High-purity transparent ceramic dielectric layer, preparation method thereof and aluminum oxide electrostatic chuck

Abstract

The application relates to the field of electronic ceramics manufacturing, in particular to a high-purity transparent ceramic dielectric layer, a preparation method thereof and an alumina electrostatic chuck. The high-purity transparent ceramic dielectric layer is prepared from alpha-Al2O3 powder with a purity of greater than or equal to 99.99% and a sintering aid as main raw materials, and is sintered through a two-stage process of hydrogen pressureless sintering and 3-5 MPa high-pressure hydrogen sintering after flow casting, isostatic pressing and degassing, so that the prepared ceramic is completely dense, free of pores and free of grain boundary impurity phases; the alumina electrostatic chuck has the above high-purity transparent ceramic dielectric layer as a medium layer directly contacting a wafer, has the characteristics of low metal contamination, resistance to plasma corrosion, high dielectric strength, good thermal matching and long service life, and can meet the strict requirements of advanced semiconductor processes.

Description

Technical Field

[0001] This invention relates to the field of electronic ceramics manufacturing, specifically to a high-purity transparent ceramic dielectric layer and its preparation method, and an alumina electrostatic chuck. Background Technology

[0002] Electrostatic chucks are key components in semiconductor manufacturing processes, widely used in semiconductor equipment for etching, chemical vapor deposition (CVD), physical vapor deposition (PVD), and ion implantation. Their function is to firmly hold wafers (such as silicon wafers and silicon carbide wafers) onto the chuck surface using electrostatic force, ensuring wafer positioning accuracy, temperature uniformity, and effective backside gas cooling during the process. As integrated circuit process nodes continue to shrink towards 5nm, 3nm, and even more advanced levels, the requirements for controlling particulate contamination, metal contamination, and backside defects during wafer processing are becoming increasingly stringent, correspondingly placing higher demands on the material properties of electrostatic chucks.

[0003] Currently, the dielectric layer (i.e., the insulating layer that directly contacts the wafer) of electrostatic chucks is mainly made of ceramic materials, with alumina (Al2O3) ceramic being the most widely used. Ordinary alumina ceramic (typically with a purity of 95%–99.5%) has high mechanical strength, good insulation properties, and relatively low cost, thus dominating the use of electrostatic chucks in low-to-mid-range or more mature processes. However, with the stringent restrictions on metal contamination (especially Na, Fe, Ni, Cu, etc.) in advanced processes, ordinary alumina ceramic, containing a certain amount of impurity phases (such as glassy phases, sintering aids, and metal oxide impurities), gradually releases metal contaminants during use, leading to metal contamination on the back of the wafer, severely affecting device yield and reliability. Simultaneously, the microstructure of ordinary alumina ceramic contains a certain number of pores and grain boundary impurities, making it insufficiently corrosion-resistant in strong plasma environments, prone to surface corrosion and particle shedding, shortening chuck life and increasing equipment maintenance frequency.

[0004] In addition, although conventional opaque high-purity alumina ceramics (purity ≥99.9%) reduce the content of metal impurities to a certain extent, the sintering process fails to achieve complete densification and transparency. As a result, the grain size is large and there may still be residual micropores and grain boundary defects inside, leading to unstable resistivity and low dielectric strength. In high-power radio frequency plasma environments, abnormal discharge or decreased adsorption force is likely to occur.

[0005] Another dielectric material commonly used in electrostatic chucks is aluminum nitride (AlN). Aluminum nitride has extremely high thermal conductivity (160–260 W / m·K) and a coefficient of thermal expansion close to that of silicon wafers (approximately 4.5 × 10⁻⁶). -6Aluminum nitride (AN) has advantages in power device manufacturing processes requiring efficient heat dissipation (temperatures up to 100°C). However, AN is expensive (typically 3 to 6 times more expensive than alumina) and its corrosion resistance in plasma environments is lower than that of high-purity alumina. Furthermore, AN ceramics are generally opaque, making it impossible to directly assess their internal defects or contamination using optical methods, which limits their application in scenarios requiring extremely high cleanliness and detectability.

