Silicon carbide single crystal manufacturing apparatus and method for manufacturing silicon carbide single crystal

Abstract

To provides a silicon carbide single crystal manufacturing apparatus that can reduce poor bonding between a silicon carbide seed crystal and a graphite base.SOLUTION: A silicon carbide single crystal manufacturing apparatus 100 includes: a crucible 10 constituted by a crucible body 1 and a crucible lid 2; and a base 20 having a crucible lid-side surface 20A, which is supported by an underside 2A of the crucible lid 2, and a seed crystal mounting surface 20B, which is opposite the crucible lid-side surface 20A and has a seed crystal S to be mounted thereon. The base 20 is made of a graphite material. An area of the seed crystal mounting surface 20B is larger than the area of the crucible lid-side surface 20A. The base 20 has a portion in which a cross-sectional area of the base 20 orthogonal to a straight line connecting the crucible lid-side surface 20A and the seed crystal mounting surface 20B is gradually reduced from the seed crystal mounting surface 20B toward the crucible lid-side surface 20A.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a silicon carbide single crystal growth apparatus and a method for producing a silicon carbide single crystal. [Background technology]

[0002] Silicon carbide (SiC) has an electric breakdown field one order of magnitude larger than silicon (Si) and a band gap three times larger. Silicon carbide (SiC) also has properties such as a thermal conductivity about three times higher than silicon (Si). For this reason, silicon carbide (SiC) is expected to be applied to power devices, high-frequency devices, high-temperature operating devices, and the like. For this reason, SiC epitaxial wafers have come to be used in the above-mentioned semiconductor devices in recent years.

[0003] SiC epitaxial wafers are manufactured by growing an SiC epitaxial film, which will become the active region of a SiC semiconductor device, on a silicon carbide single crystal substrate by chemical vapor deposition (CVD).

[0004] The silicon carbide single crystal substrate is produced by cutting out a silicon carbide single crystal. This silicon carbide single crystal can generally be obtained by the sublimation method. The sublimation method is a method in which a seed crystal made of a silicon carbide single crystal is placed on a pedestal placed in a graphite crucible, and the sublimation gas sublimated from the raw material powder in the crucible is supplied to the seed crystal by heating the crucible, thereby growing the seed crystal into a larger silicon carbide single crystal.

[0005] In the sublimation method, the seed crystal needs to be held on the pedestal, and an adhesive is generally used for holding the seed crystal on the pedestal. In addition, a stress buffer may be used to reduce the stress (shear stress) that occurs parallel to the bonding surface due to the difference in thermal expansion between the seed crystal and the graphite pedestal (Patent Document 1).

[0006] The above-mentioned stresses when holding the seed crystal cause adhesion failure or cracks in the stress buffer (hereinafter, these are collectively referred to as "bonding failure"), which causes localized temperature distribution within the seed crystal surface. If this temperature distribution is large, macro defects are likely to occur in the single crystal, which can lead to a problem of reduced quality of the single crystal. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2004-269297 A [Patent Document 2] JP 2008-88036 A [Patent Document 3] JP 2009-120419 A Summary of the Invention [Problem to be solved by the invention]

[0008] To address this issue, Patent Document 2 proposes a method of suppressing the shear stress generated between the seed crystal and the graphite pedestal by using a member for holding the seed crystal that has a linear expansion coefficient close to that of silicon carbide at room temperature. Patent Document 3 also proposes a method of suppressing the shear stress by forming a multilayer structure of three or more graphite members on the pedestal and bringing the average value of the linear expansion coefficient of each graphite member close to the thermal expansion coefficient of the seed crystal.

[0009] In the sublimation method, the members are exposed to a wide temperature range from room temperature to over 2400° C. It is not easy to more accurately grasp the linear expansion coefficient of the members, which have temperature dependency in this range, and to match the linear expansion coefficient of the silicon carbide single crystal and the graphite base in each temperature range, and it is difficult to completely suppress the occurrence of macro defects even when the growth methods described in Patent Documents 2 and 3 are used.

