JP2008244147A - Electrostatic chuck, manufacturing method thereof, and attraction method of glass substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck capable of attracting and fixing an insulating glass substrate at relatively low temperature uniformly with sufficient attraction force. <P>SOLUTION: The electrostatic chuck for attracting and fixing a glass substrate at a temperature range of 80-150°C comprises: an insulator layer 2 made of oxide-based ceramics formed by flame spraying onto a base material 1; a bipolar comb-like teeth electrode 3 formed by flame spraying on the insulator layer; and a dielectric layer 4 mainly made of oxide-based ceramics formed by flame spraying so that the bipolar comb-like teeth electrode is covered. The comb-like teeth width W of the comb-like teeth electrode 3 ranges from 2.5 to 5.0 mm; distance L between comb-like teeth ranges from 2.5 to 5.0 mm; and the thickness of the dielectric layer 4 ranges from 100 to 600 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an electrostatic chuck for attracting and fixing a glass substrate, and more particularly to an electrostatic chuck formed by thermal spraying a bipolar comb-tooth electrode and a dielectric layer covering the comb-tooth electrode. .

Conventionally, bipolar electrostatic chucks have been frequently used. In a bipolar electrostatic chuck, when a positive or negative voltage is applied to each of a pair of electrostatic electrodes, positive and negative charges are generated on the dielectric surface adjacent to the electrodes. At this time, the conductive substrate placed on the dielectric surface Since a charge opposite to that of the dielectric surface is generated, this utilizes the fact that the forces attracting each other, that is, the Johnsenlerbeck force is developed. Therefore, when an insulating glass substrate is attracted and fixed by an electrostatic chuck, a conductive film such as ITO is applied and adsorbed because no electric charge is generated on the glass substrate. However, since it takes time and cost to form the conductive film only for adsorption fixation, a means for adsorption fixation without applying the conductive film has been desired. Thus, as an electrostatic chuck that attracts an insulating glass substrate, an electrostatic chuck using a gradient force that is a force acting on an electric field has been proposed (for example, see Patent Documents 1 and 2). Furthermore, an electrostatic chuck that electrostatically attracts the glass substrate by changing the resistivity of the glass substrate to 10 ¹⁵ Ω · cm or less by heating the glass substrate has also been proposed (see, for example, Patent Document 3).
JP 2006-66857 A JP 2006-49852 A JP 2005-32858 A

However, the electrostatic chuck using the above-described gradient force has a problem that a sufficient attracting force cannot be obtained as compared with the electrostatic chuck using the Johnsenler-Beck force. According to the study by the present inventors, the chucking force of the electrostatic chuck using the Johnsenler Beck force is several hundred g / cm ² , whereas the chucking force of the electrostatic chuck using the gradient force is It is several tens of g / cm ² , which is not sufficient. Further, in order to exert the gradient force, it is required that the distance between the comb teeth is small as in the electrostatic chuck described in Patent Document 1, so that it is easy to discharge between the electrodes, the withstand voltage is lowered, and the dielectric breakdown occurs. There was a case to get up. In particular, the electrostatic chuck described in Patent Document 1 requires a high vacuum in order to prevent dielectric breakdown due to discharge between the electrodes because the electrodes are exposed. Since the voltage could not be applied at the time of low vacuum until the glass substrate was made, the glass substrate could not be fixed and the position could be displaced.
The electrostatic chuck described in Patent Document 2 is characterized in that the dielectric layer is formed to a thickness of 0.2 to 2.0 mm, and the dielectric layer can be formed by a vapor deposition method such as CVD. It is manufactured using a sintering method because it is difficult. However, it is possible to embed an electrode in a sintered body and to accurately form a thin dielectric layer on the electrode even if it is possible to use a small electrostatic chuck for a small glass substrate. However, it is difficult to produce a large electrostatic chuck that can cope with a glass substrate that is markedly low.

Similarly, the electrostatic chuck according to Patent Document 3 is manufactured by a sintering method, so that it is difficult to apply to a large glass substrate. In addition, the electrostatic chuck is heated to a maximum temperature of 350 ° C. There is a problem that distortion is generated due to a difference in thermal expansion between the material and the glass substrate, and fine and precise processing such as film formation and etching on the glass substrate is difficult.

