SiC polycrystal powder, preparation method and device

Abstract

According to the SiC polycrystal powder and the preparation method and device, the gaseous carbon source and the gaseous silicon source which do not contain chlorine serve as the unique carbon source and the unique silicon source, and introduction of the chlorine element is completely eradicated from the source; by accurately controlling the temperature gradient, the gas ratio and the flow velocity of the high-temperature pyrolysis zone and the sub-high-temperature reaction zone, the gaseous carbon source and the gaseous silicon source are subjected to instantaneous thermal decomposition to form pyrolysis mixed gas containing active silicon, carbon atoms and free radicals, and then nucleation and growth are carried out in a thermodynamically stable hexagonal crystal phase under the condition of no solid carrier to form SiC polycrystal powder. In the application, the reaction byproducts are only hydrogen, unreacted carrier gas and trace undecomposed gaseous carbon source and gaseous silicon source, and do not contain HCl, tar or toxic chlorosilane, and the tail gas can be directly discharged or simply recovered, so that the environment-friendly treatment cost is greatly reduced. The preparation method is clean, high in efficiency, high in product purity, single in crystal phase and suitable for large-scale preparation of the high-quality hexagonal crystal phase SiC powder.

Description

Technical Field

[0001] This invention belongs to the field of wide bandgap semiconductor materials technology, and relates to a SiC polycrystalline powder, its preparation method, and its apparatus. Background Technology

[0002] SiC polycrystalline powder is a key starting material for preparing SiC single-crystal substrates. Its purity, crystal phase structure and particle morphology directly affect the quality and efficiency of subsequent crystal growth.

[0003] In recent years, the preparation of SiC polycrystalline powder by chemical vapor deposition (CVD) has been widely studied due to its ability to achieve high-purity synthesis. For example, patent CN119082876A discloses a method for depositing SiC polycrystalline bulk on a "gate-shaped graphite rod," which obtains a dense deposition layer by controlling the temperature gradient and gas flow rate, and then crushes it to obtain powder. Patent CN119082862A adopts a similar approach, performing CVD deposition on the surface of a "vertical graphite rod array," emphasizing the optimization of the deposition rate by adjusting the precursor ratio. Patent CN116815318A proposes depositing SiC bulk on the "inner wall of a graphite crucible" and using a rotating structure to improve uniformity. While patent CN117966264A attempts to improve the precursor system, it is still based on a "gate-shaped carrier," using chlorosilane sources such as methyltrichlorosilane (MTS) for deposition, and the product still requires mechanical crushing.

[0004] While the existing methods mentioned above have improved deposition efficiency and equipment structure, they suffer from three common shortcomings: First, they all rely on solid supports such as graphite rods and crucibles for heterogeneous deposition, requiring post-processing steps such as crushing and grinding of the final powder, which easily introduces metal wear impurities or causes lattice defects. Second, the raw materials generally use chlorine-containing precursors such as MTS, generating corrosive or toxic byproducts such as HCl and chlorosilanes during the reaction. These byproducts not only contaminate the powder but also require complex exhaust gas treatment systems, increasing preparation costs. Third, the deposition temperature is usually controlled below 1500℃, making it difficult to effectively control the crystal phase. The resulting powder is often a polymorphic mixture of 3C, 6H, and 15R, which is not conducive to subsequent single-crystal growth of a single crystal. Therefore, there is an urgent need for a method that can directly synthesize high-purity single-phase SiC powder without solid supports or chlorine-containing precursors. Summary of the Invention

[0005] The purpose of this invention is to provide a SiC polycrystalline powder, a preparation method, and an apparatus to solve the problems of powder contamination and lattice defects in existing preparation methods.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, this application provides a SiC polycrystalline powder, the preparation method of which includes: The carbon-containing mixed gas and the silicon-containing mixed gas undergo pyrolysis at a temperature of 2050-2300℃ and a pressure of 1.0-1.5 bar for 50-60 ms to form a pyrolysis mixed gas; The nucleation reaction is carried out at a temperature of 1850-1950℃, a pressure of 1.0-1.5 bar, and with continuous hydrogen gas flow for 1-12 hours, followed by cooling to obtain SiC polycrystalline powder.

