Ceramic heater

Abstract

To provide a ceramic heater capable of suppressing cracking from grinding traces left on a ground surface.SOLUTION: A ceramic heater 100 includes a ceramic substrate 110, a metal electrode foil 120 embedded in the ceramic substrate 110, and a shaft 130, and a joint portion 180 between a convex portion 113 and a pedestal portion 133 of the shaft 130, and rounded portions 114 and 134 are both ground surfaces, and a plurality of grinding marks SM parallel to the longitudinal direction 6 of the shaft 130 remain.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a ceramic heater.

Background Art

[0002] Patent Document 1 discloses a ceramic heater with a shaft, which includes a ceramic substrate on which an object to be heated is placed on the upper surface, a heating resistor embedded in the ceramic substrate, and a support member (shaft) for supporting the ceramic substrate. The support member is a substantially cylindrical member. At the upper end portion of the support member that is joined to the ceramic substrate, a diameter-expanded portion where the outer diameter is partially increased and a rounded portion where the outer diameter continuously increases toward the diameter-expanded portion are formed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Generally, the rounded portion is formed by grinding using a cylindrical processing machine. Specifically, grinding is performed by pressing a grindstone against the rounded portion while rotating the ceramic heater around a rotation axis parallel to the longitudinal direction of the support member (shaft). In this case, grinding marks (scratch marks) remain on the ground surface of the rounded portion along the rotation direction, that is, the direction orthogonal to the longitudinal direction of the support member (shaft). According to the inventors' findings, as described later, when stress acts along the longitudinal direction of the support member (shaft) due to the heat history, the grinding marks are pulled in the direction in which the width of the grinding marks expands, and there is a risk of cracks entering from the grinding marks.

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide a ceramic heater capable of suppressing cracks from occurring in a ground surface from grinding marks remaining on the ground surface.

Means for Solving the Problems

[0006] According to an aspect of the present invention, a long cylindrical shaft in the longitudinal direction, a ceramic base material joined to one end of the shaft in the longitudinal direction, the ceramic base material having a placement surface on which an object to be heated is placed, a back surface facing the placement surface in the longitudinal direction, and a convex portion protruding from the back surface toward the other side in the longitudinal direction, a heating element embedded in the ceramic base material, and a side surface of the convex portion of the ceramic base material or a joint portion between the convex portion and the shaft is a ground surface, the side surface of the convex portion or the joint portion between the convex portion and the shaft has grinding marks parallel to the longitudinal direction and the joint portion between the convex portion and the shaft has a polygonal shape when viewed from the longitudinal direction A ceramic heater is provided, which is characterized by the above.

Effects of the Invention

[0007] In the above aspect, both the side surface of the convex portion and the joint portion between the convex portion and the shaft are ground surfaces. And, grinding marks parallel to the longitudinal direction of the shaft remain on the side surface of the convex portion or the joint portion between the convex portion and the shaft. In such a case, even when a stress parallel to the longitudinal direction of the shaft is applied, the grinding marks are not pulled in a direction in which the width expands. Therefore, it is possible to suppress cracks from occurring from the grinding marks.

Brief Description of the Drawings

[0008] [Fig. 1] FIG. 1 is a schematic view of a ceramic heater 100. [Fig. 2] FIG. 2 is a schematic view of an electrode foil 120. [Fig. 3]Figs. 3(a) to 3(e) are diagrams showing the process of the method for manufacturing the ceramic substrate 110. [Fig. 4] Figs. 4(a) to 4(e) are diagrams showing the process of another method for manufacturing the ceramic substrate 110. [Fig. 5] Fig. 5 is an explanatory diagram for explaining the grinding process using the shaft grinding wheel 119. [Fig. 6] Fig. 6 is an explanatory diagram for explaining a plurality of grinding marks SM parallel to the longitudinal direction of the shaft 130 remaining on the grinding surface. [Fig. 7] It is a table summarizing the results of Examples 1 to 4 and Comparative Example 1. [Fig. 8] It is a table summarizing the results of Examples 5 to 9 and Comparative Example 2. [Fig. 9] Fig. 9 is an explanatory diagram for explaining a plurality of grinding marks SM parallel to the longitudinal direction of the shaft 130 remaining in the rounded portion 185.

DETAILED DESCRIPTION OF THE INVENTION

[0009] <Ceramic heater 100> The ceramic heater 100 according to an embodiment of the present invention will be described with reference to Fig. 1. The ceramic heater 100 is used for heating a semiconductor wafer such as a silicon wafer (hereinafter simply referred to as wafer 10). In the following description, the vertical direction 5 is defined based on the state in which the ceramic heater 100 is installed for use (the state in Fig. 1). As shown in Fig. 1, the ceramic heater 100 according to the present embodiment includes a ceramic substrate 110, an electrode foil 120, a shaft 130, and a power supply line 140.

