Wafer carrying table

Abstract

A wafer placement table 10 is provided with: a ceramic plate 20 having a wafer placement surface 21 on the upper surface thereof, provided with pores 26 penetrating in the vertical direction, and having built-in electrodes 22; a conductive plate (30) which is bonded to the lower surface of the ceramic plate (20) and in which a gas supply passage (31) is provided; a plug chamber 32 configured as a recess provided from the upper surface of the conductive plate 30 toward the lower surface of the conductive plate 30, the plug chamber 32 communicating with the pores 26 and the gas supply passage 31; an insulating gas passage plug (40) which is disposed in the plug chamber (32) and through which gas can pass; and a dense insulating film 50. The dense insulating film (50) permits ventilation of an insulating gas through a gas outlet portion (44) of the upper surface of the plug (40), the gas outlet portion (44) being a gas flow path toward the pores (26). The insulating gas-passing plug 40 is disposed so as to extend across the upper surface of the conductive plate 30 and the upper surface of the insulating gas-passing plug 40, thereby covering the boundary portion between the upper surface of the conductive plate 30 and the upper surface of the insulating gas-passing plug 40.

Description

Technical Field The present invention relates to a wafer loading platform. Background Art Conventionally, a wafer carrier is known that includes a ceramic plate having a wafer placement surface on its upper surface, and a substrate bonded to the lower surface of the ceramic plate and having a gas inlet passage. Patent Document 1 discloses a wafer carrier comprising an insulating first porous portion disposed within a through-hole of the ceramic plate, and an insulating second porous portion embedded in a recessed portion provided on the side of the ceramic plate on the substrate so as to oppose the first porous portion. Gas supplied to the gas inlet passage flows from the second porous portion and the first porous portion into the space between the wafer placement surface and the wafer, thereby cooling the object. The second porous portion comprises a ceramic porous body and a ceramic insulating film formed on the side of the ceramic porous body by thermal spraying. The ceramic insulating film contacts the inner circumferential surface of the recessed portion of the substrate. It is described that the presence of such a second porous portion enables high insulation performance. Prior art literature Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 2020-72262 Summary of the Invention However, even if an insulating second porous portion is present as in Patent Document 1, discharge may occur in the second porous portion along a path between the side surface of the ceramic porous body and the ceramic insulating film. The present invention has been made to solve the above-mentioned problems, and its main object is to suppress the occurrence of discharge around the side surfaces of the insulating gas passage plug. The present invention adopts the following means to achieve the above-mentioned main object.

[0001] The wafer loading platform of the present invention comprises: a ceramic plate having a wafer placement surface on its upper surface, provided with fine holes extending therethrough in the vertical direction, and having electrodes built therein; a conductive plate bonded to the lower surface of the ceramic plate and provided with a gas supply passage; a plug chamber configured as a recessed portion extending from the upper surface of the conductive plate toward the lower surface of the conductive plate and communicating with the fine hole and the gas supply passage; an insulating gas passage plug, the insulating gas passage plug being disposed in the plug chamber and capable of passing gas therethrough; and A dense insulating film allows ventilation of the insulating gas through a gas outlet portion of the upper surface of the plug, which serves as a gas flow path toward the fine hole, and is arranged so as to span the upper surface of the conductive plate and the upper surface of the insulating gas passage plug to cover a boundary portion between the upper surface of the conductive plate and the upper surface of the insulating gas passage plug. In this wafer stage, a dense insulating film is disposed across the upper surface of the conductive plate and the upper surface of the insulating gas passage plug, thereby covering the boundary between the upper surface of the conductive plate and the upper surface of the insulating gas passage plug. The presence of this dense insulating film suppresses discharge from the boundary between the upper surface of the conductive plate and the upper surface of the insulating gas passage plug along a vertical path along the side surface of the insulating gas passage plug. Furthermore, the dense insulating film allows the insulating gas to vent through the gas outlet portion of the passage plug, allowing gas to flow from the gas supply path through the insulating gas passage plug toward the fine pores.

[0002] In the above-mentioned chip carrier (the chip carrier described in [1] above), a convex portion whose upper surface becomes the gas outlet portion can be formed on the upper surface of the plug through which the insulating gas passes, and the upper surface of the dense insulating film and the upper surface of the convex portion are located on the same plane.

[0003] In the wafer placement table (the wafer placement table described in [1] or [2] above), the dense insulating film may be a sprayed film or an aerosol deposited film. This allows for relatively easy production of the dense insulating film.

