Crucible and thermal field system for growing silicon carbide single crystals by PVT method

Abstract

The invention relates to the technical field of silicon carbide, in particular to a crucible for growing silicon carbide single crystals through a PVT method and a thermal field system.The crucible comprises a crucible body and a crucible cover, and the crucible cover detachably covers the top of the crucible body; graphite paper and a seed crystal are sequentially adhered to the surface, facing the crucible body, of the crucible cover body, and the outer edge of the graphite paper shrinks inwards relative to the outer edge of the crucible cover body and the outer edge of the seed crystal, so that a gap is formed between the crucible cover body and the seed crystal; the crucible body comprises a lower crucible, a graphite outer ring and a seed crystal ring, the bottom of the graphite outer ring is detachably connected with the top of the lower crucible, an annular step part is arranged in the graphite outer ring, and the seed crystal layer is arranged on the annular step part; in the direction from the bottom to the top, the side wall of the seed crystal ring gradually inclines towards the central axial direction of the seed crystal ring, the top of the seed crystal ring is provided with a protruding part facing the central axial direction of the seed crystal ring, and the protruding part is arranged in the gap in a matched mode. The crucible can effectively improve the quality of silicon carbide single crystals.

Description

Technical Field

[0001] The present application relates to the technical field of silicon carbide, and in particular to a crucible and a thermal field system for growing silicon carbide single crystals using a PVT method. Background Art

[0002] PVT (Physical Vapor Transport) is a crystal growth technique used to prepare high-quality semiconductor materials. PVT is particularly suitable for growing silicon carbide (SiC) single crystals, which are widely used in semiconductor, electronics, optics and high-temperature fields due to their excellent physical and chemical properties.

[0003] However, there are still some defects in the PVT method of silicon carbide crystallization, which are mainly divided into three categories. The first category, which is also the crystallization defect that has a fatal impact on the performance of the crystal, is microtubes and severe TSD (screw dislocation). The second category is polymorphic phase transition. The third category is carbon encapsulation caused by graphitization. Specifically, microtubes and large TSD seriously affect the crystallization quality of the crystal. Most of the dislocations are dense, linear and high dislocation areas are usually inherited from the seed crystal itself or affected by the initial growth. In general, the quality of the seed crystal will be strictly controlled, and high-quality seed crystals with "zero microtubes" and low defect density are usually selected. However, the inherent defects of the seed crystal bonding process itself will also lead to the generation of fatal defects in the early growth stage or even throughout the entire crystal growth process, such as back corrosion, voids, impurities, microtubes and dislocation aggregation related to bonding quality. In addition, because of the long-term growth at high temperature, carbon encapsulation defects also have a fatal effect on the crystal. In the PVT method, there are two main sources of carbon encapsulation: first, the graphite part that constitutes the thermal field itself; second, the carbon in the silicon carbide powder source. Graphitization occurs when there is a net loss of Si in SiC powder. Graphitization is very likely to occur at temperatures above 2000°C.

[0004] Therefore, the relevant technology of growing silicon carbide single crystals by the PVT method still needs to be improved. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the present invention provides a crucible and a thermal field system for growing silicon carbide single crystals by a PVT method.

[0006] In a first aspect of the present application, a crucible for growing silicon carbide single crystals by a PVT method is provided. According to an embodiment of the present application, the crucible comprises a crucible body and a crucible cover, wherein the crucible cover is a detachable cover disposed on the top of the crucible body;

[0007] Graphite paper and a seed crystal are sequentially pasted on the surface of the crucible cover facing the crucible body, and the outer edge of the graphite paper is retracted relative to the outer edge of the crucible cover and the outer edge of the seed crystal, so that a gap is formed between the crucible cover and the seed crystal;

[0008] The crucible body comprises a lower crucible, a graphite outer ring and a seed crystal ring, the bottom of the graphite outer ring is detachably connected to the top of the lower crucible, a first annular step portion is provided inside the graphite outer ring, and the seed crystal layer is provided on the first annular step portion;

[0009] In the direction from the bottom to the top, the side wall of the seed crystal ring gradually tilts toward the central axis thereof, and the top of the seed crystal ring is provided with a protrusion facing the central axis thereof, and the protrusion is matched and arranged in the gap.

[0010] In the crucible of the present application, the seed crystal ring initially clamps the edge of the seed crystal, which can play a supporting and fixing role to offset the technical effect of seed crystal bonding on crystal fixation, so as to reduce the dependence on bonding quality during the growth of silicon carbide single crystals. The seed crystal ring is arranged in a close fit with the seed crystal to prevent polycrystalline formation at the edge of the seed crystal, thereby avoiding quality problems of silicon carbide single crystals caused by edge polycrystalline (such as crack extension, phase change and polycrystalline, etc.).

[0011] At the same time, in the present application, the raised portion of the seed crystal ring is embedded in the gap between the seed crystal and the crucible cover. The seed crystal ring wraps the seed crystal, and while having a clamping effect, the seed crystal ring has a certain angle from top to bottom, that is, the side wall of the seed crystal ring gradually tilts toward its central axis. At this time, during the growth of the silicon carbide single crystal, the diameter of the growing silicon carbide single crystal is larger than the diameter of the seed crystal, leaving some unqualified areas for removal, and high-quality silicon carbide single crystals can grow with the same diameter as the seed crystal, thereby obtaining high-quality, large-sized silicon carbide single crystals. The above-mentioned crucible can significantly improve the defects of ablation, virtual adhesion, and back corrosion caused by over-reliance on seed crystal bonding and fixation; other growth defects caused by edge polycrystalline, thereby obtaining high-quality silicon carbide single crystals with low defect density and uniform resistivity.

