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 principal surface. The principal surface is a (001) plane of a beta digallium trioxide single crystal, and has a central part including the center thereof. The beta digallium trioxide single-crystal substrate has birefringent retardations obtained by performing measurements of birefringent retardation at the following measurement wavelengths by using visible light for five predetermined locations in the central part of: in all of the five locations, 3.3×10-2 to 3.7×10-2 inclusive when the measurement wavelength is 400 nm; 3.5×10-2 to 3.9×10-2 inclusive when the measurement wavelength is 500 nm; 3.6×10-2 to 4.0×10-2 inclusive when the measurement wavelength is 600 nm; 3.6×10-2 to 4.1×10-2 inclusive when the measurement wavelength is 700 nm; and 3.7×10-2 to 4.1×10-2 inclusive when the measurement wavelength is 800 nm.

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] WO 2015 / 147101 (Patent Document 1) discloses a method for growing a beta-type gallium trioxide single crystal (hereinafter referred to as "beta-type Ga ) by using a hydride vapor phase epitaxy (HVPE) method on a sapphire substrate that has lost rotational symmetry by providing an off-angle. ２ O ３ By forming a film on a free-standing beta-type gallium trioxide single crystal substrate (hereinafter referred to as "beta-type Ga ２ O ３ JP 2015-163566 A (Patent Document 2) discloses that a beta-type Ga single crystal substrate having an X-ray rocking curve half width of less than 75 seconds is obtained by using an EFG (Edge-defined Film-fed Growth) method. ２ O ３ Obtaining a single crystal substrate is disclosed.

[0003] International Publication No. 2015 / 147101 Japanese Patent Application Laid-Open No. 2015-163566 International Publication No. 2021 / 048950

[0004] Beta-type Ga ２ O ３ The single crystal substrate is a beta-type GaAs substrate having a circular main surface. ２ O ３ The beta type Ga single crystal substrate ２ O ３ The diameter of the single crystal substrate is 100 mm or more. ２ O ３The main surface has a central portion including the center and an outer peripheral portion surrounding the central portion. The outer peripheral portion is a chamfered region. The beta-type GaAs was obtained by performing birefringence phase difference measurements at five points in the central portion represented by the following coordinates using visible light at measurement wavelengths of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm. ２ O ３ The birefringence retardation of the single crystal substrate was 3.3×10 at all five points when the measurement wavelength was 400 nm. －２ 3.7 x 10 －２ or less, and when the measurement wavelength is 500 nm, it is 3.5 × 10 －２ 3.9 x 10 －２ When the measurement wavelength is 600 nm, it is 3.6 × 10 －２ Above 4.0 x 10 －２ When the measurement wavelength is 700 nm, the －２ 4.1 x 10 －２ When the measurement wavelength is 800 nm, the －２ 4.1 x 10 －２ 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 axes passing through the center and perpendicular to each other on the main surface are defined as the X-axis and the Y-axis. ２ O ３ The

[010] direction of the single crystal and the positive direction of the Y axis are the

[010] direction of the beta type Ga ２ O ３ When the direction is the [-100] direction of the single crystal, the coordinates (X, Y) of the five points defined by the X axis and the Y axis are expressed as (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 shows a beta Ga ２ O ３2 is an explanatory diagram illustrating the main surface of the single crystal substrate. ２ O ３ FIG. 3 is an explanatory diagram illustrating five measurement points set on the main surface of the single crystal substrate. ２ O ３ Beta-type Ga, including a method for producing a single crystal ２ O ３ 4 is a flowchart showing an example of a method for manufacturing a single crystal substrate according to the present embodiment. ２ O ３ FIG. 1 is a schematic diagram illustrating a single crystal growing apparatus used in a method for producing a single crystal.

[0006] [Problem to be Solved by the Present Disclosure] Conventionally, beta-type Ga ２ O ３ Based on the strong cleavage of the single crystal, the inherent strain in the single crystal, and other factors, beta-type Ga ２ O ３ It has been pointed out that single crystal substrates are prone to cracking. In response to this, it is thought that the cracking tendency can be improved by preparing the above single crystal with good crystallinity. For example, International Publication No. 2021 / 048950 (Patent Document 3) describes an alpha-type Ga ２ O ３ Although the subject of the paper is a single crystal film, it teaches the use of Raman spectroscopy to provide a single crystal film with good crystallinity. However, since the Raman spectroscopy only evaluates the crystallinity of the film surface, it is limited in its contribution to improving the susceptibility to cracking due to strains and the like inherent in the thick single crystal. Therefore, by detecting strains and the like inherent in the single crystal throughout the thickness direction, it is possible to produce a beta-type GaAs film that is less susceptible to cracking. ２ O ３ Single crystal substrates have not yet been obtained, and their development is eagerly awaited.

[0007] In view of the above, the object of the present disclosure is to provide a beta-type GaAs alloy that is difficult to crack. ２ O ３ Single crystal substrate, beta type Ga for manufacturing the same ２ O ３ Method for producing single crystals and beta-type Ga ２ O ３The present invention provides a method for producing a single crystal substrate.

[0008] [Advantages of the Present Disclosure] According to the present disclosure, it is possible to obtain a beta-type Ga alloy that is difficult to crack. ２ O ３ Single crystal substrate, beta type Ga for manufacturing the same ２ O ３ Method for producing single crystals and beta-type Ga ２ O ３ A method for manufacturing a single crystal substrate is provided.

[0009] [Outline of the embodiment] The outline of the embodiment of the present disclosure will be described below. The present inventors have conducted extensive research to solve the above-mentioned problems. ２ O ３ Beta-type Ga forming a single crystal substrate ２ O ３ Regarding single crystals, we focused on the fact that by preparing the single crystals with small internal residual strain, when the substrate is obtained from the single crystals, the starting point of cracks is less likely to be formed on the main surface of the substrate. ２ O ３ The single crystal is subjected to a heat treatment involving temperature fluctuations, and the single crystal is stabilized in a state in which defects within the single crystal are released to the outside, thereby producing a beta type GaAs layer with small internal residual strain. ２ O ３ It was found that a single crystal can be obtained. As a result, it was possible to obtain a beta type Ga alloy that is difficult to break from the single crystal. ２ O ３ A single crystal substrate was achieved, completing the present disclosure.

[0010] Next, embodiments of the present disclosure will be listed and described. [1] Beta Ga according to one aspect of the present disclosure ２ O ３ The single crystal substrate is a beta-type GaAs substrate having a circular main surface. ２ O ３ The beta type Ga single crystal substrate ２ O ３ The diameter of the single crystal substrate is 100 mm or more. ２ O ３The main surface has a central portion including the center and an outer peripheral portion surrounding the central portion. The outer peripheral portion is a chamfered region. The beta-type GaAs was obtained by performing birefringence phase difference measurements at five points in the central portion represented by the following coordinates using visible light at measurement wavelengths of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm. ２ O ３ The birefringence retardation of the single crystal substrate was 3.3×10 at all five points when the measurement wavelength was 400 nm. －２ 3.7 x 10 －２ or less, and when the measurement wavelength is 500 nm, it is 3.5 × 10 －２ 3.9 x 10 －２ When the measurement wavelength is 600 nm, it is 3.6 × 10 －２ Above 4.0 x 10 －２ When the measurement wavelength is 700 nm, the －２ 4.1 x 10 －２ When the measurement wavelength is 800 nm, the －２ 4.1 x 10 －２ 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 axes passing through the center and perpendicular to each other on the main surface are defined as the X-axis and the Y-axis. ２ O ３ The

[010] direction of the single crystal and the positive direction of the Y axis are the

[010] direction of the beta type Ga ２ O ３ When the direction is the [-100] direction of the single crystal, the coordinates (X, Y) of the five points defined by the X axis and the Y axis are expressed as (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 GaAs having such characteristics is ２ O ３ The single crystal substrate can have crack-resistant properties.

[0011] [2] The beta Ga compound according to [1]２ O ３ The single crystal substrate may include a dopant. The dopant may be tin or silicon. The dopant has an atomic concentration of 1×10 １９ cm －３ In this case, the beta type Ga containing the dopant ２ O ３ The single crystal substrate is provided with crack-resistant properties.

[0012] [3] The beta Ga compound according to [1] or [2] ２ O ３ The diameter of the single crystal substrate may be 305 mm or less. In this case, the beta type Ga ２ O ３ The single crystal substrate is provided with crack-resistant properties.

