Preparation method of high-purity alumina ceramic electrostatic chuck

Abstract

The invention discloses a preparation method of a high-purity alumina ceramic electrostatic chuck, and belongs to the technical field of electrostatic chucks. Carrying out tape casting; preparing an electrode; punching is conducted; performing lamination; discharging glue; sintering is performed; leveling is conducted; hot isostatic pressing (HIP) treatment is conducted, specifically, the leveled ceramic plate is placed in hot isostatic pressing equipment, the treatment temperature ranges from 1200 DEG C to 1600 DEG C, the pressure ranges from 100 MPa to 200 MPa, and the duration time ranges from 1 h to 4 h, so that the compactness and the mechanical strength of ceramic are further improved; in the hip treatment process, a pressing plate jig is used, the ceramic plate is clamped between two pressing plates, the pressing plates are made of graphite, aluminum oxide, a molybdenum plate and a tungsten plate, the thickness of the pressing plates ranges from 20 mm to 50 mm, the size of the pressing plates is larger than or equal to that of the ceramic plate, the weight of the pressing plates ranges from 2 kg to 25 kg, and the flatness ranges from 50 micrometers to 500 micrometers, so that deformation of ceramic is restrained, and the performance of the ceramic plate is further improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrostatic chucks, in particular to a preparation method of a high-purity alumina ceramic electrostatic chuck. BACKGROUND

[0002] An electrostatic chuck is a device that uses electrostatic force to attract objects, and is widely used in the semiconductor, display screen, photoelectric and precision manufacturing industries. In these fields, the stability and form precision of materials are very important, especially in high cleanliness and pollution-free environments. Compared with mechanical clamps and vacuum chucks, electrostatic chucks can more effectively prevent fragile materials (such as silicon wafers, glass substrates, etc.) from being damaged, and provide high work efficiency in high cleanliness and high temperature environments. The performance of the electrostatic chuck depends largely on the physicochemical properties of the manufacturing material.

[0003] Traditional electrostatic chucks are usually made of ordinary alumina ceramics, although these materials can meet certain application scenarios, but with the progress of fine semiconductor processes and display technologies, the limitations of traditional materials in high temperature, high humidity and high purity environments gradually emerge. In order to overcome the defects of ordinary alumina ceramics, high-purity alumina ceramics have gradually become the ideal material for electrostatic chuck materials. High-purity alumina ceramics generally refer to alumina content exceeding 99.99%. Compared with ordinary alumina ceramics, high-purity alumina ceramics exhibit significant advantages in many aspects: higher mechanical stability, excellent insulation performance, high temperature and humidity stability, better corrosion resistance, etc. The HIP process is a method for preparing high-purity alumina ceramics. After hip high temperature and high pressure treatment, the pores in the ceramic matrix can be further compacted, thereby improving its strength. However, due to the large area and thin sheet shape of the electrostatic chuck ceramic, warping occurs during the hip process due to uneven stress and uneven thermal expansion, resulting in a very low yield. The prior art prevents warping during hip by cutting tools, reinforcing networks, and changing product preparation additives. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a preparation method of a high-purity alumina ceramic electrostatic chuck, which provides uniform support force during the hip process and obtains a higher flatness electrostatic chuck ceramic plate.

[0005] In order to solve the above technical problems, the technical scheme of the present application is as follows:

[0006] A preparation method of a high-purity alumina ceramic electrostatic chuck, comprising:

[0007] Ball milling: high-purity alumina powder is mixed with an organic binder, a dispersant and a solvent, and is treated by ball milling to prepare alumina slurry with uniform particle size distribution;

[0008] Casting: the slurry is spread into a film on a casting machine by a casting process to form a ceramic green body;

[0009] Electrode preparation: electrodes are made inside the ceramic to form an electrode layer, thereby generating adsorption force;

[0010] Hole punching: electrode through holes and other holes required by design are reserved on the formed ceramic green body;

[0011] Laminating: multiple ceramic films are aligned with the electrode layer and laminated to form a ceramic green body with a multi-layer structure;

[0012] Glue removal: the laminated ceramic green body is heated and treated in a glue removal furnace to remove organic binders and adhesives;

[0013] Sintering: the glue-removed ceramic green body is sintered at high temperature to form a densified ceramic body;

[0014] Flattening: the sintered ceramic is flattened to make the ceramic surface flat;

[0015] Hot isostatic pressing (HIP): the flattened ceramic plate is placed in a hot isostatic pressing device, the processing temperature is between 1200°C and 1600°C, the pressure is between 100 and 200 MPa, and the duration is between 1 and 4 hours, to further improve the density and mechanical strength of the ceramic. During the HIP process, a pressing plate jig is used to clamp the ceramic plate between two pressing plates. The pressing plate material is self-graphite, alumina, molybdenum plate, tungsten plate, the pressing plate thickness is between 20 and 50 mm, the pressing plate size is greater than or equal to the size of the ceramic plate, the pressing plate weight is between 2 and 25 kg, and the flatness is between 50 and 500 um, to suppress the deformation of the ceramic and further improve the performance of the ceramic plate.

