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

Abstract

This beta-digallium trioxide single crystal substrate has a circular main surface. The main surface is the (001) plane of the beta-digallium trioxide single crystal, and has a central part including the center and an outer circumferential part surrounding the central part. When pole figure measurement using an X-ray diffraction method, in which the (-201) plane of the single crystal is set as a diffraction plane, is executed in a tilt angle direction and an in-plane rotation angle direction with respect to five sections represented with prescribed coordinates in the central part, five X-ray pole figures each having at least a first pole as one pole are obtained. A first full width at maximum, which is the full width at half maximum in the tilt angle direction of a first diffraction intensity obtained through first main measurement with respect to the first pole and the periphery thereof by using the X-ray diffraction method, is 0.0028-6.0000° in each of the five X-ray pole figures. The first main measurement is executed by fixing the in-plane rotation angle to an in-plane rotation angle φ1 of the first pole, and scanning the tilt angle.

Description

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

[0001] The present disclosure relates to a beta-type digallium trioxide single crystal substrate, a method for manufacturing a beta-type digallium trioxide single crystal, and a method for manufacturing a beta-type digallium trioxide single crystal substrate.

[0002] International Publication No. 2015 / 147101 (Patent Document 1) discloses the production of a free-standing beta-type digallium trioxide single crystal substrate (hereinafter also referred to as a "beta-type GaO single crystal substrate") by forming a beta-type digallium trioxide single crystal (hereinafter also referred to as a "beta-type GaO single crystal") using a hydride vapor phase epitaxy (HVPE) method on a sapphire substrate that has been made rotationally symmetry-free by being misoriented. JP 2016-155714 A (Patent Document 2) and JP 2017-007871 A (Patent Document 3) disclose the production of an alpha-type or epsilon-type digallium trioxide single crystal substrate by growing an alpha-type or epsilon-type digallium trioxide single crystal at low temperature using the HVPE method. Japanese Patent Laid-Open Publication No. 2015-163566 (Patent Document 4) discloses that a beta-type GaO single crystal having an X-ray rocking curve half-width of less than 75 seconds is obtained using an EFG (Edge-defined Film-fed Growth) method.

[0003] International Publication No. 2015 / 147101 JP 2016-155714 A JP 2017-007871 A JP 2015-163566 A

[0004] The beta-type digallium trioxide single crystal substrate according to the present disclosure is a beta-type digallium trioxide single crystal substrate having a circular main surface. The diameter of the beta-type digallium trioxide single crystal substrate is 100 mm or more. The main surface is the (001) plane of the beta-type digallium trioxide single crystal. The main surface has a central portion including its center and an outer periphery surrounding the central portion. The outer periphery is a chamfered region. Five X-ray pole figures obtained by performing pole measurements using an X-ray diffraction method with the (-201) plane of the beta-type digallium trioxide single crystal as the diffraction plane in the tilt angle direction and in-plane rotation angle direction for five locations represented by the following coordinates in the central portion have at least one pole each. The pole measurements are preliminary measurements for identifying the number of poles and the tilt angle and in-plane rotation angle of the poles. In each of the five X-ray pole figures, the pole consists of only a first pole or includes at least the first pole and a second pole. The first pole has a first pole diffraction intensity. The first pole diffraction intensity is the maximum value of the diffraction intensity obtained in the pole measurement. The second pole has a second pole diffraction intensity. The second pole diffraction intensity is the second largest maximum value among the maximum values ​​of the diffraction intensity obtained in the pole measurement and is less than 1 / 100 of the first pole diffraction intensity. A first full width at half maximum, which is the full width at half maximum in the tilt angle direction of the first diffraction intensity obtained by a first measurement using the X-ray diffraction method, is 0.0028° or more and 6.0000° or less in each of the five X-ray pole figures. The first full width at half maximum is determined from the waveform of a graph with the first diffraction intensity as the vertical axis and the tilt angle as the horizontal axis. The first main measurement is performed by fixing the in-plane rotation angle to the in-plane rotation angle φ1 of the first pole and scanning the tilt angle.When the length from the center of the main surface to the boundary between the central portion and the outer periphery is defined as r, the center is defined as the origin, and two mutually orthogonal axes on the main surface that pass through the center are defined as the X-axis and the Y-axis, the positive direction of the X-axis is defined as the

[010] direction of the beta-type digallium trioxide single crystal, and the positive direction of the Y-axis is defined as the direction obtained by projecting the [-100] direction of the beta-type digallium trioxide single crystal onto the main surface, the coordinates (X, Y) of the five locations defined by the X-axis and the Y-axis are (0, 0), (r-10, 0), (0, r-10), (-(r-10), 0), and (0, -(r-10)). The units of r and X and Y in the coordinates (X, Y) are mm.

[0005] FIG. 1 is an explanatory diagram illustrating the main surface of a beta-type GaO single crystal substrate according to this embodiment. FIG. 2 is an explanatory diagram illustrating five measurement points set on the main surface of the beta-type GaO single crystal substrate of FIG. 1 for the purpose of performing pole measurement using X-ray diffraction. FIG. 3 is an explanatory diagram illustrating X-ray pole figures obtained at the five measurement points shown in FIG. 2 by performing pole measurement using X-ray diffraction. FIG. 4 is a graph showing the first diffraction intensity on the vertical axis and the tilt angle on the horizontal axis for determining the first full width at half maximum, which is the full width at half maximum of the first pole diffraction intensity in the tilt angle direction of the first pole shown in FIG. 3. FIG. 5 is an explanatory diagram illustrating an X-ray diffraction apparatus for performing pole measurement using X-ray diffraction on the main surface of a beta-type GaO single crystal substrate according to this embodiment. FIG. 6 is a flowchart illustrating an example of a method for manufacturing a beta-type GaO single crystal substrate, including the method for manufacturing a beta-type GaO single crystal according to this embodiment. FIG. 7 is a schematic diagram illustrating a single crystal growth apparatus used in the method for producing a beta-type Ga2O3 single crystal according to this embodiment.

[0006] [Problem to be Solved by the Present Disclosure] It has been pointed out that beta-type GaO single crystal substrates are prone to cracking due to the strong cleavage of beta-type GaO single crystals, strain inherent in the single crystals, and other factors. However, a beta-type GaO single crystal substrate with improved cracking properties has not yet been obtained, and its development is eagerly awaited.

[0007] In view of the above, an object of the present disclosure is to provide a beta-type Ga2O3 single crystal substrate that is less likely to crack, a method for manufacturing a beta-type Ga2O3 single crystal for manufacturing the same, and a method for manufacturing a beta-type Ga2O3 single crystal substrate.

[0008] [Advantages of the Present Disclosure] According to the present disclosure, a beta-type Ga2O3 single crystal substrate that is not easily broken, a method for producing a beta-type Ga2O3 single crystal for producing the same, and a method for producing a beta-type Ga2O3 single crystal substrate are provided.

[0009] [Summary of the Embodiments] The following provides an overview of the embodiments of the present disclosure. The inventors conducted extensive research to solve the above-mentioned problems. First, the inventors focused on reducing the residual strain of a beta-type GaO single crystal constituting a beta-type GaO single crystal substrate, thereby imparting a property that makes it difficult for crack initiation points to form on the main surface of the substrate when the substrate is obtained from the single crystal. Specifically, the inventors discovered that by subjecting a beta-type GaO single crystal produced using a vertical boat method or the like to a heat treatment involving temperature fluctuations, the single crystal can be stabilized in a state in which defects within the single crystal are released to the outside, thereby obtaining a beta-type GaO single crystal with small residual strain. As a result, they were able to obtain a beta-type GaO single crystal substrate that is less likely to crack from the single crystal, thereby completing the present disclosure.

[0010] Next, embodiments of the present disclosure will be listed and described. [1] A beta-type digallium trioxide single crystal substrate according to one aspect of the present disclosure is a beta-type digallium trioxide single crystal substrate having a circular main surface. The diameter of the beta-type digallium trioxide single crystal substrate is 100 mm or more. The main surface is the (001) plane of the beta-type digallium trioxide single crystal. The main surface has a central portion including its center and an outer periphery surrounding the central portion. The outer periphery is a chamfered region. Five X-ray pole figures obtained by performing pole measurements using X-ray diffraction with the (-201) plane of the beta-type digallium trioxide single crystal as the diffraction plane in the tilt angle direction and in-plane rotation angle direction for five locations represented by the following coordinates in the central portion have at least one pole each. The pole measurements are preliminary measurements for identifying the number of poles and the tilt angle and in-plane rotation angle of the poles. In each of the five X-ray pole figures, the pole consists of only a first pole or includes at least the first pole and a second pole. The first pole has a first pole diffraction intensity. The first pole diffraction intensity is the maximum value of the diffraction intensity obtained in the pole measurement. The second pole has a second pole diffraction intensity. The second pole diffraction intensity is the second largest maximum value among the maximum values ​​of the diffraction intensity obtained in the pole measurement and is less than 1 / 100 of the first pole diffraction intensity. A first full width at half maximum, which is the full width at half maximum in the tilt angle direction of the first diffraction intensity obtained by a first measurement using the X-ray diffraction method, is 0.0028° or more and 6.0000° or less in each of the five X-ray pole figures. The first full width at half maximum is determined from the waveform of a graph with the first diffraction intensity as the vertical axis and the tilt angle as the horizontal axis. The first main measurement is performed by fixing the in-plane rotation angle to the in-plane rotation angle φ1 of the first pole and scanning the tilt angle.When the length from the center of the main surface to the boundary between the central portion and the outer periphery is defined as r, the center is defined as the origin, and two mutually orthogonal axes on the main surface that pass through the center are defined as the X-axis and the Y-axis, the positive direction of the X-axis is defined as the

[010] direction of the beta-type digallium trioxide single crystal, and the positive direction of the Y-axis is defined as the direction obtained by projecting the [-100] direction of the beta-type digallium trioxide single crystal onto the main surface, the coordinates (X, Y) of the five locations defined by the X-axis and the Y-axis are (0, 0), (r-10, 0), (0, r-10), (-(r-10), 0), and (0, -(r-10)). The units of r and X and Y in the coordinates (X, Y) are mm. A beta-type digallium trioxide single crystal substrate having such characteristics can have crack-resistant properties.

[0011] [2] The first full width at half maximum is preferably 0.0028° or more and 3.0000° or less in each of the five X-ray pole figures, thereby providing a beta-type gallium trioxide single crystal substrate that is less likely to crack.

[0012] [3] The first full width at half maximum is preferably 0.0028° or more and 1.0000° or less in each of the five X-ray pole figures, thereby providing a beta-type gallium trioxide single crystal substrate that is less likely to crack.

[0013] [4] The second full width at half maximum, which is the full width at half maximum of the second diffraction intensity in the in-plane rotation angle direction obtained by the second main measurement using the X-ray diffraction method for the first pole and its periphery, is preferably 0.0002° or more and 0.1000° or less in each of the five X-ray pole figures. The second full width at half maximum is preferably determined from the waveform of a graph with the second diffraction intensity as the vertical axis and the in-plane rotation angle as the horizontal axis. The second main measurement is preferably performed by fixing the tilt angle to the tilt angle ψ1 of the first pole and scanning the in-plane rotation angle. This can provide a beta-type gallium trioxide single crystal substrate that is more resistant to cracking.

