Beta-type gallium trioxide single crystal substrate, method for producing beta-type gallium trioxide single crystal, and method for producing beta-type gallium trioxide single crystal substrate

Abstract

This beta-type gallium trioxide single crystal substrate has a circular main surface and a diameter of 100 mm or more. The main surface is either the (001) plane of a [beta]-type gallium trioxide single crystal or a plane having an off angle of more than 0 DEG and 10 DEG or less with respect to the (001) plane of the single crystal, the off direction being either the [010] direction of the single crystal or the direction orthogonal to the [010] direction. The ratio of the second density to the first density, i.e., the second density / first density, is greater than 1.0, and the first density is the density of linear voids in a first region having a diameter of 0.75 D centered on the center of the main surface. The second density is the density of the linear voids in a second region, which is a region on the outer side of the first region in the main surface. The second density is 1000 cm <-2 > or less. D represents the diameter of the substrate, and the unit of D is mm. The linear cavity has a length of 10 [mu] m or more and 200 [mu] m or less, a width of 0.01 [mu] m or more and 2 [mu] m or less, and a depth of 0.1 [mu] m or more.

Description

Technical Field

[0001] The present invention relates to a beta-type gallium sesquioxide single crystal substrate, a method for manufacturing the beta-type gallium sesquioxide single crystal, and a method for manufacturing the beta-type gallium sesquioxide single crystal substrate. Background Art

[0002] Japanese Patent Application Publication No. 2016-079080 (Patent Document 1) and Japanese Patent Application Publication No. 2017-193466 (Patent Document 2) disclose methods for producing gallium trioxide single crystals (hereinafter also referred to as "Ga2O3 single crystals") by performing crystal growth using a crucible made of a platinum-rhodium alloy according to the vertical Bridgman method. The following non-patent document 1 discloses that when the density of linear voids is measured at three predetermined locations on the main surface of a gallium trioxide single crystal substrate (hereinafter also referred to as "Ga2O3 single crystal substrate") having a diameter of 2 inches, the density of the linear voids is 3.0×10 3 ~5.0×10 3 cm -2 The following non-patent document 2 discloses that when a Ga2O3 single crystal substrate with a diameter of 2 inches is obtained by crystal growth at a growth rate of 1.1 mm / hour, the density of linear voids on the surface of the substrate is 50 cm -2 The following non-patent document 3 teaches that the number of the linear voids in the Ga2O3 single crystal substrate affects the characteristics of the Schottky barrier diode.

[0003] Prior art literature

[0004] Patent Literature

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

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-193466.

[0007] Non-patent literature

[0008] Non-patent literature 1: Kanikawa et al., Journal of the Japanese Society of Crystal Growth, Vol. 44, No. 4 (2017), 44-4-03;

[0009] Non-patent literature 2: E. Ohba et al., Japanese Journal of Applied Physics, 55, 1202BF (2016);

[0010] Non-patent document 3: O. Ueda et al., Japanese Journal of Applied Physics, 61, 050101 (2022). Summary of the Invention

[0011] The β-type gallium trioxide single crystal substrate of the present invention is a β-type gallium trioxide single crystal substrate having a circular main surface. The diameter of the above-mentioned β-type gallium trioxide single crystal substrate is 100 mm or more. The above-mentioned main surface is the (001) plane of the gallium trioxide single crystal constituting the above-mentioned β-type gallium trioxide single crystal substrate, or a plane having an offset angle greater than 0° and less than 10° relative to the (001) plane of the above-mentioned gallium trioxide single crystal and the offset direction being the

[010] direction of the above-mentioned β-type gallium trioxide single crystal or a direction orthogonal to the above-mentioned

[010] direction. The ratio of the second density to the first density, i.e., the second density / first density, is greater than 1.0. The above-mentioned first density is the density of linear voids in a first region of a circle having a diameter of 0.75D centered on the center of the above-mentioned main surface, and the above-mentioned second density is the density of linear voids in a second region which is an area on the outside of the above-mentioned first region in the above-mentioned main surface. The above-mentioned second density is 1000 cm -2 Below. The above-mentioned D represents the diameter of the above-mentioned β-type gallium trioxide single crystal substrate. The unit of the above-mentioned D is mm. The above-mentioned linear voids have a length of 10 μm or more and 200 μm or less, a width of 0.01 μm or more and 2 μm or less, and a depth of 0.1 μm or more. The density of the linear voids in the above-mentioned first region and the density of the linear voids in the above-mentioned second region are per 1 cm 2 The number of the above linear voids per 1cm 2 The number of the above-mentioned linear voids is obtained by forming an imaginary grid on the above-mentioned main surface in which squares with a side length of 10 mm are arranged in a manner that does not overlap with each other as much as possible, and counting the number of the above-mentioned linear voids existing in each of the above-mentioned squares constituting the above-mentioned grid using a differential interference microscope. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is an explanatory diagram illustrating a main surface of a β-type Ga2O3 single crystal substrate according to this embodiment in a plan view.

[0013] Figure 2 This is to explain how to find the density of linear voids in the main surface. Figure 1 An explanatory diagram of a case where a virtual grid is set up by arranging squares with a side length of 10 mm in a manner that does not overlap with each other as much as possible on the main surface of a β-type Ga2O3 single crystal substrate.

[0014] Figure 3 This is a flowchart showing an example of a method for manufacturing a β-type Ga2O3 single crystal substrate according to this embodiment.

[0015] Figure 4 This is a schematic diagram illustrating a manufacturing apparatus used in the manufacturing method of a β-type Ga2O3 single crystal substrate of this embodiment, particularly in the first manufacturing method.

[0016] Figure 5 This is a schematic diagram illustrating a manufacturing apparatus used in the manufacturing method of a β-type Ga2O3 single crystal substrate of this embodiment, particularly in the second manufacturing method.

[0017] Figure 6 This is a schematic diagram illustrating a manufacturing apparatus used in the manufacturing method of a β-type Ga2O3 single crystal substrate of this embodiment, particularly in the third manufacturing method. DETAILED DESCRIPTION

[0018] [Problems to be Solved by the Invention]

[0019] Conventionally, from the perspective of improving the yield rate (hereinafter also referred to as "device yield rate") of manufacturing semiconductor devices, there has been a demand for β-type Ga2O3 single crystal substrates with a reduced density of linear voids. Furthermore, it is well known that in the above-mentioned β-type Ga2O3 single crystal substrate, when cooling after growing an epitaxial film on the main surface in order to form a semiconductor device, the substrate often cracks or breaks, i.e., so-called crack defects. Therefore, it is also required to reduce the probability of the occurrence of such crack defects (hereinafter also referred to as "crack defect rate") in the above-mentioned β-type Ga2O3 single crystal substrate. However, Patent Documents 1-2 and Non-Patent Documents 1-3 do not mention reducing the above-mentioned crack defect rate. In addition, the knowledge related to the density of linear voids in Non-Patent Documents 1-2 is based on Ga2O3 single crystal substrates with a diameter of 2 inches. Therefore, there has been no β-type Ga2O3 single crystal substrate with a diameter of 4 inches or more that reduces the density of linear voids and the above-mentioned crack defect rate, and its development is urgently desired.

[0020] In view of the above circumstances, an object of the present invention is to provide a β-type gallium trioxide single crystal substrate with reduced crack defect rate, a method for manufacturing a β-type gallium trioxide single crystal, and a method for manufacturing a β-type gallium trioxide single crystal substrate.

[0021] [Effects of the Invention]

[0022] According to the present invention, a β-type gallium sesquioxide single crystal substrate having a reduced crack defect rate, a method for manufacturing a β-type gallium sesquioxide single crystal, and a method for manufacturing a β-type gallium sesquioxide single crystal substrate can be provided.

[0023] [Overview of Embodiments]

[0024] The following is an overview of the embodiments of the present invention. The present inventors have conducted repeated in-depth studies to solve the above-mentioned problems and have thus completed the present invention. First, the present inventors focused on determining the reason why the substrate is prone to cracking when the epitaxial film is grown on the main surface of the β-type Ga2O3 single crystal substrate and then cooled. In particular, the relationship between the thermal contraction occurring in the β-type Ga2O3 single crystal substrate during the above-mentioned cooling and the distribution of linear voids in the β-type Ga2O3 single crystal constituting the above-mentioned substrate was studied. As a result, the present inventors found that when the density of linear voids in the central portion of the main surface of the above-mentioned substrate is smaller than the density of linear voids in the peripheral portion, the above-mentioned central portion further thermally contracts compared with the above-mentioned peripheral portion, thereby generating compressive stress in the above-mentioned peripheral portion, making it less likely to crack. In addition, it is known that crystals with strong cleavage properties such as the above-mentioned β-type Ga2O3 single crystal are generally prone to cracking not due to compressive stress but due to tensile stress. From the above, it can be seen that in a β-type Ga2O3 single crystal substrate in which the density of linear voids in the peripheral portion of the main surface is higher than that in the central portion, the crack defect rate can be reduced, thereby completing the present invention.

[0025] Next, embodiments of the present invention will be listed and described.

[0026] [1] A β-type gallium trioxide single crystal substrate according to one embodiment of the present invention has a circular main surface. The diameter of the β-type gallium trioxide single crystal substrate is 100 mm or more. The main surface is the (001) plane of the gallium trioxide single crystal constituting the β-type gallium trioxide single crystal substrate, or a plane having an offset angle greater than 0° and less than 10° relative to the (001) plane of the gallium trioxide single crystal and the offset direction being the

[010] direction of the β-type gallium trioxide single crystal or a direction orthogonal to the

[010] direction. The ratio of the second density to the first density, i.e., the second density / first density, is greater than 1.0. The first density is the density of linear voids in a first region of a circle having a diameter of 0.75D centered on the center of the main surface, and the second density is the density of linear voids in a second region of the main surface that is further outside the first region. The second density is 1000 cm -2 Below. The above-mentioned D represents the diameter of the above-mentioned β-type gallium trioxide single crystal substrate. The unit of the above-mentioned D is mm. The above-mentioned linear voids have a length of 10 μm or more and 200 μm or less, a width of 0.01 μm or more and 2 μm or less, and a depth of 0.1 μm or more. The density of the linear voids in the above-mentioned first region and the density of the linear voids in the above-mentioned second region are per 1 cm 2 The number of the above linear voids per 1cm 2The number of linear voids is determined by forming a virtual grid of 10 mm squares on the main surface, arranging them in a manner that maximizes the number of non-overlapping squares. The number of linear voids within each of the squares forming the grid is then counted using a differential interference microscope. β-GaO3 single crystal substrates with these characteristics can reduce the crack defect rate.

[0027] [2] The second density is preferably 1 cm -2 Over 100cm -2 As described below, it is possible to provide a β-type gallium trioxide single crystal substrate having improved performance and yield.

[0028] [3] The second density / first density ratio is preferably 2.5 or less. This can provide a β-type gallium trioxide single crystal substrate having a further reduced crack defect rate.

[0029] [4] The β-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 5.0×10 19 cm -3 As described below, the crack defect rate can be reduced in a β-type gallium trioxide single crystal substrate containing a dopant.