[0004] The wafer stage (the wafer stage described in any one of [1] to [3]) may include an elastic member disposed between the lower surface of the insulating gas passage plug and the bottom surface of the plug chamber. The presence of the elastic member can prevent the insulating gas passage plug from being pushed upward when the wafer stage is heated during use, for example, and the conductive plate warps into an upwardly convex shape. This can suppress cracking of the dense insulating film. In this case, a gap can be provided between the lower surface of the insulating gas passage plug and the bottom surface of the plug chamber by the elastic member.

[0005] In the wafer placement table (the wafer placement table described in [4] above), the elastic member may be made of a heat-resistant resin. This allows the elastic member to be manufactured relatively easily.

[0006] In the above-mentioned wafer placement table (the wafer placement table described in any one of the above-mentioned [1] to [5]), the insulating gas passage plug may be a porous body. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a longitudinal sectional view of the wafer stage 10 . Figure 2 yes Figure 1 Magnified view of part A. Figure 3 yes Figure 2 BB cross-section diagram. Figure 4 It is a manufacturing process diagram of the wafer stage 10. Figure 5 The comparison method of the wafer stage 910 is Figure 2 Corresponding enlarged image. Figure 6 The wafer stage 110 is connected to Figure 2 Corresponding enlarged image. DETAILED DESCRIPTION Preferred embodiments of the present invention will be described below using the accompanying drawings. Figure 1 is a longitudinal sectional view of the wafer stage 10, Figure 2 yes Figure 1 A magnified view of part A, Figure 3 yes Figure 2 BB cross-sectional view (the main view (overall view) of the wafer placement table 10 is shown in FIG. Figure 2 (See the cross-sectional view taken along the BB cutting line.) In this specification, the terms "up" and "down" indicate relative positions, not absolute positions. Therefore, depending on the orientation of the wafer stage 10, "up" and "down" may be replaced with "down" and "up," or with "left" and "right," or with "front" and "back." like Figure 1 As shown in FIG. 1 , the wafer stage 10 includes a ceramic plate 20, a conductive plate 30, and an insulating gas passing plug 40. Figure 2 As shown, the wafer stage 10 includes a dense insulating film 50 and an adhesive sheet 60 . The ceramic plate 20 is a circular plate made of ceramic such as alumina sintered body or aluminum nitride sintered body (for example, 300 mm in diameter and 5 mm in thickness). The upper surface of the ceramic plate 20 serves as a wafer loading surface 21 on which the wafer W is loaded. The ceramic plate 20 has a built-in electrode 22. The electrode 22 is a planar mesh electrode used as an electrostatic electrode and is connected to an external DC power supply via a power supply component (not shown). A low-pass filter may be arranged in the middle of the power supply component. The power supply component is electrically insulated from the conductive plate 30. When a DC voltage is applied to the electrode 22, the wafer W is adsorbed and fixed to the wafer loading surface 21 by electrostatic adsorption force; when the application of the DC voltage is released, the adsorption and fixation of the wafer W on the wafer loading surface 21 is released. The ceramic plate 20 is provided with fine holes 26. The fine holes 26 serve as a gas passage that penetrates the ceramic plate 20 in the vertical direction and reaches the wafer loading surface 21 from the lower surface of the ceramic plate 20. The ceramic plate 20 has a plurality of fine holes 26. The conductive plate 30 is a circular plate with good thermal conductivity (a circular plate with a diameter the same as or larger than that of the ceramic plate 20). The conductive plate 30 has a gas supply passage 31 and a plug chamber 32. The plug chamber 32 is open on the upper surface of the conductive plate 30 (the surface on the ceramic plate 20 side) and is configured as a recessed portion arranged from the upper surface toward the lower surface. The internal space of the plug chamber 32 is, for example, cylindrical. The gas supply passage 31 is a gas passage that reaches the lower surface of the conductive plate 30 from the plug chamber 32. In the present embodiment, the gas supply passage 31 is configured as a through hole in the conductive plate 30 that passes from the bottom surface of the plug chamber 32 along the up and down directions to the lower surface of the conductive plate 30. A refrigerant flow path (not shown) is formed inside the conductive plate 30. The refrigerant flowing in the refrigerant flow path is preferably a liquid, and is preferably electrically insulating. As an electrically insulating liquid, for example, a fluorine-based inactive liquid can be cited. The refrigerant flow path is formed in a single stroke across the entire conductive plate 30, from one end (inlet) to the other end (outlet) when viewed from above. The refrigerant flow path is connected to the supply and return ports of an external refrigerant device (not shown), respectively, at one end and the other end. The conductive plate 30 is connected to a high-frequency (RF) power source and also serves as an RF electrode. Examples of the material of the conductive plate 30 include metal materials and composite materials of metal and ceramics. Examples of metal materials include Al, Ti, Mo, or alloys thereof. Examples of composite materials of metal and ceramics include metal matrix composite materials (MMC) and ceramic matrix composite materials (CMC). Specific examples of such composite materials include materials containing Si, SiC, and Ti (also referred to as SiSiCTi), materials