[0010] The ceramic substrate 110 is a member having a circular plate shape with a diameter of 12 inches (about 300 mm), and the wafer 10 to be heated is placed on the placement surface 111 which is the upper surface thereof. In FIG. 1, the wafer 10 and the placement surface 111 of the ceramic substrate 110 are shown separated from each other for easy viewing of the drawing. Although not shown in FIG. 1, a plurality of protrusions (a plurality of convex portions) are formed on the placement surface 111 by performing sandblasting as described later. Further, as shown in FIG. 5, a convex portion 113 protruding downward is provided at substantially the center of the back surface 112 which is the lower surface of the ceramic substrate 110. The ceramic substrate 110 can be formed of, for example, a ceramic sintered body such as aluminum nitride, alumina, or silicon nitride.

[0011] As shown in FIG. 1, an electrode foil 120 (an example of the heating element of the present invention) is embedded inside the ceramic base material 110. As shown in FIG. 2, the electrode foil 120 is a metal foil cut into a strip shape and has a symmetric shape. The outer diameter of the electrode foil 120 is about 300 mm. At approximately the center of the electrode foil 120, a terminal portion 121 connected to a power supply line 140 (see FIG. 1) is provided. The electrode foil 120 is formed of a foil of a heat-resistant metal (high melting point metal) such as a tungsten (W) foil, a molybdenum (Mo) foil, or a foil of an alloy containing molybdenum and / or tungsten. The purity of the tungsten foil and the molybdenum foil is preferably 99% or more. The thickness of the electrode foil 120 is 0.15 mm or less. From the viewpoint of increasing the resistance value of the electrode foil 120 to reduce the current consumption of the ceramic heater 100, the thickness of the electrode foil 120 is preferably 0.1 mm or less. Also, the width of the electrode foil 120 cut into a strip shape is preferably 2.5 mm to 20 mm, and more preferably 5 mm to 15 mm. In the present embodiment, the electrode foil 120 is cut into the shape shown in FIG. 2, but the shape of the electrode foil 120 is not limited to this and can be changed as appropriate. Note that, in addition to the electrode foil 120, at least one of an electrostatic chuck electrode for attracting the wafer 10 to the mounting surface 111 by the Johnsen-Rahbek force and a plasma electrode for generating plasma above the ceramic base material 110 may be embedded inside the ceramic base material 110.

[0012] As shown in FIG. 5, a convex portion 113 protruding downward is provided substantially at the center of the back surface 112 of the ceramic base material 110, and the lower end of the convex portion 113 is connected to a shaft 130 extending downward. The shaft 130 has a hollow substantially cylindrical cylindrical portion 131, a large-diameter portion 132 (see FIG. 1) provided below the cylindrical portion 131, and a pedestal portion 133 provided above the cylindrical portion 131. The large-diameter portion 132 and the pedestal portion 133 have a diameter 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 FIG. 1, in the state where the ceramic heater 100 is used, the longitudinal direction 6 of the shaft 130 is parallel to the vertical direction 5. The upper surface of the pedestal portion 133 is fixed to the convex portion 113 of the ceramic base material 110 by an adhesive such as ceramic or glass. Note that the upper surface of the pedestal portion 133 and the convex portion 113 of the ceramic base 110 can be fixed by diffusion bonding. Alternatively, these can be fixed by screwing, brazing, or the like. Note that the shaft 130 may be formed of a ceramic sintered body such as alumina, aluminum nitride, or silicon nitride, similar to the ceramic base material 110. Alternatively, in order to enhance heat insulation, it may be formed of a material having a lower thermal conductivity than the ceramic base material 110.

[0013] As described above, the shaft 130 has a hollow cylindrical shape, and a through hole extending in the longitudinal direction 6 is formed therein. As shown in FIG. 1, a power supply line 140 for supplying power to the electrode foil 120 is disposed in the hollow portion (through hole) of the shaft 130. The upper end of the power supply line 140 is electrically connected to a terminal portion 121 (see FIG. 2) disposed at the center of the electrode foil 120. A power supply terminal is provided at the lower end of the power supply line 140 and is connected to a heater power supply (not shown). Thereby, power is supplied to the electrode foil 120 via the power supply line 140.

[0014] Next, a method for manufacturing the ceramic heater 100 will be described. Hereinafter, the case where the ceramic base material 110 and the shaft 130 are formed of aluminum nitride will be described as an example.

[0015] First, a method for manufacturing the ceramic substrate 110 will be described. As shown in FIG. 3(a), granulated powder P mainly composed of aluminum nitride (AlN) powder is put into a carbon floor type 501 and temporarily pressed with a punch 502. It is preferable that the granulated powder P contains a sintering aid (for example, Y2O3) of 5 wt% or less. Next, as shown in FIG. 3(b), an electrode foil 120 cut into a predetermined shape is disposed on the temporarily pressed granulated powder P. The electrode foil 120 is disposed so as to be parallel to a plane (the bottom surface of the floor type 501) perpendicular to the pressing direction. At this time, a W pellet or a Mo pellet may be embedded at the position of the terminal 121 of the electrode foil 120.

