GRAPHITE CRUCIBLE, MANUFACTURING METHOD OF SiC SINGLE CRYSTAL, AND REGENERATION METHOD OF GRAPHITE CRUCIBLE

Abstract

To suppress a defect and a crack of a SiC single crystal to be manufactured.SOLUTION: A graphite crucible is for growing a SiC single crystal on a main plane of a seed crystal substrate by a sublimation recrystallization method. An inner space of the graphite crucible is surrounded by the main plane and inner planes except the main plane. A flexible graphite sheet is attached in a vicinity of the main plane among the inner planes. A manufacturing method of a SiC single crystal includes: a seed crystal attachment step where a seed crystal substrate is attached to the graphite crucible such that the main plane is exposed to the inner space; a sheet arrangement step where the flexible graphite sheet is attached in a vicinity of the main plane among the inner planes contacting to the inner space; a raw material entry step for entering a raw material to the graphite crucible; and a heating step where a SiC sublimation gas is formed in the inner space by heating the graphite crucible in which the raw material is entered to grow a SiC single crystal on the main SiC plane exposed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a graphite crucible, a method for manufacturing a SiC single crystal, and a method for recycling a graphite crucible.

Background Art

[0002] Conventionally, a method for manufacturing a SiC single crystal ingot by a sublimation recrystallization method has been widely known. For example, Patent Document 1 describes that silicon carbide obtained by heating and synthesizing a carbon raw material and a silicon raw material is placed in a graphite crucible, the graphite crucible is heated to sublime the silicon carbide, and a SiC single crystal is grown on a seed crystal substrate to obtain a SiC single crystal ingot (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the process of growing a SiC single crystal, defects or cracks may occur in the SiC single crystal. Defects include deviations in the atomic arrangement of the crystal, etc., and cracks include shape defects. The object of the present invention is to suppress defects and cracks in the SiC single crystal to be manufactured.

Means for Solving the Problems

[0005] The graphite crucible of the present invention is a graphite crucible for growing a SiC single crystal by a sublimation recrystallization method on the main surface of a seed crystal substrate, the internal space of the graphite crucible is surrounded by the main surface and the inner surface excluding the main surface, and a flexible graphite sheet is attached to the vicinity of the main surface of the inner surface.

[0006] Before explaining the reason why the above graphite crucible can suppress defects and cracks in SiC single crystals (hereinafter sometimes simply referred to as "single crystals"), the mechanism by which defects and cracks occur in single crystals will be explained.

[0007] SiC polycrystals (hereinafter sometimes simply referred to as "polycrystals") grow on the inner surface of the graphite crucible except for the main surface of the seed crystal substrate. Polycrystals are not the purpose of manufacturing. On the contrary, when polycrystals grow, they will contact the single crystal growing on the seed crystal substrate. In this specification, the contact between polycrystals and single crystals means not only that polycrystals and single crystals come into contact, but also that polycrystals and single crystals are bonded to each other. Then, the single crystal will be indirectly bonded to the graphite crucible through the polycrystal. The difference in the thermal expansion coefficients between the single crystal and the polycrystal is not so large, but the difference in the thermal expansion coefficients between the single crystal and the graphite constituting the crucible is large. When the temperature is lowered from the high temperature state for growing the single crystal to room temperature, the difference in dimensional changes caused by the difference in thermal expansion coefficients between the single crystal and the graphite will apply a compressive stress to one of the single crystal and the graphite crucible that are bonded with the polycrystal in between, and a tensile stress to the other. As a result, defects and cracks are caused in the single crystal. This is the mechanism by which defects and cracks occur in single crystals.

[0008] As a result of the intensive research by the present inventors, in order to suppress the occurrence of defects and cracks in single crystals and prevent this mechanism, it has been found that it is effective to attach a flexible graphite sheet to the inner surface surrounding the internal space of the graphite crucible in the vicinity of the main surface of the substrate.

[0009] It will be explained that attaching a flexible graphite sheet in the vicinity of the main surface of the substrate leads to the suppression of the occurrence of defects and cracks in the single crystal. It is difficult for polycrystals to nucleate on the flexible graphite sheet. Even if nucleation occurs on the flexible graphite sheet, the growth rate of polycrystals is slow on the flexible graphite sheet. By attaching a flexible graphite sheet in the vicinity of the main surface of the substrate, the growth of polycrystals in the vicinity of the main surface of the substrate is suppressed so that the polycrystals do not contact the single crystal.

