Patent Publication Number: US-2023154780-A1

Title: Electrostatic chuck and processing apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an electrostatic chuck and a processing apparatus including the electrostatic chuck. 
     BACKGROUND ART 
     In a manufacturing process of a semiconductor device, an electrostatic chuck is used to hold a semiconductor wafer. As the electrostatic chuck, for example, there is known an electrostatic chuck in which a chuck electrode is provided on a metal mounting table with an insulating layer interposed therebetween, a ceramic dielectric layer is further laminated so as to cover the chuck electrode, and the surface of the dielectric layer serves as an electrostatic attraction surface for holding a semiconductor wafer. 
     The electrostatic chuck is disposed, for example, in a plasma processing apparatus such as a plasma etching; apparatus. The electrostatic attraction surface of the electrostatic chuck disposed in the plasma processing apparatus is required to have corrosion resistance against a plasma gas and a cleaning liquid. This is because the electrostatic chuck is repeatedly used. 
     For example, in the plasma etching apparatus, a cleaning step is performed for each semiconductor wafer or for each lot so as to remove a reaction product generated from a processing target material attached to the inner wall of an etching chamber. In this cleaning step, for example, plasma cleaning using halogen such as fluorine (F) or a mixed gas containing halogen is performed. At this time, the electrostatic attraction surface of the electrostatic chuck is also exposed to the plasma gas used for plasma cleaning. 
     Therefore, it has been proposed to provide a protective layer for preventing corrosion due to a plasma gas (including the plasma gas used in the cleaning step) or a cleaning liquid on the electrostatic attraction surface of the electrostatic chuck disposed in the plasma processing apparatus. As means for forming the protective layer, for example, physical vapor deposition (PVD), chemical vapor deposition (CVD), thermal spraying, coating, or the like is used Among them, the thermal spraying capable of forming a coating of ceramic (e.g., yttria) with a thickness of about several 100 μm is suitable as means for forming a protective layer having high corrosion resistance. 
     Meanwhile, the coating formed by the thermal spraying often has pores, and a post-treatment called a sealing treatment may be performed to close the pores. In the sealing treatment, an organic resin such as an epoxy resin is often used, but there is also a method of applying a coating material containing an inorganic component and then volatilizing a solvent component to fill the pores with the inorganic component (e.g., see Patent Literatures 1 and 2). 
     Here, when the sealing component filling the pores of the spray coating as the protective layer disappears, the inside of the dielectric layer is exposed to the plasma gas, which may affect the characteristics of the dielectric layer. For example, the dielectric layer adheres onto the semiconductor wafer due to cracking or wear of the dielectric layer, and as a result, the yield of the semiconductor wafer may be reduced, or the electrical characteristics of the dielectric layer itself may be impaired to cause attraction failure. 
     CITATION LIST 
     Patent Literature 
     
         
         PATENT LITERATURE 1: Japanese Laid-Open Patent Publication No. 2004-190136 
         PATENT LITERATURE 2: Japanese Laid-Open Patent Publication No. 2004-260159 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The electrostatic chuck can be classified into several types such as a Johnsen-Rahbek force type and a Coulomb force type depending on a difference in an electrostatic attraction mechanism, and depending on the type, a dielectric layer having high corrosion resistance may not be formed on the electrostatic attraction surface. 
     For example, a coating of yttria has a large volume resistivity and thus cannot be used as a dielectric layer of the Johnsen-Rahbek force type electrostatic chuck through which a small amount of current flows on the outermost surface. 
     As a method of forming a dielectric layer having high corrosion resistance on the electrostatic attraction surface of the Johnsen-Rahbek force type electrostatic chuck, a method of forming a dielectric layer by the thermal spraying using spray material with low volume resistivity and excellent corrosion resistance is considered. However, at present, a spray material capable of achieving the method has not been found. 
     As another method, a method of forming a ceramic spray coating by use of a spray material inferior in corrosion resistance but low in volume resistivity, and then performing a sealing treatment using a sealing treatment agent having high corrosion resistance is also considered. With this method, it can be expected to form a dielectric layer having high corrosion resistance without significantly changing the electrical characteristics of the electrostatic attraction surface. 
     However, as in Patent Literatures 1 and 2, when the pores of the ceramic spray coating are to be sealed with yttria by the sol-gel method, it is necessary to perform heat treatment at a high temperature (e.g., a temperature of 500° C. or higher) until an organic component disappears, so that a large crack may occur in the ceramic spray coating due to a difference in thermal expansion between the ceramic spray coating and the metallic mounting table constituting the electrostatic chuck, and the ceramic spray coating may no longer function as the dielectric layer. 
