Graphite top cover for SiC epitaxial machine and processing method thereof

Abstract

This invention relates to a graphite top cover for a SiC epitaxial machine and its processing method. The graphite top cover includes a graphite top plate and a central hole formed at the center of the graphite top plate. The graphite top plate is made of high thermal conductivity isostatic graphite, which has a thermal conductivity ≥200 W / (m·K) in the temperature range of 20-1000℃, a bending strength ≥35 MPa at room temperature, and a bending strength ≥25 MPa at 1500℃. The diameter of the central hole is 200-350 mm. The processing method includes the following steps: preparing a high thermal conductivity isostatic graphite blank; cutting a blank from the high thermal conductivity isostatic graphite blank and machining an initial hole; finishing the blank and the initial hole to obtain the graphite top plate and the central hole, the diameter of which is 200-350 mm; and polishing, cleaning, and drying to obtain the graphite top cover for the SiC epitaxial machine. This invention not only significantly extends the service life of graphite top cover components and reduces equipment maintenance costs, but also simultaneously improves the stability and product yield of SiC epitaxial processes.

Description

Technical Field

[0001] This invention relates to the field of semiconductor equipment, and in particular to a graphite top cover for a SiC epitaxial machine and its processing method. Background Technology

[0002] SiC epitaxial multi-wafer stage is a device used to simultaneously realize the epitaxial growth of multiple SiC substrate wafers. Among them, the graphite top cover (Celing) is the core component at the top of the reaction chamber of the stage, which undertakes important functions such as sealing the reaction chamber, assisting temperature control, and guiding the distribution of process gases. Its structural integrity and high temperature resistance stability directly determine the continuity of the epitaxial process and the product yield. However, existing SiC epitaxial multi-wafer machines commonly suffer from severe cracking failures in their Celing components, becoming a key bottleneck restricting continuous machine operation time and increasing production costs. During actual operation, the Celing components exhibit a significant temperature difference exceeding 300°C in the axial direction (i.e., the radial direction from the component's center to its perimeter, commonly referred to in the industry as the "axial direction"). This temperature difference is characterized by a "lower temperature at the center and higher temperature at the perimeter." This is because the machine's heating system is mostly arranged around the reaction chamber, resulting in significant heat attenuation during heat transfer to the center. Consequently, the perimeter of the Celing component remains in a high-temperature region (typically 1500-1700°C) for extended periods, while the central region, being far from the heating source and potentially affected by cooling airflow, experiences a significantly lower temperature (typically 1200-1400°C). This large temperature difference between the center and the periphery causes drastic thermal deformation differences in Celing components: the periphery of the component experiences greater thermal expansion due to high temperature, while the central region experiences less thermal expansion due to low temperature, creating strong thermal stress between the two. When this thermal stress exceeds the mechanical bearing limit of the isostatic graphite used in the Celing component (the room temperature bending strength of isostatic graphite is typically 20-40 MPa), cracks will begin to appear in the Celing component from the area with the largest temperature gradient (mostly the transition area between the center and the periphery), and the cracks will continue to expand with temperature cycle (each process heating and cooling will repeatedly generate thermal stress), eventually leading to complete cracking and failure of the component. Current technologies often address the cracking problem of Celing components by increasing component thickness or optimizing heating power distribution. However, increasing thickness leads to increased heat capacity and slower temperature control response, and cannot fundamentally eliminate thermal stress. Optimizing heating power distribution is limited by the heating structure design of multi-plate machines, making it difficult to effectively reduce axial temperature differences exceeding 300°C, thus failing to completely eliminate the cracking risk. Statistics show that the average lifespan of existing Celing components is only 3-6 months. Each replacement requires 8-12 hours of downtime and incurs high component procurement costs (a single component typically costs over 50,000 yuan), severely impacting the mass production efficiency and economics of SiC epitaxial manufacturing. Summary of the Invention

[0003] This invention provides a graphite top cover for a SiC epitaxial machine, comprising a graphite top plate and a central hole at the center of the graphite top plate. The graphite top plate is made of high thermal conductivity isostatically pressed graphite, which has a thermal conductivity ≥200 W / (m·K) in the temperature range of 20-1000℃, a bending strength ≥35 MPa at room temperature, and a bending strength ≥25 MPa at 1500℃. The diameter of the central hole is 200-350 mm. The overall dimensions of the graphite top cover component are typically 800-1200 mm, and the specific diameter of the central hole needs to be selected based on the overall dimensions of the graphite top cover component and the gas flow field design of the machine's reaction chamber.

