Silicon carbide single crystal growth pre-sintering powder process, pre-sintering powder and single crystal growth method

Abstract

This invention relates to the field of silicon carbide single crystal preparation technology, specifically to a silicon carbide single crystal growth pre-sintering powder process, pre-sintered powder, and single crystal growth method. The process includes: filling silicon carbide powder into a graphite crucible and evacuating it to a vacuum level ≤1×10⁻⁶. ‑5 Pa; while maintaining a vacuum degree ≤ 1 × 10 ‑5 Under the condition of Pa, a three-stage gradient heating pre-calcination is performed. The first stage involves heating to 1200–1400℃ and holding for 1–2 hours; the second stage involves heating to 1800–2000℃ and holding for 2–3 hours; and the third stage involves heating to 2200–2400℃ and holding for 4–6 hours. After pre-calcination, high-purity argon gas is introduced to a pressure of 0.1–0.15 MPa, and the temperature is lowered to 1000℃ at a rate of 10–15℃ / min, followed by furnace cooling. The powder is then removed and sieved through a 40-mesh sieve. This method can effectively remove residual free silicon, free carbon, and metallic impurities from the powder, eliminate agglomeration and micropore defects, and improve the crystallinity and purity of the powder. When used in the PVT method for silicon carbide single crystal growth, it can reduce single crystal defects and improve yield.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide single crystal preparation technology, specifically to the process of pre-calcining powder for silicon carbide single crystal growth, the pre-calcined powder, and the single crystal growth method. Background Technology

[0002] The industrial-scale preparation of silicon carbide single crystals mainly employs the physical vapor transport method. This method uses high-purity silicon carbide powder as raw material, which is decomposed and sublimated under a high-temperature vacuum environment. The gaseous components are transported to the surface of the seed crystal under the action of a temperature gradient and deposited to grow, ultimately forming a silicon carbide single crystal. The quality of the silicon carbide powder directly determines the quality of the single crystal growth.

[0003] In the prior art, there are processes for pretreating silicon carbide powder to improve its performance. For example, patent document CN112226815A discloses a pretreatment method for silicon carbide powder used in the PVT method for growing silicon carbide single crystals. This method involves placing the silicon carbide powder in a vacuum induction furnace with stirring and evacuating it to a vacuum of 10... -3 ~10 -5 After heating to 500–800℃ and holding for 10–30 min, argon gas is introduced to 0.1–1 atm, and while stirring, heating continues to 1400–1600℃ and held for 5–15 min, finally allowing it to cool naturally. The purpose of this method is to form a graphite isolation layer on the surface of silicon carbide powder to reduce the sintering of silicon carbide under high-temperature conditions, thereby improving the stability of gas transport.

[0004] However, the pretreatment method disclosed in CN112226815A has the following defects: First, its maximum treatment temperature is only 1600℃, which is insufficient to allow the residual free silicon (melting point of about 1414℃) in the powder to fully react with the free carbon to form silicon carbide, and it is also difficult to recrystallize low-crystallinity silicon carbide particles, let alone effectively volatilize metallic impurities (such as aluminum, iron, boron, etc., whose volatilization temperatures are mostly above 2000℃); Second, the method fills the furnace with argon gas to atmospheric pressure when the temperature is raised to 1400-1600℃, resulting in a high furnace pressure, which is not conducive to the discharge of impurity gases; Third, the method uses natural cooling without controlling the atmosphere and rate of the cooling process, which can easily lead to microcracks in the powder particles due to thermal stress; Finally, the method does not limit parameters such as the particle size and filling thickness of the raw materials, and it is also difficult to guarantee the uniformity and stability of the pretreatment effect. Therefore, silicon carbide powder processed using the method of CN112226815A still has problems such as residual free impurities, insufficient crystallinity, and uneven particle morphology. When it is used for silicon carbide single crystal growth, it is easy to cause defects such as dislocations, microtubes, and inclusions in the single crystal, which affects the quality and yield of the single crystal. Summary of the Invention

[0005] The purpose of this invention is to provide a pre-calcined powder process, method, and single-crystal growth method for silicon carbide single crystals, to solve the problems in the prior art where the pretreatment temperature of silicon carbide powder is insufficient, the inability to effectively remove free silicon, free carbon, and metal impurities, and the difficulty in improving the crystallinity of the powder lead to many defects and low yield during subsequent single crystal growth. Furthermore, through the synergistic effect of three-stage gradient heating, full-process high vacuum, and inert atmosphere gradient cooling, the powder is deeply purified and its structure is optimized, so that the purity of the pre-calcined powder reaches more than 99.9999%. When used for growing silicon carbide single crystals by physical vapor transport method, it can significantly reduce microtube density and dislocation density, and improve the single crystal yield.

