Crucible for manufacturing SiC single crystals, method for manufacturing SiC single crystals

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 manufacturing a SiC single crystal. The present invention also relates to a method for manufacturing a SiC single crystal using this crucible.

Background Art

[0002] Silicon carbide (SiC) has excellent electrical properties. Compared with silicon (Si), the numerical value of the breakdown electric field strength is about one order of magnitude larger, and the numerical value of the bandgap is about three times larger. In addition, SiC has excellent thermal properties, and its thermal conductivity is about three times higher than that of Si. Due to these excellent properties, SiC is expected to be applied to various devices such as power devices, high-frequency devices, and high-temperature operation devices. These devices are manufactured by forming an epitaxial layer, which becomes the active region of the device, on a SiC single crystal substrate obtained by processing a SiC single crystal ingot using a chemical vapor deposition method (CVD) or the like.

[0003] Currently, the mainstream method for manufacturing SiC single crystals is the sublimation method (modified Lely method). In this method, SiC powder as a solid raw material is heated and sublimated at a high temperature exceeding 2000°C in a graphite crucible, and this sublimation gas is supplied to a seed crystal placed at a relatively low-temperature position, and then recrystallized on the seed crystal to obtain a single crystal ingot.

[0004] The crucible is heated to a high temperature exceeding 2000°C to sublimate the SiC solid raw material, and after sufficiently growing the SiC single crystal, it is cooled to room temperature. The thermal expansion coefficients of graphite, which is the material of the crucible, more specifically, the graphite that is the material of the pedestal inside the crucible to which the SiC seed crystal is attached, and the SiC seed crystal fixed at a predetermined position inside the crucible are different. Therefore, in the cooling process, a large stress is generated at the interface between the pedestal and the SiC seed crystal. Such stress is not preferable because it may cause cracks or fractures in the SiC single crystal, or cause the growth of crystal defects or basal plane transitions.

[0005] Conventionally, a method has been known in which a stress-relaxing layer is provided between the seed crystal and the base, and the seed crystal is attached to the base (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-131748 [Patent Document 2] International Publication No. 2016 / 006442 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a crucible that can suppress the stress applied to a SiC single crystal when used in its manufacture. Furthermore, the present invention aims to provide a method for manufacturing a SiC single crystal that can suppress the stress applied to the SiC single crystal during its manufacture. [Means for solving the problem]

[0008] The crucible for manufacturing SiC single crystals according to the present invention is A bottomed cylindrical body having sides and a bottom, wherein the bottom side has a raw material storage section capable of accommodating a SiC solid raw material, A lid portion is connected vertically upward to the raw material storage portion and closes the upper opening surface facing the bottom of the raw material storage portion, It comprises a base connected to or integrated with the lid, and having a lower surface for attaching a SiC seed crystal, The base is characterized by being made of graphite exhibiting a bending strength in the range of 5 MPa to 40 MPa.

[0009] To minimize the stress generated between the SiC seed crystal and the base during the manufacturing of SiC single crystals, one possible approach is to use a base made of a material with a thermal expansion coefficient as close as possible to that of the SiC seed crystal. During SiC single crystal manufacturing, the temperature inside the crucible can exceed 2000°C, sometimes reaching 2300°C. Therefore, graphite, which exhibits stable properties even in such high-temperature environments, is used for the base. While it cannot be ruled out that materials other than graphite may become available in the future as heat-resistant materials, from the perspective of manufacturing costs, the options for materials other than graphite are extremely limited at present.

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

[0011] More specifically, CIP molding is a method of pressurizing a mixture by filling a rubber mold with it and then applying uniform hydrostatic pressure to the mold from all directions via a liquid medium. Because it utilizes liquid pressure, the mixture is pressurized isotropically, resulting in a relatively high-density and high-strength molded product.

