Gallium oxide crystal manufacturing equipment

Abstract

To provide a gallium oxide crystal manufacturing apparatus capable of growing a crystal by the vertical Bridgman method and obtaining a large sized gallium oxide single crystal having less crystal defects served as the deterioration factor of crystal quality.SOLUTION: A gallium oxide crystal manufacturing apparatus 1 comprises: a crucible 20 for storing a raw material for gallium oxide ; a crucible support 21 for supporting the crucible 20 from below; a crucible support shaft 22 connected to the crucible support 21 from below and movably supporting the crucible 20 and the crucible support 21 in the vertical direction; a tubular furnace core tube 10 surrounding the crucible 20, the crucible support 21 and the crucible support shaft 22; a tubular furnace inner tube 11 surrounding the furnace core tube 10; and a resistance heating heater element 23 having an exothermic part 231 installed in a space between the furnace core tube 10 and the furnace inner tube 11. The melting points of the furnace core tube 10 and the furnace inner tube 11 is 1900°C or more; and the thermal conductivity of the furnace core tube 10 in a portion positioned just beside the crucible 20 is higher than that of the furnace inner tube 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for producing gallium oxide crystals. [Background technology]

[0002] Conventionally, a gallium oxide crystal manufacturing apparatus that grows crystals by the vertical Bridgman method is known (see Patent Document 1). In the gallium oxide crystal manufacturing apparatus described in Patent Document 1, a crucible is heated by a resistance heating element to melt the gallium oxide raw material contained in the crucible.

[0003] According to Patent Document 1, a crucible with an inner diameter of 2 inches was used to grow a β-Ga2O3 crystal with a diameter of 2 inches, although it was not a perfect single crystal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-193466 A Summary of the Invention [Problem to be solved by the invention]

[0005] In order to grow high-quality single crystals using the vertical Bridgman method, it is necessary to create a temperature distribution around the crucible that is suitable for crystal growth. The larger the crystal being grown, the stricter the conditions that must be met for the temperature distribution.

[0006] In order to form the desired temperature distribution, the device is required to have a configuration that appropriately controls the heat flow around the crucible. Therefore, due to its configuration, it is considered difficult to obtain gallium oxide single crystals of 2 inches or more in size with the manufacturing device described in Patent Document 1.

[0007] An object of the present invention is to provide a gallium oxide crystal manufacturing apparatus that is an apparatus for growing crystals by the vertical Bridgman method and is configured to obtain large-sized gallium oxide single crystals with few crystal defects that are factors that cause deterioration of crystal quality. [Means for solving the problem]

[0008] In order to achieve the above object, one aspect of the present invention provides the following [1] to [ 7 We provide a manufacturing apparatus for gallium oxide crystals.

[0009] [1] A crucible for containing a gallium oxide raw material, a crucible support supporting the crucible from below, a crucible support shaft connected to the crucible support from below and supporting the crucible and the crucible support so as to be movable in the vertical direction, a tubular furnace tube surrounding the crucible, the crucible support, and the crucible support shaft, a tubular inner furnace tube surrounding the core tube, and a resistance heating element having a heating portion installed in a space between the core tube and the inner furnace tube, wherein the melting points of the core tube and the inner furnace tube are 1900°C or higher, and the thermal conductivity of a portion of the core tube located directly beside the crucible is higher than the thermal conductivity of the inner furnace tube. the furnace tube has a first portion including a portion located immediately to the side of the crucible and a second portion other than the first portion, and the thermal conductivity of the first portion is higher than the thermal conductivity of the second portion; Gallium oxide crystal manufacturing equipment. [ 2 ] the above-mentioned furnace tube is provided with a plate-shaped member covering the upper end opening of the furnace tube, and a heat insulating material placed on the plate-shaped member. [1] An apparatus for producing a gallium oxide crystal according to claim 1. [ 3 The portion of the furnace core tube located immediately to the side of the crucible is made of alumina-based ceramics or magnesia-based ceramics, and the furnace inner tube is made of zirconia-based ceramics. [1] or [2] An apparatus for producing a gallium oxide crystal according to claim 1. [ 4 ] The crucible is made of a platinum-based alloy, 3 13. An apparatus for producing gallium oxide crystals according to any one of claims 1 to 12. [ 5] the crucible support has a first block made of zirconia-based ceramics at the top in direct contact with the crucible, and a second block made of alumina-based ceramics below the first block and not in contact with the crucible, 4 ] An apparatus for producing gallium oxide crystals as described in the above. [ 6 ] The furnace inner tube is surrounded by heat-insulating layers from the sides and from above and below, the heat-insulating layer is vertically separated into an upper heat-insulating layer and a lower heat-insulating layer, the upper heat-insulating layer and the lower heat-insulating layer are vertically sandwiched by a gap, and the gap is not horizontally continuous from the inside to the outside of the heat-insulating layer, 5 13. An apparatus for producing gallium oxide crystals according to any one of claims 1 to 12. [ 7 ] The furnace inner tube is surrounded by heat-insulating layers from the sides and from above and below, the heat-insulating layer can be separated into an upper heat-insulating layer and a lower heat-insulating layer in the vertical direction, and when the upper heat-insulating layer is placed on the lower heat-insulating layer, the upper heat-insulating layer and the lower heat-insulating layer are in contact with each other without any gaps in the vertical direction, [1] to [ 5 13. An apparatus for producing gallium oxide crystals according to any one of claims 1 to 12. Effect of the Invention

