WO2008010632A1

WO2008010632A1 - Electrostatic chuck with high-resistivity ceramic coating materials

Info

Publication number: WO2008010632A1
Application number: PCT/KR2007/000855
Authority: WO
Inventors: Kyeong-Ho Baik
Original assignee: University-Industry Collaboration Foundation Chungnam National University
Priority date: 2006-07-20
Filing date: 2007-02-16
Publication date: 2008-01-24

Abstract

The present invention relates to a method of manufacturing an electrostatic chuck used in stably fixing a wafer or glass substrate in a semiconductor/display panel manufacturing equipment. A core portion of the electrostatic chuck is formed through thermally- sprayed coating, and an Al2O3-YAG coating material with superior durability is applied to a portion in which electrical insulation and dielectric characteristics are required for the purpose of the increase of an adhesive strength, the uniformity of an adhesive force, the reduction of attaching/detaching time and the expansion of a life span.

Description

ELECTROSTATIC CHUCK WITH HIGH-RESISTIVITY CERAMIC COATING

MATERIALS

[Technical Field]

The present invention relates to an electrostatic chuck that is a core component in a semiconductor/display panel manufacturing apparatus, and Al₂O₃-YAG thermally-sprayed coating materials having superior insulation and dielectric properties are applied to the electrostatic chuck.

[Background Art]

In semiconductor and display panel manufacturing process technologies, technologies for a large-sized wafer or glass substrate (hereinafter, referred to as an object to be treated) , a highly integrated circuit, an ultrafine processing, a plasma etching process and the like have recently required a large innovation in a method of fixing an object to be treated in a process of depositing and etching a thin film. Conventionally, an object to be treated is fixed using a mechanical clamp or vacuum chuck. However, an electrostatic chuck using an electrostatic force has been recently used as a core component in a next-generation semiconductor/display panel process equipment. An electrostatic chuck includes two or more dielectric layers (or electrically insulating layers) and a conductive electrode layer inserted between the respective dielectric layers. The electrostatic chuck is a device in which an object to be treated has an opposite polarity due to a polarizing phenomenon of a dielectric layers when a DC voltage is applied to the conductive electrode layer, so that an attraction between the object to be treated and the dielectric layers can be produced. There is an advantage in that a strong and uniform electrostatic force is produced throughout an entire contact surface between the electrostatic chuck and the object to be treated, so that the surface smoothness of the object to be treated can be secured, a temperature can be easily controlled, and the occurrence of polluted particles can be minimized. The electrostatic chuck is classified into an anodic oxidation type, a polyimide type, a ceramic sheet type and the like depending on a kind of upper dielectric layer. The ceramic sheet type with superior durability and life span has been mainly used in the electrostatic chuck. In a conventional ceramic sheet adhesion type electrostatic chuck, an insulating sheet, a conductive electrode sheet and a ceramic dielectric sheet are sequentially adhered to a preform. The ceramic sheet adhesion type electrostatic chuck is a considerably high-priced component. In this case, it is necessary to form an adhesive layer using a polymer resin or silicate compound. There is a disadvantage in that the adhesive layer is broken due to a dielectric constant relatively lower than ceramic, a plasma resistance and a low thermal conductivity when using the adhesive layer for a long period of time. Further, it is essential to process a ceramic sheet with a thin thickness of 100 to lOOOμm in a method of using an adhesive agent. Therefore, there is a problem in that the method cannot be applied to electrostatic chucks used in manufacturing semiconductor wafers with a large diameter and large-sized flat display panels. A method of performing thermally-sprayed coating with respect of dielectric and electrode layers, which are core components, has been suggested as an alternative technology for solving such a problem of the conventional ceramic sheet adhesion type electrostatic chuck. A method of manufacturing an electrostatic chuck member with a stacked structure using a thermally-sprayed coating process as shown in Fig. 1 has been disclosed in Korean Patent Laid-open Publication No. 2002- 0070340. According to the patent, an undercoat 2 is formed on a surface of a metallic preform 1, a lower insulating layer 3 made of Al₂O₃ ceramic is formed on the undercoat, a metallic electrode layer 4 is formed on the lower insulating layer, and an upper insulating layer 5 made of Al₂O₃ ceramic as a topcoat is formed on the metallic electrode layer. Further, an electrostatic chuck in which Al₂O₃-TiO₂ ceramic is used to increase an electrostatic force in view of a dielectric layer material has been disclosed in Japanese Patent Laid-open Publication Nos . Hei 6-8089, 3-147843 and 3-204924, Korean Patent Laid-open Publication No. 1997-13180, and the like. However, there is a disadvantage in that an Al₂O₃-TiO₂ thermally-sprayed coating layer causes a high leakage current due to a lower volume resistivity in application of a voltage, and a response characteristic is bad when the application of a voltage is stopped. To overcome such a disadvantage, an electrostatic chuck in which an Al₂O₃ thermally-sprayed coating layer with a very high electric resistance is used as a dielectric layer has been disclosed in Korean Patent Laid-open Publication No. 2002-0070340. However, there is a disadvantage in that the electrostatic chuck to which the Al₂O₃ thermally- sprayed coating layer is applied also causes a high leakage current when a high voltage of a few kV or more is applied, and a response characteristic is slow. Particularly, since a process of manufacturing a large-sized display panel using glass as an object to be treated requires an electrostatic chuck capable of enduring at a high voltage of at least 3 to 5kV or more, a dielectric material having a high volume resistivity and breakdown voltage is required.