     In addition, a method of forming a ceramic spray coating by use of a spray material inferior in corrosion resistance but low in volume resistivity, and then forming a coating having corrosion resistance of about several microns by PVD or CVD so as to cover the entire surface of the ceramic spray coating instead of the sealing treatment is also considered. 
     However, also in this method, due to the heat during the processing by PVD or CVD, a crack may occur in the ceramic spray coating due to a difference in thermal expansion between the ceramic spray coating and the metal mounting table constituting the electrostatic chuck. 
     As described above, it has been difficult to form a dielectric layer having low volume resistivity and high corrosion resistance on the electrostatic attraction surface of the Johnsen-Rahbek force type electrostatic chuck, 
     [Solution to Problem] 
     The present inventors have conducted intensive studies in order to solve the above problems and have found that the use of a new sealing component makes it possible to provide a Johnsen-Rahbek force type electrostatic chuck including a layer having low volume resistivity and high corrosion resistance as a dielectric layer constituting an electrostatic attraction surface, thus completing the present invention. 
     (1) An electrostatic chuck of the present invention is a Johnsen-Rahbek force type electrostatic chuck including: a metal substrate; an electrode for electrostatic attraction provided on the metal substrate with an insulating layer interposed between the metal substrate and the electrode for electrostatic attraction; and a dielectric layer constituting an electrostatic attraction surface in contact with a workpiece. The dielectric layer includes a ceramic spray coating and a sealing component with which pores of the ceramic spray coating are filled, and the sealing component contains a metal organic salt containing a rare earth element. 
     The electrostatic chuck includes a dielectric layer containing a ceramic spray coating and a specific sealing component as the dielectric layer having the electrostatic attraction surface, and the dielectric layer is a layer having low volume resistivity and high corrosion resistance. Therefore, the electrostatic chuck is a Johnsen-Rahbek force type electrostatic chuck having excellent corrosion resistance. 
     (2) In the electrostatic chuck, it is preferable that a volume resistivity of the ceramic spray coating be 1.0×10 8  to 1.0×10 13 Ω·cm. 
     In this case, it is possible to exhibit favorable electrostatic attraction performance as the Johnsen-Rahbek force type electrostatic chuck. 
     (3) In the electrostatic chuck, it is preferable that the ceramic spray coating be made of aluminum-titanium oxide. 
     This case is particularly suitable for achieving a volume resistivity suitable for the Johnsen-Rahbek force type electrostatic chuck. 
     (4) In the electrostatic chuck, it is preferable that the rare earth element be yttrium or ytterbium. 
     These cases are particularly suitable for making the dielectric layer highly corrosion resistant. 
     (5) The processing apparatus of the present invention includes the electrostatic chuck according to any one of (1) to (4). 
     Examples of the processing apparatus include a plasma processing apparatus. At this time, the electrostatic chuck included in the plasma processing apparatus is excellent in corrosion resistance (plasma resistance). 
     Advantageous Effects of the Invention 
     According to the present invention, it is possible to provide a Johnsen-Rahbek force type electrostatic chuck, in which an electrostatic attraction surface is excellent in corrosion resistance, and a processing apparatus including the electrostatic chuck. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a longitudinal sectional view showing a schematic configuration of a plasma processing apparatus according to an embodiment of the present invention. 
         FIG.  2    is a longitudinal sectional view of an electrostatic chuck included in the plasma processing apparatus of  FIG.  1   . 
         FIG.  3    is a graph showing measurement results of Test Example 1. 
         FIG.  4 ( a )  is a view schematically showing an electrostatic chuck for evaluation produced in Test Example 2, and  FIG.  4 ( b )  is a graph showing a cumulative discharge time until cracking. 
         FIG.  5 ( a )  is an observation image of a cut surface of a region A after an exposure test, and  FIG.  5 ( b )  is a diagram showing a distribution of each component in a coating of the electrostatic chuck for evaluation. 
         FIG.  6 ( a )  and  FIG.  6 ( b )  are views each showing a distribution of fluorine in the coating of the electrostatic chuck for evaluation, in which  FIG.  6 ( a )  shows the analysis result of the region A, and  FIG.  6 ( b )  shows the analysis result of the region B. 