[0007] Secondly, this application provides an apparatus for preparing SiC polycrystalline powder, comprising: The reaction chamber and the graphite insulation layer located on the inner wall of the reaction chamber; The reaction chamber is connected from top to bottom to a high-temperature pyrolysis zone, a sub-high-temperature reaction zone, and a powder collection zone. The reaction chamber is equipped with a high-temperature induction coil and a sub-high-temperature induction coil; the high-temperature induction coil is located in the high-temperature pyrolysis zone, and the sub-high-temperature induction coil is located in the sub-high-temperature reaction zone. The top of the reaction chamber is provided with a carbon-containing mixed gas inlet, a silicon-containing mixed gas inlet, and a hydrogen inlet, and the carbon-containing mixed gas inlet, the silicon-containing mixed gas inlet, and the hydrogen inlet are all connected to the high-temperature pyrolysis zone; The reaction chamber has an air outlet on its side wall, and the air outlet is located in the powder collection area.

[0008] The present invention has the following beneficial effects: (1) This application uses chlorine-free gaseous carbon source and gaseous silicon source as the only carbon source and silicon source, which eliminates the introduction of chlorine element from the source, avoids the contamination of silicon carbide lattice by residual chlorine in traditional chlorine-containing processes, significantly improves the purity of powder, and can meet the stringent requirements of raw material cleanliness for high-end single crystal growth.

[0009] (2) The carbon source and silicon source undergo instantaneous thermal decomposition in the high-temperature pyrolysis zone to form a pyrolysis mixture containing active silicon, carbon atoms and free radicals; this pyrolysis mixture nucleates and grows into SiC polycrystalline powder in the sub-high temperature reaction zone without a solid support under thermodynamically stable hexagonal crystal phase conditions. This process does not require a support such as a graphite rod or crucible, thus avoiding the problems of impurity introduction, lattice damage and particle size inhomogeneity caused by mechanical crushing after depositing bulk material in the traditional CVD method.

[0010] (3) In this application, the reaction byproducts are only hydrogen, unreacted carrier gas and trace amounts of undecomposed gaseous carbon source and gaseous silicon source, and do not contain HCl, tar or toxic chlorosilanes. The tail gas can be directly discharged or simply recycled, which greatly reduces the cost of environmental treatment.

[0011] (4) This application uses small-molecule, highly reactive gases with a concentrated temperature range, resulting in a fast reaction rate and high energy utilization efficiency, which is conducive to achieving continuous, large-scale, and green production. At the same time, the prepared high-purity SiC polycrystalline powder can be used to prepare high-quality, high-performance third-generation semiconductor SiC single-crystal materials. Attached Figure Description

[0012] Figure 1 A schematic diagram of the structure of the SiC polycrystalline powder preparation apparatus provided in the embodiments of this application; Figure 2 The image shows the XRD pattern (X-ray diffraction analysis) of the SiC polycrystalline powder prepared in Example 1 of this application. Figure 3 The image shows the XRD pattern of the SiC polycrystalline powder prepared in Comparative Example 1 of this application. Figure 4 This is an optical microscope image of the SiC polycrystalline powder prepared in Example 1 of this application; Figure 5 This is a graph showing the GDMS (Glow Discharge Mass Spectrometry) detection data of the SiC polycrystalline powder prepared in Example 1 of this application. Figure 6 The dislocation density detection diagram of SiC single crystal prepared from SiC polycrystalline powder prepared in Example 1 of this application; Symbolic representation: 1-Reaction chamber, 2-Graphite insulation layer, 3-High temperature pyrolysis zone, 4-Sub-high temperature reaction zone, 5-Powder collection zone, 6-High temperature induction coil, 7-Sub-high temperature induction coil, 8-Carbon-containing mixed gas inlet, 9-Silicon-containing mixed gas inlet, 10-Gas outlet, 11-Baffle. Detailed Implementation

[0013] Terminology Explanation: Crystal phase: refers to the form in which the same substance exists under different crystal structures. Substances under the same crystal phase have the same structure.

