High-purity and dense silicon carbide ceramic and its preparation method without auxiliary agent and application

Abstract

This invention belongs to the field of ceramic materials technology, specifically relating to a high-purity, dense silicon carbide ceramic and its preparation method and application without additives. The preparation method of this invention includes the following steps: constructing a hollow mesoporous silicon carbide composite precursor; heat-treating the silicon carbide composite precursor to obtain a hollow mesoporous silicon carbide composite framework; uniformly mixing the hollow mesoporous silicon carbide composite framework with a fluoropolymer, and subjecting the mixture to in-situ gas-phase impurity removal and carbothermic reduction reaction to prepare high-purity hollow mesoporous silicon carbide powder; and densifying the high-purity hollow mesoporous silicon carbide powder by pressure sintering without adding additional sintering aids to obtain high-purity, dense silicon carbide ceramic. The preparation method of this invention can achieve additive-free densification of silicon carbide ceramics at relatively low temperatures. The resulting material has characteristics such as pure grain boundaries, high density, excellent mechanical properties, and strong resistance to plasma corrosion, making it suitable for application in the preparation of electrostatic chucks.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, specifically relating to a high-purity, dense silicon carbide ceramic and its preparation method and application without additives. Background Technology

[0002] In advanced semiconductor manufacturing processes, electrostatic chucks are core components used to hold, fix, and precisely temperature-control wafers. As integrated circuit manufacturing processes evolve towards sub-nanometer nodes, the extreme plasma processing environment and stringent thermal and mechanical requirements place extremely high demands on the purity, mechanical strength, thermal conductivity, and halogen corrosion resistance of electrostatic chuck materials. Due to its excellent thermal conductivity and superior resistance to plasma erosion, silicon carbide has become an ideal substrate for manufacturing high-end electrostatic chucks. Traditional liquid-phase sintering methods require the addition of sintering aids such as alumina or yttrium oxide, which results in residual amorphous glassy phases at the grain boundaries of the final ceramic. Under strong plasma etching, these impurity phases are preferentially corroded, leading to particulate contamination and excessive leakage current in the equipment. Traditional solid-phase sintering without aids typically requires extreme temperatures exceeding 2100°C, which easily causes severe grain coarsening in the ceramic and a sharp decline in the material's mechanical properties.

[0003] Developing a high-purity, high-density silicon carbide ceramic preparation technology that can achieve powder densification within a low temperature range without adding any sintering aids and meets the extreme purity requirements of semiconductor manufacturing is the key to breaking through the barriers to independent manufacturing of high-end electrostatic chucks. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-purity, dense silicon carbide ceramic and its preparation method and application without additives. This invention achieves additive-free preparation of silicon carbide ceramics at lower temperatures by constructing hollow mesoporous silicon carbide powder and combining it with the structural collapse effect during in-situ vapor-phase impurity removal and pressure sintering. The resulting silicon carbide ceramic achieves a balance of purity, density, and high mechanical properties. The additive-free preparation method of this invention solves the problems of existing silicon carbide ceramics, such as reliance on oxide sintering aids during sintering, easy formation of glassy phases at grain boundaries, insufficient resistance to plasma corrosion, and grain coarsening caused by excessively high additive-free sintering temperatures.

[0005] To achieve the above technical objectives, the technical solution adopted in the embodiments of the present invention is as follows: In a first aspect, embodiments of the present invention provide a method for preparing high-purity, dense silicon carbide ceramics without additives, comprising the following steps: (1) Precursor construction: High-purity silicon source, high-purity carbon source and structural template agent are uniformly mixed in solvent, and carbon silicon composite precursor with hollow mesoporous structure is formed by sol-gel, self-assembly or spray drying; (2) Forming a hollow mesoporous carbon silicon composite framework: The carbon silicon composite precursor described in step (1) is heat-treated in an inert atmosphere to obtain a hollow mesoporous carbon silicon composite framework. (3) In-situ gas phase impurity removal and carbothermic reduction: The hollow mesoporous silicon carbide composite skeleton obtained in step (2) is uniformly mixed with the fluoropolymer. The mixture is placed in a vacuum or inert atmosphere furnace for carbothermic reduction reaction. After the reaction is completed, an oxidizing gas is introduced for calcination to remove residual carbon and obtain high-purity hollow mesoporous silicon carbide powder. (4) Pressure densification without additives: The high-purity hollow mesoporous silicon carbide powder obtained in step (3) is directly loaded into the mold and pressure sintered without adding sintering aids to obtain high-purity, dense silicon carbide ceramics.

