Composite sintering process and surface modification method of aluminum oxide electrostatic chuck

Abstract

The invention discloses a composite sintering process and a surface modification method of an aluminum oxide electrostatic chuck, and belongs to the technical field of electrostatic chucks, the composite sintering process comprises the following steps: preparing a substrate blank: selecting high-purity aluminum oxide ceramic powder, adding a sintering aid, mixing, and carrying out dry pressing molding to obtain the substrate blank; electrode layer deposition: depositing multiple layers of composite electrodes on the surface of the substrate blank to form an electrode layer; coating a dielectric layer: coating an aluminum oxide film on the electrode layer; pre-sintering: putting the multilayer structure blank into a sintering furnace for pre-sintering; the composite sintering comprises the following steps: a first stage: vacuum sintering; in the second stage, pulse discharge plasma sintering is carried out; and cooling: cooling to room temperature at the rate of 1 DEG C / min to avoid thermal stress. By means of the composite sintering process, the density of the sintered electrostatic chuck is larger than or equal to 99.8%, the grain size is refined till the average grain size is smaller than or equal to 200 nm, and stable adsorption force can be kept in the high-temperature environment at the temperature of 1400 DEG C or above.

Description

Technical Field

[0001] This invention relates to the field of electrostatic chuck technology, and in particular to a composite sintering process and surface modification method for an alumina electrostatic chuck. Background Technology

[0002] Existing alumina electrostatic chucks generally suffer from the following problems:

[0003] 1. Traditional sintering processes struggle to balance high density and low energy consumption, resulting in high production costs and insufficient performance.

[0004] 2. Poor surface flatness and uneven adsorption force affect the precision machining accuracy;

[0005] 3. In high-temperature environments or plasma etching processes, insufficient corrosion resistance can easily lead to structural damage.

[0006] Therefore, there is an urgent need for a new preparation technology that combines high performance and low cost. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a composite sintering process and surface modification method for alumina electrostatic chuck, which can improve the density, plasma erosion resistance and surface hardness of alumina electrostatic chuck.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0009] This invention provides a composite sintering process for an alumina electrostatic chuck, the composite sintering process comprising:

[0010] Preparation of the substrate green body: High-purity alumina ceramic powder is selected, and 0.3-0.8% of rare earth oxides are added as sintering aids. After mixing, the mixture is dry-pressed into a substrate green body.

[0011] Electrode layer deposition: Depositing multiple composite electrodes on the surface of a substrate preform to form a grid-patterned electrode layer;

[0012] Dielectric layer coating: A titanium oxide-doped aluminum oxide film is coated on the electrode layer. The thickness of the aluminum oxide film is 8-12 μm to enhance the dielectric constant.

[0013] Pre-sintering: The multi-layered green body is placed in a nitrogen atmosphere sintering furnace and heated to 1000-1100℃ at a rate of 5℃ / min. It is held at that temperature for at least 2 hours to initially remove internal pores and perform low-temperature densification.

[0014] Composite sintering:

[0015] First stage: Vacuum sintering, with pressure set to less than or equal to 5 Pa, temperature raised to 1500℃, and held for at least 30 minutes;

[0016] The second stage: pulsed discharge plasma sintering, with a pressure of 50MPa and a temperature of 1550℃, is carried out by holding the temperature for at least 15 minutes for high-temperature strengthening.

[0017] Cooling: Cool to room temperature at a rate of 1°C / min to avoid thermal stress.

[0018] Preferably, the purity of the high-purity alumina ceramic powder is greater than or equal to 99.8%, and the rare earth oxide is yttrium oxide or lanthanum oxide.

[0019] Preferably, the multilayer composite electrode is formed by alternating deposition of copper and molybdenum materials, the total thickness of the multilayer composite electrode is 0.8 to 1.2 μm, the multilayer composite electrode has a grid-like electrode pattern, and the grid side length of the grid-like electrode layer is 0.2 to 0.5 mm.

[0020] Preferably, the pulse frequency of the pulsed discharge plasma sintering is 2Hz, and after the temperature is raised to 1550℃ and held, the pressure is dynamically reduced by 10MPa every 5 minutes.

[0021] Another aspect of the present invention provides a surface modification method for an alumina electrostatic chuck, the surface modification method comprising the following steps:

[0022] Laser-etched microstructures: A micron-scale honeycomb-shaped groove array is formed on the surface of the dielectric layer using femtosecond laser etching technology;

[0023] Silicon nitride coating deposition: A silicon nitride film is deposited on the surface by plasma-enhanced chemical vapor deposition to improve plasma erosion resistance and surface hardness;

[0024] Polishing and cleaning: The surface roughness is reduced to Ra less than or equal to 0.1 μm using ultra-precision polishing technology, and residual impurities are removed by ion beam cleaning.