[0006] To address the shortcomings of the prior art, attempts have been made in this field to obtain high-purity transparent ceramic dielectric layers by improving the preparation process of alumina ceramics. However, existing solutions differ significantly from the technical approach of this invention, as detailed below: For example, the application CN02123648.8, "Preparation Method of Submicron High-Purity Transparent Alumina Ceramic Material", discloses the process of α-Al2O3 powder being cold isostatically pressed and then pressureless pre-sintered. However, it does not disclose the two-stage process of first pressureless sintering with hydrogen to a density of more than 97%, and then sintering under a high-pressure hydrogen atmosphere of 3-5 MPa. This makes it difficult to eliminate residual closed pores and achieve complete densification and transparency. Another application, No. 201710756686.0, entitled "A Method for Preparing Fine-Grained, High-Strength Magnesium Aluminum Spinel Transparent Ceramics," discloses a process in which magnesium aluminum spinel powder is sintered in a muffle furnace followed by pre-sintering. The pre-sintering includes hot pressing sintering, with a sintering temperature of 600–1100°C and a sintering holding time of 2–10 hours. However, the above sintering conditions are only within the sintering temperature range for alumina degreasing. At this temperature, the diffusion rate of aluminum oxide ions is extremely low, which can only remove organic matter and achieve slight particle necking. The density is tested to be at most 89%, and complete densification cannot be achieved. Another patent application number 201810580194.5 discloses a process in which magnesium oxide powder and α-Al2O3 powder are sintered under pressure to form a pre-sintered body with a relative density of 82% to 90%, and then pressureless sintering and hot isostatic pressing are performed in sequence. The pre-sintered body of this process has a low density and it is difficult to achieve a high degree of densification. In summary, existing alumina dielectric layers may have problems such as the release of metal impurities and insufficient resistance to plasma corrosion, or they may have problems such as coarse grains, residual pores leading to unstable dielectric properties, and inability to achieve transparent detection. Existing preparation processes also make it difficult to achieve complete densification and transparency of high-purity alumina under low-cost conditions. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of the prior art by providing a high-purity transparent ceramic dielectric layer, which possesses ultra-high purity, stable insulation properties, and excellent resistance to plasma corrosion, meeting the stringent requirements of advanced processes for wafer metal contamination and dielectric properties. Another objective of this invention is to provide a method for preparing a high-purity transparent ceramic dielectric layer, which achieves complete densification and transparency of the ceramic, resulting in a high-purity transparent ceramic free of pores and grain boundary impurities, with fine and uniform grains. A further objective of this invention is to provide an alumina electrostatic chuck, characterized by low metal contamination, stable electrostatic adsorption, corrosion resistance, good thermal matching, and long service life.

[0008] The objective of this invention is achieved through the following technical solution: A high-purity transparent ceramic dielectric layer, wherein the high-purity transparent alumina ceramic dielectric layer comprises the following components in parts by weight: 99.9-99.95 parts of α-Al2O3 powder, 0.05-0.10 parts of sintering aid, 45-55 parts of solvent, 0.5-2.5 parts of dispersant, 7-11 parts of binder and 4-8 parts of plasticizer.

[0009] Furthermore, the α-Al2O3 powder has a purity of ≥99.99% and an average particle size between 0.1 and 1.0 μm.

[0010] Furthermore, the sintering aid is alumina or yttrium oxide, and may include one of magnesium oxide, magnesium nitrate, or magnesium aluminum spinel; the dispersant is at least one of castor oil, herring oil, polyethylene glycol, or phosphate ester; the binder is polyvinyl butyral; and the plasticizer is at least one of dioctyl phthalate, dimethyl phthalate, dibutyl phthalate, or diisononyl phthalate.

[0011] Furthermore, the sintering aid comprises the following components by weight percentage: 99.9-99.99% alumina, 0.01-0.1% yttrium oxide, 0-0.09% magnesium oxide, 0-0.09% magnesium nitrate, and 0-0.09% magnesium aluminum spinel.

[0012] This invention utilizes α-Al2O3 powder with a purity ≥99.99% and specific sintering aids, employing a two-stage sintering process involving tape casting, isostatic pressing, debinding, and first hydrogen pressureless sintering to achieve a density ≥97%, followed by high-pressure hydrogen sintering at 3-5 MPa. This process yields a completely dense, pore-free, and grain boundary-free high-purity transparent ceramic dielectric layer.

