Crucible for manufacturing sic single crystal and method for manufacturing sic single crystal

Abstract

To provide a crucible that can suppress stress acting on an SiC single crystal when being used for manufacturing an SiC single crystal.SOLUTION: A crucible is a bottomed cylindrical body including a side part and a bottom part that includes: a raw material storage part capable of storing an SiC solid raw material on a bottom part side; a lid part communicated vertically upward relative to the raw material storage part and blocking an upper opening face opposite to the bottom part of the raw material storage part; and a pedestal communicated to the lid part or integrated with the lid part and having an undersurface to which an SiC seed crystal is fitted. The pedestal is made of a graphite that indicates bending strength within a range of 5-40 MPa.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a crucible for producing a SiC single crystal, and also to a method for producing a SiC single crystal using the crucible. [Background technology]

[0002] Silicon carbide (SiC) has excellent electrical properties, such as an electric field strength at dielectric breakdown that is about one order of magnitude higher than that of silicon (Si), and a band gap that is about three times larger. In addition, SiC has excellent thermal properties, such as a thermal conductivity that is about three times higher than that of Si. Because of these excellent properties, SiC is expected to be applied to various devices such as power devices, high-frequency devices, and high-temperature operating devices. These devices are fabricated by forming an epitaxial layer that will become the active region of the device on a SiC single crystal substrate obtained by processing a SiC single crystal ingot, using a method such as chemical vapor deposition (CVD).

[0003] Currently, the mainstream method for producing SiC single crystals is the sublimation method (modified Lely process). In this method, solid raw material SiC powder is heated to a high temperature of over 2000°C in a graphite crucible to sublimate it, and the resulting sublimation gas is supplied to a seed crystal placed at a relatively low temperature to recrystallize on the seed crystal, producing a single crystal ingot.

[0004] The crucible is heated to a high temperature exceeding 2000°C to sublimate the SiC solid raw material, and is cooled to room temperature after sufficient growth of the SiC single crystal. The graphite that is the material of the crucible, more specifically, the graphite that is the material of the pedestal in the crucible to which the SiC seed crystal is attached, and the SiC seed crystal fixed at a predetermined position in the crucible have different thermal expansion coefficients. For this reason, during the cooling process, a large stress is generated at the interface between the pedestal and the SiC seed crystal. Such stress is undesirable because it may cause cracks or breaks in the SiC single crystal, or cause the proliferation of crystal defects and basal plane dislocations.

[0005] As a method for suppressing the generation of such stress, a method has been known in the past in which a seed crystal is attached to a pedestal with a stress relaxation layer provided between the seed crystal and the pedestal (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-131748 A [Patent Document 2] International Publication No. 2016 / 006442 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a crucible capable of suppressing stress applied to a SiC single crystal when used in the production of a SiC single crystal. Another aim of the present invention is to provide a method for producing a SiC single crystal capable of suppressing stress applied to the SiC single crystal during production. [Means for solving the problem]

[0008] The crucible for producing a SiC single crystal according to the present invention comprises: a source material storage section on the bottom side that is a bottomed cylindrical body having a side portion and a bottom portion and capable of storing a SiC solid source material; a lid portion that is connected vertically upward to the raw material storage portion and closes an upper opening surface facing the bottom portion of the raw material storage portion; a base connected to the lid portion or integral with the lid portion and having a lower surface for mounting a SiC seed crystal; The base is characterized in that it is made of graphite having a bending strength within a range of 5 MPa to 40 MPa.

[0009] In order to reduce the stress generated between the SiC seed crystal and the pedestal during the production of SiC single crystals, a method of using a pedestal made of a material with a thermal expansion coefficient as close as possible to that of the SiC seed crystal can be considered. During the production of SiC single crystals, the temperature inside the crucible can reach over 2000°C, and can even reach 2300°C, so the pedestal is made of graphite, which exhibits stable properties even in such high-temperature environments. It cannot be denied that materials other than graphite may become available in the future as heat-resistant materials, but from the perspective of production costs, there is currently very little room for choosing materials other than graphite.

[0010] Graphite is manufactured through a process of kneading carbon particles with a liquid binder to obtain a kneaded mixture, pressurizing the kneaded mixture to obtain a molded product, and heating the molded product to graphitize it. Known methods for pressurizing the kneaded mixture include CIP (Cold Isostatic Pressing) molding, in which the mixture is filled into a rubber mold (rubber case) and pressure is applied, and extrusion molding, in which the mixture is extruded from a mold.

[0011] More specifically, CIP molding is a method in which the kneaded material is filled into a rubber mold, and then a liquid medium is used to apply uniform hydrostatic pressure to the rubber mold from all directions to apply pressure. Because liquid pressure is used, the kneaded material is isotropically pressed, and a molded product with relatively high density and strength can be obtained.

