Electrostatic chuck, electrode for electrostatic chuck, and manufacturing method for electrostatic chuck

Abstract

To provide a technique of suppressing the poor insulation due to burr remaining in an opening part of a penetration hole provided in an electrode.SOLUTION: An electrostatic chuck 100 includes a ceramic base material 110, and an electrode 120 made of metal that is embedded in the ceramic base material 110. The electrode 120 is embedded at a position 0.1 mm to 10 mm away from an upper surface 111 of the ceramic base material 110 in an up-down direction. The electrode 120 has a thickness (length in the up-down direction) of 0.05 mm or more. On an upper surface of the electrode 120, an outer edge part of an opening of a plurality of penetration holes 124 does not protrude upward compared to a part of the upper surface of the electrode 120 except the outer edge part of the opening of the penetration holes 124.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electrostatic chuck, an electrode for an electrostatic chuck, and a method for manufacturing an electrostatic chuck. [Background technology]

[0002] Patent Document 1 discloses a substrate holding member including a chuck body made of a ceramic sintered body containing AlN and an electrode embedded in the chuck body, in which the electrode is made of a flat punched metal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-77995 A Summary of the Invention [Problem to be solved by the invention]

[0004] When multiple through holes are formed in an electrode by punching metal, as in the board holder described in Patent Document 1, burrs protruding above the upper surface of the electrode remain at the openings of the through holes, which may cause insulation failure.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide a technique for suppressing insulation failure caused by burrs remaining in the opening portion of a through hole provided in an electrode. [Means for solving the problem]

[0006] According to an aspect of the present invention, a ceramic substrate having an upper surface and a lower surface facing the upper surface in a vertical direction, a metal electrode embedded in the ceramic base at a position 0.1 mm to 10 mm away from the upper surface of the ceramic base in the vertical direction; The electrode has a thickness of 0.05 mm or more in the vertical direction, and has a plurality of through holes penetrating the electrode in the vertical direction; An electrostatic chuck is provided, characterized in that outer edge portions of the openings of the multiple through holes in the upper surface of the electrode do not protrude above portions of the upper surface of the electrode excluding the outer edge portions of the openings of the multiple through holes. Effect of the Invention

[0007] In the above aspect, the outer edge portions of the openings of the plurality of through holes on the upper surface of the electrode do not protrude above a portion of the upper surface of the electrode excluding the outer edge portions of the openings of the plurality of through holes, thereby making it possible to suppress insulation failure caused by burrs. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an electrostatic chuck 100 . [Diagram 2] FIG. 2 is a schematic explanatory diagram showing the shapes of the ceramic base 110 and the electrode 120. As shown in FIG. [Diagram 3] FIG. 3 is a schematic diagram of an electrode 120. [Figure 4] 1(a) to 1(e) are diagrams showing a flow of a method for producing the ceramic base 110. FIG. [Diagram 5] 1(a) to 1(d) are diagrams showing the flow of another method for producing the ceramic base 110. FIG. [Figure 6] 1(a) is an explanatory diagram showing a state in which a burr remains at the opening of through hole 124 protruding above the upper surface of electrode 120, and FIG. 1(b) is an explanatory diagram showing a state in which a burr does not remain at the opening of through hole 124 protruding above the upper surface of electrode 120. [Figure 7] 1A is an explanatory diagram showing a state in which no fraying occurs in the electrode 120, and FIG. 1B is an explanatory diagram showing a state in which fraying occurs in the electrode 120. FIG. [Figure 8] FIG. 8 is an explanatory diagram showing a state in which openings of different sizes are mixed. [Figure 9]FIG. 9 is an explanatory diagram showing a state in which the opening of the through-hole 124 is closed by a curve. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Electrostatic Chuck 100> An electrostatic chuck 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. The electrostatic chuck 100 according to this embodiment is a substrate holding member for attracting and holding a semiconductor wafer such as a silicon wafer (hereinafter simply referred to as a wafer 10). In the following description, a top-bottom direction 5 is defined based on a state in which the electrostatic chuck 100 is installed so as to be usable (the state shown in FIG. 1). As shown in FIG. 1, the electrostatic chuck 100 according to this embodiment includes a ceramic base material 110, an electrode 120 (see FIG. 2), a shaft 130, and a power supply line 140 (see FIG. 2).

