Graphite crucible and method of using graphite crucible

Abstract

To provide a graphite crucible improved in a processing efficiency while keeping high quality of growth crystals, and an SiC single crystal growing method using the graphite crucible.SOLUTION: A graphite crucible for growing an SiC single crystal on a principal surface of a seed crystal substrate by a sublimation recrystallization method, includes a container for storing raw material powder of the SiC single crystal, and a heat insulation material disposed from a bottom edge contacting with an inner surface of the container and along the inner surface. The height of the disposed heat insulation material is less than the height of a space of the graphite crucible.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a graphite crucible and a method for using the same. [Background technology]

[0002] A known method involves placing raw material powders of carbon and silicon into a graphite crucible, heating the crucible, and producing SiC single crystals by sublimation recrystallization. The structure of the graphite crucible is important for obtaining high-quality single crystals. Patent Document 1 describes forming a space between the inner surface of the graphite crucible and the aggregate of raw material powder in order to reduce temperature unevenness (radial temperature unevenness) that occurs in the raw material powder in contact with the inner surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-62451 A Summary of the Invention [Problem to be solved by the invention]

[0004] A conventional graphite crucible having a space formed between the inner surface and the aggregate of raw material powder will be described in detail with reference to the drawings. In the graphite crucible 500 shown in FIG. 8 , a space 93 (the area hatched with a dashed line in FIG. 8 ) is formed between the inner surface 92w of the container 92 of the graphite crucible 500 and the aggregate of raw material powder 91. As described above, the space 93 is provided to reduce temperature variations that occur in the raw material powder 91 in order to obtain a high-quality single crystal. Therefore, nothing is placed in the space 93. This reduces the volume in which the raw material powder 91 can be placed. Alternatively, considering that the raw material powder 91 cannot be placed in the space 93, the graphite crucible 500 must be replaced with a larger one. If the volume in which the raw material powder 91 can be placed is reduced, the processing efficiency of the grown crystal (crystal grown by sublimation recrystallization) decreases. Furthermore, even if the graphite crucible 500 is changed to a larger one, the number of graphite crucibles arranged in the heating furnace decreases, and the processing efficiency of the grown crystal decreases.

[0005] A graphite crucible that improves processing efficiency while maintaining the high quality of grown crystals, and a method for growing SiC single crystals using the graphite crucible are provided. [Means for solving the problem]

[0006] The graphite crucible is a graphite crucible for growing a SiC single crystal on a main surface of a seed crystal substrate by a sublimation recrystallization method, and the graphite crucible comprises: a container for containing the raw material powder of the SiC single crystal; a heat insulating material disposed along the inner surface from a bottom edge contacting the inner surface of the container, The height at which the heat insulating material is arranged is smaller than the height of the space in the graphite crucible.

[0007] As will be described in detail in the embodiments, the inventors, through extensive research, discovered that heat transferred from the inner surface of the graphite crucible to the outer surface of the aggregate of raw material powders reduces the quality of the SiC single crystal. Based on this discovery, a thermal insulator was placed between the inner surface of the graphite crucible and the outer surface of the aggregate to prevent heat transfer from the inner surface of the graphite crucible to the outer surface of the aggregate of raw material powders. By suppressing lateral heating of the aggregate, the occurrence of polymorphs and crystal defects in the SiC single crystal is suppressed, thereby further improving or maintaining the quality of the single crystal at a high level. Even in the case of forming a space between the inner surface of the graphite crucible and the aggregate of raw material powders without using a thermal insulator, as shown in FIG. 8, a certain degree of thermal insulation is achieved. However, when a thermal insulator is used, as in the graphite crucible of the present invention, a greater thermal insulation effect is achieved than when a space is formed between the inner surface and the aggregate. In addition, since the volume in which the insulating material is disposed is small, the amount of raw material lost due to the placement of the insulating material is suppressed, thereby improving processing efficiency. Furthermore, the height at which the insulating material is disposed in the graphite crucible is smaller than the height of the space in the graphite crucible, which means that there is a portion on the inner surface of the graphite crucible that is not surrounded by the insulating material. For the portion on the inner surface of the graphite crucible that is not in contact with the aggregate, heating from the side is more effective. By not surrounding this portion with the insulating material, heating from the side is promoted, and sublimation recrystallization is promoted.

[0008] The graphite crucible may not have a heat insulating material between the inner bottom surface of the container and the bottom surface of the aggregate of the raw material powder contained therein.