[0012] In contrast, extrusion molding is a method in which a kneaded material is placed in an extrusion mold and pressure is applied from one side to extrude it through a nozzle to obtain a molded product. As a result, the particle size becomes larger and the density decreases compared to CIP molding, so the strength tends to be lower than that of molded products made by CIP molding. In principle, molded products also exhibit directionality (anisotropy).

[0013] As described above, from the viewpoint of reducing the stress between the SiC seed crystal and the pedestal, it is a general idea to make the thermal expansion coefficient of the pedestal close to that of the SiC seed crystal. From this viewpoint, it is preferable to use a graphite material based on CIP molding as the material of the pedestal. This is because the molded product by CIP molding exhibits isotropy, and it can be said that it is easy to make the thermal expansion coefficient close to that of the SiC seed crystal to some extent by controlling the conditions during molding. Furthermore, according to CIP molding, a molded product with a relatively high density can be obtained, and therefore a higher strength can be achieved than that of a molded product by extrusion molding. For these reasons, graphite with a relatively high strength by CIP molding has been used as the material of the pedestal in the past. Such graphite materials typically have a bending strength of more than 40 MPa.

[0014] In addition, the "flexural strength" in this specification is a value measured by a method conforming to JIS R 7222: 2017 "Method of measuring physical properties of graphite material".

[0015] In reality, even for molded products produced by CIP molding, it is difficult to make the anisotropic ratio of the thermal expansion coefficient (linear expansion coefficient) completely 1, and even if the manufacturing conditions are devised, an anisotropic ratio of, for example, about 1.01 to 1.20 occurs. In addition, since the value of the thermal expansion coefficient also changes depending on the temperature, it is difficult to make the change in the thermal expansion coefficient of graphite completely match that of SiC from temperatures exceeding 2000°C to room temperature. Therefore, from the viewpoint of ensuring the strength of the pedestal while bringing the thermal expansion coefficient closer to that of SiC to some extent, a method has been proposed in which the pedestal is made of a graphite material produced by CIP molding, and a stress relaxation layer is separately provided between the pedestal and the SiC seed crystal.

[0016] In contrast, the base of the crucible for producing SiC single crystals according to the present invention is made of graphite with a bending strength in the range of 5 MPa to 40 MPa. This graphite has a significantly lower bending strength than graphite produced by conventional CIP molding. In other words, the crucible according to the present invention is characterized in that it deliberately employs graphite with a lower bending strength than conventional graphite as the material for the base.

[0017] Even if the crucible according to the present invention is used to grow a SiC single crystal by heating to a temperature exceeding 2000°C and then cooled to room temperature, stress occurs at the interface between the SiC seed crystal and the pedestal due to the difference in thermal expansion coefficient between the two, according to the above-mentioned principle. Here, the pedestal of the crucible according to the present invention is made of a material that exhibits a relatively low bending strength of 40 MPa or less. Therefore, when the stress generated at the interface increases during the cooling process, the stress at the interface exceeds the yield stress of the material constituting the pedestal at a certain point. At this time, a portion of the pedestal close to the SiC seed crystal (a portion close to the bottom surface) undergoes plastic deformation, and microcracks occur. The occurrence of the microcracks reduces the contact state between the pedestal and the SiC seed crystal, and the stress between them is alleviated and reduced.

[0018] In other words, with the crucible having the above configuration, by intentionally plastically deforming the base side before strong stress is applied to the SiC seed crystal in the cooling process after the SiC single crystal is grown, it is possible to suppress the occurrence of breakage or cracks in the SiC seed crystal and, ultimately, the SiC single crystal.

[0019] If the bending strength of the pedestal is too low, the surface of the pedestal may be deformed by the external force applied to the pedestal when the SiC seed crystal is attached to the pedestal. From this viewpoint, the bending strength of the pedestal is set to 5 MPa or more.

[0020] In the cooling step after the growth of the SiC single crystal, the stress generated at the interface between the pedestal and the SiC seed crystal becomes more significant as the SiC seed crystal becomes larger. That is, the crucible having the above configuration is particularly useful when it is a crucible for a SiC single crystal having a diameter of 150 mm or more. In other words, the lower surface of the pedestal may have a circular shape having a diameter of 150 mm or more. More specifically, the crucible having the above configuration is useful as a crucible for growing a SiC single crystal having a diameter of 6 inches (152.4 mm) or a SiC single crystal having a diameter of 8 inches (203.2 mm). It can also be used as a crucible for growing a SiC single crystal having a diameter of more than 8 inches.