         FIG.  7    is a graph showing a measurement result of Fourier-transform infrared spectroscopy (FT-IR) analysis performed in Test Example 3. 
         FIG.  8    is a chromatogram obtained by gas chromatography-mass spectrometry (GC-MS) analysis performed in Test Example 3. 
         FIG.  9 ( a )  and  FIG.  9 ( b )  are mass spectra of some of detection peaks detected in the chromatogram of  FIG.  8   , and  FIG.  9 ( c )  to  FIG.  9 ( e )  are database search results. 
         FIG.  10    is a chromatogram obtained by the GC analysis performed in Test Example 3. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described hereinafter with reference to the drawings. 
     First Embodiment 
     Here, an embodiment of the present invention will be described using a plasma processing apparatus as an example. 
       FIG.  1    is a longitudinal sectional view showing a schematic configuration of a plasma processing apparatus according to the present embodiment. 
     The processing apparatus shown in  FIG.  1    is a plasma processing apparatus  10 . The plasma processing apparatus  10  can be suitably used as, for example, a plasma etching apparatus. 
     The plasma processing apparatus  10  roughly includes three portions. Specifically, the plasma processing apparatus  10  includes a plasma formation part  11 , a vacuum vessel  12 , and an exhaust system  13 . 
     The plasma formation part  11  includes a microwave source  101 , a waveguide  103 , and a solenoid coil (static magnetic field generator)  104 . The microwave source  101  is connected to the ground via a power source, and a load impedance can be adjusted by an adjacent automatic matcher  102  to automatically reduce a reflected wave. The waveguide  103  has a cross section changed from a square shape to a circular shape and transmits microwaves to a cylindrical cavity resonance part  105 . The solenoid coil  104  is disposed so as to cover the upper side and the lateral side of the vacuum vessel  12 , and the distribution of the static magnetic field can be controlled by changing a current applied to the electromagnet. 
     The vacuum vessel  12  includes a dielectric window (microwave introduction window)  111 , a shower plate  112 , a gas ring (gas introduction part)  113 , and a plasma processing chamber  110 . In the vacuum vessel  12 , a desired reactive gas with its flow rate controlled by a mass flow controller  141  and a gas supply valve  142  is introduced from the gas source  140  to between the dielectric window (microwave introduction window)  111  and the shower plate  112  via the gas ring (gas introduction part)  113 , and is supplied into the plasma processing chamber  110  via the shower plate  112 . 
     The shower plate  112  is provided with a large number of holes at positions facing a semiconductor wafer  150  electrostatically attracted to the electrostatic chuck  120  and is configured to be able to supply the processing gas from the gas source  140  into the vacuum vessel  12 . 
     The shower plate  112  is installed facing the electrostatic chuck  120  with a space therebetween. 
     The vacuum vessel  12  further includes an electrostatic chuck  120  in the lower portion in the plasma processing chamber  110 . 
     The electrostatic chuck  120  has a disk shape, can adsorb and hold a semiconductor wafer (also simply referred to as a wafer in the present specification)  150  as a workpiece by static electricity, and can control the temperature of the wafer  150 . Further, a radio frequency (RF) power source  121  is connected to a metal substrate  201  of the electrostatic chuck  120  via a matching device  122  and the electrostatic chuck  120  is configured to be able to apply RF to the wafer  150 . 
     The exhaust system  13  includes a movable valve  130  and a turbomolecular pump (TMP)  131 . The gas in the plasma processing chamber  110  is exhausted from the TMP  131 . The movable valve  130  provided in the upstream portion of the TMP controls the exhaust speed of the gas to be exhausted, thereby controlling the pressure in the plasma processing chamber  110 . 
     The structure of the electrostatic chuck  120  will be described in detail with reference to  FIG.  2   , 
       FIG.  2    is a longitudinal sectional view of an electrostatic chuck included in the plasma processing apparatus  10  of  FIG.  1   . 
     The electrostatic chuck  120  includes a metal substrate  201  made of metal, an insulating layer  202  disposed on the upper surface of the metal substrate  201 , a chuck electrode (electrode for electrostatic attraction)  205  disposed on the insulating layer  202 , and a dielectric layer  206  provided so as to cover the chuck electrode  205 . 
     The insulating layer  202  includes a heater (heater layer)  203  therein. The heater  203  is energized and heated by a heater direct current (DC) power source (not shown). 