[0009] When the height at which the heat insulating material is arranged is represented by H1 (mm) and the height of the aggregate of the raw material powder is represented by H2 (mm), 0.9H2< H1< 2H2 (1) It is acceptable to satisfy the above.

[0010] H1-H2≦ 20 (2) It is acceptable to satisfy the above.

[0011] The heat insulating material may be mainly made of graphite felt, and the thickness of the heat insulating material mainly made of graphite felt may be 5 mm or less.

[0012] The heat insulating material may be mainly composed of a flexible graphite sheet or a carbon fiber reinforced graphite material. The thickness of the heat insulating material mainly composed of a flexible graphite sheet or a carbon fiber reinforced graphite material may be 3 mm or less.

[0013] The present invention provides a method for growing a SiC single crystal on a main surface of a seed crystal substrate by a sublimation recrystallization method using a graphite crucible, the method comprising: a step of arranging a heat insulating material along the inner surface from a bottom edge that contacts the inner surface of a container for containing the SiC single crystal raw material powder; a step of adding the raw material powder after the step of placing the heat insulating material; and growing a SiC single crystal by a sublimation recrystallization method after the step of introducing the raw material powder, The height at which the heat insulating material is arranged is smaller than the height of the space in the graphite crucible.

[0014] In the step of introducing the raw material powder, when the height at which the heat material is arranged is represented by H1 (mm) and the height of the aggregate of the raw material powder is represented by H2 (mm), 0.9H2< H1< 2H2 (1) The raw material powder may be charged in an amount that satisfies the above. [Effects of the Invention]

[0015] This makes it possible to provide a graphite crucible that improves processing efficiency while maintaining the high quality of the grown crystal, and a SiC single crystal growth method that uses the graphite crucible. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view of a graphite crucible. [Figure 2] FIG. 2 is a perspective view showing only the inner surface and the interior of the container. [Figure 3] FIG. 1 shows a first variant of the graphite crucible. [Figure 4] FIG. 1 shows a second variant of the graphite crucible. [Figure 5] FIG. 1 is a diagram showing an area to be observed on a fracture surface of a grown crystal. [Figure 6] 10 is a graph showing experimental results of the first embodiment. [Figure 7] 10 is a graph showing experimental results of the second embodiment. [Figure 8] FIG. 1 is a cross-sectional view of a conventional graphite crucible. DETAILED DESCRIPTION OF THE INVENTION

[0017] The following description will be made with reference to the drawings as appropriate. Note that the drawings disclosed in this specification, except for graphs, are schematic illustrations. In other words, the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

[0018] In this specification, the XYZ coordinate system will be referred to as appropriate. In this specification, when a direction is expressed and a distinction is made between positive and negative directions, it is described with a positive or negative sign, such as "+X direction" and "-X direction." In addition, when a direction is expressed without distinguishing between positive and negative directions, it is simply described as "X direction." In other words, in this specification, when simply referring to "X direction," it includes both "+X direction" and "-X direction." The same applies to the Y direction and Z direction. In this embodiment, the X direction and Y direction are horizontal directions, and the -Z direction is the direction of gravity.

[0019] [Graphite crucible overview] The graphite crucible of this embodiment will be described. Fig. 1 is a cross-sectional view of a graphite crucible 100 of this embodiment. As shown in Fig. 1, the graphite crucible 100 has a container 12 having an opening facing upward (in the +Z direction), a lid 16 that closes the opening of the container 12 and, together with the container 12, forms a space 2 partitioned from the outside, a base 14 for attaching a seed crystal substrate 11, and a heat insulating material 7.

[0020] The pedestal 14 is located inside the lid 16. FIG. 1 shows the graphite crucible 100 with the seed crystal substrate 11 attached to the pedestal 14. When the lid 16 is attached to the container 12, a space 2 is formed inside the graphite crucible 100, surrounding the seed crystal substrate 11. When raw material powder of a SiC single crystal is contained in the container 12, the space 2 is separated from the outside of the graphite crucible 100. The graphite crucible 100 is placed in a heating furnace, and the raw material powder inside the graphite crucible 100 is heated by a heat source (not shown) located outside the graphite crucible 100, such as to the side or below, causing the raw material powder to sublimate, and the space 2 inside the graphite crucible 100 becomes a sublimation gas atmosphere. Then, by maintaining seed crystal substrate 11 attached to pedestal 14 at a temperature lower than that of the raw material powder, a SiC single crystal grows on the main surface of seed crystal substrate 11.

