A SiC single crystal growth method using a complexing agent

Abstract

The application belongs to the technical field of crystal growth, and particularly relates to a SiC single crystal growth method by means of a dissolving agent. The method comprises the following steps: mixing high-purity silicon, metal chromium and metal cobalt, placing the mixture in a graphite crucible or a SiC crucible, heating and smelting under an inert atmosphere or a hydrogen-containing mixed atmosphere, forming a Si-Cr-Co alloy, controlling the Cr content in the alloy to be less than or equal to 60 at.%, the Co content in the alloy to be less than or equal to 20 at.%, and the balance being Si, continuously increasing the temperature to not less than 1800 DEG C, dissolving carbon in the alloy to obtain a Si-Cr-Co-C melt saturated with SiC and carbon, and then growing a SiC single crystal in the melt by means of a top-seed solution growth method or a crucible lowering method. The application introduces cobalt to cooperate with chromium, thereby improving the carbon solubility, inhibiting the aggregation of crystal surface steps, and reducing the doping concentration of the dissolving agent elements in the crystal.

Description

Technical Field

[0001] This invention belongs to the field of crystal growth technology, specifically relating to a flux-assisted growth method for SiC single crystals. Background Technology

[0002] To improve the solubility of carbon in silicon melt, researchers have attempted to add fluxing agents to the silicon melt. Patent document CN116145258B discloses a method for growing SiC crystals using a low-temperature solution method. This method involves mixing and melting Si, metallic Fe or Cr, and rare earth metals (RE) to obtain a Si-Me-RE alloy (Me being Fe or Cr), which is then subjected to carbon saturation treatment before SiC crystal growth.

[0003] However, the technical solution in this paper has the following shortcomings: First, it requires the addition of rare earth metals (RE) as a fluxing agent. Rare earth metals are expensive and chemically reactive, and are prone to react with the crucible to form rare earth carbides, which affect the purity of the melt. Second, this paper does not address the issue of Cr doping into the SiC crystal when Cr is used alone. Third, this paper does not address the issue of step aggregation.

[0004] On the other hand, when cobalt (Co) is used alone as a flux, although Co has low solid solubility in SiC crystals and low step height, its carbon solubility is insufficient, resulting in a slow crystal growth rate.

[0005] Therefore, how to suppress step aggregation and reduce the doping concentration of cosolvent elements while maintaining high carbon solubility and high growth rate is a technical problem that has not yet been solved in the prior art. Summary of the Invention

[0006] The purpose of this invention is to provide a fluxing growth method for SiC single crystals, in order to solve the problems of high chromium doping concentration and step aggregation when using chromium fluxing solvent alone, and the problems of low carbon solubility and slow growth rate when using cobalt fluxing solvent alone.

[0007] The technical solution of this invention is: to provide a method for solvent-assisted growth of SiC single crystals, comprising the following steps: (1) Mix high-purity silicon, chromium and cobalt, put them into a crucible, and heat and melt them under a protective atmosphere to obtain a Si-Cr-Co alloy, wherein the Si-Cr-Co alloy does not contain rare earth metals; (2) The Si-Cr-Co alloy is heated to not less than 1800°C under a protective atmosphere so that the carbon provided by the crucible dissolves in the Si-Cr-Co alloy to obtain a Si-Cr-Co-C melt that is doubly saturated with SiC and carbon. (3) Using a crystal growth method, SiC single crystals are grown in the Si-Cr-Co-C melt.

[0008] Preferably, in step (1), the Si-Cr-Co alloy contains ≤60 at.% chromium, ≤20 at.% cobalt, and the balance is high-purity silicon.

[0009] Preferably, in step (1), the Si-Cr-Co alloy contains 25~60 at.% chromium and 2~20 at.% cobalt.

[0010] Preferably, in step (1), the crucible is a high-purity graphite crucible or a SiC crucible.

[0011] Preferably, in steps (1) and (2), the protective atmosphere is a high-purity inert gas, or a mixture of a high-purity inert gas and hydrogen, wherein the volume content of hydrogen in the mixture is ≤10%.

[0012] Preferably, in step (1), the heating and melting time is 5 to 30 minutes.

[0013] Preferably, in step (2), after the Si-Cr-Co alloy is heated to not less than 1800°C, it is held at that temperature for at least 1 hour to allow the carbon to dissolve to reach saturation.