[0010] In this specification, the main surface of the seed crystal substrate refers to a surface having a larger area than other surfaces (the side surfaces of the substrate). The two surfaces, i.e., the front surface and the back surface of the single crystal substrate, correspond to the main surfaces. Here, the back surface is the main surface fixed to the graphite crucible (base). And the front surface is the main surface exposed to the internal space. In this specification, the vicinity of the main surface of the seed crystal substrate refers to a range in which polycrystals grown starting from that position can connect to the main surface of the seed crystal substrate or the grown single crystal. That is, even if polycrystals grow, a flexible graphite sheet is arranged so that the grown polycrystals do not connect to the main surface (front surface or back surface) of the seed crystal substrate or the single crystal. Specifically, the arrangement of the flexible graphite sheet shown in the first embodiment, the second embodiment, the third embodiment, the fourth embodiment, the fifth embodiment, the sixth embodiment, and the seventh embodiment disclosed as the embodiments for carrying out the invention corresponds to the vicinity of the main surface of the seed crystal substrate. As a criterion for determining whether the place where the flexible graphite sheet is arranged corresponds to the "vicinity of the main surface of the seed crystal substrate", when a graphite crucible without arranging the flexible graphite sheet at that place is used 10 times, if polycrystals connect from that place to the main surface of the seed crystal substrate or the grown single crystal even once, it can be determined that that place is the "vicinity of the main surface of the seed crystal substrate".

[0011] By the way, graphite crucibles after being used in the production of SiC single crystals are reused in the production of SiC single crystals again. A large amount of polycrystals adhere to the inner surface of the used graphite crucible without the flexible graphite sheet attached. In order to reuse the graphite crucible, a regeneration operation of the graphite crucible is required to remove the polycrystals attached to the graphite crucible and return it to the state before production. However, the SiC polycrystals grown from the surface of the graphite crucible are strongly adhered to the surface of the graphite crucible. Therefore, it is difficult for the SiC polycrystals to detach from the graphite crucible. Also, the SiC polycrystals themselves are very hard and it is extremely difficult to break them off and detach them. However, when a flexible graphite sheet is attached to the inner surface of the graphite crucible, even if the polycrystals start to grow in the gap between the flexible graphite sheet and the crucible graphite surface or from the edge of the graphite sheet, the growth rate is slow, and furthermore, it only grows horizontally on the sheet so as to cover the flexible graphite sheet. Therefore, by simply detaching the flexible graphite sheet together from the used graphite crucible, the polycrystals can be removed from inside the graphite crucible. This simplifies the regeneration operation and reduces the man-hours required, leading to an improvement in the production efficiency of SiC single crystals and a reduction in the production cost. The improvement in the production efficiency of SiC single crystals and the reduction in the production cost by simplifying the regeneration operation can be said to be a secondary effect.

[0012] In the graphite crucible, the vicinity of the main surface to which the flexible graphite sheet is attached may be the side surface of an inner convex portion protruding toward the center of the internal space. The inner convex portion is an expression that includes both the seed crystal substrate and the pedestal for attaching the seed crystal substrate. That is, the pedestal for attaching the seed crystal substrate is the inner convex portion, and the seed crystal substrate attached to the graphite crucible without passing through the pedestal is also the inner convex portion. The generation of polycrystals can be suppressed on at least one side surface of the seed crystal substrate and the pedestal for attaching the seed crystal substrate that constitute the inner convex portion.

[0013] In the graphite crucible, the vicinity of the main surface to which the flexible graphite sheet is attached may include at least a part of the side surface of the seed crystal substrate. The generation of polycrystals on the side surface of the seed crystal substrate can be suppressed.

[0014] The vicinity of the main surface to which the flexible graphite sheet is attached may be disposed across the side surface of the seed crystal substrate and the side surface of the pedestal for attaching the seed crystal substrate. This can prevent the sublimation gas from entering the gap between the seed crystal substrate and the pedestal and suppress the formation of polycrystals in the gap.

[0015] At least a part of the side surface of the inner convex portion may have a protruding portion extending outward from the side surface of the inner convex portion. The outward direction is the radial direction from the center of the seed crystal substrate on the plane along the main surface of the seed crystal substrate. The protruding portion functions as a polycrystal growth stopper to prevent the growing polycrystals from contacting the grown crystal on the seed crystal substrate. The surface of the protruding portion is covered with a flexible graphite sheet, or the protruding portion itself is formed of a flexible graphite sheet.

[0016] The vicinity of the main surface to which the flexible graphite sheet is attached may be the ceiling surface around the inner convex portion protruding toward the center of the internal space. As described above, the growth rate of polycrystals is slow on the flexible graphite sheet. By attaching the flexible graphite sheet to the region where polycrystals are likely to grow, the amount of polycrystals generated can be suppressed.

