Porous filter, preparation method and use thereof in silicon carbide single crystal growth

Abstract

The present application provides a porous filter, a preparation method and its use in the growth of silicon carbide single crystals. The porous filter of the present application comprises a porous substrate and a tantalum carbide coating on the pore surface of the porous substrate. During the growth of silicon carbide single crystals, by placing the porous filter between the silicon carbide raw material and the seed crystal, impurities such as carbon particles in the gas phase components of the raw material can be blocked on the porous filter, thereby reducing the contamination of the growing crystal. In addition, the high temperature resistant tantalum carbide coating prevents the porous substrate from becoming a new source of carbon inclusions, thereby further reducing the carbon inclusions in the growing silicon carbide single crystal and improving the crystal quality.

Description

Technical Field

[0001] The present application relates to the field of crystal growth technology, and in particular to a porous filter, a preparation method and use thereof in the growth of silicon carbide single crystals. Background Art

[0002] Physical vapor transport is a common method for growing silicon carbide single crystals. Generally, silicon carbide raw materials are placed at the bottom of a graphite crucible, and silicon carbide seed crystals are fixed on the graphite seed crystal holder at the top of the graphite crucible. The crucible is sealed, and the periphery of the bottom of the graphite crucible is heated by a side heater (the heating method is resistance heating or induction heating). The silicon carbide raw materials are decomposed and sublimated into gas phase components under high temperature conditions. The gas phase components are transported to the silicon carbide seed crystals in the low temperature zone driven by the axial temperature gradient, and are deposited on the surface of the silicon carbide seed crystals to form silicon carbide single crystals.

[0003] Since various impurities are inevitably present in the silicon carbide raw materials, these impurities sublimate with the silicon carbide raw materials at high temperatures, forming impurity particle inclusions on the growth surface of the silicon carbide seed crystal and in the crystal, which in turn causes defects such as microtubes and dislocations. Secondly, since the gas phase component coming out of the silicon carbide raw materials is a silicon-rich gas, it will react with the graphite crucible, causing the surface of the graphite crucible to pulverize, and the pulverized carbon particles will rise to the silicon carbide seed crystal with the airflow, and form carbon inclusions on the growth surface of the silicon carbide crystal, which will then induce defects such as microtubes and dislocations, which will have a great impact on the performance of crystal devices and the yield rate of mass-produced crystals. Summary of the invention

[0004] The purpose of this application is to provide a porous filter, a preparation method and its use in the growth of silicon carbide single crystals, so as to reduce the crystal defects caused by the presence of a large amount of carbon inclusions during the growth of silicon carbide single crystals and improve the crystal quality of silicon carbide single crystals. The specific technical solution is as follows:

[0005] In a first aspect, the present application provides a porous filter comprising a porous substrate and a tantalum carbide coating on the pore surfaces of the porous substrate.

[0006] In one embodiment of the present application, the porous substrate is selected from a porous graphite sheet or a porous silicon carbide sheet; the porous filter has a porosity of 5%-50% and a pore size of 30-90 μm.

[0007] In one embodiment of the present application, the thickness of the tantalum carbide coating is 8-50 μm.

[0008] In one embodiment of the present application, the X-ray diffraction spectrum of the tantalum carbide coating has characteristic peaks at 2θ of 34.81°, 40.42°, 58.48°, 69.98° and 73.49°, with an error range of ±0.02°.

[0009] The second aspect of the present application provides a method for preparing the porous filter according to any one of the embodiments of the first aspect of the present application, which comprises the following steps:

[0010] Using argon as carrier gas, gaseous tantalum pentachloride and reaction gas are introduced into the reaction chamber;

[0011] In the reaction chamber, the gaseous tantalum pentachloride and the reaction gas diffuse into the pores of the porous substrate to perform a chemical vapor deposition reaction, forming the tantalum carbide coating on the surface of the pores to obtain the porous filter.

[0012] In one embodiment of the present application, the porous substrate is selected from a porous graphite sheet, the reaction gas is selected from hydrogen; the volume flow ratio of the gaseous tantalum pentachloride, the argon gas and the hydrogen is (1-4): (2-5): (2-6); the volume flow ratio of the gaseous tantalum pentachloride and the diameter of the porous graphite sheet is (1-4): (1.5-3) mL·min -1 / mm.