     The dielectric layer  206  has an electrostatic attraction surface  207  in contact with a wafer  150 . The dielectric layer  206  is provided so as to cover the upper surface and the side surface of the electrostatic chuck  120  and also functions as a protective layer of the electrostatic chuck  120 . 
     Inside the electrostatic chuck  120  (metal substrate  201 ), flow paths (refrigerant grooves)  204  are disposed concentrically or spirally. A refrigerant having a temperature and a flow rate (flow velocity) adjusted by a temperature control unit (not shown) is introduced into the flow path  204 . 
     A heat transfer gas flow path (not show is provided between the dielectric layer  206  of the electrostatic chuck  120  and the back surface of the wafer  150 . The heat transfer gas flow path is formed of a groove provided on the surface of the dielectric layer  206  and a semiconductor wafer, and the groove functions as a gas flow path. A gas having a heat transfer property such as He is supplied from a heat transfer gas supply source to the heat transfer gas flow path. 
     In the electrostatic chuck  120 , a DC voltage chuck voltage) is applied to the chuck electrode  205  by using a DC power source (not shown) to generate a Johnsen-Rahbek force, and the semiconductor wafer  150  can be adsorbed and held on the electrostatic attraction surface  207  of the electrostatic chuck  120 . 
     The metal substrate  201  is made of, for example, titanium, aluminum, molybdenum, tungsten, an alloy containing at least one of these, or the like. When an aluminum metal substrate is used, for example, the surface may be subjected to alumite treatment. 
     The insulating layer  202  is made of, for example, aluminum oxide (Al 2 O 3 ) or the like. The insulating layer  202  is, for example, a spray coating formed by thermal spraying. The insulating layer  202  may be formed of one spray coating or may be formed of two or more spray coatings. 
     The dielectric layer  206  includes a ceramic spray coating and a sealing component with which pores of the ceramic spray coating are filled. The sealing component prevents moisture in the atmosphere and a reaction product generated during the etching process from entering the pores in the spray coating or microcracks generated during the surface polishing. 
     The sealing treatment for filling the pores of the ceramic spray coating with the sealing component is performed, for example, by applying a sealing agent to the surface of the ceramic spray coating, impregnating the surface with the sealing agent for a certain period of time, and then performing heat treatment to volatilize the solvent component in the sealing agent. 
     The ceramic spray coating constituting the dielectric layer  206  is, for example, a coating made of aluminum-titanium oxide. 
     It is preferable that the aluminum-titanium oxide contain 2.0 to 12.0 wt % of titanium oxide and the rest be aluminum oxide. 
     The dielectric layer  206  may be formed of one spray coating or may be formed of two or more spray coatings. 
     The thickness of the insulating layer  202  is, for example, about 200 to 500 μm. 
     The thickness of the dielectric layer  206  is, for example, about 100 to 500 μm. 
     The volume resistivity of the ceramic spray coating constituting the dielectric layer  206  is preferably 1.0×10 8  to 1.0×10 13 Ω·cm. 
     This range is a volume resistivity suitable for electrostatically attracting the workpiece by the Johnsen-Rahbek force. 
     When the volume resistivity is less than 1.0×10 8 Ω·cm, the amount of current flowing through the dielectric layer  206  becomes excessively large, and the electrostatic attraction performance by the Johnsen-Rahbek force is hardly exhibited. When the volume resistivity exceeds 1.0×10 13 Ω·cm, the amount of current flowing through the dielectric layer  206  becomes excessively small, and the electrostatic attraction performance by the Johnsen-Rahbek force is hardly exhibited. 
     The ceramic spray coating containing 2.0 to 12.0 wt % of titanium oxide and the rest being aluminum oxide has a volume resistivity of 1.0×10 8 Ω·cm to 1.0×10 11 Ω·cm and is thus suitable as the dielectric layer  206  of the Johnsen-Rahbek force type electrostatic chuck. 
     The sealing component contains a metal organic salt containing a rare earth element. The sealing component is preferably a solidified material containing the metal organic salt and a resin. In this case, the resin serves as a binder for holding the metal organic salt. 
     Such a solidified material is excellent in environment isolation property and prevents a cleaning liquid and a corrosive gas from entering the inside of the ceramic spray coating. The solidified material contains a metal organic salt containing a rare earth element, and the rare earth element is oxidized by the influence of oxygen plasma or the like at the time of using the plasma processing apparatus to form a rare earth oxide (yttria or the like). Therefore, a deterioration due to plasma hardly occurs, and a favorable sealed state can be maintained for a long period of time. As a result, the corrosion of the chuck electrode  205 , the metal substrate  201 , and the like is prevented, and corrosion resistance is excellent. 