[0012] In contrast, extrusion molding is a method of obtaining a molded product by placing a mixture into an extrusion mold and applying pressure from one side to push it out through a nozzle. As a result, the particle size becomes larger and the density decreases compared to CIP molding, and therefore the strength tends to be lower compared to molded products produced by CIP molding. Also, in principle, the molded product exhibits directionality (anisotropy).

[0013] As mentioned above, from the viewpoint of reducing the stress between the SiC seed crystal and the base, the general approach is to bring the thermal expansion coefficient of the base closer to that of the SiC seed crystal. From this viewpoint, it is preferable to use graphite material produced by CIP molding as the base material. This is because molded products produced by CIP molding exhibit isotropy, and by controlling the molding conditions, it is relatively easy to bring the thermal expansion coefficient closer to that of the SiC seed crystal to some extent. Furthermore, since CIP molding yields relatively high-density molded products, higher strength is achieved compared to molded products produced by extrusion molding. For these reasons, relatively high-strength graphite produced by CIP molding has conventionally been used as the base material. Such graphite materials typically have a bending strength exceeding 40 MPa.

[0014] In this specification, "flexural strength" refers to a value measured according to the method specified in JIS R 7222: 2017 "Method for measuring the physical properties of graphite materials".

[0015] In reality, even with molded products produced by CIP molding, it is difficult to make the anisotropy of the coefficient of thermal expansion (coefficient of linear expansion) exactly 1, and even with careful manufacturing conditions, an anisotropy of, for example, 1.01 to 1.20 occurs. Furthermore, since the value of the coefficient of thermal expansion changes with temperature, it is difficult to perfectly match the way in which the coefficient of thermal expansion of graphite changes from temperatures exceeding 2000°C to room temperature with that of SiC. Therefore, from the viewpoint of ensuring the strength of the base while bringing the coefficient of thermal expansion closer to that of SiC to some extent, a method has been proposed in which the base is constructed from graphite material produced by CIP molding, and a stress relaxation layer is separately provided between the base and the SiC seed crystal.

[0016] In contrast, the base of the crucible for SiC single crystal manufacturing according to the present invention is made of graphite exhibiting a bending strength in the range of 5 MPa to 40 MPa. This graphite has significantly lower bending strength compared to graphite produced by conventional CIP molding. In other words, a key feature of the crucible according to the present invention is that it deliberately uses graphite with lower bending strength than conventional graphite as the constituent material of the base.

[0017] Even when growing a SiC single crystal by heating to a temperature exceeding 2000°C using the crucible according to the present invention, and then cooling to room temperature, stress is generated at the interface between the SiC seed crystal and the base due to the difference in thermal expansion coefficients of the two, as described above. Here, the base 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, if the stress generated at the interface increases during the cooling process, this interface stress will exceed the yield strength of the base's constituent material at a certain point. At this time, the part of the base closest to the SiC seed crystal (the part closest to the bottom surface) undergoes plastic deformation, and microcracks are generated. The generation of microcracks reduces the contact state between the base and the SiC seed crystal, and the stress between them is relieved and reduced.

[0018] In other words, with the crucible configuration described above, during the cooling process after SiC single crystal growth, by intentionally causing plastic deformation of the base side before strong stress is applied to the SiC seed crystal, it becomes possible to suppress the occurrence of cracks and fractures in the SiC seed crystal, and consequently in the SiC single crystal.

[0019] Furthermore, if the bending strength of the base is too low, the surface of the base may deform due to the external force applied to the base when attaching the SiC seed crystal. From this perspective, the bending strength of the base is set to 5 MPa or higher.

[0020] In the cooling process after SiC single crystal growth, the stress generated at the interface between the base and the SiC seed crystal becomes more pronounced as the SiC seed crystal size increases. In other words, the crucible with the above configuration is particularly useful when it is a crucible for SiC single crystals with a diameter of 150 mm or more. To put it another way, the lower surface of the base may be circular in shape with a diameter of 150 mm or more. More specifically, the crucible with the above configuration is useful as a crucible for growing SiC single crystals with a diameter of 6 inches (152.4 mm) or 8 inches (203.2 mm). It can also be used as a crucible for growing SiC single crystals with a diameter exceeding 8 inches.