[0010] The ceramic base 110 is a member having a circular plate shape with a diameter of 12 inches (about 300 mm), and the wafer 10 to be held is placed on its upper surface 111. In FIG. 1, the wafer 10 and the ceramic base 110 are shown separated from each other to make the drawing easier to see. As shown in FIG. 1, an annular convex portion 152 (hereinafter simply referred to as the annular convex portion 152) and a plurality of convex portions 156 are provided on the upper surface 111 of the ceramic base 110. In FIG. 1, the number of the plurality of convex portions 156 is reduced compared to FIG. 2 to make the drawing easier to see. As shown in FIG. 2, a first gas flow passage 164, which will be described later, is formed inside the ceramic base 110. The ceramic base 110 can be formed of a ceramic sintered body such as aluminum nitride, silicon carbide, alumina, silicon nitride, or the like.

[0011] As shown in FIGS. 1 and 2, the annular convex portion 152 is an annular convex portion arranged on the outer periphery (outer edge) of the upper surface 111 of the ceramic base 110, and protrudes upward from the upper surface 111. As shown in FIG. 2, when the wafer 10 is placed on the ceramic base 110, the upper surface 152a of the annular convex portion 152 abuts against the lower surface of the wafer 10. That is, when the wafer 10 is placed on the ceramic base 110, the annular convex portion 152 is arranged at a position that overlaps with the wafer 10 in the up-down direction 5. A plurality of convex portions 156 are provided on the inner side of the annular convex portion 152 on the upper surface 111 of the ceramic base 110. All of the plurality of convex portions 156 have a cylindrical shape. In FIG. 2, in order to simplify the drawing, one of the plurality of convex portions 156 is arranged at approximately the center of the upper surface 111, and the remaining convex portions 156 are illustrated as being arranged on the circumference of four equally spaced concentric circles. However, the positions and / or number of the protrusions 156 are appropriately set depending on the application, action, and function.

[0012] The height of the annular convex portion 152 can be in the range of 5 μm to 50 μm. Similarly, the height of the plurality of convex portions 156 can be in the range of 5 μm to 50 μm. In this specification, the height of the annular convex portion 152 and the height of the plurality of convex portions 156 are defined as the length in the vertical direction from the upper surface 111 of the ceramic substrate 110. In addition, when the upper surface 111 of the ceramic substrate 110 is not flat and has, for example, a step, the highest position of the upper surface 111 of the ceramic substrate 110 is used as a reference and the height is defined as the length in the vertical direction from that point.

[0013] 2, an opening 164a of a first gas flow passage 164 is formed on the upper surface 111 between the innermost concentric circle in which the multiple protrusions 156 are arranged and the second innermost concentric circle. The first gas flow passage 164 is a gas flow passage having the opening 164a, and is formed inside the ceramic base material 110. The first gas flow passage 164 extends downward from the opening 164a. As described later, a lower end of the first gas flow passage 164 is joined to an upper end of a second gas flow passage 168 formed inside the shaft 130.

[0014] The first gas flow passage 164 can be used as a flow passage for supplying gas to a space (gap) defined by the upper surface 111 of the ceramic base 110 and the lower surface of the wafer 10. For example, a heat transfer gas for heat transfer between the wafer 10 and the ceramic base 110 can be supplied. For example, an inert gas such as helium or argon, or nitrogen gas can be used as the heat transfer gas. The heat transfer gas is supplied through the first gas flow passage 164 at a pressure set within a range of 100 Pa to 40000 Pa. In addition, when the process gas invades the gap inside the annular protrusion 152 from the gap between the upper surface 152a of the annular protrusion 152 and the lower surface of the wafer 10, the gas can be exhausted through the first gas flow passage 164. At this time, the differential pressure between the pressure outside the gap and the pressure inside the gap can be adjusted by adjusting the exhaust pressure. As a result, the wafer 10 can be adsorbed toward the upper surface of the ceramic base 110.

[0015] An electrode 120 cut into the shape shown in FIG. 2 is embedded inside the ceramic base 110. The electrode 120 can be formed of a foil or plate material of molybdenum (Mo), tungsten (W), an alloy containing molybdenum and / or tungsten, or the like. The foil is a metal material with a thickness of less than 0.1 mm, and the plate is a metal material with a thickness of 0.1 mm or more. The purity of tungsten and molybdenum may be 99% or more. Alternatively, as described later, molybdenum to which rare earth elements are added can be used as the electrode 120. The thickness of the electrode 120 is preferably 0.05 mm or more, and more preferably 0.16 mm or more and 10 mm or less. The details of the shape of the electrode 120 will be described later. In addition to the electrode 120, a high-frequency electrode for generating plasma above the ceramic base 110 may be embedded inside the ceramic base 110.

