Thermal field system of silicon carbide single crystal

Abstract

The utility model discloses a thermal field system for silicon carbide single crystals, which comprises a crucible, the crucible comprises a crucible cover and a crucible body, the crucible cover is detachably connected with the crucible body, a seed crystal is adhered to the bottom of the crucible cover, and the thickness of the part, opposite to the seed crystal, of the crucible cover is gradually increased in the direction from the edge to the center of the crucible cover; the graphite soft felt wraps the outer side of the crucible, a temperature measuring hole is defined in the top of the graphite soft felt, and the center line of the temperature measuring hole and the center axis of the crucible are located on the same straight line; and the pyrometer is arranged above the graphite soft felt and is opposite to the temperature measuring hole. According to the thermal field system of the silicon carbide single crystal, the flux of outward heat dissipation of the center of the crucible through the temperature measuring hole can be reduced, the radial temperature gradient can be improved, silicon carbide crystals can grow downwards in a micro-convex manner, the dislocation density of the grown silicon carbide single crystal can be reduced, and the crystal quality can be improved.

Description

Technical Field

[0001] The utility model relates to the field of silicon carbide single crystal growth, in particular to a thermal field system of silicon carbide single crystal. Background Art

[0002] The PVT method is the mainstream method for growing large-diameter SiC crystals in the industry. Its principle is to heat silicon carbide powder to above 2000°C, and after high-temperature sublimation, the gas phase components are transported under the action of the temperature gradient, and finally recrystallized on the surface of the seed crystal at a lower temperature, which promotes the growth of the crystal. In current research and development, the induction heating thermal field system is more widely used because it has a simpler structure, higher thermal efficiency, and fewer graphite parts that need to be replaced regularly, and the daily maintenance cost is relatively low compared to the resistance heating thermal field system.

[0003] However, the induction heating thermal field system in the related art generally sets a temperature measuring hole on the top of the thermal field to measure the temperature of the seed crystal area in the crucible. During crystal growth, the temperature in the center of the crucible is low and the temperature of the surrounding wall of the crucible is high. That is, the radial temperature gradient at the seed crystal in the crucible is too large, causing the silicon carbide crystal to grow convexly downward, resulting in large internal thermal stress and a high dislocation density. Utility Model Content

[0004] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model proposes a thermal field system for a silicon carbide single crystal, which can reduce the flux of heat dissipated from the center of the crucible to the outside, increase the temperature of the center of the crucible, improve the radial temperature gradient, make the silicon carbide crystal grow slightly convexly downward, reduce thermal stress, and help reduce the dislocation density of the grown six-inch silicon carbide single crystal, thereby improving the crystal quality.

[0005] A thermal field system for a silicon carbide single crystal according to an embodiment of the utility model comprises: a crucible, wherein the crucible comprises a crucible cover and a crucible body, wherein the crucible cover is detachably connected to the crucible body, a seed crystal is pasted on the bottom of the crucible cover, and the thickness of the portion of the crucible cover opposite to the seed crystal gradually increases in the direction from the edge to the center of the crucible cover; graphite felt, wherein the graphite felt is wrapped around the outside of the crucible, wherein a temperature measuring hole is defined at the top of the graphite felt, and the center line of the temperature measuring hole is in the same straight line as the center axis of the crucible; and a pyrometer, wherein the pyrometer is arranged above the graphite felt and opposite to the temperature measuring hole.

[0006] According to the thermal field system of the silicon carbide single crystal in the embodiment of the utility model, the thickness of the part of the crucible cover opposite to the seed crystal is gradually increased in the direction from the edge to the center of the crucible cover. In other words, the crucible cover is thin at the edge and thick in the middle. This can reduce the flux of heat dissipated outward from the center of the crucible through the temperature measuring hole, increase the temperature of the center of the crucible, improve the radial temperature gradient, reduce thermal stress, and make the silicon carbide crystal grow slightly convexly downward, which is beneficial to reduce the dislocation density of the grown six-inch silicon carbide single crystal and improve the crystal quality.

[0007] In some embodiments of the present invention, the crucible cover includes a first cover body portion and a second cover body portion, the first cover body portion and the second cover body portion are arranged in the up and down directions, the diameter of the first cover body portion is larger than the diameter of the second cover body portion, the outer periphery of the second cover body portion is provided with a first external thread segment, the inner peripheral wall of the top of the crucible body is provided with a first internal thread segment, and the first external thread segment is threadedly matched with the first internal thread segment.

[0008] In some embodiments of the present invention, the top of the first cover body has an arc portion, the height of the arc portion is 10mm-15mm, the diameter of the first cover body is 200mm-300mm, the second cover body is formed into a circular plate shape, and the thickness of the second cover body is 15mm-20mm.