[0017] The SiC single crystal manufacturing method includes a seed crystal mounting step of fixing a seed crystal substrate to a graphite crucible such that the main surface is exposed to the internal space, a sheet arrangement step of attaching a flexible graphite sheet to the vicinity of the main surface among the inner surfaces in contact with the internal space, a raw material input step of introducing a raw material into the graphite crucible, a heating step of heating the graphite crucible into which the raw material has been introduced to form SiC sublimation gas in the internal space and grow a SiC single crystal on the exposed main surface, and includes.

[0018] In the sheet arrangement step, the flexible graphite sheet may be attached using an organic adhesive. The components of the adhesive are less likely to remain as impurities in the graphite crucible.

[0019] After manufacturing by the SiC single crystal manufacturing method, the SiC single crystal including the seed crystal substrate is removed from the graphite crucible, and the used graphite crucible is regenerated by detaching the flexible graphite sheet from the surface to which the flexible graphite sheet is attached.

Advantages of the Invention

[0020] Thereby, defects and cracks in the SiC single crystal to be manufactured can be suppressed.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7A

Figure 7B

Figure 8

Figure 9

Figure 10A

Figure 10B

Modes for Carrying Out the Invention

[0022] The following will be described with reference to the drawings as appropriate. Note that each drawing disclosed in this specification is schematically illustrated, except for graphs and flowcharts. That is, the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios do not necessarily match between the drawings either.

[0023] In this specification, the XYZ coordinate system is described with reference as appropriate. In this specification, when expressing a direction, when distinguishing between positive and negative directions, it is described with positive and negative signs, such as "+X direction" and "-X direction". Also, when expressing a direction without distinguishing between positive and negative directions, it is simply described as "X direction". That is, in this specification, when simply described as "X direction", both "+X direction" and "-X direction" are included. The same applies to the Y direction and Z direction. In this embodiment, the X direction and the Y direction are horizontal directions, and the -Z direction is the gravitational direction.

[0024] <First Embodiment> [Overview of Graphite Crucible] The graphite crucible of the first embodiment will be described. FIG. 1 is a cross-sectional view of the graphite crucible 100 of this embodiment. As shown in FIG. 1, the graphite crucible 100 includes a container 12 having an opening in the upward direction (+Z direction), a lid 16 that closes the opening of the container 12 and forms an internally partitioned space, a seed crystal substrate 11, a pedestal 14 for attaching the seed crystal substrate 11, and a flexible graphite sheet 17 (hereinafter sometimes simply referred to as "graphite sheet 17"). Both the container 12 and the lid 16 are mainly composed of graphite. The "main component" in this specification means that the carbon content constituting graphite is 90 wt% or more of the total mass. The carbon content of the container 12 and the lid 16 is more preferably 99 wt% or more, and even more preferably 99.9 wt% or more. Also, the carbon contents of the container 12 and the lid 16 may be different. Also, the graphite used for the graphite crucible may be graphite obtained by the CIP (Cold Isostatic Press) molding method, graphite obtained by the mold molding method, or graphite obtained by the extrusion molding method.

[0025] The container 12 includes a bottom of the container 12 and a side wall provided so as to extend upward from the periphery of the bottom of the container 12. In the present embodiment, the bottom surface of the container 12 is circular, and the side wall is cylindrical. Therefore, the container 12 has a hollow cylindrical shape with the upper end (+Z side end) being open as a whole. The raw material 1 (not shown in FIG. 1, see FIG. 2) is accommodated in the container 12. Note that the raw material 1 itself is not an element constituting the graphite crucible 100.

[0026] The thickness of the side wall of the container 12 is preferably, for example, 5 mm or more and 30 mm or less. The thickness of the bottom of the container 12 is preferably, for example, 3 mm or more and 20 mm or less. The thickness of the pedestal 14 is preferably greater than 0 mm and 100 mm or less.

[0027] The lid 16 of the present embodiment includes a top plate of the lid 16 and a side wall provided so as to extend downward from the periphery of the top plate. In the present embodiment, the top plate of the lid 16 is circular, and the side wall is cylindrical. The shape of the lid 16 shown in the present embodiment is an example, and other shapes may be used. For example, the lid 16 may have a shape without a side wall. Also, the bottom surface of the container 12 and the top plate of the lid 16 do not have to be circular. The bottom surface of the container 12 and the top plate of the lid 16 may be, for example, square or hexagonal. The lid 16 is preferably shaped to fit with the container 12.