obtained by impregnating a SiC porous body with Al and / or Si, and composite materials of Al2O3 and TiC. The material of the conductive plate 30 is preferably a material having a thermal expansion coefficient close to that of the material of the ceramic plate 20. The insulating gas passage plug 40 is an insulating component through which gas can pass, and is arranged in the plug chamber 32. In the present embodiment, the insulating gas passage plug 40 is a porous body. The insulating gas passage plug 40 is connected to the gas supply passage 31 and the pore 26, so that the gas in the gas supply passage 31 can reach the chip loading surface 21. The insulating gas passage plugs 40 are provided on the conductive plate 30 in the same number as the pore 26, the gas supply passage 31 and the plug chamber 32, and they correspond to each other one to one. The insulating gas passage plug 40 has: a cylindrical main body 41, and a cylindrical protrusion 42 provided in the center of the upper surface of the main body 41 and having a smaller diameter than the main body 41. The upper surface of the protrusion 42 is located directly below the pore 26, and serves as a gas outlet from the insulating gas passage plug 40 toward the pore 26. More specifically, the portion of the upper surface of the protrusion 42 that is not in contact with the adhesive sheet 60 ( Figure 3The circular area (indicated by the dashed line in the figure) serves as the gas outlet portion 44. Regarding the insulating gas passage plug 40, the side surface (outer circumference) of the main body 41 may be bonded to the inner circumference of the plug chamber 32, or the external thread provided on the side surface of the insulating gas passage plug 40 may be screwed into the internal thread provided on the inner circumference of the plug chamber 32. The upper surface of the insulating gas passage plug 40, excluding the protrusion 42, is flush with the upper surface of the conductive plate 30. The insulating gas plug 40 can be a porous block obtained by sintering ceramic powder. Examples of ceramics include alumina and aluminum nitride. The insulating gas plug 40 preferably has a porosity of 30% or greater, and an average pore diameter of 15 μm or greater. The porosity of the insulating gas plug 40 can be 70% or less. An elastic member 48 is disposed between the lower surface of the insulating gas plug 40 and the bottom surface of the plug chamber 32 of the conductive plate 30. In this embodiment, the elastic member 48 has an annular shape centered on the opening of the gas supply passage 31 when viewed from above. The elastic member 48 contacts only a portion of the lower surface of the insulating gas plug 40 and a portion of the bottom surface of the plug chamber 32. This creates a gap S between the lower surface of the insulating gas plug 40 and the bottom surface of the plug chamber 32 of the conductive plate 30. The vertical height of the gap S can be, for example, between 0.1 mm and 1 mm. The elastic member 48 is disposed on the bottom surface of the plug chamber 32, excluding the opening of the gas supply passage 31, so as not to obstruct the passage of gas from the gas supply passage 31 to the insulating gas plug 40. For example, a heat-resistant resin can be used as the elastic member 48. Examples of heat-resistant resins include fluorine-based resins such as Teflon (Teflon is a registered trademark), acrylic resins, and polyimide resins. These resins are preferred because they have heat resistance of 200° C. or higher required for the wafer stage 10 and are less likely to generate gas even when used in a vacuum. The dense insulating film 50 is a dense insulating film that covers the upper surface of the conductive plate 30 and the insulating gas passage plug 40. More specifically, the dense insulating film 50 is arranged so as to span the upper surface of the conductive plate 30 and the upper surface of the main body 41 of the insulating gas passage plug 40. Thus, the dense insulating film 50 covers the boundary portion (see FIG. 1 ) between the upper surface of the conductive plate 30 and the upper surface of the main body 41 of the insulating gas passage plug 40. Figure 3In addition, the dense insulating film 50 does not cover the upper surface of the protrusion 42, and therefore does not cover the gas outlet portion 44 which is a part of the protrusion 42. Accordingly, the dense insulating film 50 allows ventilation of the gas outlet portion 44. The thickness of the dense insulating film 50 is equal to the height of the protrusion 42, and therefore, the upper surface of the dense insulating film 50 and the upper surface of the protrusion 42 are located on the same plane. It should be noted that, in this specification, the so-called being located on the same plane includes the situation where they are located on approximately the same plane, and also includes, for example, the situation where there is a height difference that is inevitably generated during manufacturing, and the situation where there are fine bumps on the upper surface of the dense insulating film 50 and / or the upper surface of the protrusion 42. In the present embodiment, the dense insulating film 50 covers all of the upper surface of the conductive plate 30 (the bonding surface with the ceramic plate 20) and the upper surface of the main body 41 of the insulating gas passing plug 40. The dense insulating film 50 is in contact with the side surface of the protrusion 42 and covers the entire side surface of the protrusion 42 . The dense insulating film 50 is, for example, a sprayed film or an aerosol deposited film (AD film). When the dense insulating film 50 is a sprayed film, the sprayed film is made of the same material as the insulating gas passage plug 40. For example, when the insulating gas passage