Sintering method of composite SiC aluminum oxide electrostatic chuck ceramic plate

Abstract

The invention discloses a sintering method of a composite SiC aluminum oxide electrostatic chuck ceramic plate, and belongs to the technical field of electrostatic chucks, the sintering method comprises the following steps: S1, modification and pre-oxidation treatment modification: controlling the residual amount of carbon black in reaction in the process of synthesizing silicon carbide to obtain nano silicon carbide powder with different carbon contents; pre-oxidizing, namely pre-oxidizing the modified silicon carbide, and then annealing and crystallizing under the protection of argon atmosphere; s2, tape casting: carrying out ball milling on the modified nano silicon carbide in a bedroom sand mill, pre-grinding the ball-milled nano silicon carbide powder, a solvent and a dispersing agent in a planetary mill, then mixing and grinding with aluminum oxide powder, finally adding an adhesive for grinding, and carrying out tape casting after grinding to obtain a ceramic green body; and S3, high-temperature sintering is carried out, specifically, a ceramic green body obtained through tape casting is subjected to glue discharging in wet nitrogen, pressurized sintering is carried out in a certain Ar atmosphere in an HP furnace, and the composite SiC aluminum oxide electrostatic chuck ceramic disc is obtained through sintering.

Description

Technical Field

[0001] The invention relates to the technical field of electrostatic chucks, and in particular to a sintering method for a composite SiC alumina electrostatic chuck ceramic disc. Background Art

[0002] In recent years, the preparation technology of nanocomposite ceramics has attracted the attention of many scholars. The mechanical, electrical, magnetic, optical, thermal and other properties of different components in the composite material can be coupled or induced by each other. The composite material can obtain better performance than a single component or properties that a single component does not have. The composite effect is greater than the simple addition effect. Al2O3 / SiC composite ceramics have attracted much attention due to their excellent mechanical, thermal and electrical properties.

[0003] Adding nano-silicon carbide to nano-alumina for sintering can bring the following effects:

[0004] 1. Improve fracture toughness: The addition of nano-silicon carbide can improve the fracture toughness of the material, because silicon carbide particles can act as an obstacle to crack propagation, thereby improving the toughness of the material;

[0005] 2. Enhance hardness: The addition of nano silicon carbide can increase the hardness of the material, because silicon carbide is a material with very high hardness;

[0006] 3. Improve wear resistance: Due to the high hardness and wear resistance of silicon carbide, adding nano silicon carbide can improve the wear resistance of alumina-based composite materials;

[0007] 4. Improve thermal conductivity: Silicon carbide has high thermal conductivity, so adding nano-silicon carbide can slightly improve the thermal conductivity of alumina, which is very important for thermal management applications;

[0008] 5. Grain refinement: The addition of nano-silicon carbide may affect the grain growth of alumina, helping to obtain a finer grain structure, thereby improving the strength and toughness of the material;

[0009] 6. Influence of sintering temperature: The addition of nano-SiC may affect the sintering temperature. Due to the pinning effect of SiC, sintering densification becomes difficult.

[0010] 7. Adjustment of thermal expansion coefficient: The thermal expansion coefficient of nano-silicon carbide is different from that of alumina and close to that of wafers. Its addition can adjust the thermal expansion coefficient of the composite material to meet specific application requirements;

[0011] 8. Improve flexural strength: In some cases, the addition of nano-silicon carbide can improve the flexural strength of the material;

[0012] 9. Optimization of microstructure: The addition of nano-SiC may affect the microstructure of the material, including grain size and distribution, thereby affecting the macroscopic properties of the material, such as electrical properties, compressive strength and breakdown voltage.