[0028] When the lid 16 is attached to the container 12, an internal space is formed in the graphite crucible 100. The internal space is partitioned from the outside of the graphite crucible 100. FIG. 2 is a diagram for explaining the names of the respective parts of the graphite crucible 100 (container 12 and lid 16) that form the internal space S1. In FIG. 2, for clarity, the illustration of the graphite sheet 17 and the raw material 1 is omitted. A pedestal 14 for attaching the seed crystal substrate 11 is disposed inside the lid 16, and the seed crystal substrate 11 is attached to the pedestal 14. Both the pedestal 14 and the seed crystal substrate 11 constitute an inwardly protruding portion 13 that protrudes from the ceiling inside the lid 16 toward the center of the internal space S1.

[0029] As shown in FIG. 2, the internal space S1 is surrounded by the inner bottom surface 12b of the container 12, the inner side surface 12w of the container 12, the inner side surface 16w of the lid 16, the ceiling surface 16s of the lid 16, the side surface 13s of the inner convex portion 13 (pedestal 14 and seed crystal substrate 11), and the exposed main surface 11s of the seed crystal substrate 11. The surfaces surrounding the internal space S1 of the graphite crucible can be divided into the exposed main surface 11s of the seed crystal substrate 11 and the inner surfaces excluding the exposed main surface 11s. The "inner surfaces excluding the exposed main surface 11s" refers to the inner bottom surface 12b of the container 12, the inner side surface 12w of the container 12, the inner side surface 16w of the lid 16, the ceiling surface 16s of the lid 16, and the side surface 13s of the inner convex portion 13.

[0030] Returning to FIG. 1, the graphite sheet 17 will be described. In the present embodiment, the graphite sheet 17 is arranged so as to include a position higher than the seed crystal substrate 11. More specifically, the graphite sheet 17 is wound around the side surface 13s of the columnar inner convex portion 13, and the sheet surface of the graphite sheet 17 is attached so as to be in contact with a part of the side surface 13s of the inner convex portion 13. The graphite sheet 17 is attached across the side surface of the pedestal 14 and the side surface of the seed crystal substrate 11 from the boundary between the pedestal 14 and the ceiling surface 16s of the lid 16 to the middle of the side surface of the seed crystal substrate 11. Note that the graphite sheet 17 may be attached so that its sheet surface covers the entire side surfaces of the pedestal 14 and the seed crystal substrate 11. At least a part of the side surface of the seed crystal substrate 11 may be covered by the sheet surface of the graphite sheet 17. The role of the graphite sheet 17 in the present embodiment will be described with reference to FIGS. 3A and 3B.

[0031] [Flexible graphite sheet] FIG. 3A shows the graphite crucible 100 after heating the graphite crucible 100 using the graphite crucible 100 of FIG. 1 to form the single crystal 19. FIG. 3B shows the graphite crucible 900 after heating the graphite crucible 900 without using the graphite sheet 17 to form the single crystal 19. The difference in the structure of the graphite crucible between the graphite crucible 100 shown in FIG. 3A and the graphite crucible 900 shown in FIG. 3B is only the presence or absence of the graphite sheet 17.

[0032] As shown in FIGS. 3A and 3B, the polycrystal 20 is nucleated from the SiC sublimation gas (hereinafter sometimes simply referred to as "sublimation gas") on the ceiling surface 16s of the graphite crucible (100, 900), which has the lowest temperature in the graphite crucible (100, 900), and the polycrystal 20 often grows starting from this nucleus. The reason why the polycrystal 20 rather than the single crystal grows is that the surface of the graphite crucible (100, 900) has an irregular atomic arrangement.

[0033] In FIG. 3B without the graphite sheet 17, a large amount of the polycrystal 20 adheres to the side surface 13s of the inner convex portion 13. The grown polycrystal 20 contacts the single crystal 19 grown on the seed crystal substrate 11, and the polycrystal 20 adheres to the single crystal 19. Then, the polycrystal 20 also adheres to the pedestal 14 and the lid 16. Both the pedestal 14 and the lid 16 are made of graphite. The thermal expansion coefficients of the pedestal 14 and the lid 16 are different from that of the single crystal 19. Therefore, in the process of cooling from the high-temperature state for growing the single crystal to room temperature, the difference in dimensional changes caused by the difference in thermal expansion coefficients between the pedestal 14 and the lid 16 and the single crystal 19 applies a compressive stress to one of the single crystal 19 and the pedestal 14 and the lid 16 that are joined with the polycrystal in between, and a tensile stress to the other. As a result, defects are introduced and cracks occur in the single crystal. In particular, the thermal expansion coefficient of the graphite crucible formed from an extruded block is smaller than that of the single crystal, and tensile internal stress is applied to the single crystal, so it is easy to cause defect introduction and cracks in the single crystal.