[0030] [5] One embodiment of the present invention is a method for producing a β-type gallium trioxide single crystal using a vertical boat method, the method comprising the following steps. Specifically, the method comprises: preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible; placing a seed crystal at the bottom of the crucible and placing a bulk gallium trioxide mass within the crucible above the seed crystal; heating the crucible with the heating device to melt the bulk gallium trioxide mass and a portion of the seed crystal to obtain a gallium trioxide melt, while simultaneously bringing the gallium trioxide melt into contact with the remaining portion of the seed crystal; and growing a crystal from the gallium trioxide melt on the remaining portion of the seed crystal to obtain the β-type gallium trioxide single crystal. The crucible is made of a platinum-rhodium alloy. The step of obtaining the β-type gallium trioxide single crystal includes inserting a stirring rod made of a platinum-rhodium alloy into the gallium trioxide melt and causing the crystal to grow while stirring the gallium trioxide melt with the stirring rod. This manufacturing method with these characteristics can produce a β-type gallium trioxide single crystal for use in manufacturing a β-type gallium trioxide single crystal substrate with a reduced crack defect rate.

[0031] [6] One embodiment of the present invention is a method for producing a β-type gallium trioxide single crystal using a vertical boat method, the method comprising the following steps. Specifically, the method comprises: preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device disposed so as to surround the outer periphery of the crucible; placing a seed crystal at the bottom of the crucible and placing a bulk gallium trioxide mass within the crucible above the seed crystal; heating the crucible with the heating device to melt the bulk gallium trioxide mass and a portion of the seed crystal to obtain a gallium trioxide melt, while simultaneously bringing the gallium trioxide melt into contact with the remaining portion of the seed crystal; and growing a crystal from the gallium trioxide melt on the remaining portion of the seed crystal to obtain the β-type gallium trioxide single crystal. The crucible is made of a platinum-rhodium alloy. The process of obtaining the β-type gallium trioxide single crystal includes inserting a hollow tube made of a platinum-rhodium alloy into the gallium trioxide melt and causing the crystal to grow while blowing an inert gas into the gallium trioxide melt through the hollow tube. This manufacturing method with these characteristics can produce a β-type gallium trioxide single crystal for use in manufacturing a β-type gallium trioxide single crystal substrate with a reduced crack defect rate.

[0032] [7] The step of obtaining the β-type gallium trioxide single crystal preferably includes a step of stirring the gallium trioxide melt using the hollow tube. This allows for obtaining a β-type gallium trioxide single crystal for use in manufacturing a β-type gallium trioxide single crystal substrate having a further reduced crack defect rate.

[0033] [8] In the above-mentioned manufacturing method, the single crystal growth apparatus is preferably housed in a pressure vessel. Furthermore, preferably, after the step of bringing the gallium trioxide melt into contact with the remaining portion of the seed crystal and before the step of obtaining the β-type gallium trioxide single crystal, a step of reducing the pressure in the pressure vessel from one atmosphere and then returning it to the one atmosphere is repeated three or more times. This can produce a β-type gallium trioxide single crystal for manufacturing a β-type gallium trioxide single crystal substrate with a further reduced crack defect rate.

[0034] [9] A method for manufacturing a β-gallium trioxide single crystal substrate according to one embodiment of the present invention includes processing the β-gallium trioxide single crystal obtained by the above-described method for manufacturing a β-gallium trioxide single crystal to obtain a β-gallium trioxide single crystal substrate having a circular main surface. This manufacturing method having these characteristics enables the production of a β-gallium trioxide single crystal substrate having a reduced crack defect rate.

[0035]

[10] In the above-mentioned β-type gallium trioxide single crystal substrate, the above-mentioned second density is preferably 1 cm -2 Over 90cm -2The second density / first density is preferably 1.1 or more and 2 or less. The β-type gallium trioxide single crystal substrate preferably contains a dopant. The dopant is preferably tin. The atomic concentration of the dopant is preferably 5.0×10 19 cm -3 As described below, in a β-type gallium trioxide single crystal substrate containing tin as a dopant, the performance yield can be improved and the crack defect rate can be reduced.

[0036] [Details of the implementation method]

[0037] Hereinafter, an embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described in more detail, but the present invention is not limited thereto. Figure 1 While explaining, the same or corresponding elements in this specification and the drawings are marked with the same reference numerals, and the same description will not be repeated for them. Furthermore, in the drawings, the scales of the components are adjusted appropriately to facilitate understanding, and the scales of the components shown in the drawings may not necessarily match the scales of the actual components.

[0038] In this specification, descriptions in the form of "A to B" mean the upper and lower limits of a range (i.e., greater than or equal to A and less than or equal to B). When no unit is described for A but only for B, the unit for A is the same as the unit for B. Furthermore, in this specification, when compounds are represented by chemical formulas, unless the atomic ratio is particularly limited, all conventionally known atomic ratios are encompassed and are not necessarily limited to the stoichiometric range.

[0039] In this specification, the "main surface" of a β-type gallium trioxide single crystal substrate refers to both of the two circular surfaces in the above-mentioned β-type gallium trioxide single crystal substrate. In the above-mentioned β-type gallium trioxide single crystal substrate, if at least any one of the two surfaces meets the claims of the present invention, it belongs to the technical scope of the present invention. In addition, in this specification, the "surface" used in the term "in-plane" refers to the "main surface". Furthermore, when the diameter of the β-type gallium trioxide single crystal substrate is recorded as "100 mm", it means that the above-mentioned diameter is about 100 mm (about 95 to 105 mm) or 4 inches. When the above-mentioned diameter is recorded as "150 mm", it means that the above-mentioned diameter is about 150 mm (about 145 to 155 mm) or 6 inches. In addition, the above-mentioned diameter can be measured by using a conventionally known outer diameter measuring instrument such as a vernier caliper.

[0040] In this specification, "linear voids" refer to oxygen voids of a specified size formed in a β-type gallium trioxide single crystal when grown using the vertical boat method. The "specified size" of the linear voids refers to a length of 0 μm to 200 μm, a width of 0.01 μm to 2 μm, and a depth of 0.1 μm or more. It is speculated that these "linear voids" are generated by the following process: in the gallium trioxide melt described later, gallium trioxide decomposes into gallium oxide (gas) and oxygen (gas) due to high temperatures. These gases are adsorbed at the solid-liquid interface of gallium trioxide or at the interface between the inner surface of the crucible and the gallium trioxide melt (i.e., the inner surface of the crucible), thereby forming linear voids. This is because when the gallium trioxide melt solidifies, the gases are unable to escape from the gallium trioxide melt and instead form pores that enter the crystal, forming linear voids.

[0041] In this specification, "element yield" refers to the yield obtained by multiplying the processing yield by the performance yield. The processing yield indicates the proportion of various semiconductor devices that can be obtained from a β-type gallium trioxide single crystal substrate without cracks, breakage, etc. during processing. The performance yield indicates the proportion of the semiconductor devices obtained from the substrate that can meet the required specified performance. The "performance yield" in the above-mentioned "element yield" can be evaluated by calculating the leakage current defect rate of the Schottky barrier diode described later. The above-mentioned "leakage current defect rate of the Schottky barrier diode" can be expressed as a percentage. In this specification, the "crack defect rate" can be expressed by the proportion of cracks, breakage, etc. generated in the substrate during a series of processes, from the process of forming a semiconductor layer on the β-type gallium trioxide single crystal substrate by epitaxial growth to the process of manufacturing the semiconductor device. The above-mentioned "crack defect rate" can be expressed as a percentage. The "crack defect rate" is an important factor in determining the "processing yield" within the "device yield" described above, satisfying the relationship: 100% - "crack defect rate" = "processing yield." In this specification, the "device yield" is represented by the device yield index, which is the product of the "crack defect rate" and the "Schottky barrier diode leakage current defect rate." A lower value for the "device yield index" indicates a better device yield.

[0042] In the crystallographic descriptions in this specification, individual orientations are indicated by [], collective orientations by <>, individual planes by (), and collective planes by {}. Furthermore, negative crystallographic indices are typically indicated by adding a "- (bar)" above the number, but in this specification, a minus sign is added before the number.

[0043] [Gallium oxide single crystal substrate]

[0044] The β-gallium oxide single crystal substrate (β-Ga2O3 single crystal substrate) of this embodiment is a β-gallium oxide single crystal substrate having a circular main surface. The diameter of the β-gallium oxide single crystal substrate is 100 mm or greater. The main surface is the (001) plane of the β-gallium oxide single crystal (β-Ga2O3 single crystal) constituting the β-gallium oxide single crystal substrate, or a plane having an off-angle greater than 0° and less than 10° relative to the (001) plane of the β-gallium oxide single crystal, and the off-angle direction is the

[010] direction of the β-gallium oxide single crystal or a direction orthogonal to the

[010] direction. The ratio of the second density to the first density, i.e., the second density / first density, is greater than 1.0. The first density is the density of linear voids in a first region of a circle having a diameter of 0.75D centered on the center of the main surface, and the second density is the density of linear voids in a second region of the main surface located outside the first region. The second density is 1000 cm -2 Below. The above-mentioned D represents the diameter of the above-mentioned β-type Ga2O3 single crystal substrate. The unit of the above-mentioned D is mm. The above-mentioned linear voids have a length of 10 μm or more and 200 μm or less, a width of 0.01 μm or more and 2 μm or less, and a depth of 0.1 μm or more. The density of the linear voids in the above-mentioned first region and the density of the linear voids in the above-mentioned second region are per 1 cm 2 The number of the above linear voids per 1cm 2 The number of linear voids is determined by forming an imaginary grid of 10 mm squares on the main surface, arranging them in a manner that maximizes the number of non-overlapping squares. Using a differential interference microscope, the number of linear voids within each of the squares forming the grid is counted. β-Ga2O3 single crystal substrates with these characteristics can reduce the crack defect rate.

[0045] The present inventors speculate that the reason why the crack defect rate can be reduced in the above-mentioned β-type Ga2O3 single crystal substrate is as follows. In addition, the following speculation is explained based on the premise that the main surface of the β-type Ga2O3 single crystal substrate is a plane with strong cleavage (for example, the (001) plane of the β-type Ga2O3 single crystal constituting the above-mentioned substrate, or a plane with a deviation angle greater than 0° and less than 10° relative to the (001) plane of the above-mentioned single crystal and the deviation direction is the

[010] direction of the above-mentioned single crystal or a direction orthogonal to the above-mentioned

[010] direction). This is because crystals with strong cleavage planes have the characteristic that they are generally prone to cracking when stretched, but the effect of cracking is small even when compressed.

[0046] During the process of fabricating a semiconductor device from the β-Ga2O3 single crystal substrate, an epitaxial film is grown on the main surface and then cooled. During this process, the β-Ga2O3 single crystal substrate, with its entire surface constrained by the epitaxial film, generates different thermal stresses across the surface, reflecting the distribution of the density of linear voids within the β-Ga2O3 single crystal constituting the substrate. Specifically, when the main surface is divided into a first circular region centered on the main surface and a second region, which is an area further outward from the first region, if the density of linear voids in the first region is greater than that in the second region, the second region thermally contracts further than the first region. As a result, tensile stress is generated in the second region, corresponding to the outer periphery of the substrate, and cracks are more likely to form. On the other hand, if the density of linear voids in the first region is less than that in the second region, as in the β-Ga2O3 single crystal substrate of this embodiment, the first region thermally contracts further than the second region. In this case, compressive stress is generated in the second region, so it is estimated that the adverse effect on cracking is minimal. Furthermore, by causing the first region to thermally contract further than the second region, tensile stress is generated in the first region. However, since the first region corresponds to the center of the substrate, the tensile stress in the first region is unlikely to develop into cracks in the substrate. Furthermore, while thermal stress is generated in the substrate during the temperature increase of the epitaxial film grown on the main surface, since the entire main surface is not constrained by the epitaxial film, the likelihood of cracking in the substrate due to this thermal stress during temperature increase is estimated to be low.