[0016] Preferably, in the hot isostatic pressing (HIP) step, the pressing plate is a square pressing plate, and the side length of the square pressing plate is between 350 mm and 450 mm.

[0017] Preferably, in the hot isostatic pressing (HIP) step, the weight of the pressing plate is between 5 and 15 kg.

[0018] Preferably, in the ball milling step, the solvent is one or a mixture of two or more of toluene, ethanol, ethyl acetate, and isopropyl alcohol, the volume of the solvent accounts for 40% to 60% of the total amount of the slurry, the binder is any one of polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and acrylic ester polymer, and the mass of the binder accounts for 2% to 5% of the total amount of the ceramic powder; the dispersant is any one of polyacrylic acid ammonium salt, polyacrylic acid sodium salt, and triethanolamine, and the addition amount of the dispersant accounts for 0.2% to 1% of the total amount of the ceramic powder.

[0019] The above technical solution has the following beneficial effects:

[0020] In the hot isostatic pressing (HIP) step, the alumina ceramic body is clamped by using the pressing plate, so that the deformation problem of the ceramic can be effectively controlled in the hot isostatic pressing process, and the ceramic can be kept flat in the high-temperature and high-pressure environment. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The structure of the pressing plate of the present application is shown in the figure. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present application, but does not constitute a limitation on the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0023] A preparation method of a high-purity alumina ceramic electrostatic chuck, comprising the following steps:

[0024] S1: ball milling, mixing high-purity alumina powder, organic binder, dispersant and solvent, and preparing alumina slurry with uniform particle size distribution by ball milling treatment;

[0025] Specifically, after mixing the alumina powder, the organic binder, the dispersant and the solvent and then ball milling, the alumina slurry can be obtained to facilitate the subsequent casting forming;

[0026] In some embodiments, the solvent in the above ball milling step is one or two or more of toluene, ethanol, ethyl acetate and isopropanol, the volume of the solvent accounts for 40% to 60% of the total amount of the slurry, the binder is any one of polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone and acrylic ester polymer, and the mass of the binder accounts for 2% to 5% of the total amount of the ceramic powder; the dispersant is any one of ammonium polyacrylate, sodium polyacrylate and triethanolamine, and the addition amount of the dispersant accounts for 0.2% to 1% of the total amount of the ceramic powder;

[0027] In other embodiments of the present application, the solvent is any one of toluene, ethanol, ethyl acetate and isopropanol, the volume of the solvent accounts for 40% or 60% of the total amount of the slurry, or 50%, the binder is any one of polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone and acrylic ester polymer, and the mass of the binder accounts for 2% or 5% of the total amount of the ceramic powder; the dispersant is any one of ammonium polyacrylate, sodium polyacrylate and triethanolamine, and the addition amount of the dispersant accounts for 0.2% or 1% of the total amount of the ceramic powder;

[0028] S2: casting, spreading the slurry on a casting machine by a casting process to form a ceramic green body in a film;

[0029] Specifically, in the casting step, the thickness of the ceramic green body formed by casting is between 50 and 500 microns, and the thickness can also be 250 microns. The desired thickness can be controlled by adjusting the gap of the casting blade and the viscosity of the slurry, and adjusted according to the specific thickness requirement;

[0030] S3: preparing an electrode, making an electrode inside the ceramic to form an electrode layer, thereby generating an adsorption force, i.e. the adsorption force of the electrostatic chuck when working;

[0031] Specifically, in the above electrode preparation step, screen printing, sputter deposition, evaporation, and compression method can be used for preparation. The conductive material of the electrode is metal or conductive ceramic, such as molybdenum metal, tungsten metal, silver metal or conductive oxide. The actual situation or design requirement can be selected according to the actual situation or design requirement;

[0032] S4: punching, reserving electrode through holes and other design required holes on the formed ceramic green body;

[0033] Specifically, in the above punching step, the diameter and position of the hole are accurately controlled according to the design of the electrode and the connecting piece to ensure the alignment of the hole with the electrode after lamination;

[0034] S5: lamination, aligning and laminating the multilayer ceramic film with the electrode layer to form a multilayer ceramic green body;