     The sealing treatment for filling the pores of the ceramic spray coating with the solidified material can be performed at a low temperature of 200° C. or lower. 
     Therefore, it is possible to avoid the occurrence of cracking or the like in the ceramic spray coating due to a difference in thermal expansion between the metal substrate  201  and the ceramic spray coating when the sealing treatment is performed. 
     Furthermore, since the solidified material has little influence on the volume resistivity of the ceramic spray coating, it is possible to maintain electrical characteristics suitable for electrostatically attracting the workpiece by the Johnsen-Rahbek force of the ceramic spray coating. 
     In the metal organic salt containing a rare earth element, yttrium or ytterbium is preferable as the rare earth element. This is because these oxides have high corrosion resistance (plasma resistance). 
     Examples of the metal organic salt containing a rare earth element include salts of a carboxyl group-containing compound and a rare earth element-containing compound. Specific examples thereof include yttrium 2-ethylhexanoate, yttrium caprylate, yttrium decanoate, yttrium stearate, and yttrium naphthenate. 
     As described above, the sealing component is preferably a solidified material containing a resin from the viewpoint of improving the environment isolation property and corrosion resistance of the dielectric layer  206 . 
     The resin may be either a natural resin or a synthetic resin. The natural resin is preferably a terpenoid. Among them, rosin mainly composed of a diterpene-based carboxylic acid, such as abietic acid or pimaric acid, is preferable. The reason for this is that the hydroxyl group contained in the diterpene-based carboxylic acid has high affinity with the oxide ceramic, so that the adhesion between the ceramic spray coating and the sealing component is improved to make the environment isolation property excellent. 
     The content of the metal organic salt containing a rare earth element in the sealing component is preferably 20 wt % or more. When the content of the metal organic salt is less than 20 wt %, a rare earth oxide may not be sufficiently formed. The content of the metal organic salt is more preferably 40 wt % or more from the viewpoint of further excellent corrosion resistance. 
     The content of the resin in the sealing component is preferably 10 wt or more, and when the content is less than 10 wt %, the sealing may not be sufficient. The content is more preferably 40 wt % or more, and an excellent environment isolation property can be obtained. 
     The dielectric layer  206  having such a configuration can be formed, for example, by the following method. 
     (1) A spray material such as aluminum-titanium oxide is sprayed on the insulating layer  202  so as to cover the chuck electrode  205  to form a ceramic spray coating made of a metal oxide and having pores. 
     At this time, the spraying method is not particularly limited, and for example, plasma spraying, flame spraying, or the like cats be adopted. 
     (2) Separately from the step (1), a metal organic salt containing the rare earth element is prepared, diluted with a resin oil, and further added with an organic solvent to adjust the concentration so as to have an appropriate viscosity. 
     Here, examples of the organic solvent include acetic acid esters. 
     Examples of the Resin Oil Include Turpentine Oil 
     (3) The solution prepared in the step (2) is applied to the ceramic spray coating formed in the step (1), and the solution is allowed to permeate the pores of the ceramic spray coating. 
     (4) Thereafter, for example, a heat treatment is performed at a heating temperature of 120 to 200° C. to volatilize a part or the whole of the organic solvent, thereby baking and solidifying the sealing agent. 
     Through the steps as thus described, the pores of the ceramic spray coating are filled with a sealing component formed of a solidified material in which a metal organic salt containing a rare earth element and a resin containing rosin are mixed, and the dielectric layer  206  containing the ceramic spray coating and the sealing component can be formed. 
     Next, a processing method using the plasma processing apparatus  10  will be described. 
     First, the semiconductor wafer  150  is loaded into the vacuum vessel  12  from a loading port (not shown), placed on the electrostatic chuck  120 , and the loading port is closed. Next, the gas in the plasma processing chamber  110  is exhausted by the TMP  131  while the exhaust speed is adjusted by the movable valve  130 . 
     Thereafter, a DC voltage is applied from a DC power source (not shown) to the chuck electrode  205  to electrostatically attract the semiconductor wafer  150  to the electrostatic attraction surface  207  of the dielectric layer  206 , and the processing gas is supplied from the gas source  140  into the plasma processing chamber  110  via the mass flow controller  141  and the gas supply valve  142 . 