[0047] It is speculated from the above that the density of linear voids in the first region is lower than the density of linear voids in the second region in the β-type Ga2O3 single crystal substrate of this embodiment can reduce the crack defect rate. Furthermore, the β-type Ga2O3 single crystal substrate of this embodiment, as described above, represents the density of linear voids in the second region, and the second density is 1000 cm -2 Therefore, it can be evaluated below that the density of the linear voids in the entire surface of the substrate is also low.

[0048] <Diameter>

[0049] The diameter of the above-mentioned β-type Ga2O3 single crystal substrate is greater than 100 mm. In particular, the diameter of the above-mentioned β-type Ga2O3 single crystal substrate is preferably greater than 100 mm and less than 152.4 mm. Specifically, the diameter of the β-type Ga2O3 single crystal substrate with a diameter of greater than 100 mm and less than 152.4 mm is preferably 100 mm or 152.4 mm in diameter. In other words, the diameter is preferably 4 inches or 6 inches. Thus, in a large-diameter β-type Ga2O3 single crystal substrate with a diameter of greater than 100 mm and less than 152.4 mm, the crack defect rate can be reduced. Here, for the diameter of the β-type Ga2O3 single crystal substrate, even if the above-mentioned main surface is not a geometrically circular shape due to the influence of the orientation flat (hereinafter also referred to as "OF"), the index flat (hereinafter also referred to as "IF"), etc., it can be obtained based on the circular shape before the above-mentioned OF, IF, etc. are formed. As described above, the diameter of the β-type Ga2O3 single crystal substrate can be measured using a conventionally known outer diameter measuring device such as a vernier caliper. In addition, in this specification, the definition of "circular shape" representing the shape of the main surface is described below.

[0050] <Main surface>

[0051] (Circular shape)

[0052] The β-Ga2O3 single crystal substrate of the present embodiment has a circular main surface as described above. In this specification, the "circular shape" representing the shape of the main surface includes, in addition to a geometric circular shape, a shape in which the main surface does not form a geometric circular shape by forming at least one of a notch, OF, or IF on the periphery of the above-mentioned main surface. Here, "the shape in which the main surface does not form a geometric circular shape" refers to a shape in which, among the line segments extending from an arbitrary point on the periphery of the main surface to the center of the above-mentioned main surface, the length of the line segment extending from an arbitrary point on the above-mentioned notch, OF, and IF to the center of the main surface becomes shorter. Furthermore, "the shape in which the main surface does not form a geometric circular shape" also includes a shape in which the total lengths of the line segments extending from an arbitrary point on the periphery of the main surface to the center of the above-mentioned main surface are not necessarily the same due to the shape of the β-Ga2O3 single crystal as the raw material of the β-Ga2O3 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 β-type Ga2O3 single crystal substrate refers to the length of the longest line segment among the line segments starting from any point on the periphery of the β-type Ga2O3 single crystal substrate, passing through the center of the above-mentioned main surface and extending to other points on the above-mentioned periphery.

[0053] ((001) plane of β-type Ga2O3 single crystal)

[0054] The above-mentioned main surface is the (001) plane of the β-type Ga2O3 single crystal constituting the β-type Ga2O3 single crystal substrate, or a plane having an offset angle greater than 0° and less than 10° relative to the (001) plane of the above-mentioned β-type Ga2O3 single crystal and the deviation direction being the

[010] direction of the above-mentioned β-type Ga2O3 single crystal or a direction perpendicular to the above-mentioned

[010] direction. It is known that the (001) plane of the above-mentioned β-type Ga2O3 single crystal is a strong cleavage plane second only to the (100) plane, and has the characteristic of being easily cracked when stretched as described above. However, in the above-mentioned β-type Ga2O3 single crystal substrate, when cooling after the growth of the epitaxial film that is prone to cracking in the process of manufacturing semiconductor devices, compressive stress is generated in the above-mentioned second region corresponding to the outer periphery of the above-mentioned substrate, and no tensile stress is generated. Therefore, the above-mentioned β-type Ga2O3 single crystal substrate is not easy to crack, thereby being able to reduce the crack defect rate.

[0055] Here, in this specification, the crystal plane of the above-mentioned main surface has an accuracy error of ±0.5°. For example, the case where the above-mentioned main surface is the "(001) plane" of the β-type Ga2O3 single crystal means that the above-mentioned main surface may be a (001) just plane, or may be a plane with an offset angle of -0.5 to +0.5° relative to the above-mentioned main surface (001) plane. The offset angle and deviation direction relative to the (001) plane in the main surface of the β-type Ga2O3 single crystal substrate can be measured using a conventionally known crystal orientation measuring device (for example, the trade name (model): "FSASIII", manufactured by Rigaku Corporation).

[0056] (Linear void)

[0057] As described above, in the β-type Ga2O3 single crystal substrate, the ratio of the second density to the first density, i.e., the second density / first density, is greater than 1.0. The first density is the density of linear voids in a first region of a circle having a diameter of 0.75D centered on the center of the main surface, and the second density is the density of linear voids in a second region of the main surface located outside the first region. The second density is 1000 cm -2 Below. The above-mentioned D represents the diameter of the above-mentioned β-type Ga2O3 single crystal substrate. The unit of the above-mentioned D is mm. The above-mentioned linear voids have a length of 10 μm or more and 200 μm or less, a width of 0.01 μm or more and 2 μm or less, and a depth of 0.1 μm or more. The density of the linear voids in the above-mentioned first region and the density of the linear voids in the above-mentioned second region are per 1 cm 2 The number of the above linear voids per 1cm 2The number of the above-mentioned linear voids is obtained by forming an imaginary grid on the above-mentioned main surface in which squares with a side length of 10 mm are arranged in a manner that does not overlap with each other as much as possible, and counting the number of the above-mentioned linear voids existing in each of the above-mentioned squares constituting the above-mentioned grid using a differential interference microscope.

[0058] As described above, the linear voids have a length of 10 μm to 200 μm, a width of 0.01 μm to 2 μm, and a depth of 0.1 μm or greater. These linear voids are oxygen vacancies formed in the β-Ga2O3 single crystal during the growth process as described above. When these linear voids have the aforementioned dimensions, they can become a structural feature of the β-Ga2O3 single crystal substrate, impacting both the "performance yield" and "processing yield" that constitute the aforementioned device yield. When these linear voids have a length of less than 10 μm, a width of less than 0.01 μm, or a depth of less than 0.1 μm, they may have no or substantially no impact on the "performance yield" and "processing yield" that constitute the aforementioned device yield. On the other hand, in the β-Ga2O3 single crystal substrate, it is difficult to imagine these linear voids having a length greater than 200 μm or a width greater than 2 μm. This is because linear voids of this size can be visually detected during the manufacturing process of a β-Ga2O3 single crystal using a specified manufacturing method, and therefore are generally not selected as a material for manufacturing a β-Ga2O3 single crystal substrate. The upper limit of the depth of the linear voids is not particularly limited and can be, for example, 100 μm.

[0059] 1) First area and second area

[0060] Figure 1 This is an explanatory diagram illustrating the main surface of the β-type Ga2O3 single crystal substrate of this embodiment in the form of a top view. Figure 1As shown, in a β-Ga2O3 single crystal substrate 1, the main surface 10 can be divided into a first region 11 including its center and a second region 12 surrounding the first region 11. Specifically, the first region 11 is circular, centered on the center of the main surface 10 and having a diameter of 0.75D as described above. The second region 12 is a region of the main surface 10 located further outward than the first region 11. D represents the diameter of the β-Ga2O3 single crystal substrate 1. The unit of D is mm. Therefore, if the diameter of the β-Ga2O3 single crystal substrate 1 is 100 mm, the first region 11 is a circular region centered on the center of the main surface 10 and having a diameter of 75 mm. Specifically, the second region 12 is an annular region surrounding the outer periphery of the first region 11 with a width of 25 mm. If the diameter of the β-Ga2O3 single crystal substrate 1 is 150 mm, the first region 11 is a circular region centered on the center of the main surface 10 and having a diameter of 112.5 mm. In this case, the second region 12 is an annular region surrounding the outer periphery of the first region 11 with a width of 37.5 mm. Figure 1 In the embodiment, the positioning edge OF of the β-type Ga2O3 single crystal substrate 1 is set in a direction parallel to the

[010] direction of the β-type Ga2O3 single crystal. Figure 1 In the figure, for the convenience of description, the boundary 13 between the first area 11 and the second area 12 is indicated by a dotted line.

[0061] 2) First Density and Second Density

[0062] The first density is the density of the linear voids 1a in the first region 11. The second density is the density of the linear voids 1a in the second region 12. In the β-type Ga2O3 single crystal substrate 1, the ratio of the second density to the first density, i.e., the second density / first density, is greater than 1.0. In addition, the second density is 1000 cm -2 Therefore, the first density is less than 1000cm -2 In addition, the method of measuring the number and density of linear voids 1a will be described below.

[0063] The above-mentioned second density / first density is preferably less than 2.5. The above-mentioned second density / first density is more preferably greater than 1.1 and less than 2.0. Thus, a β-type Ga2O3 single crystal substrate with a further reduced crack defect rate can be provided. In addition, the above-mentioned second density is preferably 1 cm -2 Over 100cm -2 The second density is more preferably 1 cm -2 Over 90cm -2 As a result, a β-type Ga2O3 single crystal substrate with a further reduced crack defect rate can be provided. The first density is preferably 0.1 cm -2Over and less than 90cm -2 .

[0064] 3) Method for measuring the density of linear voids

[0065] Hereinafter, a measurement method for obtaining the density of the linear voids 1 a will be outlined. Figure 2 This is to explain how to find the density of linear voids in the main surface. Figure 1 This is an illustration of a situation where an imaginary grid is set up by arranging squares with a side length of 10 mm in a manner that does not overlap with each other on the main surface of a β-type Ga2O3 single crystal substrate. Figure 2 As shown, the imaginary grid G ​​is set by arranging the lines DL that divide the grid into the main surface 10 so that the lines DL do not overlap with each other and fill the squares with a side length of 10 mm. The density of the linear voids 1a in the first area 11 and the density of the linear voids 1a in the second area 12 are obtained by counting the number of linear voids 1a existing in each of the squares constituting the grid G ​​using a differential interference microscope. 2 The above-mentioned measurement method can be performed using, for example, a differential interference microscope (trade name (model): "LV-150", manufactured by Nikon Corporation). Figure 2 In the figure, for the convenience of description, the boundary 13 between the first area 11 and the second area 12 is indicated by a dotted line.