[0035] Specifically, in the above lamination step, mechanical compression lamination, hot pressing lamination, wip, and vacuum lamination can be used for lamination. The existing technology alignment clamp is used to ensure the accurate alignment of each ceramic film and the electrode layer. The structure after lamination forms a stable laminate under heating and pressing;

[0036] S6: degassing, placing the laminated ceramic green body in a degassing furnace for heat treatment to remove organic binder and adhesive;

[0037] Specifically, in the above degassing step, degassing is carried out at a temperature of 300-600°C, and can also be carried out at a temperature of 450°C. The degassing time is 50-100h, and the degassing time can also be 75h. The organic matter is completely removed while the integrity of the ceramic green body is maintained;

[0038] S7: sintering, high temperature sintering of the degassed ceramic green body to form a densified ceramic body;

[0039] Specifically, the high-temperature sintering of the ceramic body is performed in a vacuum, inert gas environment or reducing gas environment, the sintering temperature is 1400-1800°C, specifically 1600°C, and the holding time is 2-6h to prevent oxidation and enable sintering into porcelain, specifically 4h, to ensure high purity and high performance of the ceramic;

[0040] S8: flattening, performing flattening treatment on the sintered ceramic to make the ceramic surface flat;

[0041] Specifically, in the flattening step, flattening can be achieved by mechanical grinding and polishing, and pressure sintering, the flatness is controlled to be 50-500um, the pre-flatness is reduced, and the subsequent processing can better improve the flatness;

[0042] S9: hot isostatic pressing (HIP), the flattened ceramic plate is placed in a hot isostatic pressing device, the processing temperature is 1200-1600°C, the pressure is 100-200MPa, and the duration is 1-4h to further improve the density and mechanical strength of the ceramic; during the hip processing, a pressing jig is used to clamp the ceramic plate between two pressing plates 1, the pressing plate 1 is made of graphite, alumina, molybdenum plate, tungsten plate, the thickness of the pressing plate 1 is 20-50mm, the size of the pressing plate 1 is greater than or equal to the size of the ceramic plate, the weight of the pressing plate is 2-25kg, and the flatness is 50-500um to suppress the deformation of the ceramic and further improve the performance of the ceramic plate.

[0043] Specifically, in the hot isostatic pressing step, the processing temperature can be 1400°C, the processing pressure can be 150MPa, and the duration can be 3h to further improve the density and mechanical strength of the ceramic, and during the hot isostatic pressing, a pressing jig is used to clamp the ceramic plate between two pressing plates 1, the pressing plate 1 is made of any one of graphite, alumina, molybdenum plate, and tungsten plate, the thickness of the pressing plate 1 can be 20mm or 50mm, or 35mm, the size of the pressing plate 1 is greater than or equal to the size of the ceramic plate to facilitate clamping the ceramic, and the flatness of the pressing plate 1 is 50um or 500um, or 350um to ensure the flatness of the ceramic plate, and the weight of the pressing plate 1 is selected according to actual needs to suppress the deformation of the ceramic and further improve the performance of the ceramic plate.

[0044] Compared with the alumina electrostatic chuck ceramic prepared without the jig, the alumina electrostatic chuck ceramic prepared with the jig is fixed by the pressing plate 1 through the uniformly distributed force on the ceramic plate, which limits the free deformation of the ceramic under high pressure and high temperature conditions. In this way, even if stress differences occur in the ceramic material during the isostatic pressing process, the presence of the pressing plate 1 can effectively offset or disperse these stresses, maintain the flatness of the ceramic plate, and reduce the risk of bending or warping. In addition, using the pressing plate 1 can obtain a relatively flat ceramic plate after HIP processing, and subsequent mechanical processing becomes simpler and more efficient. Because the surface flatness of the product is higher, the workload of grinding and polishing is reduced, and the yield is improved. At the same time, because the shape of the ceramic plate is more stable, the scrap rate is reduced, thereby improving the overall production efficiency and reducing the production cost.

[0045] In some embodiments, with reference to Figure 1 In the above-mentioned hot isostatic pressing (HIP) step, the pressing plate 1 is a square pressing plate 1, and the side length of the square pressing plate 1 is 350mm-450mm.

[0046] Specifically, the pressing plate 1 used during hot isostatic pressing is square, and the side length thereof is 350mm or 450mm. In addition, the side length of the pressing plate 1 can also be 400mm.

[0047] In some embodiments, in the above-mentioned hot isostatic pressing (HIP) step, the weight of the pressing plate 1 is 5-15kg.