plug 40 is alumina, the sprayed film can also be made of alumina. Alternatively, the sprayed film can be made of the same material as the ceramic material contained in the conductive plate 30. The AD film is a film formed by an AD method (including a plasma AD method). The AD method can form ceramic particles into a film by the impact hardening phenomenon, so there is no need to sinter the ceramic particles at a high temperature. When the dense insulating film 50 is an AD film, the same material as the above-mentioned sprayed film can also be used. In this specification, "dense" refers to a density that prevents gas from flowing through. For example, the dense insulating film 50 can have a porosity of less than 3%, preferably less than 1%. The porosity is defined as the area ratio of pores observed in a representative cross-section image observed at 50x magnification using a scanning electron microscope (SEM). The bonding sheet 60 is an insulating adhesive layer disposed between the lower surface of the ceramic plate 20 and the upper surface of the dense insulating film 50, and is, for example, a resin sheet. The conductive plate 30 is bonded to the lower surface of the ceramic plate 20 via the bonding sheet 60 and the dense insulating film 50. A through hole having a diameter equal to or slightly larger than the opening diameter of the pore 26 is provided in the bonding sheet 60 directly below the pore 26. The gas outlet portion 44 and the pore 26 are connected by means of the space inside the through hole, which is referred to as the pore side space 27. The portion of the upper surface of the protrusion 42 of the plug 40 that is exposed in the pore side space 27 through which the insulating gas passes is the gas outlet portion 44. The portion of the upper surface of the protrusion 42 other than the gas outlet portion 44 is bonded to the lower surface of the bonding sheet 60. Next, an example of using the wafer stage 10 constructed in this manner will be described. First, with the wafer stage 10 installed in a chamber (not shown), a wafer W is placed on the wafer placement surface 21. The chamber is then depressurized using a vacuum pump to a predetermined vacuum level, and a DC voltage is applied to the electrode 22 of the ceramic plate 20 to generate an electrostatic attraction force, thereby adsorbing and fixing the wafer W to the wafer placement surface 21. Next, a reaction gas atmosphere of a predetermined pressure (e.g., tens to hundreds of Pa) is created in the chamber. In this state, an RF voltage is applied between an upper electrode (not shown) located at the top of the chamber and the conductive plate 30 of the wafer stage 10 to generate plasma. The surface of the wafer W is processed using the generated plasma. A refrigerant circulates in the refrigerant flow path of the conductive plate 30. Backside gas is introduced into the gas supply passage 31 from a gas cylinder (not shown). A heat-conductive gas (e.g., He gas) is used as the backside gas. The backside gas introduced into the gas supply passage 31 passes sequentially from the gap S in the plug chamber 32, the insulating gas through the plug 40, the pore-side space 27, and the pore 26 to the backside of the wafer W. The presence of this backside gas allows efficient heat conduction between the wafer W and the ceramic plate 20. Next, based on Figure 4 , a manufacturing example of the wafer placement table 10 is described. Figure 4 1 is a manufacturing process diagram of the wafer stage 10. First, the ceramic plate 20 and the conductive plate 30 are prepared before being bonded to each other, and the insulating gas is passed through the plug 40 ( Figure 4 (A)). The ceramic plate 20 is obtained as follows, for example, by making a molded body of ceramic powder having an electrode 22 built therein, and hot pressing and sintering the molded body, thereby obtaining the ceramic plate 20. In addition, fine pores 26 are pre-formed in the ceramic plate 20, and a gas supply passage 31, a plug chamber 32, and a refrigerant flow path are pre-formed in the conductive plate 30. The plug chamber 32 can be formed when the conductive plate 30 is formed, or the plug chamber 32 can be formed by processing after the conductive plate 30 is made. When making the conductive plate 30, a plurality of MMC disc components can be first made, and after grooves or holes are formed in these MMC disc components by machining, the plurality of MMC disc components can be joined using a metal bonding material, and the grooves or holes can eventually become the gas supply passage 31, the plug chamber 32, and the refrigerant flow path. Next, the elastic member 48 is attached to the lower surface of the insulating gas passage plug 40 ( Figure 4 (B)), the insulating gas passing plug 40 is assembled on the conductive plate 30 ( Figure 4(C)). The insulating gas passage plug 40 can be assembled as follows. For example, after applying adhesive to at least one of the inner peripheral surface of the plug chamber 32 and the outer peripheral surface of the insulating gas passage plug 40, the insulating gas passage plug 40 is inserted from above the plug chamber 32, thereby bonding and fixing the outer peripheral surface of the insulating gas passage plug 40 to the inner peripheral surface of the plug chamber 32. Next, the upper surface of the conductive plate 30 and the insulating gas passage plug 40 is subjected to a spraying or AD method using the material of the dense insulating film 50 to form a dense insulating film 70 ( Figure 4 (D)). The dense insulating film 70 is formed to be thicker than the dense insulating film 50 and is formed to cover the entire upper surface of the conductive plate 30 including the upper surface of the protrusion 42 and the insulating gas through-plug 40. Thereafter, the upper surface of the