Apparatus for growing single crystal, and method for producing single crystal

Abstract

This apparatus 10a for growing a single crystal comprises: a growing vessel 20; a heat-insulating material 30 for retaining heat; and a cylindrical heat-insulating material 40 for soaking. The growing vessel 20 comprises: a crucible 22 for holding a sublimation raw material 12; a pedestal 24 for holding a seed crystal 14; a cylindrical member 26; and a lower heater 28. The heat-insulating material 30 for retaining heat comprises: an upper temperature measurement hole 32 that is provided on the upper surface of the heat-insulating material 30; and a lower temperature measurement hole 34 that is provided on the bottom surface of the heat-insulating material 30. The cylindrical heat-insulating material 40 for soaking is inserted into a region where the sublimation raw material 12 can be heated to a uniform temperature and a temperature difference necessary for growing a single crystal can be formed between the sublimation raw material 12 and the seed crystal 14. This method for producing a single crystal comprises a step for growing a bulk single crystal by a sublimation method using the device 10a for growing a single crystal.

Description

Single crystal growth apparatus and method for manufacturing a single crystal

[0001] The present invention relates to a single crystal growth apparatus and a method for manufacturing a single crystal, and more particularly, to a single crystal growth apparatus capable of growing a large-diameter single crystal and a method for manufacturing a single crystal using the same.

[0002] SiC single crystals and AlN single crystals are generally manufactured using the sublimation method. Here, the "sublimation method (also called sublimation recrystallization method or sublimation reprecipitation method)" refers to a method of sublimating a sublimation raw material and re-precipitating (condensing) the sublimation gas on the surface of a seed crystal. In order to manufacture a single crystal using the sublimation method, it is necessary to make the temperature of the seed crystal lower than the temperature of the sublimation raw material. In addition, since the sublimation gas generated from the sublimation raw material is highly corrosive, the crucible holding the sublimation raw material deteriorates due to the sublimation gas, and the deterioration products may cause inclusions in the single crystal. Therefore, various proposals have been made conventionally to solve this problem.

[0003] For example, Patent Document 1 discloses a silicon carbide single crystal manufacturing apparatus in which a temperature distribution forming member for making the temperature distribution on the surface of a seed crystal asymmetric with respect to the center of a crucible is arranged around the seed crystal arranged at the center of the crucible. This document describes that (A) when a temperature distribution forming member is arranged around the seed crystal, the region where screw dislocations of the seed crystal can occur can be maintained at a low temperature, and (B) thereby, the generation of polytypes and crystals with different orientations can be suppressed.

[0004] Patent Document 2 discloses a crucible for manufacturing a silicon carbide single crystal in which a part of the inner wall surface of a graphite crucible is covered with a graphite sheet. This document describes that (A) when the graphite crucible is used as it is for the growth of a silicon carbide single crystal, the surface of the graphite crucible deteriorates, and graphite fine particles as deterioration products cause carbon inclusion in the silicon carbide single crystal, and (B) when a part of the inner wall of the graphite crucible is covered with a graphite sheet, carbon inclusion in the silicon carbide single crystal can be suppressed.

[0005] In recent years, 150 mm has become the standard size for SiC wafers used in power semiconductor applications, and is soon moving towards 200 mm. Consequently, the diameter of the bulk crystals used in bulk SiC single crystal growth, as well as the diameter of the crucibles used for growth, have also increased. However, as the raw material crucibles become larger, uniform heating of the crucibles is becoming increasingly difficult. In particular, when heating raw material crucibles using high-frequency induction heating, uniform heating of large-diameter crucibles is challenging. Non-uniformity of the raw material temperature leads to uneven generation of sublimation gas, resulting in reduced raw material utilization efficiency (<50%). Furthermore, non-uniformity of the raw material temperature also limits the growth height of SiC single crystals (h < 30 mm).

[0006] Japanese Patent Publication No. 2011-011926 Japanese Patent Publication No. 2014-122140

[0007] The problem that this invention aims to solve is to provide a single crystal manufacturing apparatus capable of efficiently producing large-diameter single crystals. Another problem that this invention aims to solve is to provide a method for manufacturing single crystals using such a single crystal manufacturing apparatus.

[0008] To solve the above problems, the single crystal growth apparatus according to the present invention has the following configuration: (1) The single crystal growth apparatus comprises a growth container for growing a single crystal, a heat insulating material for heat retention covering the top, side and bottom surfaces of the growth container, and a cylindrical heat-uniform insulating material inserted between the outer surface of the growth container and the inner surface of the heat insulating material. (2) The growth container comprises a crucible for holding a sublimation raw material, which also serves as a heating element that generates heat by high-frequency induction heating, and a base for holding a seed crystal, which is positioned above the crucible. (3) The heat insulating material for heat retention has an upper temperature measuring hole provided on its top surface and a lower temperature measuring hole provided on its bottom surface. (4) The cylindrical heat-uniform insulating material is inserted in a region that can heat the sublimation raw material to a uniform temperature and create a temperature difference between the sublimation raw material and the seed crystal necessary for growing a single crystal.

[0009] The method for manufacturing a single crystal according to the present invention comprises a step of growing a bulk single crystal by sublimation using a single crystal growth apparatus according to the present invention.

[0010] By placing heat-insulating material around the growth vessel for growing single crystals, inserting a cylindrical heat-uniform insulation material between the growth vessel and the heat-insulating material, and optimizing the length of the cylindrical heat-uniform insulation material, the sublimation raw material can be heated uniformly, and an appropriate temperature difference can be formed between the sublimation raw material and the seed crystal. As a result, raw material utilization efficiency is improved even when using a large-diameter crucible. Furthermore, even when growing large-diameter single crystals, a high growth height can be achieved.

[0011] This is a schematic diagram of a single crystal growth apparatus according to the first embodiment of the present invention. This is a schematic diagram of a single crystal growth apparatus according to the second embodiment of the present invention. This is a schematic diagram of a single crystal growth apparatus according to the third embodiment of the present invention. This is a schematic diagram of a single crystal growth apparatus of Comparative Example 1.