A thermally-sprayed coating layer made of Al₂O₃ used in the conventional electrostatic chuck has a high porosity and defect as compared with a sintered ceramic material. For example, an Al₂O₃ thermalIy-sprayed dielectric layer a porosity of 1 to 8% has been disclosed in Korean Patent Laid-open Publication No. 2002-0070340. A reason why pores and defect is produced in the thermally-sprayed coating layer is caused by stacked inclusion of unmelted particles and solidified shrinkage of melted liquid. Each of the pores has a size of a few to a few tens μm, and is isolated in a local region. However, the pores form a three-dimensional network to be connected to one another through an entire coating layer in most cases. Fig. 2 is a photograph showing a fine structure of a plasma-sprayed Al₂O₃ coating layer used in the aforementioned conventional electrostatic chuck, in which pores with a size of about 5 to 15/im are randomly produced throughout the entire coating layer. The porosity through an image analysis at 200 magnifications, which is a generally used porosity measuring method, shows about 1 to 2%. However, as shown in Fig. 3, in an Al₂O₃ thermally-sprayed coating layer observed at a higher modifications (1000 modifications or more) , thin porous layers exist at an interface between stacked particles except besides slightly large pores shown in Fig. 2, and fine cracks are produced in the stacked particle. These porous layers and fine cracks are connected to one another so as to form a three dimensional pore network, and are linked up to a surface of the coating layer. The pore network of the aforementioned Al₂O₃ thermally-sprayed dielectric layer serves as a conduction path due to the penetration of a polluted substance having an electric charge. Here, the polluted substance may be various particles each having an electric charge, moisture, and plasma particles in an apparatus having the electrostatic chuck. Therefore, there is a problem in that, if a high voltage is applied the conventional ceramic coating type electrostatic chuck formed by thermally spraying Al₂O₃, the leakage current of the electrostatic chuck is greatly increased due to existence of polluted substances showing a breakdown voltage relatively lower than an Al₂O₃ dielectric layer, and thus an electrostatic force is lost. As disclosed in Korean Patent Laid-open Publication No. 2002-0070340, a method may be used for solving such a problem, in which an organic or inorganic sealant is inserted in an Al₂O₃ thermally-sprayed coating layer for the purpose of preventing the penetration of polluted substances from the outside to the coating layer so that the resistance of the electrostatic chuck can be enhanced. However, it is difficult to completely remove pores in the coating layer through the insertion of the sealant. As a large amount of sealant with a dielectric constant and plasma etching resistance relatively lower than Al₂O₃ are used, the electrostatic chuck may cause the reduction of electrostatic force, durability and life span. Therefore, it is necessary to minimize the porosity of the ceramic coating layer formed through a thermally spraying method. Further, a method of forming a coating layer by thermally spraying a ceramic powder including a garnet crystal structure has been disclosed in PCT Patent Publication No. WO 03/059615. In the patent, a coating layer of a garnet crystal structure with a thickness of a few tens μm is formed on surfaces of various components including an electrostatic chuck in a semiconductor etching chamber, so that corrosion resistance for plasma gas can be enhanced. This is a method for protecting the surface of the components, and it is difficult to expect that an electrostatic characteristic can be enhanced through the method.