[0013] In one embodiment of the present application, the porous substrate is selected from a porous silicon carbide sheet, the reaction gas is selected from hydrogen and propylene gas; the volume flow ratio of the gaseous tantalum pentachloride, the argon gas, the hydrogen gas and the propylene gas is (1-4): (2-5): (2-6): (0.5-3); the volume flow ratio of the gaseous tantalum pentachloride and the diameter of the porous silicon carbide sheet is (1-4): (1.5-3) mL·min -1 / mm.

[0014] In one embodiment of the present application, the reaction temperature of the chemical vapor deposition reaction is 1300-1700° C., the reaction pressure is 1000-3000 Pa, and the reaction time is 2-10 h.

[0015] In one embodiment of the present application, the gaseous tantalum pentachloride is obtained by gasifying tantalum pentachloride powder in a gasification chamber, with a gasification temperature of 100-300° C. and a gasification pressure of 1000-3000 Pa.

[0016] The third aspect of the present application provides use of the porous filter described in any embodiment of the first aspect of the present application in the growth of silicon carbide single crystals.

[0017] Beneficial effects of this application:

[0018] The present application provides a porous filter, a preparation method and its use in the growth of silicon carbide single crystals. The porous filter of the present application comprises a porous matrix and a tantalum carbide coating on the pore surface of the porous matrix. In the growth process of silicon carbide single crystals, by placing the porous filter of the present application between the silicon carbide raw material and the silicon carbide seed crystal, on the one hand, the porous structure of the porous filter filters the gas phase components of the silicon carbide raw material, and the impurities in the gas phase components, especially the carbon particle impurities in the gas phase components, are blocked on the porous filter, thereby reducing the probability of impurities such as carbon particles being transmitted to the crystal growth surface of the seed crystal with the air flow and contaminating the crystal. On the other hand, since the tantalum carbide coating on the surface of the porous filter has good high temperature resistance, the porous matrix inside the porous filter is prevented from becoming a new source of carbon inclusions under the corrosion of high temperature and silicon-rich gas, reducing the carbon inclusions in the silicon carbide single crystal, thereby reducing the crystal defects such as microtubes and dislocations caused by the carbon inclusions, and improving the crystal quality of the grown silicon carbide single crystal.

[0019] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solution in the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0021] Figure 1 is a schematic diagram of a silicon carbide single crystal growth device;

[0022] Figure 2 A partial cross-sectional schematic diagram of a porous filter in one embodiment of the present application;

[0023] Figure 3 The X-ray diffraction spectrum of tantalum carbide (C-TaC) calculated from the tantalum carbide coating and single crystal data in Example 1;

[0024] Figure 4 This is a scanning electron microscope photograph of the porous filter prepared in Example 1.

[0025] Description of reference numerals:

[0026] 10-silicon carbide single crystal growth device; 11-crucible cover; 12-graphite seed crystal holder; 13-silicon carbide seed crystal; 14-graphite crucible; 15-porous filter; 16-side heater; 17-silicon carbide raw material; 151-porous substrate; 152-pores of porous substrate; 153-tantalum carbide coating. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0028] like Figure 1 In the silicon carbide single crystal growth device 10 shown, a silicon carbide raw material 17 is placed at the bottom of a graphite crucible 14, a graphite seed crystal holder 12 is fixed on the crucible cover 11, a silicon carbide seed crystal 13 is fixed on the graphite seed crystal holder 12 at the top of the graphite crucible 14, and a porous filter 15 is arranged between the silicon carbide raw material 17 and the silicon carbide seed crystal 13. The graphite crucible 14 is sealed, and the periphery of the bottom of the graphite crucible 14 is heated by a side heater 16. The silicon carbide raw material 17 is decomposed and sublimated into gas phase components under high temperature conditions. The gas phase components are driven by the axial temperature gradient and transported to the silicon carbide seed crystal 13 in the low temperature zone. The gas phase components from which impurities have been filtered by the porous filter 15 are deposited on the surface of the silicon carbide seed crystal 13 to generate a silicon carbide single crystal.