[0012] Figure 5(A) is a photograph of the external appearance of the cylindrical heat-uniform insulation material. Figure 5(B) is a photograph of the external appearance of the plate-shaped heat-uniform insulation material placed on the heat-insulating insulation material. Figure 5(C) is a photograph of the external appearance of the temperature sensor inserted into the lower temperature sensing hole of the heat-insulating insulation material. This is a schematic diagram of the configuration of the single crystal growth apparatus used in the computer simulation. This is a diagram showing the relationship between the thickness of the cylindrical heat-uniform insulation material and the initial growth rate.

[0013] [Configuration 1] A single crystal growth apparatus having the following configuration: (1) The single crystal growth apparatus comprises a growth container for growing a single crystal, a heat insulating material covering the top, side and bottom surfaces of the growth container, and a cylindrical heat-uniform insulating material inserted between the outer surface of the growth container and the inner surface of the heat insulating material. (2) The growth container comprises a crucible for holding a sublimation raw material, which also serves as a heating element that generates heat by high-frequency induction heating, and a base for holding a seed crystal, positioned above the crucible. (3) The heat insulating material comprises an upper temperature measuring hole provided on the top surface and a lower temperature measuring hole provided on the bottom surface. (4) The cylindrical heat-uniform insulating material is inserted in a region that can heat the sublimation raw material to a uniform temperature and create a temperature difference between the sublimation raw material and the seed crystal necessary for growing a single crystal.

[0014] [Configuration 2] The single crystal growth apparatus according to Configuration 1, wherein the cylindrical heat-uniform insulation material is a graphite sheet or a laminate thereof.

[0015] [Configuration 3] The single crystal growth apparatus according to Configuration 1 or 2, wherein the cylindrical heat-uniform insulation material has a thermal conductivity of 30 W / (m·K) or less in the thickness direction at room temperature and a thermal conductivity of 100 W / (m·K) or more in the in-plane direction at room temperature.

[0016] [Configuration 4] The single crystal growth apparatus according to any one of Configurations 1 to 3, wherein the cylindrical heat-uniform insulation material has a thickness of 1 mm or more and 50 mm or less.

[0017] [Configuration 5] The single crystal growth apparatus according to any one of Configurations 1 to 4, wherein the growth vessel further comprises a cylindrical member inserted between the crucible and the base.

[0018] [Configuration 6] The single crystal growth apparatus according to Configuration 5, wherein the cylindrical heat-uniform insulating material is inserted in the region from the lower end of the crucible to the upper end of the crucible.

[0019] [Configuration 7] The single crystal growth apparatus according to any one of Configurations 1 to 6, wherein the growth vessel further comprises a lower heater located at the bottom of the crucible, which generates heat by the high-frequency induction heating.

[0020] [Configuration 8] The single crystal growth apparatus according to Configuration 7, wherein the cylindrical heat-uniform insulating material is inserted in the region from the lower end of the lower heater to the upper end of the crucible.

[0021] [Configuration 9] The single crystal growth apparatus according to configuration 7 or 8, further comprising a plate-shaped heat-uniform insulation material inserted between the outer bottom surface of the lower heater and the inner bottom surface of the heat-insulating material.

[0022] [Configuration 10] The single crystal growth apparatus according to Configuration 9, wherein the plate-shaped heat-uniform insulation material is a graphite sheet or a laminate thereof.

[0023] [Configuration 11] The single crystal growth apparatus according to Configuration 9 or 10, wherein the plate-shaped heat-uniform insulation material has a thermal conductivity of 30 W / (m·K) or less in the thickness direction at room temperature and a thermal conductivity of 100 W / (m·K) or more in the in-plane direction at room temperature.

[0024] [Configuration 12] The single crystal growth apparatus according to any one of Configurations 9 to 11, wherein the plate-shaped heat-uniform insulation material has a thickness of 1 mm or more and 50 mm or less.

[0025] [Configuration 13] A single crystal growth apparatus according to any one of configurations 1 to 12, further comprising a temperature measuring material inserted into the lower temperature measuring hole.

[0026] [Configuration 14] The single crystal growth apparatus according to Configuration 13, wherein the temperature measuring material consists of (a) a graphite sheet or a laminate thereof, or (b) a molded body of glassy carbon, coal, charcoal, or porous carbon.

[0027] [Configuration 15] The single crystal growth apparatus according to configuration 13 or 14, wherein the temperature measuring material has a thermal conductivity in the thickness direction at room temperature of 10 W / (m·K) or less.

[0028] [Configuration 16] The single crystal growth apparatus according to any one of Configurations 13 to 15, wherein the temperature measuring material has a thickness of 1 mm or more and 50 mm or less.

[0029] [Configuration 17] A method for manufacturing a single crystal, comprising a step of growing a bulk single crystal by sublimation using a single crystal growth apparatus described in any one of Configurations 1 to 16.

[0030] [1. Single Crystal Manufacturing Apparatus (1)] Figure 1 shows a schematic diagram of a single crystal growth apparatus according to the first embodiment of the present invention. In Figure 1, the single crystal growth apparatus 10a comprises a growth container 20, a heat-insulating material 30, and a cylindrical heat-uniforming heat-insulating material 40.

[0031] [1.1. Growth Container] The growth container 20 is a container for growing single crystals. In Figure 1, the growth container 20 comprises a crucible 22, a base 24, a cylindrical member 26, and a lower heater 28.

[0032] [1.1.1. Crucible] [A. Materials] The crucible 22 is for holding the sublimation raw material 12 and also serves as a heating element that generates heat through high-frequency induction heating. The material of the crucible 22 is not particularly limited, as long as it can hold the sublimation raw material 12 and generate heat through high-frequency induction heating. Since the sublimation gas generated from the sublimation raw material 12 is highly corrosive, the material of the crucible 22 is preferably one that has high corrosion resistance to the sublimation gas.

[0033] Examples of crucibles 22 include: (a) a crucible made of isotropic graphite; (b) a crucible made of isotropic graphite with a coating of high-melting-point metal carbides such as TaC and WC formed on its surface; (c) a crucible made of high-melting-point metal carbides such as TaC and WC; and (d) a crucible made of high-melting-point metals such as Ta and W.