[0013] [4] Beta-type Ga according to one embodiment of the present disclosure ２ O ３ The method for producing a single crystal is a method for producing a beta Ga single crystal according to any one of [1] to [3]. ２ O ３ Beta-type Ga used for single crystal substrate ２ O ３ The method includes the steps 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, placing a beta-type digallium trioxide seed crystal in the bottom of the crucible and placing 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, and bringing the digallium trioxide melt into contact with the remainder of the seed crystal, and growing a beta-type Ga 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 using a vertical boat method. ２ O ３ A step of obtaining a single crystal of the beta-type Ga ２ O ３and heat-treating the 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 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. 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 beta-type GaAs held in the temperature holding step ２ O ３ The temperature of the single crystal is 1200° C. or more and 1700° C. or less. ２ O ３ The temperature of the single crystal and the beta type Ga immediately after the temperature drop step ２ O ３ The difference in temperature between the single crystal and the GaN crystal is 50°C or more and 100°C or less. ２ O ３ Beta-type Ga for producing single crystal substrates ２ O ３ Single crystals are obtained.

[0014] [5] The beta Ga according to [4] ２ O ３ In the method for producing a single crystal, the beta Ga ２ O ３ The temperature of the single crystal may be 1300° C. or higher and 1700° C. or lower. In this case, the beta type Ga ２ O ３ Beta-type Ga for producing single crystal substrates ２ O ３ Single crystals can be obtained with good yield.

[0015] [6] Beta-type Ga according to one embodiment of the present disclosure ２ O ３ The method for producing a single crystal substrate is a method for producing a beta Ga single crystal substrate according to [4] or [5]. ２ O ３The beta type Ga obtained by the method for producing a single crystal ２ O ３ By processing the single crystal, a beta-type Ga with a circular main surface is obtained. ２ O ３ The manufacturing method having such characteristics includes a step of obtaining a single crystal substrate. ２ O ３ A single crystal substrate is obtained.

[0016] [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.

[0017] 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.

[0018] In this specification, beta-type Ga ２ O ３ The "main surface" of the single crystal substrate is the beta type Ga ２ O ３ This refers to both of the two circular faces of the single crystal substrate. ２ O ３ A single crystal substrate falls within the technical scope of the present disclosure when at least one of these two surfaces satisfies the scope of the claims of the present disclosure. In addition, the "surface" used in the term "in-plane" in this specification means the "main surface." Furthermore, beta-type Ga ２ O３ When the diameter of a 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 205 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 diameters are measured using a known outer diameter measuring device such as a vernier caliper.

[0019] 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.

[0020] [Beta type Ga ２ O ３ Single Crystal Substrate] ２ O ３ The single crystal substrate is a beta-type GaAs substrate having a circular main surface. ２ O ３ The beta type Ga single crystal substrate ２ O ３ The diameter of the single crystal substrate is 100 mm or more. ２ O ３ The main surface has a central portion including the center and an outer peripheral portion surrounding the central portion. The outer peripheral portion is a chamfered region. The beta-type GaAs was obtained by performing birefringence phase difference measurements at five points in the central portion represented by the following coordinates using visible light at measurement wavelengths of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm. ２ O ３The birefringence retardation of the single crystal substrate was 3.3×10 at all five points when the measurement wavelength was 400 nm. －２ 3.7 x 10 －２ or less, and when the measurement wavelength is 500 nm, it is 3.5 × 10 －２ 3.9 x 10 －２ When the measurement wavelength is 600 nm, it is 3.6 × 10 －２ Above 4.0 x 10 －２ When the measurement wavelength is 700 nm, the －２ 4.1 x 10 －２ When the measurement wavelength is 800 nm, the －２ 4.1 x 10 －２ 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 axes passing through the center and perpendicular to each other on the main surface are defined as the X-axis and the Y-axis. ２ O ３ The

[010] direction of the single crystal and the positive direction of the Y axis are the

[010] direction of the beta type Ga ２ O ３ When the direction is the [-100] direction of the single crystal, the coordinates (X, Y) of the five points defined by the X axis and the Y axis are expressed as (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 GaAs having such characteristics is ２ O ３ The single crystal substrate can have the property of being hard to break. ２ O ３ The single crystal substrate can have crack-resistant properties.

[0021] <Diameter> The above beta type Ga ２ O ３ The diameter of the single crystal substrate is 100 mm or more as described above. ２ O ３ The diameter of the single crystal substrate may be 305 mm or less. ２ O３ The diameter of the single crystal substrate may be 100 mm or more and 205 mm or less. ２ O ３ Specifically, the single crystal substrate is a beta type Ga substrate having a diameter of 100 mm, 150 mm, 200 mm, or 300 mm. ２ O ３ Single crystal substrates, i.e., beta-type GaAs substrates with diameters of 4 inches, 6 inches, 8 inches, or 12 inches. ２ O ３ The substrate may be a single crystal. ２ O ３ The single crystal substrate is a large-diameter beta-type Ga ２ O ３ The single crystal substrate can have the characteristic of being difficult to crack. ２ O ３ The diameter of the 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. ２ O ３ The diameter of the single crystal substrate is measured using a known outer diameter measuring device such as a vernier caliper.

[0022] In addition, the beta Ga ２ O ３ The thickness of the single crystal substrate may be 600 μm or more. ２ O ３ The thickness of the single crystal substrate may be 650 μm or more and 700 μm or less. ２ O ３ The single crystal substrate is a beta type Ga substrate having a commonly used thickness. ２ O ３ The single crystal substrate can have the characteristic of being difficult to crack. ２ O ３The thickness of the single crystal substrate is measured, for example, by using a non-contact thickness measuring instrument (trade name (model): "TAP-2H-200XY", manufactured by COMS Co., Ltd.). The positioning accuracy of the measuring instrument is 25 μm. The display resolution of the measuring instrument is 0.01 μm. The repeatability accuracy of the measuring instrument is 0.01 μm. ２ O ３ As a measuring instrument used for measuring the thickness of a single crystal substrate, other measuring instruments may be used in addition to the above measuring instruments, as long as they have equivalent or higher positioning accuracy, display resolution, and repeatability. ２ O ３ The thickness of the single crystal substrate is ２ O ３ It means the thickness at the center of the main surface of the single crystal substrate.

[0023] <Main surface> (Circular shape) The above beta type Ga ２ O ３ The single crystal substrate has a circular main surface as described above. In this specification, the term "circular shape" referring to 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 refers to 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 shorter than those of beta-type Ga ２ O ３ Beta-type Ga, the raw material for single crystal substrates ２ O ３ The shape may not be the same depending on the shape of the single crystal. In this case, the center of the main surface refers to the position of the center of gravity, and the beta type Ga ２ O ３ The diameter of the single crystal substrate is ２ O ３It refers to the length of the longest line segment that extends from any point on the periphery of the single crystal substrate, passes through the center of the main surface, and extends to another point on the periphery.

[0024] (Beta type Ga ２ O ３ The main surface is the (001) plane of the single crystal. ２ O ３ This is the (001) plane of the single crystal. ２ O ３ Beta-type Ga with the (001) plane of the single crystal as the main surface ２ O ３ Generally, the (001) plane of a single crystal substrate has a strong cleavage property, and therefore it is known that the substrate is prone to cracks and breakage due to external stress. ２ O ３ Beta-type Ga with the (001) plane of the single crystal as the main surface ２ O ３ In the single crystal substrate, the occurrence of cracks can be reduced.

[0025] In the present disclosure, the crystal plane of the main surface has an accuracy error of ±0.5°. For example, when the main surface is a beta Ga ２ O ３ When referring to the "(001) plane" of a single crystal, the main surface may be the (001) just plane, or the main surface may be a plane having an off-angle of -0.5 to +0.5 degrees from the (001) plane. ２ O ３ The off-angle from the (001) plane on the main surface of the single crystal substrate is measured using a known crystal orientation measuring device (for example, product name (product number) "2991G2" manufactured by Rigaku Corporation).

[0026] (Center and Outer Periphery) The main surface has a center including the center thereof and an outer periphery surrounding the center. The outer periphery is a region that has been chamfered. ２ O ３ 1 is an explanatory diagram illustrating a main surface of a single crystal substrate. ２ O３ The main surface 10 of the single crystal substrate 100 has a central portion 11 including the center thereof and an outer peripheral portion 12 surrounding the outer periphery of the central portion 11. The central portion 11 is a β-type Ga ２ O ３ The outer peripheral portion 12 is a region of the single crystal substrate 100 where epitaxial layers for forming electronic devices, for example, are stacked. The outer peripheral portion 12 is a region that has been chamfered. By chamfering the outer peripheral portion 12, the beta-type Ga ２ O ３ In single crystal substrate 100, the occurrence of cracks and chips at the outer edge of outer periphery 12 during handling can be reduced. A known method is used to chamfer outer periphery 12.