[0048] Specifically, the weight of the pressing plate 1 used in the hot isostatic pressing (HIP) step is 5kg or 15kg, and can also be 10kg. Specifically, the material of the pressing plate 1 is graphite, and the flatness is 50um. With different side lengths of the pressing plate 1: 350mm, 400mm, 450mm, and different weights: 5kg, 10kg, 15kg, the flatness of the ceramic after HIP is compared, and the results are as shown in the following table:

[0049] Platen Material Platen Weight (kg) Platen Size (mm) Ceramic Size (mm) Flatness after HIP (um) Graphite 5 350*350 350*350 213 Graphite 10 350*350 350*350 117 Graphite 15 350*350 350*350 95 Graphite 10 400*400 350*350 81 Graphite 10 450*450 350*350 93

[0050] As can be seen from the above table, when the size of the pressing plate 1 is close to the size of the ceramic, specifically, when the size of the pressing plate 1 and the size of the ceramic are both 350*350mm, the flatness control of the lighter pressing plate 1 is weaker. With the increase of the weight of the pressing plate 1, the flatness is improved, but because the sizes are similar, the improvement of the flatness is limited.

[0051] When the size of the pressing plate 1 is slightly larger than the size of the ceramic, specifically, when the pressing plate 1 is 400*400mm and the ceramic is 350*350mm, the flatness of the product is obviously improved. When the size of the pressing plate 1 is further increased, the improvement of the flatness is not as obvious as when the size is 400x400mm.

[0052] Therefore, if the ceramic has a size of 350*350 mm and the pressing plate 1 is made of graphite, a pressing plate 1 having a size of 400*400 mm can be selected.

[0053] The embodiments of the present application are described in detail above with reference to the accompanying drawings, but the present application is not limited to the described embodiments. Various changes, modifications, replacements, and variations of the embodiments can be made by those skilled in the art without departing from the principles and spirits of the present application, and still fall within the protection scope of the present application.

Claims

1. A method for preparing a high-purity alumina ceramic electrostatic chuck, characterized in that, include: Ball milling: High-purity alumina powder is mixed with organic binder, dispersant and solvent, and ball milled to prepare alumina slurry with uniform particle size distribution; Casting: The slurry is spread into a thin film on a casting machine through a casting process to form a ceramic blank; Electrode fabrication: Electrodes are fabricated inside the ceramic to form an electrode layer, thereby generating adsorption force; Drilling: Pre-drilling electrode through holes and other holes required by the design on the formed ceramic blank; Stacking: Aligning and stacking multiple ceramic thin films with electrode layers to form a multi-layered ceramic preform; Debinding: The stacked ceramic blanks are placed in a debinding furnace for heat treatment to remove organic binders and adhesives; Sintering: The ceramic blank after debinding is sintered at high temperature to form a dense ceramic body; Leveling: Leveling the sintered ceramics to make the ceramic surface flat; Hot Isostatic Pressing (HIP): The leveled ceramic plate is placed in a hot isostatic pressing apparatus at a temperature between 1200℃ and 1600℃, a pressure of 100 to 200 MPa, and a duration of 1 to 4 hours to further improve the density and mechanical strength of the ceramic. During the HIP process, a clamping fixture is used to hold the ceramic plate between two clamping plates. The clamping plate materials are graphite, alumina, molybdenum, or tungsten plates, with a thickness between 20 and 50 mm. The size of the clamping plate is greater than or equal to the size of the ceramic plate, the weight of the clamping plate is 2 to 25 kg, and the flatness is 50 to 500 μm to suppress ceramic deformation and further improve the performance of the ceramic plate.

2. The method for preparing a high-purity alumina ceramic electrostatic chuck according to claim 1, characterized in that, In the hot isostatic pressing (HIP) step, the pressure plate is a square pressure plate with a side length of 350mm to 450mm.

3. The method for preparing a high-purity alumina ceramic electrostatic chuck according to claim 2, characterized in that, In the hot isostatic pressing (HIP) step, the weight of the press plate is 5 to 15 kg.

4. The method for preparing a high-purity alumina ceramic electrostatic chuck according to claim 1, characterized in that, In the ball milling step, the solvent is one or a mixture of two or more of toluene, ethanol, ethyl acetate, and isopropanol, and the volume of the solvent accounts for 40% to 60% of the total slurry volume. The binder is any one of polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and acrylate polymers, and the mass of the binder accounts for 2% to 5% of the total ceramic powder volume. The dispersant is any one of ammonium polyacrylate, sodium polyacrylate, and triethanolamine, and the amount of dispersant added is 0.2% to 1% of the total ceramic powder volume.

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