[0029] A first aspect of the present application provides a porous filter comprising a porous substrate and a tantalum carbide (TaC) coating on the pore surfaces of the porous substrate.

[0030] like Figure 2 As shown, the porous filter 15 of the present application is a layered object or a sheet-like object including a porous structure. The porous filter 15 includes a porous substrate 151 and a tantalum carbide coating 153 on the surface of the pores 152 of the porous substrate.

[0031] The inventors have found that by applying the porous filter of the present application to Figure 1 In the silicon carbide single crystal growth device shown. On the one hand, the porous structure of the porous filter of the present application can intercept most of the impurities in the gas phase component of the silicon carbide raw material from the bottom of the graphite crucible, especially the carbon particle impurities, on the porous filter, thereby reducing the probability of impurities such as carbon particles being transmitted with the airflow to the crystal growth surface of the seed crystal at the top of the graphite crucible. On the other hand, since the tantalum carbide coating on the surface of the porous filter of the present application has good high temperature resistance, it can reduce the formation of new sources of carbon inclusions due to the contact reaction between the internal porous graphite sheet or porous silicon carbide sheet and the silicon-rich gas under high temperature conditions, thereby reducing the number of carbon inclusion impurities in the silicon carbide single crystal and improving the crystal quality of the silicon carbide single crystal.

[0032] In one embodiment of the present application, the porous substrate is selected from a porous graphite sheet or a porous silicon carbide sheet; the porosity of the porous filter is 5%-50%, and the pore size is 30-90 μm. By regulating the porosity and pore size of the porous filter within the above range, the porous filter can contain a suitable porous structure to filter and intercept most of the impurities from the gas phase components of the silicon carbide raw material, especially the carbon particle impurities generated by the reaction of the silicon-rich gas and the graphite crucible, thereby reducing the probability of impurities such as carbon particles being transmitted to the crystal growth surface of the seed crystal with the gas flow, reducing crystal contamination, and improving the crystal quality of the silicon carbide single crystal.

[0033] In the present application, the size and shape of the porous filter are not particularly limited, as long as the purpose of the present application can be achieved. For example, the porous filter is a circular layer; the diameter of the porous filter is 150-300 mm, and the thickness is 1-10 mm; for another example, the porous filter is a square layer, the length / width are 150-300 mm, 150-300 mm, and the thickness is 1-10 mm.

[0034] It is easy to understand that in order to achieve the purpose of this application, the size and shape of the porous filter should be consistent with the shape and size of the inner wall of the graphite crucible so that the porous filter can be easily applied to Figure 1 The silicon carbide single crystal growth device 10 is shown.

[0035] In one embodiment of the present application, the thickness of the tantalum carbide coating is 8-50 μm. By regulating the thickness of the high temperature resistant tantalum carbide coating within the above range, the porous matrix inside is prevented from contacting and reacting with the silicon-rich gas in the gas phase component under the high temperature environment of single crystal growth, thereby avoiding the generation of new carbon inclusions; and after the tantalum carbide coating with a thickness within the above range is formed on the pore surface of the porous matrix, the porous filter still contains a suitable porous structure to filter out impurities such as carbon particles in the gas phase component of the silicon carbide raw material, thereby reducing crystal contamination on the growth surface.

[0036] In one embodiment of the present application, the X-ray diffraction spectrum of the tantalum carbide coating has characteristic peaks at 2θ of 34.81°, 40.42°, 58.48°, 69.98° and 73.49°, with an error range of ±0.02°. The inventors found that when the tantalum carbide coating has the characteristic peaks in the above X-ray diffraction spectrum, the tantalum carbide coating has a higher degree of crystallinity. The tantalum carbide coating with the above characteristic peaks is conducive to reducing the crystal defects caused by the presence of a large amount of carbon inclusions during the growth of silicon carbide single crystals, thereby improving the crystal quality of silicon carbide single crystals.

