Silicon carbide dense-pored honeycomb ceramic and method of making

Abstract

The application discloses a silicon carbide dense pore wall honeycomb ceramic and a preparation method thereof. The preparation method comprises the following steps: firstly, preparing a graphite mold with a cavity array matched with a target honeycomb ceramic pore structure; then, depositing silicon carbide on the cavity surface of the graphite mold through a chemical vapor deposition (CVD) technology; realizing one-time integral molding of the silicon carbide dense pore wall honeycomb ceramic; and finally, removing the graphite mold tightly combined with the silicon carbide blank through demolding treatment and post-processing, so as to obtain the silicon carbide dense pore wall honeycomb ceramic. The silicon carbide dense pore wall honeycomb ceramic is prepared by adopting the CVD process, the product has excellent characteristics such as high purity and high thermal conductivity, and the pore wall of the product is free of connected micropores and has high density, so that secondary pollution caused by adsorption and desorption of other gases and particle shedding in the gas shunting process is avoided, and the product meets the demand of advanced semiconductor process ultra-high cleanliness.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, specifically to a silicon carbide dense-walled honeycomb ceramic and its preparation method. Background Technology

[0002] Honeycomb ceramics are composed of parallel, interconnected channels in a honeycomb pattern and thin-walled structures. Based on the microstructure of the pore walls, they can be divided into two types: porous wall and dense wall. Porous wall honeycomb ceramics contain numerous interconnected micropores in their pore walls and are mainly used in filtration, separation, and catalytic reactions. Dense wall honeycomb ceramics, on the other hand, have no interconnected micropores in their pore walls, resulting in high density and superior mechanical strength. This prevents secondary pollution caused by the adsorption / desorption of other gases and particle shedding during gas separation. Silicon carbide itself possesses excellent properties such as high-temperature stability, strong corrosion resistance, high thermal conductivity, and a low coefficient of thermal expansion. Therefore, silicon carbide dense wall honeycomb ceramics are widely used in semiconductor manufacturing, meeting the requirements of ultra-high cleanliness processes and serving as precision airflow control components.

[0003] Extrusion molding has become the mainstream molding process for silicon carbide porous honeycomb ceramics due to its outstanding production efficiency. However, in order to ensure good continuous extrusion properties of the clay, this process usually requires the clay to have a high moisture content and a relatively low extrusion pressure. This results in a low density of the green body after molding, making it difficult to obtain dense silicon carbide honeycomb ceramics through sintering.

[0004] Currently, the mainstream forming method for silicon carbide dense-walled honeycomb ceramics is a two-step process: "densification followed by machining to create the openings." This involves first preparing a dense silicon carbide ceramic preform, and then machining the pre-designed honeycomb channel structure. The advantage of this process is that the shape, size, and spatial distribution of the channels can be freely designed, offering extremely high process flexibility. However, this process also faces insurmountable technical bottlenecks: From an equipment and technical requirements perspective, due to the extremely high hardness and wear resistance of silicon carbide, the process requires diamond tools, and the processing cycle is long; the complex honeycomb channel structure and stringent dimensional accuracy requirements necessitate multiple cutting heads on the equipment to ensure one-time forming, avoiding alignment problems caused by downtime for cutting head replacement. From a cleanliness perspective, this process inevitably generates a large amount of scattered silicon carbide debris. This debris easily adheres firmly to the inner wall of the processed channels through electrostatic adsorption, and even subsequent cleaning processes are difficult to completely remove, posing a serious risk of particulate contamination to subsequent high-cleanliness semiconductor manufacturing processes.

[0005] Therefore, it is still necessary to develop a new method for preparing silicon carbide dense porous wall honeycomb ceramics to solve the problems existing in the above-mentioned technologies. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a silicon carbide dense-walled honeycomb ceramic and its preparation method. The core of this method lies in first preparing a graphite mold with a cavity array that matches the pore structure of the target honeycomb ceramic, and then directionally depositing silicon carbide on the cavity surface of the graphite mold using chemical vapor deposition (CVD) technology, thereby achieving one-time integral molding of the silicon carbide dense-walled honeycomb ceramic.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A silicon carbide dense-walled honeycomb ceramic, characterized by having the same diffraction peak positions as conventional β-SiC, and whose diffraction peaks differ from those of conventional β-SiC when measured using Cu Kα lines by powder X-ray diffraction:

[0009] (220) Crystal plane diffraction peak (corresponding to 2θ value of 59.99°) 0.2°) or (111) crystal plane diffraction peak (corresponding to 2θ value of 36.67°) 0.2°) One of them is the highest diffraction peak, and the other crystal plane diffraction peak is the second highest diffraction peak; the peak height of the highest diffraction peak is the same as that of the (200) crystal plane diffraction peak (corresponding to a 2θ value of 41.40°). The peak height ratio of 0.2° is greater than 10. In a special case, when the diffraction peak of the (200) crystal plane is extremely weak, there may be no obvious diffraction peak of the (200) crystal plane, and the peak height ratio is close to infinity.

[0010] In some specific implementation schemes, GDMS testing shows that the purity of the silicon carbide dense pore wall honeycomb ceramic can reach over 99.99%.

[0011] Preferably, the porosity of the ceramic portion is less than 0.5%;

[0012] More preferably, the overall thickness of the ceramic is 1-10 mm, and the thickness of the pore wall is 0.2-3 mm;

[0013] Preferably, the silicon carbide dense pore wall honeycomb ceramic has honeycomb ceramic pores with any regular or irregular shape, and the pores in the same honeycomb ceramic can have one or more shapes and / or sizes; more preferably, the honeycomb ceramic pores can be through or not through in the thickness direction, and can be arranged regularly or irregularly in the ceramic surface.

[0014] In some specific implementations, the silicon carbide dense porous wall honeycomb ceramic material contains 1-10 wt% free carbon.

[0015] In another aspect of the present invention, the method for preparing the aforementioned silicon carbide dense porous wall honeycomb ceramic includes the following steps:

[0016] S1. Preparation of a graphite mold with a cavity: A cavity matching the target honeycomb ceramic channel structure is formed on the surface of a graphite plate by machining to obtain a graphite mold with a cavity.

[0017] S2. Preparation of silicon carbide preform by chemical vapor deposition: The graphite mold with cavity is placed in a CVD deposition furnace, and the reaction gas and carrier gas are continuously introduced. The deposition process parameters are controlled so that silicon carbide is directionally deposited in the cavity area of ​​the mold to obtain a silicon carbide preform that is complementary to the cavity structure of the graphite mold.

[0018] S3. Demolding and post-processing: The graphite mold that is tightly bonded to the silicon carbide blank is removed by the post-processing process to obtain silicon carbide dense pore wall honeycomb ceramic.

[0019] In some specific implementation schemes, in step S1, the graphite mold is purified after processing and forming, and the impurity content of the purified graphite mold is less than 50 ppm, preferably less than 10 ppm.

[0020] In some specific implementations, in step S1, the cavity depth on the graphite plate is 1-10 mm, and the cross-sectional size is 0.2-3 mm;

[0021] Preferably, the cavities on the graphite plate are distributed in an array, and the horizontal cross-sectional shape of the protrusion structure formed by adjacent cavities is preferably any regular or irregular shape, such as a circle, triangle, square or hexagon.

[0022] More preferably, the outer edge of the cavity opening on the graphite plate is designed with an outer rounded corner, and the inner edge inside the cavity is designed with an inner rounded corner;

[0023] More preferably, the radii of the outer and inner fillets are 0.1-1 mm and do not exceed 1 / 4 of the cavity depth.

[0024] In some specific implementation schemes, in step S2, the inlet direction of the reaction gas and the carrier gas is perpendicular to the plate surface of the graphite mold and directly opposite the upper cavity area of ​​the graphite mold.

[0025] Preferably, the air intake direction is tilted at 2-15° relative to the direction perpendicular to the plate surface.

[0026] In some specific implementation schemes, in the CVD deposition process of step S2, methyltrichlorosilane (MTS) gas is used as the single reaction gas to simultaneously provide silicon and carbon sources; or, silane or trichlorosilane is used as the silicon source gas and propane or ethylene is used as the carbon source gas; and hydrogen is used as the carrier gas.

[0027] Preferably, the working gas pressure in the CVD deposition furnace is 5-50 kPa, and the deposition temperature is 1100-1600℃;

[0028] More preferably, the volumetric flow rate ratio of the carrier gas to the reactant gas is (2-40):1.