[0014] High-purity gaseous carbon source: refers to gaseous carbon source with a purity of 99.999% or higher.

[0015] High-purity gaseous silanes refer to gaseous silanes with a purity of 99.999% or higher.

[0016] High-purity hydrogen refers to hydrogen with a purity of 99.999% or higher.

[0017] This application provides an apparatus for preparing SiC polycrystalline powder, which includes a reaction chamber 1 and a graphite insulation layer 2, as shown in the attached figure. Figure 1As shown. The reaction chamber 1 is an external component of the preparation device, which is made of high-purity graphite or high-purity tantalum. A graphite insulation layer 2 is provided on the inner wall of the reaction chamber 1, and the inner wall of the graphite insulation layer 2 is coated with a silicon carbide coating.

[0018] The interior of the reaction chamber 1 is sequentially connected from top to bottom to include a high-temperature pyrolysis zone 3, a sub-high-temperature reaction zone 4, and a powder collection zone 5. Therefore, there are no physical partitions inside the reaction chamber 1, meaning there is no solid deposition carrier inside the reaction chamber 1. As a result, the SiC polycrystalline powder prepared in this embodiment does not require crushing or grinding, thus avoiding the introduction of metal wear impurities or lattice defects.

[0019] To control the reaction temperature, a high-temperature induction coil 6 and a sub-high-temperature induction coil 7 are installed outside the reaction chamber 1. The high-temperature induction coil 6 is located in the high-temperature pyrolysis zone 3, and the sub-high-temperature induction coil 7 is located in the sub-high-temperature reaction zone 4. The high-temperature induction coil 6 heats the high-temperature pyrolysis zone 3, and the sub-high-temperature induction coil 7 heats the sub-high-temperature reaction zone 4. The temperature difference between the high-temperature pyrolysis zone 3 and the sub-high-temperature reaction zone 4 is 100-450℃. Thus, the high-temperature pyrolysis zone 3 is heated by external heating, and the sub-high-temperature reaction zone 4 is heated by external heating and natural radiation, forming an axial temperature gradient and achieving temperature control in different regions.

[0020] To facilitate the flow of gas within the reaction chamber 1, the top of the reaction chamber 1 is equipped with a carbon-containing mixed gas inlet 8 and a silicon-containing mixed gas inlet 9, both of which are connected to the high-temperature pyrolysis zone 3 to allow the introduction of the carbon-containing mixed gas and silicon-containing mixed gas into the high-temperature pyrolysis zone 3. The side wall of the reaction chamber 1 is equipped with a gas outlet 10, which is connected to the powder collection zone 5 to allow excess gas to be discharged.

[0021] The preparation device in this embodiment is used in a medium-frequency induction heating furnace. The carbon-containing mixed gas inlet 8 and the silicon-containing mixed gas inlet 9 are both connected to a gas mass flow controller, and the preparation device is connected to a pressure regulating valve and a powder collector.

[0022] In this embodiment, the inner diameter of the reaction chamber 1 is 20-100 mm, and the height of the high-temperature pyrolysis zone 3 is 20-40% of the height of the reaction chamber 1, so as to facilitate the complete pyrolysis of the carbon-containing mixed gas and the silicon-containing mixed gas into active silicon, carbon atoms and free radicals. To facilitate the collection of SiC polycrystalline powder, a baffle 11 is also provided in the powder collection zone 5.

[0023] In addition, this application embodiment also provides a method for preparing SiC polycrystalline powder, the method comprising: S01: A carbon-containing mixed gas and a silicon-containing mixed gas undergo pyrolysis at a temperature of 2050-2300℃ and a pressure of 1.0-1.5 bar for 50-60 ms to form a pyrolysis mixed gas.

[0024] A gaseous carbon source and hydrogen are mixed at a volume ratio of 1:10 to 1:50 to form a carbon-containing mixed gas. Simultaneously, gaseous silane and hydrogen are mixed at a volume ratio of 1:10 to 1:50 to form a silicon-containing mixed gas. In this embodiment, the gaseous carbon source is a high-purity gaseous carbon source with a purity greater than 99.999%, including one or more of methane, ethane, ethylene, and propylene; the gaseous silane is a high-purity gaseous silane with a purity greater than 99.999%, including one or more of silane, disilane, and trisilane. Neither the gaseous carbon source nor the gaseous silane in this embodiment contains chlorine, so no corrosive or toxic byproducts such as HCl or chlorosilanes are generated during the preparation of SiC polycrystalline powder, thus preventing contamination of the SiC polycrystalline powder.