     An electric field oscillated by the microwave source  101  and introduced into the processing chamber  110  via the waveguide  103 , the dielectric window  111 , and the shower plate  112  generates an interaction with a magnetic field formed by the magnetic field generation coil  104 , dissociates the processing gas supplied into the processing chamber  110 , and generates plasma in the processing chamber  110 . The etching processing is performed on the semiconductor wafer  150  adsorbed on the electrostatic chuck  120  by the plasma of the processing gas thus formed. 
     At this time, the temperature of the semiconductor water  150  is controlled to a predetermined temperature by using the heater layer  203 , the flow path  204 , and the like included in the electrostatic chuck  120 . 
     OTHER EMBODIMENTS 
     In the first embodiment, the insulating layer  202  is an insulating layer made of ceramics formed by thermal spraying, but in the electrostatic chuck according to the embodiment of the present invention, the insulating layer may be formed by molding a sintered body. In this case, the insulating layer is fixed to the upper surface of the metal substrate with an adhesive layer, made of an epoxy resin-based adhesive, a silicone resin-based adhesive, or the like, interposed therebetween. 
     In the electrostatic chuck according to the embodiment of the present invention, the heater layer and the flow path (refrigerant groove) are not essential but may be provided as necessary. 
     The plasma method applicable to the plasma processing apparatus according to the embodiment of the present invention is not limited to the microwave electron cyclotron resonance (ECR) plasma method, and other plasma methods such as a capacitively-coupled plasma method and an inductively-coupled plasma method can also be applied. 
     The processing apparatus according to the embodiment of the present invention is not limited to the plasma etching apparatus but may be another processing apparatus such as an ashing apparatus or a film forming apparatus. 
     In the embodiment of the present invention, the workpiece is not limited to the semiconductor wafer but may be, for example, a glass substrate for LCD or the like. 
     [Evaluation Test] 
     In the electrostatic chuck according to the embodiment of the present invention, the electrostatic attraction surface has excellent corrosion resistance. In order to show this, the following evaluation test was performed. 
     Test Example 1 
     in the present test example, test pieces subjected to various thermal spraying and sealing treatments were formed and subjected to a test of exposure to a plasma etching atmosphere (hereinafter, also referred to as an exposure test). In the present test example, a change in strain amount until cracking occurs due to bending deformation of the test piece was evaluated. 
     (1) Test Substrate 
     Titanium (TP340) was used as a test substrate, and a plurality of substrate pieces having dimensions of 16 mm wide×100 mm long×4 mm thick were prepared from this substrate. 
     (2) Formation of Spray Coating and Sealing Treatment 
     On one surface of each substrate piece, alumina-10 wt % titania powder was sprayed using atmospheric plasma spraying to form a ceramic spray coating having a thickness of 0.3 mm. Next, the various sealing treatments were performed on the ceramic spray coating. The sealing treatment was performed by the following two methods (sealing treatments A and B). 
     Sealing treatment A: A mixed solution containing 55 wt % of turpentine oil, 15 wt % of yttrium 2-ethylhexanoate, and 30 wt % of acetic acid ester was applied and impregnated on the surface of the ceramic spray coating and was fired at 150° C. for two hours. In this way, a test piece (No. 1) was prepared in which the pores of the ceramic spray coating were filled with a sealing component containing yttrium 2-ethylhexanoate and a resin. 
     Sealing treatment B: A mixed solution containing 10 wt % of monomethyl triisocyanate silane and 90 wt % of acetic acid ester was applied and impregnated on the surface of the ceramic spray coating and was fired at 70° C. for six hours. In this way, a test piece (No. 2) was prepared in which the inside of pores of the ceramic spray coating were sealed with the silicone resin. 
     In addition, a test piece (No. 3) having a ceramic spray coating formed thereon and not subjected to the sealing treatment was also prepared. 
     (3) Test Method and Conditions Thereof 
     In order to investigate a change in strain amount until the test piece was cracked before and after being exposed to the plasma etching atmosphere, the test piece (No. 1 to No, 3) was exposed to the plasma etching atmosphere for 200 hours under the following conditions. 
     &lt;Plasma etching conditions&gt; 
     Ar gas flow rate: 60 ml/min 
     NF 3  gas flow rate: 750 ml/min 
     Pressure: 40 Pa 
     Discharge output: 1000 W 
     Next, a strain gauge was bonded to the sprayed surface of each test piece before and after the exposure test, bending deformation was applied at 90°, and the strain amount at the time of occurrence of cracking was measured. 