[0025] Preferably, the depth of the micron-scale honeycomb groove array is 5–10 μm and the spacing is 50 μm.

[0026] Preferably, the thickness of the silicon nitride film is 1 to 2 μm.

[0027] Preferably, the ultra-precision polishing technology is magnetorheological polishing.

[0028] The above technical solution has the following beneficial effects:

[0029] Through the composite sintering process of this application, the sintered electrostatic chuck has a density greater than or equal to 99.8%, a grain size refined to an average particle size less than or equal to 200 nm, an adsorption accuracy less than or equal to ±0.05 μm, and can maintain stable adsorption force in high-temperature environments above 1400℃.

[0030] The surface modification method of this application improves plasma erosion resistance by 50% and the surface hardness reaches HRA90 or higher.

[0031] The composite sintering process and surface modification method of this application reduce energy consumption by 25% and increase production efficiency by 30% compared with traditional processes. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments 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 composite sintering process for an alumina electrostatic chuck specifically includes the following steps:

[0035] Preparation of the substrate green body: High-purity alumina ceramic powder is selected, and 0.3% to 0.8% of rare earth oxides are added as sintering aids. After mixing, the mixture is dry-pressed to form the substrate green body. Specifically, the substrate green body preparation material is high-purity alumina ceramic powder with a purity of ≥99.8%. 0.3% or 0.8% by weight of rare earth oxides are added to the high-purity alumina ceramic powder as sintering aids. The amount of rare earth oxides added can also be 0.5%. After mixing, the mixture is dry-pressed to form the substrate green body.

[0036] Electron layer deposition: Electron beam evaporation technology is used to deposit multilayer composite electrodes on the surface of the substrate preform to form a grid-like electrode layer; specifically, multilayer composite electrodes are deposited on the surface of the substrate preform prepared in the above steps using electron beam evaporation technology. The shape of the deposited multilayer composite electrodes is a grid-like pattern, and the specific number of layers is determined according to the required electrode layer thickness and the thickness of each layer.

[0037] Dielectric layer coating: A titanium oxide-doped aluminum oxide film is coated on the electrode layer using the sol-gel method. The thickness of the aluminum oxide film is 8-12 μm to enhance the dielectric constant. Specifically, a titanium oxide-doped aluminum oxide film is coated on the electrode layer using the sol-gel method to form a dielectric layer. The thickness of the aluminum oxide film is 8 μm or 12 μm, and the thickness of the aluminum oxide film can also be 10 μm.

[0038] Pre-sintering: The multi-layered green body is placed in a nitrogen atmosphere sintering furnace and heated to 1000-1100°C at a rate of 5°C / min, and held for at least 2 hours to initially remove internal pores and perform low-temperature densification; specifically, the base green body is formed into a multi-layered green body after electrode layer deposition and dielectric layer coating, and then placed in a nitrogen atmosphere sintering furnace for pre-sintering. After being placed in, the temperature in the sintering furnace is heated to 1000°C or 1100°C at a rate of 5°C / min, and then held for 2 hours to initially remove internal pores and perform low-temperature densification. In other embodiments of this example, the temperature in the sintering furnace can also be raised to 1050°C and held for 2.5 hours or 3 hours.

[0039] Composite sintering, which involves pre-sintering followed by composite sintering, specifically includes:

[0040] The first stage is vacuum sintering, with the pressure set to less than or equal to 5 Pa, the temperature raised to 1500°C, and held for at least 30 minutes. Specifically, the first stage is vacuum sintering. Based on the pre-sintering, the pressure in the sintering furnace is set to 5 Pa, the temperature is raised from 1000-1100°C in the pre-sintering stage to 1500°C, and held for 30 minutes after reaching 1500°C. In other embodiments of this example, the pressure in the sintering furnace can be set to 3 Pa or 4 Pa, and the temperature is held for 35 minutes or 40 minutes after reaching 1500°C.