[0014] [5] The beta-type gallium trioxide single crystal substrate preferably contains a dopant. The dopant is preferably tin or silicon. The atomic concentration of the dopant is preferably 1×10 19 cm -3 It is preferable that the beta-type gallium trioxide single crystal substrate has the following characteristics: It is therefore possible for the beta-type gallium trioxide single crystal substrate containing a dopant to have crack-resistant properties.

[0015] [6] A method for producing a beta-type digallium trioxide single crystal according to one embodiment of the present disclosure is a method for producing a beta-type digallium trioxide single crystal using a vertical boat method. The method includes the steps of: preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; placing a seed crystal at the bottom of the crucible and a massive digallium trioxide bulk body above the seed crystal in the crucible; heating the crucible with the heating device to melt the digallium trioxide bulk body and a portion of the seed crystal to obtain a digallium trioxide melt; The method includes the steps of contacting a digallium trioxide melt with the remainder of the seed crystal, growing a crystal from the digallium trioxide melt on the remainder of the seed crystal in a first mixed gas atmosphere having an oxygen concentration of 30% by volume or more to obtain a beta-type digallium trioxide single crystal, and heat-treating the beta-type digallium trioxide single crystal obtained in the step of obtaining the beta-type digallium trioxide single crystal in a second mixed gas atmosphere having an oxygen concentration of 50% by volume or more. The heat-treating step has the following cyclic annealing conditions. The cyclic annealing conditions are heat treatment conditions in which a temperature-raising step, a temperature-holding step after the temperature-raising step, and a temperature-lowering step after the temperature-holding step constitute one cycle, and the cycle is repeated two or more times. The temperature-raising rate in the temperature-raising step is 1°C or more and 20°C or less per minute. The holding time in the temperature-holding step is 0.5 hours or more and 10 hours or less. The temperature-lowering rate in the temperature-lowering step is -1°C or more and -0.05°C or less per minute. The temperature of the beta-type digallium trioxide single crystal maintained in the temperature maintaining step is 1200° C. or higher and 1700° C. or lower. The difference between the temperature of the beta-type digallium trioxide single crystal maintained in the temperature maintaining step and the temperature of the beta-type digallium trioxide single crystal immediately after completion of the temperature lowering step is 50° C. or higher and 100° C. By using a manufacturing method having such characteristics, a beta-type digallium trioxide single crystal for manufacturing a beta-type digallium trioxide single crystal substrate having crack-resistant properties can be obtained.

[0016] [7] The temperature of the beta-type digallium trioxide single crystal maintained in the temperature maintaining step is preferably 1300° C. or higher and 1700° C. or lower. This allows for the production of beta-type digallium trioxide single crystals with crack-resistant properties, with a high yield.

[0017] [8] A method for producing a beta-type digallium trioxide single crystal substrate according to one embodiment of the present disclosure includes a step of processing the beta-type digallium trioxide single crystal obtained by the method for producing a beta-type digallium trioxide single crystal to obtain a beta-type digallium trioxide single crystal substrate having a circular main surface. A production method having such characteristics can produce a beta-type digallium trioxide single crystal substrate that is resistant to cracking.

[0018] [Details of the embodiment] One embodiment according to the present disclosure (hereinafter also referred to as "the present embodiment") will be described in further detail below, but the present disclosure is not limited thereto. The following description may be made with reference to the drawings, and the same or corresponding elements in the present specification and drawings will be designated by the same reference numerals, and the same description will not be repeated. Furthermore, the scale of the drawings has been adjusted appropriately to facilitate understanding of each component, and the scale of each component shown in the drawings does not necessarily coincide with the scale of the actual component.

[0019] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and only a unit is specified for B, the units of A and B are the same. Furthermore, when a compound or the like is expressed by a chemical formula in this specification, the chemical formula is intended to include any known atomic ratio unless the atomic ratio is particularly limited, and is not necessarily limited to only those within a stoichiometric range.

[0020] In this specification, the "main surface" of a beta-type GaO single crystal substrate refers to both of the two circular faces of the beta-type GaO single crystal substrate. The beta-type GaO single crystal substrate falls within the technical scope of the present disclosure if at least one of the two faces satisfies the scope of the claims of the present disclosure. Furthermore, in this specification, the "face" used in the term "in-plane" refers to the "main surface." Furthermore, when the diameter of a beta-type GaO single crystal substrate is described as "100 mm" or "4 inches," this means that the diameter is approximately 100 mm (approximately 95 to 105 mm). When the diameter is described as "150 mm" or "6 inches," this means that the diameter is approximately 150 mm (approximately 145 to 155 mm). When the diameter is described as "200 mm" or "8 inches," this means that the diameter is approximately 200 mm (approximately 195 to 215 mm). When the diameter is described as "300 mm" or "12 inches," this means that the diameter is approximately 300 mm (approximately 295 to 305 mm). The diameter is measured using a known outer diameter measuring device such as a vernier caliper.

[0021] In the crystallographic descriptions in this specification, individual directions are represented by [ ], collective directions by < >, individual planes by ( ), and collective planes by {}. In addition, negative indices in crystallography are usually represented by placing a "- (bar)" above the number, but in this specification, a negative sign is placed before the number.

[0022] [Beta-type gallium trioxide single crystal substrate (beta-type GaO single crystal substrate)] The beta-type GaO single crystal substrate according to this embodiment is a beta-type GaO single crystal substrate having a circular main surface. The diameter of the beta-type GaO single crystal substrate is 100 mm or more. The main surface is the (001) plane of the beta-type GaO single crystal. The main surface has a central portion including its center and an outer peripheral portion surrounding the central portion. The outer peripheral portion is a chamfered region. Five X-ray pole figures obtained by performing pole measurements using X-ray diffraction with the (-201) plane of the beta-type GaO single crystal as the diffraction plane for the tilt angle direction and the in-plane rotation angle direction for five locations represented by the following coordinates in the central portion have at least one pole each. The pole measurements are preliminary measurements for identifying the number of poles and the tilt angle and in-plane rotation angle of the poles. In each of the five X-ray pole figures, the pole consists of only a first pole or includes at least the first pole and a second pole. The first pole has a first pole diffraction intensity. The first pole diffraction intensity is the maximum value of the diffraction intensity obtained in the pole measurement. The second pole has a second pole diffraction intensity. The second pole diffraction intensity is the second largest maximum value among the maximum values ​​of the diffraction intensity obtained in the pole measurement and is less than 1 / 100 of the first pole diffraction intensity. A first full width at half maximum, which is the full width at half maximum in the tilt angle direction of the first diffraction intensity obtained by a first measurement using the X-ray diffraction method, is 0.0028° or more and 6.0000° or less in each of the five X-ray pole figures. The first full width at half maximum is determined from the waveform of a graph with the first diffraction intensity as the vertical axis and the tilt angle as the horizontal axis. The first main measurement is performed by fixing the in-plane rotation angle to the in-plane rotation angle φ1 of the first pole and scanning the tilt angle.Let r be the length from the center of the main surface to the boundary between the central portion and the outer periphery, let the center be the origin, and let two mutually orthogonal axes on the main surface that pass through the center be the X-axis and the Y-axis. Let the positive direction of the X-axis be the

[010] direction of the beta-type GaO single crystal substrate, and let the positive direction of the Y-axis be the direction obtained by projecting the [-100] direction of the beta-type GaO single crystal onto the main surface. The coordinates (X, Y) of the five locations defined by the X-axis and the Y-axis are (0, 0), (r-10, 0), (0, r-10), (-(r-10), 0), and (0, -(r-10)). The units of r and X and Y in the coordinates (X, Y) are mm. A beta-type GaO single crystal substrate having such characteristics can be crack-resistant.

[0023] <Diameter> As described above, the diameter of the beta-type GaO single crystal substrate is 100 mm or more. In particular, the diameter of the beta-type GaO single crystal substrate is preferably 305 mm or less. The diameter of the beta-type GaO single crystal substrate is more preferably 100 mm or more and 205 mm or less. Specifically, such a beta-type GaO single crystal substrate is preferably a beta-type GaO single crystal substrate having a diameter of 100 mm, 150 mm, 200 mm, or 300 mm, in other words, a beta-type GaO single crystal substrate having a diameter of 4 inches, 6 inches, 8 inches, or 12 inches. This allows the beta-type GaO single crystal substrate to have the characteristic of being less likely to crack, even when it is a large-diameter beta-type GaO single crystal substrate. The diameter of the beta-type GaO single crystal substrate is determined based on the circular shape before the formation of the orientation flat (hereinafter also referred to as "OF"), index flat (hereinafter also referred to as "IF"), etc., even if the main surface does not have a geometrically circular shape due to the influence of the orientation flat (hereinafter also referred to as "OF"), index flat (hereinafter also referred to as "IF"), etc. As described above, the diameter of the beta-type GaO single crystal substrate is measured using a known outer diameter measuring instrument such as a vernier caliper.

[0024] In addition, the thickness of the beta-type GaO single crystal substrate is preferably 600 μm or more. In particular, the thickness of the beta-type GaO single crystal substrate is preferably 650 μm or more and 700 μm or less. This allows the beta-type GaO single crystal substrate to have the characteristic of being less susceptible to cracking, compared to beta-type GaO single crystal substrates having commonly used thicknesses. The thickness of the beta-type GaO single crystal substrate is measured, for example, using a non-contact thickness gauge (product name (model): "TAP-2H-200XY", manufactured by COMS Co., Ltd.). The positioning accuracy of the gauge is 25 μm. The display resolution of the gauge is 0.01 μm. The repeatability of the gauge is 0.01 μm. The gauge used to measure the thickness of the beta-type GaO single crystal substrate is not limited to the above-mentioned gauge, and other gauges may also be used as long as they have equivalent or better positioning accuracy, display resolution, and repeatability. In this specification, the "thickness of the beta-type Ga2O3 single crystal substrate" means the thickness at the center of the main surface of the beta-type Ga2O3 single crystal substrate.

[0025] <Main Surface> (Circular Shape) As described above, the beta-type GaO single crystal substrate has a circular main surface. In this specification, the term "circular shape" used to describe the shape of the main surface includes not only a geometric circular shape but also a shape in which the main surface does not form a geometric circular shape due to the formation of at least one of a notch, OF, or IF on the periphery of the main surface as described above. Here, "a shape in which the main surface does not form a geometric circular shape" refers to a shape in which, among line segments extending from any point on the periphery of the main surface to the center of the main surface, the lengths of line segments extending from any point on the notch, OF, or IF to the center of the main surface are shorter. Furthermore, "a shape in which the main surface does not form a geometric circular shape" also includes a shape in which the lengths of all line segments extending from any point on the periphery of the main surface to the center of the main surface are not necessarily the same due to the shape of the beta-type GaO single crystal used as the raw material for the beta-type GaO single crystal substrate. In this case, the center of the main surface refers to the position of the center of gravity, and the diameter of the beta-type GaO single crystal substrate refers to the length of the longest line segment extending from any point on the outer periphery of the beta-type GaO single crystal substrate, passing through the center of the main surface, to another point on the outer periphery.

[0026] (The (001) plane of the beta-type GaO single crystal) The above-mentioned main surface is the (001) plane of the beta-type GaO single crystal. It is known that a beta-type GaO single crystal substrate having the (001) plane of the beta-type GaO single crystal as its main surface is susceptible to cracks and other defects caused by external stress, as the (001) plane generally has strong cleavage properties. In other words, this embodiment can suppress the occurrence of cracks in a beta-type GaO single crystal substrate having the (001) plane of the beta-type GaO single crystal as its main surface.