[0016] As shown in FIGS. 1 and 2, a shaft 130 is connected to a lower surface 113 of the ceramic base 110. The shaft 130 has a hollow, generally cylindrical cylindrical portion 131 and two large diameter portions 132 and 133. The large diameter portion 132 is provided above the cylindrical portion 131 (see FIG. 2), and the large diameter portion 133 is provided below the cylindrical portion 131 (see FIG. 1). The large diameter portions 132 and 133 have a diameter larger than that of the cylindrical portion 131. In the following description, the longitudinal direction of the cylindrical portion 131 is defined as the longitudinal direction 6 of the shaft 130. As shown in FIG. 1, in a state in which the electrostatic chuck 100 is in use, the longitudinal direction 6 of the shaft 130 is parallel to the up-down direction 5.

[0017] 2, a protrusion 114 for joining to a shaft 130 (hereinafter referred to as a joining protrusion 114) is provided on a lower surface 113 of the ceramic base material 110. There is no particular upper limit on the height of the joining protrusion 114, but in consideration of ease of manufacture, the height of the joining protrusion 114 is preferably 20 mm or less.

[0018] The upper surface of the cylindrical portion 131 is fixed to the lower surface 114B of the joining protrusion 114 of the ceramic base 110. The shaft 130 may be made of a ceramic sintered body such as aluminum nitride, silicon carbide, alumina, silicon nitride, or the like, like the ceramic base 110. Alternatively, in order to improve heat insulation, the shaft 130 may be made of a material having a lower thermal conductivity than the ceramic base 110.

[0019] As shown in Fig. 2, the shaft 130 has a hollow cylindrical shape, and a through hole extending in the longitudinal direction 6 (see Fig. 1) is formed inside the shaft 130 (region inside the inner diameter). A power supply line 140 for supplying power to the electrode 120 is arranged in the hollow portion (through hole) of the shaft 130. An upper end of the power supply line 140 is electrically connected to a terminal portion 121 (see Fig. 3) arranged on the electrode 120. The power supply line 140 is connected to a power source (not shown). As a result, power is supplied to the electrode 120 via the power supply line 140.

[0020] 2, the second gas flow passage 168 extending in the up-down direction 5 is formed in the cylindrical portion 131 of the shaft 130. As described above, the upper end of the second gas flow passage 168 is connected to the lower end of the first gas flow passage 164. Note that in the above description, the shaft 130 is provided in the ceramic base 110. However, in the electrostatic chuck 100, there may be cases where the shaft 130 is not provided in the ceramic base 110.

[0021] Next, the shape of the electrode 120 will be described with reference to FIG. 3. The electrode 120 has two semicircular electrodes 120a and 120b arranged to face each other with a predetermined distance between them, and has a generally circular shape. In this embodiment, the outer diameter of the electrode 120 is 292 mm. The wafer 10 can be electrostatically attracted by applying a predetermined voltage (e.g., ±500 V) to each of the two semicircular electrodes 120a and 120b.

[0022] As shown in the enlarged view of FIG. 3, a plurality of through holes 124 are formed so as to be distributed throughout the electrode 120. In the following description, the ratio of the total open area of ​​the through holes 124 to the area of ​​the upper surface of the electrode 120 when no through holes are formed is called the aperture ratio. A plurality of through holes 124 are distributed in the electrode 120 so that the aperture ratio is 55% or more. By adjusting the aperture ratio, the electrostatic adsorption force and the impedance of the electrode 120 can be adjusted. The plurality of through holes 124 can be formed by etching. For example, the plurality of through holes 124 can be formed by forming a mask of a predetermined shape on the upper surface of the molybdenum foil (or tungsten foil) using a photoresist or dry film, and performing etching using an etching solution containing a mixture of phosphoric acid, nitric acid, acetic acid, and water. Other etching solutions are selected according to the metal to be etched.