[Disclosure] [Technical Problem] An object of the present invention is to provide a method of manufacturing a ceramic coating electrostatic chuck using a thermally spraying method, wherein a coating layer with a high volume resistivity and breakdown voltage is applied to a lower insulating layer or/and an upper dielectric layer, so that a leakage current of the electrostatic chuck can be reduced, an electrostatic force can be increased, and a superior electrostatic characteristic can be displayed in application of a high voltage .

Another object of the present invention is to provide a method of manufacturing a ceramic coating layer, wherein the production of a defect such as a pore network and a fine crack is prevented, so that penetration of various polluted substance can be prevented and the use of a sealant can be minimized.

[Technical Solution]

To achieve these objects of the present invention, in an electrostatic chuck member and a method of manufacturing the same according to the present invention, the electrostatic chuck member includes a lower dielectric (insulating) layer, a conductive electrode layer and an upper dielectric

(insulating) layer, and at least one of the lower and upper dielectric layers is formed as an Al₂O₃-YAG composite oxide amorphous coating layer. Preferably, the Al₂O₃-YAG composite oxide amorphous coating layer is formed through a process of thermally spraying an Al₂O₃-YAG composite oxide powder, and the Al₂O₃-YAG composite oxide powder is prepared by preparing a slurry containing alumina and YAG powers each having a degree of purity of 98.0% and then spraying and drying the slurry.

Preferably, the Al₂O₃-YAG composite oxide powder is made of YGA of 5 to 95wt% and Al₂O₃ of 95 to 5wt%. This is because there is a problem in that it is difficult to form an amorphous phase in the thermally-sprayed coating layer when the content of the YAG is below 5wt%, and an occurrence frequency of fine cracks is greatly increased when the content of the YAG is over 95wt%. By virtue of the production of the amorphous phase in the Al₂O₃-YAG composite) oxide powder, the solidified shrinkage of stacked particles can be minimized and the bonding force between the stacked particles can be increased. Consequently, the occurrence of porous layers and fine cracks at an interface between the stacked particles can be prevented. Preferably, the dielectric layer made of an Al₂O₃-YAG thermally-sprayed coating layer has a thickness of 100 to 1000 IM. The dielectric layer formed by performing thermally spraying an Al₂O₃-YAG composite oxide has a volume resistivity of IxIO¹² Ω ^• cm or more, and a breakdown voltage of 15kV/mm or more in the air. The porosity of the coating layer is below 2%, which is excellent. Further, at least any one or more of the lower and upper dielectric (insulating) layers formed by thermally sprayed coating the Al₂O₃-YAG composite oxide powder is subjected to sealing treatment by being impregnated in a liquid organic or inorganic sealing solution, so that the volume resistivity and breakdown voltage of the coating layer can be more enhanced. With the sealing treatment, The coating layer is a superior dielectric (insulating) layer for an electrostatic chuck having a volume resistivity of IxIO¹⁵ Ω ^• cm or more and a breakdown voltage of 30kV/mm or more in the air. Hereinafter, the present invention will be described in detail. The present invention relates to a method of manufacturing an electrostatic chuck through a thermally spraying method in which a lower dielectric layer, a conductive electrode layer and an upper dielectric layer are stacked on a preform. One or more of the lower and upper dielectric layers is formed as an Al₂O₃-YAG amorphous coating layer.