[0009] In some embodiments of the utility model, the crucible body includes a graphite outer ring, a graphite inner ring and a lower crucible body, the top of the graphite outer ring is connected to the crucible cover through the first internal thread section, the bottom of the graphite outer ring is connected to the lower crucible body, the graphite inner ring is arranged inside the graphite outer ring, the interior of the graphite outer ring is provided with an annular step portion suitable for supporting the graphite inner ring, the distance between the outer peripheral wall of the graphite inner ring and the graphite inner ring is t1, and t1 satisfies: 0.5mm≤t1≤1mm.

[0010] In some embodiments of the present invention, the graphite inner ring includes a plurality of inner ring petals, and the plurality of inner ring petals are cut from the same graphite ring, and the removal amount of two adjacent inner ring petals is t2, and t2 satisfies: 0.2mm≤t2≤0.6mm.

[0011] In some embodiments of the present invention, two adjacent inner ring petals are connected by epoxy resin glue.

[0012] In some embodiments of the utility model, the graphite outer ring has a guide hole, the central axis of the guide hole coincides with the central axis of the crucible, and in the direction from bottom to top, the hole wall of the guide hole extends in a direction close to the central axis of the crucible, and the angle between the hole wall of the guide hole and the horizontal plane is 45°-80°.

[0013] In some embodiments of the present invention, the thermal field system further comprises: a graphite tube, the graphite tube is arranged in the temperature measuring hole, the central axis of the graphite tube coincides with the central axis of the temperature measuring hole, and the inner tube wall of the graphite tube is provided with a tantalum carbide coating.

[0014] In some embodiments of the present invention, the wall thickness of the graphite tube is 4 mm-6 mm, and the thickness of the tantalum carbide coating is 0.01 mm-0.08 mm.

[0015] In some embodiments of the utility model, the thermal field system also includes: a quartz tube, an upper flange, a lower flange and an induction coil, the quartz tube, the upper flange and the lower flange define a storage space suitable for placing the graphite soft felt and the crucible, the upper flange is provided with a through hole arranged opposite to the temperature measuring hole, the interior of the quartz tube has a flow channel suitable for cooling water to pass through, the induction coil is wound around the outside of the quartz tube, and the number of turns of the induction coil is 15 turns to 20 turns.

[0016] Additional aspects and advantages of the present invention will be given in part in the following description, and in part will become apparent from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of a thermal field system for a silicon carbide single crystal according to an embodiment of the utility model, wherein the crucible is in an initial position for crystal growth;

[0018] Figure 2 It is a structural schematic diagram of a crucible according to an embodiment of the utility model;

[0019] Figure 3 yes Figure 2 The enlarged schematic diagram of point A in the middle;

[0020] Figure 4 It is a schematic structural diagram of a graphite inner ring according to an embodiment of the utility model;

[0021] Figure 5 It is a schematic diagram of a thermal field system for a silicon carbide single crystal according to an embodiment of the utility model, wherein the crucible is in a crystal growth termination position.

[0022] Reference numerals:

[0023] Thermal field system 100;

[0024] Crucible 10;

[0025] Crucible cover 11; first cover body 111; second cover body 112; first external thread section 113; arc portion 114; seed crystal 115;

[0026] Crucible body 12;

[0027] Graphite outer ring 121; first internal thread section 1211; second external thread section 1212; annular step portion 1213; guide hole 1214;

[0028] Graphite inner ring 122; inner ring petal 1221;

[0029] Lower crucible body 123; second internal thread section 1231;

[0030] Graphite soft felt 20; Temperature measuring hole 21;

[0031] Pyrometer 30;

[0032] Graphite tube 40; quartz tube 50; flow channel 51;

[0033] Upper flange 60; through hole 61; lower flange 70;

[0034] Induction coil 80; porous graphite plate 90; filter hole 91;

[0035] Silicon carbide raw material 200;

[0036] Silicon carbide crystal 300. DETAILED DESCRIPTION

[0037] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0038] The disclosure below provides many different embodiments or examples for realizing different structures of the utility model. In order to simplify the disclosure of the utility model, the components and settings of specific examples are described below. Of course, they are merely examples, and the purpose is not to limit the utility model. In addition, the utility model can repeat reference numbers and / or letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the utility model provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the applicability of other processes and / or the use of other materials.

[0039] Reference below Figure 1-Figure 5 A thermal field system 100 for a silicon carbide single crystal 300 according to an embodiment of the present invention is described.