[0006] Furthermore, in step (1), the purity of the high-purity silicon source is not less than 99.9%, and it is one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, silica sol and fumed silica. The purity of the high-purity carbon source is not less than 99%, and it adopts one or more combinations of phenolic resin, polyacrylonitrile, sucrose, glucose, carbon nanotubes, graphite powder and carbon black. The solvent is one or a combination of deionized water, ethanol, methanol, isopropanol and N,N-dimethylformamide.

[0007] Further, in step (1), the structural template agent is one or more of Pluronic F127, P123, cetyltrimethylammonium bromide, polyethylene glycol and polyvinylpyrrolidone.

[0008] Furthermore, the addition ratio of the high-purity silicon source to the high-purity carbon source is 3-6 according to the C / Si molar ratio, the amount of the structural template agent added accounts for 1%-30% of the total mass of the carbon-silicon composite precursor, and the mass ratio of the solvent to the carbon-silicon composite precursor is 2:1-10:1.

[0009] Furthermore, in step (2), the heat treatment is carried out at 600-900℃ and the holding time is 2-8h.

[0010] Further, in step (3), the fluoropolymer is polytetrafluoroethylene or polyvinylidene fluoride with a purity higher than 99%, and its addition amount is 1%-20% of the total mass of the carbon silicon composite precursor.

[0011] Furthermore, in step (3), the carbothermic reduction reaction is carried out at 1000-1600℃ and the holding time is 1-6h.

[0012] Further, in step (4), the pressure sintering is carried out in one of the following ways: spark plasma sintering, hot pressing sintering, hot isostatic pressing sintering, gas pressure sintering or oscillating pressure sintering, and the sintering temperature is 1500-2100℃.

[0013] Secondly, embodiments of the present invention provide a high-purity, dense silicon carbide ceramic, which is prepared by the preparation method described in the first aspect. The silicon carbide ceramic has a polymorphic coexistence structure, a purity higher than 99%, an average grain size of 50-500 nm, a relative density higher than 99%, a Vickers hardness of not less than 30 GPa, and a flexural strength of not less than 600 MPa.

[0014] Thirdly, embodiments of the present invention provide an application of high-purity, dense silicon carbide ceramic, which is used to prepare electrostatic chucks.

[0015] Compared with the prior art, the technical solution of the embodiments of the present invention has the following beneficial effects: (1) In constructing hollow mesoporous silicon carbide powder, the present invention uses fluorine-containing gas generated by the pyrolysis of fluorine-containing polymers for in-situ gas phase impurity removal, which can effectively remove metal impurities and avoid the pollution problems caused by traditional acid washing process.

[0016] (2) The hollow mesoporous silicon carbide powder constructed by the present invention can significantly improve the sintering activity of the powder and realize the densification of silicon carbide ceramics at a lower temperature without additives.

[0017] (3) The preparation method of the present invention does not require the introduction of oxides or metal sintering aids during the entire sintering process, and can obtain high-purity silicon carbide ceramics with pure grain boundaries.

[0018] (4) The silicon carbide ceramic prepared by the present invention has high density, ultrafine crystal structure and excellent mechanical properties and anti-plasma corrosion properties, and is suitable for high-end manufacturing fields such as semiconductor electrostatic chucks. Attached Figure Description

[0019] Figure 1 This is a TEM image of the hollow mesoporous silicon carbide powder obtained in Example 1.

[0020] Figure 2 The image shows the HADDF-STEM image of the silicon carbide ceramic obtained in Example 1.

[0021] Figure 3 The image shows the HRTEM image of the silicon carbide ceramic obtained in Example 1.

[0022] Figure 4 The image shows the Vickers hardness indentation pattern of the silicon carbide ceramic obtained in Example 1.

[0023] Figure 5The graph shows the nitrogen adsorption-desorption curve of the hollow mesoporous silicon carbide powder obtained in Example 2.

[0024] Figure 6 This is a SEM image of the cross-section of the silicon carbide ceramic obtained in Example 2.

[0025] Figure 7 The image shows the stress-strain curve of the silicon carbide ceramic obtained in Example 2.

[0026] Figure 8 This is a SEM image of the cross-section of the silicon carbide ceramic obtained in Example 3.