[0004] Preferably, the thickness of the graphite top plate is 7-12 mm.

[0005] A method for processing a graphite top cover for a SiC epitaxial machine includes the following steps: High thermal conductivity isostatic graphite blanks are prepared with the following properties: thermal conductivity ≥200W / (m・K) in the temperature range of 20-1000℃, flexural strength ≥35MPa at room temperature, and flexural strength ≥25MPa at 1500℃. A blank is cut from the high thermal conductivity isostatic graphite blank, and an initial hole is cut out. The blank and the initial hole are precision machined to obtain a graphite top plate and a center hole of the target size, wherein the diameter of the center hole is 200-350mm; After polishing, cleaning, and drying, a graphite top cover for SiC epitaxial machine is obtained.

[0006] Preferably, the steps for preparing high thermal conductivity isostatically pressed graphite blanks include: Flake graphite, aramid film fragments and pitch are mixed in a mass ratio of (15-20):(1-3):(2-4), heated and stirred, and then crushed to obtain a mixed powder. The mixed powder is subjected to isostatic pressing to obtain the billet; The billet is subjected to plasma sintering to obtain a high thermal conductivity isostatically pressed graphite billet. Testing shows that the radial thermal conductivity of the graphite top cover is not less than 220 W / (m·K), the flexural strength at room temperature is ≥35 MPa, and the flexural strength at 1500℃ is ≥25 MPa.

[0007] Flake graphite is the dominant thermal aggregate; aramid film fragments are obtained by breaking down para-aramid (poly(p-phenylene terephthalamide)) films, which, during subsequent high-temperature graphitization, promote highly ordered growth of graphite crystals due to the inherent orientation of their polymer chains; pitch serves as a binder and carbon source. Under specific proportions, these three components can form a dense, highly oriented, and low-defect composite structure after sintering, which is the core of the formulation for achieving a thermal conductivity of ≥200 W / (m·K).

[0008] In a preferred embodiment, the aramid film fragments are obtained by cryogenic pulverization of para-aramid films and are in sheet form. Preferably, the process includes the following steps: selecting a para-aramid film with a thickness of 10-50 micrometers; cutting the aramid film into small pieces with an area no larger than 1cm × 1cm; completely immersing the aramid film pieces in liquid nitrogen (-196℃) for 15-20 minutes to fully embrittle them; placing the embrittled aramid film pieces in a high-energy ball mill or a dedicated cryogenic pulverizer for pulverization, and then immediately classifying and sieving them using a standard sieve to obtain aramid film fragments of the target size.

[0009] Preferably, the heating and stirring temperature is 220-250℃, and the heating time is 30-90 minutes. Precise temperature and time control achieves microscale homogenization of the raw materials, avoiding localized performance weaknesses caused by uneven mixing. This ensures that the asphalt completely melts and evenly coats each graphite and aramid fragment, forming a highly homogeneous plastic paste.

[0010] Preferably, the particle size of the flake graphite is 80-150 micrometers, the particle size of the aramid film fragments is 50-200 micrometers, and the particle size of the mixed powder is 70-100 micrometers.

[0011] Preferably, the isostatic pressing pressure is 180-220 MPa, the holding time is 30-40 minutes, and the pressure increase / decrease rate is 2-5 MPa / s. This process yields green bodies with high density, low porosity, and good isotropy. High pressure ensures density, while slow pressure increases / decreases prevent density gradients or cracks from forming within the green body.

[0012] Preferably, the plasma sintering steps include: heating to 600°C at a rate of 3-5°C / h under a nitrogen atmosphere, then heating to 1000-1200°C at a rate of 8-10°C / h and holding at that temperature for 12-24 hours; then heating to 2400-2600°C at a rate of 8-10°C / h and holding at that temperature for 2-4 hours. The low-temperature stage (600-1200°C) allows the organic matter to decompose slowly and removes volatiles, preventing bubbling and cracking in the subsequent high-temperature stage.

[0013] In the high-temperature section (2400-2600℃), under the activation of plasma, carbon atoms are rearranged into perfect graphite crystals and finally densified, thereby obtaining a billet with high thermal conductivity and high strength.