[0010] According to the present invention, it is possible to provide a gallium oxide crystal manufacturing apparatus that is configured to grow crystals by the vertical Bridgman method and that is capable of obtaining large-sized gallium oxide single crystals with few crystal defects that are factors that cause deterioration of crystal quality. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a vertical cross-sectional view of a gallium oxide crystal manufacturing apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a furnace tube and its peripheral members according to an embodiment of the present invention. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of a crucible, a crucible support, and a crucible support shaft according to an embodiment of the present invention. [Figure 4]4(a) and 4(b) are respectively a perspective view and a side view of a heating element according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a photograph showing an example of mounting a heating element on a manufacturing device. [Figure 6] FIG. 6 is a vertical cross-sectional view of a modified example of a gallium oxide crystal manufacturing apparatus relating to an embodiment of the present invention. [Figure 7] Figure 7(a) is a photograph of a linear heating element, and Figure 7(b) is a photograph showing an example of mounting a linear heating element on a manufacturing device. [Figure 8] FIG. 8 is a vertical cross-sectional view of another modified example of the gallium oxide crystal manufacturing apparatus relating to an embodiment of the present invention. [Figure 9] FIG. 9 is a photograph of two β-Ga2O3 single crystals, among the gallium oxide single crystals according to this embodiment, each having a cylindrical shape with a diameter of 2 inches at the fixed diameter portion, and two wafers cut out from each of the crystals. [Figure 10] Fig. 10(a) is a photograph of a β-Ga2O3 single crystal of the gallium oxide single crystal according to this example, in which the constant diameter portion is cylindrical with a diameter of 2 inches and the cross section in the radial direction of the constant diameter portion is a (100) plane. Fig. 10(b) is a photograph of a processed wafer cut from the β-Ga2O3 single crystal of Fig. 10(a) and having a main surface of a (100) plane. [Figure 11] Fig. 11(a) is a photograph of a β-Ga2O3 single crystal of the gallium oxide single crystal according to this example, in which the constant diameter portion is cylindrical with a diameter of 2 inches and the cross section in the radial direction of the constant diameter portion is a (010) plane. Fig. 11(b) is a photograph of a processed wafer cut from the β-Ga2O3 single crystal of Fig. 11(a) and having a main surface of a (010) plane. [Figure 12] FIG. 12 is a photograph of a β-Ga2O3 single crystal (right side) grown using a manufacturing apparatus according to an embodiment of the present invention, the constant-diameter portion being cylindrical with a diameter of 3 inches and the cross section of the constant-diameter portion in the radial direction being the (010) plane, and a β-Ga2O3 single crystal (left side) grown using another manufacturing apparatus according to an embodiment of the present invention, the constant-diameter portion being cylindrical with a diameter of 4 inches and the cross section of the constant-diameter portion in the radial direction being the (010) plane. [Figure 13]FIG. 13 is an observation image by X-ray topography of a gallium oxide single crystal wafer doped with 0.2 mol % Sn and having a (001) principal surface that was cut from the gallium oxide single crystal according to this example. [Figure 14] 14(a) to (d) show (001) plane diffraction peaks obtained by X-ray rocking curve measurement in regions 1 to 4 on the wafer shown in FIG. 13, respectively. [Figure 15] FIG. 15 is an optical photograph of a gallium oxide single crystal wafer doped with 0.2 mol % Sn and having a (001) primary surface according to this example. [Figure 16] FIG. 16 is a graph showing the distribution of the half-width of the (001) plane diffraction peak on the wafer shown in FIG. 15, obtained by X-ray rocking curve measurement. [Figure 17] FIG. 17 is a graph showing the distribution of dislocation density on the wafer shown in FIG. [Figure 18] 18(a) to (c) are images observed by an optical microscope showing examples of etch pits that appeared on the wafer surface. [Figure 19] 19(a), (b), and (c) are graphs showing the half-width of the (001) plane diffraction peak and the dislocation density distribution in the upper, middle, and lower rows of the wafer shown in FIG. 15, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Embodiment] (Configuration of manufacturing equipment) 1 is a vertical cross-sectional view of a gallium oxide crystal manufacturing apparatus 1 according to an embodiment of the present invention. The manufacturing apparatus 1 is an apparatus for growing gallium oxide crystals by the vertical Bridgman method. Here, the gallium oxide crystal refers to a β-Ga2O3 crystal or a β-Ga2O3 crystal containing substitutional impurities such as Al, In, or dopants such as Sn, Si.

[0013] The manufacturing apparatus 1 includes a crucible 20 for containing gallium oxide raw material, a crucible support 21 that supports the crucible 20 from below, a crucible support shaft 22 that is connected to the crucible support 21 from below and supports the crucible 20 and the crucible support 21 so that they can be moved in the vertical direction, a tubular furnace tube 10 that surrounds the crucible 20, the crucible support 21, and the crucible support shaft 22, a tubular furnace inner tube 11 that surrounds the furnace core tube 10, and a heating element 23 having a heating section 231 installed in the space between the furnace core tube 10 and the inner furnace tube 11.

[0014] The manufacturing apparatus 1 also includes an inner furnace tube support plate 12 that serves as the base of the inner furnace tube 11, a thermal insulation layer 13 that is disposed outside the inner furnace tube 11 and surrounds the space for crystal growth inside the inner furnace tube 11 from the sides and above and below to suppress the outflow of heat to the outside of the apparatus, an exhaust pipe 16 that passes through the thermal insulation layer 13 from the inside of the manufacturing apparatus 1 to the outside of the apparatus, and a base 17 on which each component of the manufacturing apparatus 1 is placed. The outside of the thermal insulation layer 13 may be covered with an outer wall not shown.

[0015] The melting points of the furnace core tube 10 and the inner furnace tube 11 are 1900° C. or higher, and the furnace core tube 10 and the inner furnace tube 11 can withstand high temperatures for growing gallium oxide. In addition, the inner furnace tube 11 preferably has a softening point of 1800° C. or higher.

[0016] Generally, in crystal growth by the vertical Bridgman method, if the gradient of the temperature distribution around the crucible is large, it is difficult to grow a high-quality crystal, and this tendency becomes more pronounced as the size of the crystal to be grown increases. In the manufacturing apparatus 1, the furnace tube 10 controls the heat flow around the crucible 20, and a temperature distribution with a small gradient suitable for growing large, high-quality gallium oxide crystals can be formed around the crucible 20.

[0017] In order to form a temperature distribution with a smaller gradient around the crucible 20, it is preferable that the furnace core tube 10 has a high thermal conductivity, and it is preferable to use dense, high-purity alumina-based ceramics or magnesia-based ceramics as a material. For example, 4NA manufactured by TEP Corporation can be suitably used as the material for the furnace core tube 10.