[0013] This invention also provides a method for preparing a high-purity transparent ceramic dielectric layer, comprising the following steps: (1) Slurry preparation: Take α-Al2O3 powder, sintering aid, solvent and dispersant by weight, mix them in proportion to obtain mixed powder; put the mixed powder into a ball mill for ball milling; then add binder and plasticizer, and continue ball milling; then degas the ball milled slurry to obtain cast slurry; (2) Casting and cutting: The casting machine is used to make the casting slurry into a ceramic green porcelain strip, and then the cutting machine is used to cut the ceramic green porcelain strip into multiple ceramic green porcelain pieces; (3) Drilling: Processing structural holes and positioning holes into the raw ceramic slab; (4) Isostatic pressing: The ceramic green porcelain sheets are stacked to a certain thickness and then sealed in plastic; the sealed stacked sheets are pressed to make them tightly bonded into a whole green body; (5) Debinding: Place the ceramic raw porcelain plate on the corundum mullite firing plate and put it into the debinding furnace to debind the adhesive, and then obtain the ceramic debinding plate. (6) Sintering: Place the ceramic debonding plate into the sintering furnace and perform pressureless sintering at a high temperature of 1450-1550℃ in a hydrogen atmosphere for 2-4 hours to form a dense ceramic part with a density of over 97%; reduce the temperature by 20-50℃, increase the hydrogen pressure in the furnace to 3-5MPa, and hold for 1-3 hours in a high-pressure hydrogen atmosphere to obtain a high-purity transparent ceramic dielectric layer.

[0014] The high-purity transparent ceramic dielectric layer preparation method of the present invention adopts a process route combining tape casting and two-stage sintering. First, pressureless sintering is carried out until the density exceeds 97%, and then sintering is carried out under high pressure hydrogen atmosphere to eliminate residual closed pores and inhibit abnormal grain growth, so as to obtain a highly dense and highly transparent ceramic dielectric layer.

[0015] Furthermore, in step (5), the adhesive removal step involves slowly heating the material to 400-500°C at a heating rate of 0.3-1°C / min under a nitrogen atmosphere and holding it at that temperature for 3-6 hours.

[0016] The present invention also provides an alumina electrostatic chuck, comprising a ceramic body, an adhesive layer, and a base arranged sequentially from top to bottom. The ceramic body includes at least one high-purity transparent ceramic dielectric layer and an electrode layer disposed on the high-purity transparent ceramic dielectric layer, with a solder layer disposed between two adjacent high-purity transparent ceramic dielectric layers. The high-purity transparent ceramic dielectric layer is used for direct contact with the wafer.

[0017] Furthermore, the upper surface of the high-purity transparent ceramic dielectric layer at the top end is provided with multiple upwardly protruding protrusions.

[0018] Furthermore, the base is made of an aluminum-based alloy and its surface is anodized.

[0019] Furthermore, the welding layer is printed with welding paste, which is at least one of alumina, magnesium oxide, calcium fluoride, and magnesium fluoride.

[0020] Furthermore, the welding slurry comprises the following components by weight percentage: 99.5-99.9% aluminum oxide, 0.05-0.45% magnesium oxide, 0.03-0.43% calcium fluoride, and 0.02-0.42% magnesium fluoride.

[0021] The alumina electrostatic chuck of the present invention uses a high-purity transparent ceramic dielectric layer as the dielectric layer that directly contacts the wafer, and has the characteristics of low metal contamination, resistance to plasma corrosion, high dielectric strength, good thermal matching, and long service life.

[0022] Furthermore, the preparation method of the alumina electrostatic chuck includes the following steps: S1. Printing: Metal paste is printed on the upper surface of the high-purity transparent ceramic dielectric layer to form an electrode layer, and solder paste is printed to obtain a pre-fabricated ceramic dielectric layer. S2. Welding: Take another high-purity transparent ceramic dielectric layer, place it on top of the pre-made ceramic dielectric layer obtained in step S1, put it into a welding furnace, and weld it at 1300-1350℃ and 0.5-3MPa pressure, so that the welding slurry forms a welding layer between the two high-purity transparent ceramic dielectric layers. S3. Machining: The welded dense and transparent ceramic plate is processed using machining equipment according to the drawing requirements to obtain the ceramic body; S4. Assembly: The ceramic sheet is bonded to the anodized metal base to obtain the finished high-purity transparent alumina electrostatic chuck.