[0013] In terms of mechanical properties, the pinning effect of silicon carbide particles improves the fracture strength and fracture toughness of composite ceramics. Niihara's research on Al2O3 / SiC nanocomposites found that by adding 5vol% nano-SiC particles, the three-point bending strength increased from 320MPa of a single piece of Al2O3 to 1050MPa of the nanocomposite. In terms of thermal behavior and electrical conductivity, et al. studied the effect of SiC nanoparticle addition on the electrical conductivity and thermal conductivity of Al2O3 / SiC micro-nanocomposites at room temperature and high temperature. Different samples with SiC volume fractions ranging from 3 vol% to 20 vol% were prepared by hot pressing at 1740°C and 30 MPa pressure in an argon atmosphere. The results show that the thermal properties (thermal diffusivity and thermal conductivity) of Al2O3 / SiC nanocomposites are not affected by the size and shape of SiC particles, but by the volume content of these particles. The thermal conductivity increases with the increase of the SiC nanoparticle content. When the volume fraction of these nanoparticles is 20 vol%, the thermal conductivity can be increased by up to 35% (from 28 W / mK to 38 W / m K). Regarding electrical conductivity, et al. showed that the conductivity increases with the increase of SiC nanoparticle content, especially in composites with SiC volume fraction greater than or equal to 10 vol%. The results show that at low SiC contents, SiC particles cannot connect to each other to form a continuous conductive network, and this result is confirmed when the SiC content is higher than 10%, and the conductivity increases from 10~5S / m (5vol%) to 10~3S / m (10vol%). Other studies have also confirmed the same trend, such as the study of Sawaguchi et al. or Stauffer and Aharony, who proposed adding 17vol% of the second phase to create an effective conductive path based on a mathematical model.

[0014] Although the mechanical and electrical properties of Al2O3 / SiC nanocomposites have been greatly improved, these advantages depend to a large extent on the dispersion of the second phase and the degree of densification of the ceramic sintering. Nano-silicon carbide will overflow from the matrix and pollute the furnace due to its high activity during sintering in a high-temperature atmosphere furnace, commonly known as oxidation of silicon carbide. How to ensure that the silicon carbide of the matrix is ​​retained during high-temperature sintering is a challenge to obtaining high-performance alumina silicon carbide composite ceramics. At present, there are very few domestic manufacturers that can produce high-performance nano-silicon carbide, and most of them are micron-level silicon carbide. The nano-silicon carbide produced by a few manufacturers still has problems such as insufficient purity, large specific surface area and uneven microstructure, which adds technical difficulties to the dispersion and sintering of nano-silicon carbide. Summary of the invention

[0015] The technical problem to be solved by the present invention is to provide a sintering method for a composite SiC alumina electrostatic chuck ceramic disc to obtain a composite silicon carbide alumina ceramic disc with a fine crystal structure, thereby improving the mechanical and electrical properties and the performance of the electrostatic chuck.

[0016] In order to solve the above technical problems, the technical solution of the present invention is:

[0017] A method for sintering a composite SiC alumina electrostatic chuck ceramic disc, the sintering method comprising:

[0018] S1: Modification and pre-oxidation treatment of nano-SiC

[0019] Modification: In the process of synthesizing silicon carbide, the residual amount of carbon black in the reaction is controlled to obtain nano silicon carbide powder with different carbon contents. The encapsulation of carbon black can inhibit the decomposition of silicon carbide to a certain extent;

[0020] Pre-oxidation: First, pre-oxidize the modified nano-silicon carbide at low temperature for 95 to 110 hours, then anneal at 1100 to 1300 ° C for 50 to 120 hours under argon atmosphere protection for crystallization, and then oxidize. By comparing the oxidation rates of re-oxidation and pre-oxidation, the oxidation rate constant of pre-oxidation is greater than the oxidation rate constant of re-oxidation, that is, the crystallization of SiO2 film by pre-oxidation can reduce the oxidation rate;

[0021] S2: Tape Casting

[0022] The modified nano-silicon carbide is ball-milled in a bedroom sand mill to make the particle size distribution narrower and eliminate the influence of large particles on the performance of subsequent ceramic products. The ball-milled nano-silicon carbide powder, solvent, and dispersant are pre-grinded in a planetary mill for 2 to 4 hours, and then mixed and ground with alumina powder for 2 to 4 hours, and finally a binder is added and ground for 36 to 38 hours. After the mixed grinding is completed, the ceramic green body is tape-casted to obtain the green body;

[0023] S3: High temperature sintering

[0024] The ceramic green body obtained by tape casting is debinded in wet nitrogen, and the debinding temperature and atmosphere are controlled to ensure that the green body will not be stratified. The product obtained by debinding is bisque-fired in an HP furnace under a certain atmosphere and pressure. The product is surrounded by a graphite fixture. The sintering shrinkage rate of the obtained sample reaches more than 10%. The sample is then sintered in a HIP mold at high temperature and high pressure for 2 hours. Finally, the obtained product is pressurized and sintered in a HP furnace in a certain Ar atmosphere to sinter into an electrostatic chuck ceramic disk.