[0037] The second aspect of the present application provides a method for preparing a porous filter, which comprises the following steps:

[0038] Using argon as carrier gas, gaseous tantalum pentachloride (TaCl5) and reaction gas are introduced into the reaction chamber;

[0039] In the reaction chamber, gaseous TaCl5 and reaction gas diffuse into the pores of the porous substrate to carry out chemical vapor deposition reaction, forming a tantalum carbide coating on the surface of the pores to obtain a porous filter.

[0040] In the present application, the device for implementing the method for preparing the porous filter is a high-temperature chemical vapor deposition furnace, referred to as a high-temperature CVD furnace. When preparing the porous filter of the present application, the porous substrate is placed in the reaction chamber of the high-temperature CVD furnace in advance. In addition, the reaction chamber is evacuated to prevent air from affecting the subsequent chemical vapor deposition reaction. Then, using argon as a carrier gas and a protective gas, gaseous tantalum pentachloride and reaction gas are introduced into the reaction chamber, diffused into the pores of the porous substrate for chemical vapor deposition reaction, and the tail gas after the reaction is continuously discharged during the reaction process to promote the chemical vapor deposition reaction equilibrium to move in the positive direction.

[0041] In the present application, there is no special restriction on the model and size of the high temperature CVD furnace, as long as the purpose of the present application can be achieved. For example, a high temperature CVD furnace of appropriate size is selected according to the size of the porous substrate.

[0042] In one embodiment of the present application, the porous substrate is selected from a porous graphite sheet, the reaction gas is selected from hydrogen; the volume flow ratio of gaseous TaCl5, argon and hydrogen is (1-4): (2-5): (2-6); the volume flow ratio of gaseous tantalum pentachloride and the diameter of the porous graphite sheet is (1-4): (1.5-3) mL·min -1 / mm. For example, the flow rate of gaseous tantalum pentachloride is 100-400mL / min, the flow rate of argon is 200-500mL / min, and the flow rate of hydrogen is 200-600mL / min. By regulating the volume flow ratio of gaseous TaCl5, Ar and H2 introduced into the reaction chamber within the above range, gaseous TaCl5 and H2 are subjected to a vapor deposition reaction as shown in the chemical reaction formula (1) in the pores of the porous graphite sheet, thereby forming a tantalum carbide coating on the pore surface of the porous graphite sheet. Among them, gaseous TaCl5 serves as a tantalum source, hydrogen (H2) serves as a reducing gas, the porous graphite sheet itself provides a carbon source, and argon (Ar) serves only as a transport and dilution gas.

[0043]

[0044] In one embodiment of the present application, the porous substrate is selected from a porous silicon carbide sheet, the reaction gas is selected from hydrogen and propylene gas; the volume flow ratio of gaseous TaCl5, argon, hydrogen and propylene gas is (1-4): (2-5): (2-6): (0.5-3); the volume flow ratio of gaseous tantalum pentachloride and the diameter of the porous silicon carbide sheet is (1-4): (1.5-3) mL·min -1 / mm. For example, the flow rate of gaseous tantalum pentachloride is 100-400mL / min, the flow rate of argon is 200-500mL / min, the flow rate of hydrogen is 200-600mL / min, and the flow rate of propylene gas is 50-300mL / min. The inventors found that when the volume flow ratio of gaseous TaCl5, argon, hydrogen and propylene gas introduced into the reaction chamber is within the above range, gaseous TaCl5, H2 and C3H6 react as shown in chemical reaction formula (2) on the pore surface of porous silicon carbide sheet to form tantalum carbide coating. Among them, gaseous TaCl5 is used as tantalum source, hydrogen (H2) is used as reducing gas, propylene gas (C3H6) provides carbon source, and argon (Ar) is only a transport and dilution gas.

[0045]

[0046] In the present application, the volume flow rates of gaseous TaCl5, argon and hydrogen introduced into the reaction chamber are directly proportional to the size of the porous graphite sheet serving as the substrate. For example, when the flow rate of gaseous tantalum pentachloride is 100-400 mL / min, the flow rate of argon is 200-500 mL / min, and the flow rate of hydrogen is 200-600 mL / min, the size of the porous graphite sheet or porous silicon carbide sheet is 150-300 mm in diameter.