[0006] The technical solution of the present invention is as follows: Firstly, a process for pre-sintering silicon carbide single crystal growth powder is provided, comprising the following steps: (1) Fill the graphite crucible with silicon carbide powder, and evacuate the furnace cavity containing the graphite crucible to make the vacuum degree in the furnace cavity ≤1×10 -5 Pa; (2) Maintaining a vacuum level of ≤1×10⁻⁶ within the furnace cavity -5 Under the condition of Pa, silicon carbide powder was pre-calcined in a three-stage gradient heating process: First stage: Heat to the first temperature range and hold at that temperature to remove impurities adsorbed on the surface of the powder; The second stage involves heating to the second temperature range and holding the temperature there, causing the residual free silicon and free carbon in the powder to react and form silicon carbide. The third stage involves heating to the third temperature range and holding the temperature to allow metallic impurities in the powder to volatilize and eliminate micropore defects. The third temperature range is 2200–2400℃; (3) After the pre-firing is completed, inert gas is introduced into the furnace cavity to make the pressure in the furnace cavity reach the predetermined pressure, and then the temperature is reduced to the predetermined temperature at a controlled cooling rate, and then cooled to room temperature with the furnace. (4) Take out the cooled silicon carbide powder, sieve it, and obtain pre-burned powder.

[0007] Preferably, in step (2), the first temperature range is 1200 to 1400°C, and the second temperature range is 1800 to 2000°C.

[0008] Preferably, in step (2), the heat preservation time of the third stage is 4 to 6 hours.

[0009] Preferably, in step (2), the heating rate of the first stage is 8-12℃ / min, the heating rate of the second stage is 5-8℃ / min, and the heating rate of the third stage is 3-5℃ / min.

[0010] Preferably, in step (3), the inert gas is high-purity argon, the predetermined pressure is 0.1 to 0.15 MPa, the controlled cooling rate is 10 to 15 °C / min, and the predetermined temperature is 1000 °C.

[0011] Preferably, in step (1), the particle size of the silicon carbide powder is 8 to 40 mesh, and the filling thickness is 80 to 100 mm.

[0012] Preferably, in step (1), before filling with silicon carbide powder, the step of screening and cleaning the coarse silicon carbide powder is also included: using a vibrating sieve combined with airflow classification, the powder with a particle size of 8 to 40 mesh is screened out, and then the screened powder is placed in ultrapure water and ultrasonically cleaned for 30 to 60 minutes with an ultrasonic power of 200 to 300 W. After filtration, it is dried in a vacuum drying oven at 100 to 120°C for 3 to 5 hours.

[0013] Secondly, a silicon carbide single crystal growth pre-sintered powder is provided, prepared using any of the processes described above, wherein the pre-sintered powder has a purity ≥99.9999% and a bulk density of 1.3–1.5 g / cm³. 3 .

[0014] Thirdly, a method for growing silicon carbide single crystals is provided, in which silicon carbide single crystal growth pre-calcined powder prepared by the above method is used as raw material, and silicon carbide single crystals are grown by physical vapor transport method.

[0015] Preferably, the microtube density of the silicon carbide single crystal is lower than that of the silicon carbide single crystal grown using unburned silicon carbide powder.

[0016] Compared with the prior art, the advantages of the present invention are: In the three-stage gradient heating process, the first stage (1200–1400℃) effectively removes adsorbed moisture and volatile organic impurities from the powder surface, preventing them from carbonizing and contaminating the powder at higher temperatures. The second stage (1800–2000℃) allows residual free silicon and free carbon in the powder to fully react and form silicon carbide, while simultaneously recrystallizing low-crystallinity silicon carbide particles, thus improving the overall crystallinity of the powder. The third stage (2200–2400℃) allows metallic impurities (such as Al, Fe, B, etc.) to fully volatilize, while eliminating microporous defects inside the powder, combined with a total temperature ≤1×10⁻⁶ throughout the process. -5 The high vacuum environment of Pa enables deep purification and improved crystallinity of the powder, and the purity of the powder after pre-calcination can reach over 99.9999%.