[0012] According to an embodiment of the present application, the depth of the gap in the horizontal direction is 5 mm to 10 mm.

[0013] According to an embodiment of the present application, the angle between the side wall of the seed crystal ring and the horizontal direction is 69° to 85°.

[0014] According to an embodiment of the present application, the seed crystal ring includes a plurality of ring petals, and specifically may include 2 to 4 ring petals.

[0015] According to an embodiment of the present application, at least one exhaust hole is provided on the side wall of the seed crystal ring.

[0016] According to an embodiment of the present application, a plurality of exhaust holes are provided on the side wall of the seed crystal ring and are spaced apart along the circumference of the seed crystal ring.

[0017] According to an embodiment of the present application, a first through hole is provided on the side wall of the graphite outer ring above the first annular step portion.

[0018] According to an embodiment of the present application, the crucible further comprises a pressing plate, wherein the pressing plate cover is arranged above the crucible cover body, the pressing plate has a second through hole at its center, and the thickness of the pressing plate gradually decreases from the outside to the inside.

[0019] According to an embodiment of the present application, the angle between the surface of the pressing sheet away from the crucible cover and the horizontal direction is 35° to 45°.

[0020] According to an embodiment of the present application, the crucible further comprises a first filter element and a second filter element disposed inside the crucible body, wherein the first filter element is located below the second filter element, and in a direction from the bottom to the top, a first accommodation space, a second accommodation space and a third accommodation space for accommodating silicon carbide powder raw materials are defined inside the crucible body;

[0021] The first filter element includes a first porous graphite plate, a second porous graphite plate, and a filling layer sandwiched between the first porous graphite plate and the second porous graphite plate;

[0022] The second filter element includes a graphite plate having a through hole, and a center line of the through hole is non-straight.

[0023] According to an embodiment of the present application, the second filter element includes a first graphite plate and a second graphite plate stacked together, the first graphite plate has a third through hole, the second graphite plate has a fourth through hole, and the central axis direction of the third through hole is not parallel to the central axis direction of the fourth through hole.

[0024] According to an embodiment of the present application, the central axis of the third through hole and the central axis of the fourth through hole are both straight lines, and the angle between the direction of the central axis of the third through hole and the direction of the central axis of the fourth through hole is 45° to 135°.

[0025] According to an embodiment of the present application, diameters of the third through hole and the fourth through hole are independently 1.35 mm to 1.65 mm.

[0026] According to an embodiment of the present application, the porosity of the first porous graphite and the second porous graphite are independently 30% to 35%.

[0027] According to an embodiment of the present application, the pore sizes of the first porous graphite and the second porous graphite are independently 50 μm to 80 μm.

[0028] According to an embodiment of the present application, the thickness of the first porous graphite and the second porous graphite are independently 2 mm to 8 mm.

[0029] According to an embodiment of the present application, the filling layer includes at least one of metal carbides or nitrides thereof, and preferably the filling layer includes at least one of TiC, TiN, TaC, HfC, ZrO, etc.

[0030] According to an embodiment of the present application, the diameter of the material particles of the filling layer is greater than 100 μm, and specifically may be 0.5 mm to 1.0 mm.

[0031] According to an embodiment of the present application, the crucible further includes: a crucible lining, and the crucible lining is arranged in contact with the inner wall of the lower crucible.

[0032] According to an embodiment of the present application, the first accommodating space, the second accommodating space and the third accommodating space are respectively provided with a first silicon carbide powder raw material, a second silicon carbide powder raw material and a third silicon carbide powder raw material, and the particle size of the first silicon carbide powder raw material is less than the particle size of the second silicon carbide powder raw material and less than the particle size of the third silicon carbide powder raw material.

[0033] According to an embodiment of the present application, the particle size of the first silicon carbide powder raw material is 35 mesh to 45 mesh.

[0034] According to an embodiment of the present application, the particle size of the second silicon carbide powder raw material is 15 mesh to 25 mesh.

[0035] According to an embodiment of the present application, the particle size of the third silicon carbide powder raw material is 6 mesh to 8 mesh.

[0036] According to an embodiment of the present application, the third silicon carbide powder raw material is in at least one of a bulk needle shape and a flake shape, and specifically can be in a flake shape.

[0037] According to an embodiment of the present application, a distance L between a top surface of the third silicon carbide powder raw material in the third containing space and a surface of the seed crystal facing the third containing space is 20 mm to 30 mm.

[0038] In a second aspect of the present application, a thermal field system for growing silicon carbide single crystals by a PVT method is provided. According to an embodiment of the present application, the thermal field system includes the aforementioned crucible. The thermal field system has all the features and advantages of the aforementioned crucible, which will not be described one by one here.

[0039] According to an embodiment of the present application, the thermal field system also includes a first graphite felt structure, which includes: a soft graphite felt, which is arranged on the outer surfaces of the bottom wall and the side wall of the crucible body, and the top surface of the soft graphite felt arranged on the side wall of the crucible body is flush with the bottom of the first through hole on the graphite outer ring; a soft felt block, which is annular and arranged on the top of the soft graphite felt, and the top surface of the soft felt block is flush with the top surface of the pressing sheet; and a hard felt block, which is annular and arranged on the top of the soft felt block.