[0010] The shear stress caused by the difference in the linear expansion coefficient between the silicon carbide seed crystal and the graphite base becomes larger at the outer periphery where the difference in the amount of thermal expansion becomes larger. Shear stress occurs when contacting parts try to shift relative to each other due to thermal expansion, and this shift is greater at the outer periphery. Adhesion failure often occurs in this area as well. This phenomenon becomes more evident as the diameter of the seed crystal becomes larger.

[0011] The present invention has been made in consideration of the above circumstances, and provides an apparatus for producing a silicon carbide single crystal and a method for producing a silicon carbide single crystal, which are capable of reducing bonding defects between a silicon carbide seed crystal and a graphite pedestal. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides the following means.

[0013] A silicon carbide single crystal manufacturing apparatus according to a first aspect of the present invention comprises a crucible consisting of a crucible body and a lid, and a pedestal having a lid side surface supported on the underside of the lid and a seed crystal mounting surface on the opposite side of the lid side, wherein the pedestal is made of graphite material, the area of ​​the seed crystal mounting surface is larger than the area of ​​the lid side surface, and the pedestal has at least one of a portion in which the cross-sectional area perpendicular to the vertical direction connecting the lid side surface and the seed crystal mounting surface gradually decreases from the seed crystal mounting surface toward the lid side surface, and a portion in which the cross-sectional area decreases in stages.

[0014] In the silicon carbide single crystal manufacturing apparatus according to the above aspect, the base portion may be shaped like a truncated cone.

[0015] The silicon carbide single crystal manufacturing apparatus according to the above aspect may be such that, when the lid side surface of the pedestal portion is circular with a radius r1, the seed crystal mounting surface is circular with a radius r2, and the height of the pedestal portion is h, (r2-r1) / h>0.15 is satisfied.

[0016] In the silicon carbide single crystal manufacturing apparatus according to the above aspect, the radius r1, the radius r2, and the height h may satisfy (r2-r1) / h>0.30.

[0017] In the silicon carbide single crystal manufacturing apparatus according to the above aspect, the base may be made of a graphite material having a Young's modulus of 5 GPa or more.

[0018] A second aspect of the present invention relates to a method for producing a silicon carbide single crystal, which method uses a crucible consisting of a crucible body and a lid, and a pedestal having a lid side surface supported on the underside of the lid and a seed crystal mounting surface on which a seed crystal is attached on the opposite side of the lid side, and comprises arranging a seed crystal consisting of a silicon carbide single crystal and a silicon carbide raw material in the crucible, and causing sublimation gas sublimated from the silicon carbide raw material to precipitate on the seed crystal to grow a silicon carbide single crystal, wherein the pedestal is made of graphite material, an area of ​​the seed crystal mounting surface is larger than an area of ​​the lid side surface, and the pedestal has at least one of a portion in which a cross-sectional area perpendicular to a vertical direction connecting the lid side surface and the seed crystal mounting surface gradually decreases from the seed crystal mounting surface toward the lid side surface and a portion in which the cross-sectional area decreases in stages.

[0019] In the method for producing a silicon carbide single crystal according to the above aspect, a stress buffer member may be disposed between the seed crystal and the pedestal portion.

[0020] In the method for producing a silicon carbide single crystal according to the above aspect, the stress buffer member may have a Young's modulus of less than 5 GPa.

[0021] In the method for producing a silicon carbide single crystal according to the above aspect, the seed crystal may have an outer diameter of 150 mm or more.

[0022] In the method for producing a silicon carbide single crystal according to the above aspect, the seed crystal may have an outer diameter of 200 mm or more. Effect of the Invention

[0023] According to the present invention, it is possible to provide a silicon carbide single crystal manufacturing apparatus capable of reducing the shear stress caused by the difference in linear expansion coefficient between a silicon carbide seed crystal and a graphite pedestal. [Brief description of the drawings]