[0040] Reference Figure 1 and Figure 2As shown, the thermal field system 100 of the silicon carbide single crystal 300 according to the embodiment of the present invention includes: a crucible 10 , a graphite soft felt 20 and a pyrometer 30 .

[0041] Reference Figure 1 and Figure 2 As shown, the crucible 10 includes a crucible cover 11 and a crucible body 12 , and the crucible cover 11 is detachably connected to the crucible body 12 . For example, the crucible cover 11 and the crucible body 12 can be connected by threaded connection or fasteners.

[0042] Reference Figure 1 and Figure 2 As shown, a seed crystal 115 is pasted to the bottom of the crucible cover 11, and the thickness of the portion of the crucible cover 11 opposite to the seed crystal 115 gradually increases in the direction from the edge to the center of the crucible cover 11. In other words, the portion of the crucible cover 11 opposite to the seed crystal 115 in the up and down directions is thin at the edge and thick in the middle, and the crucible body 12 contains silicon carbide raw material 200.

[0043] Reference Figure 1 and Figure 2 As shown, the graphite felt 20 is wrapped around the outside of the crucible 10, and a temperature measuring hole 21 is defined at the top of the graphite felt 20. The center line of the temperature measuring hole 21 is in the same straight line as the center axis of the crucible 10, and the pyrometer 30 is arranged above the graphite felt 20 and opposite to the temperature measuring hole 21.

[0044] It should be noted that for a good thermal field system, the structure of the crucible determines the form of the temperature field and the flow field. In the related art, the thickness of the crucible cover is uniform. Due to the existence of the temperature measuring hole, the heat flux of the crucible cover is mainly concentrated at the temperature measuring hole, resulting in the formation of an "M"-shaped temperature field in the crucible during crystal growth. According to the thermal field system 100 of the silicon carbide single crystal 300 of the utility model embodiment, the thickness of the part of the crucible cover 11 opposite to the seed crystal 115 is gradually increased in the direction from the edge to the center of the crucible cover 11. In other words, the crucible cover 11 is thin at the edge and thick in the middle, which can reduce the flux of heat dissipated to the outside through the temperature measuring hole 21 at the center of the crucible 10, increase the temperature at the center of the crucible 10, reduce the radial temperature gradient, and facilitate the downward slightly convex growth of the silicon carbide single crystal 300, which can reduce thermal stress, and help reduce the dislocation density of the grown six-inch silicon carbide single crystal 300, thereby improving the crystal quality.

[0045] In some embodiments of the present invention, referring to Figure 2 and Figure 3As shown, the crucible cover 11 includes a first cover body portion 111 and a second cover body portion 112, the first cover body portion 111 and the second cover body portion 112 are arranged in the up and down direction, the diameter of the first cover body portion 111 is larger than the diameter of the second cover body portion 112, the outer periphery of the second cover body portion 112 is provided with a first external thread segment 113, the inner peripheral wall of the top of the crucible body 12 is provided with a first internal thread segment 1211, and the first external thread segment 113 is threadedly matched with the first internal thread segment 1211. It can be understood that the threaded connection has the advantages of simple structure and easy assembly, and the crucible cover 11 and the crucible body 12 can be tightly connected by the first external thread segment 113 and the first internal thread segment 1211. In addition, while ensuring the connection strength between the crucible cover 11 and the crucible body 12, the cost can also be reduced.

[0046] In some embodiments of the present invention, referring to Figure 2 and Figure 3 As shown, the top of the first cover body 111 has an arc portion 114, the height of the convex arc portion 114 is 10mm-15mm, and the diameter of the first cover body 111 is 200mm-300mm. In other words, the height of the convex arc portion 114 can take any value between 10mm-15mm, and the diameter of the first cover body 111 can take any value between 200mm-300mm.

[0047] It can be understood that by making the height of the convex arc portion 114 10mm-15mm and the diameter of the first cover body portion 111 200mm-300mm, on the one hand, the thickness of the middle portion of the first cover body portion 111 will not be too large, thereby avoiding the excessive heat dissipation flux outward from the temperature measuring hole 21 to be too small, which is beneficial to preventing the temperature at the center of the crucible cover 11 from being too high, and further avoiding the silicon carbide single crystal 300 from growing toward the downward concave surface, thereby ensuring the normal expansion growth of the silicon carbide single crystal 300, and on the other hand, the thickness of the middle portion of the first cover body portion 111 will not be too small, thereby avoiding the excessive heat dissipation flux outward from the temperature measuring hole 21 to be too large, which is beneficial to preventing the temperature at the center of the crucible cover 11 from being too low, and further helping to overcome the "M"-shaped temperature field formed in the crucible 10 during crystal growth, reduce thermal stress, and help reduce the dislocation density of the grown silicon carbide single crystal 300, thereby improving the crystal quality.