dense insulating film 70 is ground to reduce the thickness of the dense insulating film 70 and expose the upper surface of the protrusion 42 ( Figure 4 (E)). Thus, the dense insulating film 70 becomes the dense insulating film 50. Then, the ceramic plate 20 and the conductive plate 30 equipped with the dense insulating film 50 are bonded to each other via the bonding sheet 60 to obtain the wafer stage 10 ( Figure 4 (F)). In the wafer stage 10 of the present embodiment described in detail above, a dense insulating film 50 is disposed across the upper surface of the conductive plate 30 and the upper surface of the main body 41 of the insulating gas passage plug 40, thereby covering the boundary between the upper surface of the conductive plate 30 and the upper surface of the insulating gas passage plug 40. The presence of such a dense insulating film 50 suppresses discharge from occurring along a vertical path along the side surface of the insulating gas passage plug 40 at the boundary between the upper surface of the conductive plate 30 and the upper surface of the insulating gas passage plug 40. Furthermore, the dense insulating film 50 allows the insulating gas to vent through the gas outlet portion 44 of the plug 40. Therefore, even with the presence of the dense insulating film 50, gas can flow from the gas supply passage 31 through the insulating gas passage plug 40 toward the fine hole 26. Here, for comparison with the above embodiment, Figure 5 , a wafer placement table 910 in a mode (referred to as a comparative mode) not including the dense insulating film 50 will be described. Figure 5 The comparison method of the wafer stage 910 is Figure 2Corresponding enlarged view. It should be noted that the same reference numerals are used for the description of components identical to those of the wafer stage 10. The wafer stage 910 includes a cylindrical insulating gas passage plug 940, which does not include the protrusion 42, in the plug chamber 32, in place of the insulating gas passage plug 40. Furthermore, the wafer stage 910 includes a dense insulating film 951 provided on the outer peripheral surface of the insulating gas passage plug 940 and a dense insulating film 952 covering the upper surface of the conductive plate 30, but does not include the dense insulating film 50. In this wafer stage 910, the side surface (outer peripheral surface) of the insulating gas passage plug 940 contacts the dense insulating films 951 and 952, so the contact surfaces of the insulating gas passage plug 940 with the dense insulating films 951 and 952 are in the vertical direction. Furthermore, the potential difference generated by the voltage applied to the wafer stage 910 during use also extends in the vertical direction. Therefore, discharge is likely to occur in the area between the insulating gas passage plug 940 and the dense insulating films 951 and 952, that is, around the side surfaces of the insulating gas passage plug 940. As a result, discharge may occur along a discharge path R1 (see the dashed line) that runs from the side surfaces of the insulating gas passage plug 940, through the top surface of the insulating gas passage plug 940, and the inner circumference of the fine hole 26 to the wafer W. Furthermore, during the manufacture of the wafer stage 910, the dense insulating film 951 on the side surfaces of the insulating gas passage plug 940 and the dense insulating film 952 on the top surface of the conductive plate 30 are separately formed. Therefore, discharge is likely to occur at the interface between the dense insulating films 951 and 952. As a result, discharge may occur along a discharge path R2 (see the dashed line) from the interface between the dense insulating film 951 and the dense insulating film 952 through the side and top surfaces of the insulating gas passage plug 940 and the inner circumference of the fine hole 26 to the wafer W. In contrast, in the wafer stage 10 of the present embodiment, the dense insulating film 50 is disposed on the top surface of the insulating gas passage plug 40 rather than on the side surface. The contact surface between the dense insulating film 50 and the insulating gas passage plug 40 is oriented in the left-right direction, making the path between the dense insulating film 50 and the insulating gas passage plug 40 less likely to serve as a discharge path. Furthermore, the dense insulating film 50 is formed so as to span the top surface of the conductive plate 30 and the top surface of the insulating gas passage plug 40. Consequently, no interface exists between the portion of the dense insulating film 50 covering the top surface of the conductive plate 30 and the portion covering the top surface of the insulating gas passage plug 40. Therefore, the boundary between the conductive plate 30 and the insulating gas passage plug 40 is less likely to become a discharge path. In summary, in the wafer stage 10, the presence of the dense insulating film 50 can suppress discharge from occurring along the vertical path along the side surface of the insulating gas passage plug 40 at the boundary between the upper surface of the conductive plate 30 and the upper surface of the insulating gas passage plug 40. Furthermore, in the wafer stage 910, the upper surface of the insulating gas passage plug 140 is in direct contact with the bonding sheet 60. If the insulating gas passage plug 140 is porous, the upper surface of the insulating gas passage plug 140 may have irregularities due to the open pores, thereby reducing the adhesion between the insulating gas passage plug 140 and the bonding sheet 60. In contrast, in the wafer stage 10, the dense insulating film 50 is interposed between the insulating gas passage plug 40 and the bonding sheet 60, thereby easily improving the adhesion between the insulating gas