[0034] Also, although the seed crystal substrate 11 is fixed to the pedestal 14 with an adhesive or the like, there is a minute gap without an adhesive between the seed crystal substrate 11 and the pedestal 14. When there is no graphite sheet 17 as shown in FIG. 3B, the sublimation gas may penetrate into the gap between the seed crystal substrate 11 and the pedestal 14, and polycrystal growth may start in this gap. This polycrystal also fixes the graphite pedestal 14 and the single crystal seed crystal substrate 11, and causes stress to be applied to the single crystal on the seed crystal substrate 11, resulting in defects and cracks.

[0035] In contrast, in FIG. 3A with the graphite sheet 17, the growth rate of the polycrystal 20 on the graphite sheet 17 is slow, and the polycrystal 20 does not connect to the single crystal 19. Since the polycrystal 20 does not connect to the single crystal 19, no stress is generated in the single crystal 19. Also, since the graphite sheet 17 covers the gap between the seed crystal substrate 11 and the pedestal 14, the sublimation gas enters this gap, suppressing the generation of the polycrystal 20 and suppressing the adhesion between the graphite pedestal 14 and the single crystal seed crystal substrate 11.

[0036] In addition to the above, in the case of the graphite crucible 900 in FIG. 3B, to regenerate the graphite crucible 900, after single crystal production, it is necessary to separate the polycrystal 20 adhered to the portions surrounding the internal space S1 such as the side surface 13s of the inner convex portion 13, the ceiling surface 16s of the lid 16, and the inner surface 16w of the lid 16. In particular, since the polycrystal 20 is strongly adhered to the ceiling surface 16s, separating the polycrystal 20 is a difficult operation. In contrast, in the graphite crucible 100 in FIG. 3A with the graphite sheet 17, after single crystal production, by simply detaching the graphite sheet 17 attached to the ceiling surface 16s, a large amount of polycrystal 20 on the side surface 13s of the inner convex portion 13 can be separated. As a result, easy regeneration of the graphite crucible 900 becomes possible.

[0037] In addition, suppressing the generation of the polycrystal 20 itself leads to the promotion of the growth of the single crystal 19, so the production of the single crystal 19 is completed in a short time. The reduction of the production time contributes to the improvement of the production efficiency.

[0038] The reason for the slow growth of polycrystal 20 on graphite sheet 17 will be explained. The graphite sheet 17, also called an expanded graphite sheet, is manufactured by subjecting acid-treated natural graphite to an expansion treatment and then compression-molding it into a sheet form. The graphite sheet 17 is mainly composed of carbon atoms. Specifically, the graphite sheet 17 has a structure in many parts where a plurality of layers (graphene) in which the benzene ring structure spreads two-dimensionally are stacked. Therefore, the surface of the graphite sheet 17 is a chemically stable surface in which the benzene ring structure, that is, carbon atoms form a regular honeycomb structure. Therefore, even when a sublimation gas having a sufficient supersaturation contacts the surface of the graphite sheet 17, it is difficult to cause nucleation by the sublimation gas, and the rate of polycrystal growth on the surface of the graphite sheet 17 decreases. Note that the supersaturation represents the driving force when recrystallization proceeds due to the difference in gas partial pressure at each temperature when the sublimation gas generated in the high-temperature part contacts the low-temperature part.

[0039] Furthermore, the graphite sheet 17 has the property of having high thermal conductivity in the direction in which the sheet extends and low thermal conductivity in the thickness direction of the sheet. Therefore, when the graphite sheet 17 covers the upper part of the graphite crucible 100 where the temperature is particularly low, the action of keeping the inside of the graphite crucible warm works due to the low thermal conductivity in the thickness direction of the sheet. By maintaining a high temperature, an effect of suppressing the generation and growth of polycrystals that easily occur at the upper part of the graphite crucible 100 can also be obtained.

[0040] The graphite sheet 17 has high workability to the extent that it can be cut with a cutter knife, scissors, or the like. Since the graphite sheet 17 has flexibility, it is also easy to attach the graphite sheet 17 to a curved surface.

[0041] It is advisable to use an adhesive for attaching the graphite sheet 17. As the adhesive, it is preferable to use a component that does not contain metallic elements (excluding silicon). As the adhesive, an organic adhesive may be used. Before the graphite crucible 100 is heated, the adhesive holds the graphite sheet 17, but when the graphite crucible 100 is heated, the components of the adhesive are decomposed or oxidized. Therefore, it is difficult for the components of the adhesive to remain as impurities in the graphite crucible 100. On the other hand, the adhesive effect of the adhesive is lost during the process of decomposition or oxidation of the adhesive components, but the graphite sheet 17 can maintain its shape during adhesion due to the overlap of the graphite sheets 17 and a small amount of polycrystals growing on the graphite sheet 17 from the vicinity of the graphite sheet 17.