First, a method of preparing an Al₂O₃-YAG composite oxide powder will be discussed. The Al₂O₃-YAG composite oxide powder is prepared by spraying and drying an Al₂O₃-YAG powder granule of 5 to 100/iln, which is a size suitable for a thermally spraying method, using a raw material powder of YAG(Y₃Al₃Oi₂) with perovskite structure and Al₂O₃. However, if a powder with a range of the particle size can be prepared, the method of manufacturing the composite oxide power is not limited. At this time, it is preferred that an initial raw material powder has a degree of purity of 98% or more, and a range of a particle size of 0.05 to 5.0/im. Preferably, the content of YAG for the total weight of the composite oxide is 5 to 95wt% for the purpose of implementing an advantage of the present. As an example of the method of preparing the Al₂O₃-YAG composite oxide powder, a preparation method through a spraying and drying method will be described as follows: A uniformly mixed slurry is prepared by inserting an Al₂O₃ powder, a YAG powder, a binder and a dispersant into a liquid solvent and ball milling them. An Al₂O₃-YAG granule powder is prepared by spraying the mixed slurry as a liquid drop with a micron size using an atomizer rotating at a high speed or a high-pressure gas atomizer such that the solvent is removed under the high- temperature air or inert gas. Preferably, the sprayed and dried Al₂O₃-YAG composite oxide has a spherical shape and a range of a granule size of 5 to lOOμm. In a case where the granule size of the sprayed and dried Al₂O₃-YAG composite oxide is smaller than 5μm, or the Al₂O₃-YAG composite oxide does not have a spherical shape, uniform spraying into a plasma flame is difficult due to the lowering of fluidity of the powder. On the other hand, in a case where the granule size of the powder is more than lOOμm, a large amount of defect is formed in the coating layer as complete melting does not occur in the plasma flame. The sprayed and dried granule powder may be immediately used in thermally-sprayed coating. Further, the sprayed and dried granule powder may be used in thermally-sprayed coating by performing thermal treatment at a temperature of 1000 to 1600 ^°C so as to increase the strength of the granule powder. In a case where the temperature of the thermal treatment is lower than 1000^°C, the breakdown of the powder occurs due to a low strength of the granule powder. On the other hand, in a case where the temperature of the thermal treatment is higher than 1600^°C, a large particle size of the powder is shown due to sinter between the granule powders. Hereinafter, a method of manufacturing an electrostatic chuck, in which lower and upper dielectric layers are formed by thermally-sprayed coating the Al₂O₃-YAG composite oxide powder, will be described in detail with reference to Fig. 1. As shown in Fig. 1, an undercoat, a lower dielectric layer, an conductive electrode layer and an upper dielectric layer are sequentially formed on a surface of a mechanically processed or polished preform through a thermally-sprayed coating method. The surface of the preform is subjected to blast treatment so as to increase an interface adhesive force of a thermally- sprayed coating layer, and the undercoat is then formed by spraying a metallic material on the surface of the preform subjected to roughing treatment. The undercoat is required to provide a high interface adhesive force between the preform of the electrostatic chuck and the lower dielectric layer. If the preform of the electrostatic chuck has a thermal expansion coefficient similar to the lower dielectric layer, the undercoat may be omitted.