[0027] Figure 9 The image shows the stress-strain curve of the silicon carbide ceramic obtained in Example 3. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Example 1 A method for preparing high-purity, dense silicon carbide ceramics without additives includes the following steps: (1) Mix 40 mL of anhydrous ethanol, 20 mL of deionized water and 1.0 g of structural template agent (Pluronic F127), and stir magnetically for 30 min at room temperature until completely dissolved; then add 10 mL of tetraethyl orthosilicate (purity 99.9%), and continue stirring for 30 min; add 6 g of phenolic resin (purity 99%) to the above system, stir at room temperature for 1 h, transfer to a sealed container, react at 40 °C for 12 h, and the obtained product is centrifuged, washed and dried at 60 °C for 12 h to obtain a carbon silicon composite precursor with a hollow mesoporous structure; (2) Place the silicon-carbon composite precursor from step (1) in a vacuum furnace and heat it at 10°C. -3 Under the protection of Pa and argon gas with a purity of 99.99%, the temperature was increased to 800℃ at a heating rate of 5℃ / min and held for 1 h to obtain a hollow mesoporous carbon silicon composite framework. (3) The hollow mesoporous silicon carbide composite framework obtained in step (2) is uniformly mixed with 10% by mass of polytetrafluoroethylene powder (purity 99.9%). The mixture is then heated to 1500℃ at a rate of 10℃ / min and held for 2 h for carbothermic reduction reaction. During the heating process, the highly active fluorine-containing gas generated by the decomposition of polytetrafluoroethylene reacts with trace metal impurities in the hollow mesoporous silicon carbide composite framework to generate volatile metal fluorides. After the reaction is completed, air is introduced to separate the volatile metal fluoride gas, and the temperature is lowered to 700℃. The mixture is then calcined at 700℃ for 2 h to remove residual carbon, resulting in high-purity hollow mesoporous silicon carbide powder with high specific surface area. TEM observation shows that it has a significant hollow structure, such as... Figure 1 As shown; (4) The hollow mesoporous silicon carbide powder obtained in step (3) is loaded into a graphite mold and densified using a spark plasma sintering device without adding any additional sintering aids: 60 MPa unidirectional pressure is applied under vacuum, and the temperature is raised to 1650℃ at a heating rate of 100℃ / min. After holding at this temperature for 10 min, the powder is cooled with the furnace. Under the coupling effect of temperature and external pressure, the hollow mesoporous silicon carbide powder skeleton undergoes strong local stress concentration and collapses and breaks into highly active nano-fragments, thereby inducing the powder to eliminate all pores and achieve complete densification, and finally obtaining high-purity, dense silicon carbide ceramics.

[0030] The density of the high-purity, dense silicon carbide ceramic prepared using Archimedes' displacement method was determined to be 3.1843 g / cm³. 3 The relative density reached 99.2%. ICP testing showed that the total metal impurity content was less than 0.05 wt%, and the SiC main phase content in the obtained silicon carbide ceramic was 99.9 wt%. Figure 2 As shown, HADDF-STEM observation revealed that the grains are distributed in the 200-300 nm range. Figure 3 As shown, HRTEM reveals that the ceramic interior is rich in nanotwinned structures. The Vickers hardness indentation pattern of the silicon carbide ceramic is shown below. Figure 4 As shown, its Vickers hardness reaches 31.8 GPa, exhibiting extremely excellent mechanical wear resistance. After a three-point bending test, the bending strength of silicon carbide ceramic reaches 636.24 MPa.