[0040] According to an embodiment of the present application, the thermal field system also includes a second graphite felt structure, which includes: a first graphite hard felt, which is arranged on the outer surface of the first graphite felt structure, and a second annular step portion is provided on the inner side of the top of the side wall of the first graphite hard felt, and the top surface of the second annular step portion is flush with the top surface of the soft felt block; a second graphite hard felt, which is annular, arranged on the second annular step portion, and covers the outer side surface and top surface of the hard felt block; the second graphite hard felt is provided with a third annular step portion protruding toward the center axis direction thereof; a lower thermal insulation graphite soft felt, which is cooperatively arranged on the third annular step portion.

[0041] According to an embodiment of the present application, the thermal field system also includes: a third graphite hard felt, which is annular and arranged on the top of the first graphite hard felt and the second graphite hard felt; a gradient graphite soft felt, which is annular and arranged on the inner side of the third graphite hard felt and located on the top of the lower thermal insulation graphite soft felt, and a fourth annular step portion is provided on the inner side of the gradient graphite soft felt; an upper thermal insulation graphite soft felt, which is arranged on the top of the three graphite hard felts and the gradient graphite soft felt; a graphite pressure plate, which is arranged on the top of the upper thermal insulation graphite soft felt. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the cross-sectional structure of a crucible according to an embodiment of the present application.

[0043] Figure 2 It is a schematic diagram of a partial cross-sectional structure of a crucible according to another embodiment of the present application.

[0044] Figure 3 It is a schematic diagram of the cross-sectional structure of silicon carbide single crystal growth in the related art.

[0045] Figure 4 It is a schematic diagram of the side structure of a seed crystal ring according to an embodiment of the present application.

[0046] Figure 5 It is a schematic diagram of a partial cross-sectional structure of a crucible according to another embodiment of the present application.

[0047] Figure 6 It is a schematic diagram of a partial cross-sectional structure of a crucible according to another embodiment of the present application.

[0048] Figure 7 It is a schematic diagram of a partial cross-sectional structure of a crucible according to another embodiment of the present application.

[0049] Figure 8 It is a schematic diagram of a partial cross-sectional structure of a crucible according to another embodiment of the present application.

[0050] Fig. 9 It is a schematic diagram of a partial cross-sectional structure of a crucible according to another embodiment of the present application.

[0051] Fig.10 It is a schematic cross-sectional structure diagram of a thermal field system according to an embodiment of the present application.

[0052] Fig.11 It is a schematic cross-sectional structure diagram of a thermal field system according to another embodiment of the present application.

[0053] Fig.12 It is a schematic cross-sectional structure diagram of a thermal field system according to another embodiment of the present application.

[0054] Fig.13 It is a schematic cross-sectional structure diagram of a thermal field system according to another embodiment of the present application. DETAILED DESCRIPTION

[0055] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0056] In a first aspect of the present application, a crucible for growing silicon carbide single crystals by a PVT method is provided. Figure 1 and Figure 2 The crucible comprises a crucible body 10 and a crucible cover 20, wherein the crucible cover 20 is detachably disposed on the top of the crucible body 10;

[0057] A graphite paper 21 and a seed crystal 22 are sequentially attached to the surface of the crucible cover 20 facing the crucible body 10, and the outer edge of the graphite paper 21 is retracted relative to the outer edge of the crucible cover 20 and the outer edge of the seed crystal 22, so that a gap 23 is formed between the crucible cover 20 and the seed crystal 22;

[0058] The crucible body 10 includes a lower crucible 11, a graphite outer ring 12 and a seed crystal ring 13, the bottom of the graphite outer ring 12 is detachably connected to the top of the lower crucible 12, a first annular step portion 121 is provided inside the graphite outer ring 12, and the seed crystal layer 13 is provided on the annular step portion 121;

[0059] In the direction from bottom to top, the side wall of the seed crystal ring 13 gradually tilts toward its central axis, and the top of the seed crystal ring 13 is provided with a protrusion 131 facing the central axis, and the protrusion 131 is fitted in the gap 23 .

[0060] In the crucible of the present application, the seed crystal ring initially clamps the edge of the seed crystal, which can play a supporting and fixing role to offset the technical effect of seed crystal bonding on crystal fixation, so as to reduce the dependence on bonding quality during the growth of silicon carbide single crystals. The seed crystal ring is arranged in a close fit with the seed crystal to prevent polycrystalline formation at the edge of the seed crystal, thereby avoiding quality problems of silicon carbide single crystals caused by edge polycrystalline (such as crack extension, phase change and polycrystalline, etc.).

[0061] It can be understood that the protrusion is placed on the edge of the surface of the seed crystal away from the crucible cover (that is, the seed crystal contacts the seed crystal ring by the edge and rests on the protrusion of the seed crystal ring), which can directly get rid of the seed crystal adhesion, that is, the seed crystal can be directly placed on the seed crystal ring by contact force without bonding. However, the inventors found that there will be two serious problems at this time:

[0062] 1. In the early stage of growth of the silicon carbide single crystal 211, because the seed crystal is on the top and the seed crystal ring is on the bottom, the raised portion of the seed crystal ring and the contact portion of the seed crystal will adhere to each other, that is, the seed crystal will wrap the raised portion of the seed crystal ring into the silicon carbide single crystal 211, such as Figure 3 As shown. At this time, during the growth of the silicon carbide single crystal, the seed crystal ring is restricted and cannot move outward, and the stress of the silicon carbide single crystal is relatively large. In addition, after the growth of the silicon carbide single crystal is completed, the process of removing the silicon carbide single crystal is very difficult. What is more fatal is that cracks are very likely to appear at the position where the protrusion and the silicon carbide single crystal are embedded, resulting in growth stress cracking of the silicon carbide single crystal, and in the early stage of growth, the seed crystal needs to bypass the protrusion of the seed crystal ring for a distance and then grow downward. The silicon carbide single crystal grown in this mode has serious edge collapse (increased growth stroke), and the edge stress, BPD and surface shape of the silicon carbide single crystal are very poor.

