Apparatus and method for liquid phase method growth of silicon carbide crystals

Abstract

The application provides a device for growing silicon carbide crystals by a liquid phase method. When the device is used, a top support is screwed into a seed crystal seat, a graphite paper is clamped at the joint as a buffer layer. Then, a boss on a ring sleeve is clamped in a ring groove on a seed crystal ingot, and the seed crystal ingot is connected with the seed crystal seat through the threads on the ring sleeve so that the seed crystal ingot is in close contact with the top support. The device can reliably clamp the seed crystal ingot. The application also provides a method for preparing silicon carbide crystals, which uses the device for growing silicon carbide crystals by a liquid phase method. The device can reuse the seed crystal, saves the process of sticking the seed crystal and subsequent hot pressing for fixing the seed crystal, and reduces the cost. The device can also eliminate the growth defects caused by the seed crystal sticking, and can adjust the axial temperature field during the crystal growth by changing the thickness of the top support, so as to improve the quality of the silicon carbide crystals grown by the liquid phase method. The method can prepare the silicon carbide crystals with excellent quality.

Description

Technical Field

[0001] This invention belongs to the field of liquid-phase growth technology for silicon carbide single crystals. Specifically, this invention relates to an apparatus and method for growing silicon carbide crystals using a liquid-phase method. Background Technology

[0002] Silicon carbide (SiC) is a widely studied wide-bandgap semiconductor material, possessing advantages such as low density, large bandgap (3.2 eV at room temperature), high breakdown field strength (approximately 10 times that of Si), high saturated electron mobility (approximately twice that of Si), high thermal conductivity (3 times that of Si and 10 times that of GaAs), and good chemical stability. It is an ideal substrate material for fabricating high-frequency, high-voltage, high-power devices and blue light-emitting diodes. Silicon carbide has significant application potential in electric vehicles, rail transportation, high-voltage power transmission and transformation, photovoltaics, and 5G communications.

[0003] The main growth method for SiC is currently the physical vapor transport method, but it suffers from problems such as difficulty in controlling growth stability, diameter expansion, and p-type doping. The liquid phase method, on the other hand, has a lower growth temperature, a relatively stable growth environment, and a growth process close to thermodynamic equilibrium conditions, resulting in better crystal quality. It also shows promising potential in diameter expansion and p-type doping, and has received widespread attention from academia and industry in recent years.

[0004] Seed bonding and hot pressing are crucial steps in the liquid-phase growth of silicon carbide. The quality of the seed bonding directly affects the quality of the grown silicon carbide crystal. Current techniques typically involve manually applying organic adhesive to the seed and graphite substrate surfaces using a scraper, then bonding them together (sometimes with a graphite paper layer sandwiched between them as a buffer), followed by heating and pressure to cure the adhesive. This method currently has several drawbacks:

[0005] 1. Adhesion uniformity cannot be guaranteed. Current technology generally uses manual methods to apply adhesive, which cannot guarantee the thickness and uniformity of the adhesive layer. Uneven adhesive layer will directly lead to uneven heat dissipation from the back of the seed crystal, affecting the crystal quality.

[0006] 2. Heating introduces pores. During the carbonization process of the organic adhesive, low-boiling substances in the adhesive will volatilize, causing pores in the adhesive layer and even agglomerating to form large-scale bubbles. Due to the difference in thermal conductivity between the pores and the adhesive layer, the temperature in the pore area is higher than that in the bonding area during crystal growth, causing the seed crystal to sublimate backward and escape along the pores, eventually forming hexagonal void defects.

[0007] 3. Adhesion strength cannot be guaranteed. Although organic adhesives (such as glucose, graphite adhesive, photoresist, AB adhesive, phenolic resin adhesive and epoxy resin adhesive, etc.) are widely used as adhesives in the vapor phase growth of silicon carbide, and the adhesion strength can be guaranteed, the up-and-down movement and high-speed rotation of the seed crystal in the liquid phase method require higher adhesion strength, and the reliability of the adhesive method cannot be guaranteed.

[0008] 4. The melt can penetrate the bonding surface, causing stress-induced defects. After the seed crystal contacts the molten surface, if the wettability between the melt and silicon carbide is good, the melt will "climb" upwards along the seed crystal and enter the bonding surface between the seed crystal and the graphite support, affecting the bond strength and thermal conductivity uniformity. After cooling, these metals will solidify at the bonding surface, introducing stress into the crystal, which can lead to cracking in severe cases.