[0042] Although the heat resistance of the graphite sheet 17 is high, if the graphite sheet 17 is too thin, it may react with the sublimation gas with a partially Si-rich composition among the sublimation gases and be consumed, and holes may be formed in the graphite sheet 17. The thickness should be such that no holes are formed in the graphite sheet 17 even after the single crystal growth process. The thickness of the graphite sheet 17 is preferably 0.3 mm or more, and more preferably 0.5 mm or more.

[0043] Among the regions where the internal space S1 of the graphite crucible 100 is in contact, polycrystals 20 may grow in the portion excluding the main surface 11s of the seed crystal substrate 11 that is exposed. It is advisable to attach the graphite sheet 17 to the region where polycrystals 20 may grow. In the present embodiment, in particular, the graphite sheet 17 is attached to a position that is higher than the seed crystal substrate 11 where polycrystals 20 are likely to grow and that straddles the side surface of the seed crystal substrate 11 and the side surface of the pedestal 14 where the attachment of polycrystals has a great influence.

[0044] [Overview of Single Crystal Manufacturing Method and Graphite Crucible Recycling Method] FIG. 4 is a flowchart from single crystal manufacturing to graphite crucible regeneration. The single crystal manufacturing method includes a seed crystal attachment step S10 of attaching a seed crystal substrate 11 to a prepared graphite crucible 100, a sheet placement step S20 of placing a graphite sheet 17 inside the graphite crucible 100, a raw material input step S30 of charging a raw material 1 for SiC single crystal, and a heating step S40 of closing the lid 16 of the graphite crucible 100 and heating the graphite crucible 100. The order of performing the seed crystal attachment step S10, the sheet placement step S20, and the raw material input step S30 does not have to be the above-described order. The crucible regeneration step S50 is performed after the single crystal manufacturing method (S10 to S40). Note that the regeneration of the graphite crucible is not necessarily a technical matter to be performed in this specification, but is a technical matter to be performed as necessary.

[0045] The details of the heating step S40 will be described. The heating step S40 is performed by putting the graphite crucible 100 that has completed from the seed crystal attachment step S10 to the raw material input step S30 into a heating furnace and heating the graphite crucible 100. The method of the heating furnace is not particularly limited, and for example, a high-frequency induction heating method or a resistance heating method may be used. The temperature at which the raw material is heated (the maximum temperature inside the raw material) is preferably 1900 ° C or higher and 2500 ° C or lower, and more preferably 2000 ° C or higher and 2300 ° C or lower.

[0046] In the crucible regeneration step S50, the seed crystal substrate 11 on which the single crystal 19 has grown is removed from the graphite crucible 100, the remaining raw material 1 is removed, and the polycrystal 20 attached to the graphite crucible 100 is removed. As described above, a large amount of polycrystal 20 can be removed from the graphite crucible 100 only by detaching the graphite sheet 17 from the side surface of the inner convex portion 13.

[0047] <Second Embodiment> FIG. 5 is a view showing a graphite crucible of the second embodiment. Except for the matters described below, it can be implemented in the same manner as the above-described embodiment. The same applies to the third embodiment and subsequent embodiments. In the graphite crucible 150 of the present embodiment, unlike the first embodiment, the graphite sheet 17 exists only on the side surface of the pedestal 14 among the inner convex portions 13 and does not cover the side surface of the seed crystal substrate 11. Further, the graphite sheet 17 does not cover the ceiling surface 16s. In the present embodiment, since the graphite sheet 17 does not cover the gap between the seed crystal substrate 11 and the pedestal 14, the graphite sheet 17 does not lead to suppression of polycrystalline growth between the seed crystal substrate 11 and the pedestal 14. However, in the present embodiment, since the graphite sheet 17 covers the side surface of the pedestal 14, similarly to the first embodiment, it has the effect of reducing the growth rate of the polycrystal 20 adhering to the pedestal 14. In the present embodiment, since the graphite sheet 17 does not cover the ceiling surface 16s, adhesion of the polycrystal to the ceiling surface 16s cannot be suppressed, and thus, in the regeneration work, there may be a need to remove the polycrystal adhering to the ceiling surface 16s.