[0066] The method for determining the density of the linear voids 1a is as follows. First, for example, a β-type Ga2O3 single crystal substrate 1 is obtained according to the manufacturing method described below. Figure 2 As shown, a grid G ​​is set for the main surface 10 of the β-Ga2O3 single crystal substrate 1 using lines DL that divide the main surface 10 into a grid. This grid G ​​is formed by paving the main surface 10 with squares with a side length of 10 mm in a manner that maximizes the number of squares arranged without overlapping each other. Furthermore, by observing each of the squares constituting the grid G ​​using the differential interference microscope, the number of linear voids 1a appearing in one field of view of the differential interference microscope is counted. In this case, observation using the differential interference microscope is performed at a magnification of 10x. Thus, one field of view of the differential interference microscope is 10 mm x 10 mm, corresponding to the size of the squares. Therefore, the number of linear voids 1a per field of view is calculated as the density of linear voids 1a per square constituting the hypothetical grid G. As linear voids 1a, only those confirmed to have the aforementioned length, width, and depth are counted. Furthermore, the depth of the linear voids 1a can be calculated by shifting the focus position of the differential interference microscope in the depth direction.

[0067] Finally, the number of linear voids 1a obtained by counting each square constituting the imaginary grid G ​​is converted into 2 . Thus, the density of the linear voids 1a of each of the above-mentioned squares constituting the lattice G set in the first region 11 and the density of the linear voids 1a of each of the above-mentioned squares constituting the lattice G set in the second region 12 are calculated respectively. Next, the first density is obtained by dividing the sum of the densities of the linear voids 1a in the first region 11 by the number of the above-mentioned squares constituting the lattice G set in the first region 11. Similarly, the second density is obtained by dividing the sum of the densities of the linear voids 1a in the second region 12 by the number of the above-mentioned squares constituting the lattice G set in the second region 12. In this specification, "the squares are filled up on the main surface in a manner that does not overlap with each other as much as possible" means that when the main surface 10 is filled up with the above-mentioned squares in a manner that does not overlap with each other, when the outside of the main surface 10 is included in the above-mentioned square, the square is excluded from the elements constituting the imaginary lattice G. This is to obtain the above-mentioned second density as a more appropriate and proper value. Furthermore, when the square includes both the first region 11 and the second region 12 of the main surface 10, the linear voids 1a counted in the square are regarded as the linear voids 1a in the second region 12. This is to appropriately evaluate the relationship between the ratio of the second density to the first density (second density / first density) in the β-type Ga2O3 single crystal substrate 1 and the crack defect rate.

[0068] <Dopant>

[0069] The β-type Ga2O3 single crystal substrate of this embodiment preferably contains a dopant. The dopant is preferably tin (Sn) or silicon (Si). The atomic concentration of the dopant is preferably 5.0×10 19 cm -3 As a result, the above-mentioned β-type Ga2O3 single crystal substrate can be given the characteristics of n-type (electron-donating type) as a conductive type, and the crack defect rate can be reduced in the β-type Ga2O3 single crystal substrate containing a dopant.

[0070] The atomic concentrations of Sn or Si in the above-mentioned β-type Ga2O3 single crystal substrate are measured by using Glow Discharge Mass Spectrometry (GDMS). In the case of obtaining a β-type Ga2O3 single crystal substrate by a β-type Ga2O3 single crystal obtained by a manufacturing method of a β-type Ga2O3 single crystal as described later, the above-mentioned β-type Ga2O3 single crystal substrate containing a dopant can be obtained by adding a predetermined amount of a gallium sesquioxide bulk (hereinafter also referred to as a "Ga2O3 bulk") as a raw material into a crucible. The above-mentioned dopant is more preferably Sn. The atomic concentration of the above-mentioned dopant is more preferably 5.0×1017 cm -3 Above and 4.0×10 19 cm -3 the following.

[0071] [Method for producing β-type gallium trioxide single crystal]

[0072] The method for producing a β-type gallium trioxide single crystal (β-type Ga2O3 single crystal) according to this embodiment is preferably a method for producing a β-type Ga2O3 single crystal, such as a β-type Ga2O3 single crystal substrate having a circular main surface. The method for producing a β-type Ga2O3 single crystal is a method for producing a Ga2O3 single crystal using a vertical wafer boat method and can include the following steps. Specifically, the manufacturing method includes the steps of: preparing a single crystal growth apparatus (hereinafter also referred to as a "Ga2O3 single crystal growth apparatus") having at least a cylindrical crucible and a heating device disposed so as to surround the outer circumference of the crucible; placing a seed crystal at the bottom of the crucible and placing a bulk gallium trioxide (Ga2O3 bulk) within the crucible above the seed crystal; heating the crucible with the heating device to melt the Ga2O3 bulk and a portion of the seed crystal to obtain a gallium trioxide melt (Ga2O3 melt), while simultaneously bringing the Ga2O3 melt into contact with the remaining portion of the seed crystal; and growing a crystal from the Ga2O3 melt on the remaining portion of the seed crystal to obtain the β-type Ga2O3 single crystal. The crucible is made of a platinum-rhodium alloy.

[0073] In particular, in the first method described below, which is one embodiment of the method for producing a β-Ga2O3 single crystal, the step of obtaining the β-Ga2O3 single crystal includes inserting a stirring rod made of a platinum-rhodium alloy into the Ga2O3 melt and causing the crystal to grow while stirring the Ga2O3 melt with the stirring rod. In the second method described below, which is another embodiment of the method for producing a β-Ga2O3 single crystal, the step of obtaining the β-Ga2O3 single crystal includes inserting a hollow tube made of a platinum-rhodium alloy into the Ga2O3 melt and causing the crystal to grow while blowing an inert gas into the Ga2O3 melt through the hollow tube. Furthermore, the third method described below, which is yet another embodiment of the method for producing a β-Ga2O3 single crystal, includes combining the following features with the single crystal growth apparatus and the like, and implementing the first or second method. Specifically, in the third method, the single crystal growth apparatus is housed in a pressure vessel. Furthermore, after the step of bringing the Ga2O3 melt into contact with the remaining portion of the seed crystal and before the step of obtaining the β-Ga2O3 single crystal, the step of reducing the pressure in the pressure vessel from one atmosphere and then returning it to the one atmosphere is repeated three or more times. The method for producing a β-Ga2O3 single crystal having such characteristics can produce a β-Ga2O3 single crystal that can be used to form a β-Ga2O3 single crystal substrate with a reduced crack defect rate.

[0074] Figure 3 This is a flow chart showing an example of a method for manufacturing a β-type Ga2O3 single crystal substrate according to this embodiment. The method for manufacturing a β-type Ga2O3 single crystal according to this embodiment is preferably, for example, Figure 3 The β-type Ga2O3 single crystal manufacturing step S100 shown in the flowchart is included in the above-mentioned β-type Ga2O3 single crystal substrate manufacturing method. Figure 3The manufacturing method of the β-type Ga2O3 single crystal substrate of the present embodiment includes a β-type Ga2O3 single crystal manufacturing step S100 and a β-type Ga2O3 single crystal substrate manufacturing step S200. The β-type Ga2O3 single crystal manufacturing step S100 includes: a step of preparing a Ga2O3 single crystal growth device having at least a cylindrical crucible and a heating device arranged so as to surround the outer circumference of the crucible (first step: preparation step S110). In the preparation step S110, in addition to preparing the Ga2O3 single crystal growth device, it is preferred to prepare a seed crystal, a massive Ga2O3 block, and solid boron oxide (B2O3). The β-type Ga2O3 single crystal manufacturing step S100 includes: a step of accommodating the seed crystal at the bottom of the crucible and accommodating the Ga2O3 block at a position above the seed crystal in the crucible (second step: raw material loading step S120). In the raw material charging step S120, it is preferred that after the Ga2O3 block is placed in the crucible at a position higher than the seed crystal, solid B2O3 is placed on the Ga2O3 block. The β-Ga2O3 single crystal manufacturing step S100 includes: heating the crucible with the heating device to melt the Ga2O3 block and a portion of the seed crystal to obtain a Ga2O3 melt, and simultaneously bringing the Ga2O3 melt into contact with the remaining portion of the seed crystal (third step: raw material melting step S130). The raw material melting step S130 preferably includes a step of making the B2O3 liquid. Furthermore, the β-Ga2O3 single crystal manufacturing step S100 includes: growing a crystal from the Ga2O3 melt on the remaining portion of the seed crystal to obtain a β-Ga2O3 single crystal (fourth step: Ga2O3 single crystal growth step S140).

[0075] The present inventors have focused on controlling the density distribution of linear voids in a β-Ga2O3 single crystal, which forms a β-Ga2O3 single crystal substrate, when growing the single crystal using a vertical boat method. In particular, they have devised a method of inserting a stirring rod made of a platinum-rhodium alloy into the Ga2O3 melt in the crucible during the process of obtaining the β-Ga2O3 single crystal, and stirring the Ga2O3 melt with the stirring rod. Alternatively, they have devised a method of inserting a hollow tube made of a platinum-rhodium alloy into the Ga2O3 melt in the crucible, and blowing an inert gas into the Ga2O3 melt through the hollow tube. They have discovered that when a β-Ga2O3 single crystal is produced by the above method, and a β-Ga2O3 single crystal substrate is produced from the β-Ga2O3 single crystal, the density of linear voids in the central portion of the main surface of the substrate is lower than the density of linear voids in the peripheral portion. In this case, when the epitaxial film is grown on the main surface of the β-type Ga2O3 single crystal substrate and then cooled as described above, the substrate is less likely to crack. Thus, the present inventors have achieved a method for manufacturing a β-type Ga2O3 single crystal substrate that can form a β-type Ga2O3 single crystal substrate with a reduced crack defect rate.

[0076] Below, refer to Figures 3 to 6 The outline of the above-mentioned Ga2O3 single crystal growth apparatus and the β-type Ga2O3 single crystal manufacturing process S100 will be described separately. Figure 4 This is a schematic diagram illustrating a manufacturing apparatus used in the manufacturing method of a β-type Ga2O3 single crystal substrate of this embodiment, particularly in the first manufacturing method. Figure 5 This is a schematic diagram illustrating a manufacturing apparatus used in the manufacturing method of a β-type Ga2O3 single crystal substrate of this embodiment, particularly in the second manufacturing method. Figure 6 This is a schematic diagram illustrating a manufacturing apparatus used in the manufacturing method of a β-type Ga2O3 single crystal substrate of this embodiment, particularly in the third manufacturing method. In the manufacturing method of a β-type Ga2O3 single crystal of this embodiment (β-type Ga2O3 single crystal manufacturing step S100), in order to correspond to the first manufacturing method, the second manufacturing method, and the third manufacturing method described later, it is preferable to prepare Figures 4 to 6 The Ga2O3 single crystal growth apparatus 100 shown in FIG. The Ga2O3 single crystal growth apparatus 100 can grow Ga2O3 single crystals by a vertical boat method using a crucible 5. Hereinafter, the vertical boat method is referred to as the VB method. The VB method includes the vertical Bridgman method and the vertical temperature gradient solidification method.

[0077] Ga2O3 single crystal growth equipment

[0078] like Figure 4As shown, the Ga2O3 single crystal growth apparatus 100 includes the above-mentioned crucible 5, a crucible holding table 6 for holding the crucible 5, and a heating device 7 for heating the crucible 5. The Ga2O3 single crystal growth apparatus 100 includes a stirring rod 3 made of a platinum-rhodium alloy used in the Ga2O3 single crystal growth step S140. Figure 4 The Ga2O3 single crystal growth apparatus 100 shown is used for the first production method described later. Figure 5 As shown, the Ga2O3 single crystal growth apparatus 100 sometimes has a hollow tube 4 made of a platinum-rhodium alloy instead of the above-mentioned stirring rod. Figure 5 The Ga2O3 single crystal growth apparatus 100 shown is used in the second production method described later.