[0009] 5. High cost. A seed crystal is used for each crystal grown. Seed crystals are generally commercially available silicon carbide wafers, and in the liquid phase method, seed crystal costs account for 40%–50% of the total cost per furnace. Furthermore, due to factors such as corrosion of the seed crystal by melt vapor, inconsistencies in seed crystal doping concentration and growth area, and stress accumulation at the seed crystal, the seed crystal portion is unusable after growth and is generally removed. In addition, the processes of attaching and hot-pressing the seed crystal further increase the time and labor costs of growing silicon carbide crystals in the liquid phase method.

[0010] Therefore, there is an urgent need for a device that simplifies the process, reduces costs, and improves the quality of silicon carbide crystals grown in the liquid phase method, particularly in the seed crystal preparation stage. Summary of the Invention

[0011] The purpose of this invention is to provide an apparatus for growing silicon carbide crystals using the liquid phase method. This apparatus allows for the reuse of seed crystals, eliminating the need for seed crystal bonding and subsequent hot-pressing to fix the seed crystal, thus reducing costs. Furthermore, this apparatus can eliminate growth defects caused by seed crystal bonding and improve the quality of silicon carbide crystals grown using the liquid phase method by adjusting the thickness of the support.

[0012] Another object of the present invention is to provide a method for preparing silicon carbide crystals. The method of the present invention yields silicon carbide crystals of excellent quality.

[0013] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0014] On one hand, the present invention provides an apparatus for growing silicon carbide crystals by liquid phase method, comprising: a seed crystal rod, a seed crystal seat, a top support, a seed crystal ingot, and a ring sleeve;

[0015] The seed crystal seat includes a substrate, a first cylinder extending circumferentially along one side of the substrate, and a second cylinder extending circumferentially along the other side of the substrate; the first cylinder is provided with internal threads; the second cylinder includes a first section near the substrate and a remaining second section, wherein the inner diameter of the second section is larger than the inner diameter of the first section, and both the first section and the second section are provided with internal threads.

[0016] One end of the ring sleeve is provided with a radially inwardly extending boss, and the other end of the ring sleeve is provided with an external thread;

[0017] The seed crystal ingot is provided with a circumferential groove;

[0018] The seed crystal rod is threaded to the first cylinder;

[0019] The top support is threadedly connected to the first section of the second cylinder;

[0020] The seed crystal ingot is connected to the seed crystal seat through the ring sleeve, thereby clamping the top support between the seed crystal seat and the seed crystal ingot; wherein the boss on the ring sleeve is engaged with the groove on the seed crystal ingot, and the external thread of the ring sleeve is adapted to the internal thread of the second section of the second cylinder.

[0021] Preferably, in the apparatus of the present invention for growing silicon carbide crystals by liquid phase method, the ring sleeve includes at least two sub-ring sleeves, the external thread of each sub-ring sleeve being adaptable to the internal thread of the second section of the second cylinder.

[0022] Preferably, in the apparatus for growing silicon carbide crystals by liquid phase according to the present invention, the apparatus further includes graphite paper located between the top support and the seed crystal seat, thereby separating the top support and the seed crystal seat.

[0023] Preferably, in the apparatus for liquid-phase growth of silicon carbide crystals according to the present invention, the apparatus further includes graphite paper located between the top support and the seed crystal ingot, thereby separating the top support and the seed crystal ingot.

[0024] Preferably, in the apparatus of the present invention for growing silicon carbide crystals by liquid phase method, the top support is a solid cylinder with a thickness of 2-50 mm. The axial temperature field of the crystal can be controlled by adjusting the thickness of the top support.

[0025] Preferably, in the apparatus of the present invention for liquid-phase growth of silicon carbide crystals, the seed crystal ingot has a size of 2 to 8 inches and a thickness of 4 to 10 mm. The annular grooves on the seed crystal ingot are machined using a diamond sintered grinding head, with a width of 1 to 3 mm and a depth of 1 to 3 mm.

[0026] Preferably, in the apparatus of the present invention for growing silicon carbide crystals by liquid phase method, the top support, ring and seed crystal seat are made of high-purity graphite or molybdenum.

[0027] Preferably, in the apparatus of the present invention for growing silicon carbide crystals by liquid phase method, the ring and the seed crystal seat are provided with end faces to facilitate tightening and loosening of the ring and the seed crystal seat using tools.