[0024] [Figure 1] 1 is a cross-sectional schematic diagram showing an example of a silicon carbide single crystal manufacturing apparatus according to an embodiment of the present invention. [Diagram 2] 2 is a schematic cross-sectional view of only a base portion of the silicon carbide single crystal manufacturing apparatus shown in FIG. 1. [Diagram 3] FIG. 13 is a schematic cross-sectional view of a base portion according to another example. [Figure 4] FIG. 13 is a schematic cross-sectional view of a base portion according to another example. [Diagram 5] FIG. 13 is a schematic cross-sectional view of a base portion according to another example. [Figure 6] FIG. 13 is a schematic cross-sectional view of a base portion according to another example. [Figure 7] FIG. 13 is a schematic cross-sectional view showing a configuration in which a stress buffer member is disposed between a seed crystal and a pedestal portion. [Figure 8] 4 is a diagram for explaining shape parameters of a base part in the first embodiment. FIG. [Figure 9] The shear stress in Example 1 when the base portion is cylindrical is set to 1, and the results show the relative values ​​of the shear stress obtained for each shape. [Figure 10] Among the shapes for which the simulation was performed, the shapes of Example 1 and the simulation results are shown, excluding the case where r1=80 mm. [Figure 11] 13 is a diagram for explaining shape parameters of a pedestal part in Example 2. FIG. [Figure 12] The shear stress in Example 2 when the base portion is cylindrical is set to 1, and the results show the relative values ​​of the shear stress obtained for each shape. [Figure 13] Among the shapes for which the simulation was performed, the shapes of Example 2 and the simulation results are shown, excluding the case where r1=80 mm. [Figure 14]The shear stress obtained in Example 3 when the base portion was cylindrical was set to 1, and the results show the relative values ​​of the shear stress obtained in each shape. [Figure 15] Among the shapes for which the simulation was performed, the shapes of Example 3 and the simulation results thereof are shown, excluding the case where r1=100 mm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts may be denoted by the same reference numerals in the drawings. In addition, the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the features easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. In addition, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. The present invention can be implemented by appropriately changing the materials, dimensions, etc. within the scope of the effects of the present invention. The configuration shown in one embodiment can also be applied to other embodiments.

[0026] (Silicon carbide single crystal manufacturing equipment) Fig. 1 is a cross-sectional view showing an example of a silicon carbide single crystal manufacturing apparatus according to one embodiment of the present invention, Fig. 2 is a cross-sectional view showing only a base part of the silicon carbide single crystal manufacturing apparatus shown in Fig. 1. The silicon carbide single crystal manufacturing apparatus 100 shown in Figure 1 comprises a crucible 10 consisting of a crucible body 1 and a lid portion 2, and a pedestal portion 20 having a lid side surface (lid side surface) 20A supported by the underside 2A of the lid portion 2 and a seed crystal mounting surface 20B on the opposite side of the lid side surface 20A, where a seed crystal S is mounted, the pedestal portion 20 being made of a graphite material, the area of ​​the seed crystal mounting surface 20B being larger than the area of ​​the lid side surface 20A, and the cross-sectional area of ​​the pedestal portion 20 perpendicular to the straight line connecting the lid side surface 20A and the seed crystal mounting surface 20B gradually decreasing from the seed crystal mounting surface 20B toward the lid side surface 20A. The crucible body 1 is provided on its outer periphery with a heat insulating material (not shown) for keeping the crucible 10 warm, and a heating means (not shown). In order to aid in understanding, a raw material (raw material powder) G for single crystal growth and a seed crystal S are also shown in FIG.

[0027] When producing silicon carbide single crystals, raw material powder G is filled into the bottom of crucible 10, and a seed crystal S made of silicon carbide is placed on pedestal 20. Pedestal 20 is located opposite raw material powder G. Next, crucible 10 is heated to about 2100 to 2400°C in a reduced pressure atmosphere, and raw material powder G is sublimated to supply sublimation gas (raw material gas) onto seed crystal S. The raw material gas sublimated from raw material powder G is recrystallized on the surface of seed crystal S, resulting in crystal growth of silicon carbide single crystals.

[0028] <Crucible> Crucible 10 is a crucible for producing silicon carbide single crystals by sublimation, and is composed of crucible body 1 and lid 2. There are no limitations on the shape of crucible body 1 and lid 2 as long as they can combine to form a crystal growth space. The crucible 10 may be made of, for example, graphite. The crucible 10 becomes hot during growth. Therefore, it must be made of a material that can withstand high temperatures. Graphite has an extremely high sublimation temperature of 3550°C, and can withstand the high temperatures during growth. When the crucible 10 is made of graphite (graphite material), the surface thereof may be coated with TaC or SiC.