[0029] In some specific implementation schemes, in step S3, the post-processing includes at least one of machining, sandblasting, high-temperature oxidation and burning, and pickling;

[0030] Preferably, the process conditions for high-temperature oxidation to remove residual graphite are: heat treatment at 700-1000℃ for 0.5-2 hours in an air atmosphere.

[0031] In some specific implementation plans, the pickling operation steps include:

[0032] a) First, prepare an acid solution with a volume ratio of 48wt% hydrofluoric acid to deionized water of 1:(0.5-4);

[0033] b) The silicon carbide preform is then immersed in it for 5-60 minutes, and after immersion, it is rinsed repeatedly with plenty of deionized water.

[0034] c) Finally, air dry naturally to complete the pickling process.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] This invention uses a graphite mold with a cavity combined with CVD process to prepare silicon carbide dense porous honeycomb ceramics in one integral molding process. Compared with the traditional two-step method of "densification first and then machining to open the holes", it avoids the high threshold and long cycle of machining equipment caused by the high hardness of silicon carbide, and eliminates the risk of contamination from processing debris. At the same time, the graphite mold is easy to process and the cavity design is flexible, realizing a high degree of design freedom and low-cost preparation of the product.

[0037] This invention uses CVD process to prepare silicon carbide dense pore wall honeycomb ceramics. The product has excellent properties such as high purity and high thermal conductivity. Moreover, its pore walls have no interconnected micropores and high density, which eliminates secondary pollution caused by the adsorption and desorption of other gases and particle shedding during gas splitting. It meets the ultra-high cleanliness requirements of advanced semiconductor processes. Attached Figure Description

[0038] Figure 1 This is an XRD pattern of a silicon carbide dense porous honeycomb ceramic according to the present invention.

[0039] Figure 2 This is an XRD pattern of another silicon carbide dense porous wall honeycomb ceramic according to the present invention.

[0040] Figure 3 This is a top view of a honeycomb ceramic with regularly distributed through holes according to the present invention.

[0041] Figure 4 This is a top view of another type of honeycomb ceramic with regularly distributed through holes according to the present invention.

[0042] Figure 5 This is a top view of a honeycomb ceramic with other types of through-hole distributions according to the present invention.

[0043] Figure 6 This is a top view of a honeycomb ceramic with another type of through-hole distribution according to the present invention.

[0044] Figure 7 For the present invention and Figure 1 A schematic diagram of a graphite mold corresponding to one of the honeycomb ceramics.

[0045] Figure 8 This is a schematic diagram of the silicon carbide preform before demolding according to the present invention.

[0046] Figure 9 For the present invention Figure 8 Enlarged view of a section and a schematic diagram of the processing progress.

[0047] Among them, 1 is a dense hole wall, 2 is a square hole, 3 is a circular hole, 4 is an array of cavities, 5 is a protruding structure, 6 is a graphite substrate, 7 is a silicon carbide preform, 8 is a redundant silicon carbide layer, 9 is the rounded corner of the silicon carbide preform, 10 is the retained silicon carbide preform, and 11 is the removed graphite layer. Detailed Implementation

[0048] To make the technical problem to be solved by the present invention, the technical solution, and the beneficial effects clearer, the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0049] The first aspect of this invention provides a silicon carbide dense porous wall honeycomb ceramic, which has the following characteristics:

[0050] The silicon carbide ceramic material has the same diffraction peak positions as conventional β-SiC. Powder X-ray diffraction using Cu Kα lines determined the highest diffraction peak to be the (220) crystal plane diffraction peak (corresponding to a 2θ value of 59.99°). 0.2°) or (111) crystal plane diffraction peak (corresponding to 2θ value of 36.67°) (0.2°), the diffraction peak of the other crystal plane among the two crystal planes is the second highest diffraction peak, such as Figure 1 , Figure 2 As shown; the highest diffraction peak height is similar to that of the (200) crystal plane diffraction peak (corresponding to a 2θ value of 41.40°). The peak height ratio is 10 or higher, for example, the peak height ratio is 12, 15, 20, 25, 30, 40, 50, 100, 500, 1000, etc.; a more special extreme case is that when the diffraction peak of the (200) crystal plane is extremely weak, there may be no obvious diffraction peak of the (200) crystal plane, and the peak height ratio is close to infinity.