[0025] Preferably, in step S1, by comparing the oxidation rates of re-oxidation and pre-oxidation, it is obtained that the oxidation rate constant of pre-oxidation is at least 20 times higher than the oxidation rate constant of re-oxidation, that is, the crystallization of the SiO2 film reduces the oxidation rate by at least 20 times. Crystallization of the SiO2 film by pre-oxidation can reduce the oxidation rate.

[0026] Preferably, in the pre-oxidation of step S1, the sample is first pre-oxidized at low temperature for 100 hours, and then annealed at 1200° C. for 100 hours under argon atmosphere protection for crystallization.

[0027] Preferably, in step S2, the ball-milled nano-silicon carbide powder, solvent, and dispersant are pre-ground in a planetary mill for 2 hours, then mixed and ground with alumina for 2 hours, and finally a binder is added and ground for 36 hours.

[0028] Preferably, in step S3, the bulk density of the sintered electrostatic chuck ceramic disc is greater than or equal to 3.88 g / cm 3 .

[0029] The above technical solution has the following beneficial effects:

[0030] Effectively inhibits the oxidation and decomposition of nano-silicon carbide;

[0031] A fine-grained black alumina and silicon carbide composite ceramic was obtained, which improved the mechanical and electrical properties and can enhance the performance of the electrostatic chuck. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example 1

[0034] A method for sintering a composite SiC alumina electrostatic chuck ceramic disc comprises the following steps:

[0035] S1: Modification and pre-oxidation treatment of nano-SiC

[0036] Modification: In the process of synthesizing silicon carbide, the residual amount of carbon black in the reaction is controlled to obtain nano-silicon carbide powder with different carbon contents, so as to modify the nano-silicon carbide. The encapsulation of carbon black can inhibit the decomposition of silicon carbide to a certain extent;

[0037] Pre-oxidation: First, pre-oxidize the modified nano-silicon carbide at low temperature for 95 to 110 hours, then anneal it at 1100 to 1300 ° C for 50 to 120 hours under argon atmosphere protection for crystallization, and then oxidize it. By comparing the oxidation rates of re-oxidation and pre-oxidation, the oxidation rate constant of pre-oxidation is greater than the oxidation rate constant of re-oxidation, that is, the crystallization of SiO2 film by pre-oxidation can reduce the oxidation rate;

[0038] By comparing the oxidation rates of reoxidation and preoxidation, it is found that the oxidation rate constant of preoxidation is at least 20 times higher than that of reoxidation, that is, the crystallization of the SiO2 film reduces the oxidation rate by at least 20 times. The crystallization of the SiO2 film by preoxidation can reduce the oxidation rate.

[0039] S2: Tape Casting

[0040] The modified nano-silicon carbide is ball-milled in a bedroom sand mill to make the particle size distribution narrower and eliminate the influence of large particles on the performance of subsequent ceramic products. The ball-milled nano-silicon carbide powder, solvent, and dispersant are pre-grinded in a planetary mill for 2 to 4 hours, and then mixed and ground with alumina powder for 2 to 4 hours, and finally a binder is added and ground for 36 to 38 hours. After the mixed grinding is completed, the ceramic green body is tape-casted to obtain the green body;

[0041] S3: High temperature sintering

[0042] The ceramic green body obtained by tape casting is debinded in wet nitrogen, and the debinding temperature and atmosphere are controlled to ensure that the green body will not be delaminated. The product obtained by debinding is bisque fired in an HP furnace (i.e., hot pressing sintering furnace) under a certain atmosphere and pressure. The HP furnace is a hot pressing sintering furnace. The product is surrounded by a graphite fixture. The sintering shrinkage rate of the obtained sample reaches more than 10%. The sample is then sintered at high temperature and high pressure for 2 hours in a HIP mold. The HIP mold is a mold prepared by superhard V40. Finally, the obtained product is sintered under pressure in a certain Ar atmosphere in an HP furnace to sinter into an electrostatic chuck ceramic disk. The volume density of the sintered electrostatic chuck ceramic disk is greater than or equal to 3.88g / cm 3 .

[0043] Silicon carbide materials have good oxidation resistance under normal conditions (such as atmospheric temperatures of 1000-2000°C). This is because a very thin, dense, and firmly bonded SiO2 film is produced on the surface of the silicon carbide material under high temperature conditions. The diffusion coefficient of oxygen in the SO2 film is very small, so the oxidation of silicon carbide materials is very slow. Under such conditions, the slow oxidation of silicon carbide materials is called passive oxidation. However, under certain conditions, such as at sufficiently high temperatures or low oxygen partial pressures, a volatile SiO2 will be generated on the SiC surface, or the generated SiO2 film will be corroded by the environment, which will cause the silicon carbide material to be rapidly oxidized (active oxidation, Active Oxidation). Silicon carbide materials often encounter such environments during use.

