Apparatus and method for growing si c crystals by liquid phase method

Abstract

This invention provides an apparatus and method for liquid-phase growth of SiC crystals. The apparatus includes a graphite crucible and a seed crystal fixing mechanism. The inner wall of the graphite crucible is covered with a ring-shaped tantalum carbide coating circumferentially surrounding its inner wall. This ring-shaped tantalum carbide coating is located in the expected fluctuation region of the melt surface during crystal growth. This invention utilizes the excellent wettability and chemical stability of tantalum carbide with silicon-based melts to fundamentally solve problems such as instability of the liquid surface, uneven distribution of the thermal and solute fields, uneven crucible corrosion, and heterogeneous nucleation on the sidewalls caused by poor wettability between the melt and the graphite crucible. This method can significantly stabilize the growth interface, improve the stability and repeatability of crystal growth, and ultimately obtain SiC crystals with higher crystal quality and lower defect density.

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 SiC crystals using the liquid-phase method. Background Technology

[0002] Silicon carbide (SiC), as a core material for third-generation semiconductors, has become a key substrate for manufacturing high-voltage, high-power, and high-frequency devices due to its excellent wide bandgap, high breakdown field strength, and high thermal conductivity. Currently, physical vapor transport (PVT) is the mainstream technology for the commercial production of SiC substrates, but its inherent problems, such as slow growth rate, high defect density, and difficulty in p-type doping, restrict its further development.

[0003] Compared to the PVT method, the liquid-phase method (or solution method) for growing SiC is carried out under near-thermodynamic equilibrium conditions, theoretically yielding crystals with lower defect density and better doping uniformity, especially beneficial for achieving p-type doping. Therefore, it is considered a highly promising technological route. This method typically involves heating silicon (Si) and a flux in a high-purity graphite crucible to form a melt, using the graphite crucible itself as the carbon (C) source. By establishing an appropriate temperature gradient, the dissolved carbon is transported to the seed crystal and precipitates, thus achieving SiC crystal growth.

[0004] However, the industrial application of this technology has long been limited by a key interface problem: poor wettability between the graphite crucible wall and the silicon-based melt, and the resulting interfacial instability. Specifically, the main bottlenecks are as follows:

[0005] Melt interface behavior instability: Poor wettability between graphite and silicon-based melts leads to irregular "climbing" or "retraction" of the melt on the crucible sidewall, causing drastic fluctuations in liquid level height and shape. These fluctuations directly interfere with the stability of the solid-liquid-gas three-phase line (curved surface) and are an important cause of growth streaks, polymorphic transformations, and even parasitic nuclei.

[0006] Thermal and solute field disturbances: Unstable liquid surface contact leads to uneven heat transfer from the crucible to the melt, resulting in radial temperature gradient fluctuations, which in turn interfere with the melt convection mode. This affects the uniform transport of carbon source and dopant, potentially causing instability at the growth interface or non-uniformity in the radial properties of the crystal.

[0007] Crucible corrosion and nucleation risks: During growth, the melt continuously corrodes the graphite crucible, especially near the liquid surface where strong convection easily leads to uneven corrosion, causing uncontrollable changes in the crucible's inner diameter, thereby altering the height of the meniscus and disrupting the growth steady state. Furthermore, the graphite particles generated by corrosion or the graphite surface itself at the liquid surface may become heterogeneous nucleation centers, threatening the integrity of the single crystal.

[0008] To address these challenges, existing technologies primarily focus on optimizing peripheral process parameters, such as improving temperature field design, precisely controlling rotation and pulling speeds, and adjusting flux ratios. While these methods can alleviate the problems to some extent, they do not fundamentally improve the physicochemical nature of the melt-crucible interface. Therefore, developing a technology capable of actively controlling and stabilizing this critical interface is of urgent technical necessity and significant industrial value for improving the quality, stability, and reproducibility of SiC crystals grown using the liquid phase method. Summary of the Invention

[0009] The present invention aims to overcome the above-mentioned shortcomings of the prior art by systematically solving the long-standing problem of interface instability in the liquid phase growth of SiC through a simple interface engineering strategy—introducing a TaC functional coating in a specific area of ​​the inner wall of a graphite crucible—thereby achieving higher quality and more stable and reliable crystal growth.