[0021] The base can be made of extruded graphite. As described above, extrusion molding in principle results in lower strength than CIP molding, so it is possible to easily manufacture a graphite material with a low bending strength of 5 MPa to 40 MPa.

[0022] The pedestal may be made of graphite having a bending strength of 30 MPa or less, which allows the pedestal to be plastically deformed earlier in the cooling step after the SiC single crystal growth.

[0023] The pedestal may be made of graphite having a bending strength of 10 MPa or more, which can further reduce the possibility that the surface of the pedestal will be deformed due to an external force applied to the pedestal when the SiC seed crystal is attached to the pedestal.

[0024] The crucible includes a support member made of the same material as the base, the support member being located outside the lower surface of the base when viewed in the vertical direction and connected to the side portion of the raw material storage portion; The support member is made of a plurality of members arranged at intervals in the circumferential direction with an open area provided in the center, or a single member that is continuous in the circumferential direction, The support member may be configured to be capable of clamping an outer edge of the SiC seed crystal attached to the lower surface of the pedestal from a side opposite to the lower surface of the pedestal.

[0025] The support member supports the SiC seed crystal from the side opposite the pedestal, thereby realizing the function of stably holding the SiC seed crystal during the growth of the SiC single crystal.

[0026] In the cooling process after the growth of the SiC single crystal, stress is also generated at the interface between the support member and the SiC seed crystal. Since the support member is made of the same material as the base, the portion of the support member facing the SiC seed crystal is prone to plastic deformation during the cooling process due to the same principle as above.

[0027] As a result, during the cooling process, the lower surface of the pedestal and part of the support member undergo plastic deformation, so that the connected body of the SiC single crystal and the SiC seed crystal is easily separated from the pedestal and the support member and falls into the raw material container side. This releases stress on the SiC seed crystal and prevents the occurrence of breakage or cracks in the SiC single crystal.

[0028] Even if the SiC single crystal falls as described above, the SiC solid raw material remains in the raw material storage section, and the remaining raw material acts as a cushion to prevent the SiC single crystal from cracking. Even in a crucible for SiC single crystals with a diameter of 150 mm or more, the distance (height) between the pedestal and the bottom of the raw material storage section is at most 5 cm or less, so the SiC single crystal will not crack even if the amount of remaining raw material is very small.

[0029] The support member may have a shape such that, when viewed in the vertical direction, the cross-sectional area thereof, when cut in a horizontal plane, decreases with increasing distance from the base.

[0030] According to the above configuration, the SiC single crystal growing on the underside of the SiC seed crystal is less likely to come into contact with the support member, so that a portion of the support member undergoes plastic deformation, making the connection between the SiC single crystal and the SiC seed crystal more likely to fall.

[0031] When the lid portion is constructed as a separate body from the base, it is preferable that the lid portion is constructed from the same material as the base.

[0032] The method for producing a SiC single crystal according to the present invention is a method for producing a SiC single crystal using the crucible having the above configuration, comprising the steps of: (a) introducing the SiC solid source material into the source material container; (b) attaching the SiC seed crystal to the lower surface of the pedestal; a step (c) of heating the crucible to 2000° C. or higher after the steps (a) and (b) to sublimate a portion of the SiC solid source material and grow a SiC single crystal from a lower surface of the SiC seed crystal; After the step (c), a step (d) of lowering the temperature of the crucible to room temperature is provided; The method is characterized in that, during execution of the step (d), a crack is generated on a side of the base close to the lower surface.

[0033] The crack here refers to a minute crack that occurs in the vertical direction in a part of the pedestal, and is typically about 0.01 mm to 0.1 mm in length. The thickness of the pedestal is typically about 10 mm to several tens of mm.

[0034] In the above method, during the execution of the step (d), the coupled body of the SiC single crystal and the SiC seed crystal may be detached from the lower surface of the pedestal and dropped towards the SiC solid source material.

[0035] The crucible further includes a support member made of the same material as the base, the support member being located outside the lower surface of the base when viewed in the vertical direction and connected to the side portion of the raw material storage portion; The support member is made of a plurality of members arranged at intervals in the circumferential direction with an open area provided in the center, or a single member that is continuous in the circumferential direction, The step (b) includes a step of clamping an outer edge of the SiC seed crystal between the lower surface of the pedestal and the support member, During the execution of the step (d), a crack may occur in a part of the support member, causing the support member and the SiC seed crystal to be in a non-contact state.