[0034] [B. Shape and Dimensions] The shape of the crucible 22 is not particularly limited, as long as it is a shape that allows the sublimation raw material 12 to be heated uniformly. The shape of the crucible 22 may be a bottomed cylindrical shape, or a bottomed n-squared tube (n≧3). In order to promote uniform heating of the sublimation raw material 12, the shape of the crucible 22 is preferably a bottomed cylindrical shape or a bottomed n-squared tube with n of 8 or more. In the example shown in Figure 1, the crucible 22 has a bottomed cylindrical shape.

[0035] The dimensions of the inner and outer surfaces of the crucible 22 are not particularly limited, and the optimal dimensions can be selected according to the purpose. For example, in order to grow a single crystal with a diameter of 150 mm or more, the diameter of the inscribed circle tangent to the inner surface of the crucible 22 is preferably 190 mm or more. Also, in order to grow a single crystal with a diameter of 200 mm or more, the diameter of the inscribed circle tangent to the inner surface of the crucible 22 is preferably 240 mm or more.

[0036] The height of the crucible 22 is not particularly limited, as long as it is high enough to create an appropriate temperature difference between it and the base 24 and to secure space for single crystal growth. In the example shown in Figure 1, the height of the crucible 22 is relatively low and a cylindrical member 26 is inserted between the crucible 22 and the base 24, but this is merely an example. Instead of the configuration shown in Figure 1, the cylindrical member 26 and the crucible 22 may be integrated (i.e., the cylindrical member 26 may be omitted), and the height of the crucible 22 may be relatively high.

[0037] [1.1.2. Base] [A. Materials] The base 24 is for holding the seed crystal 14. The base 24 is positioned above the crucible 20. Here, "positioned above the crucible 20" means that (a) if a cylindrical member 26 is inserted between the crucible 20 and the base 24, the base 24 is placed on the upper end of the cylindrical member 26, and (b) if the cylindrical member 26 is omitted, the base 24 is placed directly on the upper end of the crucible 20. In the example shown in Figure 1, the base 24 is placed on the upper end of the cylindrical member 26.

[0038] The material of the base 24 is not particularly limited, as long as it can hold the seed crystal 14 under single crystal growth conditions and can cool the back surface of the base 24 (the surface opposite to the surface on the sublimation raw material 12 side). Examples of materials for the base 24 include isotropic (CIP molded) graphite, extruded graphite, and molded graphite.

[0039] [B. Shape and Dimensions] The shape of the pedestal 24 is not particularly limited as long as it can hold the seed crystal 14. In the example shown in FIG. 1, the pedestal 24 has a hat-like shape including a convex portion protruding toward the sublimation raw material 12 side and a flange portion formed around the convex portion. Similarly, the dimensions of the pedestal 24 are not particularly limited as long as it can hold the seed crystal 14.

[0040] [1.1.3. Cylindrical Member] [A. Material] The cylindrical member 26 is inserted between the crucible 22 and the pedestal 24. The cylindrical member 26 is not necessarily required. The cylindrical member 26 is used to secure a single crystal growth space between the sublimation raw material 12 and the seed crystal 14 and to form an appropriate temperature difference between the sublimation raw material 12 and the seed crystal 14 when the height of the crucible 22 is relatively low. Therefore, when the crucible 22 has a sufficient height, the cylindrical member 26 can be omitted.

[0041] However, compared with the crucible 22, the cylindrical member 26 closer to the seed crystal 14 and the grown crystal is consumed more severely. In this case, when the crucible 22 and the cylindrical member 26 are integrated, it is necessary to discard the whole. On the contrary, when the crucible 22 and the cylindrical member 26 are separated, only the cylindrical member 26 needs to be replaced, so the material cost can be reduced.

[0042] The material of the cylindrical member 26 is not particularly limited as long as it can secure a single crystal growth space and form a necessary temperature difference under the single crystal growth conditions. Examples of the material of the cylindrical member 26 include isotropic graphite, extruded graphite, molded graphite, etc.

[0043] [B. Shape and Dimensions] The shape of the cylindrical member 26 is not particularly limited as long as it can secure a single crystal growth space and form a necessary temperature difference. In the example shown in FIG. 1, the cylindrical member 26 has a cylindrical shape with a constant thickness. Similarly, the dimensions of the cylindrical member 26 are not particularly limited as long as it can secure a single crystal growth space and form a necessary temperature difference.

[0044] [1.1.4. Lower Heater] [A. Material] The lower heater 28 is a heating element that generates heat by high-frequency induction heating. The lower heater 28 is disposed at the lower part of the crucible 22. The lower heater 28 is not necessarily required. However, when the lower heater 28 is omitted, the temperature of the lower part of the crucible 22 is likely to decrease. On the contrary, when the lower heater 28 is provided at the lower part of the crucible 22, the temperature drop at the lower part of the crucible 22 can be suppressed.

[0045] The material of the lower heater 28 is not particularly limited as long as it functions as a heating element that generates heat by high-frequency induction heating under the conditions of single crystal growth. Examples of the material of the lower heater 28 include isotropic graphite, extruded graphite, and molded graphite.

[0046] [B. Shape and Dimensions] The shape of the lower heater 28 is not particularly limited as long as it can suppress the temperature drop at the lower part of the crucible 22. The lower heater 28 may be cylindrical or may be a cylindrical shape with a bottom. In the example shown in FIG. 1, the lower heater 28 has a shape in which a bottomed cylinder is reversed, and small holes are provided on its top surface. The small holes are used when measuring the temperature of the bottom surface of the crucible 22. Similarly, the dimensions of the lower heater 28 are not particularly limited as long as they can suppress the temperature drop at the lower part of the crucible 22.

[0047] [1.2. Heat Insulating Material for Heat Preservation] [A. Material] The heat insulating material 30 for heat preservation is a heat insulating material for insulating the growth container 20, and is arranged to cover the upper surface, side surface, and bottom surface of the growth container 20. The heat insulating material 30 for heat preservation includes an upper temperature measuring hole 32 provided on the upper surface and a lower temperature measuring hole 34 provided on the bottom surface. The upper temperature measuring hole 32 is for measuring the temperature of the back surface of the pedestal 24 during the growth of the single crystal. The lower temperature measuring hole 34 is for measuring the temperature of the lower surface of the growth container 20 (in the example shown in FIG. 1, the lower surface of the crucible 22) during the growth of the single crystal.