[0023] Next, a method for manufacturing the electrostatic chuck 100 will be described. In the following, a case where the ceramic base 110 and the shaft 130 are made of aluminum nitride will be described as an example.

[0024] First, a method for manufacturing the ceramic base material 110 will be described. As shown in FIG. 4(a), granulated powder Q mainly composed of aluminum nitride (AlN) powder is placed in a bed-equipped carbon mold 601 and pre-pressed with a punch 602. The granulated powder Q contains 5 wt % or less of a sintering aid (for example, Y 2 O 3 ) is preferably included. A metal foil or plate having a thickness of 0.05 mm or more is prepared as the electrode 120. Then, a plurality of through holes 124 are formed in the electrode 120 by etching. Next, as shown in FIG. 4(b), the electrode 120 cut into a predetermined shape is placed on the pre-pressed granulated powder Q. The electrode 120 is placed so as to be parallel to a surface perpendicular to the pressing direction (the bottom surface of the bed-equipped mold 601). At this time, pellets of W or pellets of Mo may be embedded at the position of the terminal 121 (see FIG. 3) of the electrode 120.

[0025] As shown in FIG. 4(c), granulated powder Q is further put into the bed mold 601 so as to cover the electrode 120, and pressed and molded with a punch 602. Next, as shown in FIG. 4(d), the granulated powder Q with the electrode 120 embedded therein is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. Also, firing is preferably performed at a temperature of 1800° C. or more. Next, as shown in FIG. 4(e), blind holes are drilled to the electrode 120 in order to form the terminal 121. In addition, when a pellet is buried, blind holes are drilled to the pellet. Furthermore, a through hole for forming the gas flow path 164 may be formed as necessary. This allows the ceramic base material 110 having the gas flow path 164 formed therein to be produced.

[0026] The ceramic substrate 110 can also be manufactured by the following method. As shown in Fig. 5(a), a binder is added to aluminum nitride granulated powder Q, which is then CIP molded and processed into a disk shape to produce an aluminum nitride compact 610. Next, as shown in Fig. 5(b), the compact 610 is degreased to remove the binder.

[0027] As shown in FIG. 5(c), a recess 611 for embedding the electrode 120 is formed in the degreased molded body 610. As described above, a metal foil or plate having a thickness of 0.05 mm or more is prepared as the electrode 120, and a plurality of through holes are formed in the electrode 120 by etching. The electrode 120 is placed in the recess 611 of the molded body 610, and another molded body 610 is laminated. The recess 611 may be formed in the molded body 610 in advance. Next, as shown in FIG. 5(d), the laminated molded bodies 610 sandwiching the electrode 120 are fired in a pressed state to produce a fired body. The pressure applied during firing is preferably 1 MPa or more. In addition, firing is preferably performed at a temperature of 1800° C. or more. The process after producing the fired body is the same as the above-mentioned process, so a description thereof will be omitted.

[0028] The upper surface 111 of the ceramic base 110 thus formed is ground and polished. This allows the distance in the vertical direction 5 from the upper surface 111 of the ceramic base 110 to the electrode 120 to be adjusted. For example, the distance in the vertical direction 5 from the upper surface 111 of the ceramic base 110 to the electrode 120 can be set to 0.1 mm to 10 mm. Furthermore, the upper surface 111 is sandblasted to form a plurality of convex portions 156 and annular convex portion 152 on the upper surface 111. Note that sandblasting is a suitable processing method for forming the plurality of convex portions 156 and annular convex portion 152, but other processing methods can also be used.

[0029] The electrostatic chuck 100 is manufactured by fixing the shaft 130 to approximately the center of the lower surface 112 of the ceramic base 110 thus formed. The shaft 130 is formed by forming granulated powder P of aluminum nitride to which several wt % of binder has been added under hydrostatic pressure (about 1 MPa), processing the formed body into a predetermined shape, and then firing it in a nitrogen atmosphere.