[0025] The reaction chamber 1 is heated to raise the temperature of the high-temperature pyrolysis zone 3 to 2050-2300℃ and the temperature of the sub-high-temperature reaction zone 4 to 1850-1950℃, with an axial temperature difference of 100-450℃ between the high-temperature pyrolysis zone 3 and the sub-high-temperature reaction zone 4. The reaction chamber 1 is then evacuated to a vacuum of 1.0 × 10⁻⁶. ⁻3 The pressure is kept below 1 bar to ensure that the pressure inside the reaction chamber 1 reaches 1.0-1.5 bar.

[0026] With a C / Si molar ratio of 0.95:1-1.05:1, the carbon-containing mixed gas and the silicon-containing mixed gas are introduced into the high-temperature pyrolysis zone 3 through the carbon-containing mixed gas inlet 8 and the silicon-containing mixed gas inlet 9 at the top of the reaction chamber 1, so that the carbon-containing mixed gas and the silicon-containing mixed gas enter the sub-high temperature reaction zone 4 from the high-temperature pyrolysis zone 3 from top to bottom.

[0027] Under conditions of 2050-2300℃ and 1.0-1.5 bar, carbon-containing mixed gas and silicon-containing mixed gas are instantaneously pyrolyzed in high-temperature pyrolysis zone 3 for 50-60 ms to form a pyrolysis mixed gas containing active silicon, carbon atoms and free radicals. This pyrolysis mixed gas enters the sub-high temperature reaction zone 4 with the gas flow.

[0028] S02: The nucleation reaction is carried out at a temperature of 1850-1950℃, a pressure of 1.0-1.5 bar, and with continuous hydrogen gas flow for 1-12 hours. After cooling, SiC polycrystalline powder is obtained.

[0029] After the pyrolysis mixture enters the sub-high temperature reaction zone 4, hydrogen is continuously introduced at a temperature of 1850-1950℃ and a pressure of 1.0-1.5 bar at a flow rate of 50-800 sccm. The overall velocity of the pyrolysis mixture and the continuously introduced hydrogen is ≥0.8 m / s. Under carrier-free conditions, homogeneous gas-phase nucleation and particle growth occur for 1-12 hours, directly generating hexagonal SiC polycrystalline powder with 6H crystal form as the main component. After the reaction is completed, heating is stopped, and high-purity hydrogen is continuously introduced to cool the reaction chamber 1 to below 200℃ at a rate of 1-10℃ / min, so as to avoid the SiC polycrystalline powder from agglomeration or sintering due to thermal stress. Subsequently, the introduction of high-purity hydrogen is stopped, and the mixture is allowed to cool naturally to room temperature, obtaining SiC polycrystalline powder with an average particle size of 50-600 μm and a 6H crystal form content ≥95%.

[0030] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0031] Example 1 This application provides a SiC polycrystalline powder, the preparation method of which includes: S01: Methane with a purity greater than 99.999% and hydrogen with a purity greater than 99.999% are mixed at a volume ratio of 1:30 to form a carbon-containing mixed gas. Simultaneously, silane with a purity greater than 99.999% and hydrogen with a purity greater than 99.999% are mixed at a volume ratio of 1:30 to form a silicon-containing mixed gas. The reaction chamber 1 is evacuated to a vacuum of 1.0 × 10⁻⁶. ⁻3 The pressure inside the reaction chamber 1 is reduced to below 1.0 bar. The intermediate frequency power supply is turned on to heat the reaction chamber 1, raising the temperature of the high-temperature pyrolysis zone 3 to 2150°C and the temperature of the sub-high temperature reaction zone 4 to 1900°C, with an axial temperature difference of 250°C between the high-temperature pyrolysis zone 3 and the sub-high temperature reaction zone 4.