[0028] On the other hand, the present invention provides a method for preparing silicon carbide crystals, which uses the apparatus of the present invention for liquid-phase growth of silicon carbide crystals, and includes the following steps:

[0029] (1) Place the growth material in a crucible and heat the crucible with an induction heating device to melt the growth material into a melt;

[0030] (2) Adjust the position of the crucible in the induction coil so that the surface of the melt is in the high temperature region, and then lower the seed crystal ingot to make it contact the surface of the melt, thereby causing the seed crystal ingot to melt back;

[0031] (3) Adjust the position of the crucible in the induction coil so that the bottom of the melt is located in the high temperature region so that silicon carbide crystal growth can occur at the contact surface between the melt and the seed crystal ingot.

[0032] (4) After growth is complete, remove the seed crystal ingot, cut off the grown part, and grind the cut surface of the seed crystal ingot for reuse.

[0033] Preferably, in the method of the present invention, the seed crystal ingot backmelting in step (2) is carried out by backmelting the seed crystal ingot to a thickness of 1 to 100 μm.

[0034] Preferably, in the method of the present invention, the cutting surface of the seed crystal ingot in step (4) is ground flat by using a surface grinder, a thinning machine or a polishing machine.

[0035] Preferably, in the method of the present invention, the crucible is a graphite crucible; more preferably, the purity of the graphite crucible is not less than 99.95%, the inner diameter of the graphite crucible is 10-150 mm larger than the diameter of the seed crystal ingot, the wall thickness of the graphite crucible is not less than 10 mm, and the density of the graphite crucible is 1.7-2.0 g / cm³. 3 .

[0036] In a specific embodiment of the present invention, the top support and the ring sleeves are provided with external threads, the seed crystal seat is provided with internal threads, the seed crystal ingot is machined with an annular groove, and the two semi-circular ring sleeves are provided with bosses. In use, the top support is screwed into the seed crystal seat, and a piece of graphite paper is clamped at the connection point as a buffer layer. Then, the bosses on the two semi-circular ring sleeves are engaged with the annular grooves on the seed crystal ingot, and the threads on the ring sleeves connect them to the seed crystal seat, ensuring tight contact between the seed crystal ingot and the top support. A piece of graphite paper can be clamped at the connection point between the seed crystal ingot and the top support as a buffer layer. The device of the present invention can reliably clamp the seed crystal ingot. The entire assembly can then be used by connecting it to a seed crystal rod.

[0037] In a specific embodiment of the present invention, a method for growing silicon carbide crystals using a liquid-phase method is provided. The method is carried out in the apparatus of the present invention, employing induction heating and using a graphite crucible placed in a heating cylinder. The heating cylinder is made of graphite soft felt or graphite hard felt wrapped around a graphite cylinder, and the purity of the graphite felt is not less than 99.9%. The growth raw materials of the present invention may contain elemental Si and Cr metals.

[0038] In a specific embodiment of the present invention, the thickness of the backmelting after the seed crystal comes into contact with the molten surface is 1 to 100 μm, and the holding time is 1 to 30 minutes. The thickness of the backmelting should be greater than the surface roughness value after processing and the corrosion thickness of the seed crystal by the molten vapor.

[0039] In a specific embodiment of the present invention, after growth is completed, the seed crystal ingot is removed, and the seed crystal ingot is cut off by a single-wire dicing machine, or by using a multi-wire dicing machine, the grown part is placed in the dicing area and the grown part is directly diced into a wafer, while the seed crystal ingot is left. The diced surface of the seed crystal ingot is then ground flat by a surface grinder, a thinning machine or a polishing machine and reused as the grown surface.

[0040] Compared with the prior art, the present invention has at least the following beneficial effects:

[0041] (1) This invention provides a seed crystal fixing method for liquid-phase growth of silicon carbide crystals, which can eliminate growth defects caused by seed crystal adhesion. Compared with the currently used seed crystal bonding method, the device of this invention does not require glue and relies on clamps to reliably hold the seed crystal ingot. In the device of this invention, the contact surface has a graphite paper as a buffer layer. Even if there is still some uneven thermal conductivity at the junction of the seed crystal and the top support, the large thickness of the seed crystal can reduce this effect, and the temperature at the growth surface is still relatively uniform. In this way, problems such as poor uniformity caused by adhesion, back evaporation of the seed crystal due to the introduction of pores, and poor firmness and reliability are avoided. In addition, since the thickness of the seed crystal ingot is much larger than that of the seed crystal wafer, the melt will basically not rise to the connection point, and there is no stress problem caused by the metal solidifying at the contact surface.