[0048] The material of the heat-insulating material 30 is not particularly limited, as long as it is capable of keeping the growth container 20 warm. Examples of materials for the heat-insulating material 30 include: (a) carbon fiber felt; (b) molded heat-insulating material obtained by impregnating a carbon fiber base material with a resin with a high carbonization rate, molding it into a desired shape, and then curing, carbonizing, and graphitizing the molded body.

[0049] [B. Shape and Dimensions] Since the heat-insulating material 30 needs to cover almost the entire circumference of the growth container 20, the heat-insulating material 30 is not a single piece but is usually divided into multiple parts. In order to cover almost the entire circumference of the growth container 20, it is preferable that the heat-insulating material 30 is divided into upper and lower plate-shaped members and one or more cylindrical members placed between the upper and lower plate-shaped members. Furthermore, in order to increase the heat insulation efficiency of the heat-insulating material 30, it is preferable that there be no gaps between the heat-insulating material 30, the growth container 20 and the cylindrical heat-distributing insulation material 40. The thickness of each part of the heat-insulating material 30 is not particularly limited as long as it is sufficient to keep the growth container 20 warm.

[0050] [1.3. Cylindrical Heat-Uniform Insulation Material] [A. Materials] The cylindrical heat-uniform insulation material 40 is an insulating material for making the temperature of the crucible 22 uniform, and is inserted between the outer surface of the growth container 20 and the inner surface of the heat-retaining insulation material 30. The larger the diameter of the crucible 22, the more difficult it becomes to make the temperature of the crucible 22 uniform. In contrast, by inserting the cylindrical heat-uniform insulation material 40 between the growth container 20 and the molded insulation material 30, the temperature of the crucible 22 can be made more uniform even when the diameter of the crucible 22 is large.

[0051] The material of the cylindrical heat-uniform insulation material 40 is not particularly limited, as long as it is capable of making the temperature of the crucible 22 uniform. The material of the cylindrical heat-uniform insulation material 40 is preferably a graphite sheet or a laminate thereof. A graphite sheet or a laminate thereof has a lower thermal conductivity in the thickness direction compared to its thermal conductivity in the in-plane direction, so heat dissipation from the crucible 22 (especially from the upper or lower end of the crucible 22) is suppressed, and the temperature of the crucible 22 can be made more uniform.

[0052] Here, "graphite sheet" refers to a sheet made by roll-molding flexible, expandable natural graphite, or a molded sheet of artificial graphite. Examples of graphite sheets include: (a) PERMA-FOIL (registered trademark) manufactured by Toyo Tanso, (b) Nikafilm (registered trademark) manufactured by Nippon Carbon, (c) Graphite™ manufactured by Panasonic, and (d) eGRAF manufactured by Graftech. Furthermore, "laminated graphite sheet" refers to a laminate made by overlapping multiple graphite sheets and bonding the graphite sheets together with a graphite-based adhesive.

[0053] The material for the tubular heat-uniform insulation material 40 is preferably one in which the thermal conductivity in the thickness direction at room temperature is 30 W / (m·K) or less, and the thermal conductivity in the in-plane direction at room temperature is 100 W / (m·K) or more. Graphite sheets or laminates thereof usually satisfy these conditions.

[0054] [B. Shape and Dimensions] In order to improve the thermal insulation efficiency of the cylindrical heat-uniform insulation material 40, it is preferable that the shape of the cylindrical heat-uniform insulation material 40 is such that it can be inserted between the crucible 22 and the heat-insulating insulation material 30 without creating gaps between the cylindrical heat-uniform insulation material 40 and the crucible 22, and between the cylindrical heat-uniform insulation material 40 and the heat-insulating insulation material 30. For example, if the crucible 22 is a bottomed cylindrical shape, it is preferable that the cylindrical heat-uniform insulation material 40 is a cylindrical shape in which the inner diameter is slightly larger than the outer diameter of the crucible 22 and the outer diameter is slightly smaller than the inner diameter of the heat-insulating insulation material 30. If a gap is created between the cylindrical heat-uniform insulation material 40 and an adjacent member, the gap may be filled with an insulating material (for example, graphite fiber felt).

[0055] The cylindrical heat-uniform insulation material 40 must be inserted in a region where the sublimation raw material 12 can be heated to a uniform temperature and where the temperature difference necessary for growing a single crystal can be formed between the sublimation raw material 12 and the seed crystal 14. Here, "the cylindrical heat-uniform insulation material 40 is inserted in a region where the sublimation raw material 12 can be heated to a uniform temperature" means that the cylindrical heat-uniform insulation material 40 is inserted in a region where the raw material yield is equal to or greater than that when a single crystal is grown under the same conditions except that the cylindrical heat-uniform insulation material 40 is not used. Furthermore, "the cylindrical heat-uniform insulation material 40 is inserted in a region where the temperature difference necessary for growing a single crystal can be formed between the sublimation raw material 12 and the seed crystal 14" means that the cylindrical heat-uniform insulation material 40 is inserted in a region where the growth rate of the single crystal is equal to or greater than that when a single crystal is grown under the same conditions except that the cylindrical heat-uniform insulation material 40 is not used.

[0056] If the height of the cylindrical heat-uniform insulation material 40 is too low, it may be difficult to maintain a uniform temperature in the crucible 22. On the other hand, if the height of the cylindrical heat-uniform insulation material 40 is too high, the temperature difference between the sublimation raw material 12 and the seed crystal 14 may become excessively small, and the growth rate of the single crystal may decrease significantly. Therefore, it is preferable to select the optimal height of the cylindrical heat-uniform insulation material 40 depending on the presence or absence of the cylindrical member 26, the presence or absence of the lower heater 28, and the shape and dimensions of each part.

[0057] For example, when a cylindrical member 26 is inserted between the crucible 22 and the base 24, it is preferable that the cylindrical heat-uniform insulating material 40 is inserted in the region from the lower end of the crucible 22 to the upper end of the crucible 22. Inserting the cylindrical heat-uniform insulating material 40 in such a region makes it possible to achieve both temperature uniformity of the sublimation raw material 12 and securing a temperature difference between the sublimation raw material 12 and the seed crystal 14.