[0014] Preferably, in step (3), the crystal growth method is the top seed crystal solution growth method or the crucible descent method.

[0015] Preferably, when using the top seed crystal solution growth method, the SiC seed crystal is brought into contact with the surface of the Si-Cr-Co-C melt, and the seed crystal pulling speed and rotation speed are controlled so that the SiC single crystal grows on the seed crystal.

[0016] Preferably, in step (3), the growth temperature of SiC single crystal is not lower than 1800℃.

[0017] Compared with the prior art, the advantages of the present invention are: (1) A binary combination of chromium and cobalt was used as a co-solvent. Compared with chromium alone, the addition of cobalt reduced the average height of the crystal surface steps from 15.6 nm (Comparative Example 1) to 2.1-2.8 nm (Examples 1-2), and the Co concentration was below the SIMS detection limit (1×10⁻⁶). 15 cm -3 When Cr is used alone, the Cr concentration is 2.3 × 10⁻⁶. 16 cm -3 This indicates that Cr and Co have a synergistic effect: the introduction of Co, without compromising Cr's high carbon solubility, simultaneously suppresses step aggregation and reduces the doping concentration. Furthermore, the use of a binary combination of chromium and cobalt as a co-solvent, without the presence of rare earth metals, avoids the problems of high cost and high reactivity associated with rare earth metals.

[0018] (2) Compared with cobalt alone (Comparative Example 4), the addition of chromium increased the carbon content from 3.5 at.% to 5.67-12.36 at.% and the growth rate from 70 μm / h to 150-210 μm / h. This indicates that Cr compensates for the insufficient carbon solubility of Co, while maintaining the low doping and step suppression characteristics of Co.

[0019] (3) The average step height (2.1 nm) of the Cr-Co combination is lower than that of Co alone (5.2 nm), indicating that there is a synergistic inhibitory effect between Cr and Co on step aggregation. At the same time, the results of carbon solubility and growth rate are significantly better than those of Cr or Co alone. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a process flow diagram of a flux-assisted growth method for SiC single crystals according to the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments: Chromium (Cr) has an affinity for carbon, which can increase the solubility of carbon in silicon melt and provide a carbon source for crystal growth. The introduction of cobalt (Co) has a synergistic effect: on the one hand, cobalt can reduce the solid-liquid interface energy between the melt and the SiC seed crystal, improve wettability, suppress the accumulation of steps at the crystal growth front, and obtain a smooth crystal surface; on the other hand, cobalt has an extremely low equilibrium segregation coefficient in SiC crystals and hardly enters the SiC lattice, which can avoid unintentional doping effects on the electrical properties of the crystal and help maintain the high purity of the crystal.

[0022] The selection of each process parameter is based on the following: a growth temperature of not less than 1800℃ is to ensure sufficient solubility of carbon in the Si-Cr-Co alloy (carbon solubility decreases significantly when the temperature is below 1800℃); a holding time of at least 1 hour is to allow carbon dissolution to reach saturation equilibrium and avoid fluctuations in carbon concentration during growth; the use of hydrogen (volume content ≤10%) in the protective atmosphere can reduce trace oxides on the melt surface, preventing the oxidation loss of chromium and cobalt, while hydrogen will not react harmfully with the melt; the pulling speed is controlled within the range of 0.4~0.6 mm / h to maintain a stable meniscus shape and avoid excessive speed leading to crystal diameter shrinkage or excessive speed leading to crystal diameter expansion; a rotation speed of 10~15 rpm can promote forced convection of the melt, making the carbon and solute distribution uniform and reducing compositional supercooling.

[0023] No rare earth metals are added in any of the following embodiments.