[0063] In the present application, the raised portion of the seed crystal ring is embedded in the gap between the seed crystal and the crucible cover. The seed crystal ring wraps the seed crystal, and while having a clamping effect, the seed crystal ring has a certain angle from top to bottom, that is, the side wall of the seed crystal ring gradually tilts toward its central axis. At this time, during the growth of the silicon carbide single crystal, the diameter of the growing silicon carbide single crystal is larger than the diameter of the seed crystal, leaving some unqualified areas for removal, and high-quality silicon carbide single crystals can grow with the same diameter as the seed crystal, thereby obtaining high-quality, large-sized silicon carbide single crystals. The above-mentioned crucible can significantly improve the defects of ablation, virtual adhesion, and back corrosion caused by over-reliance on seed crystal bonding and fixation; other growth defects caused by edge polycrystalline, thereby obtaining high-quality silicon carbide single crystals with low defect density and uniform resistivity.

[0064] According to the embodiments of the present application, the specific shape, size, etc. of the crucible cover can be flexibly selected according to actual needs, such as by referring to conventional techniques in the art, and the present application has no special restrictions.

[0065] According to the embodiments of the present application, the lower crucible and the graphite outer ring may be graphite crucibles and graphite outer rings commonly used in the art. The present application has no particular restrictions and they may be flexibly selected according to actual needs.

[0066] It can be understood that the firmness and uniformity of seed crystal bonding will directly affect the quality of the crystal growth process. For example, if the seed crystal bonding is not firm, uniform or poorly bonded, the silicon carbide single crystal will have more serious back corrosion, hexagonal voids (especially at the edge), and uneven growth surface during the subsequent growth process. Therefore, the requirements for seed crystal bonding are relatively high.

[0067] According to the embodiments of the present application, graphite paper can be graphite paper with high purity and appropriate thickness to improve the quality of seed crystal bonding, reduce its influence on the growth of silicon carbide single crystal, and thus obtain high-quality silicon carbide single crystal. In some embodiments, the thickness of the graphite paper can be 0.38mm to 0.5mm, the number can be 1 sheet, and the graphite paper is required to be purified below 5ppm wt%. As an example, there are no wrinkles, damages, or sand holes on the surface of the graphite paper. Before use, it can be scraped obliquely in one direction with a utility knife. If the scratches produced are obviously uneven, the graphite paper cannot be used for seed crystal bonding.

[0068] In some embodiments, a glue spreader can be used to evenly spin-coat a layer of adhesive on the back of the seed crystal, and then evenly spin-coat a layer of adhesive on one side of the graphite paper, and the two sides of the adhesive are bonded together to complete the bonding of the seed crystal and the graphite paper. As an example, the glue spreader speed can be 1800rad / min, and the glue spreader time can be 30s. Then, a uniform layer of adhesive is scraped on the inner surface of the crucible cover with a utility knife, and the glue is dried for a period of time (such as 5min), and then the bonded side of the graphite paper is combined with the side of the crucible cover coated with the adhesive, and the seed crystal and the crucible cover are placed in a sintering furnace. During the sintering process, a weight of 20kg to 25kg (such as a stainless steel round block, etc.) can be placed on one side of the seed crystal. The diameter of the sintering weight is required to be smaller than the diameter of the seed crystal and consistent with the diameter of the graphite paper on the back of the seed crystal to prevent the edge of the seed crystal from being suspended and stressed. As an example, the diameter of the seed crystal can be 200mm, and the diameters of the graphite paper and the sintering weight are both 180mm. In some embodiments, the adhesive may be selected from high temperature organic glue, photoresist, resin glue, etc.

[0069] According to an embodiment of the present application, the depth h of the gap in the horizontal direction may be 5 mm to 10 mm, specifically 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, etc. This depth can facilitate the seed crystal ring to clamp and fix the seed crystal, and has basically no other negative effects.

[0070] According to an embodiment of the present application, the angle α between the side wall of the seed crystal ring and the horizontal direction can be 69° to 85°, specifically 69°, 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 814°, 82°, 83°, 84°, 85°, etc. Within this angle range, the diameter of the grown silicon carbide single crystal is larger than the diameter of the seed crystal, leaving a portion of the unqualified area for removal, thereby preventing the low-quality silicon carbide crystal at the edge or the polycrystalline from eroding the high-quality silicon carbide single crystal in the middle, and then the high-quality silicon carbide single crystal can grow with the same diameter as the seed crystal, so that a high-quality, large-sized silicon carbide single crystal can be obtained.

[0071] According to the embodiments of the present application, referring to Figure 4 , the seed crystal ring can be a circular ring petal structure, and the seed crystal ring includes a plurality of ring petals 132. In some embodiments, the seed crystal ring can include 2 to 4 ring petals, for example, symmetrically divided into two petals, three petals, four petals, etc. It can be understood that a plurality of seed crystal ring petals can be cut from a graphite ring. By setting the seed crystal ring as a circular ring petal structure, the seed crystal ring can be first placed at the outermost position of the first annular step portion, and then the crucible cover body is placed on the crucible body, and then the seed crystal ring is pushed inward so that the raised portion on the seed crystal ring is matched and set in the gap between the crucible cover body and the seed crystal.

[0072] As an example, the seed crystal ring includes two ring petals, so that the assembled seed crystal ring surrounds the outer edge of the seed crystal without leaving any gap, and the raised portion on the seed crystal ring is embedded in the gap between the seed crystal and the crucible cover at a position of about 10 mm.