[0027] The central portion 11 may have 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, or a hexagon.

[0028] The width of the outer peripheral portion 12, that is, the length from the outer edge of the outer peripheral portion 12 to the boundary 13 between the central portion 11 and the outer peripheral portion 12, may be 2 to 5 mm. ２ O ３ This is because the region of the width of the outer peripheral portion 12 of the single crystal substrate 100 is known to have a possibility of residual processing distortion 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.

[0029] The central portion 11 and the peripheral portion 12 are beta-type Ga ２ O ３The difference is the thickness of the single crystal substrate 100. ２ O ３ The thickness of the single crystal substrate 100 is ２ O ３ The thickness of the outer circumferential portion 12 is less than 99% of the thickness of the single crystal substrate 100. In other words, the outer circumferential portion 12 is the region that has been chamfered as described above, and the thickness of the region is less than 99% of the thickness of the central portion 11. For example, if the thickness of the central portion 11 is 675 μm, the thickness of the outer circumferential portion 12 will be 668 μm or less. The thicknesses of the central portion 11 and the outer circumferential portion 12 are measured using the non-contact thickness measuring device described above. As a measuring device used to measure the thickness of the central portion 11 and the outer circumferential portion 12, it 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 term "beta-type Ga in the central portion 11" is used. ２ O ３ The thickness of the single crystal substrate 100 is the thickness of the beta-type Ga ２ O ３ It means the thickness at the center O of main surface 10 of single crystal substrate 100. Thus, "r", which is the length from the center O of main surface 10 to boundary 13 between central portion 11 and outer periphery 12, can be determined as a specific numerical value (unit: mm).

[0030] <Dopant> Beta-type Ga according to this embodiment ２ O ３ The single crystal substrate may include a dopant. The dopant may be tin (Sn) or silicon (Si). The dopant may have an atomic concentration of 1×10 １９ cm －３ This allows the beta Ga ２ O ３ The single crystal substrate can be given n-type (electron-donating) conductivity. ２ O ３ The single crystal substrate is a beta type Ga ２ O ３ The single crystal substrate can have crack-resistant properties.

[0031] Beta Ga ２ O ３ The atomic concentrations of Sn and Si in the single crystal substrate are measured by glow discharge mass spectrometry (GDMS). ２ O ３ The single crystal substrate is a beta type Ga ２ O ３ Beta-type Ga obtained by the method for producing single crystals ２ O ３ Beta-type Ga from single crystal ２ O ３ When obtaining a single crystal substrate, a gallium trioxide bulk (hereinafter referred to as "Ga ２ O ３ The dopant may be Sn. The atomic concentration of the dopant is 1×10 １７ cm －３ 1x10 or more １９ cm －３ It may be the following:

[0032] <Birefringence Phase Difference> Beta type Ga according to this embodiment ２ O ３ The single crystal substrate 100 is defined by the following characteristics obtained by performing birefringence phase difference measurements at five locations in the center portion 11 represented by the following coordinates using visible light at measurement wavelengths of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm. ２ O ３ The birefringence retardation of the single crystal substrate 100 was 3.3×10 at all of the five points when the measurement wavelength was 400 nm. －２ 3.7 x 10 －２ The birefringence retardation is 3.5×10 or less at all of the five points when the measurement wavelength is 500 nm. －２ 3.9 x 10 －２The birefringence retardation is 3.6×10 or less at all of the five points when the measurement wavelength is 600 nm. －２ Above 4.0 x 10 －２ The birefringence retardation is 3.6×10 or less at all of the five points when the measurement wavelength is 700 nm. －２ 4.1 x 10 －２ The birefringence retardation is 3.7×10 or less at all of the five points when the measurement wavelength is 800 nm. －２ 4.1 x 10 －２ The following is the result.

[0033] The birefringence phase difference measurement is performed on the beta Ga ２ O ３ The five points in the central portion 11 of the single crystal substrate 100 are expressed by the following coordinates: the length from the center O of the main surface 10 to the boundary between the central portion 11 and the peripheral portion 12 is defined as r, the center O is defined as the origin, and two axes passing through the center O and perpendicular to each other on the main surface 10 are defined as the X-axis and the Y-axis. ２ O ３ The

[010] direction of the single crystal substrate 100 and the positive direction of the Y axis are the beta type Ga ２ O ３ The [-100] direction of single crystal substrate 100 is defined as the direction projected onto main surface 10. In this case, 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.

[0034] The present inventors have developed a beta Ga ２ O ３ By performing the birefringence phase difference measurement on a single crystal substrate, the inventors focused on evaluating the amount of residual strain not only on the surface of the substrate but also inside the substrate. ２ O ３This refers to a measuring means for evaluating the amount of stress (strain) remaining inside a sample ("single crystal substrate") by measuring the optical path difference that occurs when predetermined intrinsic polarized light (for example, two types of circularly polarized light) passes through the sample. The birefringence phase difference can be calculated based on the following formula, so the amount of stress (strain) remaining inside the sample can be evaluated: δ (delta) = β (beta) × d × F, where δ (delta) is the birefringence phase difference [nm] (measured value), β (beta) is the photoelastic coefficient [ / Pa] specific to the material, d is the thickness of the sample [μm] (measured value), and F is the stress [Pa]. According to the above formula, it can be evaluated that the larger the value of δ (delta), the greater the stress remaining inside the sample.

[0035] Specifically, the birefringence phase difference was measured by using a birefringence phase difference measurement mode of a measuring device (trade name: "Spectroscopic Polarimeter, Poxi-spectra", manufactured by Tokyo Instruments Inc.). ２ O ３ The measured value (δ (delta)) obtained by measuring the single crystal substrate was used as the beta type Ga ２ O ３ The value can be obtained by dividing the thickness of the single crystal substrate (d, for example, 650 μm). ２ O ３ The birefringence retardation (δ (delta) / d) of the single crystal substrate was 3.3 × 10 at all five points when the measurement wavelength was 400 nm. －２ 3.7 x 10 －２ The δ (delta) / d is 3.5×10 or less when the measurement wavelength is 500 nm at all of the five points. －２ 3.9 x 10 －２ The δ (delta) / d was 3.6×10 or less at all of the five points when the measurement wavelength was 600 nm. －２ Above 4.0 x 10 －２ The δ (delta) / d was 3.6×10 or less at all of the five points when the measurement wavelength was 700 nm. －２ 4.1 x 10 －２The δ (delta) / d was 3.7×10 or less at all of the five points when the measurement wavelength was 800 nm. －２ 4.1 x 10 －２ When the birefringence retardation exhibits such a value, the beta Ga ２ O ３ The single crystal substrate can have crack-resistant properties.

[0036] δ (delta) / d is 3.3 × 10 when the measurement wavelength is 400 nm. －２ or less than 3.5 × 10 when the measurement wavelength is 500 nm. －２ or less than 3.6 × 10 when the measurement wavelength is 600 nm. －２ or less than 3.6 × 10 when the measurement wavelength is 700 nm. －２ or less than 3.7 × 10 when the measurement wavelength is 800 nm －２ If the value is less than 1, the beta Ga ２ O ３ The single crystal substrate has a small internal strain, but is relatively beta-type Ga. ２ O ３ The influence of the cleavage of a specific crystal plane of the single crystal becomes greater, which may make it more susceptible to cracking.

[0037] δ (delta) / d is 3.7 × 10 when the measurement wavelength is 400 nm. －２ or 3.9 × 10 when the measurement wavelength is 500 nm. －２ or exceeds 4.0 × 10 when the measurement wavelength is 600 nm. －２ or 4.1 × 10 when the measurement wavelength is 700 nm. －２ or when the measurement wavelength is 800 nm, 4.1 × 10 －２ If the value exceeds 1, the beta Ga ２ O ３ Single crystal substrates may have large internal strains and may be prone to cracking.