[0058] Alternatively, as shown in Figure 1, if a cylindrical member 26 is inserted between the crucible 22 and the base 24, and a lower heater 28 is inserted at the bottom of the crucible 22, it is preferable that the cylindrical heat-uniform insulation material 40 is inserted in the region from the lower end of the lower heater 28 to the upper end of the crucible 22. When the lower heater 28 is inserted at the bottom of the crucible 22, extending the length of the cylindrical heat-uniform insulation material 40 to the lower heater 28 can suppress the temperature drop at the bottom of the crucible 22.

[0059] The thickness of the cylindrical heat-uniform insulation material 40 affects its thermal insulation performance. If the thickness of the cylindrical heat-uniform insulation material 40 is too thin, the temperature of the crucible 22 may become uneven. As a result, when the diameter of the crucible 22 is large, the growth rate of the single crystal may decrease. Therefore, the thickness of the cylindrical heat-uniform insulation material 40 is preferably 1 mm or more. More preferably, the thickness is 3 mm or more, 5 mm or more, or 10 mm or more.

[0060] On the other hand, making the thickness of the cylindrical heat-uniform insulation material 40 thicker than necessary does not make a difference in effectiveness and is not beneficial. Therefore, the thickness of the cylindrical heat-uniform insulation material 40 is preferably 50 mm or less. More preferably, the thickness is 40 mm or less, 30 mm or less, or 20 mm or less.

[0061] [2. Single Crystal Manufacturing Apparatus (2)] Figure 2 shows a schematic diagram of a single crystal growth apparatus according to a second embodiment of the present invention. In Figure 2, the single crystal growth apparatus 10b comprises a growth container 20, a heat-insulating material 30, a cylindrical heat-uniform heat-insulating material 40, and a plate-shaped heat-uniform heat-insulating material 50.

[0062] [2.1. Growth Container] The growth container 20 includes a crucible 22 for holding the sublimation raw material 12, which also serves as a heating element that generates heat by high-frequency induction heating; a base 24 for holding the seed crystal 14, which is located on the upper part of the crucible 22; a cylindrical member 26 inserted between the crucible 22 and the base 24; and a lower heater 28 which generates heat by high-frequency induction heating, which is located on the lower part of the crucible 22. Details of the growth container 20 are the same as in the first embodiment, so the explanation will be omitted.

[0063] [2.2. Thermal Insulation Material] The thermal insulation material 30 is an insulating material for keeping the growth container 20 warm, and is arranged to cover the top, sides, and bottom of the growth container 20. The details of the thermal insulation material 30 are the same as in the first embodiment, so the explanation will be omitted.

[0064] [2.3. Cylindrical Heat-Uniforming Insulation Material] The cylindrical heat-uniforming insulation material 40 is an insulating material for making the temperature of the crucible 22 uniform, and is inserted between the outer surface of the growth container 20 and the inner surface of the heat-retaining insulation material 30. The details of the cylindrical heat-uniforming insulation material 40 are the same as in the first embodiment, so the explanation will be omitted.

[0065] [2.4. Plate-shaped heat-distributing insulation material] [A. Materials] The plate-shaped heat-distributing insulation material 50 is an insulating material for suppressing heat radiation from the bottom of the growth container 20, and is inserted between the outer bottom surface of the lower heater 28 and the inner bottom surface of the heat-retaining insulation material 30. The plate-shaped heat-distributing insulation material 50 is not necessarily required. However, inserting the plate-shaped heat-distributing insulation material 50 between the lower heater 28 and the heat-retaining insulation material 30 can further suppress heat radiation from the bottom of the growth container 20.

[0066] In the single crystal growth apparatus 10b shown in Figure 2, the lower temperature measuring hole 34 of the heat-insulating material 30 is used to measure the temperature of the lower surface of the plate-shaped heat-uniform insulation material 50 instead of the temperature of the lower surface of the growth container 20.

[0067] The material of the plate-shaped heat-uniform insulation material 50 is not particularly limited, as long as it can suppress heat dissipation from the bottom of the molded container 20. The material of the plate-shaped heat-uniform insulation material 50 is particularly preferably a graphite sheet or a laminate thereof. Because the thermal conductivity in the thickness direction is smaller than the thermal conductivity in the in-plane direction of a graphite sheet or laminate thereof, heat dissipation from the bottom of the growth container 20 is suppressed, and the temperature of the crucible 22 can be made more uniform. Details of the graphite sheet and laminate thereof are as described above, so a further explanation is omitted.

[0068] The material of the plate-shaped heat-uniform insulation material 50 is preferably one in which the thermal conductivity in the thickness direction at room temperature is 30 W / (m·K) or less, and the thermal conductivity in the in-plane direction at room temperature is 100 W / (m·K) or more. Graphite sheets or laminates thereof usually satisfy these conditions.

[0069] [B. Shape and Dimensions] The shape of the plate-shaped heat-distributing insulation material 50 is not particularly limited, as long as it is a shape that can suppress heat dissipation from the molded container 20. Preferably, the plate-shaped heat-distributing insulation material 50 has the same planar shape as the axial cross-sectional shape of the growth container 20.

[0070] The thickness of the plate-shaped heat-distributing insulation material 50 affects its heat-insulating performance. If the thickness of the plate-shaped heat-distributing insulation material 50 is too thin, the insulation of the lower part of the growth container 20 may become insufficient. As a result, when the diameter of the crucible 22 is large, the growth rate of the single crystal may decrease. Therefore, the thickness of the plate-shaped heat-distributing insulation material 50 is preferably 1 mm or more. More preferably, the thickness is 3 mm or more, 5 mm or more, or 10 mm or more.

[0071] On the other hand, making the thickness of the plate-shaped heat-uniform insulation material 50 thicker than necessary does not make a difference in effectiveness and is not beneficial. Therefore, the thickness of the plate-shaped heat-uniform insulation material 50 is preferably 50 mm or less. More preferably, the thickness is 40 mm or less, 30 mm or less, or 20 mm or less.