[0073] According to the embodiments of the present application, referring to Figure 2 A first through hole 122 is provided on the side wall of the graphite outer ring 12 above the annular step portion 121. Thus, bolts and other components can be conveniently passed through the first through hole to apply force to the seed crystal ring so that it is matched and arranged in the gap between the crucible cover and the seed crystal. At the same time, the first through hole can also discharge the gas near the first through hole into the crucible, thereby improving the carbon coating problem of the silicon carbide single crystal.

[0074] As an example, first place the seed crystal ring on the first annular step of the graphite outer ring, then assemble the crucible cover, first move the seed crystal ring outward to the maximum limit, then cover the crucible cover in the corresponding slot of the graphite outer ring, and then buckle the pressing sheet. After placing the above structure, screw the graphite bolt into the first through hole corresponding to the graphite outer ring. The size of the graphite bolt is M6, and the internal thread M6 is arranged corresponding to the upper through hole of the graphite outer ring. By tightening the graphite bolt, the seed crystal ring moves inward until the raised part on the seed crystal ring pushes into the gap between the seed crystal and the crucible cover. After this part is assembled, unscrew the graphite bolt to ensure smooth exhaust of the first through hole.

[0075] According to the embodiments of the present application, referring to Figure 4 , at least one exhaust hole 133 is provided on the side wall of the seed crystal ring 13. In some embodiments, a plurality of exhaust holes 133 are provided on the side wall of the seed crystal ring 13 and are arranged at intervals along the circumference of the bottom of the seed crystal ring. Specifically, silicon carbide single crystals need to be grown under high temperature conditions. In order to avoid the introduction of impurities and the degradation of crystal quality caused by thermal mismatch, the seed crystal ring is usually made of graphite. At higher temperatures, graphite will be corroded to release carbon, which may cause carbon coating to reduce the quality of the silicon carbide single crystal. The present application provides exhaust holes on the side wall of the seed crystal ring to guide the gas near the seed crystal ring to be discharged from the crucible through the exhaust holes, thereby discharging the carbon released by graphite corrosion from the crucible, thereby effectively improving the carbon coating problem of the silicon carbide single crystal and improving the crystal quality of the silicon carbide single crystal.

[0076] According to the embodiments of the present application, referring to Figure 5 The crucible further comprises a pressing sheet 30, which is arranged on the top of the crucible cover 20, and has a second through hole 31 at the center of the pressing sheet 30, and the thickness w of the pressing sheet 30 gradually decreases from the outside to the inside. By providing a pressing sheet whose thickness gradually decreases from the outside to the inside, the temperature gradient from the inside of the crucible to the outside can be increased, thereby making it easier to guide the gas at the edge of the crucible wall to discharge from the inside of the crucible, thereby improving the carbon coating problem of the silicon carbide single crystal.

[0077] In some embodiments, reference Figure 5 The angle β between the surface 32 of the pressing sheet 30 away from the crucible cover 20 and the horizontal direction is 35° to 45°, specifically 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, etc. Thus, it is more conducive to the gas at the edge of the crucible wall to be discharged from the inside of the crucible, and the effect of improving the carbon coating problem of the silicon carbide single crystal is better.

[0078] In some embodiments, the pressing sheet may be made of graphite or graphite felt, and may be an integral structure with a second through hole at the center and a slope from outside to inside, and the slope may be between 35° and 45°.

[0079] According to the embodiments of the present application, referring to Figure 6 The crucible further comprises: a crucible lining 40, which is arranged in contact with the inner wall of the lower crucible 11. Thus, the crucible lining can be corroded preferentially during the growth of the silicon carbide single crystal, reducing the damage of the powder to the inner wall of the lower crucible, and the lower crucible can be recycled. When the corrosion is serious, only the crucible lining needs to be replaced for continued use, thereby increasing the service life of the lower crucible and effectively reducing the cost.

[0080] In some embodiments, the material of the crucible lining may be graphite, specifically isostatic graphite, thereby achieving better performance.

[0081] According to the embodiments of the present application, referring to Figure 7 The crucible also includes a first filter 50 and a second filter 60 arranged inside the crucible body. The first filter 50 is located below the second filter 60. In the direction from the bottom to the top, the first accommodation space 101, the second accommodation space 102 and the third accommodation space 103 for accommodating silicon carbide powder raw materials are defined inside the crucible body; the first filter 50 includes a first porous graphite plate 51, a second porous graphite plate 52 and a filling layer 53 sandwiched between the first porous graphite plate 51 and the second porous graphite plate 52; the second filter 60 includes a graphite plate 61 with a through hole 611, and the central axis of the through hole 61 is non-linear. Through the double-layer filtering structure, the first filter can filter carbon particles in the early and middle stages of the growth of silicon carbide single crystals, and the second filter can filter carbon particles in the middle and late stages of the growth of silicon carbide single crystals, so that the carbon encapsulation problem in the growth of silicon carbide single crystals can be better improved to improve the quality of silicon carbide single crystals.

[0082] Specifically, the center line of the through hole 61 only needs to be not a straight line. As an example, the center axis of the through hole 61 can be a curve, a broken line, or a combination thereof.

[0083] According to the embodiments of the present application, referring to Figure 7 The second filter element 60 includes a first graphite plate 62 and a second graphite plate 63 which are stacked, wherein the first graphite plate 62 has a third through hole 621, and the second graphite plate 63 has a fourth through hole 631, and the central axis direction of the third through hole 621 is not parallel to the central axis direction of the fourth through hole 631. Thus, the filtering effect of the second filter element is improved.

