Covering structure and retention device

Abstract

To suppress the reduction of voltage resistance due to the occurence of cracks in a coated structure obtained by coating a base material with a spray coating.SOLUTION: A coated structure coated with a spray coating includes: a base material including metal; the spray coating for coating at least a part of the base material; and a barrier layer provided between the base material and the spray coating and formed more dense than the spray coating. The spray coating has a first surface facing a barrier layer and a second surface served as a surface on the opposite side of the first surface; and in a part including at least the second surface of the spray coating, the metal constituting the base material does not substantially include a compound formed to bond with hydroxide ions in a fine pore existing in the spray coating.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a covering structure and a retaining device including the covering structure. [Background technology]

[0002] Conventionally, in devices such as semiconductor manufacturing devices that are used under high power in a plasma environment, a configuration using a coated structure in which a metal-containing substrate is coated with a thermal sprayed film has been known. For example, Patent Documents 1 and 2 disclose a configuration in which a member in which a substrate is coated with a thermal sprayed film is used as a component of an electrostatic chuck or the like. Such a configuration can increase the voltage resistance of devices such as electrostatic chucks, i.e., can reduce the possibility of dielectric breakdown in the component due to the application of relatively high power in a plasma environment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-90074 [Patent Document 2] Japanese Patent Application Publication No. 2019-127598 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even when using a coated structure in which a substrate is coated with a thermal sprayed film, there has been a problem in some cases in that cracks occur in the thermal sprayed film during the manufacturing process of a device including such a coated structure, as a result of carrying out various steps in which the coated structure is exposed to an environment in contact with an electrolyte solution or the like, an acidic environment, an alkaline environment, etc. If cracks occur in the thermal sprayed film, there is a possibility that the voltage resistance of the coated structure will decrease. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms. (1) According to one aspect of the present disclosure, there is provided a coated structure coated with a thermal sprayed film. The coated structure includes a substrate containing a metal, the thermal sprayed film covering at least a portion of the substrate, and a barrier layer disposed between the substrate and the thermal sprayed film and formed more densely than the thermal sprayed film, the thermal sprayed film having a first surface facing the barrier layer and a second surface opposite the first surface, and the thermal sprayed film is characterized in that a portion of the thermal sprayed film including at least the second surface does not substantially contain compounds formed by bonding of the metal constituting the substrate with hydroxide ions within pores of the thermal sprayed film. In this coated structure, the barrier layer and the thermal sprayed film are formed in this order on the substrate, so that the barrier layer suppresses oxidation that progresses on the surface of the substrate facing the thermal sprayed film. In this case, the portion of the thermal sprayed film that includes at least the second surface is substantially free of compounds formed by the metal constituting the substrate bonding with hydroxide ions within the pores of the thermal sprayed film, ensuring the flexibility of the thermal sprayed film. Therefore, even when the coated structure thermally expands and contracts, the thermal sprayed film can effectively follow the expansion and contraction of the substrate, suppressing the occurrence of cracks in the thermal sprayed film. (2) In the coated structure of the above embodiment, the barrier layer may be an oxide film. With this configuration, the barrier layer is formed of an oxide film that is stable even in an oxidizing atmosphere, thereby enhancing the effect of the barrier layer in suppressing oxidation of the substrate. (3) In the coated structure of the above embodiment, the barrier layer may be made of an oxide of the metal contained in the substrate. With such a configuration, the adhesion between the barrier layer and the substrate can be improved. In addition, the difference in the thermal expansion coefficient and thermal contraction coefficient between the barrier layer and the substrate can be reduced, suppressing the stress generated between the barrier layer and the substrate, and improving the cladding strength of the thermal sprayed film. This can improve the effect of suppressing the occurrence of cracks. (4) In the coated structure of the above aspect, the barrier layer may include an anodized coating. With this configuration, the barrier layer can be easily formed by anodizing the substrate. (5) In the coated structure of the above embodiment, the thermal sprayed film may include a first layer including the first surface of the thermal sprayed film and a second layer including the second surface, and the second layer may be formed to have a higher porosity than the first layer. With this configuration, the flexibility, adhesion, and voltage resistance of the thermal sprayed film can be improved in a balanced manner. That is, the adhesion between the first layer and the barrier layer can be improved, and the voltage resistance can be improved. Furthermore, the flexibility of the thermal sprayed film can be ensured in the second layer, suppressing cracking and improving the voltage resistance. (6) In the coated structure of the above embodiment, the second layer may be configured so that the pores of the second layer are substantially free of the compound. With this configuration, the flexibility of the thermal sprayed film can be increased. (7) In the coated structure of the above embodiment, the substrate may contain aluminum as the metal, and the compound may contain at least one of aluminum hydroxide (Al(OH)3) and boehmite (AlOOH). With this configuration, it is possible to prevent a decrease in flexibility of the sprayed film caused by at least one of aluminum hydroxide (Al(OH)3) and boehmite (AlOOH) blocking pores in the sprayed film, and to suppress the occurrence of cracks in the sprayed film. The present disclosure can be realized in various forms other than those described above, for example, a holding device equipped with a coating structure, a method for manufacturing a coating structure, a semiconductor manufacturing device including a holding device, a method for manufacturing a holding device, etc. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a perspective view showing a schematic appearance of an electrostatic chuck. [Figure 2] FIG. 1 is a cross-sectional view schematically illustrating a configuration of an electrostatic chuck. [Figure 3]FIG. 2 is a cross-sectional view schematically illustrating the covering structure of the first embodiment. [Figure 4] FIG. 10 is a cross-sectional view schematically illustrating the state of a covering structure of a comparative example. [Figure 5] FIG. 10 is a diagram showing the results of observing the surface of a thermal sprayed film after treatment with an electrolyte solution. [Figure 6] FIG. 10 is an explanatory diagram showing a treatment using an electrolyte solution performed on the coated structure. [Figure 7] FIG. 10 is a diagram showing the appearance of cracks occurring on the surface of the sprayed film of the coated structure of the comparative example. [Figure 8] FIG. 10 shows an XRD pattern of the first surface after treatment with an electrolyte solution. [Figure 9] FIG. 10 is a cross-sectional view schematically illustrating the covering structure of the second embodiment. [Figure 10] FIG. 10 is a cross-sectional view schematically illustrating the covering structure of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] A. First embodiment: (A-1) Structure of electrostatic chuck: FIG. 1 is a perspective view showing an outline of the appearance of an electrostatic chuck 10 according to a first embodiment. FIG. 2 is a cross-sectional view showing a schematic configuration of the electrostatic chuck 10. In FIG. 1, a portion of the electrostatic chuck 10 is cut away. In addition, FIGS. 1 and 2 show mutually orthogonal X, Y, and Z axes to identify directions. The X, Y, and Z axes shown in each drawing each indicate the same direction. In this specification, the Z axis indicates the vertical direction, and the X and Y axes indicate the horizontal direction. Note that FIGS. 1 and 2 show the layout of each part only and do not accurately represent the dimensional ratios of each part.