[0010] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0011] Without altering the main structure of the graphite crucible, a coating material with specific functions is introduced into the key area where the inner wall of the crucible contacts the molten surface to optimize the interface properties, thereby systematically solving problems such as unstable molten surface, uneven heat and solute flow, and growth disturbances caused by crucible corrosion.

[0012] In a first aspect, the present invention provides an apparatus for growing SiC crystals by liquid phase method, comprising a graphite crucible and a seed crystal fixing mechanism, wherein an annular tantalum carbide coating is provided on the inner wall of the graphite crucible, the annular tantalum carbide coating being located in the expected fluctuation region of the melt surface during crystal growth.

[0013] Preferably, in the apparatus for liquid-phase growth of SiC crystals according to the present invention, the axial coverage width of the annular tantalum carbide coating on the inner wall of the graphite crucible is: extending upwards by 10 mm to 40 mm and downwards by 20 mm to 80 mm, centered on the expected steady-state liquid level of the melt. This design ensures that the melt remains in contact with the TaC coating and does not come into contact with the exposed graphite, even during the initial growth stage when the seed crystal contacts the liquid surface causing a rise in liquid level, during possible liquid level fluctuations during growth, and during the later stages when solute consumption and dissolution of the inner wall of the graphite crucible cause a drop in liquid level.

[0014] Specifically, in this invention, if the annular tantalum carbide coating does not extend sufficiently upward in the axial direction on the inner wall of the graphite crucible, the liquid level may rise and contact the exposed graphite after the seed crystal contacts the liquid surface. Furthermore, the forced convection caused by the rotation of the seed crystal leads to fluctuations in the liquid level. If the upward extension is insufficient, it may not cover the area of ​​these fluctuations, preventing the melt from contacting the exposed graphite. If the upward extension is too long, the good wettability between the melt and the tantalum carbide coating will cause the melt to "hang" on the wall, affecting the utilization rate of raw materials and increasing coating costs. If the annular tantalum carbide coating does not extend sufficiently downward in the axial direction on the inner wall of the graphite crucible, the liquid level will drop as solute is consumed and the inner wall of the graphite crucible dissolves during growth. The coating will not be able to cover the area where the liquid level drops, resulting in direct contact between the liquid surface and the exposed graphite. If the downward extension is too long, the area provided by the inner wall of the graphite crucible for dissolving carbon will be too small, affecting the solute supply and negatively impacting crystal growth speed and quality.

[0015] Preferably, in the apparatus for liquid-phase growth of SiC crystals according to the present invention, the thickness of the tantalum carbide coating is from 5 μm to 200 μm. This thickness range is sufficient to provide an effective physical and chemical barrier while avoiding internal stress cracking or reduced adhesion to the substrate due to excessive coating thickness. Specifically, if the tantalum carbide coating is too thick, the coating may crack or peel off during heating due to thermal compatibility between the tantalum carbide coating and graphite, and the coating cost will increase; if the tantalum carbide coating is too thin, even less than the roughness of the inner wall of the graphite crucible, it may not be able to completely cover the graphite layer and fail to provide effective protection.

[0016] Preferably, in the apparatus for liquid-phase growth of SiC crystals according to the present invention, the thickness of the tantalum carbide coating is 20 μm to 50 μm.

[0017] Preferably, in the apparatus for growing SiC crystals by liquid phase method according to the present invention, the tantalum carbide coating is formed on the inner wall surface of the graphite crucible by chemical vapor deposition, physical vapor deposition, slurry sintering or molten salt electroplating, to ensure that the coating is dense, uniform and firmly bonded to the graphite substrate.

