Ceramic heater

Abstract

To provide a ceramic heater capable of suppressing occurrence of cracks due to thermal stress at a corner of a boundary between a lower surface of a ceramic base material and a joining convex portion.SOLUTION: A ceramic heater 100 includes a disc-shaped ceramic base material 110, and an electrode 120 (heater electrode 122 and electrostatic adsorption electrode 124) embedded in the ceramic base material 110. A lower surface 113 of the ceramic base material 110 is provided with a joining convex portion 114 that projects downward. A cylindrical shaft 130 is joined to the joining convex portion 114. Center line average roughness Ra of a mirror polished region Sm is 0.1 μm or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a ceramic heater that holds and heats a substrate such as a silicon wafer. [Background technology]

[0002] Patent Document 1 discloses a ceramic heater that holds and heats a substrate such as a wafer. The ceramic heater described in Patent Document 1 comprises a ceramic substrate (plate-shaped ceramic body) on which the substrate is placed, a shaft (ceramic cylindrical support) that supports the ceramic substrate, and a joining convex portion (convex portion) that protrudes from the underside of the ceramic substrate and is joined to the shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-224044 Summary of the Invention [Problem to be solved by the invention]

[0004] In the ceramic heater described in Patent Document 1, the surface roughness (center line average roughness) of the outer surface of the joining portion of the upper shaft and the joining protrusion provided on the ceramic base is set to 2 μm or less, thereby preventing the joining portion between the joining protrusion and the upper shaft from peeling off. However, the inventors have found that when the ceramic heater is repeatedly heated and cooled, or heated at high temperatures, there is a risk of cracks occurring due to thermal stress at the corners of the boundary between the lower surface of the ceramic base and the joining protrusion.

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a ceramic heater that can suppress the occurrence of cracks due to thermal stress at the corners of the boundaries between the underside of the base and the bonding convex portions. [Means for solving the problem]

[0006] According to an aspect of the present invention, there is provided a ceramic substrate having an upper surface, a lower surface facing the upper surface in a vertical direction, and a protrusion protruding downward from the lower surface; a heating element embedded in the ceramic substrate; a cylindrical shaft joined to the protrusion of the ceramic base, The center line average roughness Ra1 of the side surface of the convex portion and the center line average roughness Ra2 of the region of the lower surface of the ceramic base within 5 mm from the boundary with the convex portion are both 0.1 μm or less. the law of nature, The side surfaces of the protrusions are free from microcracks larger than 3 μm in width and scratches larger than 3 μm in width. A ceramic heater characterized by the above features is provided. [Effects of the Invention]

[0007] The centerline average roughness Ra1 of the side surface of the convex portion and the centerline average roughness Ra2 of the region on the underside of the ceramic substrate within 5 mm from the boundary with the convex portion are set to 0.1 μm or less. This results in a mirror-polished surface (the side surface of the convex portion and the region on the underside of the ceramic substrate within 5 mm from the boundary with the convex portion) and reduces microcracks. As a result, the mirror-polished region is more resistant to thermal stress when the heating element of the ceramic heater is energized to heat it up. This suppresses cracking in the mirror-polished region, particularly cracking originating at the boundary with the bonding convex portion on the underside of the ceramic substrate. Furthermore, because the surface irregularities in the mirror-polished region are reduced, the surface area can be reduced, thereby reducing heat radiation from the mirror-polished region. As a result, temperature drop in the portion directly above the shaft on the upper surface of the ceramic substrate is suppressed, contributing to uniform heating of the substrate to be heated. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a ceramic heater 100. FIG. [Figure 2] FIG. 2 is a schematic explanatory diagram of the ceramic heater 100. As shown in FIG. [Figure 3] FIG. 3 is a schematic diagram illustrating the electrode 120. As shown in FIG. [Figure 4] FIG. 4 is a schematic diagram illustrating the heater electrode 122. As shown in FIG. [Figure 5] FIG. 5 is a partially enlarged view of the ceramic heater 100. As shown in FIG. [Figure 6] 1(a) to 1(e) are diagrams showing the flow of a method for manufacturing the ceramic base 110. FIG. [Figure 7] 10(a) to 10(d) are diagrams showing the flow of another method for manufacturing the ceramic base 110. FIG. [Figure 8] FIG. 8 is an enlarged view of a portion of the ceramic heater 100 that has been subjected to R-chamfering. [Figure 9] FIG. 9 is an enlarged view of a portion of the ceramic heater 100 that has been subjected to C-chamfering. [Figure 10] 1(a) is a partially enlarged view of the ceramic heater 100 provided with a terminal hole 142, and FIG. 1(b) is a partially enlarged view of the ceramic heater 100 provided with a recess 145. FIG. [Figure 11] FIG. 11 is a table summarizing the results of Examples 1 to 7 and the Comparative Example. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Ceramic heater 100> A ceramic heater 100 according to an embodiment of the present invention will be described with reference to Figures 1 and 2. The ceramic heater 100 according to this embodiment is a ceramic heater used to heat semiconductor wafers such as silicon wafers (hereinafter simply referred to as wafers 10). In the following description, the up-down direction 5 is defined based on the state in which the ceramic heater 100 is installed so that it can be used (the state in Figure 1). As shown in Figure 1, the ceramic heater 100 according to this embodiment comprises a ceramic substrate 110, an electrode 120 (see Figure 2), a shaft 130, and power supply wires 140 and 141 (see Figure 2).

[0010] The ceramic substrate 110 is a member having a circular plate shape with a diameter of 12 inches (approximately 300 mm), and the wafer 10 to be heated is placed on the ceramic substrate 110. Note that in FIG. 1, the wafer 10 and the ceramic substrate 110 are shown separated from each other for ease of viewing. As shown in FIG. 1, an annular protrusion 152 (hereinafter simply referred to as the annular protrusion 152) and a plurality of protrusions 156 are provided on the upper surface 111 of the ceramic substrate 110. Note that in FIG. 1, the number of the plurality of protrusions 156 is reduced compared to FIG. 2 for ease of viewing. Also, as shown in FIG. 2, a first gas flow path 164, which will be described later, is formed inside the ceramic substrate 110. The ceramic substrate 110 can be formed of a ceramic sintered body such as aluminum nitride, silicon carbide, alumina, or silicon nitride.