[0042] (2) This invention provides an apparatus for reusing seed crystals in the liquid phase growth of silicon carbide crystals. By using seed crystal ingots as seed crystals and combining them with the reverse melting process, the seed crystal ingots can be reused after simple processing after cutting, which greatly reduces the input of seed crystals in the growth process, and eliminates the processes of sticking seed crystals and hot pressing to fix the seed crystals, thus reducing time and labor costs.

[0043] (3) This invention provides an apparatus for adjusting the axial temperature field of silicon carbide crystals grown in a liquid phase method. The apparatus of this invention can adjust the back-side heat dissipation of the seed crystal by changing the thickness of the support, thereby adjusting the axial temperature field during crystal growth. The axial temperature field determines the supersaturation during growth, directly affecting the growth rate and crystal morphology. Therefore, constructing a reasonable axial temperature field can improve the quality of silicon carbide crystals grown in a liquid phase method. This objective can be achieved through the apparatus of this invention. Attached Figure Description

[0044] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0045] Figure 1 This is a schematic diagram of a device according to a specific embodiment of the present invention;

[0046] Figure 2 This is a three-dimensional structural diagram of a device according to a specific embodiment of the present invention;

[0047] Figure 3 This is a partial structural schematic diagram of a device according to a specific embodiment of the present invention;

[0048] Figure 4 This is a diagram of the silicon carbide crystal obtained in Example 1 of the present invention;

[0049] Figure 5 The seed crystal holder in Comparative Example 1 of this invention is obtained by fixing the seed crystal with adhesive.

[0050] Figure 6 This is a diagram of the silicon carbide crystal obtained in Comparative Example 1 of the present invention.

[0051] In the attached figures, the following labels are used:

[0052] 1-Water-cooled rod; 2-Seed crystal rod; 3-Heating cylinder; 4-Crucible; 5-Raw material; 6-Induction coil; 7-Crucible tray; 8-Seed crystal seat; 9-Graphite paper; 10-Top support; 11-Ring; 12-Boss; 13-Groove; 14-Seed crystal ingot; 15-End face; 16-First cylinder; 17-Second cylinder. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0054] Reference Figures 1 to 4 This invention provides an apparatus for growing silicon carbide crystals by liquid phase method, comprising: a seed crystal rod (2), a seed crystal seat (8), a top support (10), a seed crystal ingot (14), and a ring (11); the seed crystal seat (8) includes a substrate, a first cylinder (16) extending circumferentially along one side of the substrate, and a second cylinder (17) extending circumferentially along the other side of the substrate; the first cylinder (16) is provided with internal threads; the second cylinder (17) includes a first section near the substrate and a remaining second section, wherein the inner diameter of the second section is larger than the inner diameter of the first section and both the first section and the second section are provided with internal threads; one end of the ring (11) is provided with a radially inwardly oriented... The extended boss (12) and the other end of the ring (11) are provided with external threads; the seed crystal ingot (14) is provided with a circumferential groove (13); the seed crystal rod (2) is connected to the first cylinder (16) by threads; the top support (10) is connected to the first section of the second cylinder (17) by threads; the seed crystal ingot (14) is connected to the seed crystal seat (8) through the ring (11), thereby clamping the top support (10) between the seed crystal seat (8) and the seed crystal ingot (14); wherein the boss (12) on the ring (11) is engaged with the groove (13) on the seed crystal ingot (14), and the external thread of the ring (11) is adapted to the internal thread of the second section of the second cylinder (17).

[0055] In one specific embodiment of the present invention, the seed crystal ingot (14) is a 4-inch semi-insulating 4H-SiC with a thickness of 25mm; the circumferential groove (13) on the seed crystal ingot (14) is processed by a diamond sintering grinding head, with a width of 2mm and a depth of 2mm.

[0056] In one specific embodiment of the present invention, the top support (10), the ring (11), the seed crystal seat (8), the seed crystal rod (2), and the crucible (4) are made of high-purity graphite with a purity of not less than 99.95%; the heating cylinder (3) is a heating cylinder made of graphite soft felt with a purity of not less than 99.9%.

[0057] In one specific embodiment of the present invention, the seed crystal rod (2) has a diameter of 15 mm, the graphite crucible (4) has an inner diameter of 150 mm and a wall thickness of 15 mm.

[0058] In one specific embodiment of the invention, the ring sleeve (11) includes at least two sub-ring sleeves, the external threads of each sub-ring sleeve being adaptable to the internal threads of the second section of the second cylinder (17).

[0059] In one specific embodiment of the invention, the device further includes graphite paper (9) located between the top support (10) and the seed crystal seat (8), thereby separating the top support (10) and the seed crystal seat (8).