[0038] [Beta type Ga ２ O ３ Single Crystal Manufacturing Method] ２ O ３The method for producing a single crystal is as follows: ２ O ３ Beta-type Ga used for single crystal substrate ２ O ３ This is a manufacturing method for producing a single crystal. ２ O ３ The single crystal manufacturing method is a vertical boat method using beta-type Ga ２ O ３ A method for producing a single crystal includes the following steps: The method is performed by using a single crystal growth apparatus (hereinafter referred to as "Ga ２ O ３ a step of preparing a single crystal growth apparatus (also referred to as a "single crystal growth apparatus"), a step of placing a seed crystal at the bottom of the crucible and placing a lump of Ga above the seed crystal in the crucible, ２ O ３ a step of placing the bulk body in the crucible; and heating the crucible with the heating device to form the Ga ２ O ３ The bulk body and a portion of the seed crystal were melted to produce a gallium trioxide melt (Ga ２ O ３ The Ga ２ O ３ a step of contacting the melt with the remainder of the seed crystal; and a step of heating the Ga ２ O ３ growing a crystal from the melt onto the remainder of the seed crystal; ２ O ３ A step of obtaining a single crystal of the beta-type Ga ２ O ３ The beta type Ga obtained by the step of obtaining a single crystal ２ O ３ and heat treating the single crystal in a second mixed gas atmosphere having an oxygen concentration of 50% by volume or more.

[0039] The heat treatment step 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 are defined as one cycle, 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 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 beta type Ga alloy held in the temperature holding step ２ O ３ The temperature of the single crystal is 1200° C. or more and 1700° C. or less. ２ O ３ The temperature of the single crystal and the beta type Ga immediately after the temperature drop step ２ O ３ The difference in temperature between the single crystal and the GaN crystal is 50°C or more and 100°C or less. ２ O ３ Beta-type Ga for producing single crystal substrates ２ O ３ Single crystals are obtained.

[0040] In particular, the beta Ga held in the temperature holding step ２ O ３ The temperature of the single crystal may be 1300° C. or higher and 1700° C. or lower. This makes it possible to obtain a beta type Ga single crystal having crack-resistant properties. ２ O ３ Beta-type Ga for producing single crystal substrates ２ O ３ Single crystals can be obtained with good yield.

[0041] FIG. 3 shows the beta Ga ２ O ３ Beta-type Ga, including a method for producing a single crystal ２ O ３ 1 is a flowchart showing an example of a method for manufacturing a single crystal substrate. ２ O ３The method for producing a single crystal is, for example, a beta-type Ga single crystal manufacturing method including various steps (preparation step S110 to ingot annealing step S150) shown in the flowchart of FIG. ２ O ３ As a single crystal manufacturing process, the method for manufacturing a beta-type GaO single crystal substrate may be included. ２ O ３ The method for manufacturing a single crystal substrate is as follows: ２ O ３ The process includes various steps described below as a single crystal manufacturing process and a substrate manufacturing process S200. ２ O ３ The single crystal manufacturing process is carried out in a Ga single crystal manufacturing apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible. ２ O ３ The method includes a step of preparing a single crystal growth apparatus (first step: preparation step S110). ２ O ３ In addition to the single crystal growth equipment, seed crystals and bulk Ga ２ O ３ Bulk bodies may also be prepared. ２ O ３ The single crystal manufacturing process includes placing the seed crystal at the bottom of the crucible, and placing the Ga ２ O ３ The method includes a step of accommodating a bulk body (second step: raw material accommodation step S120). In the raw material accommodation step S120, the Ga bulk body is placed above the seed crystal in the crucible. ２ O ３ The bulk material is accommodated. ２ O ３ The single crystal manufacturing process involves heating the crucible with the heating device and ２ O ３ The bulk body and a portion of the seed crystal are melted to form Ga ２ O ３ A melt is obtained, and the Ga ２ O ３The method further includes a step of bringing the melt into contact with the remaining part of the seed crystal (third step: raw material melting step S130). In the raw material melting step S130, the crucible is heated by the heating device, thereby melting the Ga ２ O ３ The bulk body and a part of the seed crystal melt and Ga ２ O ３ The Ga melts. ２ O ３ The melt and the remainder of the seed crystal come into contact. ２ O ３ The single crystal manufacturing process is carried out by: ２ O ３ A crystal is grown from the melt onto the remainder of the seed crystal to form a beta Ga ２ O ３ Step 4: Obtaining a single crystal ２ O ３ Single crystal growth step S140. ２ O ３ The single crystal manufacturing process is ２ O ３ The beta type Ga obtained by the step of obtaining a single crystal ２ O ３ The method includes a step of heat treating the single crystal in a second mixed gas atmosphere having an oxygen concentration of 50% by volume or more (fifth step: ingot annealing step S150).

[0042] The present inventors have developed a method for growing beta-type GaAs using a vertical boat method. ２ O ３ In single crystals, we focused on producing single crystals with reduced residual strain. In particular, we focused on beta-type Ga grown using the vertical boat method. ２ O ３ By subjecting the single crystal to heat treatment accompanied by temperature fluctuations, the defects in the single crystal are released to the outside, and the single crystal is stabilized, thereby producing a beta type GaAs layer with small residual strain. ２ O ３ It was found that single crystals could be obtained. ２ O ３ A single crystal is produced, and the beta type Ga ２ O３ Beta-type Ga that is difficult to crack from single crystals ２ O ３ The present disclosure was arrived at by conceiving a single crystal substrate.

[0043] Hereinafter, by referring to FIG. ２ O ３ Overview of single crystal growth equipment and beta-type Ga ２ O ３ The single crystal manufacturing process will be explained below. ２ O ３ 4 is a schematic diagram illustrating a single crystal growth apparatus used in the method for producing a single crystal. ２ O ３ The single crystal growth apparatus is shown in the single crystal growth step S140. ２ O ３ In the method for producing a single crystal, Ga ２ O ３ A single crystal growth apparatus 1 may be provided. ２ O ３ The single crystal growth apparatus 1 is used to grow beta-type Ga by the vertical boat method using a crucible 5. ２ O ３ The vertical boat method can grow single crystals. 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 freezing method.

[0044] <Ga ２ O ３ Single crystal growth equipment > (crucible) Ga ２ O ３ As shown in Fig. 4, the single crystal growth apparatus 1 includes the above-mentioned crucible 5, a crucible holder 6 for holding the crucible 5, and a heating device 7 for heating the crucible 5. Furthermore, although not shown in the figure, the above-mentioned Ga ２ O ３ In addition to the single crystal growth apparatus 1, ２ O ３In order to easily set the atmosphere in which the single crystal growth step S140 is performed to have an oxygen concentration of 30% by volume or more, a chamber capable of accommodating the crucible 5, the crucible holder 6, and the heating device 7 may be prepared. The dimensions and materials of the chamber are as follows: ２ O ３ There are no particular limitations on the size and material of the chamber as long as it can accommodate the single crystal growth apparatus 1 and the like and can create an oxygen atmosphere at a predetermined concentration inside. ２ O ３ In some single crystal growth apparatuses, the heating device is located outside the chamber.

[0045] Ga ２ O ３ In the single crystal growth apparatus 1, the crucible 5 includes, from the bottom up, 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, from the bottom up, a hollow portion with a bottom wall formed therein and an opening at a position connected to 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 whose diameter expands upward in the axial direction of the crucible 5, and is connected to the seed crystal accommodation portion 51 at a position where the increasing diameter portion 52 has a small diameter. The straight body portion 53 has a hollow cylindrical shape and is connected to the increasing diameter portion 52 at a position where the increasing diameter portion 52 has a large diameter. The increasing diameter portion 52 and the straight body portion 53 contain a block of Ga 8a therein. ２ O ３ Bulk body (specifically, polycrystalline Ga ２ O ３ The increased diameter portion 52 and the straight body portion 53 have a function of holding Ga as described later. ２ O ３ The melt 82 is solidified to form a crystal of beta-type Ga. ２ O ３ It has the function of growing a single crystal 81 .

[0046] 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 may be made of a Pt-Rh alloy containing 30 mass % or more of rhodium (Rh). The crucible 5 may also be made of a Pt-Rh alloy containing 31 mass % of Rh. The inner diameter of the straight body portion 53 is set to the thickness of the beta-type GaAs to be produced. ２ O ３ Although it depends on the diameter of the single crystal 81, it is, for example, 100 mm or more and 310 mm or less.

[0047] (Cucible holding stand) Ga ２ O ３ The 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.

[0048] (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 used 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 heater output may be controlled independently for each heater. In particular, the heater may be divided into multiple sections perpendicular to the axis of the crucible 5, thereby forming multiple stages. In this case, the heater output may be controlled independently for each of the multiple stages. 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 multiple stages to heat the enlarged diameter portion 52 and the straight body portion 53, the growth rates of the crystals growing in the enlarged diameter portion 52 and the straight body portion 53 may be stabilized.