[0048] Reference Figure 2 and Figure 3As shown, the second cover 112 is formed in a circular plate shape, and the thickness of the second cover 112 is 15mm-20mm. In other words, the thickness of the second cover 112 can be any value between 15mm and 20mm. It can be understood that by making the thickness of the second cover 112 15mm-20mm, on the one hand, the thickness of the crucible cover 11 can be made not too large, so that the temperature at the seed crystal 115 can be ensured not to be too high, thereby ensuring the axial temperature gradient in the crucible 10, and on the other hand, the thickness of the crucible cover 11 can be made not too small, so that the temperature at the seed crystal 115 can be ensured not to be too low, thereby overcoming the "M" type temperature field formed in the crucible 10 during crystal growth, reducing thermal stress, and being conducive to reducing the dislocation density of the grown six-inch silicon carbide single crystal 300 and improving the crystal quality.

[0049] For example, refer to Figure 2 and Figure 3 As shown, in a specific example of the present invention, the height h1 of the convex portion of the arc portion 114 is 12 mm, the diameter of the first cover portion 111 is 220 mm, and the thickness of the second cover portion 112 is 16 mm.

[0050] In some embodiments of the present invention, referring to Figure 2 and Figure 3 As shown, the crucible body 12 includes a graphite outer ring 121, a graphite inner ring 122 and a lower crucible body 123. The top of the graphite outer ring 121 is connected to the crucible cover 11 through a first internal thread section 1211, and the bottom of the graphite outer ring 121 is connected to the lower crucible body 123. The graphite inner ring 122 is arranged in the graphite outer ring 121. The inside of the graphite outer ring 121 is provided with an annular step portion 1213 suitable for supporting the graphite inner ring 122. The distance between the outer peripheral wall of the graphite inner ring 122 and the graphite inner ring 122 is t1, and t1 satisfies: 0.5mm≤t1≤1mm. In other words, t1 can take any value from 0.5mm to 1mm, for example, t1 can take 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm or 1mm.

[0051] It can be understood that by making the graphite outer ring 121 and the graphite inner ring 122 separate and there being a spacing t1 between the graphite outer ring 121 and the graphite inner ring 122, during the crystal growth process, as the silicon carbide single crystal 300 grows, the graphite inner ring 122 can be deformed, which is beneficial to release the thermal stress in the silicon carbide single crystal 300. In addition, by supporting the graphite inner ring 122 on the annular step portion 1213 of the graphite outer ring 121, the installation of the graphite inner ring 122 in the graphite outer ring 121 can be reliable, and the structure is simple and easy to install.

[0052] For example, in one example, referring to Figure 3As shown, the thickness of the graphite inner ring 122 is 3mm-8mm. In other words, the thickness of the graphite inner ring 122 can be any value between 3mm-8mm. Therefore, on the basis of ensuring the structural strength of the graphite inner ring 122, the graphite inner ring 122 can have a certain deformation ability, which is beneficial to reducing the thermal stress in the silicon carbide single crystal 300 grown at the seed crystal 115 and reducing crystal defects.

[0053] In some embodiments of the present invention, referring to Figure 3 and Figure 4 As shown, the graphite inner ring 122 includes a plurality of inner ring petals 1221, and the plurality of inner ring petals 1221 are cut from the same graphite ring, and the removal amount of two adjacent inner ring petals 1221 is t2, and t2 satisfies: 0.2mm≤t2≤0.6mm. For example, the number of inner ring petals 1221 can be three, four, five or six, and the removal amount t2 of two adjacent inner ring petals 1221 is 0.3mm. It can be understood that by making the graphite inner ring 122 include a plurality of inner ring petals 1221, during the crystal growth period, when the silicon carbide single crystal 300 expands and grows, the inner ring petals 1221 can be pushed to fit the inner wall of the graphite outer ring 121, which is beneficial to reduce the thermal stress of the silicon carbide single crystal 300 during growth.

[0054] In some embodiments of the present invention, referring to Figure 3 and Figure 4 As shown, two adjacent inner ring petals 1221 are connected by epoxy resin glue. Figure 4 As shown, multiple inner ring petals 1221 are cut from the same graphite ring, and the cut ends of two adjacent inner ring petals 1221 are connected by epoxy resin glue. Therefore, by connecting multiple inner ring petals 1221 by epoxy resin glue in advance, the graphite inner ring 122 can be prevented from falling when installing, which is conducive to improving production efficiency.