[0008] The electrostatic chuck 10 is a device that attracts and holds an object by electrostatic attraction, and is used, for example, to fix a wafer W, which is an object, in a vacuum chamber of a semiconductor manufacturing device. The electrostatic chuck 10 includes a ceramic portion 20, a base portion 30, and a bonding portion 40. These are stacked in the order of the ceramic portion 20, the joint portion 40, and the base portion 30 in the −Z-axis direction (vertically downward). The electrostatic chuck 10 in this embodiment is also called a “holding device.”

[0009] The ceramic part 20 is a substantially circular plate-like member, and is formed mainly from ceramic (for example, aluminum oxide or aluminum nitride). In this specification, the phrase "mainly composed of" a specific component means that the content of the specific component is 50% by volume or more. The diameter of the ceramic part 20 may be, for example, about 50 mm to 500 mm, and is usually about 200 mm to 350 mm. The thickness of the ceramic part 20 may be, for example, about 1 mm to 10 mm. The ceramic part 20 is also called a "plate-like part."

[0010] As shown in FIG. 2, a chuck electrode 22 is disposed inside the ceramic portion 20. The chuck electrode 22 is formed of a conductive material such as tungsten or molybdenum. When a voltage is applied to the chuck electrode 22 from a power supply (not shown), an electrostatic force is generated, and the wafer W is attracted and fixed to the mounting surface 24 of the ceramic portion 20 by this electrostatic force. The chuck electrode 22 may be of a bipolar type or a unipolar type. In addition, a heater electrode (not shown) may be provided inside the ceramic portion 20. The heater electrode is a resistance heating element made of a conductive material (e.g., tungsten, molybdenum, etc.) and is used to heat the wafer W attracted and fixed to the mounting surface 24.

[0011] The base portion 30 is a plate-like member containing metal and formed into a substantially circular shape. The base portion 30 of this embodiment is formed using a metal containing aluminum (aluminum or an aluminum alloy). Aluminum has a relatively high thermal conductivity, is easy to process, and is low-cost. Therefore, using aluminum for the base portion 30 is desirable because it can improve the cooling efficiency of the ceramic portion 20 and the wafer W by the base portion 30 and reduce the manufacturing cost of the electrostatic chuck 10. From the viewpoint of improving the cooling efficiency of the base portion 30 while reducing the manufacturing cost, a high metal content in the base portion 30 is desirable, and the base portion 30 is preferably composed primarily of metal. For example, it is desirable for the base portion 30 to contain 90 mass% or more of highly versatile aluminum (e.g., aluminum alloys such as A6061 and A5052). However, the base portion 30 may also contain components other than metals, such as ceramic. The diameter of the base portion 30 may be, for example, approximately 220 mm to 550 mm, and is typically 220 mm to 350 mm. The thickness of the base portion 30 may be, for example, about 20 mm to 40 mm. The base portion 30 is also called a "substrate."

[0012] A plurality of coolant flow paths 32 are formed inside the base portion 30 along the XY plane. The base portion 30 is cooled by flowing a coolant such as a fluorine-based inert liquid, water, or liquid nitrogen through the coolant flow paths 32. The ceramic portion 20 is cooled by heat transfer between the base portion 30 and the ceramic portion 20 via the bonding portion 40, and the wafer W held on the mounting surface 24 of the ceramic portion 20 is cooled. This allows temperature control of the wafer W. In addition to the configuration in which the coolant flow paths 32 are formed inside the base portion 30, the base portion 30 may be provided with a cooling function by cooling the base portion 30 from the outside of the base portion 30.