[0049] Although not shown in the figure, Ga ２ O ３The single crystal growth apparatus 1 may include a thermocouple capable of measuring the temperature of the crucible 5 heated by the heater. A plurality of thermocouples may be arranged outside the crucible 5 along the axial direction.

[0050] The following is a description of the flow chart of FIG. 3 and the Ga ２ O ３ First, the beta-type Ga single crystal growth apparatus according to this embodiment will be described. ２ O ３ The following will explain the method for producing a single crystal by illustrating one embodiment of the method. ２ O ３ The method for producing a single crystal is as follows: ２ O ３ As a single crystal manufacturing process S100, the beta type Ga ２ O ３ This may be included in the method for manufacturing a single crystal substrate.

[0051] <Beta-type Ga ２ O ３ Single Crystal Manufacturing Process> (First Step: Preparation Step S110) As shown in FIG. ２ O ３ In the single crystal manufacturing process, a Ga single crystal manufacturing apparatus is used, which includes at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible. ２ O ３ A step of preparing a single crystal growth apparatus (preparation step S110) is carried out. In the preparation step S110, beta-type Ga ２ O ３ In addition to the GaO single crystal growth apparatus 1 described above for producing the single crystal 81, a seed crystal 8a and a bulk Ga ２ O ３ The seed crystal 8a is a beta-type Ga ２ O ３ Formed from a single crystal. ２ O ３ The bulk material is polycrystalline Ga ２ O ３ The seed crystal 8a and the bulk Ga ２ O ３The bulk material may be prepared by known methods or may be obtained commercially.

[0052] (Raw material accommodation step S120) In the raw material accommodation step S120, the seed crystal is accommodated at the bottom of the crucible, and a Ga lump is placed above the seed crystal in the crucible. ２ O ３ In the raw material containing step S120, a Ga bulk material is placed above the seed crystal 8a in the crucible 5. ２ O ３ The purpose of the raw material accommodation step S120 is to accommodate Ga ２ O ３ In the raw material accommodation step S120, various raw materials for crystal growth are enclosed in the crucible using the single crystal growth apparatus 1. First, beta-type Ga SiO 2 is placed in the hollow portion of the seed crystal accommodation portion 51 of the crucible 5. ２ O ３ The seed crystal 8a formed from a single crystal is placed in the crucible 5. Next, the diameter increasing portion 52 and the straight body portion 53 of the crucible 5 are filled with polycrystalline Ga. ２ O ３ A block of Ga formed from ２ O ３ In the raw material containing step S120, a Ga lump is placed in the crucible 5. ２ O ３ When a plurality of bulk bodies are accommodated, a predetermined amount of Sn or Si may be added. ２ O ３ In the single crystal manufacturing process, the beta type Ga containing Sn or Si as a dopant is ２ O ３ When Sn or Si is added, the concentration of the dopant is Ga. ２ O ３ 1×10 on a single crystal substrate １９ cm －３ or less (for example, 1 × 10 １７ cm －３ 1x10 or more １９ cm －３ The amount added may be adjusted so that the

[0053] (Third Step: Raw Material Melting Step S130) In the raw material melting step S130, the crucible is heated to Ga by the heating device. ２ O ３ and heating the Ga to a temperature exceeding the melting point of the Ga ２ O ３ The bulk body and a portion of the seed crystal are melted to form Ga ２ O ３ A melt is obtained, and the Ga ２ O ３ The purpose of the raw material melting step S130 is to bring the melt into contact with the remaining portion (solid phase) of the seed crystal other than the dissolved portion of the seed crystal. ２ O ３ The bulk body and a part of the seed crystal 8a are melted to form a Ga alloy. ２ O ３ The melt 82 is brought into contact with the beta Ga ２ O ３ The manufacturing method of the single crystal is as follows: ２ O ３ In the single crystal growth step S140, beta-type Ga is grown on the remaining portion of the seed crystal 8a. ２ O ３ In the raw material melting step S130, the seed crystal 8a and the Ga ２ O ３ The crucible 5 containing the bulk material is supported by the crucible holder 6. Then, an electric current is supplied to the heating device 7 to heat the crucible 5. As a result, the Ga ２ O ３ The bulk melts and Ga ２ O ３ Then, a part of the seed crystal 8a also melts, and the remainder of the seed crystal 8a and the Ga ２ O ３ The melt 82 comes into contact with the substrate 81 .

[0054] (Fourth step: beta-type Ga ２ O ３ Single crystal growth step S140) Beta type Ga ２ O ３The single crystal growth step S140 is performed by growing the Ga in a first mixed gas atmosphere having an oxygen concentration of 30% by volume or more. ２ O ３ A crystal is grown from the melt onto the remainder of the seed crystal to form a beta Ga ２ O ３ This is the process for obtaining a single crystal. ２ O ３ In the single crystal growth step S140, in the first mixed gas atmosphere having an oxygen concentration of 30% by volume or more, for example, the crucible 5 is gradually lowered downward along its axis (toward the seed crystal accommodating portion 51) relative to the heating device 7, so that the temperature at the position of the seed crystal 8 in the crucible 5 is low, and Ga ２ O ３ A temperature gradient is formed so that the temperature at the position of the melt 82 becomes higher. ２ O ３ The method for producing a single crystal is as follows: ２ O ３ The melt 82 is solidified, and Ga is gradually added to the remainder of the seed crystal 8a. ２ O ３ The melt 82 is made of beta-type Ga ２ O ３ The single crystal 81 can be continuously grown. ２ O ３ The temperature at the position of the melt 82 is 1800 to 1820°C. ２ O ３ Melt 82 and growing beta-type Ga ２ O ３ The temperature gradient at the interface with the 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 first mixed gas atmosphere may contain nitrogen or argon in addition to oxygen. The oxygen concentration in the first mixed gas atmosphere may be 40% by volume or more, or may be 50% by volume or more. The upper limit of the oxygen concentration in the first mixed gas atmosphere is not limited, and is, for example, 100% by volume.

[0055] Ga ２ O ３In the single crystal growth step S140, the crucible 5 is pulled downward along its axis relative to the heating device 7 to form a beta-type Ga ２ O ３ Single crystal 81 and Ga ２ O ３ The interface with the melt 82 is Ga ２ O ３ The melt 82 rises toward the surface, and Ga ２ O ３ The melt 82 is beta-type Ga ２ O ３ The beta-type GaO single crystal 81 is solidified. As a result, the crystal growth of the GaO single crystal 81 is accelerated by the Ga remaining in the body portion 53 of the crucible 5. ２ O ３ This process continues until the solidification of the melt 82 is completed. ２ O ３ An ingot of single crystal 81 is obtained.

[0056] (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 ingot annealing step S150 includes 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 (hereinafter also referred to as "Δ(T / t)r") in the temperature increase step is 1°C or more and 20°C or less per minute. The holding time (hereinafter also referred to as "tc") in the temperature holding step is 0.5 hours or more and 10 hours or less. The temperature decrease rate (hereinafter also referred to as "Δ(T / t)f") in the temperature decrease step is -1°C or more and -0.05°C or less per minute. The beta-type Ga alloy held in the temperature holding step is ２ O ３ The temperature of the single crystal (hereinafter also referred to as "T1") is 1200°C or higher and 1700°C or lower. ２ O ３ The temperature (T1) of the single crystal and the temperature of the beta Ga ２ O ３The difference between the temperature of the single crystal (hereinafter also referred to as "T2") is 50°C or more and 100°C or less. In particular, the temperature T1 maintained in the temperature holding step may be 1300°C or more and 1700°C or less. In this specification, "cyclic annealing" refers to a heat treatment in which a temperature rising step, a temperature holding step after the temperature rising step, and a temperature falling step after the temperature holding step are regarded as one cycle, and the cycle is repeated two or more times. This results in a beta type GaAs alloy having crack-resistant properties. ２ O ３ Beta-type Ga for producing single crystal substrates ２ O ３ Single crystals can be obtained with good yield.