[0029] <Base> 1 is a separate member from the lid 2, but may be formed integrally with the lid 2. When the lid 2 and the pedestal 20 are separate members, they can be joined together with, for example, a carbon adhesive.

[0030] Like the crucible 10, the pedestal 20 must be made of a material that can withstand the high temperatures used when growing a single crystal, and in this embodiment, it is made of graphite (graphite material). The pedestal is preferably made of a graphite material having a Young's modulus of 5 GPa or more at room temperature, since this provides the rigidity necessary to stably support the silicon carbide single crystal. The surface of the base 20 made of graphite material may be coated with TaC or SiC.

[0031] The area Sb of the seed crystal mounting surface 20B of the pedestal portion 20 is larger than the area Sa of the lid side surface 20A, and the cross-sectional area of ​​the pedestal portion 20 perpendicular to a straight line L extending vertically between the lid side surface 20A and the seed crystal mounting surface 20B gradually decreases from the seed crystal mounting surface 20B toward the lid side surface 20A. The symbols CS1 and CS2 in FIG. 2 indicate the positions of the two cross-sectional areas, and the cross-sectional area CS2 closer to the lid side surface 20A is smaller than the cross-sectional area CS1 closer to the seed crystal mounting surface 20B.

[0032] The base 20 shown in Fig. 2 has a truncated cone shape. In this case, in the vertical cross section shown in Fig. 2, the side surface 20a is linear, and a predetermined angle θ can be defined with respect to the lid side surface 20A or the seed crystal mounting surface 20B. In the pedestal portion 20 shown in FIG. 2, the cross-sectional area of ​​the pedestal portion 20 becomes continuously smaller from the seed crystal mounting surface 20B toward the lid portion side surface 20A, and the radius of the circle of the cross section becomes continuously smaller at a constant rate.

[0033] The linear expansion coefficient of the graphite (graphite material) constituting the pedestal 20 does not coincide with the linear expansion coefficient of the silicon carbide constituting the seed crystal over the entire wide temperature range from room temperature to 2400°C or higher in which the sublimation method is used, and shear stress occurs at the joint surface (bonding surface) between the graphite pedestal and the silicon carbide seed crystal. The difference in expansion becomes particularly large at the outer periphery of the seed crystal. When this shear stress becomes large, a gap occurs between the seed crystal and the pedestal due to poor bonding, leading to the occurrence of macroscopic defects in the crystal. In contrast, by forming the pedestal portion in a truncated cone shape, such shear stress can be suppressed, and macro defects in the silicon carbide seed crystal can be reduced.

[0034] FIG. 3 shows another example of a configuration in which the cross-sectional area of ​​the pedestal portion gradually decreases from the seed crystal mounting surface toward the side surface of the lid portion.

[0035] The pedestal portion 21 shown in Figure 3 is similar to the pedestal portion 20 shown in Figure 2 in that the area Sb of the seed crystal mounting surface 21B is larger than the area Sa of the lid side surface 21A, and the cross-sectional area gradually becomes smaller from the seed crystal mounting surface 21B to the lid side surface 21A, that is, the cross-sectional area continuously becomes smaller from the seed crystal mounting surface 21B to the lid side surface 21A.

[0036] On the other hand, the base portion 21 shown in FIG. 3 differs from the base portion 20 shown in FIG. 2 in that the cross-sectional area decreases at a smaller rate from the seed crystal mounting surface 21B toward the lid portion side surface 21A and the side surface 21a is formed in a concave (curved) shape.

[0037] FIG. 4 shows an example of a configuration in which the cross-sectional area of ​​the pedestal portion gradually decreases from the seed crystal mounting surface toward the side surface of the lid portion.

[0038] Pedestal portion 22 shown in FIG. 4 is common to pedestal portion 20 shown in FIG. 2 and pedestal portion 21 shown in FIG. 3 in that area Sb of seed crystal mounting surface 22B is larger than area Sa of lid portion side surface 22A.