[0017] During the cooling stage, high-purity argon gas is introduced and the pressure is controlled at 0.1–0.15 MPa. At the same time, gradient cooling is adopted (first reducing the temperature to 1000℃ at a rate of 10–15℃ / min, and then cooling with the furnace). This can effectively prevent microcracks from forming in the powder particles due to excessive thermal stress, and maintain the integrity of the particles and the uniformity of the packing density. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a flowchart of the silicon carbide single crystal growth pre-sintering powder process described in this invention; Figure 2 This is a flowchart illustrating the silicon carbide single crystal growth process using pre-fired powder as described in this invention. Figure 3 This is an image showing inclusion defects in a silicon carbide single crystal grown using unburned silicon carbide powder, as described in this invention. Figure 4 This is a polymorphic defect diagram of a silicon carbide single crystal grown using unburned silicon carbide powder, as described in this invention. Figure 5 This is a photograph of a silicon carbide single crystal grown from silicon carbide powder processed by the pre-burning powder process described in this invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments: The principle of the silicon carbide single crystal growth pre-sintered powder process: Three-stage gradient heating, corresponding to the temperature ranges for removing different impurities in the powder. Specifically, silicon has a melting point of 1414℃. Free silicon begins to soften at 1200–1400℃ and can react with free carbon to form silicon carbide. Therefore, the first stage temperature is chosen at 1200–1400℃ to remove surface-adsorbed impurities while preparing for the subsequent silicon-carbon reaction. Free silicon and free carbon can fully react to form silicon carbide at 1800–2000℃, and low-crystallinity silicon carbide recrystallizes in this temperature range. Therefore, the second stage temperature is chosen at 1800–2000℃. Metal impurities such as aluminum, iron, and boron have volatilization temperatures mostly above 2000℃, and micropore defects in the silicon carbide lattice can be eliminated through surface diffusion and grain boundary migration at 2200–2400℃. Therefore, the third stage temperature is chosen at 2200–2400℃. The temperature is maintained at ≤1×10⁻⁶ throughout the process. -5 The high vacuum of Pa facilitates the timely removal of impurity gases, preventing them from redepositing on the powder surface. After pre-firing, the introduction of high-purity argon gas and gradient cooling can prevent microcracks from forming in the powder particles due to excessive thermal stress, thus maintaining particle integrity and uniform packing density.

[0020] Example 1

[0021] like Figure 1 As shown, this embodiment provides a process for pre-sintering silicon carbide single crystal growth powder, and the specific steps are as follows: (1) Raw material screening and pretreatment: Silicon carbide coarse powder with a purity ≥99.999% was selected and screened using a combination of vibrating sieving and airflow classification to obtain powder with a particle size range of 8-40 mesh. The screened powder was placed in ultrapure water and ultrasonically cleaned for 45 min at an ultrasonic power of 250 W. After cleaning, it was filtered and dried in a vacuum drying oven at 110℃ for 4 h to obtain silicon carbide powder to be pre-calcined.

[0022] (2) Powder filling and furnace sealing: The dried silicon carbide powder to be pre-calcined is evenly filled into a high-purity graphite crucible with a filling thickness of 90 mm. The filled graphite crucible is placed into a high-temperature vacuum sintering furnace, the furnace door is closed, and a mechanical pump and a molecular pump are used to evacuate the furnace to a vacuum level of 1×10⁻⁶. -5 Pa.

[0023] (3) Gradient heating pre-firing treatment: while maintaining the vacuum degree of the furnace cavity ≤1×10 -5 Under the condition of Pa, pre-firing is carried out using a segmented gradient heating method: The first step involves raising the furnace temperature from room temperature to 1300℃ at a heating rate of 10℃ / min and holding it at that temperature for 1.5 hours to remove impurities adsorbed on the powder surface. This temperature range is below the melting point of silicon, which helps prevent the free silicon from melting and flowing, thus avoiding powder agglomeration. The second stage involves raising the temperature from 1300℃ to 1900℃ at a rate of 6℃ / min and holding it at that temperature for 2.5 hours. This allows the residual free silicon in the powder to react with free carbon to form silicon carbide. This temperature range is higher than the melting point of silicon, so the free silicon is in a liquid state, increasing the contact area with the free carbon and resulting in a more complete reaction. The third stage involves raising the temperature from 1900℃ to 2300℃ at a heating rate of 4℃ / min and holding it at that temperature for 5 hours to allow the metallic impurities in the powder to volatilize and eliminate microporous defects. This temperature range is higher than the volatilization temperatures of major metallic impurities such as aluminum (approximately 2050℃) and iron (approximately 2200℃), enabling deep purification.