[0057] 1) Pre-heating Step The ingot annealing step S150 is performed as follows before the cyclic annealing. First, beta-type Ga ２ O ３ The beta type Ga at room temperature obtained by the single crystal growth step S140 ２ O ３ The ingot of the single crystal 81 is placed in the crucible 5 and then placed in the assembled heating device. ２ O ３ The ingot of single crystal 81 may be heated to a temperature at which the ingot annealing step S150 is started (for example, the same temperature as T2 described above) (pre-heating step). The temperature rise rate for this heating (hereinafter also referred to as "Δ(T / t)r0") is not particularly limited, but may be the same as the temperature rise rate (Δ(T / t)r) of the heating step performed following the pre-heating step, i.e., 1°C or more and 20°C or less per minute. Δ(T / t)r0 may be 1°C or more and 5°C or less per minute.

[0058] 2) Heating step Next, beta type Ga ２ O ３ When the ingot of the single crystal 81 reaches the temperature at which cyclic annealing is started, the temperature-raising step is carried out. The temperature-raising step Δ(T / t)r is 1° C. or more and 20° C. or less per minute, and may be 1° C. or more and 5° C. or less per minute, or may be 1° C. or more and 2° C. or less per minute. This allows the beta-type Ga ２ O ３The temperature of the single crystal 81 is raised to T1, which is equal to or higher than 1200° C. and equal to or lower than 1700° C. The temperature T1 may be equal to or higher than 1300° C. and equal to or lower than 1700° C.

[0059] 3) Temperature Holding Step Next, a temperature holding step is performed to hold the beta Ga ２ O ３ The temperature of the single crystal 81 is maintained at T1 for 0.5 to 10 hours (tc). tc may be 0.5 to 5 hours, or may be 0.5 to 3 hours.

[0060] 4) Temperature-Lowering Step Next, the temperature-lowering step is carried out. The temperature-lowering rate (Δ(T / t)f) in the temperature-lowering step is −1° C. or more and −0.05° C. or less per minute, and may be −0.5° C. or more and −0.05° C. or less per minute. A specific method for lowering the temperature is, for example, air cooling. This allows the beta Ga ２ O ３ The temperature of the single crystal 81 is lowered to T2, which is 50° C. or more and 100° C. or less from T1 at which the single crystal 81 is maintained in the temperature maintaining step. That is, in the temperature lowering step, the temperature may be lowered from T1 to T2, which is 1100° C. or more and 1650° C. or less.

[0061] 5) Cyclic annealing Cyclic annealing is a heat treatment in which the above-mentioned temperature increase step, temperature holding step, and temperature decrease step are set as one cycle, and the cycle is repeated two or more times. ２ O ３ From the viewpoint of further eliminating strain inside the single crystal 81, the process may be repeated six times or more, or twelve times or more.

[0062] 6) Post-process After the repeating process is completed, beta-type Ga is heated in the heating device. ２ O ３The ingot of single crystal 81 may be cooled to room temperature using, for example, the same means as in the above-mentioned cooling step. 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 above-mentioned cooling step, that is, -1°C or more and -0.05°C or less per minute. Δ(T / t)f0 may be -0.5°C or more and -0.05°C or less per minute. The process from the pre-heating step to the post-heating step is the ingot annealing step S150.

[0063] The balance other than oxygen in the second mixed gas atmosphere in which the ingot annealing step S150 is performed may be nitrogen or argon. The oxygen concentration in the second mixed gas atmosphere may be 60% by volume or more, or may be 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.

[0064] <Effects> By carrying out the above steps, the beta Ga according to this embodiment can be obtained. ２ O ３ A single crystal is produced. ２ O ３ In the manufacturing method of the single crystal, particularly by going through the ingot annealing step S150, it is possible to obtain a beta type Ga single crystal with extremely small residual strain. ２ O ３ A single crystal ingot is obtained. ２ O ３ From the crystal ingot, the beta-type Ga ２ O ３ By going through the manufacturing method of the single crystal substrate, it is possible to obtain a beta type Ga ２ O ３ A single crystal substrate is obtained. ２ O ３ The crack defect rate can be reduced in single crystal substrates.

[0065] [Beta Ga ２ O ３ Manufacturing Method of Single Crystal Substrate] <Substrate manufacturing step S200> Beta type Ga ２ O ３ The method for producing a single crystal substrate is as follows:２ O ３ Beta-type Ga obtained by the method for producing single crystals ２ O ３ By processing the single crystal, a beta-type Ga with a circular main surface is obtained. ２ O ３ As shown in FIG. ２ O ３ The method for manufacturing a single crystal substrate is a beta-type GaAs substrate manufacturing method including various steps. ２ O ３ The process includes a single crystal manufacturing process and a substrate manufacturing process S200. The purpose of the substrate manufacturing process S200 is to manufacture beta-type Ga ２ O ３ Beta-type Ga obtained by single crystal manufacturing process ２ O ３ By processing the single crystal, beta-type Ga ２ O ３ The substrate manufacturing process S200 includes the following cutting process, outer periphery grinding process, and polishing process, and these processes are performed in this order to obtain a beta-type Ga single crystal substrate. ２ O ３ A single crystal substrate is obtained.

[0066] The cutting process is performed by cutting the beta type Ga ２ O ３ Beta-type Ga was obtained from a single crystal ingot. ２ O ３ In order to obtain a single crystal substrate, the ingot is sliced ​​into wafers having a predetermined thickness. The outer periphery grinding step grinds the outer periphery of the wafer to obtain a beta-type Ga single crystal substrate having a circular main surface. ２ O ３This is a process for obtaining a single crystal substrate. The peripheral grinding process can include, for example, a process of performing chamfering. Known cutting methods and peripheral grinding methods can be used for the cutting process and the peripheral grinding process. Furthermore, the polishing process is a process for mirror-finishing the central portion of the main surface. Known polishing methods can be used for the polishing process. By the polishing process, the central portion can have a surface roughness Ra of 10 nm or less as specified in JIS B 0681-2:2018. As a result, a beta-type Ga substrate that is resistant to cracking can be obtained. ２ O ３ A crystalline substrate is obtained.

[0067] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited thereto. In these examples, Ga ２ O ３ A single crystal manufacturing apparatus is used, and beta-type Ga is grown according to the flow chart shown in FIG. ２ O ３ Single crystal substrates were produced. ２ O ３ The single crystal substrate is the Ga ２ O ３ The beta type Ga was taken out from the crucible of the single crystal manufacturing apparatus. ２ O ３ The single crystal ingot was cut at a position 10 mm inward from the crystal growth end position toward the center of the ingot, parallel to the side of the ingot, and the outer periphery was ground and polished to obtain a beta type Ga ２ O ３ In the following description, Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39 are examples. Samples 1A to 1E, Samples 2A to 2E, and Samples 3A to 3C are comparative examples. Samples 11 to 19 and Samples 1A to 1E were grown on beta-type GaAs substrates with an 8-inch diameter. ２ O ３ Samples 21 to 29 and 2A to 2E are examples of single crystal substrates. ２ O ３ Samples 31 to 39 and 3A to 3E are examples of single crystal substrates.２ O ３ This is an example of a single crystal substrate.

[0068] [Beta type Ga ２ O ３ Manufacturing of Single Crystal Substrate] <Sample 1A> (Preparation Step S110) First, ２ O ３ Single crystal growth apparatus 1, beta-type Ga ２ O ３ A seed crystal 8a formed from a single crystal, a block of Ga ２ O ３ Polycrystalline tin oxide (SnO) as an n-type dopant was prepared by a known method or obtained commercially. The size of the seed crystal 8a was 10 mm in diameter and 45 mm in axial length. ２ O ３ The mass of the polycrystal was 10 kg (Ga ２ O ３ When melted, it has a diameter of 210 mm and an axial length of 50 mm. ２ O ３ A crucible having an inner diameter of 215 mm and made of a Pt—Rh alloy containing 31 mass % of Rh was used as the crucible 5 forming the single crystal growth apparatus 1. The thickness of the crucible 5 was 0.5 mm.

[0069] (Raw material accommodation step S120) Next, a seed crystal 8a is accommodated at the bottom of the crucible 5, and a Ga mass is placed above the seed crystal 8a by a known method. ２ O ３ Polycrystalline, and SnO ２ Specifically, the bulk Ga ２ O ３ Several polycrystals were accommodated and stacked. ２ O ３ SnO on polycrystalline ２ SnO was added. ２ The amount of beta-type Ga ２ O ３ The atomic concentration of Sn in the single crystal substrate is 3.0 × 10 １８ cm －３ The amount was as follows.