The lower dielectric layer is formed on the undercoat by thermally spraying the Al₂O₃-YAG composite oxide powder. The thickness of the lower dielectric layer is determined depending on a DC voltage applied to the electrostatic chuck. The thickness of the lower dielectric layer should be sufficiently thick such that insulation breakdown does not occur. Preferably, the thickness of the lower dielectric layer is generally in a range of 100 to 1000/zm. Similarly, the conductive electrode layer is formed on a surface of the lower dielectric layer through a thermally-sprayed coating method, preferably except a peripheral portion of the lower dielectric layer. The conductive electrode layer should have a high electric conductivity at a normal temperature. Preferably, the conductive electrode layer has a specific electrical resistance lower than IxIO^"4 Ω ^• cm in most cases. Since the conductive electrode layer should endure in application of a high DC voltage for a long period of time, it is preferred that a heat-resistant metal with a high melting point, such as W, Mo, Ta, Re, Ni or Nb, or an alloy thereof be used as the conductive electrode layer. Further, a conductive ceramic material may be applied to the conductive electrode layer. Preferably, the thickness of the conductive electrode layer is in a range of 20 to lOOμm.

The upper dielectric layer is formed on the conductive electrode layer by thermally spraying the Al₂O₃-YAG composite oxide powder like the lower dielectric layer. The upper dielectric layer functions to provide an electrostatic force directly to an object to be treated. To obtain a higher electrostatic force from the given dielectric material, the upper dielectric layer should have a thin thickness and endure in application of a high DC voltage. Preferably, the Al₂O₃-YAG dielectric layer has a thickness of 100 to 500μm. The lower and upper dielectric layers made of the Al₂O₃-YAG composite oxide should have a high volume resistivity and breakdown voltage, and a leakage current should be minimized. To this end, the Al₂O₃-YAG thermally-sprayed coating layer preferably has a porosity of 2% or less. Further, the occurrence of a fine pore channel having a three-dimensional network structure should be kept to a minimum in the coating layer.

According to the present invention, the Al₂O₃-YAG thermally- sprayed coating layer applied to the lower and upper dielectric layers does not include a fine porous network and a channel, which are observed in the conventional Al₂O₃ thermally-sprayed coating layer, due to close bonding between stacked particles. Fig. 4 is a photograph of 1000 modifications showing a fine structure of an Al₂O₃-YAG coating layer according to the present invention. No porous layer is formed between stacked particles. It has been found that the Al₂O₃-YAG thermally-sprayed coating layer has an amorphous structure with a uniform composition through X-ray diffraction analysis. That is, the Al₂O₃-YAG liquid particle completely melted due to a high-temperature flame reaches a surface of a preform, and is simultaneously solidified. At this time, a crystal structure only having short range order in a liquid phase is transformed into a solid phase due to a high amorphous formation performance of an Al₂O₃-YAG composite oxide. Thus, since solidification shrinkage occurring in transformation of a liquid phase into a solid phase is minimized, the separation of an interface between the stacked particles does not occur. As a result, porous layers are not produced at an interface between the stacked particles, and the production of a three-dimensional pore network is also prevented. As described in the embodiment of the present invention, it has been experimentally found that the electrostatic chuck to which the Al₂O₃-YAG thermalIy-sprayed coating layer is applied shows a very high volume resistivity and breakdown voltage due to a fine structural characteristic of the Al₂O₃-YAG thermally-sprayed coating layer. The upper dielectric layer is made of the Al₂O₃-YAG composite oxide may be mechanically polished so as to secure the precision of the thickness of the coating layer and to reduce a surface illumination index of the coating layer as necessary. Finally, the electrostatic chuck manufactured through thermally-sprayed coating is subject to sealing treatment by an organic or inorganic sealant, so that a volume resistivity and breakdown voltage can be more enhanced. The sealing treatment prevents the penetration of foreign substances and particles with an electric charge by filling the sealant in a fine porous portion remaining in the thermally-sprayed coating layer, so that a leakage current can be minimized in application of a voltage to the electrostatic chuck. Accordingly, an electrostatic force can be increased, and the loss of the electrostatic force due to insulation breakdown can be prevented. Since a dielectric layer of the conventional electrostatic chuck has a high defect or porosity, a large amount of sealant having a dielectric constant and plasma etching resistance relatively lower than Al₂O₃ is used. Therefore, there is a problem in that the conventional electrostatic chuck causes the reduction of electrostatic force, durability and life span. However, since the dielectric layer of the electrostatic chuck according the present invention has a porosity of below 2%, porous can be effectively sealed using a small amount of sealant. Accordingly, there is an advantage in that the performance of the electrostatic chuck can be enhanced. An organic sealant such as epoxy or phenolic resin, an inorganic sealant containing a silicon compound, or the like is used as the sealant .

