2 depends on the diameter of the Ga2O3 single crystal to be manufactured, and can be set to, for example, 90 mm or more and 165 mm or less.

[0109] Additionally, although the illustration is omitted, the Ga2O3 single crystal growth apparatus can include thermocouples capable of measuring the temperature of the crucible 2 heated by the heating device 1. Sometimes multiple thermocouples are arranged on the outside of the crucible 2 and along its axial direction. The thermocouples can employ, for example, known temperature monitoring devices.

[0110] (Cover body)

[0111] The cover 3 is not particularly limited and is sometimes made of, for example, pBN, calcium oxide (CaO) stabilized zirconium oxide, etc. In the Ga2O3 single crystal growth process S140, a cover 3 is placed on the upper part of the crucible 2 to prevent the B2O3 in the B2O3-Ga2O3 solution 52 inside the crucible 2 from evaporating to the outside due to heating. The cover 3 has holes for inserting nozzles (first nozzle 41 and second nozzle 42).

[0112] (First nozzle and second nozzle)

[0113] The first nozzle 41 and the second nozzle 42 are not particularly limited, and are sometimes made of materials such as pBN-coated carbon or sapphire. The first nozzle 41 and the second nozzle 42 penetrate the cover body 3 through the aforementioned holes, with their front ends located inside the crucible 2, thereby connecting the inside and outside of the crucible 2. Thus, the first nozzle 41 functions as a supply channel for supplying Ga2O3 from the outside into the crucible 2. The second nozzle 42 functions as a supply channel for supplying n-type dopant from the outside into the crucible 2. By supplying Ga2O3 polycrystalline or n-type dopant to the B2O3-Ga2O3 solution 52 inside the crucible 2 through the first nozzle 41 and the second nozzle 42, the concentrations of Ga2O3 polycrystalline and n-type dopant in the B2O3-Ga2O3 solution 52 can be kept constant.

[0114] (Crucible holding stand)

[0115] The Ga2O3 single crystal growth apparatus includes a crucible holding platform 8 for holding a crucible 2. The crucible holding platform 8 is connected to the bottom of the crucible 2 to hold it. The crucible holding platform 8 sometimes has a cylindrical shape. The material of the crucible holding platform 8 is not particularly limited, and can be, for example, quartz, alumina, or silicon carbide. The outer diameter of the crucible holding platform 8 depends on the diameter of the supported crucible 2, and can be, for example, 75 mm or more and 200 mm or less.

[0116] (Lower axis)

[0117] The lower shaft 9 supports the crucible 2 and the crucible holding platform 8 from below. The lower shaft 9 can be, for example, a rod-shaped material with a circular or rectangular horizontal cross-section. Materials for the lower shaft 9 can include, for example, molybdenum, carbon, or silicon carbide. Hereinafter, each step included in the above-described method for manufacturing Ga2O3 single crystals (Ga2O3 single crystal manufacturing process S100) will be described. First, the Ga2O3 single crystal manufacturing process S100 performed in an atmospheric atmosphere will be described.

[0118] <Ga2O3 Single Crystal Manufacturing Process S100>

[0119] (First step: Preparation step S110)

[0120] like Figure 4 As shown, firstly, in the Ga2O3 single crystal manufacturing process S100, a preparation step S110 is performed. Preparation step S110 is the process of preparing a Ga2O3 single crystal growth apparatus, which at least includes a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible. In preparation step S110, in addition to the Ga2O3 single crystal growth apparatus, it is preferable to prepare a seed crystal 51, a bulk or powdered Ga2O3 polycrystalline material, an n-type dopant, and solid B2O3. The seed crystal 51 is composed of a Ga2O3 single crystal, as described above. The n-type dopant is preferably prepared in the form of, for example, tin oxide (SnO2) or silicon oxide (SiO2). The seed crystal 51, the bulk or powdered Ga2O3 polycrystalline material, the n-type dopant, and the solid B2O3 can be prepared by purchasing commercially available products. The crucible 2 constituting the Ga2O3 single crystal growth apparatus is made of platinum.

[0121] (Second process: Raw material storage process S120)

[0122] Next, in the Ga2O3 single crystal manufacturing process S100, a raw material storage process S120 is performed. The raw material storage process S120 involves storing the seed crystal at the bottom of the crucible, and storing the Ga2O3 polycrystalline material, the n-type dopant, and B2O3 at a position above the seed crystal within the crucible. The purpose of the raw material storage process S120 is to store various raw materials used for crystal growth using the Ga2O3 single crystal growth apparatus within the crucible 2. In the raw material storage process S120, firstly, a seed crystal 51 composed of Ga2O3 single crystals is stored at the bottom of the crucible 2. Next, multiple block or powdered Ga2O3 polycrystalline materials are stored and stacked on the seed crystal 51 stored in the crucible 2. Then, the n-type dopant and solid B2O3 are further stored. Preferably, the amount of n-type dopant stored in the crucible 2 is predetermined so that the dopant concentration in the desired Ga2O3 single crystal is appropriate. Therefore, an n-type Ga2O3 single crystal substrate can be obtained from the Ga2O3 single crystal obtained through the Ga2O3 single crystal manufacturing process S100. As for the amount of the aforementioned n-type dopant contained in crucible 2, for example, it is preferable to adjust the atomic concentration of Sn, Si, or Ge as dopant in the Ga2O3 single crystal substrate to 2.0 × 10⁻⁶. 19 cm -3 The following (e.g., 1.0×10) 17 cm -3 Above and 2.0×10 19 cm -3 the following).