[0030] <Effects of the embodiment> In the above embodiment, the electrostatic chuck 100 includes a ceramic base 110 and a metal electrode 120 embedded in the ceramic base 110. The electrode 120 is embedded at a position 0.1 mm to 10 mm away from the upper surface 111 of the ceramic base 110 in the vertical direction 5. The thickness (length in the vertical direction 5) of the electrode 120 is 0.05 mm or more. When the multiple through holes 124 of the electrode 120 are formed by mechanical processing such as punching, burrs protruding above the upper surface of the electrode 120 remain at the openings of the through holes 124 (see FIG. 6(a)). In this case, insulation failure is likely to occur due to the burrs. In particular, when the distance (insulating layer thickness) between the electrode 120 and the upper surface 111 of the ceramic base 110 is as thin as 1 mm or less, or even 0.3 mm or less, an electric field is excessively concentrated on the burrs, which is likely to cause insulation breakdown. In contrast, in the embodiment of the present application, as described above, the multiple through holes 124 formed in the electrode 120 are formed by etching. As a result, no burrs protruding above the upper surface of the electrode 120 remain at the openings of the through holes 124 (see FIG. 6(b)). In other words, the outer edge portions of the openings of the multiple through holes 124 on the upper surface of the electrode 120 do not protrude above the portion of the upper surface of the electrode 120 excluding the outer edge portions of the openings of the multiple through holes 124. As a result, insulation failure caused by burrs can be suppressed. In addition, when viewed in cross section on a plane parallel to the vertical direction, the R dimension of the outer edge portions of the openings of the through holes 124 can be set to 0.5 mm or more. This also contributes to suppressing insulation failure.

[0031] As described above, the electrode 120 of this embodiment is formed using a metal foil (metal plate) rather than a metal mesh. Therefore, contact resistance due to contact between the wires constituting the mesh does not occur. This makes it possible to suppress variation in the resistance value of the electrode 120. In addition, when the electrode 120 is formed using a metal mesh, excessive pressure is applied to the portion where the wires overlap each other vertically when the granulated powder Q in which the electrode 120 is embedded is pressed as described above, and cracks may occur inside the wires. In contrast, the electrode 120 of this embodiment is formed using a metal foil (metal plate) rather than a metal mesh, so there is no risk of cracks occurring inside the electrode 120 even when the granulated powder Q in which the electrode 120 is embedded is pressed.

[0032] Furthermore, when the electrode 120 is formed using a metal mesh M, the metal mesh M may be cut into a predetermined shape by laser processing. In this case, fraying may occur at the outer edge of the electrode 120 (see FIG. 7(b)). FIG. 7(a) is an explanatory diagram showing a state in which the electrode 120 is not frayed, and FIG. 7(b) is an explanatory diagram showing a state in which the electrode 120 is frayed. When fraying occurs, an electric field concentrates at the tip of the fray, causing insulation failure. In contrast, the electrode 120 of this embodiment is formed using a metal foil (metal plate) instead of the metal mesh M, so that fraying does not occur at the outer edge of the electrode 120 even when the metal foil (metal plate) is cut into a predetermined shape.

[0033] In addition, since a plurality of through holes 124 are dispersed in the electrode 120 embedded inside the ceramic base 110, the regions of the ceramic base 110 positioned above and below the electrode 120 are in contact with each other via the through holes 124. As a result, the electrode 120 and the ceramic base 110 are strongly bonded to each other, so that the electrode 120 is prevented from peeling off from the ceramic base 110.

[0034] Since the through holes 124 of the electrode 120 are formed by etching, the shape, dimensions, etc. of the openings of the through holes 124 can be easily adjusted. For example, as shown in FIG. 8, openings of different dimensions can be mixed. This allows the aperture ratio to be adjusted, and the electrostatic adsorption force and the impedance of the electrode 120 to be adjusted. The shape of the openings of the through holes 124 is not limited to a circle, and can be a polygon (for example, a hexagon, a square, or a triangle). Alternatively, as shown in FIG. 9, the shape of the openings of the through holes 124 can be a shape closed by a curve. In other words, in a top view, the outer edge portion of the openings of the through holes 124 of the electrode 120 can be shaped to have a curved or broken line-shaped recess recessed toward the center of each through hole 124 and a curved or broken line-shaped protrusion protruding in a direction away from the center of each through hole. This allows the outer edge portion of the through hole 124 of the electrode 120 to function as a spring element, thereby making it possible to relieve the stress applied to the electrode 120 embedded inside the ceramic base 110.

[0035] <Modification form> The above-described embodiment is merely an example and may be modified as appropriate. For example, the shape, size, and thickness of the electrode 120 are not limited to those of the above-described embodiment and may be modified as appropriate. In addition, in the above-described embodiment, a foil or plate of molybdenum, tungsten, or an alloy containing molybdenum and / or tungsten is used as the electrode material, but the present invention is not limited to such an embodiment. For example, a foil (plate) of a metal other than molybdenum or tungsten, or a foil (plate) of an alloy may be used.