[0039] On the other hand, pedestal portion 22 shown in FIG. 4 differs from pedestal portion 20 shown in FIG. 2 and pedestal portion 21 shown in FIG. 3 in that the cross-sectional area of ​​pedestal portion 22 shown in FIG. 4 gradually decreases from seed crystal mounting surface 22B toward lid portion side surface 22A.

[0040] The base 22 shown in Fig. 4 has a shape in which four disks (or cylinders) 22-1, 22-2, 22-3, and 22-4, each having a smaller radius, are stacked from the seed crystal mounting surface 22B toward the lid side surface 22A. The cross-sectional area of ​​each disk is the same. The four disks may be integrally formed, or may be joined by, for example, a carbon adhesive. The side surface 22a of the base portion 22 consists of side surfaces 22-1a, 22-2a, 22-3a, and 22-4a extending in a direction perpendicular to the seed crystal mounting surface 22B (or the lid portion side surface 22A), and side surfaces 22-1b, 22-2b, and 22-3b extending in a direction parallel to the seed crystal mounting surface 22B (or the lid portion side surface 22A). The base portion 22 shown in FIG. 4 is configured with four disks, but this is just one example, and there is no limit to the number of disks as long as it is made up of a plurality of disks.

[0041] FIG. 5 shows an example of a base portion having a portion whose cross-sectional area gradually decreases from the seed crystal mounting surface toward the side surface of the lid portion (hereinafter, sometimes referred to as a "reduced cross-sectional area portion") and a portion whose cross-sectional area does not change (hereinafter, sometimes referred to as a "constant cross-sectional area portion"). Pedestal portion 23 shown in FIG. 5 is common to pedestal portion 20 shown in FIG. 2 in that area Sb of seed crystal mounting surface 23B is larger than area Sa of lid portion side surface 23A.

[0042] On the other hand, pedestal portion 23 shown in FIG. 5 differs from pedestal portion 20 shown in FIG. 2 in that, in addition to portion 23-1 whose cross-sectional area gradually decreases from seed crystal mounting surface 23B toward lid portion side surface 23A, it has portion 23-2 whose cross-sectional area does not change. The portion whose cross-sectional area gradually decreases from seed crystal mounting surface 23B toward lid side surface 23A and the portion whose cross-sectional area does not change may be integrally formed or may be joined together by, for example, a carbon adhesive or the like. Although the pedestal portion 23 shown in FIG. 5 is configured with one each of a reduced cross-sectional area portion and a constant cross-sectional area portion, there is no limit to the number thereof so long as the pedestal portion has at least one reduced cross-sectional area portion.

[0043] FIG. 6 shows an example of a base portion having a portion whose cross-sectional area gradually decreases from the seed crystal mounting surface toward the side surface of the lid portion (hereinafter, sometimes referred to as a "reduced cross-sectional area portion") and a portion whose cross-sectional area does not change (hereinafter, sometimes referred to as a "constant cross-sectional area portion"). Pedestal portion 24 shown in FIG. 6 is common to pedestal portion 21 shown in FIG. 3 in that area Sb of seed crystal mounting surface 24B is larger than area Sa of lid portion side surface 24A. On the other hand, pedestal portion 24 shown in FIG. 6 differs from pedestal portion 21 shown in FIG. 3 in that, in addition to portion 24-1 whose cross-sectional area gradually decreases from seed crystal mounting surface 24B toward lid portion side surface 24A, pedestal portion 24 has portion 24-2 whose cross-sectional area does not change. The portion whose cross-sectional area gradually decreases from seed crystal mounting surface 24B toward lid side surface 24A and the portion whose cross-sectional area does not change may be integrally formed or may be joined together, for example, by a carbon adhesive or the like. Although the pedestal portion 24 shown in FIG. 6 is configured with one each of a reduced cross-sectional area portion and a constant cross-sectional area portion, there is no limit to the number thereof so long as the pedestal portion has at least one reduced cross-sectional area portion.