[0021] The pedestal can be made of extruded graphite. As described above, since extrusion molding results in lower strength compared to CIP molding in principle, 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. In this case, in the cooling process after the growth of the SiC single crystal, it becomes possible to plastically deform the pedestal earlier.

[0023] The pedestal may be made of graphite having a bending strength of 10 MPa or more. According to this, the possibility of the surface of the pedestal being deformed by the external force applied to the pedestal when attaching the SiC seed crystal to the pedestal can be further reduced.

[0024] The crucible is located outside the lower surface of the pedestal when viewed in the vertical direction, and includes a support member made of the same material as the pedestal, which is connected to the side portion of the raw material storage portion. The support member is composed of a plurality of members spaced apart in the circumferential direction or a single continuous member in the circumferential direction with an opening region provided in the central portion. The support member may be configured to be able to sandwich the outer edge of the SiC seed crystal attached to the lower surface of the pedestal from the side opposite to the lower surface of the pedestal.

[0025] The support member realizes the function of stably holding the SiC seed crystal during the growth of the SiC single crystal by supporting the SiC seed crystal from the side opposite to the pedestal.

[0026] By the way, in the cooling process after the growth of the SiC single crystal, stress also occurs at the interface between the support member and the SiC seed crystal. According to the above configuration, since the support member is made of the same material as the pedestal, by the same principle as above, during the cooling process, the portion of the support member on the SiC seed crystal side is likely to plastically deform.

[0027] As a result, during the cooling process, the lower surface of the base and a portion of the support member undergo plastic deformation, causing the connected SiC single crystal and SiC seed crystal to separate from the base and support member and fall more easily into the raw material storage area. This releases stress on the SiC seed crystal, preventing cracks and fractures from occurring in the SiC single crystal.

[0028] Furthermore, even if a SiC single crystal falls as described above, solid SiC raw material remains in the raw material container, and this remaining material acts as a cushion, preventing the SiC single crystal from breaking. In addition, even in crucibles for SiC single crystals with a diameter of 150 mm or more, the distance (height) between the base and the bottom of the raw material container is at most 5 cm or less, so even if the amount of remaining raw material is minuscule, the SiC single crystal will not break.

[0029] The support member may have a shape such that, when viewed in the vertical direction, its cross-sectional area when cut in a horizontal plane decreases as it moves away from the base.

[0030] With 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. As a result, plastic deformation occurs in a portion of the support member, making it easier for the connected body of the SiC single crystal and SiC seed crystal to fall.

[0031] If the lid is constructed separately from the base, it is preferable that the lid be made of the same material as the base.

[0032] The present invention relates to a method for manufacturing a SiC single crystal, which involves manufacturing a SiC single crystal using a crucible having the above configuration. Step (a) involves introducing the SiC solid raw material into the raw material storage section, (b) A step of attaching the SiC seed crystal to the lower surface of the base, After steps (a) and (b), step (c) is performed, in which the crucible is heated to 2000°C or higher to sublimate a portion of the SiC solid raw material and grow a SiC single crystal from the lower surface of the SiC seed crystal. The process includes, after step (c), step (d) of lowering the temperature of the crucible to room temperature. The method is characterized by generating a crack on the side of the base closest to the lower surface during the execution of step (d).

[0033] The cracks referred to here are minute, vertical cracks that occur in a portion of the base, typically measuring about 0.01 mm to 0.1 mm in length. The thickness of the base is typically between 10 mm and several tens of mm.

[0034] In the above method, during the execution of step (d), the connected body of the SiC single crystal and the SiC seed crystal may detach from the lower surface of the base and fall toward the SiC solid raw material side.