[0024] (4) Atmosphere control and cooling treatment: After the pre-burning is completed, high-purity argon gas (purity 99.999%) is introduced into the furnace cavity, and the furnace cavity pressure is adjusted to 0.12MPa. Then the temperature is reduced to 1000℃ at a rate of 12℃ / min, and then the furnace is naturally cooled to room temperature.

[0025] (5) Sieving: After cooling, take out the pre-fired powder and sieve it through a 40-mesh sieve to obtain the pre-fired powder.

[0026] Testing showed that the pre-calcined powder prepared in this embodiment had a purity of 99.99992% and a bulk density of 1.42 g / cm³.3 .

[0027] Example 2

[0028] like Figure 1 As shown, this embodiment provides a process for pre-sintering silicon carbide single crystal growth powder, and the specific steps are as follows: (1) Raw material screening and pretreatment: Silicon carbide coarse powder with a purity ≥99.999% was selected and screened using a combination of vibrating sieving and airflow classification to obtain powder with a particle size range of 8-40 mesh. The screened powder was placed in ultrapure water and ultrasonically cleaned for 30 min at an ultrasonic power of 200 W. After cleaning, it was filtered and dried in a vacuum drying oven at 100℃ for 5 h to obtain silicon carbide powder to be pre-calcined.

[0029] (2) Powder filling and furnace sealing: The dried silicon carbide powder to be pre-calcined is evenly filled into a high-purity graphite crucible with a filling thickness of 80 mm. The filled graphite crucible is placed into a high-temperature vacuum sintering furnace, the furnace door is closed, and a mechanical pump and a molecular pump are used to evacuate the furnace to a vacuum level of 8 × 10⁻⁶. -6 Pa.

[0030] (3) Gradient heating pre-firing treatment: while maintaining the vacuum degree of the furnace cavity ≤1×10 -5 Under the condition of Pa, pre-firing is carried out using a segmented gradient heating method: First stage: Raise the furnace temperature from room temperature to 1200℃ at a heating rate of 8℃ / min and hold for 2 hours; Second stage: Raise the temperature from 1200℃ to 1800℃ at a heating rate of 5℃ / min and hold for 3 hours; The third stage: The temperature was increased from 1800℃ to 2200℃ at a heating rate of 3℃ / min, and held for 6 hours.

[0031] (4) Atmosphere control and cooling treatment: After the pre-burning is completed, high-purity argon gas (purity 99.999%) is introduced into the furnace cavity, and the furnace cavity pressure is adjusted to 0.1MPa. Then the temperature is reduced to 1000℃ at a rate of 10℃ / min, and then the furnace is allowed to cool naturally to room temperature.

[0032] (5) Sieving: After cooling, take out the pre-fired powder and sieve it through a 40-mesh sieve to obtain the pre-fired powder.

[0033] Testing showed that the pre-calcined powder prepared in this embodiment had a purity of 99.99991% and a bulk density of 1.38 g / cm³. 3 .

[0034] Example 3

[0035] like Figure 1As shown, this embodiment provides a process for pre-sintering silicon carbide single crystal growth powder, and the specific steps are as follows: (1) Raw material screening and pretreatment: Silicon carbide coarse powder with a purity ≥99.999% was selected and screened using a combination of vibrating sieving and airflow classification to obtain powder with a particle size range of 8-40 mesh. The screened powder was placed in ultrapure water and ultrasonically cleaned for 60 min at an ultrasonic power of 300 W. After cleaning, it was filtered and dried in a vacuum drying oven at 120℃ for 3 h to obtain silicon carbide powder to be pre-calcined.

[0036] (2) Powder filling and furnace sealing: The dried silicon carbide powder to be pre-calcined is evenly filled into a high-purity graphite crucible with a filling thickness of 100 mm. The filled graphite crucible is placed into a high-temperature vacuum sintering furnace, the furnace door is closed, and a mechanical pump and a molecular pump are used to evacuate the furnace to a vacuum level of 5 × 10⁻⁶ mm. -6 Pa.