[0123] (Third process: Raw material melting process S130)

[0124] Next, in the Ga2O3 single crystal manufacturing process S100, a raw material melting process S130 is performed. The raw material melting process S130 involves heating the crucible using the aforementioned heating device, thereby melting a portion of the seed crystal and obtaining a solution from the seed crystal and the Ga2O3 from the Ga2O3 polycrystalline material, each dissolved in B2O3 at a first concentration and the n-type dopant at a second concentration, respectively. Simultaneously, this solution is brought into contact with the remaining portion of the seed crystal. The purpose of the raw material melting process S130 is to heat the crucible 2 using the heating device 1 during crystal growth using the Ga2O3 single crystal growth apparatus, thereby melting a portion of the seed crystal 51 and simultaneously obtaining a B2O3-Ga2O3 solution 52 from the seed crystal 51 and the Ga2O3 from the Ga2O3 polycrystalline material, each dissolved in B2O3 at a first concentration and the n-type dopant at a second concentration, respectively. The B2O3-Ga2O3 solution 52 is then brought into contact with the remaining portion of the seed crystal 51. Therefore, in the Ga2O3 single crystal growth process S140, which is the next step, Ga2O3 single crystal can be grown on the remaining portion of the seed crystal 51. In the raw material melting process S130, specifically, the crucible 2 containing the seed crystal 51, the aforementioned Ga2O3 polycrystalline material, the aforementioned n-type dopant, and the aforementioned B2O3 is supported by a crucible holding platform 8. Then, an electric current is supplied to the heating device 1 to heat the crucible 2. As a result, the solid B2O3 melts into liquid B2O3, and further, the B2O3 reaches a temperature above a specified temperature (approximately 1000°C), whereby the Ga2O3 polycrystalline material slowly dissolves in the B2O3. The n-type dopant also dissolves in the B2O3. Next, a portion of the seed crystal 51 also melts and dissolves in the B2O3. Thus, the remaining portion of the seed crystal 51 comes into contact with the B2O3-Ga2O3 solution 52.

[0125] Here, the concentration of Ga2O3 in B2O3 in the B2O3-Ga2O3 solution 52, which is the first concentration, is preferably 20 to 40% by mass. The concentration of Ga2O3 that can dissolve in B2O3 depends on the temperature of B2O3. Therefore, in the raw material melting process S130, the B2O3-Ga2O3 solution 52 is preferably heated to 1200 to 1500°C. In this case, the concentration of the n-type dopant in B2O3 in the B2O3-Ga2O3 solution 52, which is the second concentration, can be any concentration used in conventionally known methods for manufacturing Ga2O3 single crystals, for example, preferably 2 to 300 ppm by mass. The first and second concentrations can be determined using the same methods as the determination of Ga2O3 concentration and n-type dopant concentration performed in the analysis process described later.

[0126] (Fourth process: Ga2O3 single crystal growth process S140)

[0127] Next, in the Ga2O3 single crystal manufacturing process S100, a Ga2O3 single crystal growth process S140 is performed. The Ga2O3 single crystal growth process S140 involves growing a crystal from the solution on the remaining portion of the seed crystal, thereby obtaining a Ga2O3 single crystal. In the Ga2O3 single crystal growth process S140, for example, the crucible 2 is slowly and gradually lowered along its axial direction (towards the bottom of the crucible 2) relative to the heating device 1, thereby creating a temperature gradient in the crucible 2 such that the temperature decreases on the seed crystal 51 side and increases on the B2O3-Ga2O3 solution 52 side. As a result, in the portion of the B2O3-Ga2O3 solution 52 in contact with the seed crystal 51, the Ga2O3 single crystal precipitates due to the solubility difference between B2O3 and Ga2O3, thereby enabling continuous crystal growth. In this case, in order to obtain a Ga2O3 single crystal in the form of a lattice-continuous single crystal ingot, it is preferable to set the downward speed of the crucible 2 along its axis to, for example, 1 to 3 mm / hour. The temperature of the portion of the B2O3-Ga2O3 solution 52 in contact with the seed crystal 51 (hereinafter also referred to as the "seed crystal portion") is preferably 1150 to 1430°C, more preferably 1200 to 1388°C.