[0014] Preferably, the material is cut using a diamond cutting machine, leaving a machining allowance of 1-2mm, and a preliminary hole is machined using a diamond tool. The diameter of the preliminary hole is 3-10mm smaller than the target size.

[0015] Preferably, polishing is performed using diamond polishing paste, followed by ultrasonic cleaning with isopropanol for 5-10 minutes, rinsing with water for 5-10 minutes, and drying at 100-120℃. After finishing, the diameter tolerance of the center hole is controlled within ±0.05mm, and the surface roughness Ra≤1.6μm. During the polishing process, three levels of polishing can be performed sequentially using diamond polishing paste with grit sizes of W7, W3.5, and W1.5.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention selects isostatically pressed graphite with "high thermal conductivity and suitable mechanical properties." The high thermal conductivity accelerates heat transfer within the graphite cap component, improving the efficiency of heat conduction from the "high temperature around the perimeter" to the "low temperature in the center," effectively reducing the temperature gradient between the center and perimeter and minimizing thermal stress generation at its source. The suitable mechanical properties enhance the material's resistance to thermal stress, making it less likely to reach the cracking threshold even with some thermal stress. Simultaneously, this invention optimizes the structure of the central hole, significantly reducing the "low-temperature zone area" in the center of the graphite cap component. The central hole also more efficiently guides the flow of hot or temperature-controlled airflow within the machine, breaking the original "low-temperature stagnation in the center" pattern. The airflow within the central hole carries some heat from the perimeter to the center, reducing the temperature difference and thermal stress. Furthermore, the enlarged central hole reduces the amount of material used in the central area of ​​the graphite cap component, further reducing thermal deformation constraints in the center and preventing "center-perimeter" thermal stress. The stress concentration caused by excessive deformation differences further reduces the risk of cracking at the structural level. The optimized graphite top cover component has a smaller temperature difference and more uniform thermal deformation, which can ensure the long-term stability of the sealing performance inside the reaction chamber (avoiding gas leakage caused by component deformation) and reduce the risk of graphite particle contamination caused by component cracking. In addition, the more uniform temperature distribution can also improve the uniformity of epitaxial layer thickness of multiple SiC substrates.

[0017] Finite element simulations and / or laboratory prototype tests revealed that the heat transfer efficiency from the "high temperature around the perimeter" to the "low temperature in the center" region was improved by more than 50%, the temperature difference between the center and the perimeter decreased from over 300℃ to below 200℃, thermal stress decreased by 40%-60%, and the material's mechanical strength limit increased by more than 20%. The cracking rate of the graphite top cover component decreased from over 85% in the existing technology to below 10%. The average service life of the graphite top cover component was extended from 3-6 months to 12-18 months, and the component replacement frequency was reduced by more than 70%. This not only reduced downtime maintenance time (by 40-60 hours per year) but also reduced the annual procurement cost of graphite top cover components per machine by 60%-70%. The epitaxial layer thickness uniformity error of the SiC substrate was reduced from ±5% to within ±3%. Detailed Implementation

[0018] The present invention will now be described in more detail. It should be noted that the description of the present invention is illustrative only and not restrictive. Various embodiments can be combined with each other to form other embodiments not shown in the following description.

[0019] Preparation Example Aramid film fragments were obtained through the following steps: A para-aramid film with a thickness of 25 μm was selected; it was cut into small pieces of 1 cm × 1 cm and immersed in liquid nitrogen (-196 °C) for 15 minutes to fully embrittle it; the embrittled film was transferred to a high-energy ball mill pre-cooled with liquid nitrogen, and intermittently pulverized for 3 cycles, each cycle lasting 2 minutes, under the condition of continuous replenishment of liquid nitrogen to maintain the low temperature; after pulverization, particles that passed through a 200-mesh (75 μm) sieve but were retained in a 70-mesh (212 μm) sieve were collected.