[0011] As shown in FIGS. 1 and 2, the annular protrusion 152 is an annular protrusion disposed 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 protrusion 152 abuts against the lower surface of the wafer 10. In other words, when the wafer 10 is placed on the ceramic base 110, the annular protrusion 152 is disposed at a position that overlaps with the wafer 10 in the vertical direction 5. A plurality of protrusions 156 are provided inside the annular protrusion 152 on the upper surface 111 of the ceramic base 110. Each of the plurality of protrusions 156 has a cylindrical shape. One of the plurality of protrusions 156 is disposed approximately at the center of the upper surface 111. The remaining protrusions 156 are arranged on the circumference of four equally spaced concentric circles. The convex portions 156 are arranged at equal intervals on the circumference of each concentric circle. The positions and / or number of the convex portions 156 are appropriately determined depending on the application, action, and function.

[0012] The height of the annular protrusion 152 can be in the range of 5 μm to 2 mm. Similarly, the height of the plurality of protrusions 156 can be in the range of 5 μm to 2 mm. In this embodiment, the height of the annular protrusion 152 and the height of the plurality of protrusions 156 are the same. In this specification, the height of the annular protrusion 152 and the height of the plurality of protrusions 156 are defined as the length in the vertical direction from the upper surface 111 of the ceramic substrate 110. In addition, if the upper surface 111 of the ceramic substrate 110 is not flat and has, for example, a step, the highest point on the upper surface 111 of the ceramic substrate 110 is used as the reference point and the height is defined as the length in the vertical direction from there.

[0013] The width of the upper surface 152a of the annular protrusion 152 is preferably constant and can be set to 0.1 mm to 10 mm. The center line average roughness Ra of the upper surface 152a of the annular protrusion 152 can be 1.6 μm or less. The center line average roughness Ra is the average of the absolute values ​​of deviations from the center line of the surface irregularities. Similarly, the center line average roughness Ra of the upper surfaces 156a of the multiple protrusions 156 can be 1.6 μm or less. The center line average roughness Ra of the upper surface 152a of the annular protrusion 152 and the upper surfaces 156a of the multiple protrusions 156 is preferably 0.4 μm or less, more preferably 0.2 μm or less, and even more preferably 0.1 μm or less.

[0014] The upper surfaces 156a of the plurality of protrusions 156 are preferably circular with a diameter of 0.1 mm to 5 mm. The distance between each of the plurality of protrusions 156 can be set within a range of 1.5 mm to 30 mm.

[0015] As described above, on the upper surface 111 of the ceramic substrate 110, the plurality of protrusions 156 are arranged on the circumference of four concentric circles. As shown in FIG. 2 , an opening 164a of a first gas flow path 164 is formed on the upper surface 111 between the innermost concentric circle on which the plurality of protrusions 156 are arranged and the second innermost concentric circle. The first gas flow path 164 is a gas flow path having the opening 164a, and is formed inside the ceramic base 110. The first gas flow path 164 extends downward from the opening 164a. As described below, the lower end of the first gas flow path 164 is joined to the upper end of a second gas flow path 168 formed inside the shaft 130.

[0016] The first gas flow path 164 can be used as a flow path for supplying gas to the 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. Examples of the heat transfer gas include an inert gas such as helium or argon, or nitrogen gas. The heat transfer gas is supplied through the first gas flow path 164 at a pressure set within a range of 100 Pa to 40,000 Pa. Furthermore, if process gas infiltrates into the gap inside the annular protrusion 152 through 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 path 164. In this case, the differential pressure between the pressure outside the gap and the pressure inside the gap can be adjusted by adjusting the exhaust pressure. This allows the wafer 10 to be adsorbed toward the upper surface of the ceramic base 110.

[0017] 2, an electrode 120 is embedded inside the ceramic base 110. The electrode 120 includes a heater electrode 122 and an electrostatic attraction electrode 124. The electrostatic attraction electrode 124 is embedded above the heater electrode 122.

[0018] 3, the electrostatic attraction electrode 124 has two semicircular electrodes 124a and 124b arranged facing each other with a predetermined distance between them, and has a generally circular shape as a whole. In this embodiment, the outer diameter of the electrostatic attraction electrode 124 is 292 mm. By applying a predetermined voltage (e.g., ±500 V) to each of the electrodes 124a and 124b, the wafer 10 can be electrostatically attracted.

[0019] As shown in FIG. 4, the heater electrode 122 is a metal mesh or foil cut into a strip shape. The heater electrode 122 has an outer diameter of 298 mm. The heater electrode 120 is not exposed from the side surfaces of the ceramic substrate 110. A terminal portion 121 connected to the power supply line 140 (see FIG. 1) is provided at approximately the center of the heater electrode 120. The heater electrode 122 is formed of a heat-resistant metal (high-melting-point metal) such as a mesh or foil woven with wires of tungsten (W), molybdenum (Mo), or an alloy containing molybdenum and / or tungsten. The purity of the tungsten and molybdenum is preferably 99% or higher. The thickness of the heater electrode 122 is 0.15 mm or less. From the viewpoint of increasing the resistance of the heater electrode 122 and reducing the current consumption of the ceramic heater 100, it is preferable to set the wire diameter to 0.1 mm or less and the thickness of the heater electrode 122 to 0.1 mm or less. Furthermore, the width of the heater electrode 122 cut into a strip shape is preferably 2.5 mm to 20 mm, and more preferably 5 mm to 15 mm. In this embodiment, the heater electrode 122 is cut into the shape shown in Fig. 4, but the shape of the heater electrode 122 is not limited to this and can be changed as appropriate. Note that in addition to or instead of the heater electrode 122, a plasma electrode for generating plasma may be embedded above the ceramic base 110 inside the ceramic base 110.

[0020] As shown in Figures 1 and 2, a shaft 130 is connected to the lower surface 113 of the ceramic base 110. The shaft 130 has a hollow, approximately 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 Figure 2), and the large-diameter portion 133 is provided below the cylindrical portion 131 (see Figure 1). The large-diameter portions 132 and 133 have diameters larger than the diameter 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 Figure 1, when the ceramic heater 100 is in use, the longitudinal direction 6 of the shaft 130 is parallel to the up-down direction 5.