[0013] As shown in FIG. 2, the surface of the base portion 30 is covered with a coating layer 61 including a sprayed film 60 and a barrier layer 62. That is, the barrier layer 62 is formed on the base portion 30, and the sprayed film 60 is formed on the barrier layer 62. In FIG. 2, the coating layer 61 is provided to cover the horizontal surface of the surface of the base portion 30 facing the ceramic portion 20 and the side surface parallel to the Z-axis direction. However, other embodiments are possible. For example, the coating layer 61 may also be provided on the back surface of the base portion 30 in the -Z-axis direction. The base portion 30 and the coating layer 61 formed on the surface of the base portion 30 are collectively referred to as a "coating structure 15." The coating layer 61 will be described in detail later.

[0014] The bonding portion 40 is disposed between the ceramic portion 20 and the covering structure 15, and bonds the ceramic portion 20 and the covering structure 15 together. The bonding portion 40 is made of an adhesive such as a silicone resin, an acrylic resin, or an epoxy resin. The bonding portion 40 may contain an inorganic filler such as ceramic powder. The thickness of the bonding portion 40 can be, for example, about 0.1 mm to 1 mm.

[0015] The electrostatic chuck 10 further includes a plurality of gas supply paths 50. The gas supply paths 50 penetrate the ceramic portion 20, the bonding portion 40, and the base portion 30 in the Z direction and open to gas discharge ports 52 formed in the mounting surface 24. An inert gas, such as helium gas, is supplied to the gas supply paths 50 from a gas supply device (not shown), and the inert gas is supplied from the gas discharge ports 52 to the space between the mounting surface 24 and the wafer W. This improves heat transfer between the ceramic portion 20 and the wafer W, further improving controllability of the temperature distribution of the wafer W. Note that the gas supply paths 50 are not essential, and the electrostatic chuck 10 may not be provided with the gas supply paths 50.

[0016] (A-2) Composition of coating layer: The following provides a detailed description of the configuration of the coating layer 61. As described above, the coating layer 61 includes the barrier layer 62 and the sprayed film 60.

[0017] The barrier layer 62 is provided between the base portion 30 and the sprayed film 60, and is formed more densely than the sprayed film 60. In this embodiment, the barrier layer 62 is formed as an oxide film, and contains an oxide of a metal contained in the base portion 30, which is the substrate, i.e., aluminum oxide. Such a barrier layer 62 can be, for example, an anodized film obtained by anodizing the member that will become the base portion 30. Alternatively, the barrier layer 62 can be an oxide film formed by treating the member that will become the base portion 30 with a solution that has an oxidizing effect (for example, by immersing it in the solution that has an oxidizing effect).

[0018] The barrier layer 62 obtained by anodization can be a porous oxide film (anodized aluminum) having fine pores perpendicular to the substrate, obtained by anodizing the base portion 30, which is the substrate, in an acidic or alkaline electrolyte solution. Alternatively, the barrier layer 62 may be a dense barrier oxide film obtained by anodizing the base portion 30 in a neutral electrolyte solution. Examples of acidic electrolytes used in anodization to form a porous oxide film (anodized aluminum) include sulfuric acid, oxalic acid, chromic acid, and phosphoric acid. Examples of alkaline electrolytes used in anodization to form a porous oxide film (anodized aluminum) include sodium hydroxide, lithium hydroxide, sodium carbonate, sodium phosphate, sodium fluoride, and ammonium hydroxide. Examples of neutral electrolytes used in anodization to form a barrier oxide film include sodium borate, ammonium tartrate, and glycolate. When the barrier layer 62 is made of a porous oxide film (anodized aluminum), it is desirable to perform a sealing treatment to close the micropores in the oxide film. The sealing treatment may be performed by a chemical method using pressurized steam or boiling water, or by an electrochemical method using electrolysis such as nickel acid treatment or chromate treatment. Alternatively, the sealing treatment may be performed using a resin.

[0019] When the barrier layer 62 is formed by a treatment using an oxidizing solution (for example, immersion in an oxidizing solution), the oxidizing solution may be any solution capable of forming an oxide film containing aluminum oxide on the surface of the aluminum-containing base portion 30. For example, various solutions can be used, such as an electrolytic solution, an alkaline solution, a neutral solution, an acidic solution, etc. Examples of the electrolytic solution include an aqueous sodium carbonate solution, tap water, or an aqueous solution of iodine. Examples of suitable solutions include solutions containing anionic surfactants (e.g., surfactant-based grinding fluid such as Noritake Cool manufactured by Noritake Co., Ltd.). Examples of alkaline solutions include aqueous solutions of aluminum hydroxide, sodium chromate, etc. Examples of neutral solutions include aqueous solutions of sodium chloride. Examples of acidic solutions include phosphoric acid, sulfuric acid, nitric acid, and hydrochloric acid. The oxide film can be formed on the base portion 30 by appropriately adjusting the concentration of the above solutions in consideration of the efficiency of forming the oxide film, ease of handling, etc.

[0020] Aluminum and aluminum alloys generally have a passive layer on their surfaces. Even if this passive layer is removed, an oxide film naturally forms. However, the thickness of such naturally formed oxide films is typically about 1 to 2 nm. By actively forming an oxide film through anodization or treatment using an oxidizing solution, as in the present embodiment, it is possible to easily form a thicker oxide film with a high barrier function. Furthermore, since such an oxide film is formed on the surface of the base portion 30 by oxidizing the metal constituting the base portion 30 through electrochemical or chemical reactions, adhesion to the base portion 30 can be easily improved.