[0018] In a second aspect, the present invention provides a method for growing silicon carbide crystals using the apparatus of the present invention, comprising the following steps:

[0019] (1) Place the growth material in the graphite crucible of the apparatus for growing SiC crystals by liquid phase method, and fix the silicon carbide seed crystal on the seed crystal fixing mechanism;

[0020] (2) Heating under a protective atmosphere to melt the growth material into a melt;

[0021] (3) Bring the silicon carbide seed crystal into contact with the melt;

[0022] (4) Maintain the liquid surface of the melt in contact with the annular tantalum carbide coating, and perform crystal growth in a temperature field where the temperature at the bottom of the graphite crucible is higher than the temperature at the seed crystal;

[0023] (5) After growth is complete, separate the crystal from the melt.

[0024] Preferably, in the method of the present invention, step (1) further includes heat-treating the graphite crucible before placing the growth raw material.

[0025] Preferably, in the method described in this invention, the heat treatment is performed in a vacuum or inert gas (e.g., argon) environment. This helps to further densify the coating, eliminate internal stress, and make its surface condition more stable.

[0026] Preferably, in the method described in this invention, the heat treatment is carried out at a temperature of 1900°C to 2300°C for 2 to 10 hours.

[0027] In one specific embodiment of the present invention, the method of the present invention includes the following steps:

[0028] S1. Place the growth material containing Si source and flux in a graphite crucible, and fix the SiC seed crystal on the seed crystal fixing mechanism;

[0029] S2. Place the graphite crucible in the growth furnace, evacuate it, fill it with a protective atmosphere, and heat it to completely melt the growth raw materials to form a melt;

[0030] S3. Lower the SiC seed crystal to make it contact the surface of the melt;

[0031] S4. Control the temperature field so that the temperature at the bottom of the graphite crucible is higher than the temperature at the seed crystal, and the liquid surface of the melt is in direct contact with the TaC coating to carry out crystal growth;

[0032] S5. After growth is complete, lift the crystal to detach it from the melt.

[0033] The key to the method of this invention is that, during the crystal growth stage, the liquid surface of the melt is always in direct contact with the TaC coating on the inner wall of the graphite crucible.

[0034] This invention achieves the following significant beneficial effects by introducing a tantalum carbide (TaC) coating into the liquid surface region of the inner wall of a graphite crucible:

[0035] (1) The growth interface is fundamentally stabilized: by utilizing the excellent wettability of TaC and silicon-based melt, the irregular "climbing" or "retraction" of the melt on the sidewall is completely suppressed, forming a stable and smooth curved surface, which provides a crucial stable solid-liquid-gas three-phase environment for crystal growth.

[0036] Specifically, TaC exhibits good wettability with silicon-based melts. For example, at 1850°C, the contact angle between Si-Cr-Ce-Al melt and tantalum carbide and graphite is as follows: Figure 9 As shown, the contact angle between the melt and tantalum carbide is 7.0°, while the contact angle between the melt and graphite is 69.2°. This indicates that the wettability of the melt with tantalum carbide is much higher than that with graphite. This allows the melt to form a stable and smooth meniscus on the coating surface, fundamentally suppressing the irregular movement of the melt at the graphite crucible wall caused by poor wettability. This provides a more stable interface environment for crystal growth and is beneficial for obtaining a flatter growth front.

[0037] (2) Ensures process stability: The TaC coating acts as a chemically inert barrier in the liquid surface area, selectively limiting the corrosion of the graphite crucible to the area below the coating. This ensures that the inner diameter of the crucible at the liquid surface remains constant during growth, thereby achieving controllable and stable meniscus height and greatly improving the repeatability and controllability of the process. In other words, this invention achieves the effects of selective corrosion and stable meniscus height.