[0044] (Method for producing silicon carbide single crystal) A method for producing a silicon carbide single crystal according to one embodiment of the present invention uses a crucible consisting of a crucible body and a lid, and a pedestal having a lid side surface supported on the underside of the lid and a seed crystal mounting surface on which a seed crystal is attached on the opposite side of the lid side, and arranges a seed crystal consisting of a silicon carbide single crystal and a silicon carbide raw material in the crucible to grow a silicon carbide single crystal by precipitating sublimation gas sublimated from the silicon carbide raw material onto the seed crystal, wherein the pedestal is made of graphite material, the area of ​​the seed crystal mounting surface is larger than the area of ​​the lid side surface, and the pedestal has at least one of a portion in which the cross-sectional area perpendicular to the vertical direction connecting the lid side surface and the seed crystal mounting surface gradually decreases from the seed crystal mounting surface toward the lid side surface and a portion in which the cross-sectional area decreases in stages.

[0045] The pedestal and the seed crystal can be bonded (joined) using a carbon adhesive, etc. Carbon adhesive is made by dispersing carbon powder in an organic solvent, and by volatilizing the solvent, the bond (join) can be achieved without impairing the properties of the carbon material.

[0046] 7 shows an example of a configuration in which a stress buffering member 30 is disposed between the seed crystal S and the pedestal 20 when the pedestal 20 shown in FIG. 2 is used. The stress buffering member may be disposed between the seed crystal S and a pedestal having another configuration.

[0047] In this method for producing a silicon carbide single crystal, a stress buffering member (stress buffering layer) may be used that is disposed between the seed crystal and the pedestal portion for the purpose of reducing the stress applied to the seed crystal S during growth. As described above, the linear expansion coefficient of the graphite (graphite material) constituting the pedestal 20 does not match the linear expansion coefficient of the silicon carbide constituting the seed crystal over the entire wide temperature range from room temperature to 2400°C or higher in which the sublimation method is used, and shear stress occurs at the joint surface (bonding surface) between the graphite pedestal and the silicon carbide seed crystal. If the shear stress becomes large, a gap occurs between the seed crystal and the pedestal due to poor bonding, leading to the occurrence of macro defects in the crystal. In response to this, by providing the stress buffering member 30 between the seed crystal S and the pedestal portion 20, such shear stress can be suppressed, and macro defects in the silicon carbide seed crystal can be reduced.

[0048] The stress buffer member preferably has a Young's modulus of less than 5 GPa. An example of a stress buffer member having a Young's modulus of less than 5 GPa is a carbon sheet.

[0049] In this method for producing a silicon carbide single crystal, the seed crystal S may have an outer diameter of 150 mm or more. Also, the seed crystal S may have an outer diameter of 200 mm or more. EXAMPLES

[0050] Example 1 The configuration shown in Fig. 2 (a configuration in which the silicon carbide seed crystal and the pedestal are directly bonded (adhered) without using a stress buffer member) was reproduced in a simulation, and the shear stress generated between the silicon carbide seed crystal and the pedestal was evaluated based on the shape parameters of the pedestal when a temperature of 1000°C, which is the elastic range of the material, was applied. Fig. 8 is a diagram for explaining the shape parameters of the pedestal, and Fig. 9 shows the results of the relative values ​​of the shear stress obtained for each shape, assuming that the shear stress when the pedestal is cylindrical is 1. The simulation was performed using the general-purpose FEM analysis software ANSYS Mechanical (ANSYS, Inc.). In order to reduce the calculation load, the simulation was performed in two dimensions, dealing with half of the structure of an arbitrary cross section passing through the central axis. The simulation conditions were as follows: Silicon carbide seed crystal thickness: 3mm Silicon carbide seed crystal radius: 80mm r2 (radius of seed crystal mounting surface (see Figure 8)): 80 mm In addition, typical values ​​shown in Table 1 were used as the physical properties of various materials.

[0051] [Table 1]

[0052] In Fig. 9, the horizontal axis is the shape parameter (r2-r1) / h, and the vertical axis is the relative value of the shear stress. Here, as shown in Fig. 8, r1 is the radius of the side surface of the lid, r2 is the radius of the seed crystal mounting surface, and h is the height (thickness) of the pedestal. Fig. 9 shows the results of a comprehensive simulation in which the radius r1 of the side surface of the lid of the pedestal and the height h of the pedestal were changed in increments of 10 mm in the ranges of 40 to 80 mm and 20 to 80 mm, respectively.