[0020] Example 1

[0021] This embodiment provides a graphite top cover for a SiC epitaxial machine, including a graphite top plate and a central hole formed at the center of the graphite top plate, which is prepared by the following steps: Step S1: Preparation of high thermal conductivity isostatically pressed graphite blank: Flake graphite, aramid film fragments obtained in the preparation example, and pitch were mixed in a mass ratio of 15:1:2, heated and stirred at 220°C for 30 minutes, and then pulverized to obtain a mixed powder. The particle size of the flake graphite was 80 micrometers, and the particle size of the mixed powder was 70 micrometers. The mixed powder was isostatically pressed to obtain a billet. The isostatic pressing pressure was 200 MPa, the holding time was 35 minutes, and the pressure increase / decrease rate was 3 MPa / s. The billet was subjected to plasma sintering under a nitrogen atmosphere, with the temperature increased to 600°C at a rate of 4°C / h, then increased to 1100°C at a rate of 9°C / h and held for 20 hours; subsequently, the temperature was increased to 2500°C at a rate of 9°C / h and held for 3 hours. Testing showed that the prepared high thermal conductivity isostatic graphite billet had a thermal conductivity of 235 W / (m·K) at room temperature, a flexural strength of 40 MPa at room temperature, and a flexural strength of 28 MPa at 1500°C.

[0022] Step S2: Use a CNC diamond wire cutting machine to cut a round plate blank with a diameter of Φ1050mm and a thickness of 8mm from the above blank (leaving machining allowance); use a diamond end mill to machine an initial hole with a diameter of Φ290mm in the center; Step S3: Use a five-axis precision machining center and diamond tools to finish the blank, and finally machine a graphite top plate with an outer diameter of Φ1000mm and a thickness of 7mm, as well as a center hole with a diameter of 300mm and a roundness tolerance of ≤0.03mm. Step S4: Polish the surface sequentially using diamond polishing paste with grit sizes W7, W3.5, and W1.5 until the surface roughness Ra ≤ 0.4μm; place the part in an ultrasonic cleaner and clean it with electronic grade isopropanol at 50°C for 8 minutes; rinse with ultrapure water for 8 minutes; and dry it in a clean oven at 110°C for 2 hours to obtain the finished graphite top cover.

[0023] Finite element thermal-stress coupling simulation analysis shows that, under the simulated actual working conditions of a SiC epitaxial machine (800℃ at the edge and 500℃ at the center), when using the graphite top cover (center hole diameter 300mm) of this embodiment, the maximum temperature difference between the center and edge regions can be reduced to below 180℃.

[0024] Further verification through laboratory thermal shock cycling tests (500℃↔800℃ rapid cooling and heating) showed that the graphite top cover of this embodiment can withstand more than 300 cycles without any cracks.

[0025] Example 2

[0026] This embodiment provides a graphite top cover for a SiC epitaxial machine, including a graphite top plate and a central hole formed at the center of the graphite top plate, which is prepared by the following steps: Step S1: Preparation of high thermal conductivity isostatically pressed graphite blank: Flake graphite, aramid film fragments obtained in the preparation example, and pitch were mixed in a mass ratio of 20:3:4, heated and stirred at 250°C for 90 minutes, and then pulverized to obtain a mixed powder. The particle size of the flake graphite was 150 micrometers, and the particle size of the mixed powder was 100 micrometers. The mixed powder was isostatically pressed to obtain a billet. The isostatic pressing pressure was 220 MPa, the holding time was 40 minutes, and the pressure increase / decrease rate was 5 MPa / s. The billet was subjected to plasma sintering under a nitrogen atmosphere, with the temperature increased to 600°C at a rate of 4°C / h, then increased to 1100°C at a rate of 9°C / h and held for 20 hours; subsequently, the temperature was increased to 2500°C at a rate of 9°C / h and held for 3 hours. Testing showed that the prepared high thermal conductivity isostatic graphite billet had a thermal conductivity of 241 W / (m·K) at room temperature, a flexural strength of 43 MPa at room temperature, and a flexural strength of 30 MPa at 1500°C.

[0027] Step S2: Use a CNC diamond wire cutting machine to cut a round plate blank with a diameter of Φ1050mm and a thickness of 8mm from the above blank (leaving machining allowance); use a diamond end mill to machine an initial hole with a diameter of Φ290mm in the center; Step S3: Use a five-axis precision machining center and diamond tools to finish the blank. The final product is a graphite top plate with an outer diameter of Φ1000mm and a thickness of 7mm, and a center hole with a diameter of Φ300mm and a roundness tolerance of ≤0.03mm. Step S4: Polish the surface sequentially using diamond polishing paste with grit sizes W7, W3.5, and W1.5 until the surface roughness Ra ≤ 0.4μm; place the part in an ultrasonic cleaner and clean it with electronic grade isopropanol at 50°C for 8 minutes; rinse it with ultrapure water with a resistivity ≥18 MΩ·cm for 8 minutes; dry it in a clean oven at 110°C for 2 hours to obtain the finished graphite top cover.

