JP2004079861A - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck having excellent withstand voltage characteristics. <P>SOLUTION: The electrostatic chuck is provided with a substrate 1, a lower insulating layer 2 arranged on the surface of the substrate 1, a bonding layer 3 which is arranged between the substrate 1 and the layer 2 for fixing the layer 2 to the substrate 1, electrode layers 4a, 4b which are formed on the layer 2, and an upper insulating layer 5 formed on the layer 2 by thermal spraying to cover the foregoing. The substrate 1 is made of metal or a metal-ceramics composite material, and the layer 2 is constituted of a sintered body having a porosity of 1% or below. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrostatic chuck. In particular, the present invention relates to a structure of an electrostatic chuck in which an electrode is provided on a base while being buried in an insulating layer.
[0002]
[Prior art]
In a thin film forming step or a dry etching step in a semiconductor manufacturing process, it is necessary to hold an article on a mounting table in order to perform a required film forming process or etching process on a flat article such as a wafer. As a holding device that meets such demands, an electrostatic chuck that tightly holds an article by using an electrostatic action is widely used.
[0003]
2. Description of the Related Art A conventional electrostatic chuck is configured by forming an insulating film on a metal disk electrode by plasma spraying a ceramic powder such as alumina so as to cover the metal disk electrode. Therefore, the electrostatic chuck can be manufactured with a relatively small number of steps, and furthermore, the obtained electrostatic chuck has an advantage of being excellent in heat resistance and durability.
[0004]
[Problems to be solved by the invention]
However, the thus obtained insulating film of the electrostatic chuck, that is, the sprayed film has a porous state in which minute pores are innumerably present, and thus does not have very high withstand voltage characteristics. Therefore, it is difficult to obtain a large holding force. In addition, a discharge phenomenon may occur in the pore portion. In other words, a problem such as current flowing through the pores between the electrode or the base and the article or the base held by suction may occur rarely, and there is still room for improvement. In view of such circumstances, a sealing process has been proposed in which the pores are filled with a resin to improve the withstand voltage characteristics (for example, Japanese Patent Application Laid-Open No. 6-196548).
[0005]
Incidentally, an electrostatic chuck used in a liquid crystal panel manufacturing apparatus is required to have a capability of adsorbing a glass substrate or the like having no conductive film, and in recent years, such needs have been increasing. In order to adsorb such an article, a particularly high voltage must be applied, and a glass substrate without a conductive film cannot be used as an electrode. For this reason, it is necessary to use a bipolar chuck which does not need to ground the glass substrate to be held by suction as the electrostatic chuck.
[0006]
However, when a high voltage necessary to make this bipolar electrostatic chuck function is applied, even if the above-mentioned sealing process is performed, the insulating layer, especially the lower insulating layer located between the base and the electrode, is applied. May have insufficient withstand voltage capability, and may cause malfunctions. Therefore, an object to be solved by the present invention is to provide an electrostatic chuck having a higher withstand voltage characteristic than before.
[0007]
[Means for Solving the Problems]
As a result of intensive research to solve the above problems, it was found that a drastic improvement in withstand voltage characteristics could not be expected in the sealing treatment. This is because if an excessive sealing treatment is applied to the lower insulating layer provided on the base, the bondability with the electrode layer formed thereon is rapidly deteriorated. In this case, peeling of the electrode layer is extremely likely to occur.
[0008]
As a result of further research based on this situation, a plate-like body composed of a sintered body having a porosity of 1% or less is disposed on the upper surface of the base via a bonding layer, and this is used as a lower insulating layer. For example, it has been found that the above problem can be solved without using the sealing treatment. That is, unlike the conventional film-like layer formed by thermal spraying or the like, the lower insulating layer thus obtained has almost no pores, so that there is virtually no defect caused by its existence. That is, the withstand voltage characteristic is greatly improved, and the suction holding ability is also increased. In addition, since the lower insulating layer and the electrode layer can be satisfactorily bonded, the problem of peeling of the electrode layer does not occur. Such a structure is particularly effective when the electrostatic chuck is of a bipolar type to which a high voltage is applied.