[0044] It is difficult to sinter silicon carbide materials to be dense without sintering aids (such as alumina, boron, carbon, etc.), but these small amounts of sintering aids or impurities will redistribute through the SiO2 film during high-temperature oxidation to achieve a balance of chemical potential. Impurities that usually diffuse into the SiO2 film will reduce the viscosity of the SiO2 film, thereby accelerating the diffusion of oxygen through the SiO2 film and accelerating the oxidation of SiC. Sintering aids or impurities may accelerate the oxidation rate of SiC, but do not fundamentally change the oxidation mechanism. When the environment contains elements that can interfere with the formation of the protective film, the SiC material may be severely damaged. Corrosion, chlorine and alkali metals are two common elements that can interfere with the formation of SiO2 protective film. Therefore, it is necessary to control the content of trace elements in aluminum oxide and silicon carbide powders. Alkali metals such as sodium have been found to greatly accelerate the oxidation of SiC. The vapor pressure of alkali metals is relatively high, which is easy to pollute the ambient atmosphere and accelerate the oxidation of SiC. Under sufficiently high temperatures or low oxygen partial pressure conditions, silicon carbide (SiC)-based materials will generate volatile rather than dense oxides during the oxidation process. Under such conditions, SiC continues to oxidize rapidly and shows the characteristics of weight loss. This oxidation is called active oxidation. Since silicon carbide cannot form a SiO2 protective film during active oxidation, it loses its good antioxidant properties during passive oxidation, resulting in rapid oxidation.

[0045] The method provided by the present invention is realized through two steps: one is surface modification, pre-oxidation and dispersion of nano-silicon carbide in nano-alumina (prepared by CVD method), and the other is tape casting and high-temperature sintering;

[0046] Through the method itself, the oxidative decomposition of nano-silicon carbide can be effectively suppressed; a black alumina / silicon carbide composite ceramic with a fine-grained structure is obtained, and the mechanical and electrical properties are greatly improved, which can enhance the performance of the electrostatic chuck.

[0047] Example 2

[0048] A method for sintering a composite SiC alumina electrostatic chuck ceramic disc comprises the following steps:

[0049] S1: Modification and pre-oxidation treatment of nano-SiC

[0050] Modification: In the process of synthesizing silicon carbide, the residual amount of carbon black in the reaction is controlled to obtain nano silicon carbide powder with different carbon contents. The encapsulation of carbon black can inhibit the decomposition of silicon carbide to a certain extent;

[0051] Pre-oxidation: First, the modified nano-silicon carbide is pre-oxidized at low temperature for 100 hours. In other embodiments of the present embodiment, the pre-oxidation time at low temperature is 95 hours or 110 hours. Then, under the protection of argon atmosphere, annealing is performed at a temperature of 1200°C for 100 hours for crystallization. In other embodiments of the present embodiment, it can also be annealed at a temperature of 1100°C or 1300°C for 50 hours or 120 hours for crystallization under the protection of argon atmosphere, and then oxidized. By comparing the oxidation rates of re-oxidation and pre-oxidation, the oxidation rate constant of pre-oxidation is greater than the oxidation rate constant of re-oxidation, that is, the crystallization of SiO2 film by pre-oxidation can reduce the oxidation rate;

[0052] By comparing the oxidation rates of reoxidation and preoxidation, it is found that the oxidation rate constant of preoxidation is at least 20 times higher than that of reoxidation, that is, the crystallization of the SiO2 film reduces the oxidation rate by at least 20 times. The crystallization of the SiO2 film by preoxidation can reduce the oxidation rate.