     (4) Test Results 
     The test results are shown in  FIG.  3   .  FIG.  3    is a graph showing measurement results of Test Example 1. Each numerical value in the table of  FIG.  3    represents a relative value based on the strain amount before exposure of the test piece (No. 2). 
     In the test piece (No. 2) and the test piece (No. 3), the strain amount until cracking was significantly reduced after exposure to the plasma etching atmosphere. 
     On the other hand, in the test piece (No. 1), a change in strain amount until cracking was hardly observed after exposure to the plasma etching atmosphere. 
     Therefore, it has been confirmed that the ceramic spray coating in which the pores are filled with the sealing component containing yttrium 2-ethylhexanoate and the resin is suitable for preventing cracking as compared to other specifications. 
     Test Example 2 
     In the present test example, after various thermal spraying and sealing treatments were performed to form an electrostatic chuck for evaluation having the configuration shown in  FIG.  2   , an exposure test was performed in which the electrostatic chuck for evaluation was exposed to a plasma etching atmosphere, and (a) a cumulative discharge time until cracking occurred in the spray coating, (b) a cross-sectional X-ray photoelectron spectroscopy (XPS) analysis after the exposure test, and (c) an electron probe microanalysis (EPMA) after the exposure test were performed. 
     (1) Test Substrate 
     In the present Test Example, the test substrate was titanium (TP340). 
     (2) Formation of Spray Coating and Sealing Treatment 
     In the present test example, an alumina powder was sprayed as a first insulating layer on the substrate piece by using atmospheric plasma spraying to form a ceramic spray coating. 
     Then, as a heater layer, tungsten powder was sprayed on the first insulating layer by using atmospheric plasma spraying to form a tungsten spray coating. 
     Next, as a second insulating layer, alumina powder was sprayed on the heater layer and the first insulating layer by using atmospheric plasma spraying to form a ceramic spray coating. 
     Subsequently, as a chuck electrode layer, tungsten powder was sprayed on the second insulating layer by using atmospheric plasma spraying to form a tungsten spray coating. 
     Next, as a dielectric layer, alumina-10 wt % titania powder was sprayed using atmospheric plasma spraying to form a ceramic spray coating. 
     Then, various sealing treatments performed in Test Example 1 were applied to the dielectric layer for each region. 
     Through such processing, an electrostatic chuck  220  for evaluation (cf.  FIG.  4 ( a ) ) was manufactured. 
     The electrostatic chuck  220  for evaluation has a region A in which the electrostatic attraction surface of the dielectric layer was subjected to the same sealing treatment as that of the test piece (No. 1) of Test Example 1, and a region B in which the electrostatic attraction surface of the dielectric layer was subjected to the same sealing treatment as that of the test piece (No. 2) of Test Example 1. 
     (3) Methods of Exposure Test 
     The electrostatic chuck  220  for evaluation was exposed to a plasma etching atmosphere under the following conditions. The heater layer of the electrostatic chuck  220  for evaluation was connected to a heater DC power source (not shown) and was repeatedly energized. 
     &lt;Plasma etching conditions&gt; 
     Ar gas flow rate: 60 ml/min 
     NF 3  gas flow rate: 750 ml/min 
     Pressure: 40 Pa 
     Discharge output: 1000 W 
     Heater output: 1200 W 
     (a) Cumulative Discharge Time to Cracking 
     The measurement result of the cumulative discharge time is shown in  FIG.  4   . 
       FIG.  4 ( a )  is a view schematically showing the electrostatic chuck  220  for evaluation prepared in Test Example 2, and  FIG.  4 ( b )  is a graph showing the cumulative discharge time until cracking measured in Test Example 2. 
     As shown in  FIG.  4 ( b ) , cracking did not occur in the region A even after discharging for 1000 hours, but cracking occurred in the region B after discharging for 180 hours. 
     (b) Cross-Sectional XPS Analysis Result 
     A part of the electrostatic chuck for evaluation after the exposure test was cut, and the cross section XPS analysis of the ceramic spray coating portion was performed. The results are shown in  FIG.  5   . 
       FIG.  5 ( a )  is an observation image of the cut surface of the region A after the exposure test, and  FIG.  5 ( b )  is a diagram showing the distribution of each component in the coating of the electrostatic chuck for evaluation measured in Test Example 2. 
     As the XPS analyzer, Quantera SXM manufactured by ULVAC-PHI, Inc. was used. 