[0024] Example 1

[0025] (1) Alloy smelting: High-purity silicon (99.9999 wt%), metallic chromium (99.99 wt%), and metallic cobalt (99.9 wt%) were mixed uniformly at an atomic percentage of 52:40:8, with a total mass of approximately 200 g. In this mixture, the chromium content was 40 at.%, which is at a moderately high level, resulting in high carbon solubility; the cobalt content was 8 at.%, ensuring a synergistic effect without excessively diluting the solubilizing effect of chromium. The mixture was loaded into a high-purity graphite crucible (50 mm inner diameter, 80 mm height, 5 mm wall thickness). The graphite crucible served not only as a container but also as a carbon source, providing carbon to the melt at high temperatures. The crucible was placed in a vacuum induction melting furnace and evacuated to a vacuum level of 1×10⁻⁶. -2 The pressure was increased to 1800°C, then high-purity argon (99.999% purity) was introduced until atmospheric pressure was reached, followed by hydrogen until the hydrogen volume content was 10%. Argon was used as a protective gas to prevent oxidation, and hydrogen was used to reduce residual oxygen and metal oxides. Induction heating was turned on, and the temperature was increased to 1800°C at a rate of 50°C / min. The mixture was melted for 30 minutes, during which the crucible was rotated at 5 rpm to ensure uniform alloy composition. After melting, high-purity argon was introduced for rapid cooling (cooling rate of approximately 100°C / min) to obtain the Si-40Cr-8Co alloy.

[0026] (2) Carbon saturation treatment: The Si-40Cr-8Co alloy obtained in step (1) was placed in a crystal growth furnace along with a graphite crucible. The crystal growth furnace was heated by resistance heating, which provides a more stable temperature field than induction heating and avoids interference from electromagnetic stirring on the convection mode of the melt. The atmosphere inside the furnace was a mixture of high-purity argon (99.999%) and 10% hydrogen, with a gas flow rate of 2 L / min. The alloy was heated to 1800℃ at a heating rate of 30℃ / min and held for 1 hour to dissolve the carbon on the inner wall of the graphite crucible into the alloy melt, forming a Si-Cr-Co-C melt that is doubly saturated with SiC and carbon. The holding time of 1 hour was determined based on previous experiments; too short a time would not saturate the carbon, while too long a time would increase energy consumption and crucible corrosion.

[0027] After the heat treatment was completed, the heating power was turned off, allowing the melt to cool with the furnace. Once cooled to room temperature, the crucible and alloy were longitudinally cut using a wire cutter. Observation of the longitudinal section revealed a continuous gray phase approximately 50-100 μm thick between the inner wall of the crucible and the melt. This phase was qualitatively analyzed using an electron probe microanalysis (EPMA) system with an accelerating voltage of 15 kV and a beam current of 20 nA. EPMA determines the type and content of elements by measuring the wavelength and intensity of characteristic X-rays, accurately distinguishing SiC from other carbides. The analysis showed that the Si:C atomic ratio of this phase was approximately 1:1, and it contained no Cr or Co, confirming it as SiC. Furthermore, no other carbides (such as Cr3C2, Cr7C3, Co2C, etc.) were observed forming inside the melt or in other locations within the crucible, indicating that SiC is a single carbide phase at high temperatures. This indicates that Cr and Co mainly exist in the metallic state in the melt and do not form stable carbide precipitates with carbon, which is beneficial to maintaining the homogeneity of the melt composition.

[0028] The alloy was separated from the crucible, and approximately 10g of the alloy block was ultrasonically cleaned with anhydrous ethanol for 15 minutes to remove any remaining crucible fragments. The alloy block was then ground into fine particles (particle size <0.1mm) using an agate mortar and pestle. After thorough mixing, a 0.5g sample was taken, and the carbon content was determined using an infrared carbon-sulfur analyzer. The principle of infrared carbon-sulfur analysis is that the sample is burned in a high-temperature oxygen stream, where carbon and sulfur are converted into CO2 and SO2, respectively, and quantified by an infrared detector. Analysis conditions: combustion temperature 2000℃, carrier gas oxygen, flow rate 3L / min. The result showed a carbon content of 12.36 at.%. This value is significantly higher than the carbon solubility of pure silicon melt at the same temperature (<0.1 at.%), demonstrating that the addition of Cr significantly improved the carbon solubility.