[0021] When the barrier layer 62 is a porous oxide film (anodized aluminum) formed by anodic oxidation, the thickness of the barrier layer 62 can be, for example, about 5 to 50 μm. When the barrier layer 62 is a dense barrier oxide film formed by anodic oxidation or when it is formed by a treatment using an oxidizing solution, the thickness of the barrier layer 62 can be, for example, about 10 to 50 nm. When the barrier layer 62 is a barrier oxide film formed by anodic oxidation or when it is formed by a treatment using an oxidizing solution, a dense and thinner oxide film can be easily formed without a sealing treatment. Here, the oxide film being "dense" as described above means that no pores are observed when a cross section of the barrier layer 62 is observed at 3000x magnification using a scanning electron microscope (SEM). In particular, when the barrier layer 62 is formed by a process using a solution having an oxidizing effect, no device or the like for performing an electrochemical method is required, and the barrier layer 62 can be easily formed at low cost by a simple method, such as immersing the base portion 30 in a solution until the reaction for forming an oxide film stops.

[0022] The sprayed film 60 can be formed by, for example, plasma spraying. Materials constituting the sprayed film 60 include, for example, yttrium oxide (yttria: Y2O3), aluminum oxide (alumina: Al2O3), aluminum nitride, zirconium oxide (zirconia: ZrO2), alumina-zirconia, spinel, aluminum yttrium garnet (YAG), yttrium fluoride (YF3), and yttrium oxyfluoride (YOF). In particular, it is desirable to use yttria. The thickness of the sprayed film 60 can be, for example, 5 to 300 μm.

[0023] In this embodiment, the porosity of the sprayed film 60 formed on the barrier layer 62 can be, for example, 1.5 to 6.0%. The porosity can be calculated as area porosity. Specifically, the area porosity can be determined by taking a cross-sectional image of the sprayed film 60 at 1000 times magnification using a scanning electron microscope (SEM) and calculating the area ratio of pores in the cross-sectional image obtained by binarizing the image. In this case, by using general-purpose software such as ImageJ as image analysis software, edge detection in the image, area digitization, and area ratio calculation can be easily performed.

[0024] When forming a thermal spray coating, a base material to be treated is generally subjected to a blasting treatment to clean and roughen the surface of the base material. In this embodiment, when the barrier layer 62 is made of a porous oxide film (anodized aluminum) formed by anodization, Since porous oxide coatings (anodized aluminum) are relatively hard and brittle and are likely to be scraped off by blasting, blasting of the member that will become the base portion 30 can be performed prior to the formation of the barrier layer 62. When the barrier layer 62 is formed by treatment using a solution with an oxidizing effect, such oxide coatings are relatively soft and flexible, and can be roughened integrally with the base portion 30 by blasting, so blasting can be performed after the formation of the barrier layer 62. In such cases, a roughened state can be easily ensured on the surface of the object on which the thermal sprayed film 60 is formed, thereby improving the adhesion of the thermal sprayed film 60.

[0025] The electrostatic chuck 10 of the present embodiment configured as described above includes the coated structure 15 in which the barrier layer 62 and the thermal sprayed film 60 are formed in this order on the base portion 30, and therefore, oxidation that progresses on the surface of the base portion 30 facing the thermal sprayed film 60 can be suppressed, thereby suppressing the occurrence of cracks in the thermal sprayed film 60. As a result, the withstand voltage of the electrostatic chuck 10 can be improved.

[0026] Fig. 3 is a cross-sectional view that schematically shows the appearance of the coated structure 15 of this embodiment, and Fig. 4 is a cross-sectional view that schematically shows the appearance of a coated structure 115 as a comparative example in which the sprayed film 60 is formed directly on the base portion 30 without having a barrier layer 62. The effect of suppressing crack generation in the coated structure 15 of this embodiment will be described below with reference to Figs. 3 and 4.

[0027] In the process of manufacturing an electrostatic chuck using a coated structure in which the sprayed film 60 is formed on the base portion 30, the coated structure is exposed to various chemicals such as solutions. At this time, if the coated structure comes into contact with, for example, an electrolyte solution with a relatively low resistivity, i.e., a relatively high conductivity, the surface of the base portion 30, which is the base material, may be oxidized. This is because the sprayed film 60 has fine pores, and the electrolyte solution passes through these pores and penetrates into the base material through the sprayed film 60.

[0028] Examples of processes in which the electrolytic solution may come into contact with the sprayed film 60 and lead to cracks are a blasting process for embossing the surface of the ceramic part 20 and a cleaning process after the coated structure 15 including the base part 30 and the ceramic part 20 are joined via the joining part 40, and the electrolytic solution may penetrate into the coated structure 15 through the sprayed film 60. Furthermore, in subsequent cleaning processes and the like performed until the electrostatic chuck is completed, the penetration of the cleaning solution may also cause oxidation on the surface of the base part 30.