[0027] In the present disclosure, the crystal plane of the main surface is assumed to have an accuracy error of ±0.5°. For example, when the main surface is referred to as the "(001) plane" of a beta-type GaO single crystal, the main surface may be a (001) just plane, or the main surface may be a plane having an off-angle of -0.5 to +0.5° from the (001) plane. The off-angle from the (001) plane of the main surface of a beta-type GaO single crystal substrate is measured using a known crystal orientation measurement device (for example, product name (product number) "2991G2" manufactured by Rigaku Corporation).

[0028] (Center and Outer Periphery) The main surface has a center portion including the center and an outer periphery surrounding the center portion. The outer periphery is a chamfered region. FIG. 1 is an explanatory diagram illustrating a main surface of a beta-type GaO single crystal substrate according to this embodiment. For example, in the beta-type GaO single crystal substrate 100 shown in FIG. 1, the main surface 10 has a center portion 11 including the center and an outer periphery 12 surrounding the periphery of the center portion 11. The center portion 11 is a region of the beta-type GaO single crystal substrate 100 where epitaxial layers are deposited to form, for example, an electronic device. The outer periphery 12 is a chamfered region. By chamfering the outer periphery 12, the beta-type GaO single crystal substrate 100 can be less susceptible to cracking or chipping at the outer edge of the outer periphery 12 during handling. A known method is used to chamfer the outer periphery 12.

[0029] The central portion 11 preferably has a circular shape. As a result, 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 can be expressed by a fixed numerical value "r" of 1, as described below or as shown in FIG. 2 . Here, the "circular shape" representing the shape of the central portion 11 includes not only a geometric circular shape but also a shape in which a geometric circular shape is not formed, such as an approximately circular shape, due to chamfering or the like of the outer peripheral portion 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 peripheral portion 12 refers to the length of the shortest line segment among the line segments extending from the center O of the main surface 10 to the boundary 13 between the central portion 11 and the outer peripheral portion 12. The shape of the central portion 11 may be a polygonal shape such as a triangle, a rectangle, a hexagon, or the like.

[0030] The width of the outer periphery 12, that is, the length from the outer edge of the outer periphery 12 to the boundary 13 between the central portion 11 and the outer periphery 12, is preferably 2 to 5 mm. This is because the region of the beta-type GaO single crystal substrate 100 having the width of the outer periphery 12 described above is known to have residual processing strain during chamfering, large variations in the number of dislocations between substrates, and poor flatness, and is therefore not normally used as a material for semiconductor devices.

[0031] The central portion 11 and the peripheral portion 12 are distinguished by the difference in thickness of the beta-type GaO single crystal substrate 100 at those portions. The thickness of the beta-type GaO single crystal substrate 100 at the peripheral portion 12 is less than 99% of the thickness of the beta-type GaO single crystal substrate 100 at the central portion 11. In other words, the peripheral portion 12 refers to the region that has been chamfered as described above, and the thickness at this region is less than 99% of the thickness at the central portion 11. For example, if the thickness at the central portion 11 is 675 μm, the thickness at the peripheral portion 12 will be 668 μm or less. The thicknesses at the central portion 11 and the peripheral portion 12 are each measured using the non-contact thickness measuring device described above. The measuring device used to measure the thicknesses of the central portion 11 and the peripheral portion 12 is not limited to the above measuring device, and other measuring devices may also be used as long as they have equivalent or higher positioning accuracy, display resolution, and repeatability. In this specification, the "thickness of the beta-type GaO single crystal substrate 100 at the central portion 11" refers to the thickness at the center O of the main surface 10 of the beta-type GaO single crystal substrate 100. As a result, "r", which is 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, can be determined as a specific numerical value (unit: mm).

[0032] <Pole Measurement Using X-Ray Diffraction, First Full Width at Half Maximum Determined by First Main Measurement, and Second Full Width at Half Maximum Determined by Second Main Measurement> The beta-type GaO single crystal substrate according to this embodiment is defined by the following characteristics obtained by performing a pole measurement using X-ray diffraction with the (-201) plane of the beta-type GaO single crystal as the diffraction plane, and the first main measurement following the pole measurement. Furthermore, the beta-type GaO single crystal substrate is preferably defined by the following characteristics obtained by performing a second main measurement. Hereinafter, the characteristics of the beta-type GaO single crystal substrate according to this embodiment, which are determined by performing the pole measurement, first main measurement, and second main measurement, will be described with reference to FIGS. 2 to 4. FIG. 2 is an explanatory diagram illustrating five measurement points set on the main surface of the beta-type GaO single crystal substrate of FIG. 1 for the purpose of performing pole measurement using X-ray diffraction. Fig. 3 is an explanatory diagram illustrating X-ray pole figures obtained at the five measurement points shown in Fig. 2 by performing pole measurement using an X-ray diffraction method. Fig. 4 is a graph showing the first diffraction intensity on the vertical axis and the tilt angle on the horizontal axis for determining the first full width at half maximum, which is the full width at half maximum of the first pole diffraction intensity in the tilt angle direction of the first pole shown in Fig. 3.

[0033] 2 and 3, five X-ray pole figures A obtained by performing pole measurements using X-ray diffraction with the (-201) plane of the beta-type GaO single crystal as the diffraction plane for five locations represented by the following coordinates in the central portion 11 of the beta-type GaO single crystal substrate 100 according to this embodiment, in the tilt angle direction ψ and in-plane rotation angle direction φ, each have at least one pole. This "pole" appears as a spot in the X-ray pole figure A and indicates a location where the diffraction intensity in the diffraction plane is high. The pole measurements are preliminary measurements for identifying the number of poles and the tilt angles and in-plane rotation angles of the poles.

[0034] In each of the five X-ray pole figures A, the pole consists of only a first pole P1, or includes at least a first pole P1 and a second pole. The second pole does not appear in the X-ray pole figure A in FIG. 3 . The coordinates of the first pole P1 in the X-ray pole figure A are (φ1, ψ1) when expressed in terms of (in-plane rotation angle, tilt angle). The first pole P1 has a first pole diffraction intensity. The first pole diffraction intensity is the maximum value of the diffraction intensity obtained in the pole measurement. The second pole has a second pole diffraction intensity. The second pole diffraction intensity is the second largest maximum value among the maximum values ​​of the diffraction intensity obtained in the pole measurement, and is less than 1 / 100 of the first pole diffraction intensity.

[0035] Furthermore, as shown in FIG. 4 , the first full width at half maximum W1, which is the full width at half maximum of the first diffraction intensity in the tilt angle direction obtained by the first main measurement using the X-ray diffraction method for the first pole P1 and its periphery, is 0.0028° to 6.0000° in each of the five X-ray pole figures A. From the viewpoint of providing a beta-type GaO single crystal substrate that is less likely to crack, the first full width at half maximum W1 is preferably 0.0028° to 3.0000°, and more preferably 0.0028° to 1.0000° in each of the five X-ray pole figures A. The first full width at half maximum W1 can be determined from the waveform of a graph with the first diffraction intensity as the vertical axis and the tilt angle as the horizontal axis. As will be described later, the first main measurement is performed by fixing the in-plane rotation angle to φ1 of the first pole P1 and scanning the tilt angle.

[0036] Although not shown, the second main measurement, which is performed using the X-ray diffraction method on the first pole P1 and its periphery, preferably has a second full width at half maximum (FWHM) in the in-plane rotation angle direction of the second diffraction intensity obtained in each of five X-ray pole figures A. The second full width at half maximum is more preferably 0.0002° to 0.6000° in each of the five X-ray pole figures A. This more preferably provides the beta-type GaO single crystal substrate 100 with enhanced crack resistance. The second full width at half maximum is preferably determined from a waveform of a graph with the second diffraction intensity as the vertical axis and the in-plane rotation angle as the horizontal axis. As described below, the second main measurement is preferably performed by fixing the tilt angle to the tilt angle ψ1 of the first pole and scanning the in-plane rotation angle.

[0037] The five locations in the central portion 11 of the beta-type GaO single crystal substrate 100 where the pole measurement is performed are expressed by the following coordinates: where r is the length from the center O of the main surface 10 to the boundary between the central portion 11 and the outer peripheral portion 12, the center O is the origin, two axes passing through the center O and perpendicular to each other on the main surface 10 are the X-axis and the Y-axis, the positive direction of the X-axis is the

[010] direction of the beta-type GaO single crystal substrate 100, and the positive direction of the Y-axis is the direction obtained by projecting the [−100] direction of the beta-type GaO single crystal substrate 100 onto the main surface 10, the coordinates (X, Y) of the five locations defined by the X-axis and the Y-axis are (0, 0), (r−10, 0), (0, r−10), (−(r−10), 0), and (0, −(r−10)). The units of r and X and Y in the coordinates (X, Y) are mm.

[0038] The inventors have noted that by performing the above-described pole measurement, first main measurement, and preferably the second main measurement on a beta-type GaO single crystal substrate according to this embodiment, the crystal orientation of the beta-type GaO single crystal constituting the substrate can be determined, and that the smaller the full width at half maximum in the rotation angle direction and tilt angle direction, the smaller the residual strain (better the crystallinity) of the single crystal. The pole measurement is a measurement method that focuses on a specific crystal plane (e.g., a diffraction plane) and evaluates the distribution of the crystal orientation of the sample by irradiating X-rays onto the diffraction plane of the sample from in-plane rotation angle directions of 0 to 360° and tilt angle directions of 0 to 90°. The pole measurement determines the crystal orientation and allows the magnitude of the residual strain of the single crystal to be evaluated. For example, in the case of a beta-type GaO single crystal substrate, the pole measurement may be performed using the (-201) plane as the diffraction plane. In this case, a spot-like intensity distribution is observed only at one location (hereinafter also referred to as the "first pole") at a predetermined in-plane rotation angle and tilt angle. Alternatively, at least the first pole and a spot-like intensity distribution having the second largest intensity after the first pole, the intensity of which is less than 1 / 100 of the first pole (hereinafter also referred to as the "second pole") are observed. When such observation results are obtained, the beta-type GaO single crystal substrate used as the sample is evaluated to have high crystal orientation and small residual strain.

[0039] In particular, following the preliminary measurement as the pole measurement, the first main measurement is performed on the first pole and its periphery, and the narrowness of the full width at half maximum in the tilt angle direction (hereinafter also referred to as the "first full width at half maximum") is measured, thereby evaluating that the crystallinity is good and that the residual strain of the single crystal is extremely small. If the first full width at half maximum is 6.0000° or less, the crystal orientation is extremely high and that the residual strain of the single crystal is extremely small. Hereinafter, the conditions for performing the pole measurement, first main measurement, and second main measurement on the beta-type GaO single crystal substrate according to this embodiment will be described with reference to FIG. 5. FIG. 5 is an explanatory diagram illustrating an X-ray diffraction apparatus for performing pole measurement using X-ray diffraction on the main surface of the beta-type GaO single crystal substrate according to this embodiment.