[0029] (3) SiC Single Crystal Growth: SiC single crystal growth was performed using the top seed solution growth method. The graphite crucible containing the Si-Cr-Co-C melt was placed in a crystal growth furnace. The atmosphere inside the furnace was a mixture of high-purity argon (99.999%) and 10% hydrogen, with a gas flow rate of 2 L / min. The melt temperature was maintained at 1800℃±5℃. The temperature control accuracy of ±5℃ was to avoid changes in carbon solubility due to temperature fluctuations, which would cause instability in the growth rate. A 6H-SiC seed crystal (10 mm in diameter, 0.5 mm in thickness, with the (0001) face as the growth surface, and polished) was fixed at the lower end of the graphite lifting rod. The seed crystal was first lowered to a distance of 5 mm from the melt surface and preheated for 5 minutes. Preheating was to reduce the temperature difference between the seed crystal and the melt and prevent thermal shock from causing the seed crystal to crack. Then, the seed crystal was lowered at a speed of 0.5 mm / min until the lower surface of the seed crystal contacted the melt surface. After contact, the seed crystal is pulled upwards at a pulling speed of 0.5 mm / h, while simultaneously rotating clockwise at 10 rpm. The pulling speed of 0.5 mm / h is optimized; too slow a speed would cause the crystal diameter to expand too quickly, while too fast a speed might cause the crystal diameter to shrink or even deliquinate. The rotation speed of 10 rpm generates forced convection, promoting the transport of carbon to the growth interface. The growth time is 20 hours.

[0030] After growth, the seed crystal was lifted from the melt at a speed of 2 mm / min and cooled to room temperature at a rate of 50 °C / h. Slow cooling reduces thermal stress and prevents crystal cracking. The crystal was then removed and its surface morphology was observed using optical microscopy, scanning electron microscopy, and atomic force microscopy (AFM). The AFM scanning range was 10 μm × 10 μm, and the scanning mode was tapping mode. AFM obtains the three-dimensional morphology through atomic force feedback between the probe and the sample surface, enabling precise measurement of step heights. The results showed that the crystal surface was smooth, with no obvious step aggregation observed, and the average step height was 2.1 nm (obtained by averaging the step heights of five different regions). Secondary ion mass spectrometry (SIMS) was used to analyze the Co element concentration in the crystal, with Cs as the primary ion source. + The energy was 10 keV, and the detection area diameter was 50 μm. SIMS analyzes the mass-to-charge ratio of sputtered secondary ions by sputtering high-energy ions onto the sample surface, exhibiting extremely high sensitivity (ppm to ppb level). Results showed that the Co concentration was below the detection limit (1 × 10⁻⁶). 15 cm -3 This indicates that Co has an extremely low segregation coefficient in SiC crystals, hardly entering the lattice, and therefore will not have an unintentional doping effect on the electrical performance of the device. The crystal growth rate, calculated by measuring the ratio of crystal thickness to growth time, is approximately 210 μm / h.

[0031] Example 2

[0032] (1) Alloy smelting: High-purity silicon (99.9999 wt%), metallic chromium (99.99 wt%), and metallic cobalt (99.9 wt%) were mixed uniformly at an atomic percentage of 56:40:4. The mixture was placed in a high-purity graphite crucible and smelted under the same conditions and steps as in Example 1 to obtain the Si-40Cr-4Co alloy.

[0033] (2) Carbon saturation treatment: Following the same method as in Example 1, the Si-40Cr-4Co alloy was heated to 1800℃ and held for 1 hour to obtain a Si-Cr-Co-C melt doubly saturated with SiC and carbon. The carbon content was determined by infrared carbon-sulfur analysis, and the result was 8.25 at.%.

[0034] (3) SiC single crystal growth: SiC single crystal growth was performed under the same crystal growth conditions as in Example 1. After growth, the crystal surface morphology was observed using OM, SEM, and AFM. The average height of the surface steps was 2.8 nm. SIMS analysis showed that the Co concentration was below the detection limit (1×10⁻⁶). 15 cm -3 The crystal growth rate is approximately 185 μm / h.

[0035] Example 3

[0036] (1) Alloy smelting: High-purity silicon (99.9999 wt%), metallic chromium (99.99 wt%), and metallic cobalt (99.9 wt%) were mixed uniformly at an atomic percentage of 60:30:10. The mixture was placed in a high-purity SiC crucible (inner diameter 50 mm, height 80 mm, wall thickness 5 mm) and smelted under the same conditions and steps as in Example 1 to obtain the Si-30Cr-10Co alloy.

[0037] (2) Carbon saturation treatment: The Si-30Cr-10Co alloy, together with the SiC crucible, was placed in a crystal growth furnace and heated to 1850℃. The temperature was maintained for 1.5 hours to dissolve the carbon in the SiC crucible into the alloy melt, thus obtaining a SiC-saturated Si-Cr-Co-C melt. Infrared carbon-sulfur analysis determined the carbon content to be 5.67 at.%.