[0009]
The present invention has been made based on such findings, and the above-described problems
A base,
A lower insulating layer disposed on an upper surface of the base;
A bonding layer disposed between the base and the lower insulating layer, and fixing the lower insulating layer to the base;
An electrode layer formed on the lower insulating layer,
An electrostatic chuck comprising an upper insulating layer formed by thermal spraying on the lower insulating layer so as to cover the electrode layer,
The base is made of a metal or a metal-ceramic composite material, and the lower insulating layer is made of a sintered body having a porosity of 1% or less (lower limit is 0%). The problem is solved by an electrostatic chuck.
[0010]
In the electrostatic chuck of the present invention, the difference between the average thermal expansion coefficient of the base at 20 to 30 ° C. and the average thermal expansion coefficient of the lower insulating layer at 20 to 30 ° C. is 2 × 10 It is preferable that the temperature is set to ⁻⁶ / ° C. or less (the lower limit is 0). By doing so, peeling between the respective layers is less likely to occur.
[0011]
Further, as the lower insulating layer constituting the electrostatic chuck of the present invention, a layer formed of machinable ceramics (free-cutting ceramics) is particularly suitable. For reference, machinable ceramics are extremely easy to machine compared to general ceramics, which have extremely high hardness and are extremely difficult to machine. Refers to special ceramics that have the property that they can be freely processed into a desired shape. Specific examples include Photoveil (registered trademark) manufactured by Sumikin Ceramics Co., Ltd., and Macor (registered trademark) manufactured by Corning Co., USA.
[0012]
Furthermore, in joining the base and the lower insulating layer, glass, an aluminum alloy brazing material, or the like can be used in addition to the adhesive. In this case, the bonding layer is, of course, composed of a cured adhesive, glass, an aluminum alloy brazing material, or the like. Which joining method is adopted is selected in consideration of the use conditions of the electrostatic chuck.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be specifically described with reference to FIGS. 1 is a plan view of the electrostatic chuck according to the present embodiment, and FIG. 2 is a schematic cross-sectional view of the electrostatic chuck taken along line XX in FIG.
[0014]
The electrostatic chuck according to the present embodiment (hereinafter, referred to as the present electrostatic chuck) is of a bipolar type as shown in FIG. 1 and has a rectangular flat outer shape. Further, as can be seen from FIG. 2, the present electrostatic chuck includes, as main components, a base 1, a lower insulating layer 2, a bonding layer 3, two adjacent electrode layers 4a and 4b, and an upper insulating layer (dielectric layer). ) 5 is provided. The base 1 is made of a metal-ceramic composite material (MMC), and actually has a plurality of holes for installing electrode terminals to be described later. However, the material of the base 1 may be basically any material, and besides the above-mentioned metal-ceramic composite material, is composed of, for example, a simple metal such as aluminum, an aluminum alloy, or another low thermal expansion alloy. You. Which material is used is selected in consideration of the operating temperature of the electrostatic chuck.
[0015]
Next, the lower insulating layer 2 disposed on the upper surface of the base 1 is formed of a sintered body having a porosity of 1% or less. More specifically, the lower insulating layer 2 is a thin plate (a rectangular thin plate in the present embodiment) made of machinable ceramics, and is mounted on the base 1 via the bonding layer 3. The bonding layer 3 disposed between the base 1 and the lower insulating layer 2 serves to fix the lower insulating layer 2 to the base 1 so that no gap is formed between them. Here, the bonding layer 3 is made of a Si-based heat-resistant adhesive. That is, the lower insulating layer 2 was bonded to the base 1 with a Si-based adhesive. In the present embodiment, the difference between the average thermal expansion coefficient of the base 1 at 20 to 30 ° C. and the average thermal expansion coefficient of the lower insulating layer 2 at 20 to 30 ° C. is 2 × 10 ⁻⁶ / It is set so that it is below ° C.
[0016]
The electrode layers 4a and 4b provided adjacent to each other on the lower insulating layer 2 are rectangular like the base 1, and for example, nickel (or tungsten, aluminum, silver, etc.) is The surface of the layer 2 is formed by plasma spraying. A voltage is applied to these electrode layers 4a and 4b such that one is a positive electrode and the other is a negative electrode.