An object of the present invention is to provide an electrostatic chuck capable of attracting and fixing an insulating large glass substrate with a sufficient attracting force at a relatively low temperature.

An object of the present invention described above is an electrostatic chuck for adsorbing and fixing a glass substrate, which is formed by thermal spraying on an insulator layer made of an oxide ceramic formed on a base material by thermal spraying. An electrostatic chuck comprising: a bipolar comb-teeth electrode; and a dielectric layer mainly composed of an oxide-based ceramic formed by spraying so as to cover the bipolar comb-teeth electrode Can be achieved.

The present invention does not use a sintered dielectric layer as in the prior art, but an insulator layer, a comb electrode, and a dielectric layer are formed by thermal spraying. As a result, the bonds of each layer are strengthened by the anchor effect, and the adhesion can be improved. Therefore, when the thermal spray structure as in the present invention is applied, it is possible to manufacture an electrostatic chuck having comb-tooth electrodes that can adsorb a large glass substrate in a relatively low temperature range.

In the electrostatic chuck of the present invention, the comb teeth width of the bipolar comb electrode is 2.5 to 5.0 mm, the distance between the comb teeth is 2.5 to 5.0 mm, and the thickness of the dielectric layer is 100. It is -600 micrometers.

According to the present invention, the comb-teeth width of the comb-teeth electrode and the inter-comb distance are set to 2.5 to 5.0 mm, and the thickness of the dielectric layer is set to 100 to 600 μm. An insulating glass substrate can be adsorbed in a temperature range of 80 to 150 ° C., and a large electrostatic chuck can be produced by providing an electrode and a dielectric layer by a thermal spraying method on a base material.

Moreover, the electrostatic chuck of the present invention is characterized in that the glass substrate is attracted and fixed in a temperature range of 80 to 150 ° C. By setting it as the above-mentioned structure, a large sized glass substrate can be adsorb | sucked in a comparatively low temperature range compared with the past.

The present invention also includes a step of forming an insulator layer made of an oxide ceramic on a substrate by thermal spraying, and a step of forming a bipolar comb-teeth electrode by thermal spraying on the insulator layer using a masking jig. A step of forming a dielectric layer mainly composed of an oxide-based ceramic so as to cover the bipolar comb-teeth electrode, and a step of grinding the surface of the dielectric layer. An electric chuck manufacturing method is provided. By forming the insulator layer, the electrode layer, and the dielectric layer by thermal spraying, each layer is firmly bonded, so that peeling can be suppressed.

Furthermore, the present invention provides a method for adsorbing a glass substrate using the electrostatic chuck, wherein the glass substrate is heated to a temperature of 80 to 150 ° C. and adsorbed to the electrostatic chuck. Insulating even at low temperatures by forming the insulator layer, electrode and dielectric layer by thermal spraying, making the electrode comb-shaped, and optimizing the comb-teeth width, inter-comb distance and dielectric layer thickness The glass substrate can be adsorbed.

The present invention can provide an electrostatic chuck capable of uniformly adsorbing and fixing an insulating glass substrate at a relatively low temperature with a sufficient adsorbing force. In addition, since the electrodes and the dielectric layer are formed by a thermal spraying method, a large electrostatic chuck that can be applied to a large glass substrate can be manufactured.

FIG. 1 shows a plan view and an AA cross-sectional view of the electrostatic chuck according to the present invention. A comb electrode is embedded in a portion indicated by a dotted line in the plan view. FIG. 2 is a schematic plan view showing the configuration of the comb electrode of the present invention.
As schematically shown in FIGS. 1 and 2, the electrostatic chuck 10 of the present invention includes a base material 1 and an insulator layer 2 made of oxide ceramics formed on the base material 1 by thermal spraying. A bipolar comb-teeth electrode 3 formed by thermal spraying on the insulator layer 2, and a dielectric layer 4 mainly composed of an oxide-based ceramic formed by thermal spraying so as to cover the bipolar comb-teeth electrode 3. It has. In FIG. 2, W is a comb tooth width of the comb electrode, and L is a distance between comb teeth. As shown in FIG. 2, the inter-comb distance is the distance between the comb teeth of one of the bipolar electrodes and the comb teeth of the other electrode.