[0060] In one specific embodiment of the invention, the device further includes graphite paper (9) located between the top support (10) and the seed crystal ingot (14), such that the top support (10) and the seed crystal ingot (14) are separated.

[0061] In one specific embodiment of the present invention, the top support (10) is a solid cylinder with a thickness of 2-50 mm, and can be... Figure 3 The 15mm shown can also be Figure 4 The figure shows 5mm.

[0062] In a preferred embodiment of the present invention, the seed crystal ingot (14) has a size of 2 to 8 inches and a thickness of 4 to 10 mm.

[0063] In a preferred embodiment of the present invention, the top support (10), the ring (11), and the seed crystal seat (8) are made of high-purity graphite or molybdenum.

[0064] In a preferred embodiment of the present invention, the ring (11) and the seed crystal seat (8) are provided with end faces (15) to facilitate tightening and loosening of the ring and the seed crystal seat using tools.

[0065] When using the device of the present invention, the top support (10) is screwed into the seed crystal seat (8), and a piece of graphite paper (9) is clamped at the connection as a buffer. Then, the protrusions (12) on the two semi-circular rings (11) are engaged in the circumferential grooves (13) on the seed crystal ingot (14), and connected to the seed crystal seat (8) through the threads on the rings (11), and in close contact with the top support (10), with a piece of graphite paper (9) clamped at the connection as a buffer. In this way, reliable clamping of the seed crystal ingot (14) can be achieved, and the entire assembly can be connected to the seed crystal rod (2) for use.

[0066] Example 1

[0067] The device of this invention comprises: screwing the top support into the seed crystal seat; clamping a piece of graphite paper at the connection point as a buffer; securing the protrusions on the two semi-circular ring sleeves into the annular grooves on the seed crystal ingot; connecting the ring sleeves to the seed crystal seat via threads, and ensuring tight contact with the top support; and clamping a piece of graphite paper at the connection point as a buffer. This achieves reliable clamping of the seed crystal ingot. The entire assembly is then connected to the seed crystal rod for use. The top support is a solid cylinder with a thickness of 15mm. Figure 3As shown. The seed crystal ingot is a 4-inch semi-insulating 4H-SiC (purchased from Beijing Tianke Heda Semiconductor Co., Ltd.), with a thickness of 15mm. The circumferential grooves on the seed crystal ingot are machined using a diamond sintering grinding head, with a width of 2mm and a depth of 2mm. The top support, ring, seed crystal seat, seed crystal rod, and crucible are made of high-purity graphite with a purity of not less than 99.95%. The heating element is made of graphite soft felt with a purity of not less than 99.9%. The ring and seed crystal seat have end faces, and special tools are used to tighten and loosen them. The seed crystal rod has a diameter of 15mm, and the graphite crucible has an inner diameter of 150mm and a wall thickness of 15mm.

[0068] The liquid-phase growth of silicon carbide crystals includes the following steps:

[0069] (1) Place the growth material containing Si and Cr metal elements in a crucible, and heat the crucible with an induction heating device to melt the growth material containing Si and Cr metal elements.

[0070] (2) Adjust the position of the crucible in the induction coil, control the melt surface to be in the high temperature area of ​​the coil heating, lower the seed crystal to contact the melt surface, keep it for 20 minutes, and make the seed crystal melt back 50μm;

[0071] (3) Adjust the position of the crucible in the induction coil to control the bottom of the melt to be located in the high-temperature area heated by the coil for growth;

[0072] (4) After growth is complete, remove the crystal ingot, cut off the grown part using a single wire cutter, and grind the cut surface of the seed crystal ingot flat using a surface grinder to reuse it as the growth surface.

[0073] A photograph of the silicon carbide crystal obtained in Example 1 is shown below. Figure 4 As shown in the figure, the grown silicon carbide crystal has a smooth and flat surface, free from macroscopic defects such as grooves and cracks, indicating good crystal quality.

[0074] Comparative Example 1

[0075] The apparatus used in Comparative Example 1 for growing silicon carbide crystals via the liquid phase method does not include... Figure 2 The structure shown uses organic adhesive and thermoforming to fix a 4-inch semi-insulating 4H-SiC wafer (purchased from Beijing Tianke Heda Semiconductor Co., Ltd.) onto a graphite seed substrate. Figure 5 As shown, there are many air bubbles on the bonding surface. The entire assembly can be used after being connected to the seed crystal rod. The purity of the graphite seed crystal holder is not less than 99.95%; the heating element is made of graphite felt with a purity of not less than 99.9%. The seed crystal rod has a diameter of 15mm, and the graphite crucible has an inner diameter of 150mm and a wall thickness of 15mm.

