Electrostatic chuck

Abstract

To provide an electrostatic chuck capable of suppressing variations of a flow amount of a gas while preventing an insulation damage in a gas hole with a ventilation plug.SOLUTION: An electrostatic chuck 10 comprises: a dielectric substrate 100; a base plate 200 that is made of a metal member bonded to the dielectric substrate 100, and in which a gas hole 240 is formed; and a ventilation plug 400 that is arranged into an inner part of the gas hole 240. The ventilation plug 400 includes: a porous part 410 that is a part formed by a ceramic having a ventilation property; and a dense part 420 that is a part formed by a dense ceramic without having the ventilation property, and surrounds the porous part 410 over a whole periphery from an outer peripheral side. The porous part 410 and the dense part 420 are integrated with each other by sinter without nipping a bonding material formed by a material other than the ceramic.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electrostatic chuck. [Background technology]

[0002] For example, in semiconductor manufacturing equipment such as a CVD device, an electrostatic chuck is provided as a device for attracting and holding a substrate such as a silicon wafer to be processed. The electrostatic chuck includes a dielectric substrate provided with an attracting electrode and a base plate for supporting the dielectric substrate, which are joined together. When a voltage is applied to the attracting electrode, an electrostatic force is generated, and the substrate placed on the dielectric substrate is attracted and held.

[0003] An inert gas such as helium is supplied to the space between the dielectric substrate and the substrate for the purpose of adjusting the temperature of the substrate during processing, etc. For example, as described in Patent Document 1 below, the inert gas is supplied to the space through gas holes formed in each of the base plate and the dielectric substrate.

[0004] During substrate processing, the potential of the substrate and its surroundings increases due to the incidence of plasma and the application of voltage to the chucking electrode. Meanwhile, the potential of the base plate is maintained at the same potential (e.g., ground potential) as the surrounding components constituting the semiconductor manufacturing equipment. For this reason, dielectric breakdown is likely to occur between the high potential portion of the base plate, particularly on the inner surface of the gas hole. If part of the plasma flows into the inside of the gas hole, the above-mentioned dielectric breakdown becomes even more likely to occur.

[0005] Therefore, as described in, for example, Patent Document 1 below, a porous plug is placed inside the gas hole of the base plate to prevent dielectric breakdown. The porous plug is a porous member made of an insulating material such as ceramic. By placing the porous plug in the gas hole, it is possible to increase the dielectric strength while maintaining gas permeability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7175773 Summary of the Invention [Problem to be solved by the invention]

[0007] If the entire porous plug is made of a porous material, the inner surface of the gas hole, which is a metal, is exposed to the internal space of the gas hole through the porous material, and therefore the dielectric strength may not be sufficiently ensured. As a measure to reliably prevent dielectric breakdown on the inner surface of the gas hole, it is considered to cover the outer periphery of the porous material with a dense cylindrical material, as described in the above-mentioned Patent Document 1. However, since the porous material and the cylindrical material are ceramic members that are individually manufactured, it is considered that a gap is formed between the two due to dimensional tolerances, etc. This gap is undesirable because it can become a path of dielectric breakdown toward the base plate.

[0008] In order to eliminate the gap, it is conceivable to use an adhesive to bond the outer peripheral surface of the porous member and the inner peripheral surface of the cylindrical member. However, in such a configuration, part of the uncured (i.e., liquid) adhesive penetrates into the inside of the porous member during bonding and then hardens. As a result, the cross-sectional area of ​​the flow passage inside the porous member becomes smaller, and furthermore, the area is not constant, which creates a new problem that the flow rate of the gas supplied to the substrate side through the ventilation plug varies greatly.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrostatic chuck that can suppress variation in the gas flow rate while preventing dielectric breakdown in the gas hole by using a ventilation plug. [Means for solving the problem]

[0010] In order to solve the above problems, an electrostatic chuck according to the present invention includes a dielectric substrate having a first gas hole, a base plate which is a metal member bonded to the dielectric substrate and has a second gas hole formed therein and connected to the first gas hole, and a vent plug disposed inside the second gas hole. The vent plug has a porous portion which is a portion formed of porous ceramic having gas permeability, and a dense portion which is a portion formed of dense ceramic having no gas permeability and which surrounds the porous portion from the outer periphery side all around. The porous portion and the dense portion are integrated with each other by sintering without sandwiching a bonding material made of a material other than ceramic between them.