[0023] The method for preparing an alumina electrostatic chuck of the present invention integrates a high-purity transparent ceramic dielectric layer with an electrode layer and a base through printing, welding, machining and assembly, thereby producing an electrostatic chuck with ultra-high purity, stable electrostatic adsorption and strong resistance to plasma corrosion.

[0024] Furthermore, the metal paste mentioned in step S1 is at least one of platinum, ruthenium, rhodium and palladium; in step S3, the flatness of the machined ceramic body is <5μm and the surface roughness is <0.1μm.

[0025] The beneficial effects of this invention are as follows: 1. Ultra-high cleanliness: In response to the problem that ordinary alumina ceramics release metal contaminants due to impurities such as glass phase, which leads to wafer metal contamination, the dielectric layer of this invention uses high-purity transparent alumina with a purity of ≥99.99%. The release of metal ions (Na, Fe, Ni, Cu, etc.) is reduced by more than an order of magnitude compared to ordinary alumina with a purity of 95% to 99.5%, which can meet the stringent requirements for wafer metal contamination in 5nm and more advanced processes; 2. Stable and reliable electrostatic adsorption: Addressing the issues of unstable resistivity, low dielectric strength, and susceptibility to abnormal discharge in conventional opaque high-purity alumina due to residual micropores and grain boundary defects, this invention achieves a fully dense, transparent ceramic with a volume resistivity reaching 10⁻⁶. 14 With a dielectric strength of ≥45kV / mm and a dielectric strength of ≥45kV / mm, it ensures no abnormal discharge or adsorption force attenuation under long-term high voltage and radio frequency plasma environment; 3. Excellent corrosion resistance: In response to the problem that ordinary alumina ceramics are prone to corrosion and particle shedding in plasma environment due to pores and grain boundary impurities in the microstructure, the microstructure of this invention is completely dense, without pores or grain boundary impurities, which makes its corrosion rate less than 0.01nm / min, reduces the amount of surface particles shedding by more than 50%, and extends the mean time between failures of the chuck by more than 1.5 times compared with ordinary alumina electrostatic chuck. 4. Excellent thermal matching: Addressing the requirements of semiconductor processes for wafer temperature uniformity, the thermal conductivity of the dielectric layer in this invention (30–35 W / (m·K)) effectively conducts heat generated during wafer processing, achieving wafer temperature uniformity in conjunction with back-side gas cooling; the coefficient of thermal expansion is (6.5–8.5) × 10⁻⁶. -6 / ℃ and the thermal stress caused by silicon wafers within the typical semiconductor process temperature range (20~400℃) are within acceptable limits; 5. Facilitates quality inspection: Addressing the issue that existing aluminum nitride ceramics and opaque alumina ceramics cannot directly assess internal defects or contamination using optical methods, the transparent dielectric layer of this invention allows direct observation of the electrode layer's integrity, internal ceramic defects, or contaminant deposition during manufacturing and use using an optical microscope. This facilitates failure analysis and process control, and reduces inspection costs. Detailed Implementation To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0026] Example 1 This embodiment provides a high-purity transparent ceramic dielectric layer, which comprises the following components in parts by weight: 99.93 parts of α-Al2O3 powder, 0.08 parts of sintering aid, 50 parts of solvent, 1.5 parts of dispersant, 9 parts of binder, and 6 parts of plasticizer.

[0027] Furthermore, the α-Al2O3 powder has a purity of ≥99.99% and an average particle size between 0.1 and 1.0 μm.

[0028] Furthermore, the dispersant is castor oil; the binder is polyvinyl butyral; and the plasticizer is dioctyl phthalate.

[0029] Furthermore, the sintering aid is alumina, yttrium oxide, and contains one of magnesium oxide, magnesium nitrate, or magnesium aluminum spinel.