[0070] (Raw material melting step S130) Next, the seed crystal 8a and the lump Ga ２ O ３ Polycrystalline, and SnO ２ The crucible 5 containing the Ga was supported by the crucible holder 6. Then, an electric current was supplied to the heating device 7 to heat the crucible 5. ２ O ３ The polycrystal and a part of the seed crystal 8a are melted, and Ga ２ O ３ The melt 82 is formed. ２ O ３ The melt 82 came into contact with the remaining part of the seed crystal 8a.

[0071] (Beta type Ga ２ O ３ Single crystal growth step S140) Next, in a first mixed gas atmosphere in which the oxygen concentration is 50% by volume and the rest of the gas is nitrogen, the crucible 5 is gradually pulled downward (toward the bottom) along its axis relative to the heating device 7, so that the temperature at the position of the seed crystal 8a in the crucible 5 is low, and Ga ２ O ３ The temperature gradient was set so that the temperature at the position of the melt 82 was high. ２ O ３ The single crystal 81 was continuously grown. ２ O ３ The process was continued until the melt 82 was exhausted. ２ O ３ Single crystal 81 and Ga ２ O ３ The temperature of the interface with the melt 82 was set to 1815° C. The speed at which the crucible 5 was pulled downward along its axis was set to 1 mm / hour. ２ O ３ A single crystal ingot was obtained. Thirty such ingots were produced.

[0072] Beta Ga of Sample 1A ２ O ３ In the process of obtaining a single crystal substrate, beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O３ The single crystal ingot was not subjected to heat treatment in a second mixed gas atmosphere with an oxygen concentration of 50% by volume or more, or heat treatment under other conditions.

[0073] (Substrate manufacturing process S200) Finally, Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The single crystal ingot is processed in the steps of cutting, grinding, and polishing, thereby obtaining beta-type Ga. ２ O ３ A single crystal substrate was obtained. First, in the cutting step, the ingot was sliced ​​into wafers having a thickness of 700 μm using a known method. In the periphery grinding step, the periphery of the wafer was ground using a known method so as to chamfer the wafer, thereby obtaining wafers having main surfaces formed from a central portion and an outer peripheral portion surrounding the periphery of the central portion. Furthermore, in the polishing step, the central portion was polished using a known polishing method, so that the surface roughness Ra of the central portion was 0.2 nm, for example, as specified in JIS B 0681-2:2018.

[0074] As a result, the beta Ga of sample 1A was ２ O ３ A single crystal substrate was produced. ２ O ３ The single crystal substrate had a diameter of 210 mm and a thickness of 650 μm.

[0075] <Sample 1B> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 1A was the same as that of sample 1B except that the single crystal ingot was subjected to a heat treatment (ingot annealing step S150) in a second mixed gas atmosphere in which the oxygen concentration was 60 volume % and the rest of the gas was nitrogen. ２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３A single crystal was obtained, and the beta type Ga ２ O ３ Beta-type Ga of sample 1B from single crystal ２ O ３ The apparatus used for the heat treatment was a heating apparatus assembled by the inventors from known components. ２ O ３ The heat treatment conditions used to obtain the single crystal substrates are shown in Table 1. Table 1 lists the heat treatment conditions (cyclic annealing conditions) for Samples 11 to 19 and Samples 1A to 1E.

[0076] 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 cyclic annealing. Note that the beta-type Ga alloys of Sample 1B, Samples 1C to 1E, and Samples 11 to 19 described later, ２ O ３ In the heat treatment conditions used to obtain the single crystal substrate, the temperature increase rate (Δ(T / t)r0) in the pre-heating step was 1° C. / min, and the temperature decrease rate (Δ(T / t)f0) in the post-heating step was −0.05° C. / min.

[0077] <Samples 1C to 1E> Beta Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 1B was obtained by heat treatment of the single crystal ingot under the conditions shown in Table 1. ２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal was obtained, and the beta type Ga ２ O ３ Beta-type Ga of sample 1C, sample 1D, and sample 1E from single crystals２ O ３ Single crystal substrates were obtained from each of them.

[0078] <Samples 11 to 19> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 1B was obtained by heat treatment of the single crystal ingot under the conditions shown in Table 1. ２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal was obtained, and the beta type Ga ２ O ３ Beta-type Ga of Samples 11, 12, 13, 14, 15, 16, 17, 18, and 19 from single crystals ２ O ３ Single crystal substrates were obtained from each of them.

[0079] <Sample 2A> In the preparation step S110, Ga ２ O ３ The beta-type Ga of sample 1A was the same as that of sample 1A except that the crucible 5 forming the 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 % of Rh. ２ O ３ The beta type Ga of sample 2A was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal substrate was obtained. ２ O ３ The single crystal substrate had a diameter of 155 mm and a thickness of 650 μm.

[0080] <Sample 2B> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 2A was the same as that of sample 2A except that the single crystal ingot was heat-treated in a second mixed gas atmosphere in which the oxygen concentration was 60% by volume and the rest of the gas was nitrogen. ２ O ３Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal was obtained, and the beta type Ga ２ O ３ A beta-type GaO single crystal substrate of sample 2B was obtained from the single crystal. The apparatus used for the heat treatment was a heating apparatus assembled by the inventors from known parts. ２ O ３ The heat treatment conditions used to obtain the single crystal substrates are shown in Table 4. Table 4 lists the heat treatment conditions (cyclic annealing conditions) for Samples 21 to 29 and Samples 2A to 2E.

[0081] 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 cyclic annealing. The beta-type Ga alloys of Sample 2B, Samples 2C to 2E, and Samples 21 to 28, which will be described later, are ２ O ３ In the heat treatment conditions used to obtain the single crystal substrate, the temperature increase rate (Δ(T / t)r0) in the pre-heating step was 1.5°C / min, and the temperature decrease rate (Δ(T / t)f0) in the post-heating step was −0.05°C / min.

[0082] <Samples 2C to 2E> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 2B was obtained by heat treatment under the conditions shown in Table 4. ２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal was obtained, and the beta type Ga ２ O ３Beta-type Ga of sample 2C, sample 2D, and sample 2E from single crystals ２ O ３ Single crystal substrates were obtained from each of them.

[0083] <Samples 21 to 29> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 2B was obtained by heat treatment under the conditions shown in Table 4. ２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal was obtained, and the beta type Ga ２ O ３ Beta-type Ga of Samples 21, 22, 23, 24, 25, 26, 27, 28, and 29 from single crystals ２ O ３ Single crystal substrates were obtained from each of them.

[0084] <Sample 3A> In preparation step S110, Ga ２ O ３ The beta-type Ga of sample 1A was the same as that of sample 1A except that the crucible 5 forming the single crystal growth apparatus 1 had an inner diameter of 105 mm, a thickness of 0.5 mm, and was made of a Pt—Rh alloy containing 31 mass % of Rh. ２ O ３ The beta type Ga of sample 3A was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal substrate was obtained. ２ O ３ The single crystal substrate had a diameter of 100 mm and a thickness of 650 μm.

[0085] <Sample 3B> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 3A was the same as that of sample 3A except that the single crystal ingot was heat-treated in a second mixed gas atmosphere in which the oxygen concentration was 60% by volume and the rest of the gas was nitrogen.２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal was obtained, and the beta type Ga ２ O ３ Beta type Ga of sample 3B from single crystal ２ O ３ The apparatus used for the heat treatment was a heating apparatus assembled by the inventors from known components. ２ O ３ The heat treatment conditions used to obtain the single crystal substrates are shown in Table 7. Table 7 lists the heat treatment conditions (cyclic annealing conditions) for Samples 31 to 39 and Samples 3A to 3E.

[0086] 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 cyclic annealing. The beta-type Ga alloys of Sample 3B, Samples 3C to 3E, and Samples 31 to 38, which will be described later, are ２ O ３ In the heat treatment conditions used to obtain the single crystal substrate, the temperature increase rate (Δ(T / t)r0) in the pre-heating step was 2° C. / min, and the temperature decrease rate (Δ(T / t)f0) in the post-heating step was −0.05° C. / min.

[0087] <Samples 3C to 3E> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 3B was obtained by heat treatment of the single crystal ingot under the conditions shown in Table 7. ２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３A single crystal was obtained, and the beta type Ga ２ O ３ Beta-type Ga of sample 3C, sample 3D, and sample 3E from single crystals ２ O ３ Single crystal substrates were obtained from each of them.