[0076] The liquid-phase growth of silicon carbide crystals includes the following steps:

[0077] (1) Place the growth material containing Si and Cr metal elements in a crucible, and heat the crucible with an induction heating device to melt the growth material containing Si and Cr metal elements.

[0078] (2) The seed crystal holder is lowered to contact the surface of the melt for growth;

[0079] (3) After the growth is completed, the grown part is cut off with a single wire cutter to obtain silicon carbide crystals.

[0080] A photograph of the silicon carbide crystal prepared in Comparative Example 1 is shown below. Figure 6 As shown in the figure, the growth quality is significantly reduced where there are bubbles, and there are defects such as grooves and inclusions, resulting in poor crystal quality.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An apparatus for growing silicon carbide crystals by liquid phase method, comprising: Seed crystal rod, seed crystal seat, top support, seed crystal ingot, ring sleeve; The seed crystal seat includes a substrate, a first cylinder extending circumferentially along one side of the substrate, and a second cylinder extending circumferentially along the other side of the substrate; the first cylinder is provided with internal threads; the second cylinder includes a first section near the substrate and a remaining second section, wherein the inner diameter of the second section is larger than the inner diameter of the first section, and both the first section and the second section are provided with internal threads. One end of the ring sleeve is provided with a radially inwardly extending boss, and the other end of the ring sleeve is provided with an external thread; The seed crystal ingot is provided with a circumferential groove; The seed crystal rod is threaded to the first cylinder; The top support is threadedly connected to the first section of the second cylinder; The seed crystal ingot is connected to the seed crystal seat through the ring sleeve, thereby clamping the top support between the seed crystal seat and the seed crystal ingot; wherein the boss on the ring sleeve is engaged with the groove on the seed crystal ingot, and the external thread of the ring sleeve is adapted to be connected with the internal thread of the second section of the second cylinder. The device further includes graphite paper located between the top support and the seed crystal ingot, thereby separating the top support and the seed crystal ingot; The seed crystal ingot has a size of 2 to 8 inches and a thickness of 4 to 10 mm.

2. The apparatus for liquid-phase growth of silicon carbide crystals according to claim 1, wherein, The ring sleeve includes at least two sub-ring sleeves, and the external thread of each sub-ring sleeve can be adapted to connect to the internal thread of the second section of the second cylinder.

3. The apparatus for liquid-phase growth of silicon carbide crystals according to claim 1, wherein, The top support, ring, and seed crystal seat are made of high-purity graphite or molybdenum.

4. The apparatus for liquid-phase growth of silicon carbide crystals according to claim 1, wherein, The ring and the seed crystal seat are provided with end faces to facilitate tightening and loosening of the ring and the seed crystal seat using tools.

5. The apparatus for liquid-phase growth of silicon carbide crystals according to claim 1, wherein, The top support is a solid cylinder with a thickness of 2-50mm.

6. A method for preparing silicon carbide crystals, using the apparatus for liquid-phase growth of silicon carbide crystals as described in any one of claims 1-5, comprising the following steps: (1) Place the growth material in a crucible and heat the crucible with an induction heating device to melt the growth material into a melt; (2) Adjust the position of the crucible in the induction coil so that the surface of the melt is in the high temperature region, and then lower the seed crystal ingot to make it contact the surface of the melt, thereby causing the seed crystal ingot to melt back; (3) Adjust the position of the crucible in the induction coil so that the bottom of the melt is located in the high temperature region so that silicon carbide crystal growth can occur at the contact surface between the melt and the seed crystal ingot. (4) After growth is complete, remove the seed crystal ingot, cut off the grown part, and grind the cut surface of the seed crystal ingot for reuse.

7. The method according to claim 6, wherein, The seed crystal ingot backmelting in step (2) is carried out by backmelting the seed crystal ingot to a thickness of 1 to 100 μm.

8. The method according to claim 6, wherein, The cutting surface of the seed crystal ingot in step (4) is ground flat by using a surface grinder, a thinning machine or a polishing machine.

9. The method according to claim 6, wherein, The crucible is a graphite crucible.

10. The method according to claim 9, wherein, The graphite crucible has a purity of not less than 99.95%, an inner diameter 10-150 mm larger than the diameter of the seed crystal ingot, a wall thickness of not less than 10 mm, and a density of 1.7-2.0 g / cm³. 3 .

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