[0011] In an electrostatic chuck having such a configuration, the entire vent plug is not porous, and further includes a dense portion that surrounds the entire periphery of the porous portion from the outer periphery side. By providing the dense portion between the inner surface of the second gas hole and the porous portion, it is possible to prevent dielectric breakdown to the inner surface of the second gas hole.

[0012] Since the porous portion and the dense portion are integrated with each other by sintering, there is no gap between them, and therefore no dielectric breakdown occurs through the gap toward the base plate.

[0013] Furthermore, since no bonding material such as an adhesive is present between the porous portion and the dense portion, the cross-sectional area of ​​the flow passage in the porous portion does not become smaller due to the infiltration of the adhesive, and the flow rate of the gas passing through the vent plug does not vary.

[0014] The porous portion and the dense portion may be directly connected to each other without using any particular bonding material, or may be connected to each other via a bonding material made of a ceramic material. In either case, it is sufficient that the entire porous plug including the porous portion and the dense portion is integrated by sintering. Effect of the Invention

[0015] According to the present invention, it is possible to provide an electrostatic chuck that can suppress variations in the gas flow rate while preventing dielectric breakdown in the gas hole by using a ventilation plug. [Brief description of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of an electrostatic chuck according to an embodiment of the present invention. [Diagram 2] 2 is an enlarged view showing the configuration of a ventilation plug and its surrounding area in the electrostatic chuck of FIG. 1. [Diagram 3] FIG. 13 is a diagram showing the configuration of a ventilation plug. [Figure 4] 11A and 11B are diagrams for explaining problems that arise when a ventilation plug according to a comparative example is used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0018] The electrostatic chuck 10 according to this embodiment is configured to electrostatically attract and hold a substrate W to be processed inside a semiconductor manufacturing apparatus (not shown), such as a CVD film forming apparatus. The substrate W is, for example, a silicon wafer. The electrostatic chuck 10 may be used in an apparatus other than a semiconductor manufacturing apparatus.

[0019] 1 shows, in a schematic cross-sectional view, the configuration of an electrostatic chuck 10 in a state in which the electrostatic chuck 10 attracts and holds a substrate W. The electrostatic chuck 10 includes a dielectric substrate 100, a base plate 200, and a bonding layer 300.

[0020] The dielectric substrate 100 is a substantially disk-shaped member made of a sintered ceramic body. The dielectric substrate 100 contains, for example, high-purity aluminum oxide (Al2O3), but may contain other materials. The purity, type, and additives of the ceramics in the dielectric substrate 100 can be appropriately set in consideration of the plasma resistance and other properties required of the dielectric substrate 100 in semiconductor manufacturing equipment.

[0021] 1 of the dielectric substrate 100 is a "mounting surface" on which the substrate W is placed. Also, a lower surface 120 of the dielectric substrate 100 in FIG. 1 is a "bonded surface" that is bonded to a base plate 200 via a bonding layer 300 described below. The viewpoint when the electrostatic chuck 10 is viewed from the side of the surface 110 along a direction perpendicular to the surface 110 is hereinafter also referred to as a "top view".

[0022] An adsorption electrode 130 is embedded inside the dielectric substrate 100. The adsorption electrode 130 is a thin, flat layer made of a metal material such as tungsten, and is disposed so as to be parallel to the surface 110. The material of the adsorption electrode 130 may be molybdenum, platinum, palladium, or the like, in addition to tungsten. When a voltage is applied to the adsorption electrode 130 from the outside via the power supply path 13, an electrostatic force is generated between the surface 110 and the substrate W, thereby adsorbing and holding the substrate W. Two adsorption electrodes 130 may be provided as so-called "bipolar" electrodes as in this embodiment, or only one may be provided as a so-called "monopolar" electrode.