[0048] <Third Embodiment> FIG. 6 is a view showing a graphite crucible of the third embodiment. In the graphite crucible 200 of the present embodiment, the graphite sheet 17 covers only the side surface of the side surface 13s of the inner convex portion 13 around the gap between the pedestal 14 and the seed crystal substrate 11. Since the graphite sheet 17 covers the gap between the seed crystal substrate 11 and the pedestal 14, the graphite sheet 17 suppresses the growth of polycrystals between the seed crystal substrate 11 and the pedestal 14. Also, on the side surface covered by the graphite sheet 17, the adhesion amount of the polycrystal 20 decreases.

[0049] <Fourth Embodiment> FIG. 7A is a view showing a graphite crucible according to the fourth embodiment. In the graphite crucible 250 of this embodiment, it has a plate-like protruding portion 18 that extends outward from the side surface 13s of the inner convex portion 13. The outward direction is the direction that extends radially from the center of the seed crystal substrate 11 on the surface along the exposed main surface 11s of the seed crystal substrate 11. Since the protruding portion 18 surrounds the columnar inner convex portion 13, the overall shape of the protruding portion 18 is ring-shaped. The protruding portion 18 is in contact with the lower end (-Z side end) of the graphite sheet 17. FIG. 7B shows the graphite crucible 100 having the protruding portion 18 after the single crystal 19 has grown. The combination of the graphite sheet 17 and the protruding portion 18 suppresses the growth of the polycrystal 20 of the graphite sheet 17 and reduces the adhesion amount. In addition to this, it can obtain the effect as a polycrystal growth stopper that stops the progress of the polycrystal 20 that attempts to grow in the -Z direction. Thereby, the polycrystal 20 is prevented from contacting the single crystal 19.

[0050] The protruding portion 18 may be formed of a graphite sheet 17 having a thickness such that it does not bend due to its own weight. The thickness of the protruding portion 18 may be 0.5 mm or more, and preferably 1.0 mm or more. It may be formed by covering a heat-resistant material other than the graphite sheet with the graphite sheet 17.

[0051] <Fifth Embodiment> FIG. 8 is a view showing a graphite crucible according to the fifth embodiment. In the graphite crucible 300 of this embodiment, the graphite sheet 17 covers the ceiling surface 16s of the lid 16. The graphite sheet 17 formed on the ceiling surface 16s is annular. The graphite sheet 17 prevents the polycrystal 20 from adhering to the ceiling surface 16s of the lid 16. Since the side surface of the inner convex portion 13 is not covered by the graphite sheet 17, the generation of the polycrystal 20 on the side surface is not hindered, but the growth of the polycrystal 20 that grows from the ceiling surface 16s and attempts to reach the side surface of the inner convex portion 13 is suppressed. Also, in this embodiment, since the polycrystal adhering to the ceiling surface 16s can be removed only by detaching the graphite sheet 17 from the ceiling surface 16s, secondary effects such as improvement in the manufacturing efficiency of the SiC single crystal and reduction in the manufacturing cost can be obtained by simplifying the regeneration work.

[0052] <Sixth Embodiment> FIG. 9 is a view showing a graphite crucible of the sixth embodiment. In the graphite crucible 350 of this embodiment, the graphite sheet 17 not only covers the ceiling surface 16s of the lid 16, but also the graphite sheet 17 covers the upper part of the inner surface 16w of the lid 16. In particular, at the corner where the ceiling surface 16s and the inner surface 16w intersect, which is a place where polycrystals 20 are likely to nucleate, in this embodiment, since the graphite sheet 17 is arranged from the ceiling surface 16s to the upper part of the inner surface 16w of the lid 16 so as to cover the corner, nucleation and growth of the polycrystals 20 can be suppressed.

[0053] <Seventh Embodiment> FIG. 10A is a view showing a graphite crucible of the seventh embodiment. FIG. 10A is a view showing a cross-section of the graphite crucible 400. FIG. 10B is a cross-sectional view taken along the line D1-D1 of FIG. 10A, showing the state as seen from the +Z direction in the cross-section. The graphite crucible 400 has a tapered member 22 that exhibits a tapered shape inclined with respect to the XY plane from the outside in the XY direction of the graphite crucible 400 toward the center of the seed crystal substrate 11. The tapered member 22 of this embodiment is arranged for various purposes, such as collecting the sublimation gas on the single crystal growth surface and increasing (enlarging) the diameter of the single crystal as it grows. The upper end of the tapered member 22 extends to the vicinity of the seed crystal substrate. The tapered member 22 shown in FIG. 10A is arranged to be spaced apart so as to have a gap between it and the seed crystal substrate. However, the tapered member 22 may be arranged such that a part of it is in direct contact with the seed crystal substrate.