[0088] <Samples 31 to 39> Beta-type Ga ２ O ３ The beta type Ga obtained in the single crystal growth step S140 ２ O ３ The beta type Ga of sample 3B was obtained by heat treatment of the single crystal ingot under the conditions shown in Table 7. ２ O ３ Beta-type Ga was prepared in the same manner as the single crystal substrate. ２ O ３ A single crystal was obtained, and the beta type Ga ２ O ３ Beta-type Ga of Samples 31, 32, 33, 34, 35, 36, 37, 38, and 39 from single crystals ２ O ３ Single crystal substrates were obtained from each of them.

[0089] [Evaluation] <Measurement of birefringence phase difference> Beta type Ga ２ O ３ Birefringence retardation measurements were performed on five measurement points on the main surface of a single crystal substrate at various measurement wavelengths according to the measurement method described above. The results are shown in Tables 2, 3, 5, 6, 8, and 9. Specifically, the birefringence retardation values ​​of Samples 11 to 19 and Samples 1A to 1E are shown in Tables 2 and 3. The birefringence retardation values ​​of Samples 21 to 29 and Samples 2A to 2E are shown in Tables 5 and 6. The birefringence retardation values ​​of Samples 31 to 39 and Samples 3A to 3E are shown in Tables 8 and 9.

[0090] <Crack Evaluation> For the beta-type GaO single crystal substrates of Samples 11 to 19, Samples 1A to 1E, Samples 21 to 29, Samples 2A to 2E, Samples 31 to 39, and Samples 3A to 3E, beta-type GaO was cracked from 30 ingots. ２ O ３During the process of obtaining single crystal substrates, cracking of the substrates was evaluated by visually assessing whether the probability of obtaining substrates for each sample without cracking was 90% or higher. The cracking evaluations for Samples 11 to 19 and Samples 1A to 1E are shown in Tables 2 and 3. The cracking evaluations for Samples 21 to 29 and Samples 2A to 2E are shown in Tables 5 and 6. The cracking evaluations for Samples 31 to 39 and Samples 3A to 3E are shown in Tables 8 and 9. In Tables 2, 3, 5, 6, 8, and 9, "NG (Not Good)" indicates that the probability was less than 90%, and "G (Good)" indicates that the probability was 90% or higher.

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[0100] [Discussion] According to Tables 1 to 9, the beta Ga of Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39 ２ O ３ The birefringence retardation of the single crystal substrate at each measurement wavelength was as follows: That is, at all of the five points, when the measurement wavelength was 400 nm, it was 3.3×10 －２ 3.7 x 10 －２ The birefringence retardation was 0.5×10 or less at all of the five points when the measurement wavelength was 500 nm. －２ 3.9 x 10 －２The birefringence retardation was 3.6×10 or less at all of the five points when the measurement wavelength was 600 nm. －２ Above 4.0 x 10 －２ The birefringence retardation was 3.6×10 or less at all of the five points when the measurement wavelength was 700 nm. －２ 4.1 x 10 －２ The birefringence retardation was 3.7×10 or less at all of the five points when the measurement wavelength was 800 nm. －２ 4.1 x 10 －２ In contrast, the beta Ga of Samples 1A to 1E, Samples 2A to 2E, and Samples 3A to 3E was ２ O ３ The birefringence phase difference of the single crystal substrate at each measurement wavelength was sometimes outside the ranges covered by Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39.

[0101] As a result, the beta type Ga of Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39 ２ O ３ The single crystal substrates were the beta type Ga of Samples 1A to 1E, Samples 2A to 2E, and Samples 3A to 3E. ２ O ３ Unlike the single crystal substrate, the crack evaluation was good. Therefore, the beta type Ga of Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39 ２ O ３ The single crystal substrate is made of beta-type Ga ２ O ３ It was suggested that the residual strain in the single crystal was reduced, giving it crack-resistant properties.

[0102] Here, the beta type Ga of Samples 11 to 19, Samples 21 to 29, and Samples 31 to 39 ２ O ３ The single crystal substrate was a beta type Ga single crystal obtained at a position close to the end of the crystal growth of the ingot as described above. ２ O ３ Generally, the beta type Ga single crystal substrate is obtained from a position close to the end of the crystal growth of the ingot.２ O ３ The single crystal substrate is a beta type Ga obtained from another position of the ingot (for example, a position close to the crystal growth start position of the ingot, or a central position of the ingot, etc.). ２ O ３ It is known that the residual strain (stress) inside is larger than that in a single crystal substrate. ２ O ３ In an ingot cut from a single crystal substrate, beta-type Ga is ２ O ３ When a single crystal substrate is cut out, the beta type Ga ２ O ３ It is suggested that even a single crystal substrate can be provided with crack-resistant properties.

[0103] 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.

[0104] 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.

[0105] 100 Beta type Ga ２ O ３ 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 outer periphery, S110 preparation step, S120 raw material accommodation step, S130 raw material melting step, S140 GaO single crystal growth step, S150 ingot annealing step, S200 substrate manufacturing step, 1 Ga ２ O ３ 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 Ga ２ O ３ Single crystal, 82 Ga ２ O３ Melt.

Claims

1. A beta-type digallium trioxide single crystal substrate having a circular main surface, wherein the diameter of the beta-type digallium trioxide single crystal substrate is 100 mm or more, and the main surface is a (001) plane of the beta-type digallium trioxide single crystal, and the main surface has a central portion including its center and an outer periphery surrounding the central portion, and the outer periphery is a chamfered region, and five locations in the central portion represented by the following coordinates are targeted, and birefringence phase difference measurements are performed using visible light at measurement wavelengths of 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm, whereby the birefringence phase difference of the beta-type digallium trioxide single crystal substrate is 3.3 x 10 when the measurement wavelength is 400 nm at all of the five locations: －２ 3.7 x 10 －２ or less, and when the measurement wavelength is 500 nm, it is 3.5 × 10 －２ 3.9 x 10 －２ or less, and when the measurement wavelength is 600 nm, it is 3.6 × 10 －２ Above 4.0 x 10 －２ or less, and when the measurement wavelength is 700 nm, it is 3.6 × 10 －２ 4.1 x 10 －２ or less, and when the measurement wavelength is 800 nm, it is 3.7 × 10 －２ 4.1 x 10 －２ a beta-type digallium trioxide single crystal substrate in which, when r is the length from the center of the main surface to the boundary between the central portion and the outer periphery, when the center is the origin and two axes on the main surface that pass through the center are the X-axis and the Y-axis, when the positive direction of the X-axis is the [010] direction of the beta-type digallium trioxide single crystal and when the positive direction of the Y-axis is the [-100] direction of the beta-type digallium trioxide single crystal, the coordinates (X, Y) of the five locations defined by the X-axis and the Y-axis are expressed as (0, 0), (r-10, 0), (0, r-10), (-(r-10), 0), and (0, -(r-10)), and when the units of r and X and Y in the coordinates (X, Y) are mm.

2. The beta-type gallium trioxide single crystal substrate contains a dopant, the dopant being tin or silicon, and the atomic concentration of the dopant is 1×10 １９ cm －３ 2. The beta-type gallium trioxide single crystal substrate according to claim 1, wherein:

3. The beta-type digallium trioxide single crystal substrate according to claim 1 or 2, wherein the diameter of the beta-type digallium trioxide single crystal substrate is 305 mm or less.

4. A method for producing a beta-type digallium trioxide single crystal used in a beta-type digallium trioxide single crystal substrate according to any one of claims 1 to 3, said method comprising the steps of: preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged so as to surround the outer periphery of said crucible; accommodating a beta-type digallium trioxide seed crystal at the bottom of said crucible and accommodating a massive digallium trioxide bulk body above said seed crystal in said crucible; heating said crucible with said heating device, melting said digallium trioxide bulk body and a portion of said seed crystal to obtain a digallium trioxide melt, and bringing said digallium trioxide melt into contact with the remainder of said seed crystal; the step of 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 by using a vertical boat method, thereby obtaining a beta-type gallium trioxide single crystal; and the step of heat-treating the beta-type gallium trioxide single crystal in a second mixed gas atmosphere having an oxygen concentration of 50% by volume or more, wherein the heat-treating step has the following cyclic annealing conditions, the cyclic annealing conditions being 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, wherein 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, and the temperature-lowering rate in the temperature-lowering step is -1°C or more and -0.05°C or less per minute, a temperature of the beta-type digallium trioxide single crystal maintained in the temperature maintaining step being 1200°C or higher and 1700°C or lower, and a 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 being 50°C or higher and 100°C or lower.

5. The method for producing a beta-type digallium trioxide single crystal according to claim 4, 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.

6. 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 4 or 5 to obtain a beta-type digallium trioxide single crystal substrate having a circular main surface.

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