[0079] Furthermore, if Figure 6 As shown, the Ga 2 O 3 single crystal growth apparatus 100 may include a pressure vessel 9 for housing the Ga 2 O 3 single crystal growth apparatus 100 itself. Figure 6 The Ga2O3 single crystal growth device 100 shown is used in the third method described later. Here, the size and material of the pressure container 9 are not particularly limited as long as they can accommodate the Ga2O3 single crystal growth device 100 and have the function of changing the internal pressure. Figure 6 The Ga2O3 single crystal growth apparatus 100 shown has the hollow tube 4, but it can be replaced with a stirring rod.

[0080] (Crucible)

[0081] like Figures 4 to 6 As shown, in the Ga2O3 single crystal growth device 100, the crucible 5 includes a cylindrical seed crystal receiving portion 51, an expanded diameter portion 52 connected to the seed crystal receiving portion 51, and a straight body portion 53 connected to the expanded diameter portion 52. The seed crystal receiving portion 51 is cylindrical and has a hollow portion with an opening on the side connected to the expanded diameter portion 52 and a bottom wall formed on the side opposite to the expanded diameter portion 52. The seed crystal receiving portion 51 is capable of receiving and retaining the seed crystal 8a in the above-mentioned hollow portion. The expanded diameter portion 5 has a truncated cone shape that expands upward along the axial direction of the crucible 5 and is connected to the seed crystal receiving portion 51 on the small diameter side of the expanded diameter portion 52. The straight body portion 53 has a hollow cylindrical shape and is connected to the large diameter side of the expanded diameter portion 52. The expanded diameter portion 52 and the straight body portion 53 have the function of retaining a bulk Ga2O3 mass (specifically, polycrystalline Ga2O3) therein. The enlarged diameter portion 52 and the straight body portion 53 have a function of solidifying a Ga 2 O 3 melt 82 and growing a Ga 2 O 3 single crystal 81 as a crystal, as will be described later.

[0082] Crucible 5 is made of a platinum-rhodium alloy (hereinafter also referred to as a "Pt-Rh alloy"). In particular, crucible 5 is preferably made of a Pt-Rh alloy containing 35% by mass or more of rhodium (Rh). Crucible 5 may also be made of a Pt-Rh alloy containing 35% by mass of Rh. The inner diameter of the straight body portion 53 depends on the diameter of the desired β-Ga2O3 single crystal 81 and is, for example, not less than 90 mm and not more than 165 mm.

[0083] (Crucible holding table)

[0084] The Ga2O3 single crystal growth apparatus 100 includes a crucible holding table 6 for holding the crucible 5. The crucible holding table 6 is in contact with the bottom of the crucible 5 to hold the crucible 5. The crucible holding table 6 may have a cylindrical appearance. The material of the crucible holding table 6 is not particularly limited, and examples thereof include quartz, alumina, zirconia, and silicon carbide. The outer diameter of the crucible holding table 6 depends on the diameter of the supported crucible 5 and is, for example, not less than 75 mm and not more than 200 mm.

[0085] (Heating device)

[0086] The heating device 7 is provided for the purpose of heating the crucible 5. The heating device 7 can be, for example, an electric heater known in the art (hereinafter also referred to as a "heater"). There are, for example, two heaters, which are arranged so as to surround the outer circumference of the crucible 5. Sometimes the output power of each heater can be controlled independently. In particular, each heater is sometimes constructed in multiple sections by being divided into multiple parts in a direction perpendicular to the axial direction of the crucible 5. In this case, it is preferred to independently control the output power of the heater for each part constituting the multiple sections. In this way, the temperature of the contents in the crucible 5 can be finely adjusted along the axial direction of the crucible 5. For example, by independently controlling the output of the heater for each part constituting the multiple sections to heat the expanded diameter portion 52 and the straight body portion 53, the growth rates of the crystals grown in the expanded diameter portion 52 and the straight body portion 53 can be stabilized, respectively.

[0087] Although not shown, the Ga2O3 single crystal growth apparatus 100 can include a thermocouple capable of measuring the temperature of the crucible 5 heated by the heater. Multiple thermocouples may be arranged axially outside the crucible 5. The thermocouple can be, for example, a known temperature monitor.

[0088] (Stirring stick)

[0089] Figure 4The Ga2O3 single crystal growth device 100 shown has a stirring rod 3. The shape of the stirring rod 3 is sometimes a rod with a circular cross-section or a rectangular cross-section. The stirring rod 3 is composed of a Pt-Rh alloy. It is particularly preferred that the stirring rod 3 is composed of a Pt-Rh alloy containing 35% by mass or more of Rh. The stirring rod 3 is sometimes composed of a Pt-Rh alloy containing 35% by mass of Rh. The size of the stirring rod 3 depends on the size of the crucible 5, for example, it has a length of 300 mm to 1000 mm and a width of 3 mm to 10 mm. The stirring rod 3 is used to stir the Ga2O3 melt 82 in the crucible 5 in the Ga2O3 single crystal growth step S140.

[0090] (Hollow Tube)

[0091] Figure 5 The Ga2O3 single crystal growth device 100 shown has a hollow tube 4. The shape of the hollow tube 4 is sometimes cylindrical with a hollow portion in the longitudinal direction, that is, a cylindrical shape with a ring-shaped cross section. The hollow tube 4 is composed of a Pt-Rh alloy. It is particularly preferred that the hollow tube 4 is composed of a Pt-Rh alloy containing 35% by mass or more of Rh. The hollow tube 4 is sometimes composed of a Pt-Rh alloy containing 35% by mass of Rh. The size of the hollow tube 4 depends on the size of the crucible 5, for example, it has a length of more than 300 mm and less than 1000 mm and an inner diameter of more than 1 mm and less than 10 mm. The hollow tube 4 is used to blow inert gases such as nitrogen and argon into the Ga2O3 melt 82 in the crucible 5 in the Ga2O3 single crystal growth step S140.

[0092] Below, while referring to Figure 3 Flowchart and Figure 4 The Ga2O3 single crystal growth apparatus 100 shown in FIG. 1 is first described as an example of a first method of manufacturing a Ga2O3 single crystal according to the present embodiment. As described above, the manufacturing method of a β-type Ga2O3 single crystal according to the present embodiment is sometimes included as a β-type Ga2O3 single crystal manufacturing step S100. Figure 3 In the manufacturing method of the β-type Ga2O3 single crystal substrate shown as a flow chart.

[0093] <β-Ga2O3 Single Crystal Manufacturing Step S100>

[0094] (First Method)

[0095] 1) First step: preparation step S110

[0096] like Figure 3As shown, first, in the β-Ga2O3 single crystal manufacturing process S100, a process of preparing a Ga2O3 single crystal growth device having at least a cylindrical crucible and a heating device configured to surround the outer circumference of the above-mentioned crucible is implemented (preparation process S110). In the preparation process S110, in addition to preparing the above-mentioned Ga2O3 single crystal growth device 100 for manufacturing the β-Ga2O3 single crystal 81, it is preferred to also prepare a seed crystal 8a, a massive Ga2O3 block and a solid B2O3. The seed crystal 8a is composed of a β-Ga2O3 single crystal. The Ga2O3 block is sometimes composed of polycrystalline Ga2O3. The seed crystal 8a, the massive Ga2O3 block and the solid B2O3 can be prepared by a conventionally known method or by purchasing commercially available products.

[0097] 2) Second process: Raw material loading process S120

[0098] The raw material loading step S120 is a step of storing the seed crystal at the bottom of the crucible and storing a massive Ga2O3 block at a position above the seed crystal in the crucible. In the raw material loading step S120, solid B2O3 is preferably stored together with the massive Ga2O3 block at a position above the seed crystal 8a in the crucible 5. The purpose of the raw material loading step S120 is to seal the various raw materials used for crystal growth using the Ga2O3 single crystal growth device 100 into the crucible. In the raw material loading step S120, first, a seed crystal 8a composed of a β-type Ga2O3 single crystal is loaded into the hollow portion of the seed crystal storage portion 51 of the crucible 5. Then, a plurality of massive Ga2O3 blocks composed of polycrystalline Ga2O3 are loaded into the expanded diameter portion 52 and the straight body portion 53 of the crucible 5 and stacked. Then, solid B2O3 is arranged on the Ga2O3 block. In the raw material charging step S120, when a plurality of bulk Ga2O3 blocks are charged into the crucible 5, a predetermined amount of Sn or Si is preferably added. Thus, the β-Ga2O3 single crystal 81 obtained in the β-Ga2O3 single crystal production step S100 can be used to obtain a β-Ga2O3 single crystal substrate containing the above-mentioned Sn or Si as a dopant. When the above-mentioned Sn or Si is added, it is preferred that the concentration of the above-mentioned dopant in the Ga2O3 single crystal substrate be 5.0×10 19 cm -3 Below (e.g. 5.0×10 17 cm -3 Above and 4.0×10 19 cm -3 The addition amount is adjusted in the following manner.

[0099] 3) The third step: raw material melting step S130

[0100] The raw material melting step S130 is a step in which the crucible is heated using the heating device to melt the Ga2O3 bulk and a portion of the seed crystal, thereby obtaining a Ga2O3 melt, and simultaneously bringing the Ga2O3 melt into contact with the remaining portion of the seed crystal. The purpose of the raw material melting step S130 is to melt the Ga2O3 bulk and a portion of the seed crystal 8a during crystal growth using the Ga2O3 single crystal growth apparatus 100, thereby bringing the remaining portion of the seed crystal 8a into contact with the Ga2O3 melt 82. This enables the growth of a β-type Ga2O3 single crystal 81 on the remaining portion of the seed crystal 8a in the subsequent Ga2O3 single crystal growth step S140. Specifically, in the raw material melting step S130, the crucible 5 containing the seed crystal 8a, the Ga2O3 bulk, and solid B2O3 is supported on the crucible holding table 6. Then, current is supplied to the heating device 7 to heat the crucible 5. As a result, the solid B2O3 melts to become liquid B2O3 and functions as a liquid sealing material, and the Ga2O3 bulk melts to become Ga2O3 melt 82. Then, part of the seed crystal 8a also melts, and the remaining part of the seed crystal 8a contacts the Ga2O3 melt 82 at the interface.

[0101] 4) Fourth step: Ga2O3 single crystal growth step S140

[0102] The Ga2O3 single crystal growth step S140 is a step of growing a crystal from the Ga2O3 melt on the remaining portion of the seed crystal, thereby obtaining a Ga2O3 single crystal. In the Ga2O3 single crystal growth step S140, for example, by gradually lowering the crucible 5 axially relative to the heating device 7 (toward the seed crystal receiving portion 51), a temperature gradient can be formed in the crucible 5, with the temperature being lower on the seed crystal 8a side and higher on the Ga2O3 melt 82 side. This allows the Ga2O3 melt 82 in contact with the seed crystal 8a to solidify, allowing a β-type Ga2O3 single crystal 81 to continuously grow from the Ga2O3 melt 82 on the remaining portion of the seed crystal 8a. At this time, the temperature on the Ga2O3 melt 82 side is, for example, 1800-1820°C. The temperature gradient at the interface between the Ga2O3 melt 82 and the growing β-type Ga2O3 single crystal 81 is, for example, 3-8°C / cm. The speed at which the crucible 5 is lowered along its axis is not particularly limited, and can be, for example, 0.1 to 2 mm / hour.