[0055] Optionally, after the multiple inner ring petals 1221 are connected by epoxy resin glue, they are placed in a high-pressure sintering furnace for sintering and taken out for use after sintering. It is understandable that the epoxy resin glue will decompose into carbon during sintering. By sintering the multiple inner ring petals 1221 after bonding, the introduction of new impurities into the crucible 10 can be avoided. At the same time, the multiple inner ring petals 1221 are connected by the sintered carbon, which can enhance the deformation ability of the graphite inner ring 122. During the crystal growth, when the silicon carbide single crystal 300 expands its diameter and grows, the inner ring petals 1221 are pushed to fit the inner wall of the graphite outer ring 121, which is beneficial to further reduce the thermal stress of the silicon carbide single crystal 300 during growth.

[0056] In some embodiments of the present invention, referring to Figure 3 and Figure 4As shown, the graphite outer ring 121 has a guide hole 1214, the central axis of the guide hole 1214 coincides with the central axis of the crucible 10, and in the direction from bottom to top, the hole wall of the guide hole 1214 extends toward the direction close to the central axis of the crucible 10, and the angle between the hole wall of the guide hole 1214 and the horizontal plane is 45°-80°. In other words, referring to Figure 4 As shown, the angle α between the hole wall of the guide hole 1214 and the horizontal plane can be any value between 45° and 80°. It should be noted that the inclined hole wall of the guide hole 1214 can effectively block the heat radiation from the powder source surface to the corresponding part of the crucible cover 11, which is conducive to further reducing the radial temperature gradient at the crucible cover 11, and the temperature on the crystal growth surface is more uniform. On the one hand, this can make the surface morphology of the growing crystal flatter, thereby improving the utilization rate of the silicon carbide single crystal 300, and on the other hand, it can greatly reduce the thermal stress in the silicon carbide single crystal 300 to improve the quality of the crystal.

[0057] In some examples, reference Figure 2 and Figure 3 As shown, the thermal field system 100 also includes a porous graphite plate 90, which is horizontally arranged between the graphite outer ring 121 and the lower crucible 10. The porous graphite plate 90 is provided with a plurality of filter holes 91. During the crystal growth process, the porous graphite plate 90 can filter larger carbon particles in the atmosphere, thereby reducing the occurrence of microtube phenomenon, which is beneficial to reducing the growth defects of the silicon carbide single crystal 300.

[0058] In some embodiments of the present invention, referring to Figure 1 As shown, the thermal field system 100 further includes: a graphite tube 40, which is disposed in the temperature measuring hole 21, the central axis of the graphite tube 40 coincides with the central axis of the temperature measuring hole 21, and the inner tube wall of the graphite tube 40 is provided with a tantalum carbide coating.

[0059] It should be noted that the applicant has found in actual research that during the crystal growth process, due to the heating and carrier gas, the graphite felt around the temperature measuring hole will decompose and deform, resulting in changes in the shape and aperture of the temperature measuring hole, causing changes in the thermal radiation from the crucible cover to the pyrometer, affecting the accuracy of the temperature measurement of the pyrometer. The tantalum carbide coating has excellent high-temperature stability, corrosion resistance and thermal conductivity. By placing a graphite tube 40 with a tantalum carbide coating on the inner wall into the temperature measuring hole 21, the thermal radiation at the crucible cover 11 is conducted to the pyrometer 30 through the tantalum carbide coating, thereby ensuring the reliability of the temperature measurement of the pyrometer 30, which is conducive to the accurate control of the temperature field in the crucible 10.

[0060] In some embodiments of the present invention, referring to Figure 1As shown, the wall thickness of the graphite tube 40 is 4mm-6mm, and the thickness of the tantalum carbide coating is 0.01mm-0.08mm. In other words, the wall thickness of the graphite tube 40 can be any value between 4mm-6mm, and the thickness of the tantalum carbide coating can be any value between 0.01mm-0.08mm. For example, the wall thickness of the graphite tube 40 can be 5mm, and the thickness of the tantalum carbide coating is 0.03mm. It can be understood that by controlling the wall thickness of the graphite tube 40 to 4mm-6mm, while ensuring the structural strength of the graphite tube 40, materials can be saved, which is conducive to reducing costs, and by controlling the thickness of the tantalum carbide coating to 0.01mm-0.08mm, the formation of the tantalum carbide coating is facilitated, and the process is simple.

[0061] Optionally, in some examples, reference Figure 1 As shown, the entire surface of the graphite tube 40 is provided with a tantalum carbide coating. For example, the tantalum carbide coating can be coated on the entire surface of the graphite tube 40 in a tantalum carbide coating synthesis device by using a CVD method. Thus, the process is simple, which is further conducive to improving the stability of the graphite tube 40.