[0028] Finite element thermal-stress coupling simulation analysis shows that, under the simulated actual working conditions of a SiC epitaxial machine (800℃ at the edge and 500℃ at the center), when using the graphite top cover (center hole diameter 300mm) of this embodiment, the maximum temperature difference between the center and edge regions can be reduced to below 175℃.

[0029] Through laboratory thermal shock cycling tests (500℃↔800℃ rapid cooling and heating), it has been verified that the graphite top cover of this embodiment can withstand more than 300 cycles without any cracks.

[0030] Example 3

[0031] This embodiment provides a graphite top cover for a SiC epitaxial machine, including a graphite top plate and a central hole formed at the center of the graphite top plate, which is prepared by the following steps: Step S1: Preparation of high thermal conductivity isostatically pressed graphite blank: Flake graphite, aramid film fragments obtained in the preparation example, and pitch were mixed in a mass ratio of 18:2:3, heated and stirred at 230°C for 60 minutes, and then pulverized to obtain a mixed powder. The particle size of the flake graphite was 100 micrometers, and the particle size of the mixed powder was 80 micrometers. The mixed powder was isostatically pressed to obtain a billet. The isostatic pressing pressure was 200 MPa, the holding time was 35 minutes, and the pressure increase / decrease rate was 3 MPa / s. The billet was subjected to plasma sintering under a nitrogen atmosphere, with the temperature increased to 600°C at a rate of 3°C / h, then increased to 1000°C at a rate of 8°C / h and held for 12 hours; subsequently, the temperature was increased to 2400°C at a rate of 8°C / h and held for 2 hours. Testing showed that the prepared high thermal conductivity isostatic graphite billet had a thermal conductivity of 239 W / (m·K) at room temperature, a flexural strength of 44 MPa at room temperature, and a flexural strength of 32 MPa at 1500°C.

[0032] Step S2: Use a CNC diamond wire cutting machine to cut a round plate blank with a diameter of Φ1050mm and a thickness of 12mm from the above blank (leaving machining allowance); use a diamond end mill to machine an initial hole with a diameter of Φ290mm in the center; Step S3: Use a five-axis precision machining center and diamond tools to finish the blank. The final product is a graphite top plate with an outer diameter of Φ1000mm and a thickness of 10mm, as well as a center hole with a diameter of Φ300mm and a roundness tolerance of ≤0.03mm. Step S4: Polish the surface sequentially using diamond polishing paste with grit sizes W7, W3.5, and W1.5 until the surface roughness Ra ≤ 0.4μm; place the part in an ultrasonic cleaner and clean it with electronic grade isopropanol at 50°C for 8 minutes; rinse it with ultrapure water with a resistivity ≥18 MΩ·cm for 8 minutes; dry it in a clean oven at 110°C for 2 hours to obtain the finished graphite top cover.

[0033] Finite element thermal-stress coupling simulation analysis shows that, under the simulated actual working conditions of a SiC epitaxial machine (800℃ at the edge and 500℃ at the center), when using the graphite top cover (center hole diameter 300mm) of this embodiment, the maximum temperature difference between the center and edge regions can be reduced to below 174℃.

[0034] Further verification through laboratory thermal shock cycling tests (500℃↔800℃ rapid cooling and heating) showed that the graphite top cover of this embodiment can withstand more than 300 cycles without any cracks.

[0035] Example 4

[0036] This embodiment provides a graphite top cover for a SiC epitaxial machine, including a graphite top plate and a central hole formed at the center of the graphite top plate, which is prepared by the following steps: Step S1: Preparation of high thermal conductivity isostatically pressed graphite blank: Flake graphite, aramid film fragments obtained in the preparation example, and pitch were mixed in a mass ratio of 18:2:3, heated and stirred at 230°C for 60 minutes, and then pulverized to obtain a mixed powder. The particle size of the flake graphite was 100 micrometers, and the particle size of the mixed powder was 80 micrometers. The mixed powder was isostatically pressed to obtain a billet. The isostatic pressing pressure was 200 MPa, the holding time was 35 minutes, and the pressure increase / decrease rate was 3 MPa / s. The billet was subjected to plasma sintering under a nitrogen atmosphere, with the temperature increased to 600°C at a rate of 5°C / h, then increased to 1200°C at a rate of 10°C / h and held for 24 hours; subsequently, the temperature was increased to 2600°C at a rate of 10°C / h and held for 4 hours. Testing showed that the prepared high thermal conductivity isostatic graphite billet had a thermal conductivity of 244 W / (m·K) at room temperature, a flexural strength of 42 MPa at room temperature, and a flexural strength of 31 MPa at 1500°C.