[0021] The container 12 includes a bottom 12b of the container 12 and a sidewall 12s extending upward from the periphery of the bottom 12b of the container 12. The lid 16 includes a top plate 16t of the lid 16 and a sidewall 16s extending downward from the periphery of the top plate 16t. The bottom 12b of the container 12 and the top plate 16t of the lid 16 are circular, and the sidewall 12s of the container 12 and the sidewall 16s of the lid 16 are both cylindrical. Therefore, the interior of the graphite crucible 100 forms a cylindrical space 2.

[0022] The shapes of the container 12 and the lid 16 shown in this embodiment are merely examples, and other shapes may be used. For example, the lid 16 may have a shape that does not have a side wall 16s. Furthermore, the bottom 12b of the container 12 and the top plate 16t of the lid 16 do not have to be circular. The bottom 12b of the container 12 and the top plate 16t of the lid 16 may be rectangular or hexagonal, for example. The lid 16 may have a shape that fits into the container 12.

[0023] The raw material powder contained in the container 12 itself is not a component of the graphite crucible 100. The raw material powder is typically polycrystalline SiC powder. However, the raw material powder may contain a mixture of Si powder and C powder, which are also raw materials for single-crystal SiC. In this specification, the raw material powder contained in the container 12 as a whole may be referred to as "raw material powder aggregate 1" or simply as "aggregate 1" to distinguish it from the individual powder particles that make up the raw material powder.

[0024] [Insulation material] As described above, graphite crucible 100 is heated by a heat source (not shown) located outside, to the side, or below graphite crucible 100. Heat applied to aggregate 1 of raw material powder by the heat source is transmitted through bottom 12b of container 12 and side wall 12s of container 12. When a heat source is located to the side of the graphite crucible, aggregate 1 is heated mainly by heating side wall 12s of container 12. When a heat source is located below, aggregate 1 is heated mainly by heating bottom 12b.

[0025] As described above, when the side wall 12s of the container 12 is heated, the aggregate 1 is heated strongly from the side. Furthermore, even when the bottom 12b is primarily heated, the aggregate 1 may be heated strongly from the side through heat conduction to the side wall 12s. It has been found that heating the aggregate 1 from the side in this way reduces the quality of the grown crystal. The presumed mechanism is explained below.

[0026] To begin with, in order to produce SiC single crystals, it is desirable to make the space 2 a sublimation gas atmosphere with an atomic composition ratio of Si to C of 1:1. However, it is known that the sublimation gas generated from the raw material powder tends to have a Si-rich atomic composition (hereinafter sometimes simply referred to as "Si-rich") in which the number of Si atoms is greater than the number of C atoms during crystal growth, and this tendency tends to be particularly strong at relatively low temperatures in the early stages of crystal growth.

[0027] In this case, even if the raw material powder at a relatively low position in the assembly 1 (e.g., point P1 in Figure 1) sublimes and generates a Si-rich gas, the generated Si-rich gas changes to a more C-rich gas (a gas in which the number of C atoms is greater than the number of Si atoms) as it passes through unused raw material powder in the assembly 1 on its way to the space 2. As a result, the atomic composition ratio of Si to C in the sublimated gas in the space 2 approaches 1:1. In contrast, when the side of the assembly 1 is heated at a relatively low temperature in the early stages of crystal growth, the raw material powder at a relatively high position in the assembly 1 (e.g., point P2 in Figure 1) sublimes, generating a Si-rich gas as described above. The generated Si-rich gas is released from the assembly 1 without sufficiently interacting with the unused raw material powder. As a result, the space 2 is likely to become an atmosphere of a more Si-rich gas. During the recrystallization process from such a Si-rich gas, unstable Si droplets (liquid Si droplets) are generated on the surface of the growing crystal, and the generation of these Si droplets may cause polymorphism and / or defects in the growing crystal.

[0028] Furthermore, in the middle and later stages of crystal growth, when the source material temperature has risen sufficiently, the source material after generating the Si-rich gas will contain a large amount of C-rich portions, such as carbonized powder. Even if source material containing a large amount of carbonized powder continues to be heated at a relatively low position in the aggregate 1 (e.g., point P1 in Figure 1), the unused source material in the aggregate 1 located above acts as a filter, making it difficult for the carbonized powder to be released from the aggregate 1. In contrast, if source material at a relatively high position in the aggregate 1 (e.g., point P2 in Figure 1) continues to be heated, the carbonized powder will be more likely to be released from the aggregate 1 along with the sublimation gas. If this carbonized powder penetrates into the SiC single crystal, it will become carbon inclusions, which may act as starting points for the introduction of crystal heteromorphism and crystal defects.