The inventors of the present invention have found that the bipolar electrode, which has been in the form of two flat plates so far, shows a slight adsorption force even if it is an insulating glass substrate when it is changed to a comb shape. However, since it was not practical, the present invention was discovered as a result of detailed investigation of the temperature conditions, the comb shape, and the dielectric layer in order to further increase the attractive force.

The reason why the attractive force is generated by changing the shape from the flat plate shape to the comb-tooth shape is considered to be that the gradient force acts on the attractive force in addition to the John Senler Beck force. In order to apply the gradient force, it is necessary to reduce the comb tooth width W and the inter-comb distance L, but it is difficult in terms of accuracy to form electrodes by the thermal spraying method. In addition, the electrostatic chuck using a sintered body has a problem that it is difficult to form a dielectric layer with high accuracy. The present invention solves such problems all at once, and provides an electrostatic chuck in which a gradient force acts effectively while having a comb tooth width W and an inter-comb distance L capable of forming electrodes by thermal spraying. Is.

The reason why the comb tooth width W and the inter-comb distance L are in the range of 2.5 to 5.0 mm is that if the comb tooth width W and the inter-comb distance L are within the above ranges, the thermal spray method is used. Electrodes can be formed with high accuracy, variation in comb tooth width and inter-comb distance can be reduced, and adsorption force can be made uniform. In particular, if the inter-comb distance L is made small, it is not preferable because the discharge tends to occur where the inter-comb distance is small due to poor spraying accuracy. Conversely, when the comb tooth width W and the inter-comb distance L are larger than 5.0 mm, it is not preferable because a desired adsorption force cannot be obtained. This is because the gradient force does not contribute to the adsorption force when it exceeds 5.0 mm. In the present invention, since the inter-comb distance L is formed large, it is difficult for electric discharge to occur even in a low vacuum (for example, about 0.05 MPa) or in the atmosphere, and an electrostatic attraction force can be applied even if the vacuum is not high. Therefore, the glass substrate can be adsorbed with higher accuracy. In addition, since the voltage can be applied even in the atmosphere, it is easy to evaluate the adsorption force and the leakage current. The width of the connecting shaft that connects the comb teeth is not particularly limited, but it is desirable that the width of the connecting shaft is equal to the width of the comb teeth in consideration of the discharge and adsorption force near the connecting shaft. It is also desirable that the distance between and is equal to the distance between the comb teeth.

The application temperature of the electrostatic chuck of the present invention is 80 to 150 ° C. When heated to a high temperature, the volume resistivity of the insulating glass substrate is reduced, and the electrostatic adsorption force can be increased, but problems are likely to occur. Specifically, the fixing accuracy may be reduced due to a difference in thermal expansion between the glass substrate and the electrostatic chuck, which may affect the film forming process on the glass substrate. In addition, the dielectric layer of the electrostatic chuck may be subjected to a sealing treatment using a sealing agent such as a resin on thermal sprayed ceramics mainly composed of oxide ceramics. The components of the sealing agent volatilize at high temperatures. There is a risk that the glass substrate may be contaminated by oozing out. Therefore, the application temperature of the electrostatic chuck is desirably a low temperature of 150 ° C. or lower, and more desirably a temperature lower than 120 ° C. If the electrostatic chuck of the present invention is used, a glass substrate having an insulating property (volume resistivity 2.2 × 10 ¹⁵ Ω · cm at 23 ° C.) at a low temperature of 80 to 150 ° C. can be obtained without sufficient heating without heating to a high temperature. Can be adsorbed. The glass substrate can be heated through the electrostatic chuck by a method in which a fluid having a predetermined temperature is allowed to flow by providing a tunnel-like fluid path in the base material or an electrostatic chuck is placed on the heater. A heater electrode may be provided inside the electrostatic chuck.

The dielectric layer is a thermal sprayed ceramic whose main component is an oxide-based ceramic. As the oxide ceramic, Al ₂ O ₃ , alumina zirconia, spinel, mullite, or the like can be used. Among these, Al ₂ O ₃ is preferable from the viewpoint of adhesion of the sprayed film, corrosion resistance, and ease of adjusting the volume resistivity. As a material to be added to Al ₂ O ₃ , a conductive material such as TiO ₂ or SiC can be applied. The reason why such a conductive material is added is to adjust the volume resistivity and improve the adhesion of the sprayed film. From the viewpoint of adhesion of the sprayed film, TiO ₂ is preferred. A dielectric layer suitable for the application temperature of the electrostatic chuck of the present invention can be formed by adjusting the amount of TiO ₂ added to 2.5 to 20% by mass.