[0128] In the Ga2O3 single crystal growth process S140, the Ga2O3 single crystal precipitates from the B2O3-Ga2O3 solution 52 due to the solubility difference between B2O3 and Ga2O3. Therefore, as the process proceeds, the concentration of Ga2O3 and the concentration of n-type dopant in the B2O3-Ga2O3 solution 52 decrease. Therefore, the Ga2O3 single crystal growth process S140 preferably includes a step of sampling the solution in the crucible sealed by the cap through the nozzle, thereby analyzing the concentration of Ga2O3 from the seed crystal and the Ga2O3 polycrystalline material, as well as the concentration of n-type dopant in the solution (hereinafter also referred to as the "analysis step"). Furthermore, the Ga2O3 single crystal growth process S140 preferably includes a step of introducing the Ga2O3 polycrystalline material into the solution in the crucible through the nozzle at a concentration within 5% of the first concentration, based on analysis results related to the concentration of the Ga2O3 (hereinafter also referred to as the "Ga2O3 concentration adjustment process"). The Ga2O3 single crystal growth process S140 preferably includes a step of introducing the n-type dopant into the solution in the crucible through the nozzle at a concentration within 5% of the second concentration, based on analysis results related to the concentration of the n-type dopant (hereinafter also referred to as the "n-type dopant concentration adjustment process"). By incorporating these steps, the manufacturing method enables the concentrations of Ga2O3 and the n-type dopant in the B2O3-Ga2O3 solution 52 to remain constant from the initial stage to the final stage of the Ga2O3 single crystal growth process S140. Therefore, it is possible to obtain Ga2O3 single crystals with uniform B concentration in all parts of the single crystal, thereby enabling the production of Ga2O3 single crystals with high yield for manufacturing Ga2O3 single crystal substrates that can suppress crack formation.

[0129] Specifically, in the above-mentioned analysis process, during the Ga2O3 single crystal growth process S140, at predetermined intervals (e.g., every 2 hours), the B2O3-Ga2O3 solution 52 in the crucible 2 sealed by the cover body 3 is sampled using a suitable method through the first nozzle 41 or the second nozzle 42. Sampling can be performed by, for example, using a tube made of the same material as the nozzle, collecting approximately 0.5g of the B2O3-Ga2O3 solution 52 from the crucible 2 through the first nozzle 41 or the second nozzle 42. Furthermore, after dissolving this approximately 0.5g of the B2O3-Ga2O3 solution 52 in acid using a known method, the concentrations of Ga2O3 and the aforementioned n-type dopant in the B2O3-Ga2O3 solution 52 can be analyzed using inductively coupled plasma (ICP) emission spectroscopy or ICP-mass spectrometry, respectively.

[0130] In the aforementioned Ga2O3 concentration adjustment process, based on the analysis results related to the Ga2O3 concentration obtained from the analysis process performed at predetermined intervals, Ga2O3 polycrystals are added to the B2O3-Ga2O3 solution 52 in the crucible 2 through the first nozzle 41, with a concentration that differs from the first concentration by no more than 5%. Furthermore, in the aforementioned Ga2O3 concentration adjustment process, if the aforementioned analysis results for the Ga2O3 concentration differ from the first concentration by no more than 5%, then Ga2O3 polycrystals are not added.

[0131] Furthermore, during the Ga2O3 single crystal growth process S140, as the Ga2O3 single crystal precipitates, the concentration of the n-type dopant in the B2O3-Ga2O3 solution 52 decreases. Therefore, in the n-type dopant concentration adjustment process, based on the analysis results related to the Ga2O3 concentration obtained from the analysis process performed at predetermined intervals, the n-type dopant is added to the B2O3-Ga2O3 solution 52 in the crucible 2 through the second nozzle 42 at a concentration that is within 5% of the second concentration. Additionally, in the n-type dopant concentration adjustment process, if the analysis results for the n-type dopant concentration are within 5% of the second concentration, no n-type dopant is added.

[0132] In the Ga2O3 single crystal growth process S140, along with the precipitation of the Ga2O3 single crystal, B2O3 in the B2O3-Ga2O3 solution 52 is sometimes introduced into the Ga2O3 single crystal and is lost due to sublimation. Therefore, if the concentration of B2O3 in the B2O3-Ga2O3 solution 52 decreases excessively, the concentration of B2O3 can be adjusted by adding B2O3 using the first nozzle 41.

[0133] In the Ga2O3 single crystal growth process S140, the crucible 2 is lowered along its axial direction at the aforementioned speed relative to the heating device 1, thereby continuously precipitating Ga2O3 single crystals from the B2O3-Ga2O3 solution 52 within the crucible 2, increasing the thickness to form an ingot, while simultaneously causing the interface between the Ga2O3 single crystal and the B2O3-Ga2O3 solution 52 to rise towards the cap 3. The crystal growth of the Ga2O3 single crystal continues until the thickness of the Ga2O3 single crystal ingot reaches the desired thickness. Thus, a Ga2O3 single crystal can be obtained. The boron concentration in the Ga2O3 single crystal is 4 ppm by mass or more and 200 ppm by mass or less in GDMS. Preferably, the boron concentration in the Ga2O3 single crystal is 5 ppm by mass or more and 100 ppm by mass or less in GDMS. The GDMS performed on the Ga2O3 single crystal can be performed using the same key points as the GDMS performed on the Ga2O3 single crystal substrate described above.

[0134] Here, the aforementioned method for manufacturing Ga2O3 single crystals can also be performed in a nitrogen atmosphere. In this manner, the crucible 2 constituting the Ga2O3 single crystal growth apparatus is made of pBN. Furthermore, in order to perform the aforementioned series of processes in a nitrogen atmosphere, the Ga2O3 single crystal growth apparatus is housed within a chamber filled with nitrogen. In this method for manufacturing Ga2O3 single crystals, it is also possible to obtain Ga2O3 single crystals for manufacturing Ga2O3 single crystal substrates capable of suppressing crack formation.