[0036] The support member may have a shape such that the cross-sectional area, when cut in a horizontal plane, decreases with increasing distance from the base in the vertical direction. Effect of the Invention

[0037] According to the present invention, a crucible is realized which, while having a simple configuration, is capable of suppressing the stress applied to the SiC single crystal when used in producing the SiC single crystal. [Brief description of the drawings]

[0038] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of one embodiment of a crucible for producing SiC single crystals according to the present invention. [Diagram 2] 2 is a cross-sectional view showing a schematic state in which a SiC solid source material and a SiC seed crystal are placed in the crucible of FIG. 1. [Diagram 3] 3 is a cross-sectional view showing a state in which a SiC solid source material and a SiC seed crystal are placed in a crucible having a configuration different from that of FIG. 1, following FIG. 2. [Figure 4A] FIG. 4 is a schematic plan view of the support member when viewed in the vertical direction. [Figure 4B] FIG. 11 is another schematic plan view of the support member when viewed in the vertical direction. [Diagram 5] FIG. 2 is a cross-sectional view that illustrates a state in which a SiC single crystal has grown on the lower surface side of a SiC seed crystal. [Figure 6] 10 is a cross-sectional view showing a schematic view of a state in which a part of a base is plastically deformed during a cooling process. FIG. [Figure 7] 11 is a cross-sectional view showing a schematic state in which a part of the support member, in addition to a part of the base, is plastically deformed during a cooling process. FIG. [Figure 8] FIG. 11 is a cross-sectional view showing a schematic view of the SiC seed crystal being released from the pedestal during the cooling process. [Figure 9] 1 is a schematic diagram for explaining a problem that may arise when a SiC seed crystal is attached to a pedestal without being in surface contact with the pedestal. [Figure 10] 1 is a schematic diagram for explaining the reason why voids progress vertically downward. [Figure 11] 7 is a cross-sectional view, following FIG. 5, that illustrates a state in which a SiC single crystal is grown on the lower surface side of a SiC seed crystal using a crucible according to another embodiment. FIG. [Figure 12] 12 is a cross-sectional view showing a schematic state in which a part of the base is plastically deformed during cooling from the state shown in FIG. 11. FIG. [Figure 13] FIG. 13 is a schematic plan view for explaining a heating method for a crucible used in the verification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] An embodiment of a crucible for producing a SiC single crystal and a method for producing a SiC single crystal according to the present invention will be described below with reference to the drawings as appropriate. Note that the drawings are all schematic illustrations, and the dimensional ratios in the drawings do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match.

[0040] Fig. 1 is a cross-sectional view showing a schematic configuration of one embodiment of a crucible for producing a SiC single crystal, and Fig. 2 is a cross-sectional view showing a state in which a SiC solid source material 15S and a SiC seed crystal 5 are placed in the crucible 1 shown in Fig. 1.

[0041] In the following description, the XYZ coordinate system shown in FIG. 1 will be referred to as appropriate. When expressing a direction, a positive or negative sign is added, such as "+Z direction" and "-Z direction". When expressing a direction without distinguishing between positive and negative, the direction is simply described as "Z direction". In other words, in this specification, when the term "Z direction" is simply used, both the "+Z direction" and the "-Z direction" are included. In FIG. 1, the Z direction corresponds to the vertical direction.

[0042] As shown in FIGS. 1 and 2, the crucible 1 of this embodiment includes a raw material storage section 10, a lid section 7, a base 3, and a support member 9.

[0043] The raw material storage part 10 is a bottomed cylindrical body having a side part 11 and a bottom part 12. A SiC solid raw material 15S is stored in a part of an internal space 13 of the raw material storage part 10.

[0044] The lid part 7 is located on the +Z side (vertically above) of the raw material storage part 10, and closes the upper opening surface of the raw material storage part 10. In other words, the internal space 13 of the raw material storage part 10 is closed by the lid part 7.

[0045] The pedestal 3 has a lower surface 3a on which the SiC seed crystal 5 is attached, and is made of the same material as the lid 7. In the crucible 1 shown in Figures 1 and 2, the pedestal 3 and the lid 7 are integrated, but the lid 7 and the pedestal 3 may be separate members as shown in Figure 3.

[0046] As shown in Fig. 1, the support member 9 is located outside the lower surface 3a of the pedestal 3 when viewed in the Z direction, and is connected to a side portion 11 of the raw material storage unit 10. As shown in Fig. 2, the SiC seed crystal 5 attached to the lower surface 3a of the pedestal 3 has its outer edge sandwiched between the upper surface 9a of the support member 9 and the lower surface 3a of the pedestal 3. This allows the SiC seed crystal 5 to be stably held. The lower surface 5b (see Fig. 5) of the placed SiC seed crystal 5 is exposed to the internal space 13 of the raw material storage unit 10.