[0038] (3) Optimized thermal field and solute transport: The stable interface leads to uniform heat conduction and controllable convection modes, making the radial temperature gradient and solute (carbon and dopants) transport more uniform. This promotes a flatter growth front and improves the radial uniformity of crystal resistivity.

[0039] Specifically, a stable meniscus means a more uniform and controllable heat flow from the crucible wall to the melt, which helps to form a more stable radial temperature distribution. At the same time, a uniform interface also promotes the stability of the convection mode, prevents the formation of turbulence and chaotic eddies at the wall, and makes the transport of solute (C and dopant) more uniform, which is beneficial to maintaining the stability of the growth interface and improving the doping uniformity of the crystal.

[0040] (4) Effective suppression of crystal defects: Through the combined effect of the above mechanisms and the high heterogeneous nucleation barrier of the TaC surface itself, the formation of parasitic nuclei on the sidewalls and the risk of graphite particles entering the melt are significantly reduced. The direct result is that the grown SiC crystal has a lower defect density (such as a reduction in edge dislocations) and higher crystal quality (manifested as a significant reduction in the half-width at half-maximum of the X-ray rocking curve).

[0041] (5) Improved growth efficiency and crystal quality: Under the premise of stable growth, the crystal growth rate was increased. The final crystals were regular in shape, had a bright surface, and had significantly better internal quality than crystals grown by traditional methods.

[0042] Specifically, it suppresses the formation of stray nuclei: the crystal structure and chemical properties of TaC and SiC differ from those of graphite, altering the nucleation barrier on the sidewalls. Combined with a more stable thermal field and less melt retention, this helps reduce the probability of heterogeneous nucleation occurring on the crucible sidewalls. Furthermore, the more stable melt flow at the graphite crucible wall below the liquid surface reduces the likelihood of graphite fragments / particles entering the melt and becoming nucleation centers.

[0043] In summary, this invention achieves considerable beneficial effects through a relatively simple structural improvement (adding a TaC coating). Compared with existing technologies, the apparatus and method of this invention can significantly improve the stability and repeatability of crystal growth, and the grown SiC crystals have higher crystal quality, lower defect density, and better doping uniformity, providing strong technical support for the industrialization of liquid-phase SiC single crystals. 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 cross-sectional photograph of the crucible after growth using the apparatus of the present invention in Example 1;

[0047] Figure 3 This is a diagram of the silicon carbide crystal obtained in Example 1 of the present invention;

[0048] Figure 4 This is a diagram of the silicon carbide crystal obtained in Example 2 of the present invention;

[0049] Figure 5 This is a cross-sectional photograph of the crucible after growth using a conventional uncoated graphite crucible, as shown in Comparative Example 1.

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

[0051] Figure 7 This is a diagram of the silicon carbide crystal obtained in Comparative Example 3 of the present invention.

[0052] Figure 8 A comparison table of crystal growth rate, full width at half maximum (FWHM) of X-ray rocking curves, and defect density for the examples and comparative examples;

[0053] Figure 9 The image shows the contact angle test results of Si-Cr-Ce-Al melt with tantalum carbide and graphite at 1850℃.

[0054] In the attached figures, the following labels are used:

[0055] 1-Water-cooled rod; 2-Seed crystal rod; 3-Insulation material; 4-Graphite crucible; 5-Melted material; 6-Induction coil; 7-Cruise tray; 8-Seed crystal holder; 9-SiC seed crystal; 10-TaC coating. Detailed Implementation

[0056] 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.

[0057] Example 1

[0058] The apparatus of the present invention is used to prepare SiC crystals, the apparatus being as follows: Figure 1 As shown, a high-purity graphite crucible with an inner diameter of 220 mm, a height of 200 mm, and a purity of 99.99% was selected. A dense TaC coating with a thickness of approximately 40 μm was applied to the inner wall of the crucible in an axial region (i.e., a ring with a height of 30 mm) extending from the top downwards in an axial direction of 90 mm to 120 mm. Specifically, the coating was applied 10 mm upwards and 20 mm downwards from the expected steady-state liquid level of the melt (100 mm downwards from the top of the crucible's inner wall). After coating, the crucible was heat-treated in a vacuum furnace at 2100°C for 5 hours.