[0135] [Manufacturing method of gallium trioxide single crystal substrate]

[0136] <Ga2O3 single crystal substrate manufacturing process S200>

[0137] The method for manufacturing a Ga2O3 single crystal substrate according to this embodiment includes the following steps: processing the Ga2O3 single crystal obtained by the above-described Ga2O3 single crystal manufacturing method to obtain a Ga2O3 single crystal substrate with a circular main surface. Figure 4 As shown, the above-mentioned method for manufacturing a Ga2O3 single crystal substrate includes a Ga2O3 single crystal manufacturing process S100 and a Ga2O3 single crystal substrate manufacturing process S200. The purpose of the Ga2O3 single crystal substrate manufacturing process S200 is to process the Ga2O3 single crystal obtained by the Ga2O3 single crystal manufacturing process S100, thereby obtaining a Ga2O3 single crystal substrate. The Ga2O3 single crystal substrate manufacturing process S200 includes a cutting process, an outer peripheral grinding process, and a polishing process, and the Ga2O3 single crystal substrate can be obtained by sequentially performing these processes.

[0138] The slicing process is a process of slicing a Ga2O3 single crystal substrate from a Ga2O3 single crystal ingot taken from crucible 2, so that the ingot is shaped into a wafer with a specified thickness. Next, the peripheral grinding process is a process of grinding the outer periphery of the wafer to obtain a wafer with a main surface consisting of a central portion and an outer periphery surrounding the central portion. Specifically, the peripheral grinding process is a process of performing chamfering. Therefore, through the peripheral grinding process, a main surface with a chamfered area as the outer periphery can be obtained. Conventionally known slicing and peripheral grinding methods can be used as the slicing and peripheral grinding processes. Next, the polishing process is a process of mirror-polishing the central portion of the main surface. Conventionally known polishing methods can be used as the polishing process. Through the polishing process, the surface roughness Ra of the central portion can, for example, be 20 nm or less as specified in JIS B 0681-2:2018.

[0139] [Effects]

[0140] By performing the above-described processes, the Ga2O3 single-crystal substrate of this embodiment can be manufactured. In the above-described method for manufacturing Ga2O3 single crystals, particularly in the Ga2O3 single-crystal growth process S140, it is possible to grow a Ga2O3 single crystal in which B2O3 is slightly introduced into the precipitated Ga2O3 single crystal. Therefore, a Ga2O3 single-crystal substrate with appropriate strength capable of suppressing crack formation can be obtained from the aforementioned Ga2O3 single crystal containing B.

[0141] Example

[0142] The present invention will be described in more detail below with reference to specific embodiments, but the invention is not limited thereto. In this embodiment, the invention uses... Figure 5 The Ga2O3 single crystal manufacturing apparatus shown is in accordance with Figure 4 The flowchart shown illustrates the fabrication of a Ga2O3 single-crystal substrate. In the following description, samples 11 to 19 are examples, and samples a to c are comparative examples.

[0143] [Fabrication of Ga2O3 single crystal substrates]

[0144] <Sample a>

[0145] According to the method disclosed in Patent Document 1, Ga2O3 single crystals are obtained using the Vertical Bridgeman (VB) method. When obtaining the Ga2O3 single crystal, an appropriate amount of tin oxide (SnO2) is added as an n-type dopant. Then, the Ga2O3 single crystal substrate of sample a is obtained by sequentially performing the aforementioned cutting, peripheral grinding, and polishing processes. The Ga2O3 single crystal substrate of sample a has a diameter of 100 mm and a thickness of 650 μm.

[0146] <Sample b>

[0147] (Preparation step S110 in Ga2O3 single crystal manufacturing process S100)

[0148] First, the aforementioned Ga2O3 single crystal growth apparatus, seed crystal 51 composed of Ga2O3 single crystal, bulk Ga2O3 polycrystalline material, SnO2 as an n-type dopant, and solid B2O3 are prepared using conventionally known methods or by purchasing commercially available products. The crucible 2 constituting the Ga2O3 single crystal growth apparatus is a platinum crucible with an inner diameter of 105 mm.

[0149] (Raw material receiving process S120 in Ga2O3 single crystal manufacturing process S100)

[0150] Next, using a conventional method, a seed crystal 51 is placed at the bottom of crucible 2, and then, in sequence, bulk Ga2O3 polycrystalline material, SnO2, and solid B2O3 are placed above the seed crystal 51. Specifically, multiple bulk Ga2O3 polycrystalline materials are placed and stacked. Next, SnO2 is added to the Ga2O3 polycrystalline material, and solid B2O3 is then arranged. The amount of SnO2 added is such that the atomic concentration of Sn in the Ga2O3 single-crystal substrate is 3.0 × 10⁻⁶. 18 cm -3 The amount.

[0151] (Raw material melting process S130 in Ga2O3 single crystal manufacturing process S100)

[0152] Next, a crucible 2, which houses the seed crystal 51, the bulk Ga2O3 polycrystal, SnO2, and solid B2O3, is held inside by a crucible holding platform 8. Then, an electric current is supplied to the heating device 1 to heat the crucible 2, melting the solid B2O3 into liquid B2O3. Simultaneously, a portion of the seed crystal 51, the Ga2O3 polycrystal, and SnO2 are dissolved in the B2O3, thereby preparing a B2O3-Ga2O3 solution 52. The concentration of Ga2O3 in the B2O3 of the B2O3-Ga2O3 solution 52, i.e., the first concentration, is set to 20% by mass. The concentration of SnO2 in the B2O3, i.e., the second concentration, is set to 100 ppm by mass. Next, the remaining portion of the seed crystal 51 is brought into contact with the B2O3-Ga2O3 solution 52 at their interface.