[0029] As shown in FIG. 3 , in the coated structure 15 of this embodiment, even if an electrolyte solution or the like penetrates through the sprayed film 60, the barrier layer 62, which is denser than the sprayed film 60, prevents the electrolyte solution or the like from further penetrating toward the base portion 30. In FIGS. 3 and 4 , the penetration of the electrolyte solution or the like is indicated by outline arrows. Furthermore, even when the barrier layer 62 formed by oxidation of the surface of the base portion 30 comes into contact with the electrolyte solution or the like that penetrates through the sprayed film 60, the oxidation does not progress any further. In contrast, in the coated structure 115 without the barrier layer 62 as shown in FIG. 4 , the electrolyte solution or the like that penetrates through the sprayed film 60 causes oxidation of the metal that constitutes the base portion 30 at the interface 63, which is the surface of the base portion 30 facing the sprayed film 60. As a result, substances generated by the oxidation reaction are generated at the interface 63. The substances generated at the interface 63 then penetrate into the pores of the sprayed film 60.

[0030] 5 shows the results of observing the state of the surface of the sprayed film 60 facing the base portion 30 after the coated structure 115 was treated using the electrolyte solution described above and then peeled off from the base portion 30. FIG. 5(A) shows the state before treatment using the electrolyte solution, FIG. 5(B) shows the state one hour after the start of treatment using the electrolyte solution, and FIG. 5(C) shows the state two hours after the start of treatment using the electrolyte solution. are images observed at 3000 times magnification using a scanning electron microscope (SEM).

[0031] FIG. 6 is an explanatory diagram showing the state of treatment using an electrolyte solution performed on the coated structure 115 shown in FIG. 5. The treatment shown in FIG. 6 is a treatment in which electrolytic corrosion is actively performed on the coated structure 115. Here, the coated structure 115 was placed in a metal bat 70 made of stainless steel with the sprayed film 60 facing downward and in contact with the metal bat 70 while being immersed in an electrolyte solution 72, and the base portion 30 and the metal bat 70 were electrically connected by an electric wire 74. As a result, electrons flow from the coated structure 115 to the metal bat 70 via the electric wire 74, and aluminum ions migrate from the base portion 30 to the sprayed film 60 in the coated structure 115, causing electrolytic corrosion at the interface 63 with the sprayed film 60. In FIG. 6, arrows indicate the flow of electrons in the electric wire 74, and hollow arrows indicate the migration of aluminum ions from the base portion 30 to the sprayed film 60.

[0032] As shown in Fig. 5, it was observed that the longer the treatment using the electrolyte solution of Fig. 6 was performed, the more the voids on the surface of the sprayed film 60 disappeared. The disappearance of the voids in the sprayed film 60 is thought to be as follows. That is, when the electrolyte solution or the like reaches the boundary surface 63 of the base portion 30 (see Fig. 4) through the sprayed film 60, the metal (aluminum) constituting the base portion 30 is oxidized at the boundary surface 63, and a gel of a compound bonded with hydroxide ions (aluminum hydroxide gel) is produced. The produced gel then enters the pores inside the sprayed film 60, which is thought to be the cause of the disappearance of the voids in the sprayed film 60 as described above. The gel that entered the pores of the sprayed film 60 then dries, and is thought to exist in the pores of the sprayed film 60 as a compound in which aluminum is bonded with hydroxide ions, specifically, aluminum hydroxide (Al(OH)3) or boehmite (AlOOH).

[0033] 5, when the pores of the sprayed film 60 are clogged, the flexibility of the sprayed film 60 decreases. As a result, when the temperature of the electrostatic chuck changes, the sprayed film 60 cannot adequately follow the expansion and contraction of the base portion 30 caused by heating, and cracks occur in the sprayed film 60. As a result of the cracks occurring in the sprayed film 60 in this way, the voltage resistance of the electrostatic chuck decreases.

[0034] FIG. 7 is a photograph of tortoiseshell cracks that occurred on the surface of the sprayed film 60 in the comparative coated structure 115, in which the voids on the surface of the sprayed film 60 disappeared due to the progression of electrical corrosion as shown in FIG. 5(C). In FIG. 7, isopropyl alcohol (IPA) was dropped onto the surface of the sprayed film 60, allowing the isopropyl alcohol to penetrate into the cracks, thereby increasing the visibility of the cracks. In contrast, as shown in FIG. 3, in the coated structure 15 of the present embodiment, which includes the barrier layer 62, no disappearance of the voids as shown in FIG. 5 or the occurrence of cracks as shown in FIG. 7 was observed, even after the same treatment was performed for the same period of time (data not shown). In the coated structure 15 of the present embodiment, not only is the barrier layer 62 preventing the penetration of the electrolyte solution, etc., but even if the electrolyte solution, etc., reaches the interface 63 of the base portion 30 through the barrier layer 62 and generates a gel such as aluminum hydroxide, the barrier layer 62 prevents the resulting gel from moving toward the sprayed film 60. This prevents the gel from entering the pores of the thermal sprayed film 60. In Figures 3 and 4, the upward arrows indicate the movement of the generated gel. As described above, according to the electrostatic chuck 10 of this embodiment, the coating structure 15 has the barrier layer 62, which prevents the pores of the thermal sprayed film 60 from being blocked, thereby maintaining the flexibility of the thermal sprayed film 60 and preventing cracks from occurring in the thermal sprayed film 60.