[0030] This embodiment also provides a method for preparing a high-purity transparent ceramic dielectric layer, including the following steps: (1) Take α-Al2O3 powder, sintering aid, solvent and dispersant, mix them in proportion to obtain mixed powder; put the mixed powder into a ball mill for ball milling; then add binder and plasticizer, and continue ball milling; then degas the ball milled slurry to obtain cast slurry; (2) Casting and cutting: The casting machine is used to make the casting slurry into a ceramic green porcelain strip, and then the cutting machine is used to cut the ceramic green porcelain strip into multiple ceramic green porcelain pieces; (3) Drilling: Processing structural holes and positioning holes into the raw ceramic slab; (4) Isostatic pressing: The ceramic green porcelain sheets are stacked to a certain thickness and then sealed in plastic; the sealed stacked sheets are pressed to make them tightly bonded into a whole green body; (5) Debinding: Place the ceramic raw porcelain plate on the corundum mullite firing plate and put it into the debinding furnace to debind the adhesive, and then obtain the ceramic debinding plate. (6) Sintering: The ceramic debonding plate is placed in the sintering furnace and sintered at a high temperature of 1500℃ in a hydrogen atmosphere for 3 hours to form a dense ceramic part with a density of more than 97%; the temperature is reduced by 35℃ and the hydrogen pressure in the furnace is increased to 4MPa. The furnace is then held for 2 hours in a high-pressure hydrogen atmosphere to obtain a high-purity transparent ceramic dielectric layer.

[0031] Furthermore, in step (5), the glue removal step involves slowly heating the material to 450°C at a heating rate of 0.7°C / min under a nitrogen atmosphere and holding it at that temperature for 4.5 hours.

[0032] To further confirm the optimal composition and ratio of the sintering aid, various formulations of the sintering aid and their corresponding ceramic properties are shown in Tables 1 and 2 below: Table 1. Sintering aid formulation (by weight percentage)

[0033] Table 2 Comparison of ceramic properties obtained with different sintering aid formulations

[0034] The resistivity (volume resistivity) was tested according to GB / T 5594.5-2015 "Test Methods for Performance of Structural Ceramic Materials for Electronic Components - Volume Resistivity Test Method"; the dielectric strength (breakdown strength) was tested according to the DC breakdown strength test method specified in Clause 5.13 of GB / T 5593-2015; the plasma corrosion resistance was tested according to the method described in the national standard plan "Test Methods for Plasma Corrosion Resistance of Ceramic Components in Fine Ceramic Semiconductor Manufacturing Equipment" (under the jurisdiction of the National Industrial Ceramics Standardization Technical Committee TC194), using plasma etching equipment, exposing the sample to a CF4 / O2 mixed plasma atmosphere for a specified time, and characterizing the corrosion (etching) rate by measuring the etching depth; the thermal conductivity was tested according to GB / T 22588-2008 "Measuring Thermal Diffusion Coefficient or Thermal Conductivity by Flash Method"; and the coefficient of thermal expansion (average linear expansion coefficient) was tested according to GB / T 5594.3-2015 "Test Methods for Performance of Structural Ceramic Materials for Electronic Components - Part 3: Test Method for Average Linear Expansion Coefficient".

[0035] As shown in Table 2, comparing the test results of formulations 1 and 2, it can be concluded that in the high-purity alumina ceramic system, the addition of trace amounts of yttrium oxide helps improve the various properties of the ceramic after sintering, while excessive yttrium oxide addition will cause a decline in the overall performance of the ceramic. Comparing the test results of formulations 2 with those of formulations 4, 6, and 8, it can be concluded that compared with the single yttrium oxide additive system, the introduction of magnesium-containing composite additives can further optimize the overall performance of alumina ceramics on the original performance. The test results show that the ceramic with the best overall performance is prepared by formulation 4, i.e., the formulation with 99.95% alumina, 0.01% yttrium oxide, and 0.04% magnesium oxide produces the best ceramic performance. Taking all factors into consideration, the following weight percentages of sintering aids were selected: 99.95% alumina, 0.01% yttrium oxide, and 0.04% magnesium oxide as the basis for subsequent examples and comparative products or preparation methods.

[0036] Comparative Example 1 Comparative Example 1 provides a method for preparing a high-purity transparent ceramic dielectric layer. The preparation steps provided in this comparative example are the same as those in Example 1, except that step (6) is performed using only pressureless sintering. The steps are as follows: (6) Pressureless sintering: Sintering is carried out in a hydrogen atmosphere at a high temperature of 1500℃ for 5 hours to form a dense ceramic part.