[0037] Step S2: Use a CNC diamond wire cutting machine to cut a round plate blank with a diameter of Φ1050mm and a thickness of 14mm from the above blank (leaving machining allowance); use a diamond end mill to machine an initial hole with a diameter of Φ340mm in the center; Step S3: Use a five-axis precision machining center and diamond tools to finish the blank. The final product is a graphite top plate with an outer diameter of Φ1000mm and a thickness of 12mm, and a center hole with a diameter of Φ350mm and a roundness tolerance of ≤0.03mm. Step S4: Polish the surface sequentially using diamond polishing paste with grit sizes W7, W3.5, and W1.5 until the surface roughness Ra ≤ 0.4μm; place the part in an ultrasonic cleaner and clean it with electronic grade isopropanol at 50°C for 5 minutes; rinse it with ultrapure water with a resistivity ≥18 MΩ·cm for 5 minutes; dry it in a clean oven at 100°C for 2 hours to obtain the finished graphite top cover.

[0038] Finite element thermal-stress coupling simulation analysis shows that, under the simulated actual working conditions of a SiC epitaxial machine (800℃ at the edge and 500℃ at the center), when using the graphite top cover (center hole diameter 300mm) of this embodiment, the maximum temperature difference between the center and edge regions can be reduced to below 172℃.

[0039] Further verification through laboratory thermal shock cycling tests (500℃↔800℃ rapid cooling and heating) showed that the graphite top cover of this embodiment can withstand more than 300 cycles without any cracks.

[0040] Example 5

[0041] This embodiment provides a graphite top cover for a SiC epitaxial machine, including a graphite top plate and a central hole formed at the center of the graphite top plate, which is prepared by the following steps: Step S1: Preparation of high thermal conductivity isostatically pressed graphite blank: Flake graphite, aramid film fragments obtained in the preparation example, and pitch were mixed in a mass ratio of 18:2:3, heated and stirred at 230°C for 60 minutes, and then pulverized to obtain a mixed powder. The particle size of the flake graphite was 100 micrometers, and the particle size of the mixed powder was 80 micrometers. The mixed powder was isostatically pressed to obtain a billet. The isostatic pressing pressure was 200 MPa, the holding time was 35 minutes, and the pressure increase / decrease rate was 3 MPa / s. The billet was subjected to plasma sintering under a nitrogen atmosphere, with the temperature increased to 600°C at a rate of 5°C / h, then increased to 1200°C at a rate of 10°C / h and held for 24 hours; subsequently, the temperature was increased to 2600°C at a rate of 10°C / h and held for 4 hours. Testing showed that the prepared high thermal conductivity isostatic graphite billet had a thermal conductivity of 244 W / (m·K) at room temperature, a flexural strength of 43 MPa at room temperature, and a flexural strength of 32 MPa at 1500°C.

[0042] Step S2: Use a CNC diamond wire cutting machine to cut a round plate blank with a diameter of Φ1050mm and a thickness of 14mm from the above blank (leaving machining allowance); use a diamond end mill to machine an initial hole with a diameter of Φ190mm in the center; Step S3: Use a five-axis precision machining center and diamond tools to finish the blank. The final product is a graphite top plate with an outer diameter of Φ1000mm and a thickness of 12mm, as well as a center hole with a diameter of Φ200mm and a roundness tolerance of ≤0.03mm. Step S4: Polish the surface sequentially using diamond polishing paste with grit sizes W7, W3.5, and W1.5 until the surface roughness Ra ≤ 0.4μm; place the part in an ultrasonic cleaner and clean it with electronic grade isopropanol at 50°C for 10 minutes; rinse it with ultrapure water with a resistivity ≥18 MΩ·cm for 10 minutes; and dry it in a clean oven at 120°C for 2 hours to obtain the finished graphite top cover.