[0041] The second stage is pulsed discharge plasma sintering, with a pressure of 50 MPa, a pulse frequency of 2 Hz, and a temperature of 1550°C. The temperature is held for at least 15 minutes, and the pressure is dynamically reduced by 10 MPa every 5 minutes for high-temperature strengthening. Specifically, after the vacuum sintering in the first stage, the pulsed discharge plasma sintering in the second stage is carried out. The pressure inside the furnace is set to 50 MPa, the pulse frequency is 2 Hz, and the temperature is raised from 1500°C to 1550°C. The temperature is held at 1550°C for 15 minutes. In other embodiments of this example, the holding time can also be 20 minutes or 25 minutes. After the holding time is completed, dynamic pressure reduction is carried out at a rate of 10 MPa every 5 minutes to reduce the pressure inside the furnace from 50 MPa to atmospheric pressure.

[0042] Cooling: Cool to room temperature at a rate of 1℃ / min to avoid thermal stress. Specifically, the temperature inside the sintering furnace is reduced to room temperature at a rate of 1℃ / min to avoid thermal stress. Sintering is completed after cooling.

[0043] In some embodiments, the purity of the high-purity alumina ceramic powder is greater than or equal to 99.8%, and the rare earth oxide is yttrium oxide or lanthanum oxide; specifically, the purity of the high-purity alumina ceramic powder is 99.8% or 99.9%, which meets the purity requirements of high-purity alumina ceramic powder used to prepare electrostatic chucks, and the rare earth oxide used as a sintering aid is yttrium oxide or lanthanum oxide.

[0044] In some embodiments, the multilayer composite electrode is formed by alternating deposition of copper and molybdenum materials, the total thickness of the multilayer composite electrode is 0.8 to 1.2 μm, the multilayer composite electrode has a grid-like electrode pattern, and the grid side length of the grid-like electrode layer is 0.2 to 0.5 mm.

[0045] Specifically, copper and molybdenum materials are deposited alternately to form a multilayer composite electrode. The total thickness of the multilayer composite electrode is 0.8 to 1.2 μm, that is, the thickness of the electrode layer is 0.8 μm or 1.2 μm, or it can be 1 μm. The multilayer composite electrode has a grid-like electrode pattern, specifically a square grid. The side length of the square grid is 0.2 mm or 0.5 mm, or it can be 0.3 mm or 0.4 mm.

[0046] Through the composite sintering process of this application, the sintered electrostatic chuck has a density of ≥99.8%, a grain size refined to an average particle size of ≤200nm, an adsorption accuracy of ≤±0.05μm, and can maintain stable adsorption force in high-temperature environments above 1400℃.

[0047] Example 2

[0048] After the alumina electrostatic chuck is sintered using the above-mentioned composite sintering process, the surface of its dielectric layer is modified. The surface modification method for the alumina electrostatic chuck includes the following steps:

[0049] Laser etching microstructure: Femtosecond laser etching technology is used to form a micron-scale honeycomb groove array on the surface of the dielectric layer to enhance the adsorption contact area. Specifically, the micron-scale honeycomb groove array includes multiple annular grooves of different sizes, arranged in ascending order with the center of the electrostatic chuck as the center. The depth of the micron-scale honeycomb groove array is 5-10 μm, and the spacing between adjacent annular grooves is 50 μm.

[0050] Silicon nitride coating deposition: A silicon nitride film is deposited on the surface by plasma-enhanced chemical vapor deposition (PECVD) to improve plasma erosion resistance and surface hardness. Specifically, a silicon nitride film is deposited on the surface of the dielectric layer, and the thickness of the silicon nitride film is 1 to 2 μm.

[0051] Polishing and cleaning: The surface roughness is reduced to Ra less than or equal to 0.1μm using ultra-precision polishing technology, and residual impurities are removed by ion beam cleaning. Specifically, the ultra-precision polishing technology is magnetorheological polishing, which reduces the surface roughness of the dielectric layer to Ra of 0.1μm to complete the polishing and cleaning of the electrostatic chuck surface.

[0052] In some embodiments, the depth of the micron-sized honeycomb groove array is 5 to 10 μm and the spacing is 50 μm. Specifically, the groove depth of the micron-sized honeycomb groove array is 5 μm or 10 μm, or it can be 7 μm or 8 μm. The spacing between adjacent grooves of the micron-sized honeycomb groove array is 50 μm, and the width of the groove is designed as needed.

[0053] In some embodiments, the thickness of the silicon nitride film is 1 to 2 μm, specifically, the thickness of the silicon nitride film is 1 μm or 2 μm.

[0054] The surface modification method of this application improves the plasma erosion resistance of the prepared electrostatic chuck by 50%, and the surface hardness reaches HRA90 or above. The energy consumption in the process is reduced by 25% compared with the traditional process, and the production efficiency is increased by 30%.