[0051] In certain applications, to increase gas uniformity or avoid discharge phenomena, the CVD process can be controlled to ensure the final product phase is silicon carbide with 1-10 wt% free carbon (preferably 1 wt%-5 wt%), thereby improving the material's thermal conductivity and reducing its volume resistivity. For example, in CVD deposition using methyltrichlorosilane (MTS) gas as the reactant and hydrogen as the carrier gas, a smaller carrier gas to reactant gas volumetric flow rate ratio, a lower reaction temperature, and a lower vacuum (e.g., 4:1, 1200℃, 25 kPa) can yield a final product containing a small amount of free carbon. Figure 1 As shown. Alternatively, a two-component reaction gas can be used, with the proportion of carbon source gas slightly higher than that of silicon source gas. For example, silane can be used as the silicon source gas and propane as the carbon source gas, with a silane:propane ratio of 1.05. The test method for free carbon can refer to commonly used methods in the industry, such as GB / T 3045-2017.

[0052] The silicon carbide dense-walled honeycomb ceramic of the present invention has a dense honeycomb structure. From a top view, the shape of the holes can be any regular or irregular shape, preferably circular, triangular, square, or hexagonal. Within the same honeycomb ceramic, one or more shapes and sizes can exist. The holes can be continuous or incompletely continuous in the thickness direction, and can be arranged regularly or irregularly within the ceramic surface. For example, an array arrangement consisting of dense-walled holes 1 and regular or irregular shapes such as square holes 2 or circular holes 3, specifically as follows... Figure 3 , Figure 4 , Figure 5 As shown. For example... Figure 6 The circular honeycomb ceramic has a central area with densely distributed small pores, which gradually transitions to sparsely distributed large pores from the center to the edge area. This structure can improve the uniformity of the flow field after the gas flows through.

[0053] The ceramic of this invention has extremely high purity, reaching over 99.99% as measured by GDMS; the porosity of the ceramic portion is less than 0.5%; in terms of dimensions, the overall thickness of the ceramic is 1-10 mm, and the pore wall thickness is 0.2-3 mm. The pore wall thickness of this invention refers to the distance between two adjacent pores.

[0054] In this invention, the aforementioned silicon carbide dense porous wall honeycomb ceramic can be prepared by the following method, specifically including the following steps:

[0055] S1. Preparation of a graphite mold with a cavity: A cavity matching the target honeycomb ceramic channel structure is formed on the surface of a graphite plate by machining, thus obtaining a graphite mold with a cavity.

[0056] like Figure 7 As shown, cavities 4 are first formed on the surface of a graphite substrate 6 in an array that matches the target honeycomb ceramic channel structure. The cavities surround a protruding structure 5, for example, with a square cross-section, thereby obtaining a graphite mold with cavities.

[0057] S2. Preparation of silicon carbide preform by chemical vapor deposition: The graphite mold with cavity is placed in a CVD deposition furnace, and reaction gas and carrier gas are continuously introduced. The deposition process parameters are controlled to make silicon carbide be deposited in the cavity area of ​​the mold in a directional manner, so as to obtain a silicon carbide preform that is complementary to the cavity structure of the graphite mold.

[0058] Undemolded silicon carbide preform, such as Figure 8 As shown, the surface of the graphite substrate 6 originally has a raised structure 5 and a cavity. Silicon carbide is deposited in the cavity to form a silicon carbide preform 7 that is complementary to the cavity structure of the graphite mold.

[0059] S3. Demolding and post-processing: The silicon carbide blank is processed by machining, sandblasting, high-temperature oxidation and sintering, and pickling in sequence to remove the graphite mold that is tightly bonded to the silicon carbide blank, so as to obtain silicon carbide dense pore wall honeycomb ceramic.

[0060] Specifically, such as Figure 9 As shown, the method for removing the graphite mold in step S3 specifically includes the following steps:

[0061] S3-1. Take out the silicon carbide blank with graphite mold that has been deposited in step S2. First, perform a grinding and thinning process on its deposited surface to remove the redundant silicon carbide layer 8. Then, use machining to remove the graphite layer under the silicon carbide blank, that is, remove the removed graphite layer 11.

[0062] S3-2. The silicon carbide preform is sandblasted with quartz sand to initially remove the graphite residue in the honeycomb channels. Since the hardness of quartz sand is much lower than that of silicon carbide but higher than that of graphite, it can efficiently remove graphite with almost no damage to the silicon carbide preform.