The thickness of the dielectric layer is 100 to 600 μm. If the thickness is less than 100 μm, the withstand voltage is lowered and dielectric breakdown is likely to occur. This is because as the dielectric layer becomes thicker, the John Senler Beck force and gradient force decrease. Therefore, the thickness of the dielectric layer is more preferably 500 μm or less. In this range, a dielectric layer made of thermal sprayed ceramics is formed, and the comb tooth width W and the inter-comb tooth distance L are in the above ranges, and the temperature condition is set to 80 to 150 ° C., so that sufficient adsorbing power is exhibited. The

As the base material of the electrostatic chuck of the present invention, ceramics, metal, or metal matrix composite material can be used, but it has thermal conductivity, thermal expansion characteristics, mechanical strength, heat resistance, and adhesion to the sprayed film. When judging comprehensively, metal matrix composite materials are preferable. In particular, since the electrostatic chuck of the present invention is used after being heated to 80 ° C. to 150 ° C., rapid heating and soaking properties are required. Therefore, a metal matrix composite material excellent in these characteristics is suitable.

As the insulator layer, various oxide ceramics such as Al ₂ O ₃ , alumina zirconia, spinel and mullite can be used. Of these, Al ₂ O ₃ is preferable in terms of corrosion resistance and insulation.

Further, the electrode material of the comb-teeth electrode can be selected according to required characteristics, and Ni, Fe, Al, Mo, W, and alloys thereof can be used.

Here, the manufacturing method of the electrostatic chuck of the present invention shown in FIG. 1 will be described in more detail. The structure of the electrostatic chuck will be described using an example in which a base material: a metal matrix composite material, an insulator layer: Al ₂ O ₃ , an electrode material: Ni, a dielectric layer; a main component Al ₂ O ₃ . First, a metal matrix composite material to be the base material 1 is prepared. Although the shape of a base material is not specifically limited, A plate | board shape is normally employ | adopted for the objective of mounting a glass substrate. Next, an Al ₂ O ₃ insulator layer 2 as a base layer is formed to a thickness of 500 μm by a thermal spraying method on the upper surface of the base 1 on which the glass substrate is placed. In order to prevent unevenness in the thickness of the insulator layer, it is desirable that the upper surface of the base material is processed in advance to have a flatness of 3.0 μm or less.

Next, a bipolar comb electrode 3 is formed on the Al ₂ O ₃ insulator layer 2 by a thermal spraying method. A masking jig having a desired comb-shaped opening is placed on the Al ₂ O ₃ insulator layer 2 and then Ni is sprayed. Here, the thickness of the comb electrode 3 is preferably about 30 to 40 μm. By forming the electrode layer by thermal spraying, it is possible to improve the adhesion between the Al ₂ O ₃ insulator layer 2 serving as a base layer and the dielectric layer 4 mainly composed of Al ₂ O ₃ described later. This is because the comb electrode 3, the Al ₂ O ₃ insulator layer 2 and the dielectric layer 4 mainly composed of Al ₂ O ₃ are all formed by thermal spraying. This is because an anchor effect is exhibited when the sprayed layer enters. That is, a part of the comb electrodes when spraying comb electrodes in pores present in the Al ₂ O ₃ insulator layer enters present in Al ₂ O ₃ insulator layer and comb electrodes when spraying dielectric layer pore When a part of the dielectric layer enters, the bonding between the layers is strengthened and the adhesion is improved.

After the comb electrode 3 is formed by thermal spraying, the dielectric layer 4 mainly composed of Al ₂ O ₃ is sprayed. The dielectric layer 4 may be formed so as to cover the comb-teeth electrode 3, and the Al ₂ O ₃ insulator layer 2 may also be coated as the comb-teeth electrode 3 is coated. Therefore, a structure in which the dielectric layer 4 is formed so as to cover the bipolar comb-tooth electrode 3 and the Al ₂ O ₃ insulator layer 2 as in the electrostatic chuck shown in FIG. 1 can be adopted. Moreover, it is also possible to have a structure in which a part of the comb electrode is exposed for connection with a power source, like the electrostatic chuck shown in FIG.