[0153] (Ga2O3 single crystal growth process S140 in Ga2O3 single crystal manufacturing process S100)

[0154] Next, the crucible 2 is slowly and gradually lowered along its axial direction (bottom side) relative to the heating device 1, thereby creating a temperature gradient in the crucible 2 such that the temperature is low on the seed crystal 51 side and high on the B2O3-Ga2O3 solution 52 side. As a result, in the portion of the B2O3-Ga2O3 solution 52 that contacts the seed crystal 51, i.e., the seed crystal portion, Ga2O3 single crystals precipitate due to the solubility difference between B2O3 and Ga2O3, and crystal growth continues continuously. This operation is continued until the thickness of the Ga2O3 single crystal reaches 30 mm. The temperature of the seed crystal portion is set to 1100°C. The speed at which the crucible 2 is lowered along its axial direction is set to 2 mm / hour. Thus, a Ga2O3 single crystal ingot is obtained.

[0155] In the Ga2O3 single crystal growth process S140, the aforementioned analysis process, Ga2O3 concentration adjustment process, and n-type dopant concentration adjustment process are performed. As a result, the concentrations of Ga2O3 and n-type dopant in the B2O3-Ga2O3 solution 52 are controlled to differ by no more than 5% from the beginning to the end of the Ga2O3 single crystal growth process S140.

[0156] (Ga2O3 single crystal substrate manufacturing process S200)

[0157] Finally, a Ga2O3 single crystal substrate is obtained by processing the Ga2O3 single crystal ingot obtained in the Ga2O3 single crystal growth process S140 through a slicing process, a peripheral grinding process, and a polishing process. First, in the slicing process, the ingot is sliced ​​into a wafer with a thickness of 700 μm using a conventionally known method. In the peripheral grinding process, the outer periphery of the wafer is chamfered using a conventionally known method, thereby obtaining a wafer having a main surface consisting of a central portion and an outer periphery surrounding the central portion. Furthermore, in the polishing process, the central portion is polished using a conventionally known polishing method, where the surface roughness Ra specified in JIS B 0681-2:2018 is set to 0.2 nm, for example.

[0158] Thus, a Ga2O3 single-crystal substrate for sample b was fabricated. The Ga2O3 single-crystal substrate for sample b had a diameter of 100 mm and a thickness of 650 μm.

[0159] <Sample c>

[0160] The concentration of the B2O3-Ga2O3 solution 52 prepared in the raw material melting process S130 was set to 25% by mass. In the Ga2O3 single crystal growth process S140, the temperature of the seed crystal was set to 1500°C. Otherwise, the Ga2O3 single crystal substrate of sample c was manufactured using the same methods as sample b. The Ga2O3 single crystal substrate of sample c had a diameter of 100 mm and a thickness of 650 μm.

[0161] <Sample 11>

[0162] The concentration of the B2O3-Ga2O3 solution 52 prepared in the raw material melting process S130 was set to 20% by mass. In the Ga2O3 single crystal growth process S140, the temperature of the seed crystal was set to 1200°C. Otherwise, the Ga2O3 single crystal substrate of sample 11 was manufactured using the same methods as sample b. The Ga2O3 single crystal substrate of sample 11 had a diameter of 100 mm and a thickness of 650 μm.

[0163] <Sample 12>

[0164] In the Ga2O3 single crystal growth process S140, the temperature of the seed crystal section is set to 1273°C. Otherwise, the Ga2O3 single crystal substrate of sample 12 is manufactured using the same methods as sample 11. The Ga2O3 single crystal substrate of sample 12 has a diameter of 100 mm and a thickness of 650 μm.

[0165] <Sample 13>

[0166] The concentration of the B2O3-Ga2O3 solution 52 prepared in the raw material melting process S130 was set to 25% by mass. In the Ga2O3 single crystal growth process S140, the temperature of the seed crystal was set to 1323°C. Otherwise, the Ga2O3 single crystal substrate of sample 13 was manufactured using the same methods as sample 11. The Ga2O3 single crystal substrate of sample 13 had a diameter of 100 mm and a thickness of 650 μm.

[0167] <Sample 14>

[0168] In preparation step S110, a chamber for housing the single crystal growth apparatus and a crucible 2 made of pBN are prepared. Raw material melting step S130 and Ga2O3 single crystal growth step S140 are performed in a nitrogen atmosphere. In the Ga2O3 single crystal growth step S140, the temperature of the seed crystal is set to 1348°C. Otherwise, the Ga2O3 single crystal substrate of sample 14 is manufactured using the same methods as sample 13. The Ga2O3 single crystal substrate of sample 14 has a diameter of 100 mm and a thickness of 650 μm.

[0169] <Sample 15>

[0170] In the Ga2O3 single crystal growth process S140, the temperature of the seed crystal section is set to 1368°C. Otherwise, the Ga2O3 single crystal substrate of sample 15 is manufactured using the same methods as sample 13. The Ga2O3 single crystal substrate of sample 15 has a diameter of 100 mm and a thickness of 650 μm.