[0063] S3-3. High-temperature oxidation to remove residual graphite. The sandblasted silicon carbide blank is subjected to high-temperature oxidation treatment to completely burn off the residual graphite. The specific conditions for this process are: holding at a temperature range of 700-1000℃ for 0.5-2 hours in an air atmosphere.

[0064] S3-4. Remove impurities such as silicon oxide from the surface of silicon carbide by pickling. The specific pickling operation steps are as follows: First, prepare an acid solution with a volume ratio of 48wt% hydrofluoric acid to deionized water of 1:(0.5-4). Then, immerse the silicon carbide blank in the solution for 5-60 minutes. After immersion, rinse repeatedly with a large amount of deionized water and finally air dry to complete the pickling process.

[0065] As a preferred embodiment, for honeycomb ceramic areas with wider channels, the original method involves first performing quartz sand blasting followed by high-temperature oxidation. For honeycomb ceramic areas with narrower channels, the quartz sand blasting step can be skipped, and high-temperature oxidation can be performed directly. This further improves production efficiency. "Wideer channels" refers to a minimum cross-sectional area of ​​the through-holes in the horizontal section of the honeycomb ceramic exceeding 3 mm². 2 Conversely, the channel is narrower.

[0066] As a preferred embodiment, the outer edge of the cavity opening on the graphite plate is designed with an outer rounded corner, and the inner edge of the cavity is designed with an inner rounded corner; the radii of both the outer and inner rounded corners are 0.1-1 mm and do not exceed 1 / 4 of the cavity depth. The outer rounded corner design optimizes the airflow path, facilitating the entry and uniform deposition of reactive gases inside the cavity; the inner rounded corner design avoids the formation of deposition dead zones, preventing localized deposition difficulties from affecting the overall deposition quality of the silicon carbide preform. When using this embodiment, in step S3-1, after removing the graphite layer beneath the silicon carbide preform, a second grinding and thinning process is required on both the upper and lower surfaces of the silicon carbide preform until the rounded corners 9 of the silicon carbide preform are removed, leaving the remaining portion as the retained silicon carbide preform 10.

[0067] As a preferred embodiment, in step S2, the inlet direction of the reactant gas and carrier gas is perpendicular to the surface of the graphite mold and directly facing the upper cavity area of ​​the graphite mold; more preferably, the inlet direction is inclined at 2-15° relative to the direction perpendicular to the surface. By adopting an inclined inlet design, the airflow circulation in the furnace can be effectively optimized, which facilitates the rapid escape of reaction waste gas and reduces the retention of waste gas inside the cavity, thereby further improving the deposition quality and uniformity of silicon carbide.

[0068] This invention first prepares a graphite mold with a cavity array matching the target honeycomb ceramic pore structure, then uses chemical vapor deposition (CVD) technology to directionally deposit silicon carbide on the cavity surface of the graphite mold, achieving one-time integral molding of silicon carbide dense-walled honeycomb ceramic. After demolding and post-processing, the graphite mold, tightly bonded to the silicon carbide preform, is removed, resulting in silicon carbide dense-walled honeycomb ceramic. This invention uses CVD technology to prepare silicon carbide dense-walled honeycomb ceramic, resulting in a product with excellent properties such as high purity and high thermal conductivity. Furthermore, its pore walls are free of interconnected micropores, exhibiting high density and eliminating secondary pollution caused by the adsorption and desorption of other gases and particle shedding during gas splitting, thus meeting the ultra-high cleanliness requirements of advanced semiconductor processes.

[0069] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A silicon carbide dense porous wall honeycomb ceramic, characterized in that, The silicon carbide dense-walled honeycomb ceramic has the following characteristics: it has the same diffraction peak positions as conventional β-SiC, and when measured by powder X-ray diffraction using Cu Kα lines, the main difference between its diffraction peaks and those of conventional β-SiC is: (220) Crystal plane diffraction peak (corresponding to 2θ value of 59.99°) 0.2°) or (111) crystal plane diffraction peak (corresponding to 2θ value of 36.67°) 0.2°) One of them is the highest diffraction peak, and the other crystal plane diffraction peak is the second highest diffraction peak; the peak height of the highest diffraction peak is the same as that of the (200) crystal plane diffraction peak (corresponding to a 2θ value of 41.40°). The ratio of peak height to peak height (0.2°) is greater than 10.