[0053] It can be seen that in the range of (r2-r1) / h>0.30 or more, the shear stress generated between the silicon carbide seed crystal and the pedestal is suppressed by 10% or more. A 10% reduction in the shear stress occurring between the silicon carbide seed crystal and the pedestal portion can suppress bonding (adhesion) defects at the bonding (adhesion) portion.

[0054] FIG. 10 shows the shapes of the first embodiment and the simulation results thereof, excluding the case where r1=80 mm, among the shapes for which the simulation was performed. Based on the results shown in FIG. 10, when the radius r1 is the same, the lower the height h, the smaller the shear stress, and when the height h is the same, the smaller the radius r1, the smaller the shear stress. When the height h was 20 mm to 40 mm, the relative value of the shear stress was 0.90 or less for all of the radius r1 ranges from 40 mm to 70 mm. In other words, the shear stress generated between the silicon carbide seed crystal and the pedestal was suppressed by 10% or more.

[0055] Example 2 Example 2 is different from Example 1 in that a stress buffer member (stress buffer layer) is provided between the silicon carbide seed crystal and the pedestal, but the other conditions are the same. The thickness of the stress buffer member is 1 mm, and the physical property values ​​used are as shown in Table 1. Fig. 11 is a diagram for explaining the shape parameters of the pedestal, and Fig. 12 shows the relative values ​​of the shear stress obtained for each shape, with the shear stress when the pedestal is cylindrical set to 1. The shear stress generated within the stress buffer member was evaluated at a position halfway in the height direction.

[0056] FIG. 12 shows the results of a comprehensive simulation in which the radius r1 of the side surface of the lid of the pedestal and the height h of the pedestal were changed in increments of 10 mm within the ranges of 40 to 80 mm and 20 to 80 mm, respectively. As in Fig. 9, the horizontal axis is the shape parameter (r2-r1) / h, and the vertical axis is the relative value of the shear stress. As in Fig. 8, r1 is the radius of the side surface of the lid, r2 is the radius of the seed crystal mounting surface, and h is the height (thickness) of the pedestal (see Fig. 11).

[0057] It can be seen that in the range greater than (r2-r1) / h>0.15, the shear stress at the evaluation position is suppressed by 10% or more. A 10% reduction in the shear stress at the evaluation position can suppress cracks in the stress buffer material.

[0058] In FIG. 12, when the x-axis is 0, the value of the shear stress is in the range of 1 to 3 MPa, and a 10% suppression of the shear stress in this range corresponds to 0.1 to 0.3 MPa. The strength of graphite varies depending on the material, but when a graphite sheet (carbon sheet) with a Young's modulus of less than 5 GPa is used as a stress buffer material, its tensile strength is generally about a few MPa. The shear strength is smaller than the tensile strength, and in materials such as carbon sheets that have anisotropy, the shear strength is even smaller. For this reason, it is believed that suppressing stress to a few MPa or less is sufficient to prevent cracks in the stress buffer material.

[0059] FIG. 13 shows the shapes of the second embodiment and the simulation results thereof, excluding the case where r1=80 mm, among the shapes for which the simulation was performed. 13, when the radius r1 was 40 to 70 mm and the height h was 20 to 80 mm, the relative value of the shear stress was 0.81 or less, i.e., the shear stress generated between the silicon carbide seed crystal and the pedestal was suppressed by about 20%. Furthermore, when the radius r1 was 40 mm to 60 mm and the height h was 20 mm to 50 mm, the relative value of the shear stress was 0.70 or less, i.e., the shear stress generated between the silicon carbide seed crystal and the pedestal was suppressed by 30% or more.

[0060] Example 3 Example 3 differs from Example 2 in that the radius r2 of the crystal mounting surface is changed to 100 mm, but the other conditions are the same.

[0061] FIG. 14 shows the results of a simulation in which the radius r1 of the seed crystal mounting surface of the pedestal and the height h of the pedestal were changed within the ranges of 40 to 100 mm and 20 to 80 mm, respectively.