Here, any methods known in the art, such as a gas flame spraying method, a low- and high-speed flame spraying method, an explosion spraying method, an air plasma spraying method and a decompression plasma spraying method, may be used as the thermally spraying method used to form the lower and upper dielectric layers made of the Al₂O₃-YAG composite oxide in the electrostatic chuck. However, it is preferred that the air plasma spraying method or the decompression plasma spraying method be used as the thermally spraying method due to the reliability and the efficiency of the process.

[Description of Drawings]

The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:

Fig. 1 is a view schematically showing a sectional structure of an electrostatic chuck; Fig. 2 is a photograph of 200 modifications showing a fine structure of a plasma sprayed Al₂O₃ coating layer used in a conventional electrostatic chuck;

Fig. 3 is a photograph of 1000 modifications showing a fine structure of the plasma sprayed Al₂O₃ coating layer used in the conventional electrostatic chuck; and

Fig. 4 is a photograph of 1000 modifications showing a fine structure of an Al₂O₃-YAG coating layer according to a preferred embodiment of the present invention.

<Detailed Descriptions of the Reference Numerals> 10: Electrostatic chuck 1: Metallic preform

2 : Undercoat 3 : Lower insulating layer

4 : Electrode layer 5 : Upper insulating layer

6: Silicon wafer 7: DC power source [Mode for Invention]

Hereinafter, the embodiments of the present invention will be described in detail with reference to accompanying drawings. However, the scope of the present invention is not limited by the following embodiments. [Preparation Example]

An Al₂O₃-YAG composite oxide powder with a composition and average particle diameter shown in the following Table 1 has been prepared using a conventional spraying and drying process (book: Ceramic precursor technology and its applications, author: CK. Narula, publishing company: M. Dekker (N.Y.), published in 1995), which is known in the art. [Table 1]

[Embodiment 1 to 4]

One surface of a flat Al preform (100mm x 100mm x 5mm) was subjected to blasting treatment using a #100 Al₂O₃ particle so as to have a surface roughness (Ra: 2 to 3μm) . Then, an Al₂O₃- YAG coating layer that is a dielectric layer was formed at a thickness of 500μm on an entire surface of the preform through an air plasma spraying method using four kinds of Al₂O₃-YAG composite oxide powders with different compositions prepared in the preparation example. Tungsten that is a conductive electrode layer was formed at a thickness of 50μm in an area portion of 50mm x 50mm on a surface of the Al₂O₃-YAG coating layer through the air plasma spraying method. After the plasma spraying method, the coating layer was not subjected to sealing treatment. [Comparative Example 1]

A dielectric layer and a conductive electrode layer were formed through the same method as Embodiment 1, and a dielectric layer with a thickness of 500μm was formed using a spraying Al₂O₃ powder with a degree of purity of 99.9% instead of an Al₂O₃-YAG composite oxide powder when forming the dielectric layer.