[0021] In this embodiment, the centerline average roughness Ra of the side surface 132S of the large diameter portion 132 of the shaft 130 is set to 2.0 μm or less. In the following description, the centerline average roughness Ra of the side surface 132S of the large diameter portion 132 of the shaft 130 will be referred to as the centerline average roughness Ra3. The centerline average roughness Ra of other regions of the outer surface of the shaft 130 (such as the side surface of the cylindrical portion 131 and the side surface of the large diameter portion 133) can also be set to 2.0 μm or less.

[0022] As shown in FIG. 2 , a lower surface 113 of the ceramic base 110 is provided with a protrusion 114 (hereinafter referred to as a joining protrusion 114, which corresponds to a protrusion in the present invention) for joining to the shaft 130. The shape of the joining protrusion 114 is preferably the same as the shape of the upper surface of the shaft 130 to be joined, and the diameter of the joining protrusion 114 is preferably 100 mm or less. The height of the joining protrusion 114 (height from the lower surface 113) may be 2 mm or more, preferably 5 mm or more. There is no particular upper limit on the height, but considering ease of manufacture, the height of the joining protrusion 114 is preferably 20 mm or less. Furthermore, the lower surface 114B of the joining protrusion 114 is preferably parallel to the lower surface 113 of the ceramic base 100. The center line average roughness Ra of the lower surface 114B of the joining protrusion 114 may be 1.6 μm or less. The center line average roughness Ra of the lower surface 114B of the bonding convex portion 114 is preferably 0.4 μm or less, and more preferably 0.2 μm or less.

[0023] In this embodiment, the center line average roughness Ra of the side surface SL of the joining protrusion 114 is 0.1 μm or less. As shown in FIG. 8, when a corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 is subjected to R-chamfering (hereinafter simply referred to as R-chamfering), the R-chamfered region is included in the definition of the side surface 114S of the joining protrusion 114. Similarly, as shown in FIG. 9, when a corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 is subjected to C-chamfering (hereinafter simply referred to as C-chamfering), the C-chamfered region is included in the definition of the side surface 114S of the joining protrusion 114. In this case, the radially outer end of the R-chamfered (or C-chamfered) region becomes the boundary between the joining protrusion 114 and the lower surface 113 of the ceramic base 100. Furthermore, in this embodiment, the center line average roughness Ra of a region S1 of the lower surface 113 of the ceramic base 100 within 5 mm from the boundary with the joining protrusion 114 is 0.1 μm or less. In the following description, the region consisting of the side surface SL of the joining protrusion 114 and the region S1 of the lower surface 113 of the ceramic base 100 within 5 mm from the boundary with the joining protrusion 114 is referred to as the mirror-polished region Sm.

[0024] In this embodiment, there are no scratches wider than 3 μm or microcracks wider than 3 μm in width in the mirror-polished region Sm. In this embodiment, as described below, the mirror-polished region Sm is polished using abrasive grains (e.g., grit size 8000) with an average grain size smaller than 3 μm. This removes at least scratches and microcracks larger than the abrasive grain size (here, 3 μm). Note that by polishing using abrasive grains (e.g., grit size 14000) with an average grain size smaller than 1 μm, the width of the scratches and microcracks in the mirror-polished region Sm can be reduced to 1 μm or less.

[0025] 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, or silicon nitride, just like the ceramic base 110. Alternatively, to improve heat insulation, the shaft 130 may be made of a material with lower thermal conductivity than the ceramic base 110.

[0026] 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 (a region inside the inner diameter). A power supply line 140 for supplying power to the heater electrode 122 and a power supply line 141 for supplying power to the electrostatic attraction electrode 124 are arranged in the hollow portion (through-hole) of the shaft 130. Note that while FIG. 2 shows only one power supply line 140 and one power supply line 141, in reality, a plurality of power supply lines 140 and a plurality of power supply lines 141 are arranged. The upper end of the power supply line 140 is electrically connected to a terminal portion 121 (see FIG. 3) arranged in the center of the heater electrode 122. The power supply line 140 is connected to a heater power supply (not shown). As a result, power is supplied to the heater electrode 122 via the power supply line 140. Similarly, power is supplied to the electrostatic attraction electrode 124 via the power supply line 141.

[0027] 2, the cylindrical portion 131 of the shaft 130 is formed with a second gas flow path 168 extending in the vertical direction 5. As described above, the upper end of the second gas flow path 168 is connected to the lower end of the first gas flow path 164.

[0028] Next, a method for manufacturing the ceramic heater 100 will be described. In the following, an example will be described in which the ceramic base 110 and the shaft 130 are made of aluminum nitride.

[0029] First, a method for manufacturing the ceramic substrate 110 will be described. For simplicity, it is assumed that only a heater electrode 122 is embedded within the ceramic substrate 110 as the electrode 120. As shown in FIG. 6(a), granulated powder P, primarily composed of aluminum nitride (AlN) powder, is placed in a carbon mold with a bed 501 and pre-pressed with a punch 502. The granulated powder P preferably contains 5 wt% or less of a sintering aid (e.g., Y2O3). Next, as shown in FIG. 6(b), a heater electrode 122 cut to a predetermined shape is placed on the pre-pressed granulated powder P. The heater electrode 122 is placed parallel to a plane perpendicular to the pressing direction (the bottom surface of the mold with a bed 501). At this time, a W pellet or a Mo pellet may be embedded at the position of the terminal 121 (see FIG. 4) of the heater electrode 122.

[0030] As shown in FIG. 6(c), granulated powder P is further poured into the bed-type mold 501 so as to cover the heater electrode 122, and is pressed and molded with a punch 502. Next, as shown in FIG. 6(d), the granulated powder P with the heater electrode 122 embedded therein is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. Furthermore, firing is preferably performed at a temperature of 1800°C or more. Next, as shown in FIG. 6(e), blind holes are drilled to the heater electrode 122 to form the terminals 121. If a pellet is embedded, blind holes may be drilled to the pellets. Furthermore, through holes that become part of the first gas flow paths 164 are formed. This allows the production of a ceramic base 110 with the first gas flow paths 164 formed therein. In this case, it is preferable to provide a predetermined opening in the heater electrode 122 in advance so that the heater electrode 122 is not exposed from the first gas flow paths 164.