[0029] Therefore, even if the side wall 12s of the container 12 is heated, the heat insulating material 7 is arranged from the bottom edge 12bsi in contact with the inner surface 12si of the container 12 along the inner surface 12si so that the sides of the assembly 1 are not excessively heated.

[0030] FIG. 2 is a perspective view showing only the inner surface 12si of the container 12 and its interior. FIG. 2 also shows the heat insulating material 7 and the aggregates 1 (hatched area) of the raw material powder. The heat insulating material 7 is in contact with the inner surface 12si of the container 12 and has a cylindrical shape that surrounds the radially outer surface of the aggregates 1. In other words, the heat insulating material 7 is sandwiched between the inner surface 12si of the container 12 and the radially outer surface of the aggregates 1. This prevents the heat transmitted through the side wall 12s of the container 12 from excessively heating the sides of the aggregates 1. This suppresses the occurrence of crystal heteromorphism and crystal defects, maintaining high quality of the single crystal.

[0031] The heat insulating material 7 is thin, and can provide a large heat insulating effect even if the volume in which the heat insulating material 7 is placed is small. By using the heat insulating material 7, the amount of raw material powder that can be put in can be increased compared to the volume of the graphite crucible 100. The aggregate 1 can be made larger, and larger crystals can be produced, thereby improving processing efficiency.

[0032] In the above-described embodiment, the height H1 (mm) at which the insulating material 7 is disposed is higher than the height H2 (mm) of the assembly 1 (i.e., so that H1≧H2 is satisfied), but this is not limited thereto. The assembly 1 may be in contact with the inner surface 12si of the container 12 without the insulating material 7 therebetween, provided that the difference is slight. Therefore, there are cases where the height H2 of the assembly 1 may be greater than the height H1 of the insulating material 7. Such an example is shown in FIG. 3. In the graphite crucible 200 shown in FIG. 3, the height H2 of the assembly 1 is slightly greater than the height H1 of the insulating material 7. Regarding "slightly greater," it is preferable that 0.9H2

[0033] An opposite example is shown in Figure 4. In the graphite crucible 300 shown in Figure 4, the height H1 of the heat insulating material 7 is much greater than the height H2 of the assemblies 1. The height H1 of the heat insulating material 7 may be greater as long as it is less than twice the height H2 of the assemblies 1 (i.e., within the range satisfying H1 < 2H2). If the height H1 of the heat insulating material 7 is less than twice the height H2 of the assemblies 1, the shielding loss of radiant heat due to the placement of the heat insulating material 7 can be suppressed.

[0034] ​To sum up the above, it is preferable that the relationship between the height H1 of the heat insulating material 7 and the height H2 of the assembly 1 satisfies the formula (1). 0.9H2< H1< 2H2 (1)

[0035] However, it is preferable that the height H1 at which the heat insulating material 7 is arranged be close to the height H2 of the assembly 1. For example, it is preferable that the height H1 at which the heat insulating material 7 is arranged be within +20 mm of the height H2 of the assembly 1. In other words, it is more preferable that the formula (2) is satisfied. This makes it possible to further suppress the shielding loss of radiant heat caused by the arrangement of the heat insulating material 7. H1-H2≦ 20 (2)

[0036] More preferably, the heat insulating material 7 is arranged so that the height H1 of the heat insulating material 7 is approximately the same as the height H2 of the assembly 1 (i.e., so that H1 ≒ H2 is satisfied). Here, "approximately the same" height means that the absolute value of the difference between the height H1 of the heat insulating material 7 and the height H2 of the assembly 1 is within 5 mm.

[0037] 1, the insulating material 7 contacts the bottom surface 12bi but does not contact the ceiling 16ti of the top plate 16t of the lid 16. In other words, the height H1 at which the insulating material 7 is disposed is smaller than the height Hs of the space 2 in the graphite crucible 100. In this case, there is a portion of the inner surface of the graphite crucible 100 that is not surrounded by the insulating material.