[0035] Generally, the denser the sprayed film 60, the better the voltage resistance of the electrostatic chuck. However, if the sprayed film 60 is made too dense, the voids in the sprayed film 60 disappear, and the sprayed film 60 If the thermal sprayed film 60 is heated, the flexibility of the thermal sprayed film 60 will decrease, making it difficult for the thermal sprayed film 60 to follow the thermal expansion and contraction of the base portion 30. As a result, cracks will be more likely to occur in the thermal sprayed film 60, which may actually reduce the voltage resistance of the electrostatic chuck. By providing the barrier layer 62 as in this embodiment, clogging of the pores in the thermal sprayed film 60 can be suppressed, and by ensuring the porosity of the thermal sprayed film 60 to be, for example, about 1.5 to 6.0%, the flexibility of the thermal sprayed film 60 can be maintained, and the effect of suppressing cracks in the thermal sprayed film 60 can be improved.

[0036] When the barrier layer 62 is provided as in this embodiment, as described above, the compound formed by bonding aluminum with hydroxide ions is prevented from penetrating into the pores of the thermal sprayed film 60. Therefore, in this embodiment, the pores of the thermal sprayed film 60 are substantially free of the compound in at least a portion including the surface opposite to the surface facing the barrier layer 62, thereby ensuring the flexibility of the thermal sprayed film 60. In the thermal sprayed film 60, the surface facing the barrier layer 62 is also referred to as the "first surface," and the surface opposite to this first surface is also referred to as the "second surface." Furthermore, the phrase "substantially free of" the compound in the pores means that no peak for the compound appears when the opposite surface (second surface) of the thermal sprayed film 60 is analyzed by X-ray diffraction (XRD). It is desirable that the compound be substantially free of the compound in the pores over a wider range in the thermal sprayed film 60; however, the thermal sprayed film 60 may be configured so that the compound is substantially free of the compound in the pores throughout the entire film.

[0037] FIG. 8 shows an example of an XRD pattern obtained by XRD analysis of the surface (first surface) of the thermal spray coating 60 facing the barrier layer 62 after treatment using an electrolyte solution as shown in FIG. 6 , and the results for the coated structure 15 and the coated structure 115 are superimposed. After treatment using the electrolyte solution, the coated structure 15 did not have any cracks, while the coated structure 115 had tortoiseshell cracks as shown in FIG. 6 . As shown in FIG. 8 , at the diffraction angles at which boehmite (AlOOH), a compound formed by combining aluminum with hydroxide ions, exhibits an intensity peak, no intensity peak was observed in the coated structure 15, but an intensity peak was observed in the coated structure 115 (see the arrows in FIG. 8 ). Furthermore, in the coated structure 15, an XRD pattern obtained by XRD analysis of the second surface, which is the surface opposite the first surface, also showed no intensity peak corresponding to boehmite (AlOOH) (data not shown). In addition, in the coated structures 15, 115 whose XRD patterns are shown in Figure 8, no compounds formed by aluminum combining with hydroxide ions other than boehmite (AlOOH) were detected on either the first or second surface. Therefore, in the coated structure 15 whose results are shown in Figure 8, it is considered that the entire sprayed film 60 does not substantially contain compounds formed by aluminum combining with hydroxide ions. In this way, it was confirmed that the coated structure 15 including the barrier layer 62 can suppress oxidation that progresses on the surface (first surface) of the base portion 30 facing the sprayed film 60, and can suppress the penetration of compounds formed by aluminum combining with hydroxide ions into the sprayed film 60.

[0038] Moreover, according to this embodiment, the barrier layer 62 is made of an oxide of the metal contained in the base portion 30. By using a material containing the same type of metal in this way, the difference in the thermal expansion coefficient and thermal contraction coefficient between the barrier layer 62 and the base portion 30 can be reduced, thereby suppressing stress generated between the barrier layer 62 and the base portion 30 during temperature changes and enhancing the effect of suppressing cracks in the sprayed film 60. Furthermore, according to this embodiment, by suppressing cracks in the sprayed film 60, the electrostatic chuck 10 can have an improved durability as well as an improved withstand voltage.

[0039] B. Second embodiment: 9 is a cross-sectional view, similar to FIG. 3, that schematically illustrates the appearance of a coating structure 215 provided in an electrostatic chuck according to a second embodiment. The coating structure 215 of the second embodiment is provided in place of the coating structure 15 in an electrostatic chuck 10 similar to that of the first embodiment. Coating structure In 215, a barrier layer 62 similar to that in the first embodiment is formed on the base portion 30, and a sprayed film 260 is formed on the barrier layer 62. The barrier layer 62 and the sprayed film 260 are collectively referred to as a coating layer 261.

[0040] The sprayed film 260 includes a first layer 64 and a second layer 65 formed by thermal spraying. The first layer 64 is a layer including a first surface, which is the surface of the sprayed film 260 facing the barrier layer 62. The second layer 65 is a layer including a second surface, which is the surface of the sprayed film 260 opposite the first surface, and is formed to have a higher porosity than the first layer 64. The porosities of the first layer 64 and the second layer 65 constituting the sprayed film 260 may be set appropriately within the range of 1.5 to 6.0%, for example, so that the porosity of the second layer 65 is higher than the porosity of the first layer 64.