[0038] (3) SiC Single Crystal Growth: SiC single crystal growth was performed using the crucible lowering method. The SiC crucible containing the Si-Cr-Co-C melt was placed in a crystal growth furnace with a high-purity argon atmosphere (99.999%) and a gas flow rate of 2 L / min. A 6H-SiC seed crystal (10 mm in diameter, 0.5 mm in thickness, with the (0001) plane as the growth surface) was placed at the center of the crucible bottom. The melt temperature was maintained at 1850℃±5℃ for 1 hour, and then the crucible was lowered at a rate of 1 mm / h to allow the bottom of the crucible to pass through the temperature gradient region (temperature gradient of approximately 15℃ / cm). The growth time was 30 hours. After growth, the crystal was cooled to room temperature at a rate of 30℃ / h. The crystal was removed, and the surface morphology was observed. The average height of the surface steps was 2.5 nm. SIMS analysis showed that the Co concentration was below the detection limit. The crystal growth rate was approximately 175 μm / h.

[0039] Example 4

[0040] (1) Alloy smelting: High-purity silicon (99.9999 wt%), metallic chromium (99.99 wt%), and metallic cobalt (99.9 wt%) were mixed uniformly at an atomic percentage of 50:45:5. The mixture was placed in a high-purity graphite crucible and smelted under the same conditions and steps as in Example 1 to obtain the Si-45Cr-5Co alloy.

[0041] (2) Carbon saturation treatment: Following the same method as in Example 1, the Si-45Cr-5Co alloy was heated to 1850℃ and held for 1 hour to obtain a Si-Cr-Co-C melt doubly saturated with SiC and carbon. Infrared carbon-sulfur analysis determined the carbon content to be 10.8 at.%.

[0042] (3) SiC single crystal growth: The same top seed solution growth method as in Example 1 was used, with a growth temperature of 1850℃, a pulling speed of 0.6 mm / h, a rotation speed of 15 rpm, and a growth time of 20 hours. After growth, AFM showed an average surface step height of 2.3 nm, SIMS showed that the Co concentration was below the detection limit, and the growth rate was approximately 195 μm / h.

[0043] Example 5

[0044] (1) Alloy smelting: High-purity silicon (99.9999 wt%), metallic chromium (99.99 wt%), and metallic cobalt (99.9 wt%) were mixed uniformly at an atomic percentage of 70:25:5. The mixture was placed in a high-purity graphite crucible and smelted under the same conditions and steps as in Example 1 to obtain the Si-25Cr-5Co alloy.

[0045] (2) Carbon saturation treatment: Following the same method as in Example 1, the Si-25Cr-5Co alloy was heated to 1820℃ and held for 1.5 hours to obtain a Si-Cr-Co-C melt doubly saturated with SiC and carbon. Infrared carbon-sulfur analysis determined the carbon content to be 4.2 at.%.

[0046] (3) SiC single crystal growth: The same top seed solution growth method as in Example 1 was used, with a growth temperature of 1820℃, a pulling speed of 0.4 mm / h, a rotation speed of 10 rpm, and a growth time of 25 hours. After growth, AFM showed an average surface step height of 3.1 nm, SIMS showed that the Co concentration was below the detection limit, and the growth rate was approximately 150 μm / h.

[0047] Comparative Example 1 High-purity silicon and metallic chromium were mixed at an atomic ratio of 60:40, with a total mass of 200g. No cobalt was added; chromium was used alone. A Si-40Cr alloy was obtained under the same melting conditions as in Example 1 (1800℃, 30 minutes, argon + 10% hydrogen atmosphere). Carbon saturation treatment was performed using the same method as in Example 1 (1800℃, 1 hour), and infrared carbon-sulfur analysis determined the carbon content to be 10.2 at.%. SiC single crystals were grown using the top-seeded solution growth method under the same conditions as in Example 1 (1800℃, pulling speed 0.5 mm / h, rotation speed 10 rpm, growth time 20 hours). After growth, AFM observation of the crystal surface revealed obvious step aggregation, with an average step height of 15.6 nm, and localized groove-like defects. SIMS analysis showed a Cr concentration of 2.3 × 10⁻⁶ in the crystal. 16 cm -3 The crystal growth rate was 195 μm / h.