[0031] The ceramic base material 110 can also be manufactured by the following method. As shown in Fig. 7(a), a binder is added to aluminum nitride granulated powder P, which is then CIP molded and processed into a disk shape to produce an aluminum nitride compact 510. Next, as shown in Fig. 7(b), the compact 510 is degreased to remove the binder.

[0032] As shown in FIG. 7(c), a recess 511 for embedding a heater electrode 122 is formed in the degreased compact 510. The heater electrode 122 is placed in the recess 511 of the compact 510, and another compact 510 is stacked on top of it. The recess 511 may be formed in the compact 510 in advance. Next, as shown in FIG. 7(d), the stacked compacts 510, sandwiching the heater electrode 122 between them, are fired in a pressed state to produce a fired body. The pressure applied during firing is preferably 1 MPa or more. Furthermore, firing is preferably performed at a temperature of 1800°C or more. The steps after producing the fired body are the same as those described above, and therefore will not be described here.

[0033] The upper surface 111 of the ceramic base 110 thus formed is ground and then lapped. Furthermore, the upper surface 111 is sandblasted to form a plurality of protrusions 156 and an annular protrusion 152 on the upper surface 111. The plurality of protrusions 156 are machined to have the same height. The upper surface 152a of the annular protrusion 152 is also machined into a predetermined shape. Sandblasting is a suitable method for forming the plurality of protrusions 156 and the annular protrusion 152, but other machining methods can also be used. Furthermore, the lower surface 113 of the ceramic base 110 is machined into a cylindrical shape to form a joining protrusion 114 that protrudes from the lower surface 113.

[0034] Furthermore, the mirror-polished region Sm (the region S1 within 5 mm from the boundary between the side surface 114S of the bonding protrusion 114 and the lower surface 113 of the ceramic substrate 100 and the bonding protrusion 114) was subjected to mirror polishing. Specifically, first, rough polishing was performed using a grindstone having grit sizes of 120 to 240, and then polishing was performed using a finer grindstone (1000 or more). As a result, the center line average roughness Ra of the mirror-polished region Sm was set to 0.1 μm or less. Note that instead of performing polishing using a finer grindstone having grit sizes of 1000 or more, lapping (mirror polishing) can also be performed. Alternatively, polishing may be performed using other processing methods. For example, finish polishing may be performed using hand lapping. Furthermore, as will be described later, when recesses 115 are formed on the upper surfaces 114a of the bonding convex portions 114, the surfaces of the recesses 115 can also be polished to set the center line average roughness Ra of the surfaces of the recesses 115 to 0.1 μm or less. In this case, for example, the polishing can be performed with a grindstone using a machining center.

[0035] Next, a method for manufacturing the shaft 130 and a method for bonding the shaft 130 to the ceramic base 110 will be described. First, granulated aluminum nitride powder P to which several wt % of binder has been added is formed under hydrostatic pressure (approximately 1 MPa), and the molded body is processed into a predetermined shape. At this time, through holes that become second gas flow paths 168 are formed in the molded body. The outer diameter of the shaft 130 is approximately 30 mm to 100 mm. A flange portion 133 having a diameter larger than the outer diameter of the cylindrical portion 131 may be provided on the end surface of the cylindrical portion 131 of the shaft 130 (see FIG. 5). The length of the cylindrical portion 131 can be, for example, 50 mm to 500 mm. After processing the molded body into the predetermined shape, the molded body is sintered in a nitrogen atmosphere. For example, the molded body is sintered at a temperature of 1900°C for two hours. After the sintering, the sintered body is processed into the predetermined shape to form the shaft 130. The upper surface of the cylindrical portion 131 and the lower surface 114B of the bonding protrusion 114 of the ceramic base 110 can be fixed by diffusion bonding at 1600°C or higher and under a uniaxial pressure of 1 MPa or higher. In this case, the centerline average roughness Ra of the lower surface 114B of the bonding protrusion 114 of the ceramic base 110 is preferably 0.4 μm or less, and more preferably 0.2 μm or less. Alternatively, the upper surface of the cylindrical portion 131 and the lower surface 114B of the bonding protrusion 114 can be bonded using a bonding agent. For example, an AlN bonding material paste containing 10 wt% Y2O3 can be used as the bonding agent. For example, the AlN bonding agent paste can be applied to the interface between the upper surface of the cylindrical portion 131 and the lower surface 114B of the bonding protrusion 114 to a thickness of 15 μm, and then heated at 1700°C for 1 hour while applying a force of 5 kPa in a direction perpendicular to the upper surface 111 (the longitudinal direction 6 of the shaft 130). Alternatively, the upper surface of the cylindrical portion 131 and the lower surface 114B of the joining protrusion 114 can be fixed together by screwing, brazing, or the like. [Example]

[0036] The present invention will be further described below using Examples 1 to 7. However, the present invention is not limited to the Examples described below. Fig. 11 shows a table summarizing the results of Examples 1 to 7 and the Comparative Example.

[0037] [Example 1] A ceramic heater 100 (see FIG. 2) of Example 1 will be described. In Example 1, a ceramic substrate 110 having a diameter of 310 mm and a thickness of 25 mm was fabricated by the above-described fabrication method using aluminum nitride (AlN) to which 5 wt % of a sintering aid (YO) was added as the raw material. A molybdenum mesh (wire diameter 0.1 mm, mesh size #50, plain weave) cut into the shape shown in FIG. 4 was fabricated as the heater electrode 122, and this heater electrode 122 was embedded in the ceramic substrate 110. Similarly, an electrostatic attraction electrode 124 having the shape shown in FIG. 3 was embedded in the ceramic substrate 110.

[0038] An annular protrusion 152 having an inner diameter of 288 mm, an outer diameter of 298 mm, and a width of 5 mm was formed on the upper surface 111 of the ceramic base 110. Furthermore, a plurality of cylindrical protrusions 156 having a diameter of 1 mm and a height of 30 μm from the upper surface 111 were formed on the upper surface 111 of the ceramic base 110. As described above, the plurality of protrusions 156 were arranged concentrically, and the distance between each protrusion was in the range of 10 mm to 20 mm.