passage plug 40, the dense insulating film 50, and the bonding sheet 60. For example, when the insulating gas passage plug 40 is porous and the dense insulating film 50 is formed on the upper surface of the insulating gas passage plug 40 by sputtering or AD, the constituent particles of the dense insulating film 50 are incorporated into the irregularities of the upper surface of the insulating gas passage plug 40, thereby improving the adhesion between the insulating gas passage plug 40 and the dense insulating film 50. Furthermore, because the dense insulating film 50 is dense, the adhesion between the dense insulating film 50 and the adhesive sheet 60 is higher than the adhesion between the porous insulating gas passage plug 940 and the adhesive sheet 60. Furthermore, a convex portion 42 is formed on the upper surface of the main body 41 of the insulating gas passage plug 40, the upper surface of which serves as a gas outlet portion 44. The upper surface of the dense insulating film 50 and the upper surface of the convex portion 42 are located on the same plane. Figure 4 (D) and Figure 4 As described in (E), after forming a dense insulating film 70 so as to entirely cover the upper surface of the conductive plate 30 and the upper surface of the insulating gas-passing plug 40, the dense insulating film 70 is ground until the upper surface of the protrusion 42 is exposed. This allows for relatively easy formation of a dense insulating film 50 that allows for ventilation of the gas outlet portion 44. Furthermore, since the upper surface of the dense insulating film 50 and the upper surface of the protrusion 42 are coplanar, gaps other than the gas flow path are less likely to form when the conductive plate 30 and the ceramic plate 20, after forming the dense insulating film 50, are joined. This further suppresses discharge. Furthermore, the dense insulating film 50 is a sprayed film or an aerosol deposited film, and therefore the dense insulating film 50 can be formed relatively easily. The wafer stage 10 also includes an elastic member 48 disposed between the lower surface of the insulating gas passage plug 40 and the bottom surface of the plug chamber 32. The presence of this elastic member 48 prevents the insulating gas passage plug 40 from being pushed upward when the wafer stage 10 is heated during use, for example, and the conductive plate 30 warps into an upwardly convex shape. If the insulating gas passage plug 40 is pushed upward, cracks may form in the portion of the dense insulating film 50 that covers the boundary between the conductive plate 30 and the insulating gas passage plug 40. However, since the elastic member 48 acts as a buffer material, it prevents the insulating gas passage plug 40 from being pushed upward, thereby suppressing cracks in the dense insulating film 50. Furthermore, since the elastic member 48 is made of a heat-resistant resin, the elastic member can be manufactured relatively easily. It should be noted that the present invention is not limited to the above-described embodiment, and can be implemented in various forms as long as it falls within the technical scope of the present invention. For example, in the above embodiment, the insulating gas passage plug 40 has the convex portion 42 , but the present invention is not limited thereto. Figure 6 The wafer stage 110 is another example of the wafer stage 10. Figure 2 Corresponding enlarged image. Figure 6Components identical to those of the wafer stage 10 are designated by the same reference numerals, and their descriptions are omitted. Instead of the insulating gas plug 40, the wafer stage 110 includes a cylindrical insulating gas plug 140 lacking the protrusion 42. A dense insulating film 150 has an opening formed directly above the gas outlet portion 44, leaving the gas outlet portion 44 uncovered to allow ventilation of the gas outlet portion 44, which is a portion of the upper surface of the insulating gas plug 140. The dense insulating film 150 covers the entire upper surface of the insulating gas plug 140 except for the opening. The dense insulating film 150 is disposed across the upper surface of the conductive plate 30 and the upper surface of the insulating gas plug 140, thereby covering the boundary between the upper surface of the conductive plate 30 and the upper surface of the insulating gas plug 140. In this wafer stage 110, as in the above-described embodiment, the presence of the dense insulating film 150 suppresses discharge from the boundary between the upper surface of the conductive plate 30 and the upper surface of the insulating gas passage plug 140 along a vertical path along the side surface of the insulating gas passage plug 140. However, since the insulating gas passage plug 140 does not include the protrusion 42, when forming the dense insulating film 150, it is necessary to form an opening so that the dense insulating film 150 does not cover the gas outlet portion 44. For example, it is necessary to mask a portion of the upper surface of the insulating gas passage plug 140 when forming the dense insulating film 150, or to provide a hole in the dense insulating film 150 after forming the dense insulating film 150 so that the gas outlet portion 44 is exposed. Therefore, the dense insulating film 50 is easier to manufacture than the dense insulating film 150 and is therefore preferred. In addition, the wafer stage 110 has an opening provided in the dense insulating film 150 so as not to cover the gas outlet portion 44, and does not have the convex portion 42. Figure 2 Compared with the pore side space 27, Figure 5 In the embodiment, the pore side space 127 is enlarged by an amount corresponding to the thickness of the dense insulating film 150. Therefore, from the viewpoint of suppressing discharge in the space, it is preferable to