[0047] In one embodiment of the present application, the reaction temperature of the chemical vapor deposition reaction is 1300-1700°C, the reaction pressure is 1000-3000Pa, and the reaction time is 2-10h. The inventors found that by regulating the temperature, reaction pressure and reaction time of the chemical vapor deposition reaction within the above respective ranges, the thickness of the tantalum carbide coating formed on the pore surface of the porous silicon carbide sheet is 8-50μm, and the formed tantalum carbide coating has characteristic peaks at 2θ of 34.81°, 40.42°, 58.48°, 69.98° and 73.49°.

[0048] In one embodiment of the present application, gaseous TaCl5 is obtained by gasifying TaCl5 powder in a gasification chamber, with a gasification temperature of 100-300°C and a gasification pressure of 1000-3000 Pa. By regulating the gasification temperature and the gasification pressure within the above range, the TaCl5 powder can be gasified into gaseous TaCl5.

[0049] In the present application, there is no particular restriction on the purity of TaCl5 powder, as long as the purpose of the present application can be achieved. For example, the purity of TaCl5 powder is 90%-99.99%. The present application does not have any particular restriction on the particle size of TaCl5 powder, and those skilled in the art can select it according to actual needs, as long as the purpose of the present application can be achieved.

[0050] The third aspect of the present application provides a use of a porous filter in the growth of a silicon carbide single crystal. By applying the porous filter of the present application to the growth process of a silicon carbide single crystal, the carbon inclusions in the growing silicon carbide single crystal are reduced, thereby improving the crystal quality of the silicon carbide single crystal.

[0051] Example

[0052] Hereinafter, the embodiments of the present application will be described in more detail with reference to Examples and Comparative Examples. Various tests and evaluations were performed according to the following methods.

[0053] Test methods and equipment:

[0054] The pore size and porosity of the porous matrix and porous filter were measured by fully automatic mercury porosimetry.

[0055] The microscopic morphology of the porous filter surface was taken by scanning electron microscopy (SEM), and the thickness of the tantalum carbide coating was measured.

[0056] The XRD characteristic peaks of tantalum carbide on the surface of the porous filter were characterized by an X-ray diffraction (XRD) instrument.

[0057] Average density measurement of carbon inclusions in crystals

[0058] The silicon carbide single crystal prepared in the embodiment and the comparative example was cut and processed into wafers. Using an optical microscope, under a magnification of 50 times, the number of carbon inclusions in the wafer in the field of view was counted, and then divided by the area of ​​the field of view to obtain the density of the carbon inclusions in the wafer. Three wafers of the same silicon carbide single crystal were taken for parallel experiments, and the average value of the three parallel experimental data was finally taken as the average density of the carbon inclusions in the crystal, in units of pieces / cm 2 .

[0059] Example 1

[0060] <Preparation of porous filter>

[0061] A porous graphite sheet with a porosity of 70% and a pore size of 100 μm is placed in a reaction chamber of a high-temperature CVD furnace, and TaCl5 powder is placed in a gasification chamber of the high-temperature CVD furnace, wherein the purity of the TaCl5 powder is 99.99%.

[0062] At a temperature of 200°C and a pressure of 2000Pa, TaCl5 powder is vaporized to form gaseous TaCl5. Using argon as a carrier gas, gaseous TaCl5 and reaction gas are introduced into a reaction chamber of a high-temperature CVD furnace that has been evacuated in advance, wherein the reaction gas is hydrogen, the flow rate of gaseous TaCl5 is 200mL / min, the carrier gas argon is 300mL / min, and the flow rate of hydrogen is 400mL / min. In the reaction chamber, at a reaction temperature of 1500°C and a reaction pressure of 2000Pa, gaseous TaCl5 and hydrogen diffuse into the pores of the porous graphite sheet to carry out a chemical vapor deposition reaction, and a tantalum carbide coating is formed on the pore surface of the porous graphite sheet. After reacting for 5 hours, stop heating and introducing gaseous TaCl5 and reaction gas, wait for the high-temperature CVD furnace to cool, and then take out the prepared porous filter. Among them, the thickness of the tantalum carbide coating on the surface of the porous filter is 25μm, the pore size of the porous filter is 50μm, and the porosity is 17.5%.