[0035] Furthermore, the crucible is provided with a support member made of the same material as the base, located on the outside of the lower surface of the base when viewed vertically and connected to the side of the raw material storage section. The support member consists of multiple members spaced apart in the circumferential direction, with an opening region in the center, or a single member continuous in the circumferential direction. Step (b) includes the step of sandwiching the outer edge of the SiC seed crystal between the lower surface of the base and the support member, During the execution of step (d) above, a crack may occur in a part of the support member, resulting in a non-contact state between the support member and the SiC seed crystal.

[0036] Furthermore, the support member may have a shape in which the cross-sectional area when cut in a horizontal plane decreases as it moves away from the base in the vertical direction. [Effects of the Invention]

[0037] According to the present invention, a crucible is realized that, despite having a simple configuration, can suppress the stress applied to the SiC single crystal when used in the production of SiC single crystals. [Brief explanation of the drawing]

[0038] [Figure 1] This is a schematic cross-sectional view showing the configuration of one embodiment of the crucible for manufacturing SiC single crystals according to the present invention. [Figure 2] Figure 1 is a schematic cross-sectional view showing the crucible in which SiC solid raw material and SiC seed crystals are placed. [Figure 3] This is a schematic cross-sectional view, following Figure 2, showing a crucible with a different configuration than that of Figure 1, in which SiC solid raw materials and SiC seed crystals are placed. [Figure 4A] This is a schematic plan view of the support member as seen in the vertical direction. [Figure 4B] This is another schematic plan view of the support member as seen in the vertical direction. [Figure 5] This is a schematic cross-sectional view showing a state in which a SiC single crystal has grown on the underside of a SiC seed crystal. [Figure 6] This is a schematic cross-sectional view showing how a portion of the base underwent plastic deformation during the cooling process. [Figure 7] This is a schematic cross-sectional view showing how a portion of the base and a portion of the support member underwent plastic deformation during the cooling process. [Figure 8] This is a schematic cross-sectional view showing how the SiC seed crystal was released from the base during the cooling process. [Figure 9] This is a schematic diagram illustrating potential problems that may arise when a SiC seed crystal is attached to a base without surface contact with the base. [Figure 10] This is a schematic diagram illustrating why voids propagate vertically downwards. [Figure 11] This is a schematic cross-sectional view, following Figure 5, showing the state when a SiC single crystal is grown on the lower surface of a SiC seed crystal using a crucible of another embodiment. [Figure 12] This is a schematic cross-sectional view showing how a part of the base underwent plastic deformation during the cooling process from the state shown in Figure 11. [Figure 13] This is a schematic plan view illustrating the heating method used for the crucible in the verification. [Modes for carrying out the invention]

[0039] Embodiments of the crucible for manufacturing SiC single crystals and the method for manufacturing SiC single crystals according to the present invention will be described below with reference to the drawings as appropriate. Note that the following drawings are all schematic illustrations, and the dimensional ratios in the drawings do not necessarily match the actual dimensional ratios, nor do the dimensional ratios necessarily match between drawings.

[0040] Figure 1 is a schematic cross-sectional view showing the configuration of one embodiment of a crucible for manufacturing SiC single crystals. Figure 2 is a schematic cross-sectional view showing the crucible 1 shown in Figure 1 with SiC solid raw material 15S and SiC seed crystal 5 placed inside.

[0041] In the following explanation, the XYZ coordinate system shown in Figure 1 will be referenced as appropriate. When expressing direction, positive and negative directions are distinguished, and these are indicated with a sign, such as "+Z direction" and "-Z direction". When expressing direction without distinguishing between positive and negative directions, it is simply written as "Z direction". In other words, in this specification, when simply written as "Z direction", both "+Z direction" and "-Z direction" are included. In Figure 1, the Z direction corresponds to the vertical direction.

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

[0043] The raw material storage section 10 is a bottomed cylindrical body having sides 11 and a bottom 12. A portion of the internal space 13 of the raw material storage section 10 contains the SiC solid raw material 15S.

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

[0045] The base 3 has a lower surface 3a to 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 base 3 and the lid 7 are integrated, but as shown in Figure 3, the lid 7 and the base 3 may be separate components.