[0023] In Fig. 1, the entire power supply line 13 is depicted in a simplified manner. A portion of the power supply line 13 inside the dielectric substrate 100 is configured as, for example, a long and narrow via (hole) filled with a conductor, and an electrode terminal (not shown) is provided at the lower end thereof. A portion of the power supply line 13 penetrating a base plate 200 described below is a conductive metal member (for example, a bus bar) having one end connected to the electrode terminal. A through hole (not shown) for inserting the power supply line 13 is formed in the base plate 200. For example, a cylindrical insulating member may be provided between the inner surface of the through hole and the power supply line 13.

[0024] 1, a space SP is formed between the dielectric substrate 100 and the substrate W. When a process such as film formation is performed in the semiconductor manufacturing apparatus, helium gas for temperature adjustment is supplied from the outside to the space SP through gas holes 140 described below. By providing helium gas between the dielectric substrate 100 and the substrate W, the thermal resistance between them is adjusted, and the temperature of the substrate W is thereby maintained at an appropriate temperature. The gas for temperature adjustment supplied to the space SP may be a type of gas other than helium.

[0025] A seal ring 111 and dots 112 are provided on a surface 110 which is an attraction surface, and a space SP is formed around these.

[0026] The seal ring 111 is a wall that divides the space SP at the outermost position. The upper end of the seal ring 111 forms part of the surface 110 and abuts against the substrate W. Note that a plurality of seal rings 111 may be provided to divide the space SP. With this configuration, it is possible to individually adjust the pressure of the helium gas in each space SP and make the surface temperature distribution of the substrate W during processing more uniform.

[0027] 1, the portion marked with the reference symbol "116" is the bottom surface of the space SP. Hereinafter, this portion will also be referred to as the "bottom surface 116." The seal ring 111, together with the dots 112 described below, is formed by digging down a part of the surface 110 to the position of the bottom surface 116.

[0028] The dots 112 are circular protrusions protruding from the bottom surface 116. A plurality of dots 112 are provided and are distributed approximately evenly on the mounting surface of the dielectric substrate 100. The upper end of each dot 112 forms part of the surface 110 and abuts against the substrate W. By providing a plurality of such dots 112, bending of the substrate W is suppressed.

[0029] A groove 113 is formed in the bottom surface 116 of the space SP. The groove 113 is formed so as to recede further from the bottom surface 116 toward the surface 120. The groove 113 is formed for the purpose of quickly diffusing the helium gas supplied from the gas hole 140 into the space SP and making the pressure distribution in the space SP approximately uniform within a short period of time.

[0030] The dielectric substrate 100 is formed with gas holes 140 extending vertically from the surface 120 toward the surface 110. The end of the gas hole 140 on the surface 110 side opens at the bottom of the groove 113. The dielectric substrate 100 is formed with a plurality of gas holes 140, which are arranged along the groove 113. The gas holes 140 constitute a part of a flow path for supplying gas into the space SP, and are connected to the space SP at the bottom of the groove 113. When the space SP is divided into a plurality of spaces by the seal ring 111, one or more gas holes 140 are formed to be connected to each of the divided spaces SP. The gas holes 140 correspond to the "first gas hole" in this embodiment.

[0031] 1, the portion of the gas hole 140 on the side of the surface 120 has a larger diameter than the portion on the side of the surface 110, and a vent plug 145 is disposed inside the portion. The vent plug 145 is a porous body made of alumina, for example, and has air permeability throughout. By disposing such a vent plug 145 inside the gas hole 140, it is possible to suppress the occurrence of dielectric breakdown in the path through the gas hole 140 while ensuring the flow of gas through the gas hole 140.