[0039] The diameter of the opening 164a of the first gas flow path 164 is 3 mm. The center of the opening 164a is located 30 mm from the center of the ceramic base 110.

[0040] In the following description, the centerline average roughness Ra1 of the side surface SL of the joining protrusion 114 and the centerline average roughness Ra2 of the region S1 of the lower surface 113 of the ceramic base 100 within 5 mm from the boundary with the joining protrusion 114 are collectively referred to as the centerline average roughness Ra of the mirror-polished region Sm. In Example 1, the centerline average roughness Ra of the mirror-polished region Sm was set to 0.08 μm, and the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 was set to 1.6 μm. Similarly, the centerline average roughness Ra of other regions of the outer surface of the shaft 130 (such as the side surface of the cylindrical portion 131 and the side surface of the large diameter portion 133) was also set to 1.6 μm. In this case, the ratio Ra1 / Ra3 of the centerline average roughness Ra1 of the side surface SL of the joining protrusion 114 to the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 was 0.05. In addition, a corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 is rounded. The R chamfer dimension in Example 1 is 0.8 mm. In the following description, the R chamfer dimension of 0.8 mm will be simply written as R0.8 mm. The same applies when describing the C chamfer dimension.

[0041] A ceramic heater 100 having this shape was placed in a process chamber, and the temperature of the ceramic heater 100 was evaluated using the following procedure. A silicon wafer for temperature evaluation was placed on the ceramic heater 100, and an external power supply (not shown) was connected to the heater electrode 122 of the ceramic heater 100. After reducing the pressure inside the process chamber to 1 Pa or less, argon gas was introduced so that the pressure inside the process chamber reached 1,000 Pa. The output power of the external power supply was adjusted so that the temperature of the top surface of the silicon wafer reached approximately 650°C in a steady state. The temperature distribution in Region A (see FIG. 5), which is directly above the joint between the ceramic substrate 110 and the shaft 130 and the mirror-polished region Sm on its outer edge, and Region B (see FIG. 5), a 20 mm-wide ring-shaped region adjacent to the outside of Region A, was then measured using an infrared camera, and the temperature difference Δ between the average temperature of Region A and the average temperature of Region B was evaluated. The silicon wafer used for temperature evaluation was a 300 mm diameter silicon wafer coated with a 30 μm thick blackbody film on its top surface. A blackbody film is a film with an emissivity (radiation rate) of 90% or more, and can be formed by coating it with blackbody paint whose main ingredient is carbon nanotubes, for example.

[0042] Thereafter, the temperature of the upper surface of the silicon wafer was decreased to about 200° C., after which it was again increased to 650° C. and then decreased to 200° C. Such a temperature cycle of 200° C.-650° C.-200° C. was defined as one cycle.

[0043] In Example 1, even after the above temperature cycle was repeated 100 times or more, no cracks were observed in the ceramic base 110 and the shaft 130. The temperature difference Δ between the average temperature of the above region A and the average temperature of the region B, measured using a silicon wafer for temperature evaluation, was 1.8°C.

[0044] [Example 2] The ceramic heater 100 of Example 2 is similar to the ceramic heater 100 of Example 1, except that the center line average roughness Ra of the mirror-polished region Sm and the shape of the corner between the bonding convex portion 114 and the lower surface 113 of the ceramic base 100 are different. In Example 2, the center line average roughness Ra of the mirror-polished region Sm was set to 0.03 μm. In this case, the ratio Ra1 / Ra3 of the center line average roughness Ra1 to the center line average roughness Ra3 was 0.019. In addition, the corner between the bonding convex portion 114 and the lower surface 113 of the ceramic base 100 was rounded to an R of 0.3 mm.

[0045] The ceramic heater 100 having this shape was placed in a process chamber, and a silicon wafer for temperature evaluation similar to that in Example 1 was placed on the ceramic heater 100. Then, a temperature evaluation of the ceramic heater 100 was carried out using the same procedure as in Example 1. In Example 2, even after the above temperature cycle was repeated 100 times or more, no cracks were observed in the ceramic substrate 110 or shaft 130. The temperature difference Δ between the average temperature of the above-mentioned region A and the average temperature of region B, measured using the silicon wafer for temperature evaluation, was 2.2°C.

[0046] [Example 3] The ceramic heater 100 of Example 3 is similar to the ceramic heater 100 of Example 1, except that the center line average roughness Ra of the mirror-polished region Sm and the shape of the corners between the bonding convex portions 114 and the lower surface 113 of the ceramic base 100 are different. In Example 3, as in Example 2, the center line average roughness Ra of the mirror-polished region Sm was set to 0.03 μm. In this case, the ratio Ra1 / Ra3 of the center line average roughness Ra1 to the center line average roughness Ra3 was 0.019. In addition, C processing was performed to C0.3 mm on the corners between the bonding convex portions 114 and the lower surface 113 of the ceramic base 100.

[0047] The ceramic heater 100 having this shape was placed in a process chamber, and a silicon wafer for temperature evaluation similar to that in Example 1 was placed on the ceramic heater 100. Then, a temperature evaluation of the ceramic heater 100 was carried out using the same procedure as in Example 1. In Example 2, even after the above temperature cycle was repeated 100 times or more, no cracks were observed in the ceramic substrate 110 or shaft 130. The temperature difference Δ between the average temperature of the above-mentioned region A and the average temperature of region B, measured using the silicon wafer for temperature evaluation, was 2.4°C.

[0048] [Example 4] The ceramic heater 100 of Example 4 is similar to the ceramic heater 100 of Example 1, except that the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 and the shape of the corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 are different. In Example 4, the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 was set to 0.15 μm. Similarly, the centerline average roughness Ra of other regions of the outer surface of the shaft 130 (such as the side surface of the cylindrical portion 131 and the side surface of the large diameter portion 133) was also set to 0.15 μm. In this case, the ratio Ra1 / Ra3 of the centerline average roughness Ra1 to the centerline average roughness Ra3 was 0.53. In addition, the corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 was rounded to an R of 3 mm.