[0018] Furthermore, the furnace core tube 10 separates the crucible 20 from the heating element 23, making it possible to suppress contamination of impurities such as Si and Mo from the heating element 23.

[0019] By using the inner furnace tube 11, it is possible to suppress the flow of heat from the heating element 23 and suppress wear of the heating element 23. For this reason, it is preferable that the inner furnace tube 11 has excellent thermal shock resistance and has a lower thermal conductivity than the core tube 10. For this reason, it is preferable that the inner furnace tube 11 is made of a material such as porous zirconia-based ceramics, which has a lower thermal conductivity than dense high-purity alumina-based ceramics or magnesia-based ceramics, which are the materials of the core tube 10. For example, ZIR-Y manufactured by TEP Corporation can be suitably used as the material of the inner furnace tube 11.

[0020] When zirconia ceramics is used as the material for the furnace inner tube 11, it is arranged so that the portion that reaches 1800° C. or higher does not come into contact with other members, since it easily reacts with other materials.

[0021] Furthermore, the furnace inner tube 11 can suppress local sintering and deformation of the heat-retaining layer 13 arranged on the outer side of the furnace inner tube 11 .

[0022] The furnace core tube 10 and the inner furnace tube 11 are typically cylindrical. The furnace core tube 10 and the inner furnace tube 11 can each be formed by stacking annular (typically annular) members having various outer and inner diameters. The annular member constituting the inner furnace tube 11 may be formed by combining a plurality of divided pieces separated along a plurality of straight lines extending from the center of the ring to the outer periphery.

[0023] 1, the heat-insulating layer 13 is configured with a plurality of layers stacked like a nested structure from the inside (the crucible 20 side) to the outside, and among the plurality of layers, the innermost one has the highest heat-resistant temperature, and the layers closer to the outside preferably have lower heat-resistant temperatures. Since the higher the heat-resistant temperature of the heat-insulating material used in the heat-insulating layer 13, the more expensive it is, by adopting such a configuration, it is possible to reduce costs while ensuring the heat resistance of the heat-insulating layer 13.

[0024] For example, in the example shown in FIG. 1, the innermost layer 131 is made of an alumina-based fiberboard having a heat resistance temperature of approximately 1800°C, the outermost layer 132 is made of an alumina-based fiberboard having a heat resistance temperature of approximately 1700°C, and the outermost layer 133 is made of an inorganic material-based fiberboard having a heat resistance temperature of approximately 1400°C.

[0025] Each of layers 131, 132, and 133 can be formed by stacking annular (typically circular) members having various outer and inner diameters. The annular members constituting layers 131, 132, and 133 may be formed by combining a plurality of divided pieces separated along a plurality of straight lines extending from the center of the ring to the outer periphery. In this case, in order to improve heat retention, it is preferable to stack the annular members so that the boundaries of the divided pieces of adjacent annular members above and below and inside and outside do not overlap.

[0026] 2 is an enlarged cross-sectional view of the furnace tube 10 and its peripheral members. As shown in Fig. 2, the furnace tube 10 may have a portion 101 including a portion located immediately to the side of the crucible 20 and the other portion 102 made of different materials.

[0027] In this case, the portion 101 close to the crucible 20 preferably has a high thermal conductivity in order to form a desired temperature distribution around the crucible 20 as described above, and is preferably made of a material such as dense high-purity alumina-based ceramics or magnesia-based ceramics. On the other hand, the portion 102 relatively far from the crucible 20 preferably has excellent thermal shock resistance, and is preferably made of a material such as porous zirconia-based ceramics having a lower thermal conductivity than the dense high-purity alumina-based ceramics or magnesia-based ceramics that are the material of the portion 101.

[0028] When the furnace core tube 10 is composed of the portions 101 and 102, the thermal conductivity of the portion 101 is greater than that of the portion 102. Moreover, regardless of the configuration of the furnace core tube 10, the thermal conductivity of the portion of the furnace core tube 10 located directly to the side of the crucible 20 is greater than the thermal conductivity of the inner furnace tube 11.

[0029] 2, a heat insulating material 15 may be placed on the core tube 10. The use of the heat insulating material 15 prevents heat around the crucible 20 from escaping upward, making it easier to form a desired temperature distribution. The heat insulating material 15 is placed on a plate-like member 14 that covers the opening at the upper end of the core tube 10. In order to prevent local sintering or deformation of the heat insulating material 15, a tubular member 18 that covers the sides of the heat insulating material 15 or a plate-like member 19 that covers the top of the heat insulating material 15 may be used. The plate-like member 14 and the plate-like member 19 are typically disk-shaped.

[0030] The heat retaining material 15 is made of, for example, the same material as the heat retaining layer 131. The plate-like member 14, the tubular member 18 and the plate-like member 19 are all made of a material such as alumina-based ceramics or magnesia-based ceramics having a melting point of 1900° C. or higher.

[0031] The crucible 20 is made of a platinum-based alloy such as a platinum-rhodium alloy. Unlike iridium, which is generally used as a material for crucibles for growing gallium oxide crystals, platinum-based alloys hardly oxidize even in an oxygen atmosphere, so gallium oxide can be grown in an air atmosphere by using a crucible 20 made of a platinum-rhodium alloy. Gallium oxide has a weak oxidizing power, and if there is no oxygen in the atmosphere, it will decompose into gallium and oxygen when the temperature approaches its melting point. However, by growing gallium oxide in an air atmosphere containing oxygen, it is possible to obtain a high-quality single crystal of gallium oxide with few oxygen defects.

[0032] The crucible 20 has a shape and size according to the shape and size of the gallium oxide crystal to be grown. For example, when growing a crystal having a cylindrical constant diameter part with a diameter of 2 inches, a cylindrical crucible 20 having an inner diameter of 2 inches is used. When growing a crystal having a constant diameter part with a shape other than a cylindrical shape, such as a square or hexagonal column shape, a crucible 20 having a square or hexagonal column shape is used. A lid for covering the opening of the crucible 20 may be used.