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

[0047] Figure 4A is an example of a schematic plan view of the support member 9 as seen from the +Z side. The support member 9 shown in Figure 4A has a plurality of small members arranged spaced apart in the circumferential direction, with an opening region 9b provided inside them. In Figure 4A, the upper surface of each small member is shown as the upper surface 9a of the support member 9. In the configuration of the support member 9 shown in Figure 4A, the SiC seed crystal 5 is held vertically between the support member 9 and the base 3 at eight circumferentially spaced locations. However, the number of small members constituting the support member 9 in Figure 4A is not limited to eight.

[0048] As shown in Figure 4B, the support member 9 may be a single member exhibiting an annular shape with an opening region 9b formed in the center. In this case, the SiC seed crystal 5 is held vertically between the support member 9 and the base 3 in a region that is continuous in the circumferential direction.

[0049] The method for attaching the SiC seed crystal 5 to the base 3 is arbitrary. For example, it may be mechanically held using graphite screws, or it may be fixed with adhesive. In the latter method, in detail, an adhesive consisting of carbon adhesive, thermosetting resin, phenolic resin, polyimide, etc., can be applied to the lower surface 3a of the base 3 to a thickness of several micrometers, and then the SiC seed crystal 5 is bonded to it to fix the SiC seed crystal 5 to the base 3. In the former method as well, after bonding the SiC seed crystal 5 to the lower surface 3a of the base 3 to which the adhesive has been applied, the two may be further fixed with graphite screws.

[0050] In the crucible 1 of this embodiment, the base 3 is made of graphite exhibiting 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. Furthermore, the outer walls (sides 11 and bottom 12) and support members 9 that constitute the raw material storage section 10 are also preferably made of the same material as the base 3.

[0051] A heating mechanism (not shown) is installed on the outside of crucible 1, and the crucible 1 is heated by the thermal energy supplied from the heating mechanism. When crucible 1 is heated, the SiC solid raw material 15S contained in the raw material containment section 10 is heated and sublimes, changing into SiC gaseous raw material 15G. The SiC gaseous raw material 15G reaches the lower surface 5b of the SiC seed crystal 5, and a SiC single crystal grows. Figure 5 is a schematic cross-sectional view showing the state in which a SiC single crystal 20 has grown on the lower surface 5b side of the SiC seed crystal 5. In reality, polycrystalline SiC may grow on the outer wall of the base 3 in the XY plane direction, but this is omitted from the illustration in Figure 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 it begins to cool towards room temperature. At this point, there is a difference in the coefficient of thermal expansion between SiC and graphite. Therefore, as the crucible 1 cools from the state shown in Figure 5, stress is generated at the interface between the SiC seed crystal 5 and the base 3 during the cooling process. More precisely, this interface is the region where the upper surface 5a of the SiC seed crystal 5 and the lower surface 3a of the base 3 are in contact.

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

[0054] As cooling progresses, the stress generated at the interface between the SiC seed crystal 5 and the base 3 increases. In the crucible 1 of this embodiment, the base 3 is formed of a material exhibiting low bending strength, so during the cooling process, the stress generated at the interface between the SiC seed crystal 5 and the base 3 exceeds the yield strength of the constituent material of the base 3, causing plastic deformation of the lower surface 3a of the base 3. More specifically, as shown in Figure 6, microcracks 31 are generated on the lower surface 3a of the base 3. Since the bending strength of SiC is 100 MPa or more, the SiC seed crystal 5 will not undergo plastic deformation before the base 3.

[0055] The formation of microcracks 31 on the lower surface 3a side of the base 3 reduces the adhesion between the base 3 and the SiC seed crystal 5, relieving the stress on the SiC seed crystal 5, and in some cases completely releasing it. As a result, even when the crucible 1 is cooled to room temperature, the formation of cracks in the SiC seed crystal 5, and consequently in the SiC single crystal 20, is suppressed.