[0040] (Pole Measurement (Preliminary Measurement)) The pole measurement is performed using an X-ray diffraction apparatus 200 as shown in FIG. 5 under the following condition 1. Condition 1: The X-ray diffraction apparatus 200 includes: an X-ray source 21 that generates incident X-rays; a detector 22 that detects diffracted X-rays; a sample stage 23 having a flat installation surface; an XYZ operation mechanism 231 on which the sample stage 23 is placed and that moves the sample stage 23 in three mutually perpendicular directions; a φ rotation mechanism 232 incorporated in the XYZ operation mechanism 231 and that rotates a part 231a of the XYZ operation mechanism 231 and the sample stage 23 in an in-plane rotation angle direction; and a ψ cradle 233 connected to the XYZ operation mechanism 231 and that rotates the XYZ operation mechanism 231, the φ rotation mechanism 232, and the sample stage 23 in a tilt angle direction. The ψ cradle 233 comprises a rail portion 233a and a main body portion 233b that fits onto the rail portion 233a, and the main body portion 233b is connected to the XYZ operation mechanism portion 231. The main body portion 233b moves along the rail portion 233a, thereby rotating the XYZ operation mechanism portion 231, the ψ rotation mechanism portion 232, and the sample stage 23 in the tilt angle direction. The X-ray source 21 and the detector 22 constitute the optical system of the X-ray diffraction instrument 200.

[0041] When the center of the optical system is O1, an axis that passes through O1, extends along a first direction parallel to a first plane including O1, and has the first direction as its positive direction is A1, an axis that passes through O1, is within the plane of the first plane, extends along a second direction perpendicular to A1, and has the second direction as its positive direction is A2, and an axis that passes through O1, extends along a third direction perpendicular to A1 and A2, and has the third direction as its positive direction is A3, the first direction, the second direction, and the third direction form a right-handed Cartesian coordinate system.

[0042] When O1 is viewed along A1 from the opposite direction to the first direction, a straight line obtained by rotating A2 clockwise around A1 by angle ω is defined as L1, and a direction obtained by rotating the second direction clockwise around A1 by ω is defined as a fourth direction, and when O1 is viewed along A1 from the opposite direction to the first direction, a straight line obtained by rotating L1 counterclockwise around A1 by angle 2θ is defined as L2, and a direction obtained by rotating the fourth direction counterclockwise around A1 by 2θ is defined as a fifth direction, the X-ray source 21 is spaced from O1 in the opposite direction to the fourth direction and is positioned along L1. The detector 22 is spaced from O1 in the fifth direction and is positioned along L2. The X-ray source 21 and the detector 22 are linked so that the magnitude of 2θ is twice the magnitude of ω.

[0043] The X-ray source 21 is a CuK α１ (CuK alpha 1). The ω and 2θ are fixed. The ω is equal to or greater than 9.375° and equal to or less than 9.575°. The 2θ is equal to or greater than 18.850° and equal to or less than 19.050°. The incident X-rays are X-rays irradiated from an X-ray source 21 toward O1 along the fourth direction. The diffracted X-rays are X-rays that are diffracted at the (-201) plane of the beta-type Ga2O3 single crystal in O1 and travel in the fifth direction from O1.

[0044] A part 231a of the XYZ operation mechanism 231 is rotated by a φ rotation mechanism 232 so that O1 is rotated clockwise along A3 by an angle φ as viewed from the direction opposite to the third direction. At this time, the sample stage 23 placed on the part 231a of the XYZ operation mechanism 231 is also rotated by an angle φ so that O1 is rotated clockwise along A3 by an angle φ as viewed from the direction opposite to the third direction. φ is the in-plane rotation angle, and is 0° when the X axis is parallel to A2 (the symbol φ in FIG. 5 indicates the in-plane rotation angle direction). The φ rotation mechanism 232 and the XYZ operation mechanism 231 are rotated by a ψ cradle 233 so that O1 is rotated clockwise along A2 by an angle ψ as viewed from the second direction. At this time, the sample stage 23 placed on the part 231a of the XYZ operation mechanism 231 is also rotated clockwise along A2 by an angle ψ when viewing O1 from the second direction. ψ is the tilt angle, and is 0° when the Z axis, which is the normal to the main surface and passes through the origin, is parallel to A3 (the symbol ψ in FIG. 5 indicates the tilt angle direction).

[0045] In the pole measurement, the beta-type GaO single crystal substrate is placed on the sample stage 23 so that the main surface is parallel to the installation surface, the center of the main surface corresponds to the center position of the installation surface, and the three mutually orthogonal directions of the XYZ operation mechanism 231 correspond to the X-axis, the Y-axis, and the Z-axis.

[0046] The beta-type GaO single crystal substrate is fixed to the sample stage 23 via a plastic adhesive placed between the surface opposite to the main surface and the installation surface. The sample stage 23 is moved by an XYZ operation mechanism 231 in two orthogonal directions in a plane parallel to the installation surface and in a direction perpendicular to the installation surface, and is fixed at a predetermined coordinate. The beta-type GaO single crystal substrate is positioned by the XYZ operation mechanism 231 so that one of the five positions coincides with O1. The positive direction of the Z axis is the

[001] direction of the beta-type GaO single crystal, and the coordinates (X, Y, Z) of the origin are set to (0, 0, 0). The φ rotation mechanism 232 and the XYZ operation mechanism 231 are rotated sequentially in 0.5° steps within a range in which the ψ is equal to or greater than 0° and equal to or less than 80° while the φ is fixed, and for each ψ, a part 231a of the XYZ operation mechanism 231 is rotated in 0.5° steps within a range in which the φ is equal to or greater than 0° and less than 360° while the ψ is fixed.

[0047] The specifications or measurement conditions of the X-ray diffraction device 200, X-ray source 21, and detector 22 used in the pole measurement are as follows: X-ray diffraction device: SmartLab (manufactured by Rigaku Corporation) (X-ray source) X-ray used: CuK α１ (Cu_K-alpha 1) Excitation conditions: 45 kV, 200 mA Incident optical system: PSA Johansson (none) Slit size: 0.5 mm, Mask: 10 mm (Detector) Receiving optical system: HyPix-3000 (0-dimensional) Scanning method: phi scan Diffraction surface: β-type Ga2O3 (beta-Ga2O3) (-201) surface

[0048] As described above, in the beta-type GaO single crystal substrate according to this embodiment, as shown in FIG. 3, pole measurements are performed using X-ray diffraction with the (-201) plane of the beta-type GaO single crystal as the diffraction plane, thereby obtaining five X-ray pole figures A. In the example shown in FIG. 3, each of the five X-ray pole figures A has at least one pole (first pole P1). The first pole P1 has a first pole diffraction intensity. The first pole diffraction intensity is the maximum value of the diffraction intensity obtained in the pole measurement, and by performing the next first main measurement, it is possible to identify a first full width at half maximum, which is the full width at half maximum of the first diffraction intensity in the tilt angle direction.

[0049] (First Main Measurement) Following the pole measurement, the first main measurement is performed using the X-ray diffraction device 200 under the following condition 2. Condition 2: After the pole measurement is performed, the φ rotation mechanism 232 and the XYZ operation mechanism 231 rotate the φ in a range within ±10° of the ψ1 in 0.002° steps, while keeping the φ fixed at the φ1.

[0050] As described above, in the beta-type GaO single crystal substrate according to this embodiment, the first full width at half maximum W1, which is the full width at half maximum of the first diffraction intensity in the tilt angle direction, is identified by the first main measurement performed by the X-ray diffraction method on the first pole W1 and its periphery, as shown in Fig. 4. In the example shown in Fig. 4, the first full width at half maximum W1 is 4.1°, 4.2°, 4.1°, 4.0°, and 4.1° in the five X-ray pole figures, respectively.

[0051] (Second Main Measurement) In this embodiment, it is preferable that the second main measurement is performed following the pole measurement. The second main measurement is preferably performed using the X-ray diffraction apparatus 200 under the following condition 3. Condition 3: After the pole measurement is performed, the part 231a of the XYZ operation mechanism part 231 is rotated in 0.004° steps within a range of ±4° of the φ1, with the ψ fixed to the ψ1.

[0052] As described above, in the beta-type GaO single crystal substrate 100 according to this embodiment, the second full width at half maximum, which is the full width at half maximum of the second diffraction intensity in the in-plane rotation angle direction, is identified by the second main measurement, which is performed by using the X-ray diffraction method and targets the first pole W1 and its periphery. In the example shown in Fig. 3, the second full width at half maximum is 0.49°, 0.48°, 0.50°, 0.49°, and 0.48° in the five X-ray pole figures A, respectively.

[0053] <Dopant> The beta-type GaO single crystal substrate according to this embodiment preferably contains a dopant. The dopant is preferably tin (Sn) or silicon (Si). The atomic concentration of the dopant is preferably 1×10 19 cm -3 It is preferable that the beta-type GaO single crystal substrate has a conductivity type of n-type (electron-donating type). Furthermore, the beta-type GaO single crystal substrate containing a dopant can have crack-resistant properties.

[0054] The atomic concentrations of Sn or Si in the beta-type GaO single crystal substrate are measured by glow discharge mass spectrometry (GDMS). When a beta-type GaO single crystal substrate is obtained from a beta-type GaO single crystal obtained by a manufacturing method of a beta-type GaO single crystal as described below, the beta-type GaO single crystal substrate containing the dopant is obtained by adding a predetermined amount of Sn or Si to a crucible together with a raw material such as a digallium trioxide bulk (hereinafter also referred to as "GaO bulk"). The dopant is more preferably tin (Sn). The atomic concentration of the dopant is 1×10 17 cm -3 1x10 or more 19 cm -3 More preferably, it is:

[0055] [Method for Manufacturing Beta-Type Digallium Trioxide Single Crystal (Beta-Type GaO Single Crystal)] The method for manufacturing a beta-type GaO single crystal according to this embodiment is preferably a method for manufacturing a beta-type GaO single crystal that constitutes a beta-type GaO single crystal substrate having the above-mentioned circular main surface. The method for manufacturing the beta-type GaO single crystal is a method for manufacturing a beta-type GaO single crystal using a vertical boat method, and includes the following steps: That is, the manufacturing method includes the steps of preparing a single crystal growth apparatus (hereinafter also referred to as "GaO 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 at the bottom of the crucible and placing a massive GaO bulk body above the seed crystal in the crucible, and heating the crucible with the heating device to melt a portion of the GaO bulk body and the seed crystal, thereby producing a gallium trioxide melt. the step of growing a crystal from the GaO melt on the remaining portion of the seed crystal in a first mixed gas atmosphere having an oxygen concentration of 30% by volume or more, thereby obtaining a beta-type GaO single crystal; and the step of heat-treating the beta-type GaO single crystal obtained in the step of obtaining the beta-type GaO single crystal in a second mixed gas atmosphere having an oxygen concentration of 50% by volume or more.

[0056] The heat treatment step has the following cyclic annealing conditions. The cyclic annealing conditions are heat treatment conditions in which a cycle consisting of a temperature increase step, a temperature holding step after the temperature increase step, and a temperature decrease step after the temperature holding step is repeated two or more times. The temperature increase rate in the temperature increase step is 1°C or more and 20°C or less per minute. The holding time in the temperature holding step is 0.5 hours or more and 10 hours or less. The temperature decrease rate in the temperature decrease step is -1°C or more and -0.05°C or less per minute. The temperature of the beta-type GaO single crystal held in the temperature holding step is 1200°C or more and 1700°C or less. The difference between the temperature of the beta-type GaO single crystal held in the temperature holding step and the temperature of the beta-type GaO single crystal immediately after the completion of the temperature decrease step is 50°C or more and 100°C or less. By using a manufacturing method having such characteristics, a beta-type Ga2O3 single crystal for manufacturing a beta-type Ga2O3 single crystal substrate having crack-resistant properties can be obtained.

[0057] In particular, the temperature of the beta-type GaO single crystal maintained in the temperature maintaining step is preferably 1300° C. or higher and 1700° C. or lower, thereby making it possible to obtain, with a good yield, beta-type GaO single crystal for manufacturing a beta-type GaO single crystal substrate having crack-resistant properties.