[0033] The crucible support shaft 22 can be moved up and down by a drive mechanism (not shown), and the crucible 20 supported by the crucible support 21 can be moved up and down inside the furnace tube 10. The crucible support shaft 22 may also be rotatable about an axis in the vertical direction by the drive mechanism. In this case, the crucible 20 supported by the crucible support 21 can be rotated inside the furnace tube 10.

[0034] Moreover, the crucible support 21 and the crucible support shaft 22 are tubular members, inside which a thermocouple 26 for measuring the temperature of the crucible 20 passes. The crucible support 21 and the crucible support shaft 22 are both made of a material such as heat-resistant ceramics having a melting point of 1900° C. or higher.

[0035] Fig. 3 is an enlarged cross-sectional view of the crucible 20, the crucible support 21, and the crucible support shaft 22. As shown in Fig. 3, the crucible support 21 preferably has an uppermost block 21a made of zirconia-based ceramics that directly contacts the crucible 20, and a lower block 21b made of alumina-based ceramics that does not contact the crucible 20. Block 21a may be made of a plurality of blocks (blocks 211-213 in the example shown in Fig. 3) that are connected in the vertical direction. Similarly, block 21b may be made of a plurality of blocks (blocks 214-217 in the example shown in Fig. 3) that are connected in the vertical direction.

[0036] Although alumina-based ceramics are excellent as a material for the crucible support 21 in terms of their high thermal conductivity, they have the drawbacks of reacting with platinum-rhodium alloys under high-temperature conditions and of having low thermal shock resistance. For this reason, it is preferable to use zirconia-based ceramics, which do not react with a crucible made of a platinum-rhodium alloy even under high-temperature conditions exceeding 1830°C and have excellent thermal shock resistance, as the material for the block 21a that contacts the crucible 20, and to use alumina-based ceramics as the material for the block 21b provided below the block 21a.

[0037] For example, ZIR-Y manufactured by TEP Corporation can be suitably used as the material for block 21a. Also, for example, 4NA manufactured by TEP Corporation can be suitably used as the material for block 21b. Note that the joining position of block 21a made of zirconia-based ceramics and block 21b made of alumina-based ceramics needs to be selected at a position where no reaction occurs even at high temperatures.

[0038] 4(a) and (b) are respectively a perspective view and a side view of the heating element 23. The heating element 23 is a resistance heating element made of molybdenum disilicide (MoSi2) or the like that is capable of high temperature heating of 1800° C. or more. The heating element 23 has a U-shaped heating part 231 that has a small diameter and generates heat when electricity is applied, and an electrode part 232 that has a larger diameter than the heating part 231 and is used to connect an external device that supplies current to the heating element 23.

[0039] Moreover, the heating element 23 is bent into an L-shape at a bent portion 233 in the electrode portion 232, and a portion closer to the end portion on the electrode portion 232 side than the bent portion 233 is passed through and fixed in holes bored horizontally in the furnace inner tube 11 and the heat retention layer 13. Moreover, in the manufacturing apparatus 1, a plurality of (for example, 4 to 12) heating elements 23 are arranged to surround the furnace core tube 11.

[0040] In the heating element 23, the heating part 231 that generates high heat and the electrode part 232 that supplies current to the heating part 231 and mechanically stably holds the heating part 231 in the high-temperature furnace space are preferably made of the same or almost the same material, but the electrode part 232 is preferably several times larger in thickness (cross-sectional area) than the heating part 231. For example, when the ratio D1 / D2 of the diameter D1 of the heating part 231 to the diameter D2 of the electrode part 232 is set to 0.5 or less, the cross-sectional area of ​​the heating part 231 is 1 / 4 or less of the cross-sectional area of ​​the electrode part 232. In such a case, the mechanical strength of the electrode part 232 is four times or more than the mechanical strength of the heating part 231, and the heat generation amount per unit length of the heating part 231 is four times or more than the heat generation amount per unit length of the electrode part 232, thereby satisfying the function of the heating element 23 in terms of both heat generation amount and mechanical strength. For this reason, it is preferable that D1 / D2 is 0.5 or less. However, taking into consideration the required amount of expensive materials, it is preferable that D1 / D2 is close to 0.5, and preferably is 0.4 or more.

[0041] In addition, it is preferable that the portion of the heating element 23 penetrating the inner furnace tube 11 and the heat-retaining layer 13 is inserted into a pipe 24 made of sapphire or the like. By using the pipe 24, the heating element 23 can be thermally and electrically isolated from the inner furnace tube 11, and the reaction between the heating element 23 and the inner furnace tube 11 can be suppressed. When the inner furnace tube 11 is made of zirconia-based ceramics, the reaction between the inner furnace tube 11 and the pipe 24 can be suppressed by using the pipe 24 made of sapphire. In addition, sapphire is preferable as a material for the pipe 24 because it does not soften even at high temperatures of about 1800°C. In addition, the bent portion 233 of the heating element 23 can be mechanically supported by the pipe 24, and damage to the heating element 23 can be suppressed. FIG. 5 is a photograph showing an example of mounting the heating element 23 to the manufacturing apparatus 1.

[0042] The manufacturing apparatus 1 also includes a thermocouple 25 for measuring the temperature of the heating element 23. The thermocouple 25 is inserted into the apparatus through holes bored horizontally in the furnace inner tube 11 and the thermal insulation layer 13, and its tip is placed at approximately the same position as the heating part 231 of the heating element 23.

[0043] 6 is a vertical cross-sectional view of a manufacturing apparatus 2 which is a variation of the gallium oxide crystal manufacturing apparatus 1 relating to the embodiment of the present invention. Manufacturing apparatus 2 differs from manufacturing apparatus 1 mainly in the configuration of the heat retention layer.

[0044] The heat retention layer 13 of the manufacturing apparatus 2 is vertically separated into two layers, an upper heat retention layer 13a and a lower heat retention layer 13b. Typically, as shown in Fig. 6, the heat retention layer 13a covers the upper side of the inner furnace tube 11, and the heat retention layer 13b covers the sides and the lower side of the inner furnace tube 11.