[0171] <Sample 16>

[0172] In the Ga2O3 single crystal growth process S140, the temperature of the seed crystal section is set to 1388°C. Otherwise, the Ga2O3 single crystal substrate of sample 16 is manufactured using the same methods as sample 13. The Ga2O3 single crystal substrate of sample 16 has a diameter of 100 mm and a thickness of 650 μm.

[0173] <Sample 17>

[0174] In preparation step S110, a crucible 2 with an inner diameter of 160 mm is prepared. In Ga2O3 single crystal growth step S140, the temperature of the seed crystal is set to 1273 °C. Otherwise, the Ga2O3 single crystal substrate of sample 17 is manufactured using the same methods as sample 13. The Ga2O3 single crystal substrate of sample 17 has a diameter of 150 mm and a thickness of 680 μm.

[0175] <Sample 18>

[0176] In the Ga2O3 single crystal growth process S140, the temperature of the seed crystal section is set to 1323°C. Otherwise, the Ga2O3 single crystal substrate of sample 18 is manufactured using the same methods as sample 17. The Ga2O3 single crystal substrate of sample 18 has a diameter of 150 mm and a thickness of 680 μm.

[0177] <Sample 19>

[0178] In preparation step S110, a chamber for housing the single crystal growth apparatus and a crucible 2 made of pBN are prepared. Raw material melting step S130 and Ga2O3 single crystal growth step S140 are performed in a nitrogen atmosphere. In Ga2O3 single crystal growth step S140, the temperature of the seed crystal is set to 1388°C. Otherwise, the Ga2O3 single crystal substrate of sample 19 is manufactured using the same methods as sample 17. The Ga2O3 single crystal substrate of sample 19 has a diameter of 150 mm and a thickness of 680 μm.

[0179] [Compositional Analysis Using GDMS]

[0180] The Ga₂O₃ single crystal substrates of samples a–c and 11–19 were subjected to compositional analysis using the aforementioned GDMS method, thereby determining the concentration of boron (B) contained in the Ga₂O₃ single crystal substrates. The results are shown in Table 1. The concentrations of each element shown in Table 1 are in ppm by mass. Furthermore, “<0.3” in Table 1 means less than 0.3 ppm by mass.

[0181] [Determination of Nanoindentation Hardness]

[0182] The nanoindentation hardness at five specified locations on the main surface was determined by performing the above-described measurement method on Ga2O3 single crystal substrates of samples a to c and samples 11 to 19. The measuring apparatus and measuring conditions used for the above-described measurement method are described below.

[0183] Device used: Nanoindenter (trade name: "Bruker Hysitron TI980 TriboIndenter", manufactured by Bruker Japan Co., Ltd.)

[0184] Indenter used: Berkeley indenter

[0185] Maximum load: 10mN

[0186] Atmosphere being measured:

[0187] Measurement temperature: room temperature (25℃)

[0188] The angle between the direction of the Ga2O3 single crystal projected onto the main surface and at least one side of the indenter edge is 0 to 10°.

[0189] The average of the three measured values ​​obtained by measuring the same location three times on the same substrate is taken as the nanoindentation hardness. The nanoindentation hardness is then calculated at five specified locations on the main surface. Furthermore, the average value (in GPa) of the total five nanoindentation hardnesses obtained at the above five locations is calculated. The difference between the maximum and minimum values ​​of the nanoindentation hardness at each of the five specified locations on the main surface is also calculated (denoted as "maximum-minimum difference" in Table 1). The above-mentioned five specified locations refer to the following locations on the main surface. That is, when the length from the center of the main surface to the boundary between the center and the outer periphery is r, the two axes passing through the center and orthogonal to each other on the main surface are the X-axis and the Y-axis, and the Y-axis is the b-axis of the Ga2O3 single crystal, the coordinates (X, Y) of the X-axis and the Y-axis at the above nine locations are (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)). The units of r and X and Y in the coordinates (X, Y) mentioned above are mm. The r for specimens a, b, c, and 11 to 16 is 48 mm. The r for specimens 17 to 19 is 74 mm. The results are shown in Table 1.

[0190] [Crack Load Test]

[0191] For the Ga2O3 single-crystal substrates of samples a to c and samples 11 to 19, the load at which the substrates cracked was confirmed by applying a load to the center of the main surface using a force gauge. The results are shown in Table 1. The larger the measured load, the less likely the substrate is to crack. The force gauge and attachment used for the above crack load test are described below.

[0192] Force gauge: "PS-200N (model)", manufactured by Imada Co., Ltd., maximum load 200N.

[0193] Attachment: Conical (S-3).

[0194] [Resistivity, carrier concentration, and electron mobility]

[0195] For the Ga2O3 single crystal substrates of samples a to c and samples 11 to 19, Hall effect test samples were fabricated using the central portion of these substrates. The above-described measurement method was applied to each Hall effect test sample to determine the resistivity, carrier concentration, and electron mobility of each sample. The results are shown in Table 2.