[0041] The first layer 64 and the second layer 65 can be made of the same material as the thermal sprayed coating 60 of the first embodiment. The material making up the first layer 64 and the material making up the second layer 65 may be the same or different. Making the first layer 64 and the second layer 65 from the same material is preferable because it makes the thermal expansion coefficients of the first layer 64 and the second layer 65 equivalent and makes it easier to ensure adhesion between the first layer 64 and the second layer 65. The thicknesses of the first layer 64 and the second layer 65 may each be set appropriately, for example, in the range of 5 to 200 μm.

[0042] To form the first layer 64 and the second layer 65 with different porosities by thermal spraying as described above, for example, the output value of the thermal sprayer used for thermal spraying may be varied. By performing thermal spraying at a higher power, the first layer 64 with a relatively low porosity (a densely formed layer) can be formed, and by performing thermal spraying at a lower power, the second layer 65 with a relatively high porosity (a coarsely formed layer) can be formed. Furthermore, in terms of the particle size distribution of the material used for thermal spraying, the first layer 64 with a relatively low porosity can be formed by performing thermal spraying using a material containing a large number of relatively small particles, and the second layer 65 with a relatively high porosity can be formed by performing thermal spraying using a material containing a large number of relatively large particles. Furthermore, by reducing the film thickness per pass (one thermal spraying operation using a thermal spray gun) during thermal spraying, the first layer 64 with a relatively low porosity can be formed, and by increasing the film thickness per pass, the second layer 65 with a relatively high porosity can be formed. Alternatively, the porosity of the first layer 64 and the second layer 65 may be made different by using different spraying methods. Specifically, for example, the second layer 65 may be formed by ordinary plasma spraying, and the first layer 64 may be formed by suspension spraying, which uses a suspension (liquid suspension) as the spraying material.

[0043] With this configuration, the same effects as those of the first embodiment can be obtained. That is, by providing the barrier layer 62 between the base portion 30 and the sprayed film 260, the progress of oxidation on the surface of the base portion 30 is suppressed. Even if oxidation progresses, it is possible to prevent substances generated by the oxidation of the base portion 30 from clogging the pores of the sprayed film 260. Furthermore, by configuring the sprayed film 260 so that the pores of the sprayed film 260 are substantially free of compounds formed when metals constituting the base portion 30 combine with hydroxide ions in a portion of the sprayed film 260 that includes at least the second surface (the surface opposite the surface facing the barrier layer 62), the flexibility of the sprayed film 260 can be ensured, and the occurrence of cracks in the sprayed film 260 can be suppressed. Here, it is desirable that the portion substantially free of compounds formed when metals combine with hydroxide ions includes at least the second layer 65.

[0044] Furthermore, according to the second embodiment, the sprayed film 260 comprises a first layer 64, which is a layer including a first surface (the surface facing the barrier layer 62) and is formed more densely, and a second layer 65, which is a layer including a second surface that is the surface opposite to the first surface and is formed more coarsely than the first layer 64. Therefore, the flexibility, adhesion, and voltage resistance of the sprayed film 260 can be improved in a balanced manner. The denser the sprayed film is formed, the stronger the adhesion between adjacent layers. This is because the voltage resistance can be improved, and the coarser the sprayed film is formed, the more flexible the sprayed film can be. By forming the first layer 64 on the barrier layer 62 side densely, adhesion to the barrier layer 62 can be improved and the voltage resistance can be improved. Furthermore, by forming the outer second layer 65 coarsely, the flexibility of the sprayed film 260 can be ensured, thereby suppressing cracking in the sprayed film 260 and improving the voltage resistance. In particular, in a sprayed film, stress generated during thermal expansion and contraction is generally greatest at the outermost periphery. Therefore, by increasing the porosity of this portion (the second layer 65 including the second surface, which is the outermost periphery) that is subjected to particularly large loads due to thermal expansion and contraction, the effect of increasing the flexibility of the sprayed film can be enhanced. Considering the balance of the effects of the coarse and dense sprayed film described above, it is desirable to make the second layer 65 thicker than the first layer 64 to improve the performance of the sprayed film 260.

[0045] Although the coated structure 215 of the second embodiment has a two-layer structure consisting of a first layer 64 and a second layer 65, it may have a different configuration. For example, the sprayed film may have three or more layers stacked in the thickness direction, or the porosity may vary continuously. The same effect can be obtained if the layer including the second surface of the sprayed film is formed with a higher porosity than the layer including the first surface.

[0046] C. Third embodiment: 10 is a cross-sectional view, similar to FIG. 3, that schematically illustrates the appearance of a coating structure 315 included in an electrostatic chuck according to a third embodiment. The coating structure 315 of the third embodiment is provided in place of the coating structure 15 in an electrostatic chuck 10 similar to that of the first embodiment. In the coating structure 315, a barrier layer 362 is formed on the base portion 30 in place of the barrier layer 62. The barrier layer 362 and the sprayed film 60 are collectively referred to as a coating layer 361.