[0048] Comparative Example 2 High-purity silicon and metallic iron were mixed at an atomic ratio of 60:40, with a total mass of 200g. No chromium or cobalt was added, meaning Fe was used alone. A Si-40Fe alloy was obtained under the same melting conditions as in Example 1 (1800°C, 30 minutes, argon + 10% hydrogen atmosphere). Carbon saturation treatment was performed according to the same method as in Example 1 (1800°C, 1 hour), and infrared carbon-sulfur analysis determined the carbon content to be 6.8 at.%. SiC single crystals were grown using the top-seeded solution growth method under the same conditions as in Example 1. AFM observation showed severe step aggregation with an average step height of 22.4 nm, and a large amount of flux coating on the crystal surface. SIMS analysis showed an Fe concentration of 1.1 × 10⁻⁶ in the crystal. 17 cm -3 The crystal growth rate is 120 μm / h.

[0049] Comparative Example 3 High-purity silicon and metallic titanium were mixed at an atomic ratio of 70:30, with a total mass of 200 g. No chromium or cobalt was added, i.e., Ti was used alone. A Si-30Ti alloy was obtained using the same melting conditions as in Example 1 (1800°C, 30 minutes, argon + 10% hydrogen atmosphere). Carbon saturation treatment was performed using the same method as in Example 1 (1800°C, 1 hour), and infrared carbon-sulfur analysis determined the carbon content to be 5.2 at.%. SiC single crystals were grown using the top-seeded solution growth method under the same conditions as in Example 1. AFM observation showed severe step aggregation, with an average step height of 18.9 nm. SIMS analysis showed a Ti concentration of 8.7 × 10⁻⁶ in the crystal. 16 cm -3 The crystal growth rate was 105 μm / h.

[0050] Comparative Example 4 High-purity silicon and metallic cobalt were mixed at an atomic ratio of 80:20, with a total mass of 200g. No chromium was added, meaning Co was used alone. A Si-20Co alloy was obtained using the same melting conditions as in Example 1 (1800°C, 30 minutes, argon + 10% hydrogen atmosphere). Carbon saturation treatment was performed using the same method as in Example 1 (1800°C, 1 hour), and infrared carbon-sulfur analysis determined the carbon content to be 3.5 at.%. SiC single crystals were grown using the top-seeded solution growth method under the same conditions as in Example 1. AFM observation showed an average surface step height of 5.2 nm, and SIMS analysis showed a Co concentration of 8 × 10⁻⁶ in the crystal. 14 cm -3 (Below the detection limit, actually detected but at a low level), the growth rate was only 70 μm / h. This indicates that the carbon solubility is insufficient when Co is used alone, resulting in an excessively low growth rate.

[0051] The synergistic effect analysis is as follows: Comparing Example 1 (Si-40Cr-8Co) with Comparative Example 1 (Si-40Cr): After adding 8 at.% Co, the carbon content slightly increased from 10.2 at.% to 12.36 at.%, the growth rate increased from 195 μm / h to 210 μm / h, while the average step height decreased significantly from 15.6 nm to 2.1 nm, and the Cr doping concentration increased from 2.3 × 10⁻⁶. 16 cm -3 Decrease to Co < 1 × 10 15 cm -3 This indicates that the addition of Co significantly improves crystal quality without compromising the high carbon solubility of Cr.

[0052] Comparing Example 1 (Si-40Cr-8Co) with Comparative Example 4 (Si-20Co): After adding 40 at.% Cr, the carbon content increased significantly from 3.5 at.% to 12.36 at.%, the growth rate increased from 70 μm / h to 210 μm / h, while the step height further decreased from 5.2 nm to 2.1 nm. This indicates that the addition of Cr compensates for the insufficient carbon solubility of Co, and the low-doping characteristics of Co are maintained, with the step height even being superior to that of Co alone.

[0053] Comparing Example 1 (Si-40Cr-8Co) with Comparative Example 2 (Si-40Fe) and Comparative Example 3 (Si-30Ti): The step height (2.1nm) of the Cr-Co system is much lower than that of the Fe system (22.4nm) and the Ti system (18.9nm), and the carbon solubility and growth rate are significantly better than those of the Fe and Ti systems.