Figure 2 Thus, the insulating gas passage plug 40 having the protrusion 42 is used. Figure 2 In the wafer placement table 10, the convex portion 42 exists and the dense insulating film 50 covers the entire side surface of the convex portion 42. Therefore, the pore side space 27 is only the through-hole portion of the bonding sheet 60, and the pore side space 27 can be reduced. In the above embodiment, the presence of the elastic member 48 creates a gap S between the bottom surface of the insulating gas plug 40 and the bottom surface of the plug chamber 32 of the conductive plate 30, but the present invention is not limited to this. For example, the elastic member 48 may contact the entire bottom surface of the insulating gas plug 40, excluding the portion directly above the gas supply passage 31, so that no gap exists between the bottom surface of the insulating gas plug 40 and the bottom surface of the plug chamber 32, except for the gas flow path. In this case, the presence of the elastic member 48 also prevents the insulating gas plug 40 from being pushed upward. Furthermore, the shape of the elastic member 48 is not limited to a ring; it may also be a rod. The elastic member 48 may have an easily deformable shape, such as a hollow portion or a corrugated shape. The wafer stage 10 does not need to include the elastic member 48. In this case, the bottom surface of the insulating gas plug 40 may contact the bottom surface of the plug chamber 32. Alternatively, multiple elastic members 48 may be disposed on the bottom surface of a single insulating gas plug 40. In the above embodiment, a gap may exist between the outer circumferential surface of the insulating gas passage plug 40 and the inner circumferential surface of the plug chamber 32. The presence of the dense insulating film 50 makes it difficult for discharge to occur even if a gap exists between the outer circumferential surface of the insulating gas passage plug 40 and the inner circumferential surface of the plug chamber 32. In the above embodiment, the insulating gas passage plug 40 is a porous body, but is not limited to a porous body, as long as the gas can pass through it. For example, the insulating gas passage plug 40 can be a component obtained by agglomerating finely divided insulating ceramics in a gas-permeable manner using an inorganic adhesive, or it can be glass fiber, heat-resistant Teflon resin sponge (Teflon is a registered trademark), etc. Alternatively, the insulating gas passage plug 40 can be a dense plug having an internal gas flow path. The internal gas flow path can be a straight through hole along the up-down direction, or it can be a curved passage that passes through the upper and lower surfaces of the dense plug. Examples of the curved passage that passes through the upper and lower surfaces of the dense plug include spiral passages and zigzag passages. The diameter of the flow path cross section of the internal gas flow path is preferably greater than 0.1 mm and less than 1 mm. One dense plug can have multiple internal gas flow paths. The porosity of the dense portion of the dense plug is preferably less than 0.1%. As with the porous insulating gas plug 40 described above, ceramics such as alumina or aluminum nitride can be used as the dense plug. For example, the dense plug can be manufactured by firing a molded body formed using a 3D printer or by firing a molded body formed by die casting. Details of dense plugs having curved, continuous internal gas flow paths and die casting are disclosed in, for example, Japanese Patent No. 7149914. In the above embodiment, the gas supply passage 31 is a through-hole extending vertically through the conductive plate 30, but the present invention is not limited thereto. The gas supply passage 31 is not limited to extending vertically and may be curved along the way. The gas supply passage 31 may include one or more first gas passages opening on the lower surface of the conductive plate 30 and fewer in number than the plug chambers 32, and a plurality of second gas passages branching from and extending from the first gas passages and corresponding one-to-one with the plug chambers 32. In the above embodiment, the ceramic plate 20 and the conductive plate 30 are bonded together using the insulating bonding sheet 60 . However, a conductive bonding layer such as a metal bonding layer may be used instead of the bonding sheet 60 . In the above embodiment, the ceramic plate 20 has an electrostatic electrode built into it as the electrode 22. However, a heater electrode (resistive heating element) may be built into it instead of or in addition to it. In this case, a heater power supply is connected to the heater electrode. The ceramic plate 20 may have a single layer of electrodes built into it, or may have two or more layers built into it with gaps between them. In the above embodiment, lift pin holes may be provided through the wafer stage 10. These holes are holes through which lift pins are inserted to move the wafer W up and down relative to the wafer placement surface 21. If the wafer W is supported by, for example, three lift pins, three lift pin holes are provided. Industrial applicability The present invention can be utilized in, for example, an apparatus for processing wafers. Explanation of symbols 10, 110 Wafer placement table, 20 Ceramic plate, 21 Wafer placement surface, 22 Electrode, 26 Fine hole, 27, 127 Fine hole side space, 30 Conductive plate, 31 Gas supply path, 32 Plug chamber, 40, 140 Insulating gas passes through plug, 41 Main body, 42 Protrusion, 44 Gas outlet portion, 48 Elastic component, 50, 150 Dense insulating film, 60 Adhesive sheet, 70 Dense insulating film, 910 Wafer placement table, 940 Insulating gas passes through plug, 951, 952 Dense insulating film, R1, R2 discharge paths, S gap, W wafer.