[0047] FIG. 4A is an example of a schematic plan view of the support member 9 as viewed from the +Z side. The support member 9 shown in FIG. 4A has a plurality of small members arranged at intervals in the circumferential direction, and an opening region 9b is provided inside the small members. In FIG. 4A, the upper surface of each small member is shown as the upper surface 9a of the support member 9. In the case of the configuration of the support member 9 shown in FIG. 4A, the SiC seed crystal 5 is sandwiched in the vertical direction between the support member 9 and the pedestal 3 at eight points spaced apart in the circumferential direction. However, in FIG. 4A, the number of small members constituting the support member 9 is not limited to eight.

[0048] 4B, the support member 9 may be a single member having an annular shape with an open region 9b formed in the center. In this case, the SiC seed crystal 5 is vertically sandwiched between the support member 9 and the base 3 in a circumferentially continuous region.

[0049] The method of attaching the SiC seed crystal 5 to the pedestal 3 is arbitrary. For example, the SiC seed crystal 5 may be mechanically held by using a graphite screw, or may be fixed by an adhesive. In the latter method, specifically, an adhesive made of a carbon adhesive, a thermosetting resin, a phenolic resin, a polyimide, or the like may be applied to the lower surface 3a of the pedestal 3 to a thickness of several μm, and then the SiC seed crystal 5 is bonded to the adhesive, thereby fixing the SiC seed crystal 5 to the pedestal 3. In the former method, the SiC seed crystal 5 may be bonded to the lower surface 3a of the pedestal 3 to which the adhesive has been applied, and then the two may be further fixed to each other by a graphite screw.

[0050] In the crucible 1 of this embodiment, the base 3 is made of graphite having a bending strength in the range of 5 MPa to 40 MPa. The lid 7 is preferably made of the same material as the base 3. Moreover, the outer wall (side portion 11 and bottom portion 12) constituting the raw material storage portion 10 and the support member 9 are also preferably made of the same material as the base 3.

[0051] A heating mechanism (not shown) is installed outside the crucible 1, and the crucible 1 is heated by supplying thermal energy from the heating mechanism. When the crucible 1 is heated, the SiC solid raw material 15S accommodated in the raw material accommodation unit 10 is heated and sublimated to become the SiC gas raw material 15G. The SiC gas raw material 15G reaches the lower surface 5b of the SiC seed crystal 5, and the SiC single crystal grows. FIG. 5 is a cross-sectional view that shows a state in which the SiC single crystal 20 has grown on the lower surface 5b side of the SiC seed crystal 5. In reality, polycrystals of SiC may grow on the outer wall of the pedestal 3 in the XY plane direction, but this is omitted in FIG. 5. The same applies to the following drawings.

[0052] After the SiC single crystal 20 has grown sufficiently, the supply of thermal energy from the heating mechanism to the crucible 1 is stopped, and cooling to room temperature begins. Here, there is a difference in thermal expansion coefficient between SiC and graphite. Therefore, when the crucible 1 is cooled from the state shown in FIG. 5, stress is generated at the interface between the SiC seed crystal 5 and the pedestal 3 during the cooling process. Strictly speaking, this interface is the region where the upper surface 5a of the SiC seed crystal 5 and the lower surface 3a of the pedestal 3 come into contact with each other.

[0053] As described above, the base 3 of the crucible 1 of this embodiment is made of graphite with a bending strength in the range of 5 MPa to 40 MPa. This bending strength is lower than that of the bases of crucibles for SiC single crystals that have been used conventionally.

[0054] As cooling progresses, stress occurring at the interface between the SiC seed crystal 5 and the pedestal 3 increases. As in the crucible 1 of this embodiment, the pedestal 3 is formed of a material exhibiting low bending strength, and during the cooling process, the stress occurring at the interface between the SiC seed crystal 5 and the pedestal 3 exceeds the yield stress of the constituent material of the pedestal 3, and the lower surface 3a side of the pedestal 3 undergoes plastic deformation. More specifically, as shown in FIG. 6, microcracks 31 occur on the lower surface 3a side of the pedestal 3. Note that, since the bending strength of SiC is 100 MPa or more, the SiC seed crystal 5 does not undergo plastic deformation before the pedestal 3.

[0055] The occurrence of the microcracks 31 on the lower surface 3a side of the pedestal 3 reduces the adhesion between the pedestal 3 and the SiC seed crystal 5, and the stress on the SiC seed crystal 5 is alleviated and in some cases completely released. As a result, even if the crucible 1 is cooled to room temperature, the occurrence of cracks in the SiC seed crystal 5 and, in turn, in the SiC single crystal 20 is suppressed.