[0047] The barrier layer 362 of the third embodiment is formed by thermal spraying and is a layer formed more densely than the thermal sprayed film 60. The barrier layer 362 can be made of the same material as the thermal sprayed film 60 of the first embodiment. The material constituting the barrier layer 362 and the material constituting the thermal sprayed film 60 may be the same or different. Constituting the barrier layer 362 and the thermal sprayed film 60 from the same material is preferable because it makes the thermal expansion coefficients of the barrier layer 362 and the thermal sprayed film 60 similar and makes it easier to ensure adhesion between the barrier layer 362 and the thermal sprayed film 60. The thickness of the barrier layer 362 may be appropriately set, for example, in the range of 5 to 20 μm. The barrier layer 362 may be formed, for example, by suspension spraying. Forming the barrier layer 362 by suspension spraying facilitates thinning and densification of the barrier layer 362. The porosity of the barrier layer 362 is preferably, for example, 1% or less.

[0048] With this configuration, it is possible to obtain the same effects as in the first embodiment. That is, by providing the barrier layer 362 between the base portion 30 and the thermal-sprayed film 60, it is possible to suppress the progression of oxidation on the surface of the base portion 30 and to prevent substances produced by oxidation of the base portion 30 from clogging the pores of the thermal-sprayed film 60. Furthermore, in a portion of the thermal-sprayed film 60 that includes at least the second surface (the surface opposite the surface facing the barrier layer 362), the pores of the thermal-sprayed film 60 do not substantially contain compounds formed by the metals that make up the base portion 30 bonding with hydroxide ions. This ensures the flexibility of the thermal-sprayed film 60 and suppresses the occurrence of cracks in the thermal-sprayed film 60.

[0049] D. Other Embodiments: In the first and second embodiments described above, the barrier layer 62 is a layer made of an oxide of the metal contained in the base portion 30, and in the third embodiment, the barrier layer 362 is a layer formed by thermal spraying, but a different configuration may also be used. For example, the barrier layer may be formed by chemical conversion treatment such as boehmite treatment, cathodic protection, or the like. A barrier layer that is denser than the sprayed film is provided between the sprayed film and the base portion 30, and the pores of the sprayed film in the area including at least the second surface are substantially free of compounds formed when the metal constituting the base portion 30 combines with hydroxide ions, thereby achieving the same effects as those of the previously described embodiments.

[0050] In the above-described embodiments, the base portion 30 is formed using aluminum or an aluminum alloy, but a different configuration may be used. For example, the base portion 30 may be formed using a metal material containing at least one metal selected from the group consisting of magnesium, molybdenum, titanium, tungsten, chromium, and nickel. Even when using such a base portion 30, the same effects as those of the embodiments can be obtained by providing a barrier layer between the base portion 30 and the thermal sprayed film 60.

[0051] The present disclosure may be applied to holding devices other than electrostatic chucks that use electrostatic attraction to hold a wafer W. That is, the present disclosure may be similarly applied to other holding devices that include a plate-shaped member such as a ceramic member and a base portion as a coating structure bonded to the plate-shaped member and coated with a thermal spray layer, and that hold an object on the surface of the plate-shaped member, such as a heater device for a vacuum device for CVD, PVD, PLD, etc., or a vacuum chuck. Alternatively, the present disclosure may be applied to the inner wall or lid (LID) of a vacuum chamber. In a device that includes a coating structure with a thermal spray film that covers at least a portion of a metal-containing substrate, oxidation may progress on the substrate surface during processes such as grinding, polishing, and cleaning during device manufacturing. Therefore, by applying the present disclosure, it is possible to suppress cracking in the thermal spray film and achieve effects similar to those of the embodiments.

[0052] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0053] 10...Electrostatic chuck 15,115,215,315...Covering structure 20...Ceramic section 22...Chuck electrode 24...Placement surface 30...Base 32... Refrigerant flow path 40…Joint part 50...Gas supply line 52...Gas outlet 60,260...Thermal spray coating 61,261...Covering layer 62,362...Barrier layer 63...Boundary 64…1st layer 65…Second layer 70...Metal bat 72...Electrolyte solution 74...Electric wire

Claims

1. A coated structure coated with a thermal sprayed film, a substrate including a metal; the thermal sprayed film covering at least a portion of the substrate; a barrier layer provided between the substrate and the thermal sprayed film and formed more densely than the thermal sprayed film; Equipped with the thermal sprayed film has a first surface facing the barrier layer and a second surface opposite to the first surface, the XRD pattern of the thermal sprayed film at a portion including at least the second surface does not show peaks of hydroxides and oxyhydroxides of the metals constituting the substrate; the thermal sprayed film includes a first layer including the first surface of the thermal sprayed film and a second layer including the second surface of the thermal sprayed film, The second layer is formed to have a larger porosity than the first layer. Covering structure.

2. The covering structure according to claim 1, The barrier layer is an oxide film. Covering structure.

3. The covering structure according to claim 2, The barrier layer is formed of an oxide of the metal contained in the substrate. Covering structure.

4. The covering structure according to claim 2, The barrier layer is characterized by comprising an anodic oxide coating. Covering structure.

5. The covering structure according to claim 1, In the XRD pattern of the second layer at a portion including at least the second surface, no peaks of hydroxides and oxyhydroxides of the metals constituting the substrate appear. Covering structure.

6. 6. The coated structure according to claim 1, the substrate contains aluminum as the metal; The compound is aluminum hydroxide (Al(OH) ３ ) and boehmite (AlOOH), Covering structure.

7. A holding device for holding an object, a plate-like member on which the object is placed; The covering structure according to any one of claims 1 to 6, which is joined to the plate-like member; A holding device comprising:

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