Here, the dielectric layer mainly composed of Al ₂ O _{3 serving} as the surface of the electrostatic chuck may be sealed by a known method. As the treatment material to be filled in the sealing treatment, colloidal slurry such as silica sol, alumina sol, magnesia sol, or metal alkoxide polymer such as SiO ₂ , Al ₂ O ₃ , TiO ₂ , and these polymers Those containing various resins such as melamine, acrylic, phenol, fluorine, silicon, and acrylic resin can be used.

Next, the surface of the electrostatic chuck is ground and lapped so as to have a desired surface roughness (Ra: about 0.1 to 2.0 μm).
As for the connection between the external power supply 5 and the comb electrode 3, the terminal 6 may be connected to a base material having a hole for terminal connection as in the example of FIG. 1, or the comb electrode as shown in FIG. A part of 3 may be exposed and connected to that part. When inserting the terminal into the hole of the base material, if the base material is conductive, there is a possibility of short-circuiting. For the insulating tube 7, other forms, for example, an insulating filler or a method of forming a gap without anything can be employed. In the cross-sectional view of FIG. 3, only one of the bipolar electrodes is connected to the power source, but it goes without saying that the other electrode of the bipolar electrode is connected to the power source.

Hereinafter, the present invention will be described in more detail using test examples.
(1) A metal matrix composite material (dimensions: 209 × 157 mm, thickness 40 mm, SiC 70 mass%, Al alloy pressure penetration product) was used as a base material for producing an electrostatic chuck. First, the surface of the metal matrix composite material was blasted. Next, an Al ₂ O ₃ insulator layer having a thickness of 500 μm was formed on the upper surface of the substrate by a thermal spraying method. Thereafter, a masking jig having comb-shaped openings was placed on the Al ₂ O ₃ insulator layer, and then a 40 μm thick Ni electrode was sprayed. The shape of the comb-teeth electrode was adjusted by changing the opening of the masking jig to adjust the comb-teeth width W and the inter-comb distance L (see Table 1). The width of the connecting shaft connecting the comb teeth was fixed at 3 mm, and the distance between one of the bipolar connecting shafts and the tip of the other comb tooth was the same as the distance between the comb teeth. The range of the comb electrode formation is such that the width corresponding to D in FIG. 2 schematically showing the comb electrode is 150 mm, and C is approximately 180 mm although there is a slight difference depending on the comb tooth width and the inter-comb distance. And the width.
Next, a dielectric layer (Al ₂ O ₃ containing 5% by mass of TiO ₂ ) was formed so as to cover the comb electrode and the Al ₂ O ₃ insulator layer. Thereafter, the dielectric layer was ground and lapped, and the thickness (see Table 1) and surface roughness (Ra 0.2 μm) of the dielectric layer were adjusted to produce an electrostatic chuck. As shown in FIG. 3, the connection with the electrode was made by exposing a part of the comb electrode and connecting the lead wire to the exposed portion. In addition, the glass substrate used for evaluation used the thing of the magnitude | size which does not cover an exposed part.

(2) Evaluation The electrostatic chuck obtained as described above was placed on a heater, and a □ 150 mm × 2 mm glass substrate (volume resistivity at 23 ° C. was 2.2 × on the dielectric layer of the electrostatic chuck). 10 ¹⁵ Ω · cm) was placed on the wafer, the wafer was heated to a predetermined temperature, and the attractive force of each electrostatic chuck when a voltage of ± 2000 V was applied between the comb electrodes in the atmosphere was evaluated.
The adsorption force was measured by pulling up the electrostatically adsorbed glass substrate in the vertical direction and measuring the force when the glass substrate was detached from the adsorption surface of the electrostatic chuck. The results are summarized in Table 1.

As can be seen from the results in Table 1, the comb tooth width, the inter-comb distance and the dielectric layer thickness are within the scope of the present invention. For 2 to 5 and 8 to 11, an adsorption force of 100 g / cm ² or more was obtained.
On the other hand, Nos. 1, 6, 7, and 12 which are out of the scope of the present invention did not provide sufficient adsorption force, or the adsorption force could not be evaluated due to problems. In Test Example 1 where the comb tooth width and the inter-comb distance were small, when a voltage was applied to the comb electrode, dielectric breakdown occurred, and the adsorptive power could not be evaluated. Further, in Test Example 6 where the comb tooth width and the inter-comb distance were large, sufficient adsorption force could not be obtained. In Test Example 7 in which the dielectric layer thickness was small, dielectric breakdown occurred, and in Test Example 10 in which the dielectric layer thickness was large, sufficient adsorption force was not obtained.