[0059] A mixture of Si, Cr, Ce, and Al is used as the growth material, with a molar ratio of Si:Cr:Ce:Al of 40:50:3:7. The seed crystal is a 4-inch semi-insulating, non-biased 4H-SiC single wafer.

[0060] The raw materials are loaded into the prepared crucible, and the seed crystal is fixed onto the seed crystal rod. The crucible is placed in an induction heating growth furnace, and a vacuum of 5 × 10⁻⁶ is applied. -5 After Pa, high-purity argon gas was introduced to 0.5 atm. Heating was performed to completely melt the raw materials, and the temperature field was controlled to stabilize the temperature at the seed crystal at 1850℃ and the temperature at the bottom of the crucible at 1900℃. The seed crystal was lowered to contact the molten surface. At this point, the molten surface was exactly in the area covered by the TaC coating. Crystal growth began. The seed crystal rotation speed was set to 160 rpm, and the crystal pulling speed was set to 60 μm / h. After 60 hours of growth, the crystal was lifted out of the molten surface, and the temperature was programmed to decrease.

[0061] The cross-section of the crucible after growth using the apparatus of the present invention is as follows: Figure 2 As shown. Figure 2 The TaC coating region is shown to be stable, preventing the high-temperature melt from corroding the graphite crucible. The corrosion occurs in the uncoated area below the liquid surface and is uniform. The grown SiC crystals are as follows: Figure 3 As shown. Figure 3The SiC crystal surface is bright and smooth with regular edges, free from visible cracks, inclusions, or parasitic grains. The average crystal growth rate reaches 145 μm / h. X-ray diffraction rocking curve analysis of the crystal surface shows a half-width at half-maximum (FWHM) of 22 arcsec, indicating high crystal quality. After etching the crystal growth surface, no screw dislocation pits were found, and the edge dislocation density is approximately 900 dislocations / cm³. 2 ,like Figure 8 As shown.

[0062] Example 2

[0063] A high-purity graphite crucible with an inner diameter of 220 mm, a height of 200 mm, and a purity of 99.99% was selected. A dense TaC coating with a thickness of approximately 40 μm was applied to the inner wall of the crucible in an axial region (i.e., a ring with a height of 120 mm) extending from the top downwards in an axial direction of 60 mm to 180 mm. Specifically, the coating was applied 40 mm upwards and 80 mm downwards from the expected steady-state liquid level of the melt (100 mm below the top of the crucible's inner wall). After coating, the crucible was heat-treated in a vacuum furnace at 2100°C for 5 hours.

[0064] SiC crystals were grown using the same raw material ratios and process parameters as in Example 1.

[0065] The SiC crystals grown in this embodiment are as follows: Figure 4 As shown. Figure 4 The SiC crystals exhibit excellent quality, with a bright, smooth surface, regular edges, and no visible cracks, inclusions, or parasitic grains. The average crystal growth rate is 130 μm / h, slightly lower than in Example 1. This is because the coating area is larger than in Example 1, resulting in a smaller contact area between the melt and graphite and less dissolved carbon. The half-width at half-maximum (FWHM) of the X-ray rocking curve is 22.5 arcsec. After etching the crystal growth surface, no screw dislocation corrosion pits were found, and the edge dislocation density is approximately 880 dislocations / cm². 2 ,like Figure 8 As shown.

[0066] Comparative Example 1

[0067] A graphite crucible with the exact same specifications as in Example 1 but without any coating on the inner wall was used. All other raw materials, seed crystals, and growth process parameters were kept the same as in Example 1.