[0038] The advantages of having a portion not surrounded by the insulating material will be explained with reference to FIG. 2. The portion of the inner surface 12si of the container 12 that is not in contact with the aggregate 1 of raw material powder can take in radiant heat Rh from the side of the container 12 into the interior of the container 12. The radiant heat Rh heats the aggregate 1, thereby promoting sublimation recrystallization more efficiently. Because the aggregate 1 is heated mainly from the bottom 12b of the container 12, the temperature of the upper portion of the aggregate 1 is less likely to rise. The ability to provide radiant heat Rh to the upper portion of the aggregate 1 also has the effect of making the temperature of the aggregate 1 more uniform. Therefore, it is desirable to intentionally provide a portion of the inner surface 12si of the container 12 that is not surrounded by the insulating material 7. Furthermore, the inner surface 16si of the lid 16 (see FIG. 1) may also be intentionally provided with a portion not surrounded by the insulating material 7.

[0039] The heat insulating material 7 is not present between the bottom surface 12bi of the container 12 and the bottom surface of the assembly 1. In this embodiment, heating from below the assembly 1 via the bottom 12b of the container 12 is the most likely heating route for raising the temperature of the raw material. By not placing the heat insulating material 7 between the bottom surface 12bi of the container 12 and the bottom surface of the assembly 1, raw material sublimation is promoted.

[0040] The heat insulating material 7 may be mainly made of graphite felt. Graphite felt is a material that can withstand high temperatures of 2000°C or higher, to which the graphite crucible is heated. The thermal conductivity of graphite felt at 2000°C is 1.0 W / mK or less, while the thermal conductivity of a graphite crucible is approximately 40 to 85 W / mK. This indicates that the thermal conductivity of graphite felt is extremely low.

[0041] Graphite felt includes a cloth-like type with a relatively small thickness and a three-dimensional type with a relatively large thickness. The three-dimensional type is obtained by three-dimensionally molding cloth-like graphite felt. When graphite felt is mainly used, the thickness t1 (see Figure 2) of the insulating material is preferably 1 mm or more and 10 mm or less, and more preferably 2 mm or more and 5 mm or less. In this specification, the material specified by "mainly" when specifying the material that constitutes the insulating material refers to the material that constitutes the largest mass of the materials that constitute the insulating material.

[0042] The heat insulating material 7 may be mainly composed of a flexible graphite sheet or a carbon fiber reinforced graphite material. Flexible graphite sheets and carbon fiber reinforced graphite materials are mainly composed of carbon atoms. More specifically, flexible graphite sheets are sheets having a structure in which multiple layers (graphene) in which benzene ring structures extend two-dimensionally are stacked in many parts. Carbon fiber reinforced graphite material is graphite reinforced with carbon fibers, and is a material obtained by carbonizing and then graphitizing the plastic part of carbon fiber reinforced plastic by heat treatment.

[0043] The thermal conductivity of the flexible graphite sheet in the sheet surface direction at 2000°C and the thermal conductivity of the carbon fiber reinforced graphite material in the carbon fiber direction at 2000°C are 10 to 50 W / mK. Compared to the thermal conductivity of a graphite crucible, which is approximately 40 to 85 W / mK, the insulating properties of the flexible graphite sheet and the carbon fiber reinforced graphite material cannot be said to be particularly excellent. However, the thermal conductivity of the flexible graphite sheet or the carbon fiber reinforced graphite material is large and, specifically, the thermal conductivity in the thickness direction is small. The thermal conductivity of the flexible graphite sheet in the direction perpendicular to the sheet surface, i.e., the thickness direction, at 2000°C and the thermal conductivity of the carbon fiber reinforced graphite material in the direction perpendicular to the carbon fiber direction at 2000°C are 3.0 W / mK or less, and the flexible graphite sheet or the carbon fiber reinforced graphite material exhibits strong insulating properties in the thickness direction. In addition, the flexible graphite sheet or carbon fiber reinforced graphite material prevents the passage of the sublimation gas generated from the aggregate 1, and therefore also acts to keep the sublimation gas within the graphite crucible 100 and direct it to move in the +Z direction.

[0044] In terms of heat insulating effect, graphite felt is superior to flexible graphite sheet and carbon fiber reinforced graphite material, but flexible graphite sheet or carbon fiber reinforced graphite material has the advantage of being able to be processed thinner than graphite felt. When the heat insulating material is mainly composed of flexible graphite sheet or carbon fiber reinforced graphite material, the thickness t1 is preferably 0.5 mm or more and 5 mm or less, and more preferably 1 mm or more and 4 mm or less.