[0058] Fig. 6 is a flowchart showing an example of a method for manufacturing a beta-type GaO single crystal substrate, including the method for manufacturing a beta-type GaO single crystal according to this embodiment. The method for manufacturing a beta-type GaO single crystal according to this embodiment is preferably included in a method for manufacturing a beta-type GaO single crystal substrate, for example, as the beta-type GaO single crystal manufacturing step S100 shown in the flowchart of Fig. 6. According to Fig. 6, the method for manufacturing a beta-type GaO single crystal substrate according to this embodiment includes a beta-type GaO single crystal manufacturing step S100 and a beta-type GaO single crystal substrate manufacturing step S200. The beta-type GaO single crystal manufacturing step S100 includes a step (first step: preparation step S110) of preparing a GaO single crystal growth apparatus including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible. In the preparation step S110, it is preferable to prepare a seed crystal and a massive GaO bulk body in addition to the GaO single crystal growth apparatus. The beta-type GaO single crystal production step S100 includes a step of placing the seed crystal at the bottom of the crucible and placing the GaO bulk body above the seed crystal in the crucible (second step: raw material charging step S120). In the raw material charging step S120, the GaO bulk body is placed above the seed crystal in the crucible. The beta-type GaO single crystal manufacturing process S100 includes a step of heating the crucible with the heating device to melt the GaO bulk and a portion of the seed crystal to obtain a GaO melt, and bringing the GaO melt into contact with the remainder of the seed crystal (third step: raw material melting step S130). In the raw material melting step S130, the crucible is heated with the heating device, whereby the GaO bulk and a portion of the seed crystal melt to form a GaO melt, thereby bringing the GaO melt into contact with the remainder of the seed crystal. The beta-type GaO single crystal manufacturing step S100 includes a step (fourth step: beta-type GaO single crystal growing step S140) of growing a crystal from the GaO melt on the remaining portion of the seed crystal in a first mixed gas atmosphere having an oxygen concentration of 30% by volume or more, thereby obtaining a beta-type GaO single crystal.The beta-type GaO single crystal manufacturing process S100 includes a step of heat-treating the beta-type GaO single crystal obtained by the step of obtaining the beta-type GaO single crystal in a second mixed gas atmosphere having an oxygen concentration of 50% by volume or more (fifth step: ingot annealing step S150).

[0059] The present inventors have focused on producing beta-type GaO single crystals grown using the vertical boat method with reduced residual strain. They have discovered that by subjecting beta-type GaO single crystals grown using the vertical boat method or the like to heat treatment involving temperature fluctuations, defects within the single crystal are released to the outside, stabilizing the single crystal, and thereby producing beta-type GaO single crystals with reduced residual strain. This led to the idea of ​​producing beta-type GaO single crystals and obtaining beta-type GaO single crystal substrates from the beta-type GaO single crystals, which are less likely to crack, and have arrived at the present disclosure.

[0060] Hereinafter, an overview of the GaO single crystal growth apparatus and the beta-type GaO single crystal production step S100 will be described with reference to FIG. 7. In the beta-type GaO single crystal production method (beta-type GaO single crystal production step S100) according to this embodiment, it is preferable to prepare a GaO single crystal growth apparatus 1 shown in FIG. 7. The GaO single crystal growth apparatus 1 can grow beta-type GaO single crystals by the vertical boat method using a crucible 5. Hereinafter, the vertical boat method will be abbreviated as the VB method. The VB method includes the vertical Bridgman method and the vertical temperature gradient solidification method.

[0061] <GaO Single Crystal Growth Apparatus> (Crucible) As shown in FIG. 7, the GaO single crystal growth apparatus 1 includes the crucible 5 described above, a crucible holder 6 for holding the crucible 5, and a heater 7 for heating the crucible 5. Although not shown, a chamber may be provided in addition to the GaO single crystal growth apparatus 1 described above to accommodate the crucible 5, crucible holder 6, and heater 7 for easily adjusting the atmosphere used in the beta-type GaO single crystal growth step S140 to an oxygen concentration of 30% by volume or higher. The dimensions and materials of the chamber are not particularly limited, as long as they are large enough to accommodate the GaO single crystal growth apparatus 1 and other components and are capable of maintaining the internal atmosphere at a predetermined oxygen concentration. Furthermore, if the chamber's sidewalls have good thermal transmittance, the heater of the GaO single crystal growth apparatus described above may be located outside the chamber.

[0062] In the GaO single crystal growth apparatus 1, the crucible 5 includes a cylindrical seed crystal accommodation portion 51, an increasing diameter portion 52 connected to the seed crystal accommodation portion 51, and a straight body portion 53 connected to the increasing diameter portion 52. The seed crystal accommodation portion 51 is cylindrical and has a hollow portion that opens on the side connected to the increasing diameter portion 52 and has a bottom wall formed on the side opposite the increasing diameter portion 52. The seed crystal accommodation portion 51 can accommodate and hold a seed crystal 8a in the hollow portion. The increasing diameter portion 52 has a truncated cone shape that widens upward in the axial direction of the crucible 5 and is connected to the seed crystal accommodation portion 51 on the small diameter side of the increasing diameter portion 52. The straight body portion 53 has a hollow cylindrical shape and is connected to the large diameter side of the increasing diameter portion 52. The increasing diameter portion 52 and the straight body portion 53 function to hold a massive GaO bulk body (specifically, polycrystalline GaO) therein. The diameter increasing portion 52 and the cylindrical portion 53 have the function of solidifying the Ga2O3 melt 82 to grow a beta type Ga2O3 single crystal 81 as a crystal, as will be described later.

[0063] The crucible 5 is made of, for example, platinum or a platinum-rhodium alloy (hereinafter also referred to as "Pt-Rh alloy"). In particular, the crucible 5 is preferably made of a Pt-Rh alloy containing 30 mass% or more of rhodium (Rh). The crucible 5 may be made of a Pt-Rh alloy containing 31 mass% of Rh. The inner diameter of the body portion 53 depends on the diameter of the beta-type GaO single crystal 81 to be produced, but is, for example, 100 mm or more and 310 mm or less.

[0064] (Crucible Holder) The GaO single crystal growth apparatus 1 includes a crucible holder 6 that holds the crucible 5. The crucible holder 6 contacts the bottom of the crucible 5 to hold the crucible 5. The crucible holder 6 may have a cylindrical appearance. The material of the crucible holder 6 is not particularly limited, but may be, for example, quartz, alumina, zirconia, or silicon carbide. The outer diameter of the crucible holder 6 depends on the diameter of the crucible 5 it supports, but is, for example, 105 mm or more and 315 mm or less.

[0065] (Heating Device) The heating device 7 is installed for the purpose of heating the crucible 5. For example, a known electric heater (hereinafter also simply referred to as "heater") may be employed as the heating device 7. For example, two heaters may be provided, and these two heaters may be arranged to surround the outer periphery of the crucible 5. The output of each heater may be controlled independently. In particular, the heater may be divided into multiple sections perpendicular to the axis of the crucible 5, resulting in a multi-stage configuration. In this case, it is preferable to independently control the heater output for each of the multi-stage sections. This allows the temperature of the content in the crucible 5 to be precisely adjusted along the axial direction of the crucible 5. For example, by independently controlling the heater output for each of the multi-stage sections to heat the enlarged diameter section 52 and the straight body section 53, the growth rates of the crystals growing in the enlarged diameter section 52 and the straight body section 53 may be stabilized.

[0066] Although not shown in the figure, the GaO single crystal growth apparatus 1 may be provided with a thermocouple capable of measuring the temperature of the crucible 5 heated by the heater. A plurality of thermocouples may be arranged outside the crucible 5 along the axial direction.

[0067] Hereinafter, one aspect of the method for producing a beta-type GaO single crystal according to this embodiment will be illustrated and described with reference to the flowchart in Fig. 6 and the GaO single crystal growth apparatus shown in Fig. 7. As described above, the method for producing a beta-type GaO single crystal according to this embodiment may be included in the method for producing a beta-type GaO single crystal substrate shown as the flowchart in Fig. 6 as the beta-type GaO single crystal production step S100.

[0068] <Beta-type GaO single crystal manufacturing process S100> (First step: preparation step S110) As shown in FIG. 6, the beta-type GaO single crystal manufacturing process S100 first includes a step of preparing a GaO single crystal growth apparatus (preparation step S110) including at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible. In the preparation step S110, in addition to the GaO single crystal growth apparatus 1 described above for manufacturing the beta-type GaO single crystal 81, a seed crystal 8a and a massive GaO bulk body are preferably also prepared. The seed crystal 8a is made of a beta-type GaO single crystal. The GaO bulk body may be made of polycrystalline GaO. The seed crystal 8a and the massive GaO bulk body may be prepared by a known method or by purchasing commercially available products.

[0069] (Raw Material Charging Step S120) The raw material charging step S120 is a step of accommodating the seed crystal at the bottom of the crucible and accommodating a massive GaO bulk body above the seed crystal in the crucible. In the raw material charging step S120, the massive GaO bulk body is accommodated above the seed crystal 8a in the crucible 5. The purpose of the raw material charging step S120 is to seal various raw materials for crystal growth using the GaO single crystal growth apparatus 1 into the crucible. In the raw material charging step S120, first, a seed crystal 8a consisting of a beta-type GaO single crystal is charged into the hollow portion of the seed crystal accommodation portion 51 of the crucible 5. Next, a plurality of GaO bulk masses made of polycrystalline GaO are loaded into the increased diameter portion 52 and the body portion 53 of the crucible 5 and stacked. In the raw material loading step S120, it is preferable to add a predetermined amount of Sn or Si when loading a plurality of GaO bulk masses into the crucible 5. As a result, a beta GaO single crystal substrate containing the Sn or Si as a dopant is obtained from the beta GaO single crystal 81 obtained by the beta GaO single crystal manufacturing step S100. When adding Sn or Si, the concentration of the dopant is adjusted to 1×10 in the GaO single crystal substrate. 19 cm －3 or less (for example, 1 × 10 17 cm -3 1x10 or more 19 cm -3 It is preferable to adjust the amount added so that the following is satisfied:

[0070] (Third Step: Raw Material Melting Step S130) The raw material melting step S130 is a step of heating the crucible with the heating device to melt the GaO bulk and a portion of the seed crystal to obtain a GaO melt, and bringing the GaO melt into contact with the remainder of the seed crystal. The purpose of the raw material melting step S130 is to melt the GaO bulk and a portion of the seed crystal 8a to bring the remainder of the seed crystal 8a into contact with the GaO melt 82 when growing a crystal using the GaO single crystal growth apparatus 1. This allows the beta GaO single crystal 81 to grow on the remainder of the seed crystal 8a in the next step, the beta GaO single crystal growth step S140, in the method for producing a beta GaO single crystal. Specifically, in the raw material melting step S130, the crucible 5 containing the seed crystal 8a and the GaO bulk body is supported by the crucible holder 6. Thereafter, an electric current is supplied to the heating device 7 to heat the crucible 5. As a result, the GaO bulk body melts to become a GaO melt 82. Next, a portion of the seed crystal 8a also melts, and the remainder of the seed crystal 8a and the GaO melt 82 come into contact at the interface therebetween.