[0103] Furthermore, the Ga2O3 single crystal growth step S140 includes a step of inserting a stirring rod made of a platinum-rhodium alloy into the Ga2O3 melt and stirring the Ga2O3 melt with the stirring rod while causing the crystal to grow (hereinafter referred to as the "stirring step"). In this stirring step, a stirring rod 3 made of a Pt-Rh alloy is first placed in the crucible 5 with its tip inserted into the Ga2O3 melt 82 within the crucible 5. Specifically, the stirring rod 3 is placed in the crucible 5 with its tip inserted into the Ga2O3 melt 82 at a position approximately 10 to 20 mm above the interface between the Ga2O3 melt 82 and the growing β-Ga2O3 single crystal 81 within the crucible 5 and near the radial center of the crucible 5. Next, the Ga2O3 melt 82 is stirred by rotating the tip of the stirring rod 3 in an arc within the Ga2O3 melt 82. As a result, bubbles 2 composed of excess oxygen (O2) that does not form Ga2O3 at and around the aforementioned position in the Ga2O3 melt 82 are expelled to the outside of the crucible 5, or at least to the outside of the Ga2O3 melt 82. Thus, stirring the Ga2O3 melt 82 by the stirring rod 3 can suppress the formation of linear voids originating from the bubbles 2 in the β-Ga2O3 single crystal 81. In particular, the formation of linear voids can be further suppressed in the central portion of the β-Ga2O3 single crystal 81, i.e., the portion of the β-Ga2O3 single crystal 81 corresponding to the aforementioned position in and around the Ga2O3 melt 82.

[0104] In the Ga2O3 single crystal growth step S140, the crucible 5 is lowered relative to the heating device 7 along its axis, thereby raising the interface between the β-type Ga2O3 single crystal 81 and the Ga2O3 melt 82 toward the liquid B2O3 side, and solidifying the Ga2O3 melt 82 into the β-type Ga2O3 single crystal 81. Thus, the crystal growth of the β-type Ga2O3 single crystal 81 continues until the solidification of the Ga2O3 melt 82 remaining in the straight body portion 53 of the crucible 5 is complete. This results in an ingot of the β-type Ga2O3 single crystal 81 in which the formation of the linear void in the central portion is suppressed.

[0105] (Second method)

[0106] The second method can be performed using the same key points as the first method in all steps except the Ga2O3 single crystal growth step S140. Thus, the second method can also produce an ingot of β-type Ga2O3 single crystal 81 in which the formation of the linear void in the central portion is suppressed. The Ga2O3 single crystal growth step S140 in the second method differs from the first method in the following features.

[0107] That is, in the Ga2O3 single crystal growth step S140 in the second method, instead of the stirring step in the first method, a step of inserting a hollow tube made of a platinum-rhodium alloy into the Ga2O3 melt and blowing an inert gas into the Ga2O3 melt through the hollow tube while growing the crystal can be included (hereinafter also referred to as "gas blowing step"). Figure 5 As shown, in this gas injection step, a hollow tube 4 made of a Pt-Rh alloy is first placed in a crucible 5 with its tip inserted into the Ga2O3 melt 82 at a position approximately 10 to 20 mm above the interface between the Ga2O3 melt 82 and the growing β-Ga2O3 single crystal 81 within the crucible 5 and near the radial center of the crucible 5. Next, an inert gas is injected into the Ga2O3 melt 82 from the outside using the hollow tube 4. Examples of the inert gas include nitrogen and argon, with high-purity argon of 99.9999% by mass being particularly preferred. This allows bubbles 2 composed of excess O2 that does not form Ga2O3 to be expelled from the crucible 5, or at least from the Ga2O3 melt 82, at and around the Ga2O3 melt 82, along with the inert gas. Thus, by blowing the inert gas into the Ga2O3 melt 82 through the hollow tube 4, the formation of linear voids originating from the bubbles 2 in the β-Ga2O3 single crystal 81 can be suppressed. In particular, the formation of linear voids can be further suppressed in the central portion of the β-Ga2O3 single crystal 81, which corresponds to the position in the Ga2O3 melt 82, and in the surrounding portion of the β-Ga2O3 single crystal 81.

[0108] Furthermore, the Ga2O3 single crystal growth step S140 in the second method preferably includes a step of stirring the Ga2O3 melt using a hollow tube. Specifically, the tip of a hollow tube 4 made of a Pt-Rh alloy is first inserted into the aforementioned position within the Ga2O3 melt 82 within the crucible 5, and the Ga2O3 melt 82 is then stirred by the hollow tube 4. In other words, the stirring step in the first method can be performed simultaneously with the gas injection step using the hollow tube 4 in the Ga2O3 single crystal growth step S140 in the second method. This allows the bubbles 2 in the Ga2O3 melt 82 to be more efficiently expelled to the exterior of the crucible 5, or at least to the exterior of the Ga2O3 melt 82.

[0109] (Third System)

[0110] The third method is to implement the first method or the second method on the basis of combining the following features in the above-mentioned single crystal growth device, etc. That is, in the third method, the above-mentioned single crystal growth device is housed in the above-mentioned pressure vessel. Furthermore, after the process of bringing the above-mentioned Ga2O3 melt into contact with the remaining portion of the above-mentioned seed crystal and before the process of obtaining the above-mentioned β-type Ga2O3 single crystal, the process includes repeating the operation of reducing the pressure in the above-mentioned pressure vessel from one atmospheric pressure and then restoring it to the above-mentioned one atmospheric pressure for more than three times. Specifically, as Figure 6 As shown, the third method implements the first or second method described above, after housing the Ga2O3 single crystal growth apparatus 100 in a pressure vessel 9. Specifically, after the raw material melting step S130 and before the Ga2O3 single crystal growth step S140, the pressure within the pressure vessel 9 is reduced from one atmosphere to, for example, 0.1 to 0.8 atmospheres, and then restored to the aforementioned one atmosphere, repeating three or more times (hereinafter referred to as "pressure fluctuation operation"). Specifically, in the third method, the pressure fluctuation operation is performed before gradually lowering the crucible 5 axially relative to the heating device 7 in the Ga2O3 single crystal growth step S140. This, in addition to the effects of the first or second method described above, allows the bubbles 2 present in and around the Ga2O3 melt 82 to be actively expelled to the exterior of the crucible 5, or at least to the exterior of the Ga2O3 melt 82, through fluctuations in the ambient pressure. Thus, in the third production method, compared with the above-mentioned first and second production methods, an ingot of β-type Ga2O3 single crystal 81 can be obtained in which the formation of linear voids in the center portion is further suppressed.

[0111] [Method for manufacturing a β-type gallium trioxide single crystal substrate]

[0112] <β-type Ga2O3 single crystal substrate manufacturing step S200>

[0113] The manufacturing method of the β-type Ga2O3 single crystal substrate of this embodiment includes the step of processing the β-type Ga2O3 single crystal obtained by the manufacturing method of the β-type Ga2O3 single crystal to obtain a β-type Ga2O3 single crystal substrate having a circular main surface. Figure 3 As shown, the above-mentioned method for manufacturing a β-Ga2O3 single crystal substrate includes a β-Ga2O3 single crystal manufacturing step S100 and a β-Ga2O3 single crystal substrate manufacturing step S200. The purpose of the β-Ga2O3 single crystal substrate manufacturing step S200 is to process the β-Ga2O3 single crystal obtained in the β-Ga2O3 single crystal manufacturing step S100 to obtain a β-Ga2O3 single crystal substrate. The β-Ga2O3 single crystal substrate manufacturing step S200 includes the following steps: a cutting step, a peripheral grinding step, and a polishing step. By performing these steps in sequence, a β-Ga2O3 single crystal substrate can be obtained.

[0114] The cutting process is a process of slicing the ingot composed of β-type Ga2O3 single crystal taken out from the crucible into wafers of a specified thickness in order to obtain a β-type Ga2O3 single crystal substrate. Furthermore, the peripheral grinding process is a process of obtaining a β-type Ga2O3 single crystal substrate having a main surface with a circular shape by grinding the periphery of the above-mentioned wafer. The peripheral grinding process can include, for example, a process of implementing chamfering. As the cutting process and the peripheral grinding process, conventionally known cutting methods and peripheral grinding methods can be used. Furthermore, the polishing process is a process of mirror-finishing the central portion of the above-mentioned main surface. As the polishing process, conventionally known polishing methods can be used. Through the polishing process, the surface roughness Ra of the above-mentioned central portion, for example, as specified in JIS B0681-2:2018, can be made to be less than 10nm.

[0115] [Effects]

[0116] By performing the above-described steps, the β-Ga2O3 single crystal substrate of this embodiment can be manufactured. In the above-described β-Ga2O3 single crystal manufacturing method, particularly in the Ga2O3 single crystal growth step S140, a β-Ga2O3 single crystal ingot can be obtained in which the formation of linear voids in the central portion is suppressed. Consequently, a β-Ga2O3 single crystal substrate can be obtained from the above-described β-Ga2O3 single crystal ingot in which the density of linear voids in the outer periphery of the main surface is greater than that in the central portion. Consequently, the crack defect rate in the above-described β-Ga2O3 single crystal substrate can be reduced.

[0117] Example

[0118] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Figures 4 to 6 The Ga2O3 single crystal manufacturing device shown in FIG. Figure 3 In the following description, samples 11 to 15, 21 to 25, and 31 to 33 are examples, and samples 101 to 105 are comparative examples.

[0119] [Fabrication of β-type Ga2O3 single crystal substrate]

[0120] Sample 11

[0121] (β-Ga2O3 Single Crystal Manufacturing Process S100)

[0122] 1) Preparation step S110

[0123] First, a Ga2O3 single crystal growth apparatus 100, a seed crystal 8a composed of a Ga2O3 single crystal, a bulk Ga2O3 block composed of polycrystalline Ga2O3, and solid B2O3 are prepared using conventional methods or commercially available products. The crucible 5 constituting the Ga2O3 single crystal growth apparatus 100 is made of a Pt-Rh alloy containing 35% by mass of Rh. The inner diameter of the straight body portion 53 of the crucible 5 is 110 mm.

[0124] 2) Raw material loading process S120

[0125] Next, a seed crystal 8a is placed at the bottom of the crucible 5 by a conventionally known method, and a Ga2O3 block and solid B2O3 are placed at a position above the seed crystal 8a in the crucible 5. Specifically, a seed crystal 8a composed of a Ga2O3 single crystal is placed in the hollow portion of the seed crystal receiving portion 51 of the crucible 5. A plurality of massive Ga2O3 blocks are placed in the enlarged diameter portion 52 and the straight body portion 53 of the crucible 5 and stacked. Next, solid B2O3 is placed on the above-mentioned Ga2O3 blocks. Furthermore, when a plurality of massive Ga2O3 blocks are placed in the crucible 5, a prescribed amount of Sn is added. The amount of Sn added is such that the atomic concentration of Sn in the β-type Ga2O3 single crystal substrate becomes 1×10 18 cm -3 amount.

[0126] 3) Raw material melting process S130

[0127] Next, a crucible 5 containing a seed crystal 8a, a Ga2O3 bulk, and solid B2O3 is supported by a crucible holder 6 made of zirconia. Then, an electric current is supplied to a heating device 7 to heat the crucible 5, thereby melting the solid B2O3 into liquid B2O3 and melting the Ga2O3 bulk into a Ga2O3 melt 82. Subsequently, a portion of the seed crystal 8a also melts, and the remaining portion of the seed crystal 8a comes into contact with the Ga2O3 melt 82 at their interface.