[0054] As seen in FIG. 10B, the tapered member 22 in the graphite crucible 400 of this embodiment has a frustum of a cone inclined surface that is connected without a gap in the circumferential direction with respect to the crucible central axis as its inner surface shape, but the shape of the tapered member 22 is not limited to that shown in the figure. For example, it may be composed of a plurality of small members obtained by cutting the frustum of a cone inclined surface in the radial direction, and the small members may be arranged to be spaced apart so as to have a gap in the circumferential direction.

[0055] Polycrystals can also adhere to the tapered member 22. The polycrystals adhering to the tapered member 22 are likely to connect to the single crystal 19 growing on the exposed main surface 11s of the seed crystal substrate 11. Therefore, a graphite sheet 17 is attached to the tapered member 22. This suppresses the growth of polycrystals on the surface of the tapered member 22. Also, even when the grown polycrystals come into contact with the single crystal, it prevents the single crystal and the tapered member from connecting through the polycrystals. In FIGS. 10A and 10B, the graphite sheet 17 is provided only on the tapered surface of the tapered member 22, but the graphite sheet 17 may also be provided on the side surface or the upper surface of the tapered member 22.

[0056] The first to seventh embodiments have been described above, introducing appropriate modifications and the like as appropriate. The present invention is not limited to the above-described embodiments and their modifications, and various improvements and changes are possible without departing from the spirit of the present invention. It is also possible to implement the first to seventh embodiments in combinations of two or three or more.

Explanation of Reference Numerals

[0057] 1: Raw material 11: Seed crystal substrate 11s: Exposed main surface (of the seed crystal substrate) 12: Container 12b: Inner bottom surface (of the container) 12w: Inner side surface (of the container) 13: Inner convex portion 13s: Side surface (of the inner convex portion) 14: Pedestal 16: Lid 16s: Ceiling surface (of the lid) 16w: Inner side surface (of the lid) 17: Graphite sheet 18: Protruding portion 19: Single crystal 20: Polycrystals 22: Tapered member 100, 150, 20, 250, 300, 350, 400, 900: Graphite crucible S10: Seed crystal attachment step S20: Sheet Placement Process S30: Raw Material Feeding Process S40: Heating Process S50: Crucible Regeneration Process

Claims

1. A graphite crucible for growing a SiC single crystal by sublimation recrystallization method on the main surface of a seed crystal substrate, The internal space of the graphite crucible is surrounded by the main surface and the inner surface excluding the main surface, A graphite crucible, characterized in that a flexible graphite sheet is attached to the vicinity of the main surface among the inner surfaces.

2. The graphite crucible according to claim 1, wherein the vicinity of the main surface to which the flexible graphite sheet is attached is the side surface of an inner convex portion protruding toward the center of the internal space.

3. The graphite crucible according to claim 2, wherein the vicinity of the main surface to which the flexible graphite sheet is attached includes at least a part of the side surface of the seed crystal substrate.

4. The graphite crucible according to claim 3, wherein the vicinity of the main surface to which the flexible graphite sheet is attached is arranged across the side surface of the seed crystal substrate and the side surface of a pedestal for attaching the seed crystal substrate.

5. The graphite crucible according to claim 2, having a protruding portion extending outward from the side surface of the inner convex portion on at least a part of the side surface of the inner convex portion, and the outward direction is a radial direction from the center of the seed crystal substrate on a plane along the main surface of the seed crystal substrate.

6. The graphite crucible according to claim 1, wherein the vicinity of the main surface to which the flexible graphite sheet is attached is the ceiling surface around an inner convex portion protruding toward the center of the internal space.

7. A seed crystal mounting step of fixing a seed crystal substrate to a graphite crucible so that the main surface is exposed to the internal space, A sheet arrangement step of attaching a flexible graphite sheet to the vicinity of the main surface among the inner surfaces in contact with the internal space, A raw material input step of inputting a raw material into the graphite crucible, Heat the graphite crucible into which the raw material has been charged to form a sublimation gas of SiC in the internal space, and grow a single crystal of SiC on the exposed main surface, a heating step; A method for manufacturing a single crystal of SiC including this.

8. The method for manufacturing a single crystal of SiC according to claim 7, characterized in that, in the sheet arrangement step, the flexible graphite sheet is attached using an organic adhesive.

9. After manufacturing by the method for manufacturing a single crystal of SiC according to claim 7 or claim 8, the single crystal of SiC including the seed crystal substrate is removed from the graphite crucible, and the flexible graphite sheet is separated from the surface to which the flexible graphite sheet is attached, thereby regenerating the used graphite crucible. A method for regenerating a graphite crucible, characterized in that.

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