[0049] The ceramic heater 100 having this shape was placed in a process chamber, and a silicon wafer for temperature evaluation similar to that in Example 1 was placed on the ceramic heater 100. Then, a temperature evaluation of the ceramic heater 100 was carried out using the same procedure as in Example 1. In Example 2, even after the above temperature cycle was repeated 100 times or more, no cracks were observed in the ceramic substrate 110 or shaft 130. The temperature difference Δ between the average temperature of the above-mentioned region A and the average temperature of region B, measured using the silicon wafer for temperature evaluation, was 2.8°C.

[0050] [Example 5] The ceramic heater 100 of Example 5 is similar to the ceramic heater 100 of Example 1, except that the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 and the shape of the corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 are different. In Example 5, the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 was set to 0.80 μm. Similarly, the centerline average roughness Ra of other regions of the outer surface of the shaft 130 (such as the side surface of the cylindrical portion 131 and the side surface of the large diameter portion 133) was also set to 0.80 μm. In this case, the ratio Ra1 / Ra3 of the centerline average roughness Ra1 to the centerline average roughness Ra3 was 0.1. In addition, the corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 was rounded to an R of 3 mm.

[0051] The ceramic heater 100 having this shape was placed in a process chamber, and a silicon wafer for temperature evaluation similar to that in Example 1 was placed on the ceramic heater 100. Then, a temperature evaluation of the ceramic heater 100 was carried out using the same procedure as in Example 1. In Example 2, even after the above temperature cycle was repeated 100 times or more, no cracks were observed in the ceramic substrate 110 or shaft 130. The temperature difference Δ between the average temperature of the above-mentioned region A and the average temperature of region B, measured using the silicon wafer for temperature evaluation, was 3.0°C.

[0052] [Example 6] The ceramic heater 100 of Example 6 is similar to the ceramic heater 100 of Example 1, except that the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 and the shape of the corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 are different. In Example 6, the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 was set to 3.2 μm. Similarly, the centerline average roughness Ra of other regions of the outer surface of the shaft 130 (such as the side surface of the cylindrical portion 131 and the side surface of the large diameter portion 133) was also set to 3.2 μm. In this case, the ratio Ra1 / Ra3 of the centerline average roughness Ra1 to the centerline average roughness Ra3 was 0.025. In addition, the corner between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 was rounded to an R of 3 mm.

[0053] The ceramic heater 100 having this shape was placed in a process chamber, and a silicon wafer for temperature evaluation similar to that in Example 1 was placed on the ceramic heater 100. Then, a temperature evaluation of the ceramic heater 100 was carried out using the same procedure as in Example 1. In Example 2, even after the above temperature cycle was repeated 100 times or more, no cracks were observed in the ceramic substrate 110 or shaft 130. The temperature difference Δ between the average temperature of the above-mentioned region A and the average temperature of region B, measured using the silicon wafer for temperature evaluation, was 4.4°C.

[0054] [Example 7] The ceramic heater 100 of Example 7 is similar to the ceramic heater 100 of Example 1, except that the center line average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 is different. In Example 7, the center line average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 was set to 0.08 μm. Similarly, the center line average roughness Ra of other regions of the outer surface of the shaft 130 (such as the side surface of the cylindrical portion 131 and the side surface of the large diameter portion 133) was also set to 0.08 μm. In this case, the ratio Ra1 / Ra3 of the center line average roughness Ra1 to the center line average roughness Ra3 was 1.0.

[0055] The ceramic heater 100 having this shape was placed in a process chamber, and a silicon wafer for temperature evaluation similar to that in Example 1 was placed on the ceramic heater 100. Then, a temperature evaluation of the ceramic heater 100 was carried out using the same procedure as in Example 1. In Example 2, even after the above temperature cycle was repeated 100 times or more, no cracks were observed in the ceramic substrate 110 or shaft 130. The temperature difference Δ between the average temperature of the above-mentioned region A and the average temperature of region B, measured using the silicon wafer for temperature evaluation, was 2.8°C.

[0056] [Comparative Example] The substrate holding member of the comparative example was similar to the ceramic heater 100 of Example 1, except that the center line average roughness Ra of the mirror-polished region Sm was 0.5 μm. In the comparative example, the ratio Ra1 / Ra3 of the center line average roughness Ra1 to the center line average roughness Ra3 was 0.31.

[0057] A substrate holding member having such a shape was placed in a process chamber, and a silicon wafer for temperature evaluation similar to that in Example 1 was placed on the ceramic heater 100. Then, a temperature evaluation of the ceramic heater 100 was carried out using the same procedure as in Example 1. In the comparative example, cracks were found to have occurred in the ceramic base material 110 and the shaft 130 before the above temperature cycle was repeated 200 times. The temperature difference Δ between the average temperature of the above-mentioned region A and the average temperature of region B, measured using the silicon wafer for temperature evaluation, was 3.5°C.

[0058] <Effects of the embodiment> In the above embodiment and Examples 1 to 7, the ceramic heater 100 includes a disk-shaped ceramic base 110 and an electrode 120 (a heater electrode 122 and an electrostatic attraction electrode 124) embedded in the ceramic base 110. A downwardly protruding joining protrusion 114 is provided on the lower surface 113 of the ceramic base 110. A cylindrical shaft 130 is joined to the joining protrusion 114. The center line average roughness Ra of the mirror-polished region Sm is 0.1 μm or less. In other words, the center line average roughness Ra1 of the side surface SL of the joining protrusion 114 is 0.1 μm or less, and the center line average roughness Ra2 of a region S1 of the lower surface 113 of the ceramic base 100 within 5 mm of the boundary with the joining protrusion 114 is 0.1 μm or less.

[0059] Comparing Examples 1 to 7 with the Comparative Example, by setting the centerline average roughness Ra of the mirror-polished region Sm to 0.1 μm or less, it was possible to fabricate ceramic heaters in which no cracks occurred in the ceramic base 110 or shaft 130 even after the above-mentioned temperature cycle was repeated 100 times or more. According to the findings of the inventors, the reason for this is believed to be as follows. By setting the centerline average roughness Ra of the mirror-polished region Sm to 0.1 μm or less, as in Examples 1 to 7, the surface of the mirror-polished region Sm becomes mirror-like, reducing microcracks. As a result, the resistance of the mirror-polished region Sm to thermal stresses applied when the heater electrode 122 of the ceramic heater 100 is heated by passing current through it is increased. This makes it possible to suppress the occurrence of cracks in the mirror-polished region Sm, particularly cracks originating from the boundary between the lower surface 113 of the ceramic base 100 and the joining protrusion 114. Furthermore, since the surface irregularities in the mirror-polished region Sm are reduced, the surface area can be reduced, and heat radiation from the mirror-polished region Sm can be reduced. As a result, a temperature drop in the portion of the upper surface 111 of the ceramic base 100 directly above the shaft 130 can be suppressed, which contributes to uniform heating of the wafer 10 to be heated.