[0062] In some embodiments of the present invention, referring to Figure 1 and Figure 2 As shown, the thermal field system 100 also includes: a quartz tube 50, an upper flange 60, a lower flange 70 and an induction coil 80. The quartz tube 50, the upper flange 60 and the lower flange 70 define a storage space suitable for placing the graphite soft felt 20 and the crucible 10. For example, the quartz tube 50 and the upper flange 60 and the lower flange 70 can be connected by fasteners. The upper flange 60 is provided with a through hole 61 arranged opposite to the temperature measuring hole 21. The interior of the quartz tube 50 has a flow channel 51 suitable for cooling water to pass through. It can be understood that the temperature of the quartz tube 50 can be adjusted by controlling the flow rate of cooling water in the flow channel 51, so that reliable control of the temperature of the quartz tube 50 can be achieved, which is conducive to ensuring the safety of crystal growth production.

[0063] Reference Figure 1 and Figure 2 As shown, the induction coil 80 is wound outside the quartz tube 50, and the number of turns of the induction coil 80 is 15 turns to 20 turns. In other words, the number of turns of the induction coil 80 can be any value between 15 turns and 20 turns.

[0064] It should be noted that the number of turns of the induction coil is an important parameter that affects the heat distribution in the crucible. The applicant found in actual research that 11-turn and 13-turn induction coils will cause the edge temperature of the crucible cover to be too low, and the crystal edge growth rate will be much higher than other parts, thereby producing a concave crystal plane. When the number of turns of the induction coil 80 exceeds 20 turns, the edge temperature of the crucible cover will be too high, resulting in a large difference in the radial temperature gradient, which will cause the crystal edge growth rate to be much lower than other parts, thereby producing a convex crystal plane. According to the thermal field system 100 of the silicon carbide single crystal 300 of the embodiment of the utility model, by making the number of turns of the induction coil 80 15 turns-20 turns, and when the crystal growth process crucible 10 rises to the top, there are still two turns of the coil above the crucible 10, thereby further optimizing the radial temperature gradient at the crucible cover 11, which is conducive to the downward slightly convex growth of the silicon carbide single crystal 300, which can reduce thermal stress, and is conducive to reducing the dislocation density of the grown six-inch silicon carbide single crystal 300, thereby improving the crystal quality.

[0065] Please refer to the following Figure 1-5 The thermal field system 100 of the silicon carbide single crystal 300 of the present invention is described in detail. Of course, it can be understood that the following description is intended to explain the present invention, but cannot be used as a limitation of the present invention.

[0066] Reference Figure 1-Figure 5 As shown, the thermal field system 100 of the silicon carbide single crystal 300 according to the embodiment of the present invention includes: a crucible 10, a graphite felt 20, a pyrometer 30, a graphite tube 40, a quartz tube 50, an upper flange 60, a lower flange 70 and an induction coil 80.

[0067] Reference Figure 1-Figure 5 As shown, the quartz tube 50, the upper flange 60 and the lower flange 70 define a storage space suitable for placing the graphite felt 20 and the crucible 10. The graphite felt 20 is wrapped around the outside of the crucible 10. The top of the graphite felt 20 defines a temperature measuring hole 21. The center line of the temperature measuring hole 21 is on the same straight line as the center axis of the crucible 10. The graphite tube 40 is arranged in the temperature measuring hole 21. The entire graphite tube 40 is provided with a tantalum carbide coating. The thickness of the tantalum carbide coating is 0.01mm-0.08mm. The pyrometer 30 is arranged above the graphite felt 20 and opposite to the temperature measuring hole 21. The induction coil 80 is wound around the outside of the quartz tube 50. The number of turns of the induction coil 80 is 15.

[0068] Reference Figure 1-Figure 3 As shown, the quartz tube 50 and the upper flange 60 and the lower flange 70 can be connected by fasteners. The upper flange 60 is provided with a through hole 61 arranged opposite to the temperature measuring hole 21. The interior of the quartz tube 50 has a flow channel 51 suitable for cooling water to pass through.

[0069] Reference Figure 1-Figure 3As shown, the crucible 10 includes a crucible cover 11, a graphite inner ring 122, a graphite outer ring 121 and a lower crucible 10. The crucible cover 11, the graphite outer ring 121 and the lower crucible 10 are arranged in sequence from top to bottom, and the interior of the graphite outer ring 121 is provided with an annular step portion 1213 suitable for supporting the graphite inner ring 122.