[0056] Both the SiC seed crystal 5 and the SiC single crystal 20 grown from this SiC seed crystal 5 are single-crystal materials. Therefore, if stress concentrates at a specific point in the SiC seed crystal 5, cracks will occur and easily propagate in the Z direction. In other words, from the perspective of preventing cracks and fractures from occurring in the SiC single crystal 20, it is important to alleviate the stress generated in the SiC seed crystal 5.

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

[0058] In this case, based on the same principle as the lower surface 3a of the base 3, it is expected that microcracks 32 will also occur in the end region of the support member 9, as shown in Figure 7. These microcracks 32 occur near the interface between the SiC seed crystal 5 and the support member 9, and near the interface between the SiC single crystal 20 and the support member 9.

[0059] As cooling progresses, the density of microcracks 31 occurring in the base 3 and the density of microcracks 32 occurring in the support member 9 increases, and the base 3 and support member 9 can no longer support the SiC seed crystal 5. At this point, the SiC seed crystal 5 becomes non-contact with the base 3 and support member 9 and falls vertically downward (see Figure 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 Figure 2. The fall distance is limited to 5 cm or less, and no cracks or fractures occur in the SiC single crystal 20 due to the impact of the fall.

[0060] As described above, according to the crucible 1 of this embodiment, during the cooling process after the growth of the SiC single crystal 20, the base 3 to which the SiC seed crystal 5 is attached is made of a material that is prone to generating microcracks 31. This relieves or releases stress on the SiC seed crystal 5, suppressing the occurrence of cracks and fissures in the SiC seed crystal 5.

[0061] Incidentally, from the viewpoint of suppressing stress on the SiC seed crystal 5 during the cooling process, it seems possible to adopt a method of fixing the SiC seed crystal 5 to the base 93 while using a base 93 made of conventional material, without surface contact with the lower surface of the base 93, in other words, with a separation portion 60 (see Figure 9). However, in this case, there is a risk that voids 63 generated due to the presence of the separation portion 60 may penetrate into the SiC single crystal 20.

[0062] More specifically, if a separation 60 exists between the SiC seed crystal 5 and the base 93, when the crucible 1 is heated, the SiC seed crystal 5 on the side of the separation 60 is heated and sublimes, adhering to the lower surface of the base 93 and recrystallizing. This sublimation creates voids 63 in a portion of the SiC seed crystal 5.

[0063] When a void 63 is generated within the SiC seed crystal 5, the phenomena of sublimation and recrystallization continue to occur within the void 63. More specifically, as shown in Figure 10, the SiC seed crystal 5 located within the region 51 on the -Z side of the void 63 is sublimated by heating and moves in the +Z direction as sublimation gas 51G. This sublimation 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 effectively moves in the -Z direction. Subsequently, the same phenomenon is repeated, causing the void 63 to move in the -Z direction and eventually penetrate into the SiC single crystal 20. If the void 63 penetrates into the SiC single crystal 20, it affects the electrical properties of the SiC single crystal 20, which reduces the reliability of the SiC wafer obtained from the SiC single crystal 20, and is therefore undesirable.

[0064] From this perspective, in order to suppress cracking and fracture in the SiC seed crystal 5, the method of attaching the SiC seed crystal 5 to the base 93 without surface contact with the base 93 cannot be adopted.

[0065] In contrast, according to the crucible 1 of this embodiment, since the base 3 is made of graphite with a bending strength in the range of 5 MPa to 40 MPa, even if the SiC seed crystal 5 is attached to the base 3 in surface contact with the base 3, minute cracks 31 are generated in the base 3 during the cooling process, relieving and releasing stress on the SiC seed crystal 5, thus suppressing the occurrence of cracks and fractures in the SiC seed crystal 5. Furthermore, the larger the SiC seed crystal 5, the more pronounced the stress problem on the SiC seed crystal 5 during the cooling process becomes. In other words, the effects of the present invention are particularly noticeable when the lower surface 3a of the base 3 of the crucible 1 has a circular shape with a diameter of 150 mm or more.