[0068] The cross-section of the crucible after growth is as follows Figure 5 As shown, the crucible exhibits severe corrosion at the liquid surface, and uneven corrosion is observed along the circumference. The grown SiC crystals are as follows... Figure 6 As shown. Figure 6The study revealed fine grooves on the SiC crystal surface, with relatively large and non-symmetrical surface steps, indicating deviations from the ideal temperature and flow field distributions. Furthermore, parasitic SiC nuclei were visible on the crystal sides; these polycrystalline particles adhering to the grown single crystal cause stress and other problems, leading to a decrease in crystal quality. The crystal growth rate was approximately 120 μm / h. X-ray diffraction rocking curves were performed on the crystal surface, with a half-width at half-maximum (FWHM) of 36 arcsec. After etching the crystal growth surface, no screw dislocation pits were observed, and the edge dislocation density was approximately 3500 dislocations / cm². 2 ,like Figure 8 As shown.

[0069] Comparative Example 2

[0070] A high-purity graphite crucible with an inner diameter of 220 mm, a height of 200 mm, and a purity of 99.99% was selected. A dense TaC coating with a thickness of approximately 40 μm was applied to the inner wall of the crucible in an axial region (i.e., a ring with a height of 20 mm) extending 95 mm to 115 mm downwards from the top. Specifically, the coating was applied 5 mm upwards and 15 mm downwards from the expected steady-state liquid level of the melt (100 mm downwards from the top of the crucible's inner wall). After coating, the crucible was heat-treated in a vacuum furnace at 2100°C for 5 hours.

[0071] SiC crystals were grown using the same raw material ratios and process parameters as in Example 1.

[0072] The surface morphology of the SiC crystals grown in this comparative example is similar to that of Comparative Example 1, with fine grooves and large step heights. The average crystal growth rate is 115 μm / h, and the half-width at half-maximum (FWHM) of the X-ray rocking curve is 39.2 arcsec. After etching the crystal growth surface, no screw dislocation corrosion pits were found, and the edge dislocation density is approximately 3300 dislocations / cm². 2 .like Figure 8 As shown.

[0073] Comparative Example 3

[0074] A high-purity graphite crucible with an inner diameter of 220 mm, a height of 200 mm, and a purity of 99.99% was selected. A dense TaC coating with a thickness of approximately 40 μm was applied to the inner wall of the crucible in an axial region (i.e., a ring with a height of 140 mm) extending from the top downwards in an axial direction of 50 mm to 190 mm. Specifically, the coating was applied 50 mm upwards and 90 mm downwards from the expected steady-state liquid level of the melt (100 mm downwards from the top of the crucible's inner wall). After coating, the crucible was heat-treated in a vacuum furnace at 2100°C for 5 hours.

[0075] SiC crystals were grown using the same raw material ratios and process parameters as in Example 1.

[0076] The SiC crystals grown in this comparative example are as follows: Figure 7 As shown, large grooves are visible on the crystal surface, and the growth rate is low at 92 μm / h. This is because the tantalum carbide coating essentially covers the entire contact surface between the melt and the crucible sidewall, resulting in reduced dissolved carbon and insufficient solute supply. The half-width at half-maximum (WHM) of the X-ray rocking curve is 88.6 arcsec. After etching the crystal growth surface, no screw dislocation corrosion pits were found, and the edge dislocation density was approximately 4250 / cm². 2 .like Figure 8 As shown.

[0077] In summary, in Examples 1 and 2, the TaC coating area at the liquid surface remained intact and dimensionally stable; while the uncoated graphite area below the liquid surface underwent uniform corrosion and dissolution. Conversely, in the conventional crucible of Comparative Example 1, uneven pits formed near the liquid surface due to intense thermal convection and chemical corrosion, which was the direct cause of unstable growth. In Comparative Example 2, because the TaC coating did not extend sufficiently upwards and downwards, it could not cover the area where the liquid surface descended. As growth progressed, the liquid surface came into direct contact with the exposed graphite, and the tantalum carbide coating could not provide effective protection or other beneficial effects, resulting in poor crystal quality. In Comparative Example 3, because the TaC coating extended too far upwards and downwards, the contact area between the melt and the sidewall of the graphite crucible was too small, reducing carbon dissolution. The crystal growth surface could not obtain sufficient solute supply, resulting in large macroscopic trenches and poor crystal quality.