[0128] 4) Ga2O3 single crystal growth step S140

[0129] Next, by gradually lowering the crucible 5 along its axis downward (toward the seed crystal storage portion 51) relative to the heating device 7, a temperature gradient is formed in the crucible 5, in which the temperature is low on the seed crystal 8a side and high on the Ga2O3 melt 82 side. As a result, the Ga2O3 melt 82 in contact with the seed crystal 8a solidifies, and a β-type Ga2O3 single crystal 81 continuously grows from the Ga2O3 melt 82 on the remaining portion of the seed crystal 8a. This operation is continued until the solidification of the Ga2O3 melt 82 remaining in the straight body 53 of the crucible 5 is completed. At this time, the temperature on the Ga2O3 melt 82 side is 1800-1820°C. The temperature gradient at the interface between the Ga2O3 melt 82 and the growing β-type Ga2O3 single crystal 81 is 5°C / cm. The speed at which the crucible 5 descends downward along its axis is 0.8 mm / hour.

[0130] In the Ga2O3 single crystal growth step S140, a stirring step is performed as follows. Specifically, a stirring rod 3 made of a Pt-Rh alloy is placed in the crucible 5 such that its tip is inserted into the Ga2O3 melt 82 at a position approximately 10 mm above the interface between the Ga2O3 melt 82 and the growing β-Ga2O3 single crystal 81 within the crucible 5 and near the radial center of the crucible 5. Furthermore, the tip of the stirring rod 3 is rotated in an arc within the Ga2O3 melt 82. This stirs the Ga2O3 melt 82, causing bubbles 2 composed of excess O2 that does not form Ga2O3 to be discharged from the crucible 5, or at least from the Ga2O3 melt 82, at and around the aforementioned position within the Ga2O3 melt 82.

[0131] (Ga2O3 Single Crystal Substrate Manufacturing Step S200)

[0132] Finally, the ingot of β-type Ga2O3 single crystal 81 obtained in the Ga2O3 single crystal growth step S140 is processed in each step of the cutting step, the peripheral grinding step, and the polishing step, thereby obtaining a β-type Ga2O3 single crystal substrate. First, in the cutting step, the above-mentioned ingot is sliced ​​into wafers with a thickness of 700μm using a conventionally known method. The number of wafers thus obtained is 25. These 25 wafers correspond to the "number of substrates per crystal" in Tables 1 and 2 below. Next, in the peripheral grinding step, the periphery of the above-mentioned wafer is chamfered using a conventionally known method, thereby obtaining a β-type Ga2O3 single crystal substrate having a circular main surface. The main surface of the above-mentioned β-type Ga2O3 single crystal substrate is composed of: a first circular region with a diameter of 0.75D centered on the above-mentioned center; and a second region, which is an area further outward than the above-mentioned first region. Furthermore, in the polishing step, at least the first region was polished using a conventionally known polishing method, thereby achieving a surface roughness Ra of 8 nm in the first region as specified in JIS B 0681-2:2018. This produced the Ga2O3 single crystal substrate of Sample 11. The time from the completion of the raw material melting step S130 to the start of the Ga2O3 single crystal growth step S140 was 24 hours.

[0133] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 11 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0134] Sample 12

[0135] Ten wafers with a thickness of 700 μm are obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-Ga2O3 single crystal substrate of sample 12 is manufactured using the same key points as the manufacturing method of the β-Ga2O3 single crystal substrate of sample 11.

[0136] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 12 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0137] Sample 13

[0138] Thirteen wafers having a thickness of 700 μm are obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-Ga2O3 single crystal substrate of sample 13 is manufactured using the same key points as the manufacturing method of the β-Ga2O3 single crystal substrate of sample 11.

[0139] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 13 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0140] Sample 14

[0141] The β-Ga2O3 single crystal substrate of Sample 14 was manufactured using the same method as that used for manufacturing the β-Ga2O3 single crystal substrate of Sample 11, except that a crucible 5 having an inner diameter of 160 mm in the straight body portion 53 was prepared in the preparation step S110 and 16 wafers having a thickness of 700 μm were obtained by the cutting step in the β-Ga2O3 single crystal substrate manufacturing step S200. The time from the completion of the raw material melting step S130 to the start of the Ga2O3 single crystal growth step S140 was 36 hours.

[0142] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 14 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0143] Sample 15

[0144] Ten wafers having a thickness of 700 μm were obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-Ga2O3 single crystal substrate of sample 15 was manufactured using the same method as the manufacturing method of the β-Ga2O3 single crystal substrate of sample 14.

[0145] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 15 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0146] Sample 21

[0147] In the Ga2O3 single crystal growth process S140, the following gas blowing process is implemented instead of the above-mentioned stirring process, and 12 wafers with a thickness of 700 μm are obtained through the cutting process in the β-type Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-type Ga2O3 single crystal substrate of sample 21 is manufactured by the same key points as the manufacturing method of the β-type Ga2O3 single crystal substrate of sample 11.

[0148] Specifically, in the gas blowing step, the hollow tube 4, made of a Pt-Rh alloy, is first placed in the crucible 5 so that its tip is inserted into the Ga2O3 melt 82 at a position approximately 3 mm above the interface between the Ga2O3 melt 82 and the growing β-Ga2O3 single crystal 81 within the crucible 5 and near the radial center of the crucible 5. Next, high-purity argon gas containing 99.9999% by mass is blown into the Ga2O3 melt 82 from the outside using the hollow tube 4. Consequently, bubbles 2 composed of excess O2 that does not form Ga2O3 are discharged from the crucible 5, or at least from the Ga2O3 melt 82, at and around the aforementioned position in the Ga2O3 melt 82, along with the high-purity argon gas.

[0149] According to the above-mentioned crystal orientation measuring apparatus, the main surface of the Ga2O3 single crystal substrate of sample 21 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0150] Sample 22

[0151] The β-Ga2O3 single crystal substrate of sample 22 is manufactured by the same method as that of manufacturing the β-Ga2O3 single crystal substrate of sample 21 except that 22 wafers with a thickness of 700 μm are obtained by the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200.

[0152] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 22 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0153] Sample 23

[0154] Ten wafers with a thickness of 700 μm were obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-Ga2O3 single crystal substrate of sample 23 was manufactured using the same manufacturing method as the β-Ga2O3 single crystal substrate of sample 21.

[0155] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 23 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0156] Sample 24

[0157] The β-Ga2O3 single crystal substrate of Sample 24 was manufactured using the same method as that used for manufacturing the β-Ga2O3 single crystal substrate of Sample 21, except that a crucible 5 having an inner diameter of 160 mm in the straight body portion 53 was prepared in the preparation step S110 and ten wafers having a thickness of 700 μm were obtained by the cutting step in the β-Ga2O3 single crystal substrate manufacturing step S200. The time from the completion of the raw material melting step S130 to the start of the Ga2O3 single crystal growth step S140 was 36 hours.

[0158] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 24 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0159] Sample 25

[0160] Eight wafers with a thickness of 700 μm were obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-Ga2O3 single crystal substrate of sample 25 was manufactured using the same key points as the manufacturing method of the β-Ga2O3 single crystal substrate of sample 24.

[0161] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 25 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0162] Sample 31

[0163] In the raw material melting step S130, the Ga2O3 single crystal growth apparatus 100 was housed in the pressure vessel 9, and the crucible 5 was heated by the heating device 7, thereby bringing the seed crystal 8a into contact with the Ga2O3 melt 82. After the raw material melting step S130 and before the Ga2O3 single crystal growth step S140, a pressure fluctuation operation was repeated three times, wherein the pressure in the pressure vessel 9 was reduced from 1 atmosphere to 0.5 atmosphere and then returned to the 1 atmosphere pressure. Furthermore, ten wafers having a thickness of 700 μm were obtained by the cutting step in the β-Ga2O3 single crystal substrate manufacturing step S200. The β-Ga2O3 single crystal substrate of Sample 31 was manufactured using the same method as the β-Ga2O3 single crystal substrate manufacturing method of Sample 21. The time from the completion of the raw material melting step S130 to the start of the Ga2O3 single crystal growth step S140 was 20 hours.

[0164] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 31 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0165] Sample 32

[0166] Eight wafers with a thickness of 700 μm are obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-Ga2O3 single crystal substrate of sample 32 is manufactured using the same key points as the manufacturing method of the β-Ga2O3 single crystal substrate of sample 31.

[0167] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 32 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0168] <Sample 33>

[0169] The β-Ga2O3 single crystal substrate of Sample 33 was manufactured using the same method as that used for manufacturing the β-Ga2O3 single crystal substrate of Sample 31, except that a crucible 5 having an inner diameter of 160 mm in the straight body portion 53 was prepared in the preparation step S110 and five wafers having a thickness of 700 μm were obtained by the cutting step in the β-Ga2O3 single crystal substrate manufacturing step S200. The time from the completion of the raw material melting step S130 to the start of the Ga2O3 single crystal growth step S140 was 32 hours.

[0170] According to the above-mentioned crystal orientation measuring device, the main surface of the Ga2O3 single crystal substrate of sample 33 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0171] Sample 101

[0172] In the Ga2O3 single crystal growth process S140, the stirring process is not performed, and 20 wafers with a thickness of 700 μm are obtained through the cutting process in the β-type Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-type Ga2O3 single crystal substrate of sample 101 is manufactured using the same key points as the manufacturing method of the β-type Ga2O3 single crystal substrate of sample 11.

[0173] According to the above-mentioned crystal orientation measuring apparatus, the main surface of the Ga2O3 single crystal substrate of sample 101 has an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0174] <Sample 102>

[0175] The β-Ga2O3 single crystal substrate of sample 102 is manufactured using the same method as that of manufacturing the β-Ga2O3 single crystal substrate of sample 101 except that 33 wafers with a thickness of 700 μm are obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200.

[0176] According to the above-mentioned crystal orientation measuring apparatus, the main surface of the Ga2O3 single crystal substrate of sample 102 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0177] <Sample 103>

[0178] Five wafers with a thickness of 700 μm are obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200. Otherwise, the β-Ga2O3 single crystal substrate of sample 103 is manufactured using the same key points as the manufacturing method of the β-Ga2O3 single crystal substrate of sample 101.

[0179] According to the above-mentioned crystal orientation measuring apparatus, the main surface of the Ga2O3 single crystal substrate of sample 103 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0180] <Sample 104>

[0181] The β-Ga2O3 single crystal substrate of Sample 104 was manufactured using the same method as that used for manufacturing the β-Ga2O3 single crystal substrate of Sample 101, except that a crucible 5 having an inner diameter of 160 mm in the straight body portion 53 was prepared in the preparation step S110 and ten wafers having a thickness of 700 μm were obtained by the cutting step in the β-Ga2O3 single crystal substrate manufacturing step S200. The time from the completion of the raw material melting step S130 to the start of the Ga2O3 single crystal growth step S140 was 36 hours.

[0182] According to the above-mentioned crystal orientation measuring apparatus, the main surface of the Ga2O3 single crystal substrate of sample 104 is a plane having an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0183] Sample 105

[0184] The β-Ga2O3 single crystal substrate of sample 105 is manufactured using the same manufacturing method as that of the β-Ga2O3 single crystal substrate of sample 104 except that 20 wafers with a thickness of 700 μm are obtained through the cutting process in the β-Ga2O3 single crystal substrate manufacturing process S200.