[0045] The insulating material 7 may be attached to the inner surface 12si of the container 12 with an adhesive or the like. After the insulating material 7 is attached to the inner surface 12si in a ring shape, the raw material powder is poured inside the ring-shaped insulating material 7. It is preferable to use an adhesive that does not contain metal elements (except silicon). It is preferable to use an organic adhesive. Before the graphite crucible 100 is heated, the adhesive holds the insulating material 7 to the container 12. However, when the graphite crucible 100 is heated, the adhesive components are decomposed or carbonized. Therefore, the adhesive components are unlikely to remain as impurities in the graphite crucible 100. The adhesive effect of the adhesive is lost in the process of decomposition or carbonization, but after the raw material powder is poured, the raw material powder is sandwiched between the assembly 1 and the inner surface 12si of the container 12, so the loss of adhesive force does not have any particular impact.

[0046] Ideally, the raw material powder is added so that the height H2 of the assembly 1 is equal to the height H1 of the insulating material 7. However, as described above, the height at which the raw material powder is added may be lower than the height at which the insulating material 7 is disposed, or the height at which the raw material powder is added may be slightly higher than the height at which the insulating material 7 is disposed.

[0047] In Figure 2, the height H1 of the insulating material is shown to be uniform in the circumferential direction, but it does not have to be uniform in the circumferential direction. If the height H1 of the insulating material is not uniform in the circumferential direction, the position of the highest insulating material in the circumferential direction is taken as H1. In Figure 2, the height H2 of the assembly 1 is shown to be uniform along the XY plane, but it does not have to be uniform along the XY plane. If the height H2 of the assembly 1 is not uniform along the XY plane, the height of the assembly 1 from the bottom surface 12bi at the highest point of the assembly 1 is taken as H2.

[0048] [Container and lid details] Both the container 12 and the lid 16 are primarily composed of graphite. In this specification, "primarily composed" means that the carbon content of graphite is 90 wt% or more of the total mass. The carbon content of the container 12 and the lid 16 may be different.

[0049] The graphite crucible (container 12 and lid 16) of this embodiment may be formed from a block body formed by cold isostatic pressing (CIP) or from an extrusion-molded block body. Generally, the thermal conductivity of an extruded graphite crucible is greater than that of a CIP-molded graphite crucible. Therefore, when placed in the same thermal environment, the extruded graphite crucible tends to supply more heat to the assembly 1 from the side. The use of a thermal insulating material is particularly effective for a graphite crucible formed from an extrusion-molded block body. However, it should be noted that this description does not deny the use of a thermal insulating material for a graphite crucible formed from a CIP-molded block body, or deny the benefits of using a thermal insulating material.

[0050] The thickness of the side wall 12s of the container 12 is preferably 2 mm to 50 mm, more preferably 5 mm to 30 mm, and even more preferably 5 mm to 20 mm. The thickness of the bottom 12b of the container 12 is preferably 2 mm to 40 mm. The thicker the side wall 12s of the container 12, the greater the amount of heat transferred per unit time from the bottom 12b of the container 12 through the side wall 12s. On the other hand, the thinner the bottom 12b of the container 12, the greater the amount of heat transferred per unit time. However, if the side wall 12s or the bottom 12b of the container 12 is too thick, the volume inside the graphite crucible 100 will be reduced by that amount, which will limit the amount of raw material powder that can be added or will require the graphite crucible 100 to be larger. For this reason, the above upper limit is set. [Example]

[0051] An experiment was conducted to investigate the effect of using the heat insulating material 7. The experiment was conducted according to the following procedure.

[0052] [First Example] First, multiple graphite crucibles 100 with the structure shown in Figure 1 were prepared, and raw material powder was placed in the prepared graphite crucibles 100. After the powder was placed in the graphite crucibles, the SiC graphite crucibles were heated to produce single crystals. The graphite crucibles 100 had a volume large enough to grow crystals with a diameter of approximately 6 inches (approximately 150 mm).

[0053] A flexible graphite sheet was used as the heat insulating material 7 used in the first example. The flexible graphite sheet was adhered to the inner surface 12si of the container 12 of the graphite crucible 100 so that the thickness direction of the sheet was the radial direction of the container 12. A spray-type adhesive was used to adhere the flexible graphite sheet to the container 12. The thickness of the flexible graphite sheet was 1 mm, but if the thickness of the heat insulating material was thicker than the thickness of the flexible graphite sheet, an insulating material having a predetermined thickness t1 was obtained by overlapping and adhering the flexible graphite sheet.