Claims

1. A wafer loading platform, wherein: have: a ceramic plate having a wafer placement surface on its upper surface, provided with fine holes extending therethrough in the vertical direction, and having electrodes built therein; a conductive plate bonded to the lower surface of the ceramic plate and provided with a gas supply passage; a plug chamber configured as a recessed portion extending from the upper surface of the conductive plate toward the lower surface of the conductive plate and communicating with the fine hole and the gas supply passage; an insulating gas passage plug, the insulating gas passage plug being disposed in the plug chamber and capable of passing gas therethrough; and A dense insulating film allows ventilation of the insulating gas through a gas outlet portion of the upper surface of the plug, which serves as a gas flow path toward the fine hole, and is arranged so as to span the upper surface of the conductive plate and the upper surface of the insulating gas passage plug to cover a boundary portion between the upper surface of the conductive plate and the upper surface of the insulating gas passage plug.

2. The wafer stage according to claim 1, wherein: A convex portion is formed on the upper surface of the insulating gas passage plug, the upper surface of which serves as the gas outlet portion. An upper surface of the dense insulating film and an upper surface of the protrusion are located on the same plane.

3. The wafer stage according to claim 1 or 2, wherein: The dense insulating film is a sprayed film or an aerosol deposited film.

4. The wafer stage according to claim 1 or 2, wherein: The wafer stage includes an elastic member disposed between a lower surface of the insulating gas passage plug and a bottom surface of the plug chamber.

5. The wafer stage according to claim 4, wherein: The elastic component is made of heat-resistant resin.

6. The wafer stage according to claim 1 or 2, wherein: The insulating gas passage plug is a porous body.

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