[0037] The ceramic prepared in Comparative Example 1 has micron-sized closed pores in its green body. The gas pressure inside the closed pores cancels out the driving force of sintering, thus preventing further densification. Its density is at most 97%~98.2%. At the same time, in order to improve the density of the ceramic, compared with the example, the holding time during sintering in this comparative example was extended. As a result, the alumina grains grew abnormally, resulting in local coarsening and a decrease in flexural strength and thermal shock resistance.

[0038] Comparative Example 2 Comparative Example 2 provides a method for preparing a high-purity transparent ceramic dielectric layer. The preparation steps provided in this comparative example are the same as those in Example 1, except that step (6) only uses hot pressing sintering. The steps are as follows: (6) Hot pressing sintering: The ceramic matrix is ​​placed in a graphite mold and sintered in a hot pressing sintering furnace. It is kept at 1800℃ and 35MPa for 5 hours to obtain a ceramic sintered piece.

[0039] The ceramic prepared in Comparative Example 2 exhibits anisotropic mechanical and thermal properties due to residual stress inside the green body caused by unidirectional axial pressure during sintering, making it prone to cracking under semiconductor processing conditions.

[0040] Comparative Example 3 Comparative Example 3 provides a method for preparing a high-purity transparent ceramic dielectric layer. The preparation steps provided in this comparative example are the same as those in Example 1, except that step (6) sintering is first hot-pressed sintering and then pressureless sintering. The steps are as follows: (6) Sintering: Place the ceramic matrix into a graphite mold and sinter it in a hot press sintering furnace. Hold it at 1500℃, 4MPa, and hydrogen atmosphere for 2 hours. Keep the temperature inside the furnace constant, reduce the pressure to normal pressure, and hold for 3 hours.

[0041] The ceramic prepared in Comparative Example 3 is prone to warping and internal delamination cracking because hot pressing sintering is first used in step (6) followed by pressureless sintering. Hot pressing sintering introduces unidirectional residual stress, which cannot be eliminated by subsequent pressureless secondary sintering. At the same time, the second pressureless sintering has no external pressure, so the closed pores inside the green body cannot be eliminated, the increase in density is limited, and pore defects still exist.

[0042] Comparative Example 4 Comparative Example 4 provides a method for preparing a high-purity transparent ceramic dielectric layer. The preparation steps provided in this comparative example are the same as those in the example, except that the pressureless sintering and heat preservation time in step (6) is shortened. The steps are as follows: (6) Sintering: In a hydrogen atmosphere, pressureless sintering is carried out at a high temperature of 1500℃ and the holding time is 1.5 hours to form a dense ceramic part with a density of 85-90%; the furnace temperature is kept constant, the hydrogen pressure in the furnace is increased to 4MPa, and the furnace is held for 2 hours under a high-pressure hydrogen atmosphere to form a ceramic matrix with a certain strength.

[0043] The ceramic prepared in Comparative Example 3 has an excessively low density due to pressureless sintering, resulting in numerous interconnected pores within the green body. When high-pressure hydrogen is introduced, the gas expands within these pores, causing the green body to bubble, delaminate, crack, and become unusable, resulting in a low product qualification rate. Furthermore, due to insufficient densification during pressureless sintering, significant sintering shrinkage still occurs during hot pressing, leading to uneven shrinkage and easy deformation.

[0044] In summary, compared to the process routes used in Comparative Examples 1-4, which involved pure pressureless sintering, pure hot-pressing sintering, hot-pressing followed by pressureless composite sintering, and excessively short pressureless holding time, the two-stage process of "first performing pressureless hydrogen sintering to achieve a density ≥97%, then performing high-pressure hydrogen sintering at 3-5 MPa" adopted in this embodiment of the invention can effectively eliminate residual closed pores inside the green body, achieve complete densification, and avoid abnormal grain growth and the introduction of unidirectional residual stress, resulting in high-purity transparent ceramics with high density, fine and uniform grains, and excellent comprehensive performance.

[0045] Example 2 This embodiment provides an alumina electrostatic chuck, comprising a ceramic body, an adhesive layer, and a base arranged sequentially from top to bottom. The ceramic body includes at least one high-purity transparent ceramic dielectric layer and an electrode layer disposed on the high-purity transparent ceramic dielectric layer. A solder layer is provided between two adjacent high-purity transparent ceramic dielectric layers. The high-purity transparent ceramic dielectric layer is used for direct contact with the wafer.

[0046] Furthermore, the upper surface of the high-purity transparent ceramic dielectric layer at the top end is provided with multiple upwardly protruding protrusions.