[0056] The SiC seed crystal 5 and the SiC single crystal 20 grown from the SiC seed crystal 5 are both single crystal materials. For this reason, when stress is concentrated at a specific point on the SiC seed crystal 5, cracks are likely to occur and propagate in the Z direction. In other words, from the viewpoint of preventing breakage or cracks from occurring in the SiC single crystal 20, it can be said that it is important to alleviate the stress occurring in the SiC seed crystal 5.

[0057] If the thermal expansion coefficients are different at the connected parts, there is a high possibility that stress will occur during the cooling process. From this viewpoint, as described above, it is preferable that the cover part 7, the outer wall (side part 11 and bottom part 12) constituting the raw material storage part 10, and the support member 9 are all made of the same material as the base 3.

[0058] 7, due to the same principle as in the case of the lower surface 3a of the pedestal 3, it is expected that microcracks 32 will also occur in the end region of the support member 9. These microcracks 32 will occur in the vicinity of the interface between the SiC seed crystal 5 and the support member 9, and in the vicinity of the interface between the SiC single crystal 20 and the support member 9.

[0059] As cooling progresses, the density of microcracks 31 generated in the pedestal 3 and the density of microcracks 32 generated in the support member 9 increase, and the pedestal 3 and the support member 9 are no longer able to support the SiC seed crystal 5. At this time, the SiC seed crystal 5 falls vertically downward without contacting the pedestal 3 and the support member 9 (see FIG. 8). More specifically, the connected body 23 of the SiC single crystal 20 and the SiC seed crystal 5 falls in the -Z direction. The fallen connected body 23 lands on the upper surface of the SiC solid raw material 15S shown in FIG. 2. The falling distance remains at 5 cm or less, and the SiC single crystal 20 does not break or crack due to the impact of the fall.

[0060] As described above, according to the crucible 1 of the present embodiment, the pedestal 3 on which the SiC seed crystal 5 is attached is made of a material that is likely to cause microcracks 31 during the cooling process after the growth of the SiC single crystal 20. This relaxes or releases the stress on the SiC seed crystal 5, and suppresses the occurrence of breakage or cracks in the SiC seed crystal 5.

[0061] From the viewpoint of suppressing stress on the SiC seed crystal 5 during the cooling process, it would appear that a method of using a pedestal 93 made of a conventional material and fixing the SiC seed crystal 5 to the pedestal 93 without bringing the SiC seed crystal 5 into surface contact with the lower surface of the pedestal 93, in other words, with a spaced portion 60 provided, could be adopted (see FIG. 9 ). However, in this case, there is a risk that voids 63 caused by the presence of the spaced portion 60 may invade the SiC single crystal 20.

[0062] More specifically, if the separation portion 60 exists between the SiC seed crystal 5 and the pedestal 93, when the crucible 1 is heated, the SiC seed crystal 5 on the separation portion 60 side is heated and sublimated, and adheres to the lower surface of the pedestal 93 and recrystallizes. This sublimation generates a void 63 in a part of the SiC seed crystal 5.

[0063] When a void 63 occurs in the SiC seed crystal 5, the phenomenon of sublimation and recrystallization continues inside the void 63. More specifically, as shown in FIG. 10, the SiC seed crystal 5 present in the region 51 located on the -Z side of the void 63 is sublimated by heating and moves in the +Z direction as sublimated gas 51G. This sublimated gas 51G adheres to the inner wall on the +Z side of the void 63 and recrystallizes (recrystallization 51S). As a result, the void 63 essentially moves in the -Z direction. Thereafter, the same phenomenon is repeated, so that the void 63 moves in the -Z direction and eventually penetrates into the SiC single crystal 20. If the void 63 penetrates into the SiC single crystal 20, the electrical characteristics of the SiC single crystal 20 are affected, and the reliability of the SiC wafer obtained from the SiC single crystal 20 is reduced, which is undesirable.

[0064] From this viewpoint, in order to prevent the SiC seed crystal 5 from breaking or cracking, a method of attaching the SiC seed crystal 5 to the pedestal 93 without bringing the SiC seed crystal 5 into surface contact with the pedestal 93 cannot be adopted.

[0065] In contrast, according to the crucible 1 of the present embodiment, the pedestal 3 is made of graphite exhibiting a bending strength in the range of 5 MPa to 40 MPa, and therefore even if the SiC seed crystal 5 is attached to the pedestal 3 in a state of surface contact with the pedestal 3, microcracks 31 are generated in the pedestal 3 during the cooling process, and the stress on the SiC seed crystal 5 is relaxed and released, thereby suppressing the occurrence of breakage or cracks in the SiC seed crystal 5. Note that the larger the SiC seed crystal 5 is, the more likely the problem of the stress on the SiC seed crystal 5 during the cooling process becomes apparent. In other words, when the lower surface 3a of the pedestal 3 provided in the crucible 1 has a circular shape with a diameter of 150 mm or more, the effect of the present invention is likely to be prominent.