[0072] [3. Single Crystal Manufacturing Apparatus (3)] Figure 3 shows a schematic diagram of a single crystal growth apparatus according to the third embodiment of the present invention. In Figure 3, the single crystal growth apparatus 10c comprises a growth container 20, a heat-insulating material 30, a cylindrical heat-uniform heat-insulating material 40, a plate-shaped heat-uniform heat-insulating material 50, and a temperature-sensing material 60.

[0073] [3.1. Growth container, heat-insulating material, cylindrical heat-uniform insulating material, plate-shaped heat-uniform insulating material] Details of the growth container 20, heat-insulating material 30, cylindrical heat-uniform insulating material 40, and plate-shaped heat-uniform insulating material 50 are the same as in the first and second embodiments, so a description is omitted.

[0074] [3.2. Temperature Measuring Material] [A. Materials] The temperature measuring material 60 is a component for measuring the temperature of the lower part of the growth container 20, and is inserted into the lower temperature measuring hole 34 of the heat-insulating material 30. Preferably, the temperature measuring material 60 is inserted into the lower temperature measuring hole 34 so that its upper surface is in close contact with the lower surface of the plate-shaped heat-uniform insulation material 50. The temperature measuring material 60 is not necessarily required. However, inserting the temperature measuring material 60 into the lower temperature measuring hole 34 can further suppress heat dissipation from the lower temperature measuring hole 34.

[0075] The material of the temperature measuring material 60 is not particularly limited, as long as it can measure the surface temperature during the growth process of a single crystal and can suppress heat dissipation from the lower temperature measuring hole 34. Examples of materials for the temperature measuring material 60 include (a) a graphite sheet or a laminate thereof, or (b) a molded body of glassy carbon, coal, charcoal, or porous carbon.

[0076] Details of the graphite sheet and its laminate are as described above, so we will omit further explanation. Examples of molded bodies that can be used as temperature measuring material 60 include: (a) Glassy carbon (thermal conductivity: 5.8 W / (m·K)) manufactured by Tokai Fine Carbon Co., Ltd., and (b) Porous carbon material (thermal conductivity: 1 to 3 W / (m·K)) manufactured by Tanken Seal Seiko Co., Ltd.

[0077] The temperature measuring material 60 is preferably one in which the thermal conductivity in the thickness direction at room temperature is 10 W / (m·K) or less. Graphite sheets or laminates thereof usually satisfy this condition. Certain types of carbon molded bodies also satisfy this condition.

[0078] [B. Shape and Dimensions] The shape of the temperature measuring material 60 is not particularly limited, as long as it is a shape that can be inserted into the lower temperature measuring hole 34.

[0079] The thickness of the temperature-sensing material 60 is not particularly limited, as long as it does not interfere with temperature measurement at the bottom of the growth container 20. If the thickness of the temperature-sensing material 60 is too thin, the amount of heat dissipated from the lower temperature-sensing hole 34 will increase, which may cause the temperature of the crucible 22 to become uneven. Therefore, the thickness of the temperature-sensing material 60 is preferably 1 mm or more. More preferably, the thickness is 3 mm or more, 5 mm or more, or 10 mm or more.

[0080] On the other hand, making the temperature-sensing material 60 thicker than necessary does not make a difference in effectiveness and is not beneficial. Therefore, the thickness of the temperature-sensing material 60 is preferably 50 mm or less. More preferably, the thickness is 40 mm or less, 30 mm or less, or 20 mm or less.

[0081] [4. Method for Manufacturing Single Crystals] The method for manufacturing single crystals according to the present invention comprises a step of growing a bulk single crystal by sublimation using a single crystal growth apparatus according to the present invention. By filling a crucible 22 with sublimation raw material 12 and heating the sublimation raw material 12 while holding a seed crystal 14 on a base 24, a single crystal can be grown on the surface of the seed crystal 14.

[0082] [5. Effects] When heating a crucible using high-frequency induction heating, the larger the diameter of the crucible, the more likely it is that the temperature of the crucible will become non-uniform. Furthermore, if the temperature of the crucible becomes non-uniform, the efficiency of raw material utilization may decrease, or the growth height of the single crystal may be limited.

[0083] In contrast, by placing heat-insulating material around the growth vessel for growing single crystals, inserting a cylindrical heat-uniform insulation material between the growth vessel and the heat-insulating material, and optimizing the length of the cylindrical heat-uniform insulation material, the sublimation raw material can be heated uniformly, and an appropriate temperature difference can be formed between the sublimation raw material and the seed crystal. As a result, raw material utilization efficiency is improved even when using a large-diameter crucible. Furthermore, even when growing large-diameter single crystals, a high growth height can be achieved.

[0084] (Examples 1-3, Comparative Example 1) [1. Fabrication of Single Crystal Manufacturing Apparatus] The single crystal manufacturing apparatus used was: (a) single crystal growth apparatus 10a shown in Figure 1 (Example 1), (b) single crystal growth apparatus 10b shown in Figure 2 (Example 2), (c) single crystal growth apparatus 10c shown in Figure 3 (Example 3), and (d) single crystal growth apparatus 10d shown in Figure 4 (Comparative Example 1).

[0085] Note that the single crystal growth apparatus 10d shown in Figure 4 differs from the single crystal growth apparatus 10a in that it does not have a cylindrical heat-uniform insulation material 40. Other aspects of the single crystal growth apparatus 10d are the same as those of the single crystal growth apparatus 10a, so the explanation will be omitted. Details of each component used in the single crystal growth apparatuses 10a to 10d are as follows.

[0086] [1.1. Crucible, Lower Heater, Cylindrical Member, Base] The crucible 22 was an isotropic graphite crucible with an outer diameter of 190 mm, an inner diameter of 159 mm, a total height of 178 mm, and an effective depth of 165 mm. The lower heater 28 was an isotropic graphite heater with an outer diameter of 190 mm, an inner diameter of 160 mm, and a total height of 40 mm. The cylindrical member 26 was an isotropic graphite cylinder with an outer diameter of 170 mm, an inner diameter of 150 mm, and a total height of 110 mm. The base 25 was an isotropic graphite base with an outer diameter of 170 mm.