[0017]
The upper insulating layer 5 provided on the lower insulating layer 2 so as to cover the electrode layers 4a and 4b is made of, for example, alumina containing a small amount of titanium oxide on the surfaces of the electrode layers 4a and 4b, and It is formed by plasma spraying on the surface. However, other than alumina, an appropriate material can be selected and used according to the required value of the dielectric constant.
[0018]
In the present embodiment, the bipolar electrostatic chuck has been described as an example, but the technique of the present invention can be applied to a single-pole electrostatic chuck having only one internal electrode. Here, the base and the electrode layer have a rectangular shape, but needless to say, these shapes are arbitrary and can be any desired shape as needed.
[0019]
The electrode terminals 6a and 6b for power supply are connected to the electrode layers 4a and 4b, respectively. By applying a voltage to the electrode layer 4a and the electrode layer 4b using this, the present electrostatic chuck can adsorb an article on the surface of the upper insulating layer 5. In order to attach these electrode terminals 6a and 6b to the base 1, ceramic insulating tubes 7a and 7b are used. That is, the electrode terminals 6a, 6b are assembled to the insulating tubes 7a, 7b such that the upper ends are exposed from the end surfaces of the insulating tubes 7a, 7b, and further, these are fitted into the holes of the base 1, so that the electrode terminals 6a, 6b are connected. It is fixed to the table 1. As the insulating tubes 7a and 7b, those obtained by processing machinable ceramics were used.
[0020]
In the present embodiment, the thickness of the lower insulating layer 2 made of machinable ceramic (in FIG. 2, indicated by T ₁₎ was 0.5~5mm about the. When the thickness is within this range, processing and handling are particularly easy. In addition, since the difference in the amount of thermal expansion from the base 1 is suppressed to a level that does not cause any problem, cracking and breakage due to thermal shock hardly occur. On the other hand, the electrode layer 4a, 4b thickness (in FIG. 2, indicated by _{T 2)} are both about 30 to 100 [mu] m. When the thickness is within this range, a particularly uniform sprayed coating can be obtained, so that there is no unevenness in the attraction force. In addition, since the step between the electrode layers 4a and 4b and the lower insulating layer 2 can be sufficiently reduced, the withstand voltage characteristics of the upper insulating layer 5 do not deteriorate. The distance between the electrode layers 4a and 4b (indicated by D in FIG. 1) is about 5 mm. Furthermore, the effective thickness of the upper insulating layer 5 (in FIG. 2, indicated by _{T 3)} is about 300 [mu] m. The surface roughness Ra of the upper insulating layer 5 is about 0.1 to 2.0 μm.
[0021]
Subsequently, a manufacturing procedure of the present electrostatic chuck will be briefly described. In order to obtain the present electrostatic chuck, first, a thin plate made of machinable ceramics (lower insulating layer 2) is bonded to the cleaned upper surface of the base 1 using a Si-based heat-resistant adhesive (bonding layer 3). The electrode terminals 6a and 6b are attached to the base 1 via insulating tubes 7a and 7b. Subsequently, the surface of the thin plate made of machinable ceramics, that is, the surface of the lower insulating layer 2 is uniformly roughened using a blast material such as alumina or silicon carbide. After the cleaning, nickel is plasma-sprayed on the surface of the lower insulating layer 2 to form two electrode layers 4a and 4b. Thus, the electrode layer 4a and the electrode terminal 6a are connected to each other, and the electrode layer 4b and the electrode terminal 6b are connected to each other.
[0022]
Next, alumina containing a small amount of titanium oxide is plasma-sprayed on the electrode layers 4a and 4b, and thus on the lower insulating layer 2, to form an upper insulating layer (dielectric layer) 5. Finally, the surface of the upper insulating layer 5 is subjected to sealing treatment, grinding, and lapping in this order to complete the present electrostatic chuck having a cross section as shown in FIG.