[0196] [Table 1]

[0197]

[0198] Table 2

[0199]

[0200] [Inspection]

[0201] According to Tables 1 and 2, the concentration of B in GDMS for the Ga2O3 single-crystal substrates of samples 11–19 was all above 4 ppm by mass and below 200 ppm by mass. Under these conditions, the average nanoindentation hardness was above 14.8 GPa and below 22.0 GPa, and the crack load was above 90 N. In contrast, the concentration of B in GDMS for the Ga2O3 single-crystal substrates of samples a–c was all below 4 ppm by mass or above 200 ppm by mass. Under these conditions, the average nanoindentation hardness was below 14.8 GPa or above 22.0 GPa, and the crack load was below 90 N. Therefore, this suggests that the Ga2O3 single-crystal substrates of samples 11–19 suppressed crack formation.

[0202] Figure 6 This is a graph showing the relationship between nanoindentation hardness and crack load on a gallium oxide single-crystal substrate fabricated in the embodiments. Specifically, according to... Figure 6 It is understandable that when the nanoindentation hardness of the Ga2O3 single crystal substrate is in the range of 14.8 GPa or higher and 22.0 GPa or lower, the crack load is above 90 N.

[0203] Although the embodiments and examples of the present invention have been described above, it was originally intended that the above-described embodiments and examples be appropriately combined.

[0204] It should be considered that the embodiments and examples disclosed herein are illustrative in all respects and not restrictive. The scope of the invention is defined by the claims, and not by the embodiments and examples described above, and is intended to include all changes within the meaning and scope equivalent to the claims.

[0205] Explanation of reference numerals in the attached figures

[0206] 100: Gallium trioxide single crystal substrate (Ga2O3 single crystal substrate); O: center; r: length from the center of the main surface to the boundary between the center and the outer periphery; 10: main surface; 11: center; 12: outer periphery; 13: boundary; 21: electrode; 1: heating device; 2: crucible; 3: cover; 41: first nozzle; 42: second nozzle; 51: seed crystal; 52: B2O3-Ga2O3 solution; 8: crucible holding platform; 9: lower shaft; O: center; r: length from the center of the main surface to the boundary between the center and the outer periphery; S100: Ga2O3 single crystal manufacturing process; S110: preparation process; S120: raw material storage process; S130: raw material melting process; S140: Ga2O3 single crystal growth process; S200: Ga2O3 single crystal substrate manufacturing process.

Claims

1. A gallium sesquioxide single crystal substrate having a main surface of a circular shape, the gallium sesquioxide single crystal substrate has a diameter of 100 mm or more, the gallium sesquioxide single crystal substrate has a thickness of 600 μm or more, the gallium sesquioxide single crystal substrate contains boron, a concentration of the boron is 4 mass ppm or more and 200 mass ppm or less in glow discharge mass spectrometry.

2. The gallium sesquioxide single crystal substrate of claim 1, wherein a concentration of the boron is 5 mass ppm or more and 100 mass ppm or less in glow discharge mass spectrometry.

3. The gallium sesquioxide single crystal substrate according to claim 1 or 2, wherein the main surface is a (001) plane of the gallium sesquioxide single crystal, the main surface has a central portion including a center thereof and an outer peripheral portion surrounding the central portion, the outer peripheral portion is a region in which chamfer processing is performed, nanoin denter hardnesses measured at five positions on the main surface in a condition that a load is applied in a manner that a maximum load is 10 mN and an intersecting angle of a direction in which a [100] direction of the gallium sesquioxide single crystal is projected to the main surface and one side of an indentation becomes 0° or more and 10° or less, according to a nanoindentation method using a Berkovich indenter, are each 14.8 GPa or more and 22.0 GPa or less, when a length from the center of the main surface to a boundary of the central portion and the outer peripheral portion is r, two axes that pass through the center and are orthogonal to each other on the main surface are an X axis and a Y axis, and the Y axis is a b axis of the gallium sesquioxide single crystal, coordinates (X, Y) of the five positions defined by the X axis and the Y axis are (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)), and the r and X and Y in the coordinates (X, Y) are in mm.

4. The gallium sesquioxide single crystal substrate according to any one of claims 1 to 3, wherein the gallium sesquioxide single crystal substrate contains either or both of rhodium and iridium, a concentration of the rhodium and a concentration of the iridium are each 0.1 mass ppm or less in glow discharge mass spectrometry.

5. The gallium sesquioxide single crystal substrate according to any one of claims 1 to 4, wherein The resistivity of the gallium trioxide single crystal substrate determined in a Hall test using the Van der Pauw method at 25°C was 1.0 x 10 -3 Ω·cm or more and 2.0 Ω·cm or less, The carrier concentration of the gallium trioxide single crystal substrate was 4.0 x 1018 / cm3 at 25°C in a Hall test using the Van der Pauw method. 17 cm -3 The above and 1.4 x 1018 / cm3 19 cm -3 Hereinafter, The electron mobility of the gallium oxide single-crystal substrate, measured at 25°C using the van der Bauer method, was 0.2 cm⁻¹. 2 / V・s or higher and 15000cm 2 / V・s below.