[0070] Reference Figure 1-Figure 3 As shown, the crucible cover 11 includes a first cover body portion 111 and a second cover body portion 112, and the first cover body portion 111 and the second cover body portion 112 are arranged in the up and down directions. The diameter of the first cover body portion 111 is larger than the diameter of the second cover body portion 112, and the outer periphery of the second cover body portion 112 is provided with a first external thread segment 113, and the inner peripheral wall of the top of the graphite outer ring 121 is provided with a first internal thread segment 1211, and the first external thread segment 113 is threadedly matched with the first internal thread segment 1211, and the bottom of the graphite outer ring 121 is provided with a second external thread segment 1212, and the top of the lower crucible 10 is provided with a second internal thread segment 1231, and the second external thread segment 1212 is threadedly connected with the second internal thread segment 1231 to realize that the graphite outer ring 121 is connected to the lower crucible 10.

[0071] Reference Figure 1-Figure 3 As shown, the top of the first cover body portion 111 has an arc portion 114, the height of the convex arc portion 114 is 12 mm, the diameter of the first cover body portion 111 is 230 mm, the second cover body portion 112 is formed in a circular plate shape, the thickness of the second cover body portion 112 is 12 mm, the diameter of the second cover body portion 112 is also 230, the first external thread section 113 is provided on the second cover body portion 112, and the first cover body portion 111 and the second cover body portion 112 are an integral part.

[0072] Reference Figure 3 and Figure 4 As shown, the spacing t1 between the outer wall of the graphite inner ring 122 and the graphite inner ring 122 is 0.8 mm, the graphite inner ring 122 includes a plurality of inner ring petals 1221, the plurality of inner ring petals 1221 are cut from the same graphite ring with a thickness of 5 mm, the removal amount t2 of two adjacent inner ring petals 1221 is 0.5 mm, and the two adjacent inner ring petals 1221 are connected by epoxy resin glue. It should be noted that after the plurality of inner ring petals 1221 are connected by epoxy resin glue, they are placed in a high-pressure sintering furnace for sintering, and taken out for use after sintering.

[0073] Reference Figure 2 and Figure 3 As shown, the graphite outer ring 121 has a guide hole 1214, the central axis of the guide hole 1214 coincides with the central axis of the crucible 10, and in the direction from bottom to top, the hole wall of the guide hole 1214 extends toward the direction close to the central axis of the crucible 10, and the angle between the hole wall of the guide hole 1214 and the horizontal plane is 60°.

[0074] Reference Figure 2 As shown, the thermal field system 100 also includes a porous graphite plate 90, which is arranged between the graphite outer ring 121 and the lower crucible 10. During the crystal growth process, the porous graphite plate 90 can filter large carbon particles in the atmosphere, thereby reducing the occurrence of microtube phenomenon, which is beneficial to reducing the growth defects of the silicon carbide single crystal 300.

[0075] Reference Figure 1-Figure 5 As shown, the whole composed of the quartz tube 50, the upper and lower flanges 70 and the crucible 10 is placed on the carrier, and the induction coil 80 is fixed. The carrier can drive the crucible 10 to move upward from the initial position of crystal growth to the end position of crystal growth at a speed of 0.1 mm / h. At the initial position of crystal growth, refer to Figure 1 As shown, the lower flange 70 is aligned with the penultimate coil in the horizontal direction, at the crystal growth termination position, referring to Figure 5 As shown, the upper flange 60 is aligned with the top coil. At this time, there are two turns of coil above the crucible 10, which can increase the temperature of the edge of the crucible cover 11, thereby further optimizing the radial temperature gradient at the crucible cover 11, which is beneficial to the downward slightly convex growth of the silicon carbide single crystal 300, can reduce thermal stress, and is beneficial to reducing the dislocation density of the grown six-inch silicon carbide single crystal 300, thereby improving the crystal quality.

[0076] It can be understood that by gradually increasing the thickness of the portion of the crucible cover 11 that is opposite to the seed crystal 115 in the direction from the edge to the center of the crucible cover 11, in other words, the crucible cover 11 is thin at the edge and thick in the middle, the flux of heat dissipated outward from the center of the crucible 10 through the temperature measuring hole 21 can be reduced, the temperature of the center of the crucible 10 can be increased, and the radial temperature gradient can be reduced, which is conducive to the downward micro-convex growth of the silicon carbide single crystal 300, which can reduce thermal stress and help reduce the dislocation density of the grown six-inch silicon carbide single crystal 300. The degree can improve the crystal quality. At the same time, by sintering the multiple inner ring petals 1221 after bonding, the introduction of new impurities into the crucible 10 can be avoided. At the same time, the multiple inner ring petals 1221 are connected by the sintered carbon, which can enhance the deformation ability of the graphite inner ring 122. During the crystal growth, when the silicon carbide single crystal 300 expands and grows, the graphite inner ring 122 is deformed and even the inner ring petals 1221 are pushed to fit the inner wall of the graphite outer ring 121, which is beneficial to further reduce the thermal stress of the silicon carbide single crystal 300 during growth.