[0047] Furthermore, the base is made of an aluminum-based alloy and its surface is anodized.

[0048] Furthermore, the welding layer is printed with welding paste, which is at least one of alumina, magnesium oxide, calcium fluoride, and magnesium fluoride.

[0049] Furthermore, the preparation method of the alumina electrostatic chuck includes the following steps: S1. Printing: Metal paste is printed on the upper surface of the high-purity transparent ceramic dielectric layer to form an electrode layer, and solder paste is printed to obtain a pre-fabricated ceramic dielectric layer. S2. Welding: Take another high-purity transparent ceramic dielectric layer, place it on top of the pre-made ceramic dielectric layer obtained in step S1, put it into a welding furnace, and weld it at 1300-1350℃ and 0.5-3MPa pressure, so that the welding slurry forms a welding layer between the two high-purity transparent ceramic dielectric layers. S3. Machining: The welded dense and transparent ceramic plate is processed using machining equipment according to the drawing requirements to obtain the ceramic body; S4. Assembly: The ceramic sheet is bonded to the anodized metal base to obtain the finished high-purity transparent alumina electrostatic chuck.

[0050] Furthermore, in step S1, the welding paste is printed on the area of ​​the high-purity transparent ceramic dielectric layer outside the metal paste.

[0051] Furthermore, the metal paste mentioned in step S1 is at least one of platinum, ruthenium, rhodium and palladium; in step S3, the flatness of the machined ceramic body is <5μm and the surface roughness is <0.1μm.

[0052] To further confirm the optimal composition and ratio of the welding slurry, the formulation and corresponding welding properties of the welding slurry are shown in Tables 3 and 4: Table 3 Welding slurry formulation (by weight percentage)

[0053] Table 4 Comparison of welded joint performance obtained from different welding slurry formulations

[0054] The strength of the welded joint was tested according to GB / T 6569-2006 "Test Method for Bending Strength of Fine Ceramics". The three-point bending method was used to test the flexural strength of the welded ceramic specimens, and the measured bending failure strength was used to characterize the strength of the welded joint. The thermal shock resistance temperature was tested according to the thermal shock resistance (thermal stability) test method specified in Clause 5.8 of GB / T 5593-2015. The welded specimen was heated to the specified temperature in a heating furnace and then naturally cooled. After 5 cycles, the specimen was tested for cracks by penetrating it with a fuchsin solution. The maximum temperature difference that the specimen could withstand without cracking was used to characterize the thermal shock resistance temperature. The failure temperature was tested using a self-defined method. The welded specimen was heated at a heating rate of 5℃ / min, and the temperature at which the welded joint cracked, peeled, or experienced a sudden drop in strength was measured as the failure temperature. The test results of formulations A and B show that welding slurries with high fluoride content can achieve higher weld joint strength, but the failure temperature is lower. The test results of formulation F show that welding slurries with high alumina content can increase the weld failure temperature, but the welding wetting effect is worse, and the joint strength decreases. Comparing formulations C, D, and E, it can be seen that excessive magnesium oxide addition reduces the thermal shock resistance of the solder. Based on the comprehensive test data, formulation four has the best overall welding performance; that is, the welding slurry includes the following components by weight percentage: 99.70% alumina, 0.10% magnesium oxide, 0.10% calcium fluoride, and 0.10% magnesium fluoride.

[0055] The specific embodiments described above are further illustrations of the technical solution and beneficial effects of the present invention, and are not intended to limit the implementation methods. For those skilled in the art, any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A high-purity transparent ceramic dielectric layer, characterized in that: The high-purity transparent alumina ceramic dielectric layer comprises the following components in parts by weight: 99.9-99.95 parts of α-Al2O3 powder, 0.05-0.10 parts of sintering aid, 45-55 parts of solvent, 0.5-2.5 parts of dispersant, 7-11 parts of binder, and 4-8 parts of plasticizer.

2. The high-purity transparent ceramic dielectric layer according to claim 1, characterized in that: The α-Al2O3 powder has a purity of ≥99.99% and an average particle size between 0.1 and 1.0 μm.