[0023]
The substance used for the sealing treatment, that is, the substance filled in the pores may be a colloidal slurry such as silica sol, alumina sol, magnesia sol, or a metal alkoxide-based polymer such as SiO ₂ , Al ₂ O ₃ , and TiO _2. And those containing various resins such as melamine resin, phenol resin, fluorine resin, silicone resin, and acrylic resin in addition to these polymers. The filling of the pores with such a substance (impregnation into the insulating layer) is performed by setting the semi-finished electrostatic chuck in a vacuum desiccator and suctioning the vacuum. The slurry filled in the pores is dried in consideration of its properties, and then subjected to grinding.
[0024]
As described above, in the present embodiment, the lower insulating layer 2 is formed of a sintered body having a porosity of 1% or less, that is, a thin plate made of machinable ceramics. Unlike the conventional film formed by thermal spraying or the like, the lower insulating layer 2 thus obtained has almost no pores, and thus virtually no trouble such as a discharge phenomenon occurs. As a result, the withstand voltage characteristics are greatly improved, and the suction holding ability is increased. In addition, since it is not necessary to perform a sealing process on the lower insulating layer 2, the bonding property with the electrode layers 4a and 4b is good. Furthermore, when the electrostatic chuck is of a bipolar type, a higher voltage is applied than in the case of a monopolar type. For this reason, the technique of the present invention exhibits a particularly great effect when applied to a bipolar electrostatic chuck.
[0025]
【Example】
[Example 1]
As base materials, (1) 70 parts by weight of a commercially available SiC powder of # 180 (average particle size 66 μm) as a reinforcing material, and (2) a commercially available SiC powder of # 800 (average particle size 14 μm) also as a reinforcing material 30 parts by weight of SiC powder, (3) an appropriate amount of colloidal silica liquid as a binder (an amount of 2 parts by weight of silica solids), and (4) 0 of Formaster VL (manufactured by San Nopco) as an antifoaming material. 2 parts by weight and (5) 24 parts by weight of ion-exchanged water were prepared, and these were mixed for 12 hours using a pot mill. Next, the slurry thus obtained is poured into a mesh-equipped metal mold (a disk-shaped molded article having a diameter of 350 mm and a thickness of 25 mm is obtained), subjected to a filter press, demolded, and fired at 1000 ° C. to perform a preform. Was formed.
[0026]
Subsequently, an aluminum alloy (Al-12Si-3Mg-2Cu-3Ti) is non-pressurized and infiltrated into the preform at 825 ° C. for 60 hours in a nitrogen stream, and then cooled. Thus, a base (209 mm in length, 157 mm in width, and 10 mm in thickness) made of a metal-ceramic composite material having a SiC powder content of 70% by volume was produced. Incidentally, the thermal expansion coefficient of this base is 6.2 × 10 ⁻⁶ / ° C.
[0027]
Next, the surface of the base was cleaned to enhance the adhesion, and the base and the horizontal and vertical dimensions were equal and the thickness of the machinable ceramics was 0.5 mm (Photoveel L Coefficient of thermal expansion 6.1 × 10 ⁻⁶ / C) was bonded to a base with a Si-based adhesive to form a lower insulating layer. Further, in order to enhance the adhesion to the subsequently formed electrode layer, the surface of the lower insulating layer is subjected to blasting until the surface roughness becomes at least 5 μm or more in Rmax. Thereafter, a Ni electrode layer having a thickness of 50 μm is formed on the surface of the lower insulating layer by plasma spraying. In this example, the electrode layer was formed into a bipolar shape, and the distance between the two was set to 5 mm (the shape of the electrode layer is as shown in FIG. 1). Further, an Al ₂ O ₃ layer having a thickness of 400 μm, that is, an upper insulating layer is formed by plasma spraying so as to cover this electrode layer. Finally, a sealing process is performed using a SiO ₂ -based metal alkoxide in a vacuum, and a grinding process and a lapping process are sequentially performed. The thickness of the upper insulating layer is 300 μm, and the surface roughness Ra is 0.2 μm. Was obtained.
[0028]
[Example 2]
An electrostatic chuck according to the present invention was manufactured under the following conditions in the same manner as in Example 1 (basically the same applies to other examples).