[0045] The thermal insulation layer 13a is placed away from the thermal insulation layer 13b by means of thermal insulation material support plates 31, 32, 33, 36 on which it is placed, a base 34 covering the upper surface of the thermal insulation layer 13a and supporting the outermost thermal insulation material support plate 33, and a suspending member 35 fixed to the base 34 and suspending the entire thermal insulation layer 13a by suspending the base 34 and the thermal insulation material support plate 36. This forms a gap 38 between the thermal insulation layer 13a and the thermal insulation layer 13b, making it possible to suppress mutual interference caused by the expansion and contraction in the vertical direction of the layers 131, 132, 133 resulting from the difference in the thermal expansion coefficients of the layers 131, 132, 133 constituting the thermal insulation layer 13a.

[0046] More specifically, in the region outside the heating element 37, the heat-insulating material support plate 33 is supported by the vertically moving base 34, and a part of the heat-insulating layer 133, the heat-insulating material support plate 32, a part of the heat-insulating layer 132, the heat-insulating material support plate 31, and a part of the heat-insulating layer 131 are placed on top of the heat-insulating material support plate 33 in this order.

[0047] In addition, the heights of the separation surfaces of layers 131, 132, and 133 of heat-insulating layer 13a and heat-insulating layer 13b are made different to form a stepped separation surface between heat-insulating layer 13a and heat-insulating layer 13b. This allows the interval between heat-insulating layer 13a and heat-insulating layer 13b to be adjusted so that gap 38 between heat-insulating layer 13a and heat-insulating layer 13b does not continue horizontally from the inside to the outside of heat-insulating layer 13, thereby suppressing the outflow of heat from gap 38 to the outside of the device.

[0048] The method of providing the heat-insulating layers 13a and 13b with gaps therebetween is not limited to the method shown in FIG.

[0049] In the example shown in FIG. 6, a linear heating element 37 is used in the manufacturing apparatus 2. The heating element 37 has a heating part 371 and an electrode part 372 similar to the heating part 231 and the electrode part 232 of the heating element 23, and is inserted into the apparatus through holes formed vertically in the base 34, the heat-retaining layer 13a, and the heat-retaining material support plate 31, and is fixed therein. Similarly to the manufacturing apparatus 1, an L-shaped heating element 23 may be used by passing it through a hole provided in the heat-retaining layer 13a. FIG. 7(a) is a photograph of the linear heating element 37. FIG. 7(b) is a photograph showing an example of mounting the heating element 37 to the manufacturing apparatus 2.

[0050] 8 is a vertical cross-sectional view of manufacturing apparatus 3, which is a modified example of gallium oxide crystal manufacturing apparatus 2 pertaining to an embodiment of the present invention. Manufacturing apparatus 3 differs from manufacturing apparatus 2 mainly in that upper heat-retaining layer 13a and lower heat-retaining layer 13b are in contact with each other with no gap in the vertical direction.

[0051] The heat retention layer 13 of the manufacturing equipment 3, like the heat retention layer 13 of the manufacturing equipment 2, can be vertically separated into two, an upper heat retention layer 13a and a lower heat retention layer 13b, and the upper heat retention layer 13a can move vertically together with the heating element 37. On the other hand, unlike the heat retention layer 13 of the manufacturing equipment 2, when the upper heat retention layer 13a is placed on the lower heat retention layer 13b, the heat retention layer 13a and the heat retention layer 13b are in contact with each other without any gaps in the vertical direction. This has the advantage that heat dissipation is more effectively suppressed and there is no need to check the state of the gap between the heat retention layer 13a and the heat retention layer 13b. In addition, in the manufacturing equipment 3, the upper heat retention layer 13a is layered using only the heat insulating material without using the heat retention material support plates 31, 32, and 36 made of alumina-based ceramics, so that the gap around the electrode part 372 of the heating element 37 can be minimized, and heat dissipation can be effectively suppressed. In this way, the manufacturing apparatus 3 can suppress heat radiation more effectively than the manufacturing apparatus 2, and therefore can easily reach the desired temperature during crystal growth. Furthermore, in the manufacturing apparatus 3, even if the heat insulating material of the heat retention layer 13a deteriorates, it can be dealt with by simply replacing several inner peripheral parts of the stage, so that the maintenance cost can be reduced.

[0052] (Method of manufacturing gallium oxide crystals) First, gallium oxide raw material such as a β-Ga2O3 sintered body is placed in the crucible 20. In order to obtain good quality crystals, the purity of the gallium oxide raw material is preferably 5N or more. At this time, a seed crystal may or may not be placed at the bottom of the crucible 20. The orientation of the surface that serves as the base for crystal growth of the seed crystal used here may be any orientation in addition to the main surface orientations of β-Ga2O3, which are (100), (010), and (001), and β-Ga2O3 of any orientation can be grown from these seed crystals.

[0053] Next, the inside of the manufacturing apparatus 1 (inside the heat retention layer 13) is heated by the heating element 23, and a temperature gradient is formed around the crucible 20 such that the temperature is higher on the upper side and lower on the lower side, thereby melting the raw material gallium oxide in the crucible 20. Specifically, a temperature distribution is formed such that the temperature gradient in the vertical direction near the melting point of gallium oxide (approximately 1795°C) is 0.2 to 10°C / cm. The manufacturing apparatuses 1, 2, and 3 equipped with the furnace core tube 10 and the furnace inner tube 11 can stably form a temperature distribution with such a low temperature gradient, and therefore can grow a gallium oxide single crystal having a large size with a constant diameter part having a diameter of 2 inches or more and having few crystal defects.

[0054] In a typical method, first, the height of the crucible 20 is adjusted by moving the crucible support shaft 22 up and down so that the temperature of the upper region in the crucible 20 is equal to or higher than the melting point of gallium oxide. This causes a part of the upper side of the raw material in the crucible 20 to melt. Next, the crucible support shaft 22 is moved upward to melt the raw material to the lower side while raising the crucible 20 at a predetermined speed (for example, 0.5 to 15 mm / h), and finally, the whole of the raw material and a part of the seed crystal are melted. Next, the crucible support shaft 22 is moved downward to lower the crucible 20 at a predetermined speed (for example, 0.5 to 15 mm / h), and the melt is crystallized from the lower side (seed crystal side) to grow a single crystal. Note that, when melting the raw material or crystallizing the melt, in addition to raising and lowering the crucible 20, the temperature inside the manufacturing apparatus 1 may be raised and lowered by controlling the heating temperature of the heating element 23. After the gallium oxide melt has completely crystallized, the crucible 20 is peeled off to remove the grown crystal.