As described above, according to the present invention, it has been found that an electrostatic chuck capable of attracting and fixing an insulating glass substrate at a relatively low temperature with a sufficient attracting force can be obtained.

Next, an Example is shown about the electrostatic chuck for large sized glass substrates shown to FIG. 4 and FIG. FIG. 4 is an overall view showing the shape of the comb-teeth electrode of the electrostatic chuck produced in this example, and FIG. 5 is an enlarged view of one of the six electrode regions. Base material (1360 mm × 821 mm × 50 mm, metal matrix composite material: SiC 70% by mass, Al alloy pressure infiltration product), insulator layer (thickness 500 μm), 6-divided electrode (comb tooth width 3 mm, intercombination distance 3 mm, An electrode formation range of 375 mm × 312.4 mm) and a dielectric layer (thickness 500 μm, surface roughness 0.2 μm) were formed. For the connection with the electrode, a terminal insertion hole is provided in the base material so that it can be connected to a terminal connection portion (in FIG. 5, a region of 30 mm × 27 mm in FIG. 5) diagonally to the electrode region of FIG. As described above, a metal terminal (low thermal expansion alloy; Ni-resist) is inserted, and a portion corresponding to the insulating tube 7 around the metal terminal is filled with epoxy resin and fixed. An electrostatic chuck is placed on the heater, a voltage of ± 2000 V is applied between the comb electrodes, and a glass substrate (on a dielectric layer in which six divided electrodes are embedded at 115 ° C. in vacuum (0.05 MPa)). 405 mm × 342 mm × 2 mm) was adsorbed and the adsorbing power was measured, and the average was 180 g / cm ² . Furthermore, when a large glass substrate (1220 mm × 685 mm × 2 mm) was adsorbed under the same conditions, it could be adsorbed without problems.

It is the top view and AA schematic cross section of the electrostatic chuck which concern on this invention. It is a typical top view which shows the comb-tooth electrode shape of the electrostatic chuck which concerns on this invention. It is a top view and BB model sectional view showing other embodiments of the present invention. It is a top view which shows the electrode shape of the electrostatic chuck which concerns on the Example of this invention (a numerical value shows the dimension mm). It is an enlarged view which shows the electrode shape of the electrostatic chuck which concerns on the Example of this invention (a numerical value shows several-method mm).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Substrate 10; Electrostatic chuck 2; Insulator layer 3; Bipolar comb electrode 4; Dielectric layer 5; Power source 6; Electrode terminal 7; Insulation tube W;

Claims (5)

An electrostatic chuck for adsorbing and fixing a glass substrate, an insulator layer made of oxide ceramics formed by spraying on a substrate, and a bipolar comb-teeth electrode formed by spraying on the insulator layer; And a dielectric layer mainly composed of an oxide-based ceramic formed by thermal spraying so as to cover the bipolar comb-teeth electrode. The bipolar comb electrode has a comb tooth width of 2.5 to 5.0 mm, a distance between comb teeth of 2.5 to 5.0 mm, and a thickness of the dielectric layer of 100 to 600 μm. The electrostatic chuck according to claim 1. The electrostatic chuck according to claim 1 or 2, wherein the glass substrate is fixed by suction in a temperature range of 80 to 150 ° C. Forming an insulator layer made of an oxide-based ceramic on a substrate by thermal spraying;
Forming a bipolar comb-teeth electrode by thermal spraying on the insulator layer using a masking jig;
Forming a dielectric layer mainly composed of an oxide-based ceramic so as to cover the bipolar comb-teeth electrode;
The method for manufacturing an electrostatic chuck according to claim 1, further comprising a step of grinding the surface of the dielectric layer. The method for adsorbing a glass substrate using an electrostatic chuck according to claim 1, wherein the glass substrate is heated to a temperature of 80 to 150 ° C. and adsorbed to the electrostatic chuck.