[0071] (Fourth Step: Beta-Type GaO Single Crystal Growth Step S140) The beta-type GaO single crystal growth step S140 is a step of obtaining a beta-type GaO single crystal by growing a crystal from the GaO melt on the remaining portion of the seed crystal in a first mixed gas atmosphere having an oxygen concentration of 30% by volume or more. In the first mixed gas atmosphere having an oxygen concentration of 30% by volume or more in the GaO single crystal growth step S140, for example, by gradually lowering the crucible 5 downward (toward the seed crystal accommodation portion 51) along its axis relative to the heating device 7, a temperature gradient is formed in the crucible 5 such that the temperature on the seed crystal 8a side is low and the temperature on the GaO melt 82 side is high. This allows the above-described method for producing a beta-type GaO single crystal to solidify the GaO melt 82 in contact with the seed crystal 8a and continuously grow a beta-type GaO single crystal 81 from the GaO melt 82 on the remaining portion of the seed crystal 8a. At this time, the temperature on the GaO melt 82 side is, for example, 1800 to 1820°C. The temperature gradient at the interface between the GaO melt 82 and the growing beta-type GaO single crystal 81 is, for example, 3 to 8°C / cm. The speed at which the crucible 5 is pulled downward along its axis is not particularly limited, but is, for example, 0.1 to 2 mm / hour. The remainder of the first mixed gas atmosphere other than oxygen is preferably nitrogen or argon. The oxygen concentration in the first mixed gas atmosphere is preferably 40% by volume or more, more preferably 50% by volume or more. The upper limit of the oxygen concentration in the first mixed gas atmosphere should not be limited and is, for example, 100% by volume.

[0072] In the GaO single crystal growth step S140, the crucible 5 is pulled downward along its axis relative to the heating device 7, so that the interface between the beta GaO single crystal 81 and the GaO melt 82 rises toward the liquid BO side, and the GaO melt 82 is solidified as the beta GaO single crystal 81. As a result, the crystal growth of the beta GaO single crystal 81 continues until the solidification of the GaO melt 82 remaining in the straight body portion 53 of the crucible 5 is completed. In this way, an ingot of the beta GaO single crystal 81 is obtained.

[0073] (Fifth Step: Ingot Annealing Step S150) The ingot annealing step S150 is a step of performing heat treatment in a second mixed gas atmosphere with an oxygen concentration of 50% by volume or more. The heat treatment step (ingot annealing step S150) has the following cyclic annealing conditions. The cyclic annealing conditions are heat treatment conditions in which a temperature increase step, a temperature holding step after the temperature increase step, and a temperature decrease step after the temperature holding step constitute one cycle, and the cycle is repeated two or more times. Specifically, the temperature increase rate in the temperature increase step (hereinafter also referred to as "Δ(T / t)r") is 1°C or more and 20°C or less per minute. The holding time in the temperature holding step (hereinafter also referred to as "tc") is 0.5 hours or more and 10 hours or less. The temperature decrease rate in the temperature decrease step (hereinafter also referred to as "Δ(T / t)f") is -1°C or more and -0.05°C or less per minute. The temperature (hereinafter also referred to as "T1") of the beta-type GaO single crystal maintained in the temperature holding step is 1200°C or higher and 1700°C or lower. The difference between the temperature (T1) of the beta-type GaO single crystal maintained in the temperature holding step and the temperature (hereinafter also referred to as "T2") of the beta-type GaO single crystal immediately after the completion of the temperature lowering step is 50°C or higher and 100°C or lower. In particular, the temperature T1 maintained in the temperature holding step is preferably 1300°C or higher and 1700°C or lower. In this specification, "cyclic annealing" refers to a heat treatment in which a temperature raising step, a temperature holding step after the temperature raising step, and a temperature lowering step after the temperature holding step are defined as one cycle, and the cycle is repeated two or more times. This allows for a high yield of beta-type GaO single crystals for producing beta-type GaO single crystal substrates with crack-resistant properties to be obtained.

[0074] 1) Preheating Step The cyclic annealing included in the ingot annealing step S150 can be performed, for example, as follows. First, the ingot of the beta-type GaO single crystal 81 obtained in the GaO single crystal growth step S140 at room temperature is placed in a heating apparatus assembled by the inventors using known components, while still contained in the crucible 5. Furthermore, the ingot of the beta-type GaO single crystal 81 is preferably heated in the heating apparatus to a temperature at which the ingot annealing step S150 is to be started (for example, the same temperature as T2) (preheating step). The temperature-rise rate (hereinafter also referred to as "Δ(T / t)r0") for this heating is not particularly limited, but may be the same as the temperature-rise rate (Δ(T / t)r) of the temperature-rise step performed subsequent to the preheating step, i.e., 1°C or more and 20°C or less per minute. Δ(T / t)r0 is preferably 1°C or more and 5°C or less per minute.

[0075] 2) Heating Step Next, when the ingot of the beta-type GaO single crystal 81 reaches the temperature at which the ingot annealing step S150 is started, the heating step is carried out. The Δ(T / t)r in the heating step is 1°C or more and 20°C or less per minute, preferably 1°C or more and 5°C or less per minute, and more preferably 1°C or more and 2°C or less per minute. This raises the temperature of the beta-type GaO single crystal 81 to T1, which is 1200°C or more and 1700°C or less. The temperature T1 is preferably 1300°C or more and 1700°C or less.

[0076] 3) Temperature Holding Step After the temperature raising step, a temperature holding step is further carried out, in which the temperature of the beta type GaO single crystal 81 is held at T1 for 0.5 to 10 hours (tc). tc is preferably 0.5 to 5 hours, and more preferably 0.5 to 3 hours.

[0077] 4) Temperature-Reducing Step Next, the temperature-reducing step is carried out after the temperature-holding step. The temperature-reducing rate (Δ(T / t)f) in the temperature-reducing step is -1°C or more and -0.05°C or less per minute, and preferably -0.5°C or more and -0.05°C or less per minute. A specific means for reducing the temperature is, for example, air cooling. As a result, the temperature of the beta-type GaO single crystal 81 is reduced to T2, which is 50°C or more and 100°C or less from T1 maintained in the temperature-holding step. In other words, in the temperature-reducing step, the temperature is preferably reduced from T1 to T2, which is 1100°C or more and 1650°C or less.

[0078] 5) Cyclic Step The cyclic step is a step in which the temperature-raising step, the temperature-maintaining step after the temperature-raising step, and the temperature-lowering step after the temperature-maintaining step are set as one cycle, and the cycle is repeated two or more times. From the viewpoint of further eliminating the internal distortion of the beta-type GaO single crystal 81, the cycle is preferably repeated six or more times, and more preferably twelve or more times.

[0079] 6) Post-Process After the cyclic process is completed, the ingot of beta-type GaO single crystal 81 is preferably cooled to room temperature in the heating device using the same means as in the cooling process. The cooling rate (hereinafter also referred to as "Δ(T / t)f0") for this cooling is not particularly limited, but may be the same as the cooling rate (Δ(T / t)f) in the cooling process, i.e., -1°C or more and -0.05°C or less per minute. Δ(T / t)f0 is preferably -0.5°C or more and -0.05°C or less per minute.

[0080] The balance other than oxygen in the second mixed gas atmosphere in which the ingot annealing step S150 is performed is preferably nitrogen or argon. The oxygen concentration in the second mixed gas atmosphere is preferably 60% by volume or more, more preferably 70% by volume or more. The upper limit of the oxygen concentration in the second mixed gas atmosphere should not be limited, but is, for example, 100% by volume.

[0081] [Effects] By carrying out the above steps, a beta-type GaO single crystal according to this embodiment is produced. In the above-described method for producing a beta-type GaO single crystal, particularly by passing through the ingot annealing step S150, a beta-type GaO single crystal ingot with extremely small residual strain is obtained. From this beta-type GaO single crystal ingot, a beta-type GaO single crystal substrate that is less likely to crack can be obtained by passing through the beta-type GaO single crystal substrate manufacturing method described below. This can reduce the crack defect rate in the beta-type GaO single crystal substrate.

[0082] [Method for Manufacturing a Beta-Type Gallium Trioxide Single Crystal Substrate (Beta-Type GaO Single Crystal Substrate)] <Beta-Type GaO Single Crystal Substrate Manufacturing Step S200> The method for manufacturing a beta-type GaO single crystal substrate according to this embodiment includes a step of processing a beta-type GaO single crystal obtained by the above-described method for manufacturing a beta-type GaO single crystal to obtain a beta-type GaO single crystal substrate having a circular main surface. As shown in Fig. 6, the method for manufacturing the beta-type GaO single crystal substrate includes a beta-type GaO single crystal manufacturing step S100 and a beta-type GaO single crystal substrate manufacturing step S200. The purpose of the beta-type GaO single crystal substrate manufacturing step S200 is to obtain a beta-type GaO single crystal substrate by processing the beta-type GaO single crystal obtained by the beta-type GaO single crystal manufacturing step S100. The beta-type Ga2O3 single crystal substrate manufacturing process S200 includes the following cutting step, outer periphery grinding step, and polishing step, and by carrying out these steps in this order, a beta-type Ga2O3 single crystal substrate is obtained.

[0083] The cutting step is a step of slicing the ingot made of a beta-type GaO single crystal removed from the crucible into wafers having a predetermined thickness to obtain a beta-type GaO single crystal substrate. Furthermore, the periphery grinding step is a step of grinding the periphery of the wafer to obtain a beta-type GaO single crystal substrate having a circular main surface. The periphery grinding step may include, for example, a chamfering step. The cutting step and the periphery grinding step may use known cutting and periphery grinding methods. Furthermore, the polishing step is a step of polishing the center of the main surface to a mirror finish. Known polishing methods may be used for the polishing step. The polishing step may result in the center having a surface roughness Ra of 10 nm or less, as specified in JIS B 0681-2:2018. Through the above steps, a beta-type GaO single crystal substrate that is less likely to crack can be obtained.

[0084] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples. In these examples, a GaO single crystal manufacturing apparatus as shown in FIG. 7 was used to manufacture beta-type GaO single crystal substrates according to the flowchart shown in FIG. 6. In the following description, Samples 11 to 19, 21 to 29, and 31 to 39 are examples. Samples 1A to 1E, 2A to 2E, and 3A to 3C are comparative examples. Samples 11 to 19 and 1A to 1E are examples of beta-type GaO single crystal substrates with an 8-inch diameter. Samples 21 to 29 and 2A to 2E are examples of beta-type GaO single crystal substrates with a 6-inch diameter. Samples 31 to 39 and 3A to 3E are examples of beta-type GaO single crystal substrates with a 4-inch diameter.

[0085] [Manufacturing Beta-Type GaO Single Crystal Substrate] <Sample 1A> (Preparation Step S110) First, the GaO single crystal growth apparatus 1, the seed crystal 8a consisting of a beta-type GaO single crystal, a block of GaO polycrystal, and tin oxide (SnO) as an n-type dopant were prepared by known methods or commercially available. The seed crystal 8a had a diameter of 10 mm and an axial length of 45 mm. The mass of the GaO polycrystal was 10 kg (when converted into a GaO melt, the diameter would be 210 mm and the axial length would be 50 mm). The crucible 5 constituting the GaO single crystal growth apparatus 1 had an inner diameter of 215 mm and was made of a Pt—Rh alloy containing 31% by mass of Rh. The crucible 5 had a thickness of 0.5 mm.

[0086] (Raw Material Charging Step S120) Next, by a known method, a seed crystal 8a was placed at the bottom of the crucible 5, and a chunk of GaO polycrystal and SnO were placed above the seed crystal 8a in this order. Specifically, a plurality of chunks of GaO polycrystal were placed and stacked. Next, SnO was added onto the GaO polycrystal. The amount of SnO added was determined so that the atomic concentration of Sn in the beta-type GaO single crystal substrate was 3.0 × 10. 18 cm －3 The amount was as follows.