[0053] S2: Tape Casting

[0054] The modified nano-silicon carbide is ball-milled in a bedroom sand mill to make the particle size distribution narrower and eliminate the influence of large particles on the performance of subsequent ceramic products. The ball-milled nano-silicon carbide powder, solvent, and dispersant are pre-grinded in a planetary mill for 2 hours. In other embodiments of this embodiment, the pre-grinding time in the planetary mill is 4 hours. Then, it is mixed and ground with alumina powder for 2 hours. In other embodiments of this embodiment, the mixed grinding time is 4 hours. Finally, a binder is added and ground for 36 hours. In other embodiments of this embodiment, the binder is added and ground for 38 hours. After the mixed grinding is completed, tape casting is performed to obtain a ceramic green body;

[0055] S3: High temperature sintering

[0056] The ceramic green body obtained by tape casting is debinded in wet nitrogen, and the debinding temperature and atmosphere are controlled to ensure that the green body will not be delaminated. The product obtained by debinding is bisque fired in an HP furnace under a certain atmosphere and pressure, and the product is surrounded by a graphite fixture. The sintering shrinkage rate of the obtained sample reaches more than 10%. The sample is then sintered in a HIP mold at high temperature and high pressure for 2 hours. Finally, the obtained product is sintered under pressure in a certain Ar atmosphere in an HP furnace to sinter into an electrostatic chuck ceramic disk. The volume density of the sintered electrostatic chuck ceramic disk is greater than or equal to 3.88g / cm 3 .

[0057] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A method for sintering a composite SiC alumina electrostatic chuck ceramic disc, characterized in that: The sintering method comprises: S1: Modification and pre-oxidation treatment of nano-SiC Modification: In the process of synthesizing silicon carbide, the residual amount of carbon black in the reaction is controlled to obtain nano silicon carbide powder with different carbon contents. The encapsulation of carbon black can inhibit the decomposition of silicon carbide to a certain extent; Pre-oxidation: First, pre-oxidize the modified nano-silicon carbide at low temperature for 95 to 110 hours, then anneal at 1100 to 1300 ° C for 50 to 120 hours under argon atmosphere protection for crystallization, and then oxidize. By comparing the oxidation rates of re-oxidation and pre-oxidation, the oxidation rate constant of pre-oxidation is greater than the oxidation rate constant of re-oxidation, that is, the crystallization of SiO2 film by pre-oxidation can reduce the oxidation rate; S2: Tape Casting The modified nano-silicon carbide is ball-milled in a bedroom sand mill to make the particle size distribution narrower and eliminate the influence of large particles on the performance of subsequent ceramic products. The ball-milled nano-silicon carbide powder, solvent, and dispersant are pre-grinded in a planetary mill for 2 to 4 hours, and then mixed and ground with alumina powder for 2 to 4 hours, and finally a binder is added and ground for 36 to 38 hours. After the mixed grinding is completed, the ceramic green body is tape-casted to obtain the green body; S3: High temperature sintering The ceramic green body obtained by tape casting is debinded in wet nitrogen, and the debinding temperature and atmosphere are controlled to ensure that the green body will not be stratified. The product obtained by debinding is bisque-fired in an HP furnace under a certain atmosphere and pressure. The product is surrounded by a graphite fixture. The sintering shrinkage rate of the obtained sample reaches more than 10%. The sample is then sintered in a HIP mold at high temperature and high pressure for 2 hours. Finally, the obtained product is pressurized and sintered in a HP furnace in a certain Ar atmosphere to sinter into an electrostatic chuck ceramic disk.

2. The sintering method of a composite SiC alumina electrostatic chuck ceramic disc according to claim 1, characterized in that: In the step S1, by comparing the oxidation rates of re-oxidation and pre-oxidation, it is found that the oxidation rate constant of pre-oxidation is at least 20 times higher than that of re-oxidation, that is, the crystallization of the SiO2 film reduces the oxidation rate by at least 20 times. Crystallization of the SiO2 film by pre-oxidation can reduce the oxidation rate.

3. The sintering method of a composite SiC alumina electrostatic chuck ceramic disc according to claim 1, characterized in that: In the pre-oxidation of step S1, the sample is first pre-oxidized at low temperature for 100 hours, and then annealed at 1200° C. for 100 hours under argon atmosphere protection for crystallization.

4. The method for sintering a composite SiC alumina electrostatic chuck ceramic disc according to claim 3, characterized in that: In the step S2, the ball-milled nano-silicon carbide powder, solvent, and dispersant are pre-ground in a planetary mill for 2 hours, then mixed and ground with alumina for 2 hours, and finally a binder is added and ground for 36 hours.

5. The method for sintering a composite SiC alumina electrostatic chuck ceramic disc according to claim 1, characterized in that: In step S3, the volume density of the sintered electrostatic chuck ceramic disc is greater than or equal to 3.88 g / cm 3 .