Base material: metal (aluminum alloy) -ceramic composite material (SiC content 55% by volume)
Thermal expansion coefficient of base: 10.0 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Thermal expansion coefficient of lower insulating layer of photoveil: 8.5 × 10 ⁻⁶ / ° C
Thickness of lower insulating layer: 1.0 mm
Electrode layer material: W
Material of upper insulating layer: Al ₂ O ₃
[0029]
[Example 3]
The electrostatic chuck according to the present invention was manufactured under the following conditions.
Base material: metal (aluminum alloy) -ceramic composite material (SiC content 70% by volume)
Thermal expansion coefficient of base: 6.2 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Al ₂ O ₃
Thermal expansion coefficient of lower insulating layer: 6.8 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.5mm
Material of electrode layer: Al
Material of upper insulating layer: Al ₂ O ₃ -7.5% TiO ₂
[0030]
[Example 4]
The electrostatic chuck according to the present invention was manufactured under the following conditions.
Base material: metal (aluminum alloy) -ceramic composite material (SiC content 55% by volume)
Thermal expansion coefficient of base: 10.0 × 10 ⁻⁶ / ° C
Material of lower insulating layer: coefficient of thermal expansion of lower insulating layer of Macor: 9.3 × 10 ⁻⁶ / ° C.
Thickness of lower insulating layer: 2.0mm
Material of electrode layer: Ni
Material of upper insulating layer: Al ₂ O ₃
[0031]
[Example 5]
The electrostatic chuck according to the present invention was manufactured under the following conditions.
Base material: Metal (Si) -ceramic composite material (SiC content 50% by volume)
Thermal expansion coefficient of base: 2.8 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Si ₃ N ₄
Thermal expansion coefficient of lower insulating layer: 3.5 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.5mm
Electrode layer material: W
Material of upper insulating layer: Al ₂ O ₃
[0032]
[Example 6]
The electrostatic chuck according to the present invention was manufactured under the following conditions.
Base material: Metal (Si) -ceramic composite material (SiC content 50% by volume)
Thermal expansion coefficient of base: 2.8 × 10 ⁻⁶ / ° C
Material of lower insulating layer: coefficient of thermal expansion of lower insulating layer of Macor: 9.3 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.5mm
Electrode layer material: W
Material of upper insulating layer: Al ₂ O ₃
[0033]
[Example 7]
An electrostatic chuck according to the present invention was manufactured under the following conditions in the same manner as in Example 1 except that the composition of the base was different.
Base material: Aluminum alloy (5052)
Thermal expansion coefficient of base: 22.0 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Al ₂ O ₃
Thermal expansion coefficient of lower insulating layer: 6.8 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.5mm
Material of electrode layer: Ni
Material of upper insulating layer: Al ₂ O ₃ -5% TiO ₂
[0034]
[Comparative Example 1]
An electrostatic chuck for comparison was manufactured under the following conditions in the same manner as in Example 1 except that the lower insulating layer was formed of a ceramic sprayed film.
Base material: metal (aluminum alloy) -ceramic composite material (SiC content 70% by volume)
Thermal expansion coefficient of base: 6.2 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Al ₂ O ₃
Thermal expansion coefficient of lower insulating layer: 6.8 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.5mm
Material of electrode layer: Ni
Material of upper insulating layer: Al ₂ O ₃ -5% TiO ₂
[0035]
[Comparative Example 2]
As in Comparative Example 1, an electrostatic chuck for comparison was manufactured under the following conditions.
Base material: metal (aluminum alloy) -ceramic composite material (SiC content 55% by volume)
Thermal expansion coefficient of base: 10.0 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Al ₂ O ₃
Thermal expansion coefficient of lower insulating layer: 6.8 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.4mm
Material of electrode layer: Ni
Material of upper insulating layer: Al ₂ O ₃
[0036]
[Comparative Example 3]
An electrostatic chuck for comparison was produced under the following conditions in the same manner as in Comparative Example 1 except that the composition of the base was different.