[0037] (3) Gradient heating pre-firing treatment: while maintaining the vacuum degree of the furnace cavity ≤1×10 -5 Under the condition of Pa, pre-firing is carried out using a segmented gradient heating method: First stage: Raise the furnace temperature from room temperature to 1400℃ at a heating rate of 12℃ / min and hold for 1 hour; Second stage: Raise the temperature from 1400℃ to 2000℃ at a heating rate of 8℃ / min and hold for 2 hours; The third stage: The temperature is increased from 2000℃ to 2400℃ at a heating rate of 5℃ / min, and then held for 4 hours.

[0038] (4) Atmosphere control and cooling treatment: After the pre-burning is completed, high-purity argon gas (purity 99.999%) is introduced into the furnace cavity, and the furnace cavity pressure is adjusted to 0.15MPa. Then, the temperature is reduced to 1000℃ at a rate of 15℃ / min, and then naturally cooled to room temperature with the furnace.

[0039] (5) Sieving: After cooling, take out the pre-fired powder and sieve it through a 40-mesh sieve to obtain the pre-fired powder.

[0040] Testing showed that the pre-calcined powder prepared in this embodiment had a purity of 99.99995% and a bulk density of 1.45 g / cm³. 3 .

[0041] Example 4

[0042] like Figure 2 As shown, this embodiment provides a method for growing silicon carbide single crystals, using the pre-calcined powder prepared in Example 1 as raw material, and growing silicon carbide single crystals by physical vapor transport method.

[0043] The pre-calcined powder prepared in Example 1 was packed into the bottom of a graphite crucible, and a 4H-SiC seed crystal was fixed on a seed crystal holder at the top of the crucible. The growth chamber was evacuated to 1×10⁻⁶. -4 The pressure was increased to 50 mbar by introducing high-purity argon gas, and then heated to 2300°C for the powder and 2200°C for the seed crystal. The pressure was kept constant, and the growth was carried out for 50 hours. After the growth was completed, the temperature was gradually reduced to room temperature to obtain silicon carbide single crystals.

[0044] The obtained silicon carbide single crystal was sliced ​​and polished, and the microtube density was observed using an optical microscope, while the dislocation density was measured using X-ray diffraction rocking curves. The results showed that the microtube density of the obtained silicon carbide single crystal was less than 0.5 cells / cm². 2 Dislocation density less than 2000 / cm 2 The yield of single-crystal wafers reaches over 85%. For example... Figure 5 As shown, the single crystals grown from powder treated with the pre-sintered powder process of this invention have clean surfaces, free of visible inclusions or polymorphic defects. In contrast, silicon carbide single crystals grown from un-pre-sintered silicon carbide powder under the same conditions have a microtube density of approximately 5–10 cells / cm². 2 The dislocation density is approximately 5000–8000 dislocations / cm³. 2 The yield of single crystals is approximately 50% to 60%.

[0045] Example 5

[0046] like Figure 2 As shown, this embodiment provides a method for growing silicon carbide single crystals, using the pre-calcined powder prepared in Example 2 as raw material, and growing silicon carbide single crystals through physical vapor transport method.

[0047] The growth conditions were the same as in Example 4. The resulting silicon carbide single crystal had a microtube density of less than 0.8 cells / cm². 2 Dislocation density less than 2500 / cm 2 The yield of single crystals reached over 82%.

[0048] Example 6

[0049] like Figure 2 As shown, this embodiment provides a method for growing silicon carbide single crystals, using the pre-calcined powder prepared in Example 3 as raw material, and growing silicon carbide single crystals through physical vapor transport method.

[0050] The growth conditions were the same as in Example 4. The resulting silicon carbide single crystal had a microtube density of less than 0.6 cells / cm². 2 Dislocation density less than 2200 / cm 2 The yield of single crystals reached over 84%.