[0060] It is generally known that when ceramics are ground or polished, scratch marks remain on the ceramic surface, and microcracks originating from the scratch marks occur. Furthermore, when thermal stress acts on the microcracks, the microcracks may develop into larger cracks. In this embodiment, as described above, there are no scratch marks or microcracks wider than 3 μm in width in the mirror-polished region Sm. Therefore, it is possible to prevent microcracks from originating from scratch marks and the microcracks from developing into larger cracks.

[0061] In Examples 1 to 3 and 7, the R-chamfer dimension or C-chamfer dimension at the boundary between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 is both less than 1 mm. In this case, heat transfer near the joining portion between the ceramic base 110 and the shaft 130 is suppressed compared to a conventional case where the R-chamfer dimension (or C-chamfer dimension) at the corner of the boundary between the joining protrusion 114 and the lower surface 113 of the ceramic base 100 is about 5 mm. This can particularly contribute to uniform heating in the portion of the upper surface 111 of the ceramic base 100 directly above the outer edge portion of the large diameter portion 132 of the shaft 130.

[0062] In the above embodiment and Examples 1 to 7, the shaft 130 has a large diameter portion 132 that has the same diameter as the joining protrusion 114 and is joined to the joining protrusion 114. Here, as shown in Examples 1 to 5, the ratio Ra1 / Ra3 of the center line average roughness Ra1 of the side surface SL of the joining protrusion 114 to the center line average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130 can be set to be 0.01 or more and 0.9 or less.

[0063] The lower end of the shaft 130 uses a relatively heat-sensitive component, such as an O-ring, to ensure airtightness with the chamber. Therefore, if a large amount of heat is transmitted to the lower end of the shaft 130, the O-ring may be damaged. When the centerline average roughness Ra3 of the side surface 132S of the large-diameter portion 132 of the shaft 130 is greater than the centerline average roughness Ra1 of the side surface 114S of the joining protrusion 114, as in Example 1-5, heat radiation from the side surface 132S of the large-diameter portion 132 of the shaft 130 can be enhanced. Because the large-diameter portion 132 of the shaft 130 is located at the upper end of the shaft 130, enhancing heat radiation at this portion can prevent heat from being transmitted toward the lower end of the shaft 130. This can prevent damage to heat-sensitive components, such as the O-ring, provided at the lower end of the shaft 130, and contribute to extending their lifespan. The centerline average roughness Ra3 of the side surface 132S of the large-diameter portion 132 of the shaft 130 is preferably 2.0 μm or less. Therefore, if the ratio Ra1 / Ra3 is set to less than 0.01, the centerline average roughness Ra1 of the side surface 114S of the joining protrusion 114 must be set to 0.02 μm or less, which makes processing difficult. Furthermore, if the ratio Ra1 / Ra3 is set to more than 0.9, the centerline average roughness Ra1 of the side surface 114S of the joining protrusion 114 becomes equal to or greater than the centerline average roughness Ra3 of the side surface 132S of the large diameter portion 132 of the shaft 130. Therefore, heat radiation from the side surface 114S of the joining protrusion 114 increases, resulting in poor temperature uniformity in the upper surface 111 of the ceramic base 100 in the portion directly above the side surface 114S of the joining protrusion 114.

[0064] <Modification form> The above-described embodiment is merely illustrative and may be modified as appropriate. For example, the shapes and dimensions of the ceramic base 110 and the shaft 130 are not limited to those of the above-described embodiment and may be modified as appropriate. The dimensions such as the height and width of the annular protrusion 152, the cross-sectional shape of the upper surface 152a of the annular protrusion 152, and the centerline average roughness Ra of the upper surface 152a may be modified as appropriate.

[0065] The height of the multiple protrusions 156, the shape of the upper surface 156a, and the centerline average roughness Ra of the upper surface 156a may be changed as appropriate. For example, the shape of the upper surface 156a of the multiple protrusions 156 does not necessarily have to be circular and can be any shape. Even in such a case, it is preferable that the multiple protrusions 156 have an area approximately equal to that of a circle with a diameter of 0.1 mm to 5 mm. Furthermore, in the above description, the multiple protrusions 156 are arranged concentrically, but the present invention is not limited to such an embodiment. For example, the multiple protrusions 156 may be continuously arranged in a lattice pattern, distributed at the vertices of an equilateral triangle or regular rectangle, or may be arranged so that the multiple protrusions 156 are distributed at random positions. Even in such cases, the distance between each of the multiple protrusions 156 is preferably in the range of 1.5 mm to 30 mm.

[0066] In the above embodiment and Examples 1 to 7, the centerline average roughness Ra1 of the side surface SL of the joining protrusion 114 and the centerline average roughness Ra2 of the region S1 of the lower surface 113 of the ceramic base 100 within 5 μm from the boundary with the joining protrusion 114 were the same. However, the present invention is not limited to such an embodiment. As long as the centerline average roughness Ra1 is 0.1 μm or less and the centerline average roughness Ra2 is 0.1 μm or less, the centerline average roughness Ra1 and the centerline average roughness Ra2 can each be adjusted to an appropriate value.