[0078] The results from the embodiments and comparative examples show that the TaC coating apparatus and method provided by the present invention bring significant beneficial effects:

[0079] Improved growth stability: The stable meniscus in Examples 1 and 2 directly contributed to a smoother growth interface and a higher growth rate.

[0080] Improved crystal quality: The effects of more uniform heat and mass transfer and suppression of impurities are reflected in the better XRD full width at half maximum and lower defect density of the crystals in Examples 1 and 2.

[0081] Enhanced process robustness: By designing a reasonable coating coverage area, normal fluctuations in the liquid level can be easily handled, avoiding interface loss of control.

[0082] It should be noted that the above embodiments are merely preferred embodiments of the present invention. Those skilled in the art, having understood the core concept of the present invention, can make appropriate adjustments and optimizations to the preparation method, specific thickness, coverage height, and associated crystal growth process parameters (such as temperature, gradient, rotation speed, raw material formulation, etc.) of the TaC coating. Such adjustments and optimizations, as long as they do not depart from the basic principle of the present invention of "stabilizing the melt-crucible interface through a TaC coating," should fall within the scope of protection claimed by the present invention.

Claims

1. An apparatus for growing SiC crystals using a liquid-phase method, comprising a graphite crucible and a seed crystal fixing mechanism, characterized in that, The inner wall of the graphite crucible is covered with a ring-shaped tantalum carbide coating that surrounds the inner wall. The ring-shaped tantalum carbide coating is located in the expected fluctuation area of ​​the melt surface during crystal growth.

2. The apparatus for liquid-phase growth of SiC crystals according to claim 1, wherein, The axial coverage width of the annular tantalum carbide coating on the inner wall of the graphite crucible is: 10 mm to 40 mm upward and 20 mm to 80 mm downward, centered on the expected steady-state liquid level of the melt.

3. The apparatus for liquid-phase growth of SiC crystals according to claim 1, wherein, The thickness of the tantalum carbide coating is from 5 μm to 200 μm.

4. The apparatus for liquid-phase growth of SiC crystals according to claim 3, wherein, The thickness of the tantalum carbide coating is 20 μm to 50 μm.

5. The apparatus for liquid-phase growth of SiC crystals according to claim 1, wherein, The tantalum carbide coating is formed on the inner wall surface of the graphite crucible by chemical vapor deposition, physical vapor deposition, slurry sintering, or molten salt electroplating.

6. A method for growing silicon carbide crystals using the apparatus of any one of claims 1 to 5, comprising the following steps: (1) Place the growth material in the graphite crucible of the apparatus for growing SiC crystals by liquid phase method, and fix the silicon carbide seed crystal on the seed crystal fixing mechanism; (2) Heating under a protective atmosphere to melt the growth material into a melt; (3) Bring the silicon carbide seed crystal into contact with the melt; (4) Maintain the liquid surface of the melt in contact with the annular tantalum carbide coating, and perform crystal growth in a temperature field where the temperature at the bottom of the graphite crucible is higher than the temperature at the seed crystal; (5) After growth is complete, separate the crystal from the melt.

7. The method according to claim 6, wherein, Step (1) further includes heat-treating the graphite crucible before placing the growth material.

8. The method according to claim 7, wherein, The heat treatment is carried out in a vacuum or inert gas environment.

9. The method according to claim 8, wherein, The heat treatment is carried out at a temperature of 1900°C to 2300°C for 2 to 10 hours.

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