[0055] The above gallium oxide crystal is grown in an air atmosphere or a mixed gas atmosphere of O2 gas and an inert gas or neutral gas. By supplying an oxygen concentration adjusting gas to keep the oxygen concentration in the high temperature zone of 1770°C or higher in the range of more than 20% and less than 50%, it is possible to grow a crystal with fewer oxygen defects than when grown in an air atmosphere with an oxygen concentration of about 20%.

[0056] (Gallium oxide crystal and wafer characteristics) By growing a crystal using the manufacturing apparatuses 1, 2, and 3 according to the present embodiment described above, a cylindrical gallium oxide single crystal (ingot) with a diameter portion of 2 inches or more can be obtained, from which circular gallium oxide single crystal wafers with a diameter of 2 inches or more can be cut.

[0057] Furthermore, by growing a crystal using the manufacturing apparatuses 1, 2, and 3 according to the present embodiment, a cylindrical gallium oxide single crystal can be obtained whose constant diameter portion has a diameter of up to about 8 inches. For example, by installing an inner furnace tube 11 into which a crucible 20 of a desired size can be inserted and enlarging the inner diameter of the heat-retaining layer 13 in the radial direction, a gallium oxide single crystal can be obtained whose constant diameter portion has any diameter up to about 8 inches.

[0058] It is also possible to grow a crystal whose constant diameter portion is prismatic. In that case, it is preferable to grow a crystal whose cross section perpendicular to the crystal growth direction of the constant diameter portion is large enough to fit a circle having a diameter of 2 inches or more, so that a circular wafer having a diameter of 2 inches or more can be cut out. For example, when growing a crystal whose constant diameter portion is a square prism, it is preferable to grow a crystal whose cross section perpendicular to the crystal growth direction is a square with one side of 2 inches or more.

[0059] The Ir concentration in the gallium oxide single crystal according to the present embodiment and the wafer cut therefrom, which are obtained by crystal growth using the manufacturing apparatuses 1, 2, and 3 according to the present embodiment, is 0.01 ppm or less. Here, ppm is a weight ratio. In addition, 0.01 ppm is the detection limit of a GDMS (glow discharge mass spectrometry) measuring device, and being 0.01 ppm or less means that Ir could not be detected by the GDMS measuring device.

[0060] The Ir concentration in the gallium oxide single crystal and wafer according to the present embodiment is low because the crucible 20 made of a platinum-based alloy that does not contain Ir is used. When a crucible made of Ir is used instead of the crucible 20, the Ir concentration in the obtained gallium oxide single crystal is several to several tens of ppm.

[0061] Since the Ir concentration in the gallium oxide single crystal and wafer according to the present embodiment is low, the decrease in carrier mobility due to impurity scattering is suppressed. In addition, since the Ir concentration is low, there are few voids. It is believed that the reason why the gallium oxide single crystal grown by the EFG method using a crucible made of Ir contains many voids is because the Ir concentration is high. In addition, a low Ir concentration reduces light scattering by Ir, which is advantageous for optical applications.

[0062] The gallium oxide single crystal wafer according to the present embodiment has a dislocation density of 1000 pieces / cm 2 The average half-width of the XRD diffraction peak of the (001) plane of the gallium oxide single crystal and wafer according to the present embodiment is 20 arcsec or less.

[0063] When a crucible 20 made of a platinum-rhodium alloy is used, the Rh concentration in the gallium oxide single crystal and wafer according to the present embodiment falls within the range of 10 ppm to 40 ppm. Rh in gallium oxide acts as an acceptor, which is advantageous when used as a material for a high-resistance substrate.

[0064] The Rh concentration in the gallium oxide single crystal according to the present embodiment is characterized by being almost uniform along the length direction (crystal growth direction) and the radial direction. The gradient of the Rh concentration is greatest in the length direction of the gallium oxide single crystal, and since the Rh concentration in the gallium oxide single crystal is within the range of 10 ppm to 40 ppm as described above, the difference between the maximum and minimum values ​​of the Rh concentration in the length direction is 30 ppm or less. The difference between the maximum and minimum values ​​of the Rh concentration in the radial direction is far smaller than the difference between the maximum and minimum values ​​of the Rh concentration in the length direction. Therefore, the Rh concentration in the plane of the wafer cut out from the gallium oxide single crystal is almost uniform, and the variation in the Rh concentration between the wafers is small. For example, when a high resistance substrate made of gallium oxide is generally formed, Fe or Mg is added, but the uniformity of the Rh concentration in the plane direction of the gallium oxide single crystal wafer according to the present embodiment is higher than the uniformity of the Fe or Mg concentration in the plane direction in that case.

[0065] Furthermore, by growing a crystal using the manufacturing apparatuses 1, 2, and 3 according to the present embodiment, it is possible to grow a gallium oxide single crystal that is a size from which the above-mentioned wafers having a diameter of 2 inches or more can be cut, and that does not contain twins.

[0066] In addition, according to the crystal growth using the manufacturing apparatuses 1, 2, and 3 according to the present embodiment, when 0.1 mol% or more of Sn is added to a raw material of gallium oxide having a purity of 5N or more, the n-type carrier concentration in the gallium oxide single crystal and wafer is 3×10 18 cm -3 This carrier concentration can be said to be suitable as the carrier concentration of an n-type low-resistance semiconductor substrate required for fabricating a Schottky barrier diode.