[0063] <Growth of Silicon Carbide Single Crystal>

[0064] Silicon carbide single crystals are grown by physical vapor transport. The silicon carbide raw material is placed at the bottom of the graphite crucible, a Φ160mm silicon carbide seed crystal is fixed on the graphite seed crystal holder, and the prepared porous filter is fixed between the silicon carbide raw material and the silicon carbide seed crystal. The crucible is sealed and heated by a side heater to decompose and sublimate the silicon carbide material into gas phase components under high temperature conditions. Driven by the axial temperature gradient, the gas phase components are filtered through a porous filter and then transferred to the seed crystal in the low temperature zone, and deposited and grown on the surface of the silicon carbide seed crystal. The growth pressure is 2000Pa and the growth temperature is 2300℃. After 96 hours of growth, it is annealed in the furnace until the entire ingot cools to room temperature to obtain a silicon carbide single crystal.

[0065] Example 2 to Example 3

[0066] Except for the parameters shown in Table 1, the rest are the same as those in Example 1.

[0067] Example 4

[0068] Except that the porosity of the porous matrix is ​​70%, the pore diameter is 100 μm, and the parameters are as shown in Table 1, the rest are the same as those in Example 1.

[0069] Example 5

[0070] Except that the porosity of the porous matrix is ​​60%, the pore diameter is 80 μm, and the parameters are as shown in Table 1, the rest are the same as those in Example 1.

[0071] Example 6 to Example 8

[0072] Except that the reaction gases are hydrogen and propylene gases and the parameters are as shown in Table 1, the rest are the same as Example 1.

[0073] Example 9

[0074] Except that the porosity of the porous matrix is ​​75%, the pore diameter is 100 μm, and the parameters are as shown in Table 1, the rest are the same as those in Example 1.

[0075] Example 10

[0076] Except that the porosity of the porous matrix is ​​60%, the pore diameter is 80 μm, and the parameters are as shown in Table 1, the rest are the same as those in Example 1.

[0077] Comparative Example 1

[0078] Except for using a porous graphite sheet to replace the porous filter in <Growth of Silicon Carbide Single Crystal> and the parameters shown in Table 1, the rest is the same as Example 1.

[0079] Comparative Example 2

[0080] Except for using a porous silicon carbide sheet to replace the porous filter in <Growth of Silicon Carbide Single Crystal> and the parameters shown in Table 1, the rest is the same as Example 1.

[0081] Table 1

[0082]

[0083] Note: “-” in Table 1 means that there is no corresponding parameter or substance; a " is the volume flow ratio of gaseous tantalum pentachloride, argon and hydrogen. The superscript " b ” is the volume flow ratio of gaseous tantalum pentachloride, argon, hydrogen and propylene gases.

[0084] It can be seen from Table 1 that, compared with Comparative Examples 1-2, the porous filters in Examples 1-10 of the present application are used to grow silicon carbide single crystals to obtain a lower average density of carbon inclusions in the silicon carbide single crystals.

[0085] Figure 3 The XRD spectra of the tantalum carbide coating on the surface of the porous filter prepared in Example 1 and the tantalum carbide (C-TaC) calculated from the single crystal data are given. It can be seen that the tantalum carbide coating on the surface of the porous filter has characteristic peaks at 2θ of 34.81°, 40.42°, 58.48°, 69.98° and 73.49°, corresponding to the characteristic peaks of the XRD spectrum of tantalum carbide (C-TaC) calculated from the single crystal data, and has a high degree of crystallinity. When the porous filter containing the tantalum carbide coating having the above characteristics is used for the growth of silicon carbide single crystals, it can reduce the crystal defects caused by the presence of a large amount of carbon inclusions during the growth of silicon carbide single crystals, thereby improving the crystal quality of silicon carbide single crystals.

[0086] Figure 4 The SEM photo of the porous filter prepared in Example 1 is given. It can be seen that the tantalum carbide coating has a regular structure, uniform distribution, and high crystallinity.