Base material: Aluminum alloy (5052)
Thermal expansion coefficient of base: 22.0 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Al ₂ O ₃
Thermal expansion coefficient of lower insulating layer: 6.8 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.5mm
Electrode layer material: W
Material of upper insulating layer: Al ₂ O ₃
[0037]
[Comparative Example 4]
As in Comparative Example 1, an electrostatic chuck for comparison was manufactured under the following conditions.
Base material: Metal (Si) -ceramic composite material (SiC content 50% by volume)
Thermal expansion coefficient of base: 2.8 × 10 ⁻⁶ / ° C
Material of lower insulating layer: Al ₂ O ₃
Thermal expansion coefficient of lower insulating layer: 6.8 × 10 ⁻⁶ / ° C.
Lower insulating layer thickness: 0.5mm
Electrode layer material: W
Material of upper insulating layer: Al ₂ O ₃
[0038]
[Evaluation]
With respect to the electrostatic chucks of Examples 1 to 7 and Comparative Examples 1 to 4, a DC voltage of up to 10 kV was applied, and the withstand voltage characteristics were evaluated by measuring the attraction force. That is, an electrostatic chuck was fixed to a general vacuum chamber test apparatus, and helium gas was introduced between the electrostatic chuck and a sucked glass substrate (length 220 mm, width 170 mm, thickness 5 mm). Then, the pressure at the moment when the glass substrate was peeled off from the electrostatic chuck was detected, and the attraction force was calculated from this value. Separately, a temperature cycle test at room temperature (20 ° C.) to 200 ° C. was performed to check whether or not a problem such as separation occurred in the insulating layer. The results are as shown in Table 1. In Table 1, ○ means good (no problem), Δ means acceptable (acceptable range), and × means unacceptable (problem).
[0039]
Table 1
Sample Withstand voltage test Example 1 of temperature cycle test ○ ○
Example 2 ○ ○
Example 3 ○ ○
Example 4 ○ ○
Example 5 ○ ○
Example 6 ○ △
Example 7 ○ △
Comparative Example 1 × ×
Comparative Example 2 × ×
Comparative Example 3 × ×
Comparative Example 4 × ×
[0040]
From the test results, it is understood that the electrostatic chuck according to the present invention has excellent withstand voltage characteristics, has no problem such as peeling of the insulating layer, and has high durability. Moreover, when the difference in the coefficient of thermal expansion between the base and the lower insulating layer is suppressed to 2 × 10 ⁻⁶ / ° C. or less as in Examples 1 to 5, the effect of the present invention is particularly remarkable. Has become.
[0041]
【The invention's effect】
INDUSTRIAL APPLICABILITY The electrostatic chuck of the present invention is more excellent in withstand voltage characteristics than the conventional one, and exhibits a high suction holding ability. In addition, the insulating layer is hardly peeled off and has excellent durability.
[Brief description of the drawings]
FIG. 1 is a plan view of an electrostatic chuck according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the electrostatic chuck according to the embodiment of the present invention taken along line XX in FIG.
Reference Signs List 1 base 2 lower insulating layer 3 bonding layers 4a, 4b electrode layer 5 upper insulating layer (dielectric layer)
6a, 6b Electrode terminal 7a, 7b Insulated tube

Claims (3)

A base,
A lower insulating layer disposed on an upper surface of the base;
A bonding layer disposed between the base and the lower insulating layer, and fixing the lower insulating layer to the base;
An electrode layer formed on the lower insulating layer,
An electrostatic chuck comprising an upper insulating layer formed by thermal spraying on the lower insulating layer so as to cover the electrode layer,
An electrostatic chuck wherein the base is made of a metal or a metal-ceramic composite material, and the lower insulating layer is made of a sintered body having a porosity of 1% or less. The difference between the average thermal expansion coefficient of the base at 20 to 30 ° C. and the average thermal expansion coefficient of the lower insulating layer at 20 to 30 ° C. is 2 × 10 ⁻⁶ / ° C. or less. The electrostatic chuck according to claim 1, wherein: 3. The electrostatic chuck according to claim 1, wherein the lower insulating layer is made of machinable ceramics.

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