[0032] With a C / Si molar ratio of 1.02:1, a carbon-containing mixed gas and a silicon-containing mixed gas are introduced into the high-temperature pyrolysis zone 3 through the carbon-containing mixed gas inlet 8 and the silicon-containing mixed gas inlet 9 at the top of the reaction chamber 1. Under the conditions of 2150℃ and 1.0 bar, the carbon-containing mixed gas and the silicon-containing mixed gas undergo instantaneous pyrolysis for 50 ms in the high-temperature pyrolysis zone 3, forming a pyrolysis mixed gas containing active silicon, carbon atoms, and free radicals. This pyrolysis mixed gas is then carried by the gas flow into the sub-high temperature reaction zone 4.

[0033] S02: After the pyrolysis mixture enters the sub-high temperature reaction zone 4, it undergoes homogeneous gas-phase nucleation and particle growth for 12 hours under carrier-free conditions at a temperature of 1900℃, a pressure of 1.0 bar, a continuous hydrogen flow rate of 400 sccm, and a combined velocity of 1.0 m / s for both the pyrolysis mixture and the continuously introduced hydrogen. This directly generates hexagonal SiC polycrystalline powder with a predominantly 6H crystal form. After the reaction is complete, heating is stopped, and high-purity hydrogen is continuously introduced to cool the reaction chamber 1 to below 200℃ at a rate of 8℃ / min. Subsequently, the high-purity hydrogen supply is stopped, and the mixture is allowed to cool naturally to room temperature, yielding SiC polycrystalline powder.

[0034] Example 2 This application provides a SiC polycrystalline powder, which is prepared by the same method as in Example 1, except that the temperature of the high-temperature pyrolysis zone 3 is 2250°C.

[0035] Example 3 This application provides a SiC polycrystalline powder, which is prepared by the same method as in Example 1, except that the C / Si molar ratio is 1.05:1.

[0036] Example 4 This application provides a SiC polycrystalline powder, which is prepared by the same method as in Example 1, except that the C / Si molar ratio is 0.95:1.

[0037] Example 5 This application provides a SiC polycrystalline powder, which is prepared by the same method as in Example 1, except that the gaseous carbon source is propylene and the gaseous silane is methylsilane.

[0038] Example 6 This application provides a SiC polycrystalline powder, which is prepared by the same method as in Example 1, except that the gaseous carbon source is propylene and the gaseous silane is ethylsilane.

[0039] Example 7 This application provides a SiC polycrystalline powder, which is prepared by the same method as in Example 1, except that the gaseous carbon source is methane and the gaseous silane is trisilane.

[0040] Comparative Example 1 This application provides a comparative example of a SiC polycrystalline powder, which is prepared using the same method as in Example 1, except that the temperatures of the high-temperature pyrolysis zone 3 and the sub-high-temperature reaction zone 4 are both 1700°C.

[0041] In this embodiment, XRD analysis was performed on the SiC polycrystalline powders prepared in Example 1 and Comparative Example 1, respectively, to obtain the attached... Figure 2 ,3 .

[0042] From the appendix Figure 2 , 3 As can be seen, the main peak of the SiC polycrystalline powder prepared in Example 1 of this application completely matches the standard card (PDF#29-1131) for the 6H-SiC hexagonal crystal phase, and the 6H-SiC crystal phase content is ≥98%. This indicates that the SiC polycrystalline powder prepared in Example 1 of this application is of the 6H crystal form. The main peak of the SiC polycrystalline powder prepared in Comparative Example 1 corresponds to the standard card (PDF#29-1129) for the 3C-SiC cubic crystal phase and partially corresponds to the standard card (PDF#29-1131) for the 6H-SiC hexagonal crystal phase. Moreover, the peak intensity corresponding to the 6H-SiC hexagonal crystal phase is weaker. This indicates that the SiC polycrystalline powder prepared in Comparative Example 1 under the same thermal decomposition temperature and nucleation temperature conditions is of both the 6H and 3C crystal forms, and the content of the 6H crystal form is relatively low.