[0185] According to the above-mentioned crystal orientation measuring apparatus, the main surface of the Ga2O3 single crystal substrate of sample 105 has an offset angle of 0.2° relative to the (001) plane of the Ga2O3 single crystal and the offset direction is the

[010] direction of the above-mentioned Ga2O3 single crystal.

[0186] [evaluate]

[0187] <Measurement of the First Density and the Second Density, and Calculation of the Second Density / First Density>

[0188] For the β-Ga2O3 single crystal substrates of Samples 11 to 15, Samples 21 to 25, Samples 31 to 33, and Samples 101 to 105, the first and second densities were determined using the aforementioned measurement method, and the ratio of second density to first density was calculated. The results are shown in Tables 1 and 2. The values ​​of first density, second density, and second density / first density shown in Tables 1 and 2 are the average values ​​for the number of substrates per crystal in each sample. These values ​​are shown in Tables 1 and 2.

[0189] <Determination of crack defect rate>

[0190] For β-Ga2O3 single crystal substrates (Samples 11 to 15, Samples 21 to 25, Samples 31 to 33, and Samples 101 to 105), epitaxial films consisting of Ga2O3 were formed on their main surfaces using the HVPE (Hydride Vapor Phase Epitaxy) method under the conditions described below, using the reactor described below. After the epitaxial films were formed, the β-Ga2O3 single crystal substrates were cooled to room temperature within the furnace and then removed from the furnace. The number of substrates with cracks at this point was divided by the number of substrates subjected to the HPVE method and converted to a percentage to determine the crack defect rate. The results are shown in Tables 1 and 2.

[0191] (HVPE conditions for stacking a Ga2O3 film on a β-type Ga2O3 single crystal substrate)

[0192] Reactor: Hot wall type reactor made of quartz

[0193] Carrier gas: Nitrogen (N2)

[0194] Raw gas: Oxygen (O2) and gallium chloride (GaCl) gas generated by blowing hydrogen chloride (HCl) gas onto metal gallium (Ga)

[0195] Dopant: Silicon tetrachloride (SiCl4), where Nd-Na is used to form 1×10 16 cm -3 Control the doping amount by left and right

[0196] Growth temperature: 1000℃

[0197] Growth rate: 15 μm / hour

[0198] Growth thickness: 5μm.

[0199] <Measurement of the leakage current defect rate of Schottky barrier diodes>

[0200] Schottky barrier diodes were fabricated from the β-type Ga2O3 single crystal substrates of Samples 11 to 15, Samples 21 to 25, Samples 31 to 33, and Samples 101 to 105 by the method described below. The leakage current value of the Schottky barrier diodes when a reverse voltage of 50 V was applied was measured. When the leakage current value was greater than 1.0×10 -5 Ampere / cm 2 If the device was defective, it was determined to be a defective device. Using the above procedure, the number of defective devices in each sample was divided by the number of substrates used to fabricate the Schottky barrier diodes from each sample, and the result was converted to a percentage to determine the leakage current defect rate. The results are shown in Tables 1 and 2.

[0201] (Method for fabricating a Schottky barrier diode)

[0202] First, a 2.5 mm square chip was obtained from the β-Ga2O3 single crystal substrate of each sample. Then, silicon (Si) ions were implanted into the entire surface of the back side of the (001) surface of the above chip, and further annealed at 950°C for 30 minutes. Then, Ti (100 nm thick) / Ni (100 nm thick) / Au (100 nm thick) were sequentially vapor-deposited on the back side of the (001) surface of the above chip to form a full-surface electrode. On the surface side of the (001) surface of the above chip, Ni (100 nm thick) / Au (100 nm thick) was vapor-deposited through a metal mask having multiple holes with a diameter of 600 μm, thereby forming a Schottky electrode with a diameter of 600 μm at equal intervals in a checkerboard pattern. Through the above operations, a Schottky barrier diode was obtained from the β-Ga2O3 single crystal substrate of each sample.

[0203] Calculation of Component Yield Index

[0204] The device yield index for each sample was calculated by multiplying the crack defect rate obtained in the β-GaO single crystal substrates of Samples 11 to 15, Samples 21 to 25, Samples 31 to 33, and Samples 101 to 105 by the leakage current defect rate of the Schottky barrier diodes. The results are shown in Tables 1 and 2. As mentioned above, a smaller value of the device yield index indicates a better device yield.

[0205] [Table 1]

[0206] Table 1

[0207]

[0208] [Table 2]

[0209] Table 2

[0210]

[0211] [Investigation]

[0212] Tables 1 and 2 show that the crack defect rate of the β-Ga2O3 single crystal substrates of Samples 11 to 15, Samples 21 to 25, and Samples 31 to 33 is lower than that of the β-Ga2O3 single crystal substrates of Samples 101 to 105. Furthermore, the device yield index of the β-Ga2O3 single crystal substrates of Samples 11 to 15, Samples 21 to 25, and Samples 31 to 33 is lower than that of the β-Ga2O3 single crystal substrates of Samples 101 to 105, indicating an improvement in device yield. The β-Ga2O3 single crystal substrates of Samples 31 to 33 achieved comparable performance to the β-Ga2O3 single crystal substrates of Samples 11 to 15, and Samples 21 to 25, despite a shorter time from the completion of the raw material melting step S130 to the start of the Ga2O3 single crystal growth step S140, demonstrating improved manufacturing efficiency.

[0213] Although the embodiments and examples of the present invention have been described above, it has been initially intended that the configurations of the above-described embodiments and examples be appropriately combined.

[0214] The embodiments and examples disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0215] Description of Reference Numerals

[0216] 1: β-type gallium trioxide single crystal substrate (β-type Ga2O3 single crystal substrate), 10: Main surface, 11: First region, 12: Second region, 13: Boundary between the first and second regions, 1a: Linear cavity, 2: Bubble, 3: Stirring rod, 4: Hollow tube, 5: Crucible, 51: Seed crystal storage part, 52: Expanded diameter part, 53: Straight body part, 6: Crucible holding table, 7: Heating device, 8a: Seed crystal, 81: β-type gallium trioxide single crystal (β-type Ga2O3 single crystal), 82: gallium trioxide melt (Ga2O3 melt), 9: pressure vessel, 100: single crystal growth device, G: grid, DL: grid-dividing line, OF: positioning edge, S100: β-type Ga2O3 single crystal manufacturing process, S110: preparation process, S120: raw material loading process, S130: raw material melting process, S140: Ga2O3 single crystal growth process, S200: β-type Ga2O3 single crystal substrate manufacturing process.

Claims

1. A β-type gallium trioxide single crystal substrate having a circular main surface, The diameter of the β-type gallium trioxide single crystal substrate is greater than 100 mm. The main surface is the (001) plane of the β-type gallium oxide single crystal constituting the β-type gallium oxide single crystal substrate, or a plane having an off angle greater than 0° and less than 10° relative to the (001) plane of the β-type gallium oxide single crystal and an off direction that is the [010] direction of the β-type gallium oxide single crystal or a direction orthogonal to the [010] direction. A ratio of a second density to a first density, namely, second density / first density, is greater than 1.0, the first density being the density of linear voids in a first region having a circular shape centered on the center of the main surface and having a diameter of 0.75D, and the second density being the density of linear voids in a second region located outside the first region of the main surface. The second density is 1000cm -2 the following, The D represents the diameter of the β-type gallium trioxide single crystal substrate, and the unit of D is mm. The linear void has a length of 10 μm to 200 μm, a width of 0.01 μm to 2 μm, and a depth of 0.1 μm or more. The density of the linear voids in the first region and the density of the linear voids in the second region are 2 The number of linear voids per 1 cm 2 The number of the linear voids is determined by forming an imaginary grid on the main surface in which squares with a side length of 10 mm are arranged in a manner that does not overlap with each other, and counting the number of the linear voids existing in each of the squares constituting the grid using a differential interference microscope.

2. The β-type gallium trioxide single crystal substrate according to claim 1, wherein The second density is 1cm -2 Over 100cm -2 the following.

3. The β-type gallium trioxide single crystal substrate according to claim 1 or 2, wherein: The second density / first density is 2.5 or less.

4. The β-type gallium trioxide single crystal substrate according to any one of claims 1 to 3, wherein The β-type gallium trioxide single crystal substrate contains a dopant, The dopant is tin or silicon, The atomic concentration of the dopant is 5.0×10 19 cm -3 the following.

5. A method for producing a β-type gallium trioxide single crystal using a vertical wafer boat method. The manufacturing method comprises the following steps: A step of preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device disposed so as to surround the outer circumference of the crucible; a step of accommodating a seed crystal at the bottom of the crucible and accommodating a bulk gallium trioxide mass at a position 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 simultaneously bringing the gallium trioxide melt into contact with the remaining portion of the seed crystal; and a step of growing a crystal from the gallium oxide melt on the remaining portion of the seed crystal to obtain the β-type gallium oxide single crystal; The crucible is made of platinum-rhodium alloy. The step of obtaining the β-type gallium trioxide single crystal includes inserting a stirring rod made of a platinum-rhodium alloy into the gallium trioxide melt and growing the crystal while stirring the gallium trioxide melt with the stirring rod.

6. A method for producing a β-type gallium trioxide single crystal using a vertical wafer boat method. The manufacturing method comprises the following steps: A step of preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device disposed so as to surround the outer circumference of the crucible; a step of accommodating a seed crystal at the bottom of the crucible and accommodating a bulk gallium trioxide mass at a position 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 simultaneously bringing the gallium trioxide melt into contact with the remaining portion of the seed crystal; and a step of growing a crystal from the gallium oxide melt on the remaining portion of the seed crystal to obtain the β-type gallium oxide single crystal; The crucible is made of platinum-rhodium alloy. The step of obtaining the β-type gallium trioxide single crystal includes inserting a hollow tube made of a platinum-rhodium alloy into the gallium trioxide melt and growing the crystal while blowing an inert gas into the gallium trioxide melt through the hollow tube.

7. The method for producing a β-type gallium trioxide single crystal according to claim 6, wherein: The step of obtaining the β-type gallium trioxide single crystal includes the step of stirring the gallium trioxide melt using the hollow tube.

8. The method for producing a β-type gallium trioxide single crystal according to any one of claims 5 to 7, wherein: The single crystal growth device is housed in a pressure vessel. After the step of bringing the gallium trioxide melt into contact with the remaining portion of the seed crystal and before the step of obtaining the β-type gallium trioxide single crystal, the step includes repeating three or more operations of reducing the pressure in the pressure vessel from one atmospheric pressure and then restoring it to the one atmospheric pressure.

9. A method for manufacturing a β-type gallium trioxide single crystal substrate, comprising the step of processing the β-type gallium trioxide single crystal obtained by the method for manufacturing a β-type gallium trioxide single crystal according to any one of claims 5 to 8 to obtain a β-type gallium trioxide single crystal substrate having a circular main surface.

10. The β-type gallium trioxide single crystal substrate according to claim 1, wherein The second density is 1cm -2 Over 90cm -2 the following, The second density / first density is greater than or equal to 1.1 and less than or equal to 2, The β-type gallium trioxide single crystal substrate contains a dopant, The dopant is tin, The atomic concentration of the dopant is 5.0×10 19 cm -3 the following.

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