[0055] Example 3

[0056] Taking the preparation of an electrostatic chuck with a diameter of 250 mm and a thickness of 18 mm as an example, its composite sintering process includes the following steps:

[0057] The high-purity alumina ceramic powder is doped with rare earth oxides, with a doping ratio of 0.5% yttrium oxide, and the purity of the high-purity alumina ceramic powder is 99.8%.

[0058] Electrode layer deposition: Cu / Mo alternating layers, each with a total thickness of 0.6 μm, and the electrode layer thickness of 1.2 μm, with a grid spacing of 0.3 mm;

[0059] Pre-sintering: heat to 1050℃ and hold for 2 hours;

[0060] After vacuum sintering, pulsed discharge plasma sintering is performed at a temperature of 1550℃, a pressure of 50MPa, and a pulse frequency of 2Hz.

[0061] After sintering, the surface is modified. First, laser etching is performed with the following parameters: groove depth 8μm, spacing 50μm. After silicon nitride coating is deposited, polishing and cleaning are performed to complete the processing of the electrostatic chuck.

[0062] After modification, the entire electrostatic chuck was processed. The finished electrostatic chuck had the following properties: density of 99.9%, adsorption accuracy of ±0.03μm, and leakage rate of <0.001ppm at 1400℃.

[0063] The embodiments of the present invention have been 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 can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A composite sintering process for an alumina electrostatic chuck, characterized in that, The composite sintering process includes: Preparation of the substrate green body: High-purity alumina ceramic powder is selected, and 0.3-0.8% of rare earth oxides are added as sintering aids. After mixing, the mixture is dry-pressed into a substrate green body. Electrode layer deposition: Depositing multiple composite electrodes on the surface of a substrate preform to form a grid-patterned electrode layer; Dielectric layer coating: A titanium oxide-doped aluminum oxide film is coated on the electrode layer. The thickness of the aluminum oxide film is 8-12 μm to enhance the dielectric constant. Pre-sintering: The multi-layered green body is placed in a nitrogen atmosphere sintering furnace and heated to 1000-1100℃ at a rate of 5℃ / min. It is held at that temperature for at least 2 hours to initially remove internal pores and perform low-temperature densification. Composite sintering includes: First stage: Vacuum sintering, with pressure set to less than or equal to 5 Pa, temperature raised to 1500℃, and held for at least 30 minutes; The second stage: pulsed discharge plasma sintering, with a pressure of 50MPa and a temperature of 1550℃, held at that temperature for at least 15 minutes, to carry out high-temperature strengthening. Cooling: Cool to room temperature at a rate of 1°C / min to avoid thermal stress.

2. The composite sintering process for the alumina electrostatic chuck according to claim 1, characterized in that, The high-purity alumina ceramic powder has a purity of 99.8% or greater, and the rare earth oxide is yttrium oxide or lanthanum oxide.

3. The composite sintering process for the alumina electrostatic chuck according to claim 1, characterized in that, The multilayer composite electrode is formed by alternating deposition of copper and molybdenum materials. The total thickness of the multilayer composite electrode is 0.8–1.2 μm. The multilayer composite electrode has a grid-like electrode pattern, and the grid side length of the grid-like electrode layer is 0.2–0.5 mm.

4. The composite sintering process for the alumina electrostatic chuck according to claim 1, characterized in that, The pulse frequency of the pulsed discharge plasma sintering is 2Hz, and after the temperature is raised to 1550℃ and held, the pressure is dynamically reduced by 10MPa every 5 minutes.

5. A method for surface modification of an alumina electrostatic chuck, characterized in that, The surface modification method includes the following steps: Laser-etched microstructures: A micron-scale honeycomb-shaped groove array is formed on the surface of the dielectric layer using femtosecond laser etching technology; Silicon nitride coating deposition: A silicon nitride film is deposited on the surface by plasma-enhanced chemical vapor deposition to improve plasma erosion resistance and surface hardness; Polishing and cleaning: The surface roughness is reduced to Ra less than or equal to 0.1 μm using ultra-precision polishing technology, and residual impurities are removed by ion beam cleaning.

6. The surface modification method for an alumina electrostatic chuck according to claim 5, characterized in that, The depth of the micron-scale honeycomb groove array is 5–10 μm, and the spacing is 50 μm.

7. The surface modification method for an alumina electrostatic chuck according to claim 5, characterized in that, The thickness of the silicon nitride film is 1 to 2 μm.

8. The surface modification method for an alumina electrostatic chuck according to claim 5, characterized in that, The ultra-precision polishing technology is magnetorheological polishing.