3. The high-purity transparent ceramic dielectric layer according to claim 1, characterized in that: The sintering aid is alumina or yttrium oxide, and may include one of magnesium oxide, magnesium nitrate, or magnesium aluminum spinel; the dispersant is at least one of castor oil, herring oil, polyethylene glycol, or phosphate ester; the binder is polyvinyl butyral. The plasticizer is at least one of dioctyl phthalate, dimethyl phthalate, dibutyl phthalate, or diisononyl phthalate.

4. The high-purity transparent ceramic dielectric layer according to claim 1, characterized in that: The sintering aid comprises the following components by weight percentage: 99.9-99.99% alumina, 0.01-0.1% yttrium oxide, 0-0.09% magnesium oxide, 0-0.09% magnesium nitrate, and 0-0.09% magnesium aluminum spinel.

5. A method for preparing a high-purity transparent ceramic dielectric layer according to any one of claims 1-4, characterized in that: Includes the following steps: (1) Slurry preparation: Take α-Al2O3 powder, sintering aid, solvent and dispersant by weight, mix them in proportion to obtain mixed powder; put the mixed powder into a ball mill for ball milling; then add binder and plasticizer, and continue ball milling; then degas the ball milled slurry to obtain cast slurry; (2) Casting and cutting: The casting machine is used to make the casting slurry into a ceramic green porcelain strip, and then the cutting machine is used to cut the ceramic green porcelain strip into multiple ceramic green porcelain pieces; (3) Drilling: Processing structural holes and positioning holes into the raw ceramic slab; (4) Isostatic pressing: The ceramic green porcelain sheets are stacked to a certain thickness and then sealed in plastic; the sealed stacked sheets are pressed to make them tightly bonded into a whole green body; (5) Debinding: Place the ceramic raw porcelain plate on the corundum mullite firing plate and put it into the debinding furnace to debind the adhesive, and then obtain the ceramic debinding plate. (6) Sintering: Place the ceramic debonding plate into the sintering furnace and perform pressureless sintering at a high temperature of 1450-1550℃ in a hydrogen atmosphere for 2-4 hours to form a dense ceramic part with a density of over 97%; reduce the temperature by 20-50℃, increase the hydrogen pressure in the furnace to 3-5MPa, and hold for 1-3 hours in a high-pressure hydrogen atmosphere to obtain a high-purity transparent ceramic dielectric layer.

6. The method for preparing a high-purity transparent ceramic dielectric layer according to claim 5, characterized in that: In step (5), the adhesive removal step involves slowly heating the material to 400-500°C at a heating rate of 0.3-1°C / min under a nitrogen atmosphere and holding it at that temperature for 3-6 hours.

7. An alumina electrostatic chuck, characterized in that: It includes a ceramic body, an adhesive layer and a base arranged from top to bottom. The ceramic body includes at least one high-purity transparent ceramic dielectric layer and an electrode layer disposed on the high-purity transparent ceramic dielectric layer. A welding layer is provided between two adjacent high-purity transparent ceramic dielectric layers.

8. An alumina electrostatic chuck according to claim 7, characterized in that: The welding layer is printed with welding paste, which is at least one of aluminum oxide, magnesium oxide, calcium fluoride, and magnesium fluoride.

9. An alumina electrostatic chuck according to claim 8, characterized in that: The method for preparing the alumina electrostatic chuck includes the following steps: S1. Printing: Metal paste is printed on the upper surface of the high-purity transparent ceramic dielectric layer to form an electrode layer, and solder paste is printed to obtain a pre-fabricated ceramic dielectric layer. S2. Welding: Take another high-purity transparent ceramic dielectric layer, place it on top of the pre-made ceramic dielectric layer obtained in step S1, put it into a welding furnace, and weld it at 1300-1350℃ and 0.5-3MPa pressure, so that the welding slurry forms a welding layer between the two high-purity transparent ceramic dielectric layers. S3. Machining: The welded dense and transparent ceramic plate is processed using machining equipment according to the drawing requirements to obtain the ceramic body; S4. Assembly: The ceramic sheet is bonded to the anodized metal base to obtain the finished high-purity transparent alumina electrostatic chuck.

10. A high-purity transparent alumina electrostatic chuck according to claim 9, characterized in that: The metal paste mentioned in step S1 is at least one of platinum, ruthenium, rhodium and palladium; in step S3, the flatness of the machined ceramic body is <5μm and the surface roughness is <0.1μm.

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