[0043] Finite element thermal-stress coupling simulation analysis shows that, under the simulated actual working conditions of a SiC epitaxial machine (800℃ at the edge and 500℃ at the center), when using the graphite top cover (center hole diameter 300mm) of this embodiment, the maximum temperature difference between the center and edge regions can be reduced to below 170℃.

[0044] Further verification through laboratory thermal shock cycling tests (500℃↔800℃ rapid cooling and heating) showed that the graphite top cover of this embodiment can withstand more than 300 cycles without any cracks.

[0045] Comparative Example 1 Commercially available isostatic graphite (thermal conductivity approximately 120 W / (m·K)) is used, with a central hole diameter of Φ150mm and a thickness of 10mm.

[0046] A traditional graphite cap with a central hole diameter of 150mm experiences a maximum axial temperature difference exceeding 320℃. Visible cracks begin to appear at the edge of the central hole after an average of 45 cycles.

[0047] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A graphite top cover for a SiC epitaxial machine, characterized in that, The device includes a graphite top plate and a central hole at the center of the graphite top plate. The graphite top plate is made of high thermal conductivity isostatic graphite. The high thermal conductivity isostatic graphite has a thermal conductivity ≥200W / (m・K) in the temperature range of 20-1000℃, a flexural strength ≥35MPa at room temperature, and a flexural strength ≥25MPa at 1500℃. The diameter of the central hole is 200-350mm.

2. The graphite top cover for a SiC epitaxial machine according to claim 1, characterized in that, The thickness of the graphite top plate is 7-12mm.

3. A method for processing a graphite top cover for a SiC epitaxial machine, characterized in that, Includes the following steps: High thermal conductivity isostatic graphite blanks are prepared with the following properties: thermal conductivity ≥200W / (m・K) in the temperature range of 20-1000℃, flexural strength ≥35MPa at room temperature, and flexural strength ≥25MPa at 1500℃. A blank is cut from the high thermal conductivity isostatic graphite blank, and an initial hole is cut out. The blank and the initial hole are precision machined to obtain a graphite top plate and a center hole of the target size, wherein the diameter of the center hole is 200-350mm; After polishing, cleaning, and drying, a graphite top cover for SiC epitaxial machine is obtained.

4. The method for processing the graphite top cover for a SiC epitaxial machine according to claim 3, characterized in that, The steps for preparing high thermal conductivity isostatically pressed graphite blanks include: Flake graphite, aramid film fragments and pitch are mixed in a mass ratio of (15-20):(1-3):(2-4), heated and stirred, and then crushed to obtain a mixed powder. The mixed powder is subjected to isostatic pressing to obtain the billet; The blank is subjected to plasma sintering to obtain a high thermal conductivity isostatic graphite blank.

5. The method for processing the graphite top cover for a SiC epitaxial machine according to claim 4, characterized in that, The heating and stirring temperature is 220-250℃, and the heating time is 30-90 minutes.

6. The method for processing the graphite top cover for a SiC epitaxial machine according to claim 4, characterized in that, The particle size of flake graphite is 80-150 micrometers, the particle size of aramid film fragments is 50-200 micrometers, and the particle size of mixed powder is 70-100 micrometers.

7. The method for processing the graphite top cover for a SiC epitaxial machine according to claim 4, characterized in that, The isostatic pressure treatment pressure is 180-220MPa, the holding time is 30-40 minutes, and the pressure increase / decrease rate is 2-5 MPa / s.

8. The method for processing the graphite top cover for a SiC epitaxial machine according to claim 4, characterized in that, The plasma sintering process includes: heating to 600°C at a rate of 3-5°C / h under a nitrogen atmosphere, then heating to 1000-1200°C at a rate of 8-10°C / h and holding for 12-24 hours; then heating to 2400-2600°C at a rate of 8-10°C / h and holding for 2-4 hours.

9. The method for processing the graphite top cover for a SiC epitaxial machine according to claim 3, characterized in that, Cut the material using a diamond cutting machine, leaving a 1-2mm machining allowance, and then use a diamond tool to machine the initial hole. The diameter of the initial hole should be 3-10mm smaller than the target size.

10. The method for processing the graphite top cover for a SiC epitaxial machine according to claim 3, characterized in that, Polish with diamond polishing paste, ultrasonically clean with isopropyl alcohol for 5-10 minutes, rinse with water for 5-10 minutes, and dry at 100-120℃.