[0087] It can be seen from Examples 1-10 and Comparative Examples 1-2 that when the thickness, pore size and porosity of the tantalum carbide coating of the prepared porous filter are within the scope of the present application, the crystal defects caused by the presence of a large amount of carbon inclusions during the growth of silicon carbide single crystals can be reduced, thereby improving the crystal quality of silicon carbide single crystals.

[0088] In Comparative Examples 1 and 2, porous graphite sheets and porous silicon carbide sheets are used respectively to replace the porous filter provided in the present application. Although they can reduce the carbon inclusions in the initial stage, the porous graphite sheets or porous silicon carbide sheets will become new sources of carbon inclusions under the corrosion of high temperature and silicon-rich gas, which will have the opposite effect of promoting the formation of carbon inclusions, resulting in a sudden increase in the average density of carbon inclusions in the silicon carbide crystals, affecting the crystal quality and yield of the silicon carbide single crystals.

[0089] In the embodiments 1-10 of the present application, the porous filter provided by the present application is placed between the silicon carbide raw material and the silicon carbide seed crystal. On the one hand, the porous structure of the porous filter filters the gas phase components of the silicon carbide raw material, thereby blocking the impurities in the gas phase components, especially the carbon particle impurities in the gas phase components, on the porous filter, thereby reducing the probability of impurities such as carbon particles being transmitted to the crystal growth surface of the seed crystal with the airflow and contaminating the crystal. On the other hand, since the tantalum carbide coating on the surface of the porous filter has good high temperature resistance, the porous matrix inside the porous filter is prevented from becoming a new source of carbon inclusions under the corrosion of high temperature and silicon-rich gas, thereby reducing the carbon inclusions in the silicon carbide single crystal, thereby reducing the crystal defects such as microtubes and dislocations caused by the carbon inclusions, and improving the crystal quality of the grown silicon carbide single crystal.

[0090] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, apparatus or article that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, apparatus or article.

[0091] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0092] The above embodiments are preferred embodiments of the present application and are not intended to limit the protection scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application are included in the protection scope of the present application.

Claims

1. A method for preparing a porous filter, comprising the following steps: Using argon as carrier gas, gaseous tantalum pentachloride and reaction gas are introduced into the reaction chamber; In the reaction chamber, the gaseous tantalum pentachloride and the reaction gas diffuse into the pores of the porous substrate to perform a chemical vapor deposition reaction, forming a tantalum carbide coating on the surface of the pores to obtain the porous filter; The porous matrix is ​​selected from a porous graphite sheet, and the reaction gas is selected from hydrogen; the volume flow ratio of the gaseous tantalum pentachloride, the argon gas and the hydrogen is (1-4): (2-5): (2-6); the volume flow ratio of the gaseous tantalum pentachloride and the diameter of the porous graphite sheet is (1-4): (1.5-3) mL·min -1 / mm; Alternatively, the porous substrate is selected from a porous silicon carbide sheet, the reaction gas is selected from hydrogen and propylene gas; the volume flow ratio of the gaseous tantalum pentachloride, the argon gas, the hydrogen gas and the propylene gas is (1-4): (2-5): (2-6): (0.5-3); the ratio of the volume flow of the gaseous tantalum pentachloride and the diameter of the porous silicon carbide sheet is (1-4): (1.5-3) mL·min -1 / mm; Wherein, the reaction pressure of the chemical vapor deposition reaction is 1000-3000 Pa, the reaction temperature of the chemical vapor deposition reaction is 1300-1700° C., and the reaction time is 2-10 h; The porous filter comprises the porous substrate and a tantalum carbide coating on the pore surface of the porous substrate, wherein the porous substrate is selected from a porous graphite sheet or a porous silicon carbide sheet; the porosity of the porous filter is 5%-50%, and the pore size is 30-90µm; the X-ray diffraction spectrum of the tantalum carbide coating has characteristic peaks at 2θ of 34.81°, 40.42°, 58.48°, 69.98° and 73.49°, with an error range of ±0.02º; the thickness of the tantalum carbide coating is 8-50μm.

2. The preparation method according to claim 1, wherein The gaseous tantalum pentachloride is obtained by gasifying tantalum pentachloride powder in a gasification chamber, the gasification temperature is 100-300° C., and the gasification pressure is 1000-3000 Pa.

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