[0054] Samples s1 to s10 shown in Table 1 below are all graphite crucibles 100 containing raw materials obtained by the above procedure. The thickness t1 of the insulating material in sample s1 is 1 mm, the thickness t1 of the insulating material in samples s2 to s4 is 2 mm, the thickness t1 of the insulating material in samples s5 to s8 is 3 mm, and the thickness t1 of the insulating material in samples s9 to s10 is 4 mm. The height H1 of the insulating material 7 is in the range of 55 mm to 70 mm in all samples.

[0055] After attaching the heat insulating material 7, the raw material powder was placed in the container 12. Sample s0 is a graphite crucible of a comparative example. This graphite crucible was used without using a heat insulating material, and the raw material powder was placed in the container 12. The amount of raw material powder placed, in other words, the height H2 of the assembly 1, was approximately 55 mm for all samples (s1 to s10 and s0). The 11 samples (s1 to s10 and s0) were heated in a furnace under reduced pressure, and the grown crystals formed in each graphite crucible were analyzed. The analysis was performed in the following manner.

[0056] The grown crystal 5 was cleaved near its center, and the fractured surface 5s of the grown crystal was observed. Figure 5 shows the fractured surface 5s of the grown crystal 5. In particular, the cross-sectional region located at a distance d2 (60 mm in this example) from the axial center C1 of the grown crystal 5, and which grew from the start of growth until a specified time (170 hours in this example) had elapsed, was observed. In Figure 5, the observed cross-sectional region is indicated by diagonal hatching. Observation was performed using a digital microscope, and the number of traces of Si droplets or carbon inclusions present in the observation area was counted, and this number was used as the evaluation index. For example, an evaluation index of 4 indicates that there were four traces large enough to be observed with the microscope within the observation area. The observed traces indicate the possibility of introducing crystal polymorphs or crystal defects. The fewer the number of traces, the better. In other words, an evaluation index of 0 is the best result, and the larger the evaluation index value, the less desirable the result.

[0057] The growth region from the start of growth until the specified time has elapsed is identified using the following procedure. During single crystal growth, the nitrogen gas supplied to the heating furnace is increased multiple times at regular intervals. The nitrogen gas supplied to the heating furnace reaches the interior of the graphite crucible 100, and some of it is incorporated into the crystal growth surface. Therefore, as the nitrogen gas supplied to the heating furnace increases, the nitrogen concentration incorporated into the single crystal also increases. Meanwhile, differences in nitrogen concentration within the SiC single crystal can be confirmed as differences in color. Therefore, in the cross section of the grown single crystal, the areas that grew while the nitrogen supply was increased at regular intervals are represented as multiple lines. These are called nitrogen markers, and by counting the number of these nitrogen markers, the growth region corresponding to the specified time can be identified.

[0058] The raw material sublimation rate was calculated along with the evaluation index. The raw material sublimation rate represents the mass of raw material sublimated per hour. As sublimation gas is generated, the mass of the raw material after processing becomes smaller than the mass of the raw material before processing. The mass of the sublimated raw material can be calculated from the difference in mass between the raw material before and after processing. The average raw material sublimation rate can be calculated by dividing the mass of the sublimated raw material by the processing time. A higher raw material sublimation rate means that more sublimation gas is generated and the amount of recrystallization increases, resulting in a higher crystal growth rate. In other words, the raw material sublimation rate is an indicator of raw material processing efficiency and can be used to understand the effect of using insulation on crystal growth rate.

[0059] [Table 1]

[0060] Figure 6 is a graph showing the contents of Table 1, with the raw material sublimation rate on the horizontal axis and the evaluation index on the vertical axis. As can be seen from Table 1 and Figure 6, the evaluation index for sample s0 without a heat insulating material was 16, while the evaluation indexes for samples s1 to s10 with a heat insulating material were all 6 or less. This shows that the use of a heat insulating material reduced the number of crystalline polymorphs and crystal defects. Furthermore, no significant decrease in the raw material sublimation rate was confirmed when a heat insulating material was used.

[0061] Generally, as the raw material sublimation rate increases, the release rate of the sublimation gas also increases, which tends to reduce the reaction efficiency between the Si-rich sublimation gas and unused raw material. Furthermore, the carbonized powder tends to become more likely to fly up, which tends to increase the number of Si droplets and carbon inclusions. However, according to the above experimental results, even when the raw material sublimation rate increased to approximately 9 g / h, the number of traces did not increase and the evaluation index remained small. In other words, it was shown that the use of insulation material 7 can achieve both an improvement in processing speed and the suppression of Si droplets and carbon inclusions.