[0032] The base plate 200 is a substantially disk-shaped metal member that supports the dielectric substrate 100. The base plate 200 is formed of a metal material such as aluminum. The upper surface 210 of the base plate 200 in FIG. 1 is a "bonded surface" that is bonded to the dielectric substrate 100 via a bonding layer 300.

[0033] 1, the base plate 200 is formed with gas holes 240 extending vertically from the surface 210 toward the opposite surface 220. The gas holes 240 are formed at positions overlapping with the gas holes 140 of the dielectric substrate 100 in a top view, and communicate with the gas holes 140 via through holes 310 provided in the bonding layer 300. The gas holes 240, together with the gas holes 140 of the dielectric substrate 100, form part of a flow path for supplying helium gas toward the space SP. The gas holes 240 correspond to the "second gas holes" in this embodiment.

[0034] The gas holes 240 may be formed so as to extend linearly as in the present embodiment, but may be formed so as to bend on the way to the surface 220. Also, the gas holes 240 on the surface 210 side may be aggregated into a small number of flow paths inside the base plate 200, and the flow paths may be configured to extend to the surface 220 side.

[0035] 1, the portion of gas hole 240 on the surface 210 side has a larger diameter than the portion on the surface 220 side, and a vent plug 400 is disposed inside. Like vent plug 145, vent plug 400 is a member provided for the purpose of suppressing the occurrence of dielectric breakdown, but its configuration differs from that of vent plug 145. The specific configuration of vent plug 400 will be described later.

[0036] A coolant flow path 250 for flowing a coolant is formed inside the base plate 200. When a process such as film formation is performed in the semiconductor manufacturing apparatus, a coolant is supplied to the coolant flow path 250 from the outside, thereby cooling the base plate 200. Heat generated in the substrate W during the process is transferred to the coolant via the helium gas in the space SP, the dielectric substrate 100, and the base plate 200, and is discharged to the outside together with the coolant.

[0037] An insulating film may be formed on the surface of the base plate 200. The insulating film may be formed so as to cover only a part of the surface of the base plate 200, not the entire surface. For example, the insulating film may be formed so as to cover only the side surface portion excluding the surface 210 and the surface 220, that is, the exposed portion exposed to plasma or the like inside the semiconductor manufacturing apparatus. In contrast, the insulating film may be formed so as to cover a range including at least the entire surface 210. For example, an alumina film formed by thermal spraying can be used as the insulating film. By covering the surface of the base plate 200 with an insulating film, the dielectric strength voltage of the base plate 200 can be increased.

[0038] The bonding layer 300 is a layer provided between the dielectric substrate 100 and the base plate 200, and bonds the two together. The bonding layer 300 is formed by curing an adhesive made of an insulating material. In this embodiment, a silicone adhesive is used as the adhesive. However, the bonding layer 300 may be formed by curing another type of adhesive. In any case, it is preferable to use a material with as high a thermal conductivity as possible as the material for the bonding layer 300 so that the thermal resistance between the dielectric substrate 100 and the base plate 200 is small.

[0039] A specific configuration of the vent plug 400 provided in the gas hole 240 will be described below. Fig. 2 shows an enlarged view of the vent plug 400 and its vicinity in Fig. 1.

[0040] As described above, the portion of gas hole 240 on the surface 210 side is enlarged in diameter compared to the portion on the surface 220 side, and vent plug 400 is disposed in this enlarged portion. The enlarged portion of gas hole 240 is hereinafter also referred to as "enlarged diameter portion 241." Enlarged diameter portion 241 is a substantially cylindrical space, and its central axis is perpendicular to surface 210.

[0041] The vent plug 400 is a cylindrical member, and its shape is generally the same as the shape of the internal space of the enlarged diameter portion 241. In other words, the central axis of the vent plug 400 coincides with the central axis of the enlarged diameter portion 241, and the diameter of the outer circumferential surface of the vent plug 400 is generally equal to the diameter of the inner circumferential surface of the enlarged diameter portion 241.