[0051] Comparative Example 1 This comparative example pretreatment of silicon carbide powder follows the method described in Example 1 of CN112226815A. The specific steps are as follows: Silicon carbide powder with a particle size of 100 micrometers was placed in a vacuum induction furnace with stirring, and the furnace was evacuated to a vacuum level of 10. -3 Pa, heat to 600℃ at a heating rate of 1000℃ / h and hold for 15 min. Pour argon gas into the vacuum induction furnace until the furnace chamber pressure reaches 0.5 atm, turn on the stirrer, stir at a stirring speed of 50 r / min, and simultaneously continue heating to 1500℃ at a heating rate of 1500℃ / h and hold for 10 min. Turn off the heating and allow to cool naturally to room temperature.

[0052] The pretreated silicon carbide powder was used to grow silicon carbide single crystals under the same conditions as in Example 4. The resulting silicon carbide single crystals had a microtube density of approximately 3–5 cells / cm². 2 The dislocation density is approximately 4000–6000 dislocations / cm³. 2 The yield of single crystals is approximately 65% ​​to 70%.

[0053] like Figure 3 As shown, single crystals grown from powder pretreated using the CN112226815A method exhibit obvious inclusion defects (white dots in the image); for example... Figure 4 As shown, the single crystal also has polymorphic defects (large polymorphic regions in the facets).

[0054] Comparative Example 2 This comparative example uses the same method as Example 1 to pre-calcine silicon carbide powder, except that a third stage of heating is not performed, i.e., the highest pre-calcine temperature is 2000℃ and the temperature is maintained for 5 hours.

[0055] The pretreated silicon carbide powder was used to grow silicon carbide single crystals under the same conditions as in Example 4. The resulting silicon carbide single crystals had a microtube density of approximately 2–3 cells / cm². 2 The dislocation density is approximately 3000–4000 dislocations / cm³. 2 The yield of single crystals was approximately 70%–75%. The results indicate that without high-temperature treatment at 2200–2400℃, the residual metal impurities in the powder could not be fully volatilized, resulting in limited improvement in single crystal quality.

[0056] Comparative Example 3 This comparative example uses the same method as Example 1 to pre-calcine silicon carbide powder, except that: after pre-calcinement, inert atmosphere gradient cooling is not performed, but the powder is directly cooled naturally with the furnace.

[0057] The pretreated silicon carbide powder was used to grow silicon carbide single crystals under the same conditions as in Example 4. The resulting silicon carbide single crystals had a microtube density of approximately 1–2 cells / cm². 2The dislocation density was approximately 2500–3500 dislocations / cm², and the single crystal yield was approximately 75%–80%. The results showed that without gradient cooling in an inert atmosphere, microcracks were generated in the powder particles due to thermal stress during the cooling process, affecting the packing uniformity and sublimation stability. The improvement in single crystal quality was lower than that in Example 4.

[0058] Comparative Example 4 This comparative example uses the same method as Example 1 to pre-calcine silicon carbide powder, except that: the pre-calcine process does not maintain a high vacuum. That is, when the temperature is raised to the second stage (1800°C), argon gas is introduced to 0.1 MPa, and the subsequent process is carried out at atmospheric pressure.

[0059] The pretreated silicon carbide powder was used to grow silicon carbide single crystals under the same conditions as in Example 4. The resulting silicon carbide single crystals had a microtube density of approximately 1.5–3 cells / cm². 2 The dislocation density is approximately 3000–4500 dislocations / cm³. 2 The single crystal yield was approximately 72%–78%. The results indicate that the failure to maintain a high vacuum throughout the process resulted in insufficient removal of impurity gases, causing some impurities to redeposit on the powder surface and affecting the powder purity.

[0060] By comparing the test results of Examples 4-6 with those of Comparative Examples 1-4, the following conclusions can be drawn: Compared with the method in CN112226815A (Comparative Example 1), the pre-calcination process of the present invention with three-stage gradient heating (especially the third stage of high-temperature treatment at 2200-2400℃) can more thoroughly remove metal impurities in the powder, making the powder purity reach more than 99.9999%, thereby significantly reducing the microtube density and dislocation density in the single crystal and improving the yield of the single crystal.

[0061] Compared with the absence of the third stage of heating (Comparative Example 2), the high-temperature treatment of 2200-2400℃ is a key step in removing metal impurities and eliminating micropore defects, which directly determines the purity and crystallinity of the powder and thus affects the quality of single crystals.

[0062] Compared with no inert atmosphere gradient cooling (Comparative Example 3), the control of atmosphere and rate during the cooling process plays an important role in maintaining the integrity of powder particles and preventing the generation of microcracks, which in turn affects the filling uniformity and sublimation stability.