[0087] [1.2. Thermal insulation material] Thermal insulation material 30 has a bulk density of 0.16 g / cm³ 3 The main material used was a molded insulation material based on graphite fiber felt. For filling gaps, a material with equivalent insulation performance and a bulk density of 0.10 g / cm³ was used. 3 A graphite fiber felt was used. An upper temperature sensing hole 32 with a diameter of 30 mm was formed in the upper center of the heat-insulating material 30. In addition, a lower temperature sensing hole 34 with a diameter of 12 mm was formed in the lower center of the heat-insulating material 30.

[0088] For the heat-insulating material 30, a molded insulation material with an outer diameter of 270 mm and a total height of 450 mm was used. The effective internal dimensions of the heat-insulating material 30 were (a) φ190 × h320 mm (Comparative Example 1), (b) φ210 × h320 mm (Example 1), or (c) φ210 × h330 mm (Examples 2 and 3).

[0089] [1.3. Seed crystal and sublimation raw material] A 4H-SiC (0001) 3.5° off-center substrate with a diameter of 150 mm and a thickness of 350 μm was used as the seed crystal 14. The SiC substrate was bonded and fixed to the base 24 so that the C-side of the SiC substrate would be the growth surface. SiC powder with an average particle size of 500 μm was used as the sublimation raw material 12. 3.51 kg of this SiC powder was loaded into the crucible 22. The raw material height was approximately 100 mm. This corresponds to approximately 56% of the powder packing density.

[0090] [1.4. Cylindrical heat-uniform insulation material, plate-shaped heat-uniform insulation material] For the graphite sheet, we used PERMA-FOIL (registered trademark) manufactured by Toyo Tanso (product number: PH-50UHP, 500 μm thick, or product number: PH-100UHP, 1.0 mm thick). The thermal conductivity of PERMA-FOIL (registered trademark) in the thickness direction is ~5 W / (m·K) (at room temperature), and the thermal conductivity in the in-plane direction is ~200 W / (m·K) (at room temperature). In the computer simulation described later, the thermal conductivity of the graphite sheet at high temperatures exceeding 2000°C was assumed to decrease to 1 / 3 of that at room temperature (thermal conductivity in the thickness direction is 2 W / (m·K), and thermal conductivity in the in-plane direction is 70 W / (m·K)).

[0091] A cylindrical heat-uniform insulation material 40 and a plate-shaped heat-uniform insulation material 50 were manufactured by bonding and molding the above-mentioned graphite sheets. The cylindrical heat-uniform insulation material 40 was manufactured by winding a 500 μm thick graphite sheet 15 times and bonding and fixing the layers together with a graphite-based adhesive. The resulting cylindrical heat-uniform insulation material 40 had an outer diameter of 210 mm, an inner diameter of 190 mm, and a total height of 220 mm. The plate-shaped heat-uniform insulation material 50 was manufactured by laminating 10 graphite sheets with a thickness of 1.0 mm and bonding and fixing the layers together with a graphite-based adhesive. The resulting plate-shaped heat-uniform insulation material 50 had an outer diameter of 190 mm and a total height of 10 mm.

[0092] [1.5. Temperature Sensor] The temperature sensor 60 was prepared by laminating 20 graphite sheets with a thickness of 1.0 mm and bonding and fixing the layers together with a graphite-based adhesive. The resulting temperature sensor 60 had an outer diameter of 20 mm and a total height of 20 mm.

[0093] Figure 5(A) shows a photograph of the external appearance of the cylindrical heat-uniform insulation material 40. Figure 5(B) shows a photograph of the external appearance of the plate-shaped heat-uniform insulation material 50 placed on the heat-insulating insulation material 30. Figure 5(C) shows a photograph of the external appearance of the temperature measuring material 60 inserted into the lower temperature measuring hole 34 of the heat-insulating insulation material 30.

[0094] [2. Manufacturing of SiC Single Crystals by Sublimation Method] SiC single crystals were manufactured using single crystal growth apparatuses 10a to 10d. The crystal growth pressure was 200 Pa, the atmosphere was Ar: 95 vol% + N2: 5 vol, and the growth time was 96 h.

[0095] Regarding the growth temperature, in Example 1 and Comparative Example 1, the high-frequency power and coil position were adjusted so that the temperature on the underside of the base 24, measured with a radiation thermometer through the upper temperature sensing hole 32, was ~2200°C, and the temperature at the bottom of the crucible 22, measured with a radiation thermometer through the lower temperature sensing hole 34, was ~2350°C. Continuous growth was carried out for 96 hours while adjusting the temperature so that the temperature of the crucible 22 remained constant at 2350°C.

[0096] In Example 2, when the high-frequency power and coil position were adjusted to be the same as in Example 1, the temperature of the back surface of the base 24, measured with a radiation thermometer through the upper temperature sensing hole 32, was ~2200°C. Therefore, it was estimated that the bottom temperature of the crucible 22 was ~2350°C, the same as in Example 1. However, the temperature of the plate-shaped heat-distributing insulation material 50, measured with a radiation thermometer through the lower temperature sensing hole 34, was ~2200°C. Therefore, continuous growth for 96 hours was carried out while adjusting the temperature so that the temperature of the plate-shaped heat-distributing insulation material 50 remained constant at 2200°C.

[0097] In Example 3, when the high-frequency power and coil position were adjusted to be the same as in Example 1, the temperature of the back surface of the base measured with a radiation thermometer through the upper temperature sensing hole 32 was ~2200°C. Therefore, it was estimated that the bottom temperature of the crucible 22 was 2350°C, the same as in Example 1. However, the temperature of the temperature sensing material 60 measured with a radiation thermometer through the lower temperature sensing hole 34 was ~1900°C. Therefore, continuous growth for 96 hours was carried out while adjusting the temperature so that the temperature of the temperature sensing material 60 remained constant at 1900°C.

[0098] [3. Test Method and Results] After growing SiC single crystals under the above conditions, the growth height of the single crystals, the average growth rate of the single crystals, and the raw material yield were measured. Here, "raw material yield" refers to the ratio of the mass of the single crystal grown on the surface of the seed crystal 14 to the mass of the sublimation raw material 12 charged into the crucible 22. The results are shown in Table 1.