[0042] The vent plug 400 has a porous portion 410 and a dense portion 420 .

[0043] The porous portion 410 is a portion formed of porous ceramic having gas permeability. Gas passing through the gas hole 240 is supplied to the space SP through the porous portion 410 of the vent plug 400. The porosity of the porous portion 410 is appropriately set according to the balance between the gas permeability required for gas supply to the space SP and the necessary dielectric strength voltage. In this embodiment, the porous portion 410 is formed of the same porous alumina as the vent plug 145, but may be formed of other ceramic materials. The porous portion 410 is cylindrical, and its central axis coincides with the central axis of the entire vent plug 400.

[0044] The dense portion 420 is a portion formed of dense ceramic that does not have gas permeability. In other words, the dense portion 420 is a portion of the vent plug 400 through which gas does not pass. In this embodiment, the dense portion 420 is formed of alumina, but may be formed of other ceramic materials. In addition, the ceramic material forming the porous portion 410 and the ceramic material forming the dense portion 420 may be the same type of material as in this embodiment, but may also be different types of materials.

[0045] The dense portion 420 has a cylindrical shape, and its central axis coincides with the central axis of the entire vent plug 400. The above-mentioned porous portion 410 is accommodated inside the dense portion 420. The dimension of the dense portion 420 in the vertical direction in FIG. 2 is the same as the dimension of the porous portion 410 in the same direction. In this way, the dense portion 420 surrounds the porous portion 410 from the outer periphery side all around. In addition, the overall shape of the vent plug 400 including the porous portion 410 and the dense portion 420 is cylindrical as described above.

[0046] The porous portion 410 and the dense portion 420 are not separate members that can be separated from each other, but are an integral member. The porous portion 410 and the dense portion 420 are manufactured by a method described later, and are integrated with each other by sintering.

[0047] Fig. 3(A) shows a cross section of the vent plug 400 cut along a plane passing through its central axis, similar to Fig. 2 etc. Fig. 3(B) shows an example of an image obtained by observing a part of the cross section, specifically the boundary portion between the porous portion 410 and the dense portion 420, using an electron microscope. The portion marked with the reference symbol "411" in Fig. 3(B) is a cross section of a pore formed in the porous portion 410.

[0048] In this specification, "integrated with each other by sintering" refers to a state in which the ceramic particles constituting the dense portion 420 and the ceramic particles contained in the porous portion 410 are bonded directly or through grain boundaries, as illustrated in FIG. 3(B). Specifically, only Al2O3 and other impurities (SiO2), which are the ceramic materials constituting the porous portion 410 and the dense portion 420, are present at the boundary between them, and no bonding layer made of a material other than ceramic (e.g., silicone adhesive, etc.) is present. The porous portion 410 and the dense portion 420 are entirely made up of a single ceramic sintered body. The fact that they are integrated with each other by sintering can be confirmed, for example, by observing the cross section of the vent plug 400 at a magnification of 500 times using a scanning electron microscope. The observation conditions may be general observation conditions for ceramic sintered bodies, and thermal etching, etc. may be performed as necessary.

[0049] The vent plug 400 is a member for suppressing the occurrence of dielectric breakdown in the gas hole 240. If the dense portion 420 is not provided on the outer periphery of the vent plug 400 and the entire vent plug 400 is configured as the porous portion 410, the inner surface of the metal enlarged diameter portion 241 is exposed to the internal space of the gas hole 240 through the porous portion 410. Therefore, as shown by the arrow AR in FIG. 2, the possibility of dielectric breakdown occurring in the path from the dielectric substrate 100 side toward the outer periphery of the vent plug 400 increases. Therefore, in this embodiment, the dense portion 420 is provided on the outer periphery of the vent plug 400 to prevent dielectric breakdown in the above path.