[0031] Example 2 A method for preparing high-purity, dense silicon carbide ceramics without additives includes the following steps: (1) 10 g of silica sol with a solid content of 30 wt% (purity of 99.9%) was used as the silicon source and dissolved with 6 g of sucrose with a purity of 99.9% in 120 mL of deionized water. Then, 2 g of the structural template agent hexadecyltrimethylammonium bromide was added and the mixture was magnetically stirred at room temperature for 2 h to induce the formation of a mesoporous carbon-silicon composite precursor through self-assembly. (2) The carbon-silicon composite precursor described in step (1) is placed in a tube furnace and heated to 750°C at a heating rate of 5°C / min under the protection of argon gas with a purity of 99.99% and held for 1.5 h to obtain a hollow mesoporous carbon-silicon composite skeleton. (3) The hollow mesoporous silicon carbide composite framework obtained in step (2) is uniformly mixed with 5% by mass of polyvinylidene fluoride (99% purity). The mixture is then heated to 1400℃ at a heating rate of 5℃ / min for carbothermic reduction reaction and held at that temperature for 2 hours. During the reaction, polyvinylidene fluoride decomposes and releases fluorine-containing gas. The fluorine-containing gas reacts with trace metal impurities in the system to generate volatile metal fluorides. After the reaction is completed, air is introduced to remove the volatile fluorides, and the mixture is calcined at 750℃ for 2 hours to remove residual carbon, thereby obtaining high-purity hollow mesoporous silicon carbide powder with high specific surface area, such as... Figure 5 As shown, the nitrogen adsorption-desorption curves exhibit type IV isotherms, indicating a distinct mesoporous structure with a specific surface area of ​​173.48 m². 2 / g; (4) After the hollow mesoporous silicon carbide powder obtained in step (3) is cold isostatically preformed, it is put into a package and vacuum sealed. Using a hot isostatic pressing equipment with argon as the pressure transmission medium, it is kept at 1900℃ and 200MPa isotropic high pressure for 2 hours, so that the mesopores inside the powder collapse violently under high pressure and induce atoms to diffuse rapidly and fill all the pores, and finally obtain high-purity, dense silicon carbide ceramic.

[0032] The density of the high-purity, dense silicon carbide ceramic, determined by Archimedes' displacement method, is 3.2036 g / cm³. 3 The relative density is as high as 99.8%, and the purity of SiC in the resulting silicon carbide ceramic is 99.8%. For example... Figure 6 The SEM image of the ceramic cross-section shows that the average grain size is controlled at 400 nm. Three-point bending resistance tests were conducted, as shown... Figure 7 As shown, its bending strength is as high as 625.91 MPa, which can firmly lock the deformed and warped wafer without brittle fracture. Its Vickers hardness reaches 32.1 GPa according to Vickers indentation test.

[0033] Example 3 A method for preparing high-purity, dense silicon carbide ceramics without additives includes the following steps: (1) Dissolve 5.0 g of polyacrylonitrile (purity 99%) in 50 mL of N,N-dimethylformamide and stir magnetically at 60 °C for 2 h until completely dissolved to obtain a uniform and transparent solution; then add 3.0 g of polyvinylpyrrolidone (purity 99%) and continue stirring for 30 min to fully dissolve it. Add 10 mL of tetramethyl orthosilicate (purity 99%) to the above solution and continue stirring for 1 h to form a uniform sol. Allow it to stand at room temperature for 12 h to complete the gelation process. Dry the gel to obtain the carbon-silicon composite precursor. (2) The carbon-silicon composite precursor obtained in step (1) is heated to 700°C at a heating rate of 5°C / min under nitrogen (purity of 99%) atmosphere and held for 2 h to obtain a hollow mesoporous carbon-silicon composite framework. (3) Add 15% of the mass of polytetrafluoroethylene powder to the hollow mesoporous silicon carbide composite skeleton obtained in step (2), and use a planetary ball mill to mix it evenly. Place the mixture in a quartz tube furnace, and under the protective atmosphere of argon with a purity of 99.99%, heat it to 1550℃ at a heating rate of 5℃ / min and hold it for 2 h to carry out a carbothermic reduction reaction. During the reaction, polytetrafluoroethylene decomposes to generate volatile fluorine-containing gas. The fluorine-containing gas reacts with trace metal impurities in the system to generate volatile metal fluorides. After the reaction is completed, transfer the sample to an air atmosphere furnace and calcine it at 650℃ for 2 h to remove residual carbon and obtain high-purity hollow mesoporous silicon carbide powder with high specific surface area. (4) The hollow mesoporous silicon carbide powder obtained in step (3) is directly loaded into a graphite mold and hot-pressed without adding any additional sintering aids. Under an argon protective atmosphere, a unidirectional pressure of 40 MPa is applied, and the temperature is raised to 2100℃ at a heating rate of 10℃ / min. After holding at this temperature for 1 h, the temperature is cooled with the furnace. Under the coupling effect of high temperature and external pressure, the mesoporous structure inside the powder collapses and promotes the densification of the particles, ultimately obtaining high-purity, dense silicon carbide ceramics.