[0087] (Raw material melting step S130) Next, the crucible 5 containing the seed crystal 8a, the massive GaO polycrystal, and SnO therein was supported by the crucible holder 6. Thereafter, an electric current was supplied to the heating device 7 to heat the crucible 5, and the GaO polycrystal and a portion of the seed crystal 8a melted to form a GaO melt 82, which came into contact with the remainder of the seed crystal 8a.

[0088] (Beta-type GaO single crystal growth step S140) Next, in a first mixed gas atmosphere having an oxygen concentration of 50% by volume and the remainder being nitrogen, the crucible 5 was gradually pulled downward (toward the bottom) along its axis relative to the heating device 7, thereby creating a temperature gradient in the crucible 5 such that the temperature on the seed crystal 8a side was lower and the temperature on the GaO melt 82 side was higher. As a result, a beta-type GaO single crystal 81 was continuously grown on the seed crystal 8a. This operation was continued until the GaO melt 82 was exhausted. During the crystal growth, the temperature of the interface between the beta-type GaO single crystal 81 and the GaO melt 82 was 1815°C. The speed at which the crucible 5 was pulled downward along its axis was 1 mm / hour. As a result, a beta-type GaO single crystal ingot was obtained. Thirty of the above ingots were produced.

[0089] (Ingot Annealing Step S150) In the process of obtaining the beta-type GaO single crystal substrate of Sample 1A, the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 was not subjected to heat treatment in a second mixed gas atmosphere with an oxygen concentration of 50% by volume or more, or to heat treatment under other conditions.

[0090] (Beta-type GaO single crystal substrate manufacturing process S200) Finally, the beta-type GaO single crystal ingot obtained in the GaO single crystal growth process S140 was processed in the cutting process, periphery grinding process, and polishing process to obtain a beta-type GaO single crystal substrate. First, in the cutting process, the ingot was sliced ​​into wafers having a thickness of 700 μm using a known method. In the periphery grinding process, the periphery of the wafer was ground using a known method so as to be chamfered, thereby obtaining wafers having main surfaces consisting of a central portion and an outer peripheral portion surrounding the periphery of the central portion. Furthermore, in the polishing process, the central portion was polished using a known polishing method to obtain a surface roughness Ra of 0.2 nm at the central portion, as specified in JIS B 0681-2:2018, for example.

[0091] In this way, a beta-type GaO single crystal substrate was produced as sample 1A. The diameter of the beta-type GaO single crystal substrate as sample 1A was 210 mm, and the thickness was 675 μm.

[0092] <Sample 1B> A beta-type GaO single crystal was obtained in the same manner as for preparing the beta-type GaO single crystal substrate of Sample 1A, except that the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 was subjected to heat treatment (ingot annealing step S150) in a second mixed gas atmosphere containing 60 volume % oxygen and the remainder nitrogen. The beta-type GaO single crystal substrate of Sample 1B was obtained from the beta-type GaO single crystal. The heating device used for the heat treatment was a heating device assembled by the inventors using known components. The heat treatment conditions used to obtain the beta-type GaO single crystal substrate of Sample 1B are as shown in Table 1. Table 1 lists the heat treatment conditions (cyclic annealing conditions) for Samples 11 to 19 and Samples 1A to 1E.

[0093] In Table 1, "T1 [°C]" means the maximum temperature in the temperature-raising step. "T2 [°C]" means the minimum temperature in the temperature-lowering step. "Δ(T / t)r [°C / min]" means the temperature-raising rate in the temperature-raising step. "Tc [hr]" means the holding time in the temperature-holding step. "Δ(T / t)f [°C / min]" means the temperature-lowering rate in the temperature-lowering step. "Number of cycles [times]" means the number of cycles in the cyclic step. Note that, under the heat treatment conditions used to obtain the beta-type GaO single crystal substrates of Sample 1B, Samples 1C to 1E (described later), and Samples 11 to 19, the temperature-raising rate in the pre-heating step (Δ(T / t)r0) was 1°C / min, and the temperature-lowering rate in the post-heating step (Δ(T / t)f0) was -0.05°C / min.

[0094] <Samples 1C to 1E> A beta-type GaO single crystal was obtained in the same manner as in producing the beta-type GaO single crystal substrate of Sample 1B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 1, and the beta-type GaO single crystal substrates of Sample 1C, Sample 1D, and Sample 1E were obtained from the beta-type GaO single crystal.

[0095] <Samples 11 to 19> Beta-type GaO single crystals were obtained in the same manner as in producing the beta-type GaO single crystal substrate of Sample 1B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 1, and the beta-type GaO single crystal substrates of Samples 11, 12, 13, 14, 15, 16, 17, 18, and 19 were obtained from the beta-type GaO single crystals.

[0096] <Sample 2A> In preparation step S110, a beta-type GaO single crystal substrate of Sample 2A was obtained in the same manner as for producing the beta-type GaO single crystal substrate of Sample 1A, except that a crucible 5 constituting the GaO single crystal growth apparatus 1 had an inner diameter of 160 mm, a thickness of 0.5 mm, and was made of a Pt—Rh alloy containing 31 mass % Rh. The beta-type GaO single crystal substrate of Sample 2A had a diameter of 155 mm and a thickness of 650 μm.

[0097] <Sample 2B> A beta-type GaO single crystal was obtained in the same manner as for preparing the beta-type GaO single crystal substrate of Sample 2A, except that the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 was heat-treated in a second mixed gas atmosphere containing 60% oxygen by volume and the remainder nitrogen. The beta-type GaO single crystal substrate of Sample 2B was obtained from the beta-type GaO single crystal. The heating device used for the heat treatment was a heating device assembled by the inventors using known components. The heat treatment conditions used to obtain the beta-type GaO single crystal substrate of Sample 2B are as shown in Table 4. Table 4 lists the heat treatment conditions (cyclic annealing conditions) for Samples 21 to 29 and Samples 2A to 2E.

[0098] In Table 4, "T1 [°C]" means the maximum temperature in the temperature-raising step. "T2 [°C]" means the minimum temperature in the temperature-lowering step. "Δ(T / t)r [°C / min]" means the temperature-raising rate in the temperature-raising step. "Tc [hr]" means the holding time in the temperature-holding step. "Δ(T / t)f [°C / min]" means the temperature-lowering rate in the temperature-lowering step. "Number of cycles [times]" means the number of cycles in the cyclic step. In the heat treatment conditions used to obtain beta-type GaO single crystal substrates of Sample 2B, Samples 2C to 2E (described later), and Samples 21 to 28, the temperature-raising rate in the pre-heating step (Δ(T / t)r0) was 1.5°C / min, and the temperature-lowering rate in the post-heating step (Δ(T / t)f0) was -0.05°C / min.

[0099] <Samples 2C to 2E> A beta-type GaO single crystal was obtained in the same manner as in producing the beta-type GaO single crystal substrate of Sample 2B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 4, and the beta-type GaO single crystal substrates of Sample 2C, Sample 2D, and Sample 2E were obtained from the beta-type GaO single crystal.

[0100] <Samples 21 to 28> Beta-type GaO single crystals were obtained in the same manner as in producing the beta-type GaO single crystal substrate of Sample 2B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 4, and the beta-type GaO single crystals were used to obtain the beta-type GaO single crystal substrates of Samples 21, 22, 23, 24, 25, 26, 27, and 28, respectively.

[0101] <Sample 29> A beta-type GaO single crystal was obtained in the same manner as for producing the beta-type GaO single crystal substrate of Sample 2B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 4, and the beta-type GaO single crystal was obtained from the beta-type GaO single crystal. Note that, in the heat treatment conditions performed to obtain the beta-type GaO single crystal substrate of Sample 29, the temperature rise rate (Δ(T / t)r0) in the pre-heating step was 1°C / min, and the temperature fall rate (Δ(T / t)f0) in the post-heating step was -0.05°C / min.

[0102] <Sample 3A> In preparation step S110, a beta-type GaO single crystal substrate of Sample 3A was obtained in the same manner as for producing the beta-type GaO single crystal substrate of Sample 1A, except that a crucible having an inner diameter of 105 mm, a thickness of 0.5 mm, and made of a Pt—Rh alloy containing 31 mass % Rh was used as the crucible 5 constituting the GaO single crystal growth apparatus 1. The beta-type GaO single crystal substrate of Sample 3A had a diameter of 100 mm and a thickness of 600 μm.

[0103] <Sample 3B> A beta-type GaO single crystal was obtained in the same manner as for preparing the beta-type GaO single crystal substrate of Sample 3A, except that the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 was heat-treated in a second mixed gas atmosphere containing 60% oxygen by volume and the remainder nitrogen. The beta-type GaO single crystal substrate of Sample 3B was obtained from this beta-type GaO single crystal. The heating device used for the heat treatment was a heating device assembled by the inventors using known components. The heat treatment conditions used to obtain the beta-type GaO single crystal substrate of Sample 3B are as shown in Table 7. Table 7 lists the heat treatment conditions (cyclic annealing conditions) for Samples 31 to 39 and Samples 3A to 3E.

[0104] In Table 7, "T1 [°C]" means the maximum temperature in the temperature-raising step. "T2 [°C]" means the minimum temperature in the temperature-lowering step. "Δ(T / t)r [°C / min]" means the temperature-raising rate in the temperature-raising step. "Tc [hr]" means the holding time in the temperature-holding step. "Δ(T / t)f [°C / min]" means the temperature-lowering rate in the temperature-lowering step. "Number of cycles [times]" means the number of cycles in the cyclic step. In the heat treatment conditions used to obtain beta-type GaO single crystal substrates of Sample 3B, Samples 3C to 3E (described later), and Samples 31 to 38, the temperature-raising rate in the pre-heating step (Δ(T / t)r0) was 2°C / min, and the temperature-lowering rate in the post-heating step (Δ(T / t)f0) was -0.05°C / min.

[0105] <Samples 3C to 3E> A beta-type GaO single crystal was obtained in the same manner as in producing the beta-type GaO single crystal substrate of Sample 3B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 7, and the beta-type GaO single crystal substrates of Samples 3C, 3D, and 3E were obtained from the beta-type GaO single crystal.

[0106] <Samples 31 to 38> Beta-type GaO single crystals were obtained in the same manner as in producing the beta-type GaO single crystal substrate of Sample 3B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 7, and the beta-type GaO single crystals were used to obtain the beta-type GaO single crystal substrates of Samples 31, 32, 33, 34, 35, 36, 37, and 38, respectively.

[0107] <Sample 39> A beta-type GaO single crystal was obtained in the same manner as for producing the beta-type GaO single crystal substrate of Sample 3B, except that the conditions for the heat treatment performed on the beta-type GaO single crystal ingot obtained in the beta-type GaO single crystal growth step S140 were changed to the conditions shown in Table 7, and the beta-type GaO single crystal was obtained from the beta-type GaO single crystal. Note that, in the heat treatment conditions performed to obtain the beta-type GaO single crystal substrate of Sample 39, the temperature rise rate (Δ(T / t)r0) in the pre-heating step was 1°C / min, and the temperature fall rate (Δ(T / t)f0) in the post-heating step was -0.05°C / min.