[0050] As a configuration of the vent plug 400 for preventing dielectric breakdown, for example, as shown in the comparative example of FIG. 4(A), the porous portion 410 and the dense portion 420 may be formed in advance as separate sintered bodies and arranged side by side inside the enlarged diameter portion 241. However, in such a configuration, due to dimensional tolerances of the two members, a minute gap G may be formed between the porous portion 410 and the dense portion 420, and dielectric breakdown may occur along the path along the gap G. In contrast, in this embodiment, the porous portion 410 and the dense portion 420 are an integral sintered body and no gap is formed between them, so that dielectric breakdown does not occur along the above path.

[0051] If the porous portion 410 and the dense portion 420 are formed in advance as separate sintered bodies and then bonded together with, for example, a silicone adhesive, the gap G described above will not be formed. However, when bonding using an adhesive, part of the uncured (i.e., liquid) adhesive will penetrate from the outer periphery of the porous portion 410 to the inside and then harden. Figure 4(B) shows a schematic diagram of an area 425 into which the adhesive has penetrated.

[0052] In such a state, the flow passage cross-sectional area inside the porous portion 410 is reduced by the area of ​​the region 425, and furthermore, the area is not constant. This causes a new problem that the flow rate of the gas supplied to the space SP through the vent plug 400 varies greatly. In contrast, in this embodiment, since no adhesive or the like is interposed between the porous portion 410 and the dense portion 420, the entire porous portion 410 can always function as a gas flow passage, and the above-mentioned flow rate variation does not occur.

[0053] As described above, in the electrostatic chuck 10 of the present embodiment, while the ventilation plug 400 prevents dielectric breakdown in the gas hole 240, it is possible to suppress variation in the flow rate of the gas supplied to the space SP.

[0054] Instead of providing the dense portion 420 on the outer periphery of the porous portion 410, it is also possible to form a sprayed film of alumina or the like so as to cover the outer surface of the porous portion 410. However, the sprayed film may cause problems such as a reduction in the cross-sectional area of ​​the flow path and variations, as in the comparative example of FIG. 4(B), since a part of the sprayed film penetrates into the porous portion 410. Also, it may be difficult to ensure a sufficient thickness for the sprayed film to fully exert the dielectric strength voltage. Therefore, even when compared with a configuration in which a sprayed film is provided, this embodiment is still preferable.

[0055] In this embodiment, each of the porous portion 410 and the dense portion 420 is made of high-purity alumina ceramic having a purity of 92% or more. By increasing the purity of the material constituting each portion, the integrity of the entire vent plug 400 can be further improved. The purity of the material can be measured using ICP mass spectrometry, XRF elemental analysis, or the like.

[0056] The average particle diameter of the ceramic in each of the porous portion 410 and the dense portion 420 can be set arbitrarily by selecting the material. However, it is preferable to set the average particle diameter of the ceramic in the dense portion 420 smaller than the average particle diameter of the ceramic in the porous portion 410. By setting the average particle diameter of the dense portion 420 to a small value, the insulation performance of the dense portion 420 can be sufficiently ensured. In addition, since the dense portion 420 can be made thin, it is also possible to increase the diameter of the porous portion 410 to ensure the flow rate of gas.

[0057] The thickness of dense portion 420 is uniform over the entire circumference. The "thickness" here refers to the dimension of dense portion 420 along a direction perpendicular to the central axis of ventilation plug 400, and is "T" shown in Fig. 3(A). By making the thickness of dense portion 420 uniform over the entire circumference, there is no local decrease in dielectric strength voltage in a portion along the circumferential direction, and a sufficient dielectric strength voltage can be ensured over the entire circumference.

[0058] A voltage of 3 kV or more may be applied to the gas holes 240. Even in such a case, in order to reliably prevent dielectric breakdown, the thickness of the dense portion 420 is preferably 0.1 mm or more, and more preferably 0.3 mm or more. The thickness T of the dense portion 420 shown in Fig. 3(A) may be 30% or more of the diameter D of the inner surface of the dense portion 420 (which may also be the diameter of the outer surface of the porous portion 410).