[0062] It can be seen that in the range greater than (r2-r1) / h>0.15, the shear stress at the evaluation position is suppressed by 10% or more. A 10% reduction in the shear stress at the evaluation position can suppress cracks in the stress buffer material.

[0063] FIG. 15 shows the shapes of the embodiment 3 and the simulation results thereof, excluding the case where r1=100 mm, among the shapes for which the simulation was performed. 15, when the radius r1 was 40 to 90 mm and the height h was 20 to 80 mm, the relative value of the shear stress was 0.90 or less, i.e., the shear stress generated between the silicon carbide seed crystal and the pedestal was suppressed by 10% or more. Furthermore, when the radius r1 was 40 mm to 80 mm and the height h was 20 mm to 50 mm, the relative value of the shear stress was 0.72 or less, which means that the shear stress generated between the silicon carbide seed crystal and the pedestal was suppressed by nearly 30%. [Explanation of symbols]

[0064] 1 Crucible body 2 Lid 10 Crucible 20, 21, 22, 23, 24 Pedestal 20A, 21A, 22A, 23A, 24A Lid side 20B, 21B, 22B, 23B, 24B Seed crystal mounting surface 30 Stress buffer material 100 Silicon carbide single crystal manufacturing equipment

Claims

1. A crucible consisting of a crucible body and a lid; a base portion having a lid side surface supported on a lower surface of the lid portion and a seed crystal mounting surface on the opposite side of the lid side surface to which a seed crystal is attached; The base portion is made of a graphite material, the area of ​​the seed crystal mounting surface is larger than the area of ​​the lid side surface, the pedestal portion has at least one of a portion in which a cross-sectional area perpendicular to a vertical direction connecting the lid portion side surface and the seed crystal mounting surface gradually decreases from the seed crystal mounting surface toward the lid portion side surface and a portion in which the cross-sectional area decreases in a stepwise manner; The silicon carbide single crystal manufacturing apparatus, wherein the pedestal portion has a truncated cone shape.

2. A silicon carbide single crystal manufacturing apparatus as described in claim 1, wherein the base portion further has a disk-shaped portion on the seed crystal mounting surface side having an area the same as that of the seed crystal mounting surface.

3. A crucible comprising a crucible body and a lid; a base portion having a lid side surface supported on a lower surface of the lid portion and a seed crystal mounting surface on the opposite side of the lid side surface to which a seed crystal is attached; The base portion is made of a graphite material, the area of ​​the seed crystal mounting surface is larger than the area of ​​the lid side surface, the pedestal portion has a truncated cone shape with a concave side surface, and a cross-sectional area perpendicular to a vertical direction connecting the lid portion side surface and the seed crystal mounting surface decreases at a smaller rate from the seed crystal mounting surface toward the lid portion side surface.

4. A silicon carbide single crystal manufacturing apparatus as described in Claim 3, wherein the base portion further has a disk-shaped portion on the seed crystal mounting surface side having an area the same as that of the seed crystal mounting surface.

5. A crucible comprising a crucible body and a lid; a base portion having a lid side surface supported on a lower surface of the lid portion and a seed crystal mounting surface on the opposite side of the lid side surface to which a seed crystal is attached; The base portion is made of a graphite material, the area of ​​the seed crystal mounting surface is larger than the area of ​​the lid side surface, the pedestal portion has a shape in which a plurality of disks each having a smaller radius are stacked from the seed crystal mounting surface toward the lid portion side surface.

6. A method for producing a silicon carbide single crystal, using the silicon carbide single crystal production apparatus described in any one of claims 1 to 5.

7. The method for producing a silicon carbide single crystal according to claim 6 , further comprising disposing a stress buffer member between the seed crystal and the pedestal portion.

8. 8. The method for producing a silicon carbide single crystal according to claim 7, wherein the stress buffer member has a Young's modulus of less than 5 GPa.

9. The method for producing a silicon carbide single crystal according to any one of claims 6 to 8, wherein the seed crystal has an outer diameter of 150 mm or more.

10. 10. The method for producing a silicon carbide single crystal according to claim 9, wherein the seed crystal has an outer diameter of 200 mm or more.

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