6. A gallium sesquioxide single crystal production method, the production method is performed in an atmosphere, and includes the following steps: a step of preparing a single crystal growth apparatus having at least a crucible of a cylindrical shape and a heating device disposed in a manner of surrounding an outer periphery of the crucible; a step of housing a seed crystal composed of the gallium sesquioxide single crystal in a bottom portion of the crucible, and housing a gallium sesquioxide polycrystal, an n-type dopant, and boron oxide in a block shape or a powder shape at a position in the crucible that is higher than the seed crystal; a step of heating the crucible with the heating device, thereby causing a portion of the seed crystal to be dissolved, and obtaining a solution in which gallium sesquioxide from the portion of the seed crystal and the gallium sesquioxide polycrystal is dissolved at a first concentration, the n-type dopant is dissolved at a second concentration, and the solution is in contact with a remaining portion of the seed crystal; and a step of growing a crystal from the solution on the remaining portion of the seed crystal, thereby obtaining a gallium sesquioxide single crystal, the crucible is composed of platinum, a concentration of boron in the gallium sesquioxide single crystal is 4 mass ppm or more and 200 mass ppm or less in glow discharge mass spectrometry.

7. A method for producing a gallium sesquioxide single crystal, the production method is performed in a nitrogen atmosphere, and includes the following steps: a step of preparing a single crystal growth apparatus having at least a crucible having a cylindrical shape and a heating device disposed so as to surround an outer periphery of the crucible; a step of housing a seed crystal composed of the gallium sesquioxide single crystal in a bottom portion of the crucible, and housing a gallium sesquioxide polycrystal, an n-type dopant, and boron oxide in a position in the crucible that is higher than the seed crystal; a step of heating the crucible with the heating device, thereby causing a portion of the seed crystal to be dissolved, and obtaining a solution in which gallium sesquioxide from the portion of the seed crystal and the gallium sesquioxide polycrystal is dissolved in the boron oxide at a first concentration, the n-type dopant is dissolved at a second concentration, while the solution is in contact with a remaining portion of the seed crystal; and a step of growing a crystal from the solution on the remaining portion of the seed crystal, thereby obtaining a gallium sesquioxide single crystal, the crucible is composed of pyrolytic boron nitride, a concentration of boron in the gallium sesquioxide single crystal is 4 mass ppm or more and 200 mass ppm or less in a glow discharge mass spectrometry.

8. The method of producing a gallium sesquioxide single crystal according to claim 6 or 7, wherein the single crystal growth apparatus has a nozzle for feeding the gallium sesquioxide polycrystal and the n-type dopant into the crucible, and a lid for sealing the crucible, the lid has a hole into which the nozzle is inserted, the step of obtaining the gallium sesquioxide single crystal includes the following steps: a step of sampling the solution in the crucible sealed by the lid through the nozzle, thereby analyzing a concentration of gallium sesquioxide from the portion of the seed crystal and the gallium sesquioxide polycrystal and a concentration of the n-type dopant in the solution; a step of feeding the gallium sesquioxide polycrystal into the solution in the crucible through the nozzle in such a manner that the concentration becomes within 5% of the first concentration, in accordance with a result of the analysis related to the concentration of the gallium sesquioxide; and a step of feeding the n-type dopant into the solution in the crucible through the nozzle in such a manner that the concentration becomes within 5% of the second concentration, in accordance with a result of the analysis related to the concentration of the n-type dopant.

9. A method for producing a gallium sesquioxide single crystal substrate, including the following steps: processing the gallium sesquioxide single crystal obtained by the method for producing a gallium sesquioxide single crystal according to any one of claims 6 to 8, thereby obtaining a gallium sesquioxide single crystal substrate having a main surface in a circular shape.

10. The gallium sesquioxide single crystal substrate of claim 2, wherein, the main surface is a (001) plane of the gallium sesquioxide single crystal, the main surface has a central portion including a center thereof and an outer peripheral portion surrounding the central portion, the outer peripheral portion is a region in which chamfer processing is performed, the chamfer processing is processing in which a portion of the outer peripheral portion is removed. The nanoindentation hardnesses measured at five positions on the main surface in accordance with the nanoindentation method using a Berkovich indenter were each 14.8 GPa or more and 22.0 GPa or less under conditions in which a maximum load was 10 mN and the load was applied in such a manner that the intersection angle of the [100] direction of the gallium trioxide single crystal projected to the direction of the main surface and one side of the indentation was 0° or more and 10° or less, when the length from the center of the main surface to the boundary between the central portion and the outer peripheral portion was r, two axes that passed through the center and were orthogonal to each other on the main surface were an X axis and a Y axis, and the Y axis was the b axis of the gallium trioxide single crystal, the coordinates (X, Y) of the five positions defined by the X axis and the Y axis were (0, 0), (r-5, 0), (0, r-5), (-(r-5), 0), and (0, -(r-5)), the r and X and Y in the coordinates (X, Y) were in mm, the gallium trioxide single crystal substrate contained both rhodium and iridium or either one of them, the concentration of the rhodium and the concentration of the iridium were each 0.1 mass ppm or less in glow discharge mass spectrometry, The resistivity of the gallium trioxide single crystal substrate was 1.0 x 10 -3 Ω·cm or more and 2.0 Ω·cm or less, The carrier concentration of the gallium trioxide single crystal substrate was 4.0 x 1018 / cm3 at 25°C in a Hall test using the Van der Pauw method. 17 cm -3 The above and 1.4 x 1018 / cm3 19 cm -3 Hereinafter, The electron mobility of the gallium oxide single-crystal substrate, measured at 25°C using the van der Bauer method, was 0.2 cm⁻¹. 2 / V・s or higher and 15000cm 2 / V・s below.

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