[0059] In this embodiment, the vent plug 400 is simply fitted into the enlarged diameter portion 241. In other words, the outer surface of the dense portion 420 and the inner surface of the enlarged diameter portion 241 are not bonded with an adhesive or the like, and a small gap (not shown) is formed between them. However, as shown in FIG. 2, the end of the gap on the dielectric substrate 100 side is blocked by the bonding layer 300. Therefore, no dielectric breakdown occurs through the gap. To realize such a configuration, the diameter of the through hole 310 provided in the bonding layer 300 may be set to be larger than the diameter of the inner surface of the dense portion 420 and smaller than the diameter of the outer surface of the dense portion 420.

[0060] A method for manufacturing the ventilation plug 400 will be described. First, a porous member and a cylindrical molded body are prepared. The porous member is a porous ceramic sintered body and has a cylindrical shape. The porous member is a part that will eventually become the porous portion 410.

[0061] The cylindrical compact is a dense ceramic compact, and has a cylindrical shape. That is, a cylindrical hole is formed in the cylindrical compact. The cylindrical compact is a part that will eventually become the dense part 420. When the porous member and the cylindrical compact are prepared, the porous member is already a sintered body, while the cylindrical compact is an unsintered body. At this time, the diameter of the inner surface of the cylindrical compact is slightly larger than the diameter of the outer surface of the porous member.

[0062] Next, the porous member is placed inside the hole of the cylindrical molded body. In other words, the porous member is covered from the outer periphery side to the entire periphery by the cylindrical molded body. As a result, the porous member and the cylindrical molded body as a whole have a substantially cylindrical shape. The entire inner surface of the cylindrical molded body and the entire outer surface of the porous member face each other, and a gap (not shown) is formed between them.

[0063] In this state, the porous member and the cylindrical molded body are fired at the same time. During this process, the cylindrical molded body gradually shrinks as it is fired, and the gap between them becomes zero. In other words, the inner surface of the cylindrical molded body and the outer surface of the porous member are in close contact with each other with no gaps. As a result of firing in this state, the porous member and the cylindrical molded body are bonded together and integrated, and the whole becomes a single sintered body.

[0064] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Any design modifications made by a person skilled in the art to these specific examples are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples and their arrangements, conditions, shapes, etc. are not limited to those exemplified and can be changed as appropriate. The combination of each of the elements of each of the above-mentioned specific examples can be changed as appropriate as long as no technical contradiction occurs. [Explanation of symbols]

[0065] 10: Electrostatic chuck 100: Dielectric substrate 140: Gas hole 200: Base plate 240: Gas hole 400: Ventilation plug 410: Porous part 420: Dense part

Claims

1. a dielectric substrate having a first gas hole formed therein; a base plate which is a metal member joined to the dielectric substrate and has a second gas hole formed therein and connected to the first gas hole; a vent plug disposed within the second gas hole; The vent plug comprises: A porous portion formed of a porous ceramic having air permeability; a dense portion that is made of a dense ceramic that does not have gas permeability and that completely surrounds the porous portion from the outer periphery side; The electrostatic chuck is characterized in that the porous portion and the dense portion are integrated with each other by sintering without sandwiching a bonding material made of a material other than ceramic between them.

2. 2. The electrostatic chuck according to claim 1, wherein the purity of the ceramic in said porous portion and the purity of the ceramic in said dense portion are both 92% or more.

3. 2. The electrostatic chuck according to claim 1, wherein an average grain size of the ceramic in the dense portion is smaller than an average grain size of the ceramic in the porous portion.

4. 2. The electrostatic chuck according to claim 1, wherein the dense portion has a cylindrical shape and a uniform thickness over the entire circumference.

5. 5. The electrostatic chuck according to claim 4, wherein the dense portion has a thickness of 0.1 mm or more.

6. 5. The electrostatic chuck according to claim 4, wherein the thickness of the dense portion is 30% or more of the diameter of the inner surface of the dense portion.

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