[0099]

[0100] (1) In Comparative Example 1, the single crystal growth height was 18.4 mm, the average growth rate was 191 μm / h, and the raw material yield was 29.7%. Polycrystalline SiC was deposited on the surface of the raw material powder after growth. (2) In Example 1, the single crystal growth height was 28.5 mm, and the average growth rate was 297 μm / h, which was approximately 1.5 times that of Comparative Example 1. The raw material yield also improved to 45.8%. No deposition of polycrystalline SiC was observed on the surface of the raw material powder after growth. From this, it is considered that the raw material yield improved because the raw material temperature became more uniform by inserting the cylindrical heat-uniform insulation material 40.

[0101] (3) In Example 2, the single crystal growth height was 35.8 mm and the average growth rate was 373 μm / h, which was approximately 1.9 times that of Comparative Example 1. The raw material yield also improved to 57.7%. No polycrystalline SiC deposition was observed on the upper surface of the raw material powder after growth. The temperature measured from the lower temperature sensing hole 34 was 2200°C, which was 150°C lower than that of Example 1. Since radiant energy is proportional to the fourth power of the absolute temperature, it can be said that Example 2 was able to reduce the radiant power from the lower temperature sensing hole 34 by about 20% compared to Example 1. This is thought to have improved the uniformity of the raw material temperature, resulting in an improved raw material yield.

[0102] (4) In Example 3, the single crystal growth height was 41.2 mm and the average growth rate was 429 μm / h, which was approximately 2.2 times that of Comparative Example 1. The raw material yield also improved to 66.4%. No polycrystalline SiC deposition was observed on the upper surface of the raw material powder after growth. The temperature measured from the lower temperature sensing hole 34 was 1900°C, which was 450°C lower than that of Example 1. Since radiant energy is proportional to the fourth power of the absolute temperature, it can be said that Example 3 was able to reduce the radiant power from the lower temperature sensing hole 34 by about 50% compared to Example 1. This is thought to have improved the uniformity of the raw material temperature, resulting in an improved raw material yield.

[0103] (Example 4) [1. Test Method] A computer simulation of the initial growth rate was performed using a Virtual reactor manufactured by STR Japan. Figure 6 shows a schematic diagram of the single crystal growth apparatus used in the computer simulation. In the configuration shown in Figure 6, the inner diameter of the cylindrical heat-synthesizing insulation material 40 was set to 190 mm, the total height to 178 mm, and the thickness of the cylindrical heat-synthesizing insulation material 40 was set to 0 mm, 1 mm, 3 mm, 5 mm, 10 mm, or 15 mm. The initial growth rate was calculated for these six cases. The "initial growth rate" refers to the value obtained by dividing the growth height after 1 hour from the start of growth by the growth time.

[0104] [2. Results] Figure 7 shows the relationship between the thickness of the tubular heat-uniform insulation material and the initial growth rate. From Figure 7, it was found that the initial growth rate increased significantly when the thickness was 1 to 3 mm. In other words, it was shown that the tubular heat-uniform insulation material 40 is effective even with a thickness of 1 mm, and that a thickness of 3 mm or more is preferable. To ensure a more reliable effect, a thickness of 5 to 10 mm for the tubular heat-uniform insulation material 40 is considered even more preferable.

[0105] However, if the thickness of the heat-uniform insulation material 40 becomes too thick, the workpiece size may become too large, leading to higher costs or a reduction in the effective dimensions (size of the crucible 22). Therefore, it was found that the thickness of the heat-uniform insulation material 40 is preferably 50 mm or less, and more preferably 30 mm or less.

[0106] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0107] The single crystal manufacturing apparatus according to the present invention can be used to manufacture SiC single crystals and compound semiconductor single crystals such as AlN single crystals.

[0108] 10a-10d Single crystal manufacturing apparatus 12 Sublimation raw material 14 Seed crystal 20 Growth vessel 22 Crucible 24 Base 26 Cylindrical member 28 Lower heater 30 Heat-insulating material 32 Upper temperature sensing hole 34 Lower temperature sensing hole 40 Cylindrical heat-uniform insulating material 50 Plate-shaped heat-uniform insulating material 60 Temperature sensor

Claims

1. A single crystal growth apparatus having the following configuration: (1) The single crystal growth apparatus comprises a growth container for growing a single crystal, a heat-insulating material covering the top, sides, and bottom of the growth container, and a cylindrical heat-uniforming insulation material inserted between the outer surface of the growth container and the inner surface of the heat-insulating material. (2) The growth container comprises a crucible for holding a sublimation raw material, which also serves as a heating element that generates heat by high-frequency induction heating, and a base for holding a seed crystal, positioned above the crucible. (3) The heat-insulating material comprises an upper temperature-measuring hole provided on the top surface and a lower temperature-measuring hole provided on the bottom surface. (4) The cylindrical heat-uniforming insulation material is inserted in a region that can heat the sublimation raw material to a uniform temperature and create a temperature difference between the sublimation raw material and the seed crystal necessary for growing a single crystal.

2. The single crystal growth apparatus according to claim 1, wherein the cylindrical heat-uniform insulation material is a graphite sheet or a laminate thereof.

3. The single crystal growth apparatus according to claim 1, wherein the cylindrical heat-uniform insulation material has a thickness of 1 mm or more and 50 mm or less.

4. The single crystal growth apparatus according to claim 1, wherein the growth vessel further comprises a cylindrical member inserted between the crucible and the base.

5. The single crystal growth apparatus according to claim 4, wherein the cylindrical heat-uniform insulating material is inserted in the region from the lower end of the crucible to the upper end of the crucible.

6. The single crystal growth apparatus according to claim 1, wherein the growth vessel further comprises a lower heater disposed at the bottom of the crucible, which generates heat by the high-frequency induction heating.

7. The single crystal growth apparatus according to claim 6, wherein the cylindrical heat-sensing insulation material is inserted in the region from the lower end of the lower heater to the upper end of the crucible.

8. The single crystal growth apparatus according to claim 6, further comprising a plate-shaped heat-synthesizing insulating material inserted between the outer bottom surface of the lower heater and the inner bottom surface of the heat-insulating insulating material.

9. The single crystal growth apparatus according to claim 1, further comprising a temperature measuring material inserted into the lower temperature measuring hole.

10. A method for manufacturing a single crystal, comprising the step of growing a bulk single crystal by sublimation using the single crystal growth apparatus described in claim 1.

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