A DC voltage was applied to both sides of the Al preform and the tungsten coating layer using a test piece prepared in Embodiments 1 to 4 and Comparative example 1 so as to measure a resistance, and a volume resistivity was then calculated. Further, a breakdown voltage of the coating layer was measured by increasing the applied voltage by 0.5kV. The result of the experiment is shown in Table 2. [Table 2 ]

As can be known from the result shown in Table 2, the Al₂O₃-YAG coating layer of the present invention displayed a volume resistivity and breakdown voltage about over 1000 times higher than a conventional Al₂O₃ coating layer regardless of a measuring condition. Both the coating layers displayed an electrical insulation characteristic sensitive to humidity. Particularly, in case of the Al₂O₃ coating layer, a large leakage current was produced with respect to a very low applied voltage of 1.5kV/mm or less. That is, as shown in Fig. 3, a large amount of fine pore network/channel contained in the Al₂O₃ coating layer serves as a conduction path due to humidity penetrated from the surroundings. Since a real environment in which the electrostatic chuck is used is exposed by plasma having an electric charge, the Al₂O₃ coating layer cannot be used as the dielectric layer of the electrostatic chuck. On the other hand, the Al₂O₃-YAG coating layer maintains a relatively high breakdown voltage even in an environment with a high humidity due to a pore network/channel limited in all compositions shown in Table 1. [Embodiments 5 to 8]

A dielectric layer and a conductive electrode layer were formed through the same method as Embodiments 1 to 4 except that an organic liquid sealant (Metcoseal ERS, Sulzer Metco Inc., USA) was coated on a surface of an upper dielectric (insulating) layer, and was then subjected to sealing treatment of heating at 150^°C for 3 hours under vacuum. [Comparative Example 2] The dielectric layer and conductive electrode layer subjected to sealing treatment were formed through the same method as Embodiment 5, and an Al₂O₃ spraying powder with a degree of purity of 99.9% instead of an Al₂O₃-YAG composite oxide powder was used as the dielectric layer.

Table 3 shows electrical insulation characteristics of the Al₂O₃ coating layer subjected to sealing treatment in Comparative example and the Al₂O₃-YAG coating layer in Embodiment 2. [Table 3]

The conventional Al₂O₃ plasma coating layer displayed a volume resistivity and breakdown voltage greatly increased by performing the sealing treatment. However, the conventional Al₂O₃ plasma coating layer displayed a volume resistivity and breakdown voltage similar to the Al₂O₃-YAG coating layer of the present invention, which was not subjected to sealing treatment, even after performing the sealing treatment. On the other hand, the Al₂O₃-YAG coating layer according to the embodiment of the present invention displayed a very high volume resistivity of 1 x 10¹⁵ Ω ^• cm or more through the sealing treatment in all the compositions shown in table 1, and an insulation breakdown was not produced in application of a DC voltage of 44 kV/mm or more. [Embodiment 9] Embodiment 9 is a result obtained by estimating an electrical insulation characteristic in accordance with the application of a conventional Al₂O₃ plasma coating layer an Al₂O₃-YAG plasma coating layer according to the embodiment of the present invention to a real electrostatic chuck. To this end, a preform of an Al electrostatic chuck with a reduced size (100mm x 120mm) , which includes a metal electrode rod capable of applying a DC voltage, was processed. An undercoat, a lower insulating (dielectric) layer, a conductive electrode layer and an upper dielectric (insulating) layer were sequentially stacked on a surface of the Al preform using a plasma spraying method. At this time, a coating area of the conductive electrode layer was 80mm x 100mm. The metal electrode rod was directly connected to the conductive electrode layer, and was insulated from the Al preform by processing the surroundings of the metal electrode rod with the same material as the lower insulating (dielectric) layer. A Ni coating layer with a thickness of lOOμrn was formed as the undercoat, and a W coating layer with a thickness of 5OiMi was formed as the conductive electrode layer. In a comparative example, an Al₂O₃ coating layer with a degree of purity of 99.9% was formed at a thickness of 400μm as the lower and upper dielectric (insulating) layers. In the embodiment of the present invention, an Al₂O₃-YAG coating layer was formed at a thickness of 400μm through a plasma spraying method using the Al₂O₃-YAG composite oxide powder (Al₂O₃: YAG weight ratio = 50:50, average granule diameter 35μm) of Preparation Example 2.