[0084] According to the embodiments of the present application, referring to Figure 8 The central axis of the third through hole 621 and the central axis of the fourth through hole 631 are both straight lines, and the angle γ between the direction of the central axis of the third through hole 621 and the direction of the central axis of the fourth through hole 631 is 45° to 135° (specifically, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, 90°, 95°, 100°, 105°, 110°, 115°, 120°, 125°, 130°, 135°, etc.). Thus, the filtering effect of the second filter element can be further improved.

[0085] According to an embodiment of the present application, the diameters of the third through hole and the fourth through hole are independently 1.35 mm to 1.65 mm (specifically 1.35 mm, 1.4 mm, 1.45 mm, 1.5 mm, 1.55 mm, 1.6 mm, 1.65 mm, etc.). Within the above diameter range, sufficient mass transfer efficiency of the sublimation components can be maintained, and the problem of crystallization blocking can be improved. At the same time, a double-layer graphite plate is provided, and a certain angle is formed between the through holes of the two layers of graphite plates, thereby achieving a more excellent filtering effect.

[0086] According to an embodiment of the present application, the porosity of the first porous graphite and the second porous graphite is independently 30% to 35%, such as 30%, 31%, 32%, 33%, 34%, 35%, etc.

[0087] According to an embodiment of the present application, the pore sizes of the first porous graphite and the second porous graphite are independently 50 μm to 80 μm, such as 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, etc.

[0088] According to an embodiment of the present application, the thickness of the first porous graphite and the second porous graphite are independently 2 mm to 8 mm, such as 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, etc.

[0089] Specifically, the first porous graphite and the second porous graphite meet the above requirements, can effectively filter the carbon particles generated during the growth of the silicon carbide single crystal, improve the carbon coating problem of the silicon carbide single crystal, and thus improve the quality of the obtained silicon carbide single crystal.

[0090] According to an embodiment of the present application, the filling layer includes at least one of metal carbides or nitrides thereof. In some specific embodiments, the filling layer includes at least one of TiC, TiN, TaC, HfC, ZrO, etc. According to an embodiment of the present application, the diameter of the material particles of the filling layer can be greater than 100μm, specifically 0.5mm~1.0mm (specifically 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, etc.). As a result, the filter layer has a better filtering effect, thereby improving the carbon coating problem of silicon carbide single crystals and improving the quality of the obtained silicon carbide single crystals.

[0091] According to the embodiments of the present application, in order to better improve the carbon encapsulation problem, the silicon carbide powder raw material can also be appropriately adjusted and set. Fig. 9The first accommodating space 101, the second accommodating space 102 and the third accommodating space 103 are respectively provided with a first silicon carbide powder raw material 1, a second silicon carbide powder raw material 2 and a third silicon carbide powder raw material 3, and the particle size of the first silicon carbide powder raw material 1 is less than the particle size of the second silicon carbide powder raw material 2 and less than the particle size of the third silicon carbide powder raw material 3.

[0092] Specifically, the first silicon carbide powder raw material has a finer particle size, and the temperature of the bottom high temperature zone at the initial stage of silicon carbide single crystal growth is relatively high, so that the silicon carbide single crystal maintains a higher growth rate at the initial stage of growth. At this time, under the condition of high growth rate and axial temperature gradient, the first filter element is used to realize the first stage of filtration by using the microporous structure and filling layer of porous graphite. However, as the growth of silicon carbide single crystal proceeds, porous graphite is gradually corroded due to the influence of long time, high temperature and high silicon-rich components, becoming another important source of carbon encapsulation. At this time, the second silicon carbide powder raw material mainly provides the source of components in the middle and late stages of silicon carbide single crystals. Since the particle size of the second silicon carbide powder raw material is large, the rate of sublimation and decomposition is reduced, which causes the carbon encapsulation of silicon carbide single crystal growth to be reduced. With the second filter element, it plays a role of re-filtration, thereby effectively improving the carbon encapsulation problem. The third silicon carbide powder raw material is located in the third containing space, and has a larger particle size. The third silicon carbide powder raw material can be in an area with a lower growth temperature of silicon carbide single crystal, so that the large-particle silicon carbide powder raw material itself can be used to play the role of the last layer of isolation and filtration to improve the carbon encapsulation problem.

[0093] In some embodiments, the particle size of the first silicon carbide powder raw material is 35-45 mesh, the particle size of the second silicon carbide powder raw material is 15-25 mesh, and the particle size of the third silicon carbide powder raw material is 3mm-6mm. In some specific embodiments, the third silicon carbide powder raw material is in the form of large needles or flakes, and can be flakes.

[0094] In some embodiments, the distance L between the top surface of the third silicon carbide powder raw material in the third accommodation space and the surface of the seed crystal facing the third accommodation space is 20 mm to 30 mm. Thus, it can be better ensured that this area is in an area with a lower crystal growth temperature, give full play to the filtering effect of the third silicon carbide powder raw material, and improve the problem of packaging.

[0095] By adopting the above crucible, during the growth of silicon carbide single crystal, the carbon inclusions caused by the silicon carbide powder raw material and the graphite plates in the silicon carbide powder raw material can be effectively filtered, so that the growth of the silicon carbide single crystal can maintain a relatively high growth rate in the axial direction, reducing the occurrence of carbon inclusions; at the same time, the free carbon generated by the corrosion of the crucible lining can be discharged from the sublimation atmosphere through the exhaust holes on the seed crystal ring and the through holes on the graphite outer ring, thereby improving the carbon inclusion problem; the obtained silicon carbide single crystal has low defect density, uniform resistivity and high quality.