[0062] [Second Example] Graphite felt was used as the insulating material in the second example. A graphite crucible 100 similar to that in the first example was prepared, and graphite felt was placed along the inner wall of the container 12 of the graphite crucible 100. Samples s11 to s12 shown in Table 2 below differ in the thickness of the insulating material (graphite felt). The insulating material in sample s11 is 3 mm thick, while the insulating material in sample s12 is 5 mm thick. In both samples s11 and s12, the height H1 of the insulating material is 65 mm, and the height H2 of the assembly 1 is 55 mm. For ease of comparison, the experimental results for sample s0, which does not use an insulating material, are also listed in Table 2.

[0063] [Table 2]

[0064] Figure 7 is a graph of the contents of Table 2, with the raw material sublimation rate on the horizontal axis and the evaluation index on the vertical axis. As can be seen from Table 2 and Figure 7, the evaluation index for sample s0, which has no heat insulating material, is 16, while the evaluation index for samples s11 to s12, which have heat insulating material, is all 4 or less, confirming the effectiveness of suppressing Si droplets and carbon inclusions. Furthermore, no significant decrease in the raw material sublimation rate was confirmed when heat insulating material was used. [Explanation of symbols]

[0065] 1: Aggregate (of raw powder) 2: Space (inside the graphite crucible) 5: Growing crystals 5s: Fracture surface (of growing crystal) 7: Insulation material 7a: First part (of insulation) 7b: Second part (of insulation) 11: Seed crystal substrate 12: Container 12b: bottom (of a container) 12bi: inner bottom (of a container) 12s: (container) side wall 12si: inner surface (of a container) 14: Base 16: Lid 16s: Side wall (of the lid) 16t: Top plate (of the lid) 100, 200, 300: Graphite crucible

Claims

1. A graphite crucible for growing a SiC single crystal on a main surface of a seed crystal substrate by a sublimation recrystallization method, the graphite crucible comprising: a container for containing the raw material powder of the SiC single crystal; a heat insulating material disposed along the inner surface from a bottom edge contacting the inner surface of the container, A graphite crucible, wherein the height at which the heat insulating material is arranged is smaller than the height of the space in the graphite crucible.

2. 2. The graphite crucible according to claim 1, wherein there is no heat insulating material between the inner bottom surface of the container and the bottom surface of the aggregate of raw material powder contained therein.

3. The height at which the heat insulating material is arranged is H １ The height of the aggregate of the raw material powder is expressed in mm. ２ When expressed in mm, 0.9H ２ < H １ <2H ２ ・・・(1) The graphite crucible according to claim 1 or 2, wherein the above-mentioned conditions are satisfied.

4. H １ ―H ２ ≦ 20 ・・・(2) The graphite crucible according to claim 3, wherein the above-mentioned conditions are satisfied.

5. 3. The graphite crucible according to claim 1, wherein the heat insulating material is mainly composed of graphite felt.

6. 6. The graphite crucible according to claim 5, wherein the heat insulating material has a thickness of 5 mm or less.

7. 3. The graphite crucible according to claim 1, wherein the heat insulating material is mainly composed of a flexible graphite sheet or a carbon fiber reinforced graphite material.

8. 8. The graphite crucible according to claim 7, wherein the thickness of the heat insulating material is 3 mm or less.

9. A method for growing a SiC single crystal on a main surface of a seed crystal substrate by a sublimation recrystallization method using a graphite crucible, comprising: a step of arranging a heat insulating material along the inner surface from a bottom edge that contacts the inner surface of a container for containing the SiC single crystal raw material powder; a step of adding the raw material powder after the step of placing the heat insulating material; and a step of growing a SiC single crystal by a sublimation recrystallization method after the step of introducing the raw material powder, The method, wherein the height at which the heat insulating material is arranged is smaller than the height of the space in the graphite crucible.

10. In the step of adding the raw material powder, the height at which the heat material is placed is H １ The height of the aggregate of the raw material powder is expressed in mm. ２ When expressed in mm, 0.9H ２ < H １ <2H ２ ・・・(1) The method according to claim 9, wherein the raw material powder is charged in an amount that satisfies the following:

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