[0034] The density of the obtained high-purity, dense silicon carbide ceramic, determined by Archimedes' displacement method, was 3.1972 g / cm³. 3 The relative density is 99.6%, and the purity of SiC in the resulting silicon carbide ceramic is 99.9%. For example... Figure 8 The image shown is a cross-sectional SEM image of silicon carbide ceramic, with an average grain size of 400±50 nm. Its polymorphic interface characteristics greatly enhance phonon conduction efficiency, and as a substrate for electrostatic chucks, it exhibits a thermal conductivity exceeding 200 Kelvin per meter. Three-point bending tests were conducted, as shown... Figure 9 As shown, its bending strength is as high as 629.88 MPa, and its Vickers hardness reaches 31.4 GPa according to the Vickers indentation test.

[0035] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-purity, dense silicon carbide ceramics without additives, characterized in that, Includes the following steps: (1) Precursor construction: High-purity silicon source, high-purity carbon source and structural template agent are uniformly mixed in solvent, and carbon silicon composite precursor with hollow mesoporous structure is formed by sol-gel, self-assembly or spray drying; (2) Forming a hollow mesoporous carbon silicon composite framework: The carbon silicon composite precursor described in step (1) is heat-treated in an inert atmosphere to obtain a hollow mesoporous carbon silicon composite framework. (3) In-situ gas phase impurity removal and carbothermic reduction: The hollow mesoporous silicon carbide composite skeleton obtained in step (2) is uniformly mixed with the fluoropolymer. The mixture is placed in a vacuum or inert atmosphere furnace for carbothermic reduction reaction. After the reaction is completed, an oxidizing gas is introduced for calcination to remove residual carbon and obtain high-purity hollow mesoporous silicon carbide powder. (4) Pressure densification without additives: The high-purity hollow mesoporous silicon carbide powder obtained in step (3) is directly loaded into the mold and pressure sintered without adding sintering aids to obtain high-purity, dense silicon carbide ceramics.

2. The method for preparing high-purity, dense silicon carbide ceramics without additives according to claim 1, characterized in that, In step (1), the purity of the high-purity silicon source is not less than 99.9%, and it is one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, silica sol and fumed silica. The purity of the high-purity carbon source is not less than 99%, and it adopts one or more combinations of phenolic resin, polyacrylonitrile, sucrose, glucose, carbon nanotubes, graphite powder and carbon black. The solvent is one or a combination of deionized water, ethanol, methanol, isopropanol and N,N-dimethylformamide.

3. The method for preparing high-purity, dense silicon carbide ceramics without additives according to claim 1, characterized in that, In step (1), the structural template agent is one or more of Pluronic F127, P123, cetyltrimethylammonium bromide, polyethylene glycol and polyvinylpyrrolidone.

4. The method for preparing high-purity, dense silicon carbide ceramics without additives according to claim 1, characterized in that, In step (1), the addition ratio of the high-purity silicon source to the high-purity carbon source is 3-6 according to the C / Si molar ratio, the amount of the structural template agent added accounts for 1%-30% of the total mass of the carbon-silicon composite precursor, and the mass ratio of the solvent to the carbon-silicon composite precursor is 2:1-10:

1.

5. The method for preparing high-purity, dense silicon carbide ceramics without additives according to claim 1, characterized in that, In step (2), the heat treatment is carried out at 600-900℃ and the holding time is 2-8h.

6. The method for preparing high-purity, dense silicon carbide ceramics without additives according to claim 1, characterized in that, In step (3), the fluoropolymer is polytetrafluoroethylene or polyvinylidene fluoride with a purity higher than 99%, and its addition amount is 1%-20% of the total mass of the carbon silicon composite precursor.

7. The method for preparing high-purity, dense silicon carbide ceramics without additives according to claim 1, characterized in that, In step (3), the carbothermic reduction reaction is carried out at 1000-1600℃ and the holding time is 1-6h.

8. The method for preparing high-purity, dense silicon carbide ceramics without additives according to claim 1, characterized in that, In step (4), the pressure sintering is carried out in one of the following ways: spark plasma sintering, hot pressing sintering, hot isostatic pressing sintering, gas pressure sintering or oscillating pressure sintering, and the sintering temperature is 1500-2100℃.

9. A high-purity, dense silicon carbide ceramic, characterized in that, The silicon carbide ceramic is prepared by any one of the preparation methods described in claims 1-8. The silicon carbide ceramic has a polymorphic coexistence structure, a purity higher than 99%, an average grain size of 50-500 nm, a relative density higher than 99%, a Vickers hardness of not less than 30 GPa, and a flexural strength of not less than 600 MPa.

10. An application of a high-purity, dense silicon carbide ceramic, characterized in that, The high-purity, dense silicon carbide ceramic is used to prepare electrostatic chucks.

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