[0063] Compared with not maintaining a high vacuum throughout the process (Comparative Example 4), the high vacuum environment throughout the pre-firing process is conducive to the timely discharge of impurity gases and prevents impurities from redepositing, which is a necessary condition to ensure the purity of the powder.

[0064] In summary, the silicon carbide single crystal growth pre-sintering powder process and method of the present invention, through the synergistic effect of key steps such as three-stage gradient heating (especially high-temperature treatment at 2200-2400℃), full-process high vacuum, and inert atmosphere gradient cooling, achieves deep purification and structural optimization of silicon carbide powder, significantly improving the growth quality and yield of subsequent silicon carbide single crystals.

[0065] 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 process for pre-sintering silicon carbide single crystal growth powder, comprising the following steps: (1) Fill the graphite crucible with silicon carbide powder, and evacuate the furnace cavity containing the graphite crucible to make the vacuum degree in the furnace cavity ≤1×10 -5 Pa; (2) Maintaining a vacuum level of ≤1×10⁻⁶ within the furnace cavity -5 Under the condition of Pa, silicon carbide powder was pre-calcined in a three-stage gradient heating process: First stage: Heat to the first temperature range and hold at that temperature to remove impurities adsorbed on the surface of the powder; The second stage involves heating to the second temperature range and holding the temperature there, causing the residual free silicon and free carbon in the powder to react and form silicon carbide. The third stage involves heating to the third temperature range and holding the temperature to allow metallic impurities in the powder to volatilize and eliminate micropore defects. The third temperature range is 2200–2400℃; (3) After the pre-firing is completed, inert gas is introduced into the furnace cavity to make the pressure in the furnace cavity reach the predetermined pressure, and then the temperature is reduced to the predetermined temperature at a controlled cooling rate, and then cooled to room temperature with the furnace. (4) Take out the cooled silicon carbide powder, sieve it, and obtain pre-burned powder.

2. The silicon carbide single crystal growth pre-sintering powder process according to claim 1, characterized in that, In step (2), the first temperature range is 1200 to 1400°C, and the second temperature range is 1800 to 2000°C.

3. The silicon carbide single crystal growth pre-sintering powder process according to claim 1, characterized in that, In step (2), the heat preservation time for the third stage is 4 to 6 hours.

4. The silicon carbide single crystal growth pre-sintering powder process according to claim 1, characterized in that, In step (2), the heating rate of the first stage is 8-12℃ / min, the heating rate of the second stage is 5-8℃ / min, and the heating rate of the third stage is 3-5℃ / min.

5. The silicon carbide single crystal growth pre-sintering powder process according to claim 1, characterized in that, In step (3), the inert gas is high-purity argon, the predetermined pressure is 0.1 to 0.15 MPa, the controlled cooling rate is 10 to 15 °C / min, and the predetermined temperature is 1000 °C.

6. The silicon carbide single crystal growth pre-sintering powder process according to claim 1, characterized in that, In step (1), the particle size of the silicon carbide powder is 8 to 40 mesh, and the filling thickness is 80 to 100 mm.

7. The silicon carbide single crystal growth pre-sintering powder process according to claim 1, characterized in that, In step (1), before filling the silicon carbide powder, the process also includes screening and cleaning the coarse silicon carbide powder: using a vibrating sieve combined with airflow classification, the powder with a particle size of 8 to 40 mesh is screened out, and then the screened powder is placed in ultrapure water and ultrasonically cleaned for 30 to 60 minutes with an ultrasonic power of 200 to 300 W. After filtration, it is dried in a vacuum drying oven at 100 to 120°C for 3 to 5 hours.

8. A pre-sintered powder for silicon carbide single crystal growth, characterized in that, The pre-calcined powder is prepared using the process described in any one of claims 1 to 7, wherein the purity is ≥99.9999% and the bulk density is 1.3–1.5 g / cm³. 3 .

9. A method for growing silicon carbide single crystals, characterized in that, Using the silicon carbide single crystal growth pre-calcined powder as described in claim 8 as raw material, silicon carbide single crystals are grown by physical vapor transport method.

10. The method for growing silicon carbide single crystals according to claim 9, characterized in that, The microtube density of the silicon carbide single crystal is lower than that of silicon carbide single crystals grown using unburned silicon carbide powder.

Images