[0036] Alternatively, molybdenum with rare earth added can be used as the electrode material. When the electrode 120 is formed from a foil or plate of a metal material containing molybdenum as the main component (50 wt% or more) and rare earth oxide, and is sintered and embedded simultaneously with AlN ceramic raw material powder, the electrode 120 made of Mo, C, and rare earth oxide is formed. The electrode 120 thus formed has a lower resistance value than an electrode made of molybdenum without rare earth oxide added. This makes it possible to keep the impedance of the electrode 120 low. In addition, the structure to which rare earth oxide is added maintains a small molybdenum particle size. Therefore, grain boundary sliding occurs at high temperatures during manufacturing (sintering), making it easy for plastic deformation to occur. As a result, it is possible to alleviate the stress generated between the electrode and the ALN ceramic insulating layer, which is thin and has low strength, and to suppress peeling and cracks between the ALN ceramic and the electrode.

[0037] Although the present invention has been described above using the embodiment and its modified form, the technical scope of the present invention is not limited to the above description. It is obvious to those skilled in the art that various modifications or improvements can be made to the above embodiment. It is also clear from the claims that such modifications or improvements can be included in the technical scope of the present invention.

[0038] The order of execution of each process in the manufacturing method shown in the specification and drawings is not particularly specified, and may be any order unless the output of a previous process is used in a subsequent process. For convenience, even if the description uses "first," "next," etc., it does not mean that the process must be performed in that order. [Explanation of symbols]

[0039] 100 Electrostatic Chuck 110 Ceramic substrate 120 electrodes 130 Shaft 140 Feed line

Claims

1. A ceramic substrate having an upper surface and a lower surface facing the upper surface in a vertical direction; a metal electrode embedded in the ceramic base at a position 0.1 mm to 10 mm away from the upper surface of the ceramic base in the vertical direction; The electrode has a thickness of 0.05 mm or more in the vertical direction, and has a plurality of through holes penetrating the electrode in the vertical direction; An electrostatic chuck, characterized in that outer edge portions of openings of the plurality of through holes in the upper surface of the electrode do not protrude above portions of the upper surface of the electrode excluding the outer edge portions of the openings of the plurality of through holes.

2. 2. The electrostatic chuck according to claim 1, wherein, in a cross-sectional view taken along a plane parallel to the vertical direction, the R dimension of the outer edge portion of the openings of the plurality of through holes of the electrode is R0.5 mm or more.

3. 2. The electrostatic chuck according to claim 1, wherein, in a top view, the outer edge portions of the openings of the plurality of through holes of the electrode have curved or broken line-shaped concave portions recessed toward the center of each through hole, and curved or broken line-shaped convex portions protruding in a direction away from the center of each through hole.

4. 2. The electrostatic chuck of claim 1, wherein the plurality of through holes includes a first through hole having a first opening area and a second through hole having a second opening area larger than the first opening area.

5. 2. The electrostatic chuck according to claim 1, wherein the opening ratio of the electrode is 55% or more.

6. The ceramic substrate contains AlN as a main component, 6. The electrostatic chuck according to claim 1, wherein the electrode contains Mo as a main component and also contains a rare earth oxide.

7. The electrode has a thickness of 0.05 mm or more and is made of a metal and has a plurality of through holes extending through the electrode in the thickness direction. an electrode for an electrostatic chuck, characterized in that outer edge portions of openings of the plurality of through holes in an upper surface of the electrode do not protrude above a portion of the upper surface of the electrode excluding the outer edge portions of the openings of the plurality of through holes.

8. Providing an electrode having a thickness of 0.05 mm or more; forming a plurality of through holes in the electrode by etching; embedding the electrode having the plurality of through holes formed therein in a ceramic granulated powder or a ceramic molded body; sintering the ceramic granulated powder or the ceramic molded body having the electrodes embedded therein to form a ceramic substrate; adjusting a position where the electrode is embedded in the ceramic granulated powder or the ceramic molded body, or processing the upper surface of the ceramic base so that a distance between the upper surface of the ceramic base and an upper surface of the electrode is 0.1 mm to 10 mm.

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