[0067] As shown in FIG. 10( a), terminal holes 142 are provided in an area of ​​the lower surface 114B of the bonding protrusion 114 inside the large diameter portion 132 of the shaft 130, for arranging a power supply line 140 for supplying power to the heater electrode 122 and a power supply line 141 for supplying power to the electrostatic attraction electrode 124. There is a risk of cracks occurring in these terminal holes 142. Therefore, by setting the centerline average roughness of the surface of the inner wall of the terminal hole 142 to 0.1 μm or less, it is possible to prevent cracks from occurring in the terminal hole 142. Furthermore, by setting the centerline average roughness of the surface of the inner wall of the terminal hole 142 to 0.1 μm or less, it is possible to further prevent cracks from occurring in the terminal hole 142. It is considered that cracks are more likely to occur in the corners of the inner wall of the terminal hole 142, between the side wall and the bottom wall. Therefore, by setting the center line average roughness Ra of the side walls of terminal hole 142 and the center line average roughness Ra of the bottom wall within 5 mm from the boundary between the side walls and the bottom wall to 2.0 μm or less, it is possible to prevent cracks from occurring at the corners between the side walls and the bottom wall on the inner wall of terminal hole 142. Furthermore, by setting the center line average roughness Ra of the side walls of terminal hole 142 and the center line average roughness Ra of the bottom wall within 5 mm from the boundary between the side walls and the bottom wall to 0.1 μm or less, it is possible to further prevent cracks from occurring at the corners between the side walls and the bottom wall on the inner wall of terminal hole 142.

[0068] As shown in FIG. 10( b), a recess 145 can be provided on the lower surface 114B of the joining protrusion 114 in a region inside the large-diameter portion 132 of the shaft 130. By providing the recess 145, the annular portion of the lower surface 114B of the joining protrusion 114 that joins with the upper surface of the large-diameter portion 132 of the shaft 130 can be protruded downward relative to the remaining portions. This reduces the area of ​​the lower surface 114B, which is the joining surface of the joining protrusion 114, that is subjected to mirror polishing, thereby improving productivity. However, cracks may also occur in the recess 145. Therefore, by setting the centerline average roughness of the surface of the inner wall of the recess 145 to 2.0 μm or less, cracks can be prevented from occurring in the recess 145. Furthermore, by setting the centerline average roughness of the surface of the inner wall of the recess 145 to 0.1 μm or less, cracks can be further prevented from occurring in the recess 145. It is considered that there is a high possibility of cracks occurring at the corners between the side walls and the bottom wall of the inner walls of the recess 145. Therefore, by setting the center line average roughness Ra of the side walls of the recess 145 and the center line average roughness Ra of the bottom wall within 5 mm from the boundary between the side walls and the bottom wall to 2.0 μm or less, it is possible to prevent cracks from occurring at the corners between the side walls and the bottom wall of the inner walls of the recess 145. It is also possible to further prevent cracks from occurring at the corners between the side walls and the bottom wall of the inner walls of the recess 145 by setting the center line average roughness Ra of the side walls of the recess 145 and the center line average roughness Ra of the bottom wall within 5 mm from the boundary between the side walls and the bottom wall to 0.1 μm or less.

[0069] In the above embodiment, molybdenum, tungsten, or an alloy containing molybdenum and / or tungsten is used as the heater electrode 122, but the present invention is not limited to such an embodiment. For example, metals or alloys other than molybdenum and tungsten may also be used. Furthermore, the electrode 120 includes the heater electrode 122 as a heating element. However, the electrode 120 does not necessarily need to include the heater electrode 122 as a heating element, and may include, for example, a high-frequency electrode as a heating element.

[0070] In the above embodiment, the ceramic heater 100 includes the electrodes 120 (heater electrode 122 and electrostatic attraction electrode 124) embedded in the ceramic base 110, but the present invention is not limited to such an embodiment, and the electrodes 120 do not have to be embedded in the ceramic base 110 of the ceramic heater 100. For example, the heater electrode 122 or high-frequency electrode serving as the electrode 120 may be attached to the rear surface 113 of the ceramic base 110.

[0071] In the above embodiment, shaft 130 includes large diameter portions 132 and 133, but the present invention is not limited to such an embodiment, and shaft 130 does not necessarily have to include large diameter portions 132 and 133. Furthermore, second gas flow path 168 extending in vertical direction 5 does not have to be formed in cylindrical portion 131 of shaft 130. For example, instead of second gas flow path 168, a separate gas pipe can be provided in the hollow region of cylindrical portion 131 (the region where power supply line 140 is provided).

[0072] Although the present invention has been described above using embodiments and modifications thereof, the technical scope of the present invention is not limited to the scope of the above description. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0073] The order of execution of each process in the manufacturing method shown in the specification and drawings is not particularly specified, and the processes may be executed in any order unless the output of a previous process is used in a subsequent process. For convenience, even if a description is made using "first," "next," etc., it does not mean that the processes must be executed in this order. [Explanation of symbols]

[0074] 100 Substrate holding member 110 Ceramic substrate 120 electrodes 130 shaft 140 Feed line 152 Annular convex part 156 Multiple protrusions

Claims

1. a ceramic substrate having an upper surface, a lower surface facing the upper surface in the vertical direction, and a protrusion protruding downward from the lower surface; a heating element embedded in the ceramic substrate; a cylindrical shaft joined to the protrusion of the ceramic base, a center line average roughness Ra1 of the side surface of the convex portion and a center line average roughness Ra2 of the lower surface of the ceramic base within 5 mm from the boundary with the convex portion are both 0.1 μm or less, A ceramic heater characterized in that the side surfaces of the protrusions are free of microcracks larger than 3 μm in width and scratches larger than 3 μm in width.

2. A ceramic heater as described in claim 1, wherein the R chamfer dimension or C chamfer dimension of the boundary between the lower surface of the ceramic substrate and the convex portion is less than 1 mm.

3. A recess is provided on the lower surface of the convex portion, the recess being recessed upward from the lower surface of the convex portion, 2. A ceramic heater according to claim 1, wherein the center line average roughness of the recesses is 2.0 μm or less.

4. A recess is provided on the lower surface of the convex portion, the recess being recessed upward from the lower surface of the convex portion, 3. A ceramic heater according to claim 2, wherein the center line average roughness of the recesses is 2.0 μm or less.

5. The shaft has the same diameter as the convex portion and has a joining portion that is joined to the convex portion, A ceramic heater according to any one of claims 1 to 4, wherein the ratio Ra1 / Ra3 of the center line average roughness Ra1 of the side surface of the convex portion to the center line average roughness Ra3 of the side surface of the joint portion of the shaft is 0.01 or more and 0.9 or less.

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