[0067] (Effects of the embodiment) According to the manufacturing apparatuses 1, 2, and 3 equipped with the furnace core tube 10 and the furnace inner tube 11 of the above-described embodiment, it is possible to grow a gallium oxide single crystal having a large size capable of cutting out circular wafers having a diameter of 2 inches or more and having few crystal defects that are a cause of deterioration of crystal quality. EXAMPLES

[0068] The following describes the evaluation results of the properties of the gallium oxide single crystal (ingot) obtained by crystal growth using the manufacturing apparatus according to the present embodiment and the wafers cut out therefrom. The gallium oxide single crystal according to this embodiment is a β-Ga2O3 single crystal grown by placing a seed crystal made of a β-Ga2O3 single crystal at the bottom of a crucible 20 made of a platinum-rhodium alloy with a cylindrical constant diameter portion.

[0069] Figure 9 is a photograph of two β-Ga2O3 single crystals, among the gallium oxide single crystals according to this embodiment, in which the constant diameter portion is cylindrical with a diameter of 2 inches, and two wafers cut out from them. The two gallium oxide single crystals shown in Figure 9 both have a (001) plane in the radial cross section of the constant diameter portion, and by slicing in the radial direction, wafers with a (001) plane main surface can be cut out.

[0070] FIG. 10(a) is a photograph of a β-Ga2O3 single crystal of the gallium oxide single crystal according to this embodiment, in which the constant diameter part is cylindrical with a diameter of 2 inches and the cross section in the radial direction of the constant diameter part is a (100) plane. FIG. 10(b) is a photograph of a processed wafer cut out from the β-Ga2O3 single crystal of FIG. 10(a) and having a main surface of a (100) plane. FIG. 11(a) is a photograph of a β-Ga2O3 single crystal of the gallium oxide single crystal according to this embodiment, in which the constant diameter part is cylindrical with a diameter of 2 inches and the cross section in the radial direction of the constant diameter part is a (010) plane. FIG. 11(b) is a photograph of a processed wafer cut out from the β-Ga2O3 single crystal of FIG. 11(a) and having a main surface of a (010) plane.

[0071] FIG. 12 is a photograph of a β-Ga2O3 single crystal (right side) grown using manufacturing apparatus 1, in which the constant-diameter portion is cylindrical with a diameter of 3 inches and the cross section in the radial direction of the constant-diameter portion is the (010) plane, and a β-Ga2O3 single crystal (left side) grown using manufacturing apparatus 3, in which the constant-diameter portion is cylindrical with a diameter of 4 inches and the cross section in the radial direction of the constant-diameter portion is the (010) plane.

[0072] In addition, a 2-inch diameter β-Ga2O3 single crystal grown in the (100) plane orientation using a manufacturing apparatus according to an embodiment of the present invention and a processed wafer cut from it are disclosed in the non-patent document K. Hoshikawa, T. Kobayashi, Y. Matsuki, E. Ohba, T. Kobayashi, “2-inch diameter of (100) β-Ga2O3 crystal growth by the vertical Bridgman technique in a resistance heating furnace in ambient air”, Journal of Crystal Growth 545 (2020) 125724. In addition, the growth results of β-Ga2O3 single crystals with the (100), (010), and (001) plane orientations are disclosed in the non-patent document Etsuko Ohba, Takumi Kobayashi, Toshinori Taishi, Keigo Hoshikawa, “Growth of (100), (010) and (001) β-Ga2O3 single crystals by vertical Bridgman method”, Journal of Crystal Growth 556 (2021) 125990.

[0073] Fig. 13 is an observation image by X-ray topography of a gallium oxide single crystal wafer doped with 0.2 mol % Sn and having a (001) principal surface, cut from a gallium oxide single crystal according to this embodiment obtained by crystal growth using the manufacturing apparatus 1. Figs. 14(a) to (d) are (001) plane diffraction peaks obtained by X-ray rocking curve measurement in regions 1 to 4 on the wafer shown in Fig. 13, respectively.

[0074] The half-widths (degrees, arcsec) of the (001) plane diffraction peaks in regions 1 to 4 shown in FIGS.

[0075] [Table 1]

[0076] Fig. 15 is an optical photograph of a gallium oxide single crystal wafer according to this embodiment, doped with 0.2 mol % Sn and having a (001) principal surface, obtained by crystal growth using the manufacturing apparatus 1. Fig. 16 is a graph showing the distribution of half-widths of the (001) diffraction peaks on the wafer shown in Fig. 15, obtained by X-ray rocking curve measurement. The "upper", "middle" and "lower" sections of Fig. 16 are the half-widths of the diffraction peaks measured at 1 mm x 1 mm intervals along the lines A, B and C shown in Fig. 15, respectively.

[0077] It is believed that crystal defects exist where the half-width is high. For this reason, according to Fig. 16, it is believed that there are no crystal defects in the upper row, crystal defects exist in the range of 20 to 25 mm in the middle row, and crystal defects exist in the ranges of -10 to -5 mm, 0 to 5 mm, and 15 to 20 mm in the lower row. It should be noted that the concentration of Sn in the gallium oxide single crystal wafer does not affect the half-width of the diffraction peak.

[0078] FIG. 17 is a graph showing the distribution of dislocation density on the wafer shown in FIG. 15. The "upper", "middle" and "lower" rows of FIG. 17 are dislocation densities measured at intervals of 1 mm x 1 mm along lines A, B and C shown in FIG. 15, respectively. The dislocation density was measured by etching the surface of the wafer with potassium hydroxide (KOH) and observing the etch pits that appeared. According to FIG. 17, the dislocation density was 1000 pcs / cm 2 The wafer contains multiple 1 mm x 1 mm areas that are:

[0079] Figures 18(a) to (c) are images observed by an optical microscope showing examples of etch pits that appeared on the wafer surface. Here, bullet-shaped etch pits with cores as shown in Figures 18(a) and (b) were determined to be caused by dislocations, and the number of such etch pits was counted as the number of dislocations. On the other hand, the etch pit without a core as shown in Figure 18(c) was not determined to be caused by dislocations. Note that the magnifications of the images observed in Figures 18(a) to (c) are the same.

[0080] Figures 19(a), (b), and (c) are graphs showing the distribution of the half-width of the (001) plane diffraction peak and the dislocation density in the upper, middle, and lower rows of the wafer shown in Figure 15. Figures 19(a), (b), and (c) show that the dislocation density is 1000 / cm at the position where the half-width of the (001) plane diffraction peak is particularly large. 2 Since the distribution trends are similar, it is believed that there is a correlation between the half-width of the (001) diffraction peak and the dislocation density. Note that the distribution trends do not match near -10 mm in Figure 19(c), but this is believed to be because depressions caused by factors other than crystallinity (such as polishing marks) were determined to be etch pits caused by dislocations.