[0066] Furthermore, according to the above, it is found that it is preferable that the pedestal 3 and the SiC seed crystal 5 continue to be in surface contact during the heating step. From this viewpoint, it is preferable that the lower surface 3a of the pedestal 3 is configured with a surface that is as flat as possible, and typically has a flatness of 20 μm or less. The flatness referred to here refers to the flatness defined in JIS B 0621-1984 "Definition and indication of geometric deviation". The method for measuring the flatness may be any method that can measure the flatness defined above, and may be a contact method or a non-contact method.

[0067] 11, the support member 9 may have a shape in which the cross-sectional area when cut in the XY plane decreases as the distance increases in the -Z direction. In this case, the size of the opening region 9b located inside the support member 9 increases as the distance increases in the -Z direction. With this configuration, the support member 9 comes into contact with the outer edge portion of the lower surface 5b of the SiC seed crystal 5, but is less likely to come into contact with the grown SiC single crystal 20. When the growth of the SiC single crystal 20 is completed and the cooling of the crucible 1 progresses, the connection body 23 between the SiC single crystal 20 and the SiC seed crystal 5 is released from the pedestal 3 earlier and is more likely to fall.

[0068] The crucible 1 of this embodiment may not include the support member 9.

[0069] [Verification 1] A number of crucible samples were created with the same dimensions but different materials. A SiC seed crystal was attached to the base of each crucible sample, and a SiC solid source material was placed in the source material storage section. The crucible was then heated to grow a SiC single crystal. The crucible was then cooled to room temperature, and the grown SiC single crystal was checked for cracks.

[0070] 13, a plurality of crucible samples 71, 71, ... made of the same material were placed in a single heating vessel 70, and the crucible samples 71, 71, ... were heated from a bottom 72 and a side wall 73, thereby growing a SiC single crystal using each of the crucible samples 71, 71, .... After that, the heating was stopped and the samples were cooled to room temperature, and then a SiC single crystal was taken out from each of the crucible samples 71, 71, ....

[0071] Next, while shining illumination light on the SiC single crystal, it was judged whether or not cracks had occurred in the SiC single crystal. Then, the number of SiC single crystals produced from samples 71, 71, ... in multiple crucibles made of the same material, that is, the ratio of the number of SiC single crystals in which cracks had occurred to the total number of samples, was calculated. Those with a crack occurrence rate of 0% were given an evaluation of A, those with a crack occurrence rate of 10% to 30% were given an evaluation of B, and those with a crack occurrence rate of over 30% were given an evaluation of C. The evaluation results are shown in Table 1.

[0072] [Table 1]

[0073] In Table 1, the bending strength of each sample was measured using a method conforming to JIS R 7222: 2017 "Measurement method for physical properties of graphite material."

[0074] Samples A1 to A8 are crucibles manufactured using graphite material derived from a molded product by CIP molding. On the other hand, samples B1 to B8 are crucibles manufactured using graphite material derived from a molded product by extrusion molding. In addition, each of samples A1 to A8 differs in at least one condition among the particle size of carbon particles used in the kneading process, the type of binder used in the kneading process, and the time of the kneading process. Similarly, each of samples B1 to B8 differs in at least one condition among the particle size of carbon particles used in the kneading process, the type of binder used in the kneading process, and the time of the kneading process.

[0075] It can be seen from Table 1 that the incidence of cracks in the SiC single crystal generally increases as the bending strength of the material constituting the crucible increases. In view of this and the content described above with reference to Fig. 6, it can be seen that the occurrence of cracks in the SiC single crystal can be suppressed by lowering the bending strength of the pedestal on which the SiC seed crystal is attached.

[0076] More specifically, it has been confirmed that by setting the bending strength of the pedestal to 40 MPa or less, the occurrence rate of cracks in the SiC single crystal can be suppressed to less than 30%. Furthermore, it has been confirmed that by setting the bending strength of the pedestal to 32 MPa or less, cracks do not occur in the SiC single crystal. More preferably, the bending strength of the pedestal is 30 MPa or less, and particularly preferably, the bending strength of the pedestal is 28 MPa or less.