[0096] In a second aspect of the present application, a thermal field system for growing silicon carbide single crystals by a PVT method is provided. According to an embodiment of the present application, the thermal field system includes the aforementioned crucible. The thermal field system has all the features and advantages of the aforementioned crucible, which will not be described one by one here.

[0097] According to the embodiments of the present application, referring to Fig.10 The thermal field system further includes a first graphite felt structure 70, which includes: a graphite soft felt 71, which is arranged on the outer surface of the bottom wall and the side wall of the crucible body 10, and the top surface of the graphite soft felt 71 arranged on the side wall of the crucible body 10 is flush with the bottom of the through hole on the graphite outer ring 12; a soft felt block 72, which is annular and arranged on the top of the graphite soft felt 71, and the top surface of the soft felt block 72 is flush with the top surface of the pressing sheet 30; a hard felt block 73, which is annular and arranged on the top of the soft felt block 72. The first graphite felt structure is arranged near the exhaust position, wherein the function of the soft felt block is to allow the atmosphere to be exhausted and partially corroded, and the consumables need to be replaced for each furnace, and the function of the hard felt block is to allow partial corrosion to occur at this position, and it is replaced as appropriate according to the corrosion situation to reduce the cost of the hard felt. In addition, a first graphite felt structure is provided, which can, on the one hand, adjust the larger temperature gradient at the edge of the thermal field so that a large amount of silicon-rich components are discharged outward from the exhaust holes on the side wall of the seed crystal ring and the through holes on the graphite outer ring; on the other hand, soft felt blocks and hard felt blocks are provided on the gas discharge path; the soft felt blocks can effectively absorb gas and guide gas discharge, while the hard felt blocks can play a better role in heat preservation, and at the same time, partial replacement of a single furnace can be achieved (that is, only the soft felt blocks or the hard felt blocks can be replaced, and other graphite components can be reused) to protect other graphite components in the thermal field.

[0098] According to the embodiments of the present application, referring to Fig.11 The thermal field system also includes a second graphite felt structure 80, which includes: a first graphite hard felt 81, which is arranged on the outer surface of the first graphite felt structure 70, and a second annular step portion 811 is arranged on the inner side of the top of the side wall of the first graphite hard felt 81, and the top surface of the second annular step portion 811 is flush with the top surface of the soft felt block 72; a second graphite hard felt 82, which is annular, arranged on the second annular step portion 811, and covers the outer side and top surface of the hard felt block 73; the second graphite hard felt 82 is provided with a third annular step portion 821 protruding toward the central axis thereof; and a lower thermal insulation graphite soft felt 83, which is arranged on the third annular step portion 821. The second graphite felt structure can effectively maintain the temperature required for the growth of silicon carbide single crystals and achieve a thermal insulation effect.

[0099] According to the embodiments of the present application, referring to Fig.12The thermal field system also includes: a third graphite hard felt 91, which is annular and arranged on the top of the first graphite hard felt 81 and the second graphite hard felt 82; a gradient graphite soft felt 92, which is annular and arranged on the inner side of the third graphite hard felt 91 and located on the top of the lower thermal insulation graphite soft felt 83, and a fourth annular step portion 921 is provided on the inner side of the gradient graphite soft felt 92; an upper thermal insulation graphite soft felt 93, which is arranged on the top of the third graphite hard felt 91 and the gradient graphite soft felt 92; a graphite pressure plate 94, which is arranged on the top of the upper thermal insulation graphite soft felt 93. Specifically, through the structural design of the top graphite pressure plate, the upper insulating graphite soft felt, the gradient graphite soft felt and the third graphite hard felt, the larger temperature gradient at the edge of the hot field is adjusted, so that a large amount of silicon-rich components are discharged outward from the exhaust holes of the seed crystal ring and the through holes on the graphite outer ring, and single-consumption soft felt and hard felt blocks are set on the discharge path to realize partial replacement of a single furnace and protect other graphite components in the hot field.

[0100] As an example, the thermal field system may be an induction heating thermal field system, see Fig.13 , which may also include structures such as a graphite tray 95 and an induction coil 96. It is understood that, in addition to the aforementioned structures, graphite tray 95, induction coil 96, etc., the induction heating thermal field system also includes necessary structures and components of a conventional induction heating thermal field system, which will not be described in detail here.

[0101] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0102] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0103] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0104] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0105] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0106] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A crucible for growing silicon carbide single crystals by a PVT method, characterized in that: It comprises a crucible body and a crucible cover, wherein the detachable cover of the crucible cover is arranged on the top of the crucible body; Graphite paper and a seed crystal are sequentially pasted on the surface of the crucible cover facing the crucible body, and the outer edge of the graphite paper is retracted relative to the outer edge of the crucible cover and the outer edge of the seed crystal, so that a gap is formed between the crucible cover and the seed crystal; The crucible body comprises a lower crucible, a graphite outer ring and a seed crystal ring, the bottom of the graphite outer ring is detachably connected to the top of the lower crucible, a first annular step portion is provided inside the graphite outer ring, and the seed crystal layer is provided on the first annular step portion; In the direction from the bottom to the top, the side wall of the seed crystal ring gradually tilts toward the central axis thereof, and the top of the seed crystal ring is provided with a protrusion facing the central axis thereof, and the protrusion is matched and arranged in the gap.

2. The crucible according to claim 1, characterized in that The depth of the gap in the horizontal direction is 5 mm to 10 mm.