[0066] Furthermore, as described above, it is preferable that the base 3 and the SiC seed crystal 5 remain in surface contact during the heating process. From this viewpoint, it is preferable that the lower surface 3a of the base 3 be composed of a surface with the highest possible flatness, and typically, it is preferable that it has a flatness of 20 μm or less. The flatness referred to here is the flatness as defined in JIS B 0621-1984 "Definition and indication of geometric deviation". The method for measuring the flatness is arbitrary as long as it is a method that can measure the flatness as defined above, and it may be a contact method or a non-contact method.

[0067] As shown in Figure 11, the support member 9 may have a shape in which the cross-sectional area when cut in the XY plane decreases as it progresses in the -Z direction. In this case, the size of the opening region 9b located inside the support member 9 increases as it progresses in the -Z direction. With this configuration, the support member 9 contacts the outer edge portion of the lower surface 5b of the SiC seed crystal 5, but does not easily come into contact with the grown SiC single crystal 20. Once the growth of the SiC single crystal 20 is complete and cooling to the crucible 1 progresses, the connected body 23 of the SiC single crystal 20 and the SiC seed crystal 5 becomes more likely to be released from the base 3 and fall off earlier.

[0068] In addition, the crucible 1 in this embodiment may be configured without the support member 9.

[0069] [Verification 1] Multiple crucible samples were created with identical dimensions but different materials. A SiC seed crystal was attached to the base of each crucible sample, and a solid SiC raw material was placed in the raw material container. The crucible was then heated to grow a SiC single crystal. Next, after the crucible was cooled to room temperature, the presence or absence of cracks in the grown SiC single crystal was checked.

[0070] More specifically, as schematically shown in the plan view of Figure 13, samples 71, 71, ... from multiple crucibles made of the same material were placed in a single heating container 70, and SiC single crystals were grown using the samples 71, 71, ... from each crucible by heating from the bottom 72 and side walls 73. After heating was stopped and the samples cooled to room temperature, SiC single crystals were removed from each of the samples 71, 71, ... from each crucible.

[0071] Next, the presence or absence of cracks in the SiC single crystals was determined while illuminating them with light. Then, the ratio of the number of SiC single crystals with cracks to the total number of samples (71,71,...) produced from multiple crucibles made of the same material was calculated. Samples with a crack incidence rate of 0% were rated A, those with a crack incidence rate of 10% to 30% were rated B, and those with a crack incidence rate exceeding 30% were rated 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 compliant with JIS R 7222: 2017 "Method for measuring the physical properties of graphite materials".

[0074] Samples A1 to A8 are crucibles manufactured using graphite material derived from molded products produced by CIP molding. On the other hand, samples B1 to B8 are crucibles manufactured using graphite material derived from molded products produced by extrusion molding. Furthermore, each of samples A1 to A8 differs in at least one of the following conditions: the particle size of the carbon particles used in the kneading process, the type of binder used in the kneading process, and the duration of the kneading process. Similarly, each of samples B1 to B8 differs in at least one of the following conditions: the particle size of the carbon particles used in the kneading process, the type of binder used in the kneading process, and the duration of the kneading process.

[0075] Table 1 shows that as the bending strength of the materials constituting the crucible increases, the rate of crack occurrence in the SiC single crystal generally increases. Considering this point and the above-mentioned points with reference to Figure 6, it can be understood that crack occurrence in the SiC single crystal can be suppressed by lowering the bending strength of the base to which the SiC seed crystal is attached.

[0076] More specifically, it was confirmed that by setting the bending strength of the base to 40 MPa or less, the crack occurrence rate in the SiC single crystal could be suppressed to less than 30%. Furthermore, it was confirmed that by setting the bending strength of the base to 32 MPa or less, cracks did not occur in the SiC single crystal at all. More preferably, the bending strength of the base was 30 MPa or less, and particularly preferably, the bending strength of the base was 28 MPa or less.