[0054] The above comparison shows that there is a synergistic effect between Cr and Co: Cr increases carbon solubility, while Co inhibits step aggregation and reduces doping. The synergistic effect of the two achieves the comprehensive effect of high carbon solubility, high growth rate, low step height and low doping concentration that cannot be achieved simultaneously by a single co-solvent (Cr, Co, Fe, Ti) and the Cr-RE system.

[0055] The alloy composition, carbon content, average height of surface steps, impurity concentration and growth rate of Examples 1-5 and Comparative Examples 1-4 are summarized, and the specific data comparison is shown in Table 1.

[0056] Table 1: Summary of Results from Examples and Comparative Examples

[0057] As shown in the table above, Examples 1-5, which used the Cr-Co binary cosolvent system, maintained high carbon solubility (4.2~12.36 at.%) and high growth rate (150~210 μm / h), while significantly reducing the average height of the crystal surface steps (2.1~3.1 nm), and the concentration of Co in the crystal was below the SIMS detection limit (1×10⁻⁶). 15 cm -3 This indicates that Co is almost not incorporated into the SiC crystal. In contrast, in Comparative Examples 1-3, although the carbon solubility and growth rate differed when Cr, Fe, or Ti were used alone, severe step aggregation (step height 15.6~22.4 nm) was observed, and the doping concentration of the co-solvent element in the crystal was relatively high (10⁻⁶). 16 ~10 17 cm -3 (Order level). Comparative Example 4 shows that when Co is used alone, the carbon solubility is insufficient (3.5 at.%), the growth rate is too low (70 μm / h), and it cannot meet the requirements for rapid growth.

[0058] The above examples and comparative examples show that the present invention uses a binary combination of chromium and cobalt as a co-solvent, wherein chromium provides high carbon solubility, and cobalt inhibits step aggregation and reduces doping. The two work synergistically to achieve a comprehensive effect of high carbon solubility, low step height and low doping concentration.

[0059] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all changes falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

Claims

1. A method for solvent-assisted growth of SiC single crystals, comprising the following steps: (1) Mix high-purity silicon, chromium and cobalt, put them into a crucible, and heat and melt them under a protective atmosphere to obtain a Si-Cr-Co alloy, wherein the Si-Cr-Co alloy does not contain rare earth metals; (2) The Si-Cr-Co alloy is heated to not less than 1800°C under a protective atmosphere so that the carbon provided by the crucible dissolves in the Si-Cr-Co alloy to obtain a Si-Cr-Co-C melt that is doubly saturated with SiC and carbon. (3) Using a crystal growth method, SiC single crystals are grown in the Si-Cr-Co-C melt.

2. The method for fluxing SiC single crystal growth according to claim 1, characterized in that, In step (1), the Si-Cr-Co alloy contains ≤60 at.% chromium, ≤20 at.% cobalt, and the balance is high-purity silicon.

3. The method for fluxing SiC single crystal growth according to claim 2, characterized in that, In step (1), the Si-Cr-Co alloy contains 25~60 at.% chromium and 2~20 at.% cobalt.

4. The method for fluxing SiC single crystal growth according to claim 1, characterized in that, In step (1), the crucible is a high-purity graphite crucible or a SiC crucible.

5. The method for fluxing SiC single crystal growth according to claim 1, characterized in that, In steps (1) and (2), the protective atmosphere is a high-purity inert gas, or a mixture of high-purity inert gas and hydrogen, wherein the volume content of hydrogen in the mixture is ≤10%.

6. The method for fluxing SiC single crystal growth according to claim 1, characterized in that, In step (1), the heating and melting time is 5 to 30 minutes.

7. The method for fluxing SiC single crystal growth according to claim 1, characterized in that, In step (2), the Si-Cr-Co alloy is heated to no less than 1800°C and held for at least 1 hour to allow carbon dissolution to reach saturation.

8. The method for fluxing SiC single crystal growth according to claim 1, characterized in that, In step (3), the crystal growth method is either the top seed crystal solution growth method or the crucible descent method.

9. The method for fluxing SiC single crystal growth according to claim 8, characterized in that, When using the top seed crystal solution growth method, the SiC seed crystal is brought into contact with the surface of the Si-Cr-Co-C melt, and the seed crystal pulling speed and rotation speed are controlled to allow the SiC single crystal to grow on the seed crystal.

10. The method for fluxing SiC single crystal growth according to claim 1, characterized in that, In step (3), the growth temperature of SiC single crystal is not lower than 1800℃.

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