[0081] Next, the concentrations of impurities contained in the gallium oxide single crystal according to this embodiment measured by GDMS are shown. Table 2 shows the concentrations of impurities contained in the gallium oxide single crystal wafer not intentionally doped with Sn, Table 3 shows the concentrations of impurities contained in the gallium oxide single crystal wafer doped with 0.05 mol% Sn, Table 4 shows the concentrations of impurities contained in the gallium oxide single crystal wafer doped with 0.1 mol% Sn, and Table 5 shows the concentrations of impurities contained in the gallium oxide single crystal wafer doped with 0.2 mol% Sn. The unit of concentration "ppm" is the weight ratio.

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] [Table 5]

[0086] As shown in Tables 3 to 5, the Ir concentration contained in these gallium oxide single crystals was 0.01 ppm or less. Also, as shown in Tables 2 to 5, the Rh concentration contained in these gallium oxide single crystals was within the range of 10 ppm or more and 50 ppm or less. This is believed to be due to the use of the crucible 20 made of a platinum-rhodium alloy that does not contain Ir.

[0087] Furthermore, according to Table 2, the Rh concentration at the position where the solidification rate is 0.5 is approximately equal to the Rh concentration at the position where the solidification rate is 0.9.

[0088] The following Table 6 shows the characteristics of nine gallium oxide wafers (specimens A to I) according to this embodiment. In Table 6, "doping amount" refers to the amount of Sn doped. "UID" indicates that Sn was not intentionally doped. "Solidification rate" refers to the solidification rate of the gallium oxide single crystal (ingot) from which the wafer was sliced.

[0089] [Table 6]

[0090] The characteristics of the four gallium oxide single crystals according to this example (referred to as samples J to M) are shown in Table 7. "UID" in Table 7 indicates that Si and Sn were not intentionally doped.

[0091] [Table 7]

[0092] According to Tables 6 and 7, the n-type carrier concentration of Sample A and Sample K is 3×10 18 cm -3 That is, by growing a crystal using the manufacturing apparatuses 1 and 2 according to the embodiment of the present invention, the n-type carrier concentration is 3×10 18 cm -3 The above gallium oxide single crystal and wafers cut therefrom can be obtained.

[0093] The characteristics of the β-Ga2O3 single crystals and wafers according to the above-mentioned embodiments of the present invention are disclosed, along with scientific considerations, in the non-patent document K. Hoshikawa, T. Kobayashi, E. Ohba, T. Kobayashi, “50 mm diameter Sn-doped (001) β-Ga2O3 crystal growth using the vertical Bridgeman technique in ambient air”, Journal of Crystal Growth 546 (2020) 125778.

[0094] Although the embodiment and examples of the present invention have been described above, the present invention is not limited to the above embodiment and examples, and various modifications can be made without departing from the spirit and scope of the invention.

[0095] In addition, the above-described embodiments and examples do not limit the scope of the invention according to the claims. It should be noted that not all of the combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention. [Explanation of symbols]

[0096] Reference Signs List 1, 2, 3... manufacturing apparatus, 10... furnace core tube, 11... furnace inner tube, 14... plate-shaped member, 15... heat-insulating material, 20... crucible, 21... crucible support, 22... crucible support shaft, 23... heating element, 231... heating section

Claims

1. a crucible for containing a source of gallium oxide; A crucible support that supports the crucible from below; a crucible support shaft connected to the crucible support from below and supporting the crucible and the crucible support so as to be movable in the up and down direction; a tubular furnace tube surrounding the crucible, the crucible support, and the crucible support shaft; a tubular furnace inner tube surrounding the furnace core tube; a resistance heating element having a heating portion disposed in a space between the furnace core tube and the furnace inner tube; Equipped with The melting point of the furnace core tube and the furnace inner tube is 1900° C. or higher, the thermal conductivity of a portion of the furnace core tube located immediately beside the crucible is higher than the thermal conductivity of the furnace inner tube; the furnace tube has a first portion including a portion located immediately to the side of the crucible, and a second portion other than the first portion; the first portion has a higher thermal conductivity than the second portion; Gallium oxide crystal manufacturing equipment.

2. a plate-shaped member covering an opening at an upper end of the furnace tube; A heat insulating material installed on the plate-like member; Equipped with An apparatus for producing gallium oxide crystals according to claim 1.

3. a portion of the furnace tube located immediately to the side of the crucible is made of alumina-based ceramics or magnesia-based ceramics, The furnace inner tube is made of zirconia-based ceramics. The apparatus for producing gallium oxide crystals according to claim 1 or 2.

4. The crucible is made of a platinum-based alloy. The gallium oxide crystal manufacturing apparatus according to any one of claims 1 to 3.

5. the crucible support has a first block made of zirconia-based ceramics at the top in direct contact with the crucible, and a second block made of alumina-based ceramics below the first block and not in contact with the crucible; The apparatus for producing gallium oxide crystals according to claim 4.

6. The furnace inner tube is surrounded by heat-retaining layers from the sides and above and below, The heat retention layer is vertically separated into an upper heat retention layer and a lower heat retention layer, The upper heat-insulating layer and the lower heat-insulating layer are arranged with a gap therebetween in the vertical direction, and the gap is not horizontally continuous from the inside to the outside of the heat-insulating layer. The apparatus for producing gallium oxide crystals according to any one of claims 1 to 5.

7. The furnace inner tube is surrounded by heat-retaining layers from the sides and above and below, The thermal insulation layer can be separated into two layers, an upper thermal insulation layer and a lower thermal insulation layer, in the vertical direction. When the upper thermal insulation layer is placed on the lower thermal insulation layer, the upper thermal insulation layer and the lower thermal insulation layer are in contact with each other without any gaps in the vertical direction. The apparatus for producing gallium oxide crystals according to any one of claims 1 to 5.

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