[0108] [Evaluation] <Crack occurrence rate> For each sample, 30 ingots obtained by performing the heat treatment step or ingot annealing step S150 (Samples 1A, 2A, and 3A were 30 ingots obtained by performing the beta-type GaO single crystal growth step S140) were visually inspected for the presence or absence of cracks (crack occurrence rate). The crack occurrence rates for Samples 11 to 19 and Samples 1A to 1E are shown in Table 2. The crack occurrence rates for Samples 21 to 29 and Samples 2A to 2E are shown in Table 5. The crack occurrence rates for Samples 31 to 39 and Samples 3A to 3E are shown in Table 8.

[0109] <Pole Measurement, First Main Measurement, and Second Main Measurement> For each sample, the beta-type GaO single crystal substrate was subjected to pole measurement, first main measurement, and second main measurement at five measurement points on the main surface according to the measurement method described above. The results are shown in Tables 2, 3, 5, 6, 8, and 9. Specifically, the number of poles obtained from the pole measurement and the first full width at half maximum values ​​obtained from the first main measurement for Samples 11 to 19 and Samples 1A to 1E are shown in Table 2. The second full width at half maximum values ​​obtained from the second main measurement for Samples 11 to 19 and Samples 1A to 1E are shown in Table 3. The number of poles obtained from the pole measurement and the first full width at half maximum values ​​obtained from the first main measurement for Samples 21 to 29 and Samples 2A to 2E are shown in Table 5. The values ​​of the second full width at half maximum obtained from the second main measurement for Samples 21 to 29 and Samples 2A to 2E are shown in Table 6. The number of poles obtained from the pole measurement and the values ​​of the first full width at half maximum obtained from the first main measurement for Samples 31 to 39 and Samples 3A to 3E are shown in Table 8. The values ​​of the second full width at half maximum obtained from the second main measurement for Samples 31 to 39 and Samples 3A to 3E are shown in Table 9.

[0110] <Measurement of the Defective Rate of Schottky Barrier Diodes (SBDs)> Schottky barrier diodes (SBDs) were fabricated from the beta-type GaO single crystal substrates of Samples 11 to 19, 1A to 1E, 21 to 29, 2A to 2E, 31 to 39, and 3A to 3E by the method described below. The leakage current value was measured when a reverse voltage of -1000 V was applied to the SBDs, and the leakage current value was 1.0 x 10 -5 ampere / cm 2 If the value exceeded 0.01, it was determined to be a defective element. Furthermore, the ratio of the number of defective elements to the total number of SBDs obtained from one beta-type Ga2O3 single crystal substrate for each sample was calculated as the SBD defect rate (%). The BD defect rates for Samples 11 to 19 and Samples 1A to 1E are shown in Table 3. The BD defect rates for Samples 21 to 29 and Samples 2A to 2E are shown in Table 6. The BD defect rates for Samples 31 to 39 and Samples 3A to 3E are shown in Table 9.

[0111] (Method for Fabricating Schottky Barrier Diodes (SBDs)) First, a 2 mm square chip was obtained from the beta-type GaO single crystal substrate of each sample. Next, silicon (Si) ions were implanted into the entire backside of the (001) plane of the chip, followed by annealing at 950°C for 30 minutes. Subsequently, Ti (100 nm thick), Ni (100 nm thick), and Au (100 nm thick) were sequentially vapor-deposited on the backside of the (001) plane of the chip, forming a full-surface electrode. On the front side of the (001) plane of the chip, Ni (100 nm thick) and Au (100 nm thick) were vapor-deposited through a metal mask with multiple holes each 600 μm in diameter, forming a Schottky electrode with a 600 μm diameter in an evenly spaced grid pattern. As a result, a Schottky barrier diode was obtained from the beta-type GaO single crystal substrate of each sample.

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121] [Discussion] According to Tables 1 to 9, the beta-type GaO single crystal substrates of Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39 had reduced crack occurrence rates and SBD failure rates compared to the beta-type GaO single crystal substrates of Samples 1A to 1E, Samples 2A to 2E, and Samples 3A to 3E, respectively. This suggests that the beta-type GaO single crystal substrates of Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39 have reduced residual strain in the beta-type GaO single crystal constituting the substrates, and that when the substrates are obtained from the single crystals, they have the property that crack initiation points are less likely to form on the main surfaces of the substrates, thereby reducing the SBD failure rate.

[0122] Although the embodiments and examples of the present disclosure have been described above, it is also intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined.

[0123] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0124] 100 beta-type gallium trioxide single crystal substrate (beta-type Ga2O3 single crystal substrate), 10 main surface, 11 center, 12 outer periphery, 13 boundary, O center, r length from the center of the main surface to the boundary between the center and the outer periphery, A X-ray pole figure, P1 first pole, φ in-plane rotation angle direction, ψ tilt angle direction, W1 first full width at half maximum, 200 X-ray diffraction apparatus, 21 X-ray source, 22 detector, 23 sample stage, 231 XYZ operation mechanism, 231a part of the XYZ operation mechanism, 232 φ rotation mechanism, 233 ψ cradle, S100 Ga2O3 single crystal production process, S110 preparation process, S120 raw material accommodation process, S130 raw material melting process, S140 Ga2O3 single crystal growth process, S150 Ingot annealing step, S200 Ga2O3 single crystal substrate manufacturing step, 1 Ga2O3 single crystal growth apparatus, 5 crucible, 51 seed crystal accommodation section, 52 diameter increasing section, 53 straight body section, 6 crucible holding stand, 7 heating device, 8a seed crystal, 81 Ga2O3 single crystal, 82 Ga2O3 melt.

Claims

A beta-type gallium trioxide single crystal substrate having a circular main surface, The diameter of the beta-type gallium trioxide single crystal substrate is 100 mm or more, the main surface is a (001) plane of a beta-type gallium sesquioxide single crystal; the main surface has a central portion including a center thereof and an outer periphery surrounding the central portion, The outer periphery is a chamfered region, Five X-ray pole figures obtained by performing pole measurements using an X-ray diffraction method with the (-201) plane of the beta-type gallium trioxide single crystal as a diffraction plane for five points in the central portion represented by the following coordinates have at least one pole each in the tilt angle direction and the in-plane rotation angle direction: the pole measurement is a preliminary measurement for identifying the number of poles and the tilt angles and in-plane rotation angles of the poles; In each of the five X-ray pole figures, the poles consist of only a first pole or include at least the first pole and a second pole; the first pole has a first pole diffraction intensity; the first polar diffraction intensity is a maximum value of the diffraction intensity obtained in the polar measurement, the second pole has a second pole diffraction intensity; the second polar diffraction intensity is the second largest maximum value among the maximum values ​​of the diffraction intensity obtained in the pole measurement, and is less than 1 / 100 of the first polar diffraction intensity; a first full width at half maximum, which is a full width at half maximum of a first diffraction intensity in the tilt angle direction obtained by a first main measurement performed by using the X-ray diffraction method on the first pole and its periphery, is 0.0028° or more and 6.0000° or less in each of the five X-ray pole figures; the first full width at half maximum is obtained from a waveform of a graph having the first diffraction intensity as a vertical axis and the tilt angle as a horizontal axis, the first main measurement is performed by fixing the in-plane rotation angle to an in-plane rotation angle φ1 of the first pole and scanning the tilt angle; a beta-type digallium trioxide single crystal substrate, wherein r is the length from the center of the main surface to the boundary between the central portion and the outer periphery, the center is the origin, and two axes on the main surface that pass through the center and are perpendicular to each other are the X-axis and the Y-axis, the positive direction of the X-axis is the [010] direction of the beta-type digallium trioxide single crystal, and the positive direction of the Y-axis is the direction obtained by projecting the [−100] direction of the beta-type digallium trioxide single crystal onto the main surface, the coordinates (X, Y) of the five locations defined by the X-axis and the Y-axis are (0, 0), (r−10, 0), (0, r−10), (−(r−10), 0), and (0, −(r−10)), and the units of r and X and Y in the coordinates (X, Y) are mm.

2. The beta-type gallium trioxide single crystal substrate according to claim 1, wherein the first full width at half maximum is equal to or greater than 0.0028° and equal to or less than 3.0000° in each of the five X-ray pole figures.

3. The beta-type gallium trioxide single crystal substrate according to claim 1, wherein the first full width at half maximum is equal to or greater than 0.0028° and equal to or less than 1.0000° in each of the five X-ray pole figures. 　 a second full width at half maximum, which is a full width at half maximum of a second diffraction intensity in the in-plane rotation angle direction obtained by a second main measurement performed by using the X-ray diffraction method on the first pole and its periphery, is 0.0002° or more and 0.1000° or less in each of the five X-ray pole figures; the second full width at half maximum is obtained from a waveform of a graph having the second diffraction intensity as a vertical axis and the in-plane rotation angle as a horizontal axis, 4. The beta-type gallium trioxide single crystal substrate according to claim 1, wherein the second main measurement is performed by fixing the tilt angle to a tilt angle ψ1 of the first pole and scanning the in-plane rotation angle. 　 the beta-type gallium trioxide single crystal substrate contains a dopant, the dopant is tin or silicon; The atomic concentration of the dopant is 1×10 19 cm -3 The beta-type digallium trioxide single crystal substrate according to any one of claims 1 to 4, wherein: 　 A method for producing a beta-type gallium trioxide single crystal using a vertical boat method, comprising the steps of: The manufacturing method includes: A step of preparing a single crystal growth apparatus including at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible; A step of placing a seed crystal at the bottom of the crucible and placing a block of gallium trioxide bulk material above the seed crystal in the crucible; heating the crucible with the heating device to melt the gallium trioxide bulk and a portion of the seed crystal to obtain a gallium trioxide melt, and bringing the gallium trioxide melt into contact with the remainder of the seed crystal; growing a crystal from the gallium trioxide melt on the remaining portion of the seed crystal in a first mixed gas atmosphere having an oxygen concentration of 30% by volume or more, thereby obtaining a beta-type gallium trioxide single crystal; and a step of heat-treating the beta-type digallium trioxide single crystal obtained by the step of obtaining the beta-type digallium trioxide single crystal in a second mixed gas atmosphere having an oxygen concentration of 50% by volume or more, The heat treatment step has the following cyclic annealing conditions: The cyclic annealing conditions are heat treatment conditions in which one cycle is a temperature increase step, a temperature holding step after the temperature increase step, and a temperature decrease step after the temperature holding step, and the cycle is repeated two or more times, The temperature increase rate in the temperature increase step is 1°C or more and 20°C or less per minute, The temperature holding time is 0.5 hours or more and 10 hours or less, The temperature decreasing rate in the temperature decreasing step is −1° C. or more and −0.05° C. or less per minute, the temperature of the beta-type gallium trioxide single crystal maintained in the temperature maintaining step is 1200°C or higher and 1700°C or lower; A method for producing a beta-type digallium trioxide single crystal, wherein the difference between the temperature of the beta-type digallium trioxide single crystal maintained in the temperature maintaining step and the temperature of the beta-type digallium trioxide single crystal immediately after completion of the temperature decreasing step is 50°C or more and 100°C or less. The method for producing a beta-type digallium trioxide single crystal according to claim 6, wherein the temperature of the beta-type digallium trioxide single crystal maintained in the temperature maintaining step is 1300°C or higher and 1700°C or lower.

8. A method for producing a beta-type digallium trioxide single crystal substrate, comprising a step of processing the beta-type digallium trioxide single crystal obtained by the method for producing a beta-type digallium trioxide single crystal according to claim 6 or 7 to obtain a beta-type digallium trioxide single crystal substrate having a circular main surface.

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