[0077] Other structures and operations of the thermal field system 100 of the silicon carbide single crystal 300 according to the embodiment of the present invention are known to those skilled in the art and will not be described in detail here.

[0078] In the description of the present invention, it should 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" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and 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 a limitation on the present invention.

[0079] 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 one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0080] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or a communication; 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. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0081] In the present utility model, 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.

[0082] 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 utility model. 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.

[0083] Although the embodiments of the present invention have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A thermal field system for silicon carbide single crystal, characterized in that: include: A crucible, the crucible comprising a crucible cover and a crucible body, the crucible cover being detachably connected to the crucible body, a seed crystal being pasted to the bottom of the crucible cover, and a thickness of a portion of the crucible cover opposite to the seed crystal gradually increasing in a direction from the edge to the center of the crucible cover; A graphite soft felt, wherein the graphite soft felt is wrapped around the outside of the crucible, a temperature measuring hole is defined on the top of the graphite soft felt, and a center line of the temperature measuring hole is in the same straight line as a center axis of the crucible; A pyrometer is arranged above the graphite soft felt and opposite to the temperature measuring hole.

2. The thermal field system of silicon carbide single crystal according to claim 1, characterized in that: The crucible cover includes a first cover body portion and a second cover body portion, the first cover body portion and the second cover body portion are arranged in the up and down direction, the diameter of the first cover body portion is larger than the diameter of the second cover body portion, the outer periphery of the second cover body portion is provided with a first external thread segment, the inner peripheral wall of the top of the crucible body is provided with a first internal thread segment, and the first external thread segment is threadedly matched with the first internal thread segment.

3. The thermal field system of silicon carbide single crystal according to claim 2, characterized in that: The top of the first cover body has an arc portion, the height of the arc portion is 10mm-15mm, the diameter of the first cover body is 200mm-300mm, the second cover body is formed into a circular plate shape, and the thickness of the second cover body is 15mm-20mm.

4. The thermal field system of silicon carbide single crystal according to claim 2, characterized in that: The crucible body includes a graphite outer ring, a graphite inner ring and a lower crucible body, the top of the graphite outer ring is connected to the crucible cover through the first internal thread section, the bottom of the graphite outer ring is connected to the lower crucible body, the graphite inner ring is arranged inside the graphite outer ring, the interior of the graphite outer ring is provided with an annular step portion suitable for supporting the graphite inner ring, the distance between the outer peripheral wall of the graphite inner ring and the graphite inner ring is t1, and t1 satisfies: 0.5mm≤t1≤1mm.

5. The thermal field system of silicon carbide single crystal according to claim 4, characterized in that: The graphite inner ring includes a plurality of inner ring petals, and the plurality of inner ring petals are cut from the same graphite ring. The removal amount of two adjacent inner ring petals is t2, and t2 satisfies: 0.2mm≤t2≤0.6mm.

6. The thermal field system of silicon carbide single crystal according to claim 5, characterized in that: Two adjacent inner ring petals are connected by epoxy resin glue.

7. The thermal field system of silicon carbide single crystal according to claim 4, characterized in that: The graphite outer ring has a guide hole, the central axis of the guide hole coincides with the central axis of the crucible, and in the direction from bottom to top, the hole wall of the guide hole extends in a direction close to the central axis of the crucible, and the angle between the hole wall of the guide hole and the horizontal plane is 45°-80°.

8. The thermal field system of silicon carbide single crystal according to claim 1, characterized in that: Also includes: A graphite tube is arranged in the temperature measuring hole, the central axis of the graphite tube coincides with the central axis of the temperature measuring hole, and the inner tube wall of the graphite tube is provided with a tantalum carbide coating.

9. The thermal field system of silicon carbide single crystal according to claim 8, characterized in that: The wall thickness of the graphite tube is 4 mm-6 mm, and the thickness of the tantalum carbide coating is 0.01 mm-0.08 mm.

10. The thermal field system of silicon carbide single crystal according to any one of claims 1 to 9, characterized in that: Also includes: A quartz tube, an upper flange, a lower flange and an induction coil, wherein the quartz tube, the upper flange and the lower flange define a storage space suitable for placing the graphite felt and the crucible, the upper flange is provided with a through hole arranged opposite to the temperature measuring hole, the interior of the quartz tube has a flow channel suitable for cooling water to pass through, the induction coil is wound around the outside of the quartz tube, and the number of turns of the induction coil is 15-20 turns.

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