     As shown in  FIG.  5   , it was confirmed that the amount of fluorine in the region A was smaller than that in the region B. 
     (c) Cross-Sectional EPMA Analysis Result 
     A part of the electrostatic chuck for evaluation after the exposure test was cut, and cross-section EPMA analysis near the surface of the ceramic spray coating was performed. The results are shown in  FIG.  6   . 
       FIG.  6 ( a )  and  FIG.  6 ( b )  are diagrams showing the distribution of fluorine in the coating of the electrostatic chuck for evaluation measured in Test Example 2, in which  FIG.  6 ( a )  shows the analysis result of the region A, and  FIG.  6 ( b )  shows the analysis result of the region B.  FIG.  6 ( a )  and  FIG.  6 ( b )  are views in which color display is performed. 
     As an EPMA analyzer, JXA-8500 F manufactured by JEOL Ltd. was used. 
     As shown in  FIG.  6   , it was confirmed that the amount of fluorine in the region A was smaller than that in the region B and that the permeation range front the surface was also narrow. 
     Test Example 3 
     In Test Example 3, the sealing component contained in the spray coating of the test piece (No. 1) prepared in Test Example 1 was analyzed. 
     First, the same sealing agent as used in Test Example 1 was placed in a crucible, fired at 150° C. for two hours, and solidified. 
     Next, the obtained solidified material was subjected to FT-IR analysis. 
     For FT-IR analysis. Fourier transform type infrared spectrometer 3100 manufactured by Agilent Technologies, Inc. was used. 
       FIG.  7    is an IR spectrum obtained by FT-IR analysis. 
     This FT-IR analysis confirmed that the solidified material contained yttrium 2-ethylhexanoate. 
     Next, the solidified material obtained by firing at 150° C. for two hours was subjected to GC-MS analysis. 
     For GC-MS analysis, a gas chromatography mass spectrometer 5977A MSD manufactured by Agilent Technologies, Inc. was used. As a derivatization treatment, the solidified material was dissolved in a 5 wt % hydrochloric acid methanol solution by hermetic heating at 80° C. (holding for 18.5 hours) to perform methyl esterification. 
       FIG.  8    is a chromatogram obtained by GC-MS analysis. 
       FIG.  9 ( a )  and  FIG.  9 ( h )  are mass spectra of some (peak 3 and peak 4) of detection peaks detected in the chromatogram of  FIG.  8   , and  FIG.  9 ( c )  to  FIG.  9 ( e )  are database search results. 
     In this GC-MS analysis, it was confirmed that the solidified material contained ethylhexanoic acid and an abietic acid-related compound derived from turpentine oil. 
     Further, the sample (solidified material) was subjected to GC analysis by GC2010 manufactured by Shimadzu Corporation. 
     Here, as a column, DB-17 manufactured by Agilent Technologies was used. As a derivatization treatment, the solidified material was dissolved in a 5 wt % hydrochloric acid methanol solution by hermetic heating at 80° C. (holding for 18.5 hours) to perform methyl esterification. 
       FIG.  10    is a chromatogram obtained by GC analysis. 
     In this GC analysis, it was confirmed that the solidified material contained 41 wt % of 2-ethylhexanoic acid. 
     Next, the solidified material was subjected to inductively coupled plasma (ICP) analysis. 
     For ICP analysis, ICP AES 5110 VDV type manufactured by Agilent Technologies was used. 
     As a result, Y was detected in an amount of 13 wt %. 
     From the above, it was confirmed that the component of the solidified material was about 54 wt % of yttrium 2-ethylhexanoate and that the rest was a rosin substance mainly composed of an abietic acid-related compound. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  plasma pro processing apparatus 
               11  plasma formation part 
               12  vacuum vessel 
               13  exhaust system 
               101  microwave source 
               102  automatic matcher 
               103  waveguide 
               104  solenoid coil 
               110  plasma processing chamber 
               111  dielectric window 
               112  shower plate 
               113  gas ring (gas introduction part) 
               120  electrostatic chuck 
               121  RF power source 
               122  matching device 
               130  movable valve 
               131  TMP 
               140  gas source 
               141  mass flow controller 
               142  gas supply valve 
               150  (semiconductor) wafer 
               201  metal substrate 
               202  insulating layer 
               203  heater (heater layer 
               204  flow path (refrigerant groove) 
               205  chuck electrode 
               206  dielectric layer 
               207  electrostatic attraction surface 
               220  electrostatic chuck for evaluation