3. The crucible according to claim 1, characterized in that The seed ring satisfies at least one of the following conditions: The angle between the side wall of the seed crystal ring and the horizontal direction is 69° to 85°; The seed crystal ring includes a plurality of ring petals, preferably 2 to 4 ring petals; At least one exhaust hole is provided on the side wall of the seed crystal ring. Preferably, a plurality of exhaust holes are provided on the side wall of the seed crystal ring and are spaced apart along the circumference of the seed crystal ring.

4. The crucible according to claim 1, characterized in that A first through hole is provided on the side wall of the graphite outer ring above the first annular step portion.

5. The crucible according to claim 1, characterized in that Also comprising at least one of a pellet and a crucible liner; The pressing sheet cover is arranged above the crucible cover body, the pressing sheet has a second through hole at its center, and the thickness of the pressing sheet gradually decreases from the outside to the inside; preferably, the angle between the surface of the pressing sheet away from the crucible cover body and the horizontal direction is 35° to 45°; The crucible liner is arranged to fit the inner wall of the lower crucible.

6. The crucible according to claim 1, characterized in that The crucible body further comprises a first filter and a second filter, wherein the first filter is located below the second filter, and in a direction from the bottom to the top, a first accommodation space, a second accommodation space and a third accommodation space for accommodating silicon carbide powder raw materials are defined inside the crucible body; The first filter element includes a first porous graphite plate, a second porous graphite plate, and a filling layer sandwiched between the first porous graphite plate and the second porous graphite plate; The second filter element includes a graphite plate having a through hole, and a center line of the through hole is non-straight.

7. The crucible according to claim 6, characterized in that The second filter element comprises a first graphite plate and a second graphite plate which are stacked, the first graphite plate having a third through hole, the second graphite plate having a fourth through hole, and the central axis direction of the third through hole is not parallel to the central axis direction of the fourth through hole; Preferably, the central axis of the third through hole and the central axis of the fourth through hole are both straight lines, and the angle between the direction of the central axis of the third through hole and the direction of the central axis of the fourth through hole is 45° to 135°; Preferably, the diameters of the third through hole and the fourth through hole are independently 1.35 mm to 1.65 mm.

8. The crucible according to claim 6 or 7, characterized in that The first filter element satisfies at least one of the following conditions: The porosity of the first porous graphite and the second porous graphite are independently 30% to 35%; The pore sizes of the first porous graphite and the second porous graphite are independently 50 μm to 80 μm; The thickness of the first porous graphite and the second porous graphite are independently 2 mm to 8 mm; The filling layer includes at least one of metal carbides or metal nitrides, and preferably the filling layer includes at least one of TiC, TiN, TaC, HfC, and ZrO; The diameter of the material particles of the filling layer is greater than 100 μm, preferably 0.5 mm to 1.0 mm.

9. The crucible according to claim 6, characterized in that The first accommodating space, the second accommodating space and the third accommodating space are respectively provided with a first silicon carbide powder raw material, a second silicon carbide powder raw material and a third silicon carbide powder raw material, and the particle size of the first silicon carbide powder raw material is less than the particle size of the second silicon carbide powder raw material and less than the particle size of the third silicon carbide powder raw material.

10. The crucible according to claim 9, characterized in that Meet at least one of the following conditions: The particle size of the first silicon carbide powder raw material is 35 mesh to 45 mesh; The particle size of the second silicon carbide powder raw material is 15 mesh to 25 mesh; The particle size of the third silicon carbide powder raw material is 6 mesh to 8 mesh; The third silicon carbide powder raw material is in at least one of bulk needle-shaped and flake-shaped, preferably in flake-shaped; A distance L between a top surface of the third silicon carbide powder raw material in the third containing space and a surface of the seed crystal facing the third containing space is 20 mm to 30 mm.

11. A thermal field system for growing silicon carbide single crystals by PVT method, characterized in that: The crucible according to any one of claims 1 to 10 is included.

12. The thermal field system according to claim 11, characterized in that: Also included is a first graphite felt structure and a second graphite felt structure, wherein: The first graphite felt structure comprises: A graphite soft felt, wherein the graphite soft felt is arranged on the outer surfaces of the bottom wall and the side wall of the crucible body, and the top surface of the graphite soft felt arranged on the side wall of the crucible body is flush with the bottom of the first through hole on the graphite outer ring; A soft felt block, which is annular and arranged on the top of the graphite soft felt, and the top surface of the soft felt block is flush with the top surface of the pressing sheet; A hard felt block, which is ring-shaped and arranged on the top of the soft felt block; The second graphite felt structure comprises: A first graphite hard felt, wherein the first graphite hard felt is arranged on the outer surface of the first graphite felt structure, a second annular step portion is arranged on the inner side of the top of the side wall of the first graphite hard felt, and the top surface of the second annular step portion is flush with the top surface of the soft felt block; A second graphite hard felt, which is annular and arranged on the second annular step portion and covers the outer side surface and the top surface of the hard felt block; the second graphite hard felt is provided with a third annular step portion protruding toward the central axis direction thereof; The lower thermal insulation graphite soft felt is arranged on the third annular step portion.

13. The thermal field system according to claim 12, characterized in that: Also includes: A third graphite hard felt, which is ring-shaped and disposed on the top of the first graphite hard felt and the second graphite hard felt; A gradient graphite soft felt, wherein the gradient graphite soft felt is annular, arranged on the inner side of the third graphite hard felt and located on the top of the lower thermal insulation graphite soft felt, and a fourth annular step portion is arranged on the inner side of the gradient graphite soft felt; An upper thermal insulation graphite soft felt, wherein the upper thermal insulation graphite soft felt is arranged on top of the third graphite hard felt and the gradient graphite soft felt; A graphite pressure plate is arranged on the top of the upper thermal insulation graphite soft felt.

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