After the completion of the plasma coating, an epoxy liquid sealant (Metcoseal ERS, Sulzer Metco Inc., USA) was coated on a surface of the upper dielectric (insulating) layer, and was then subjected to sealing treatment of heating at 150^°C for 3 hours under vacuum.

To estimate the electrical characteristic of the manufactured electrostatic chuck, the leakage current and insulation resistance of the electrostatic chuck were measured by applying a DC voltage of 0.5 to 5. OkV to the metal electrode rod for 60 seconds in the air. [Table 4 ]

The conventional electrostatic chuck including the Al₂O₃ plasma coating layer displayed a rapid increase of the leakage current together with an increase of the applied voltage. A breakdown phenomenon was produced in an applied voltage of about 3.IkV. On the other hand, the electrostatic chuck including the Al₂O₃-YAG coating layer according to the present invention displayed an insulation resistance 5 times higher than the Al₂O₃ electrostatic chuck with respect to the same applied voltage. The increase of a leakage current in accordance with an increase of the applied voltage was not large. Further, although, a DC voltage of 5.OkV is applied for 10 minutes to the electrostatic chuck including the Al₂O₃-YAG coating layer, the insulation breakdown of the dielectric (insulating) layer was not produced. [Embodiment 10]

An electrostatic chuck for display panel equipment with a real size (1950mm x 2150mm) was manufactured through the same method as Embodiment 9 on the basis of a characteristic of the electrostatic chuck with a reduced size in Embodiment 9, and an electrical insulation characteristic of the electrostatic chuck was estimated. In the conventional electrostatic including an Al₂O₃ thermally-sprayed coating layer, an applied voltage and a leakage current were greatly increased. Since arcing or insulation breakdown was produced under a low applied voltage of 1 to 2kV, the function of the electrostatic chuck was lost. On the other hand, in the electrostatic chuck including the Al₂O₃-YAG coating layer of the present invention, a sufficient electrostatic force for fixing a glass substrate in an applied voltage of 2.5 to 3.OkV was produced. Further, insulation breakdown was produced, and a leakage current in a permission range was shown even in a voltage more than the applied voltage.

[industrial Applicability]

As described above, in a method of manufacturing an electrostatic chuck using a thermally-sprayed coating method according to the present invention, an Al₂O₃-YAG coating layer with a very high volume resistivity and breakdown voltage is applied to a lower or/and upper layer, so that the electrostatic force of the electrostatic chuck can be increased, and the durability and life span of the electrostatic chuck can be enhanced.

Further, according to the present invention, a dielectric layer constituting the electrostatic chuck is formed as an Al₂O₃-YAG thermally-sprayed coating layer, so that the penetration of various polluted substances into the coating layer from the outside can be prevented, and the use of a sealant can be minimized.

Claims

[CLAIMS]

[Claim l]

A method of manufacturing an electrostatic chuck in which a lower dielectric layer, a conductive electrode layer and an upper dielectric layer are stacked on a metallic preform, wherein one or more of the lower and upper dielectric layers is formed by thermally-sprayed coating an Al₂O₃-YAG composite oxide powder.

[Claim 2] The method as set forth in claim 1, wherein the Al₂O₃-YAG composite oxide is made of YGA of 5 to 95wt% and Al₂O₃ of 95 to 5wt%. [Claim 3]

The method as set forth in claim 2, wherein surfaces of any one or more of the upper and lower layers are subjected to sealing treatment with a liquid organic or inorganic sealing solution, and the dielectric layer subjected to sealing treatment has a volume resistivity of IxIO¹⁵ Ω ^• cm or more and a breakdown voltage of 30kV/mm or more. [Claim 4]

The method as set forth in claim 1, wherein the Al₂O₃-YAG composite oxide powder is prepared at a size of 5 to 100 by spraying and drying a slurry mixed solution including Al₂O₃ and YAG powders. [Claim 5] An electrostatic chuck having an Al₂O₃-YAG complex composite oxide dielectric layer, which is manufactured through a manufacturing method of any one of claims 1 to 4.