[0077] It is understood that, in order to lower the bending strength of the base, it is preferable to use graphite derived from extruded products (extruded graphite) as the base material. However, by devising the manufacturing conditions, it is possible to reduce the bending strength to 40 MPa or less even with graphite derived from CIP molded products (Samples A1, A5~A7). However, since CIP molding is usually used to produce high-density graphite, it is not very common to use graphite derived from CIP molded products from the standpoint of lowering bending strength. However, any crucible using a graphite material with a bending strength of 40 MPa or less as the base is within the scope of the present invention, and it is not limited whether the graphite material is derived from CIP molded products or extruded products.

[0078] [Verification 2] When a 20mm thick SiC single crystal was fixed to a φ150mm base and the temperature was lowered from 2300°C to room temperature, the maximum principal stress generated at the interface between the base and the SiC single crystal was determined by simulation to be 40 MPa. 40 MPa is about 1 / 10th of the bending strength of polycrystalline SiC, but in the case of a single crystal, stress of this magnitude in the cleavage direction can induce cracking or fracture. On the other hand, when the contact between the base and the SiC single crystal was eliminated during the cooling process, the maximum principal stress generated in the SiC single crystal at the interface between the base and the SiC single crystal was 0 MPa. [Explanation of Symbols]

[0079] 1: Crucible 3: Pedestal 3a: Underside of the 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: Opening area formed on the inside of the support member 10: Raw material storage section 11: Side 12: Bottom 13: Interior space 15G: SiC gas raw material 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 the heating container 73: Side wall of heating container 93: Pedestal

Claims

1. A crucible for manufacturing SiC single crystals, A bottomed cylindrical body having sides and a bottom, wherein the bottom side has a raw material storage section capable of accommodating a SiC solid raw material, A lid portion is connected vertically upward to the raw material storage portion and closes the upper opening surface facing the bottom of the raw material storage portion, It comprises a base which is connected to or integrated with the lid and has a lower surface for attaching a SiC seed crystal, The crucible is characterized in that the base is made of graphite exhibiting a bending strength in the range of 6.3 MPa to 39.2 MPa.

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

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 is provided, located on the outside of the lower surface of the base when viewed in the vertical direction and connected to the side of the raw material storage section, The support member consists of multiple members spaced apart in the circumferential direction, with an opening region in the center, or a single member 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 the outer edge of the SiC seed crystal attached to the lower surface of the base from the side opposite to the lower surface of the base.

5. The crucible according to claim 4, characterized in that the support member has a shape in which the cross-sectional area when cut in a horizontal plane decreases as it moves away from the base in the vertical direction.

6. The crucible according to claim 1 or 2, characterized in that 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 described in claim 1 or 2, Step (a) of introducing the SiC solid raw material into the raw material storage section, (b) A step of attaching the SiC seed crystal to the lower surface of the base, After steps (a) and (b), step (c) is performed, in which the crucible is heated to 2000°C or higher to sublimate a portion of the SiC solid raw material and grow a SiC single crystal from the lower surface of the SiC seed crystal. The process includes, after step (c), step (d) of lowering the temperature of the crucible to room temperature. A method for manufacturing a SiC single crystal, characterized in that a crack is generated on the side of the base closest to the lower surface during the execution of step (d).

8. The method for manufacturing a SiC single crystal according to claim 7, characterized in that during the execution of step (d), the connected body of the SiC single crystal and the SiC seed crystal detaches from the lower surface of the base and falls toward the SiC solid raw material side.

9. The crucible is provided with a support member made of the same material as the base, located on the outside of the lower surface of the base when viewed vertically and connected to the side of the raw material storage section. The support member consists of multiple members spaced apart in the circumferential direction, with an opening region in the center, or a single member continuous in the circumferential direction. Step (b) includes the step of sandwiching the outer edge of the SiC seed crystal between the lower surface of the base and the support member, The method for manufacturing a SiC single crystal according to claim 8, characterized in that during the execution of step (d), a crack occurs in a part of the support member, and the support member and the SiC seed crystal become non-contact.

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