2. The silicon carbide dense porous wall honeycomb ceramic according to claim 1, characterized in that, According to GDMS testing, the purity of the silicon carbide dense pore wall honeycomb ceramic can reach over 99.99%. Preferably, the porosity of the ceramic portion is less than 0.5%; more preferably, the overall thickness of the ceramic is 1-10 mm, and the pore wall thickness is 0.2-3 mm. Preferably, the silicon carbide dense pore wall honeycomb ceramic has honeycomb ceramic pores with any regular or irregular shape, and the pores in the same honeycomb ceramic can have one or more shapes and / or sizes; more preferably, the honeycomb ceramic pores can be through or not through in the thickness direction, and can be arranged regularly or irregularly in the ceramic surface.

3. The silicon carbide dense porous wall honeycomb ceramic according to claim 1 or 2, characterized in that, The silicon carbide dense porous wall honeycomb ceramic contains 1-10 wt% free carbon.

4. The method for preparing silicon carbide dense porous wall honeycomb ceramic according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Preparation of a graphite mold with a cavity: A cavity matching the target honeycomb ceramic channel structure is formed on the surface of a graphite plate by machining to obtain a graphite mold with a cavity. S2. Preparation of silicon carbide preform by chemical vapor deposition: The graphite mold with cavity is placed in a CVD deposition furnace, and the reaction gas and carrier gas are continuously introduced. The deposition process parameters are controlled so that silicon carbide is directionally deposited in the cavity area of ​​the mold to obtain a silicon carbide preform that is complementary to the cavity structure of the graphite mold. S3. Demolding and post-processing: The graphite mold that is tightly bonded to the silicon carbide blank is removed by the post-processing process to obtain silicon carbide dense pore wall honeycomb ceramic.

5. The preparation method according to claim 4, characterized in that, In step S1, the graphite mold is purified after processing and forming. After purification, the impurity content of the graphite mold is less than 50 ppm, preferably less than 10 ppm.

6. The preparation method according to claim 4 or 5, characterized in that, In step S1, the cavity depth on the graphite plate is 1-10 mm, and the cross-sectional dimension is 0.2-3 mm. Preferably, the cavities on the graphite plate are distributed in an array, and the horizontal cross-sectional shape of the protrusion structure formed by adjacent cavities is preferably any regular or irregular shape, such as a circle, triangle, square or hexagon. More preferably, the outer edge of the cavity opening on the graphite plate is designed with an outer rounded corner, and the inner edge inside the cavity is designed with an inner rounded corner; More preferably, the radii of the outer and inner fillets are 0.1-1 mm and do not exceed 1 / 4 of the cavity depth.

7. The preparation method according to claim 4, characterized in that, In step S2, the inlet direction of the reaction gas and the carrier gas is perpendicular to the plate surface of the graphite mold and directly opposite the upper cavity area of ​​the graphite mold. Preferably, the air intake direction is tilted at 2-15° relative to the direction perpendicular to the plate surface.

8. The preparation method according to claim 4 or 7, characterized in that, In the CVD deposition process of step S2, methyltrichlorosilane (MTS) gas is used as the single reaction gas to simultaneously provide silicon and carbon sources; alternatively, silane or trichlorosilane is used as the silicon source gas and propane or ethylene is used as the carbon source gas; hydrogen is used as the carrier gas. Preferably, the working gas pressure in the CVD deposition furnace is 5-50 kPa, and the deposition temperature is 1100-1600℃; More preferably, the volumetric flow rate ratio of the carrier gas to the reactant gas is (2-40):

1.

9. The preparation method according to claim 4, characterized in that, In step S3, the post-processing includes at least one of machining, sandblasting, high-temperature oxidation and annealing, and pickling. Preferably, the process conditions for high-temperature oxidation to remove residual graphite are: heat treatment at 700-1000℃ for 0.5-2 hours in an air atmosphere.

10. The preparation method according to claim 9, characterized in that, The pickling process includes: a) First, prepare an acid solution with a volume ratio of 48wt% hydrofluoric acid to deionized water of 1:(0.5-4); b) The silicon carbide preform is then immersed in it for 5-60 minutes, and after immersion, it is rinsed repeatedly with plenty of deionized water. c) Finally, air dry naturally to complete the pickling process.

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