[0077] It is understood that in order to reduce the bending strength of the base, it is preferable to use graphite derived from an extrusion molded product (extrusion molded graphite) as the material of the base. However, by devising the manufacturing conditions, it is possible to reduce the bending strength to 40 MPa or less even with graphite derived from a CIP molded product (samples A1, A5 to A7). However, since CIP molding is usually used to manufacture high-density graphite, it is not very common to use graphite derived from a CIP molded product in terms of reducing bending strength. However, as long as the crucible uses a graphite material with a bending strength of 40 MPa or less as a base, it is within the scope of the present invention, and there is no limitation as to whether the graphite material is derived from a CIP molded product or an extrusion molded product.

[0078] [Verification 2] When a 20 mm thick SiC single crystal was fixed to a φ150 mm pedestal and the temperature was lowered from 2300°C to room temperature, the maximum principal stress generated at the interface between the pedestal and the SiC single crystal was calculated by simulation to be 40 MPa. 40 MPa is about 1 / 10 of the bending strength of SiC polycrystal, but in the case of a single crystal, such a stress in the cleavage direction is large enough to induce breakage or cracks. On the other hand, when the contact between the pedestal and the SiC single crystal was released during the cooling process, the maximum principal stress generated in the SiC single crystal at the interface between the pedestal and the SiC single crystal was 0 MPa. [Explanation of symbols]

[0079] 1: Crucible 3: Pedestal 3a: Underside of base 5:SiC seed crystal 5a: Top surface of SiC seed crystal 5b: Bottom surface of SiC seed crystal 7: Lid 9: Support member 9a: Upper surface of the support member 9b: Open area formed on the inside of the support member 10: Raw material storage section 11: Side 12: Bottom 13: Interior space 15G: SiC gas source 15S:SiC solid raw material 20: SiC single crystal 23: Concatenation 31: Microcracks 32: Microcracks 60: Separation part 63: Void 70: Heating container 71: Sample 72: Bottom of heating vessel 73: Side wall of heating vessel 93: Pedestal

Claims

1. A crucible for producing a SiC single crystal, comprising: a source material storage section that is a bottomed cylindrical body having a side and a bottom and that is capable of storing a SiC solid source material on the bottom side; a lid portion that is connected vertically upward to the raw material storage portion and closes an upper opening surface facing the bottom portion of the raw material storage portion; a base connected to the lid portion or integral with the lid portion and having a lower surface for mounting a SiC seed crystal; The crucible is characterized in that the base is made of graphite having a bending strength within a range of 5 MPa to 40 MPa.

2. 2. The crucible according to claim 1, wherein the base is made of graphite having a bending strength within a range of 5 MPa to 30 MPa.

3. 3. The crucible according to claim 1 or 2, characterized in that the base is made of extruded graphite.

4. a support member made of the same material as the base, the support member being located on the outer side of the lower surface of the base when viewed in the vertical direction and connected to the side portion of the raw material storage section; The support member is made of a plurality of members arranged at intervals in the circumferential direction with an open area provided in the center, or a single member that is continuous in the circumferential direction, The crucible according to claim 1 or 2, characterized in that the support member is configured to be able to clamp an outer edge of the SiC seed crystal attached to the lower surface of the pedestal from the side opposite the lower surface of the pedestal.

5. 5. The crucible according to claim 4, wherein the support member has a shape such that a cross-sectional area when cut in a horizontal plane decreases with increasing distance from the base in the vertical direction.

6. 3. The crucible according to claim 1, wherein the lower surface of the base has a circular shape with a diameter of 150 mm or more.

7. A method for producing a SiC single crystal using the crucible according to claim 1 or 2, (a) introducing the SiC solid source material into the source material container; (b) attaching the SiC seed crystal to the lower surface of the pedestal; (c) after the steps (a) and (b), heating the crucible to 2000° C. or higher to sublimate a portion of the SiC solid source material and grow a SiC single crystal from a lower surface of the SiC seed crystal; After the step (c), a step (d) of lowering the temperature of the crucible to room temperature is provided; A method for producing a SiC single crystal, comprising: generating a crack on a side of the pedestal close to the lower surface during execution of the step (d).

8. 8. The method for producing a SiC single crystal according to claim 7, wherein, during execution of the step (d), the coupled body of the SiC single crystal and the SiC seed crystal is detached from the lower surface of the pedestal and falls toward the SiC solid source material side.

9. The crucible includes a support member made of the same material as the base, the support member being located outside the lower surface of the base when viewed in the vertical direction and connected to the side portion of the raw material storage portion; The support member is made of a plurality of members arranged at intervals in the circumferential direction with an open area provided in the center, or a single member that is continuous in the circumferential direction, The step (b) includes a step of clamping an outer edge of the SiC seed crystal between the lower surface of the pedestal and the support member, 9. The method for producing a SiC single crystal according to claim 8, wherein a crack occurs in a part of the support member during execution of the step (d), so that the support member and the SiC seed crystal are brought into a non-contact state.

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