[0043] The particle size and elemental purity of the SiC polycrystalline powder prepared in Example 1 of this application were determined using optical microscopy and glow discharge mass spectrometry, respectively. Figure 4 , 5 From the appendix Figure 4 , 5 As can be seen, the particle size distribution of the SiC polycrystalline powder prepared in Example 1 of this application is concentrated in the range of 50-600 μm, and there is no obvious agglomeration; the purity of the SiC polycrystalline powder reaches more than 99.999%.

[0044] In addition, using the SiC polycrystalline powder prepared in Example 1 as raw material, SiC single crystals were prepared by the PVT method, and the dislocation density of the prepared SiC single crystals was measured to obtain the attached... Figure 6 From the appendix Figure 6 It is evident that the prepared SiC single crystals are free of polytype inclusions, and the dislocation density is less than 3000 dislocations / cm². 2 This meets the application requirements of high-end power devices.

[0045] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing SiC polycrystalline powder, characterized in that, include: The carbon-containing mixed gas and the silicon-containing mixed gas undergo pyrolysis at a temperature of 2050-2300℃ and a pressure of 1.0-1.5 bar for 50-60 ms to form a pyrolysis mixed gas; The nucleation reaction is carried out at a temperature of 1850-1950℃, a pressure of 1.0-1.5 bar, and with continuous hydrogen gas flow for 1-12 hours, followed by cooling to obtain SiC polycrystalline powder.

2. The method for preparing SiC polycrystalline powder according to claim 1, characterized in that, The carbon-containing mixed gas is a mixture of gaseous carbon source and hydrogen with a volume ratio of 1:10 to 1:50; the silicon-containing mixed gas is a mixture of gaseous silane and hydrogen with a volume ratio of 1:10 to 1:

50.

3. The method for preparing SiC polycrystalline powder according to claim 2, characterized in that, The gaseous carbon source includes one or more of methane, ethane, ethylene, and propylene; the gaseous silane includes one or more of silane, disilane, and trisilane.

4. The method for preparing SiC polycrystalline powder according to claim 1, characterized in that, The C / Si molar ratio in the carbon-containing mixed gas and the silicon-containing mixed gas is 0.95:1-1.05:

1.

5. The method for preparing SiC polycrystalline powder according to claim 1, characterized in that, The flow rate of continuously introduced hydrogen is 50-800 sccm; the bus speed of the pyrolysis mixture and the continuously introduced hydrogen is ≥0.8 m / s.

6. The method for preparing SiC polycrystalline powder according to claim 1, characterized in that, When the temperature is greater than 200℃, the cooling rate is 1-10℃ / min.

7. The method for preparing SiC polycrystalline powder according to claim 1, characterized in that, The SiC polycrystalline powder has an average particle size of 50-600 μm and a 6H crystal content of ≥95%.

8. SiC polycrystalline powder prepared by the preparation method according to any one of claims 1-7.

9. The apparatus for preparing SiC polycrystalline powder according to claim 8, characterized in that, include: The reaction chamber (1) and the graphite insulation layer (2) located on the inner wall of the reaction chamber (1); The reaction chamber (1) is connected from top to bottom to a high-temperature pyrolysis zone (3), a sub-high temperature reaction zone (4), and a powder collection zone (5). The reaction chamber (1) is provided with a high-temperature induction coil (6) and a sub-high-temperature induction coil (7) outside; the high-temperature induction coil (6) is located in the high-temperature pyrolysis zone (3), and the sub-high-temperature induction coil (7) is located in the sub-high-temperature reaction zone (4); The top of the reaction chamber (1) is provided with a carbon-containing mixed gas inlet (8) and a silicon-containing mixed gas inlet (9), and both the carbon-containing mixed gas inlet (8) and the silicon-containing mixed gas inlet (9) are connected to the high-temperature pyrolysis zone (3). The reaction chamber (1) has an air outlet (10) on its side wall, and the air outlet (10) is located in the powder collection area (5).

10. The apparatus for preparing SiC polycrystalline powder according to claim 9, characterized in that, The inner diameter of the reaction chamber (1) is 20-100 mm, and the height of the high-temperature pyrolysis zone (3) is 20-40% of the height of the reaction chamber (1).

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