[0016] As shown in FIG. 3(c), further granulated powder P is put into the floor type 501 so as to cover the electrode foil 120, and pressed with a punch 502 to be formed. Next, as shown in FIG. 3(d), the granulated powder P in which the electrode foil 120 is embedded is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. Also, it is preferable to fire at a temperature of 1800 ° C or higher. Next, as shown in FIG. 3(e), necessary processing such as drilling a stop hole up to the electrode foil 120 is performed to form the terminal 121, and the ceramic substrate 110 is formed. When a pellet is embedded, it is only necessary to drill a stop hole up to the pellet.

[0017] Note that the ceramic substrate 110 can also be manufactured by the following method. As shown in FIG. 4(a), a binder is added to the granulated powder P of aluminum nitride and CIP molded, and processed into a disk shape to produce a molded body 510 of aluminum nitride. Next, as shown in FIG. 4(b), the molded body 510 is degreased to remove the binder.

[0018] As shown in FIG. 4(c), a recess 511 for embedding the electrode foil 120 is formed in the degreased molded body 510. The electrode foil 120 is disposed in the recess 511 of the molded body 510, and another molded body 510 is laminated. Note that the recess 511 may be formed in the molded body 510 in advance. Next, as shown in FIG. 4(d), the molded bodies 510 laminated so as to sandwich the electrode foil 120 are 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 higher. Next, as shown in FIG. 4(e), necessary processing such as drilling a stop hole up to the electrode foil 120 is performed to form the terminal 121, and the ceramic substrate 110 is formed.

[0019] Flat grinding is performed on the upper surface (mounting surface 111) of the ceramic substrate 110 thus formed, and lapping (mirror polishing) is performed. Further, by performing sandblasting on the mounting surface 111, a plurality of protrusions (a plurality of convex portions) are formed on the mounting surface 111. Note that sandblasting is a preferable processing method for forming a plurality of protrusions on the mounting surface 111, but other processing methods can also be used.

[0020] Furthermore, the lower surface (back surface 112) of the ceramic substrate 110 is processed to form a convex portion 113 substantially at the center of the back surface 112. Then, the pedestal portion 133 of the shaft 130 is fixed to the lower end of the convex portion 113. Note that the shaft 130 is formed by molding granulated powder P of aluminum nitride added with several wt% of a binder under a hydrostatic pressure (about 1 MPa), processing the molded body into a predetermined shape, and then firing in a nitrogen atmosphere.

[0021] Next, as shown in FIG. 5, the joint portion 180 between the convex portion 113 of the ceramic base material 110 and the pedestal portion 133 of the shaft 130 is ground using the shaft-mounted grinding wheel 191. A machining center is used for the grinding process. The joint portion 180 is a region that straddles the joint interface between the convex portion 113 and the pedestal portion 133, covering the side surfaces of the convex portion 113 and the pedestal portion 133. When grinding the joint portion 180, the longitudinal direction of the shaft-mounted grinding wheel 191 is arranged to be perpendicular to the longitudinal direction 6 of the shaft 130. Then, as shown in FIG. 5, the grinding of the joint portion 180 is performed by moving the shaft-mounted grinding wheel 191 in a direction perpendicular to its longitudinal direction. In other words, the grinding of the joint portion 180 is performed by moving the shaft-mounted grinding wheel 191 along the longitudinal direction 6 of the shaft 130. As a result, a plane parallel to the longitudinal direction 6 of the shaft 130 is formed on the side surfaces of the convex portion 113 and the pedestal portion 133. At this time, by moving the shaft-mounted grinding wheel 191 to the base end of the convex portion 113 of the ceramic base material 110 and performing the grinding process, a rounded portion 114 is formed at the base end of the convex portion 113 of the ceramic base material 110. Also, by moving the shaft-mounted grinding wheel 191 to the boundary portion between the pedestal portion 133 and the cylindrical portion 131 of the shaft 130 and performing the grinding process, a rounded portion 134 (an example of the tapered surface of the present invention) is formed at the boundary portion between the pedestal portion 133 and the cylindrical portion 131 of the shaft 130.

[0022] Thereafter, the ceramic base material 110 is rotated by a predetermined angle in the circumferential direction 7, and the same grinding process is performed. By repeating this, the shapes of the convex portion 113 of the ceramic base material 110 and the pedestal portion 133 of the shaft 130 become regular polygons when viewed from the longitudinal direction 6 of the shaft 130. For example, the shapes of the convex portion 113 of the ceramic base material 110 and the pedestal portion 133 of the shaft 130 can be made into regular hexagons to regular 36-gons when viewed from the longitudinal direction 6 of the shaft 130. Instead of rotating the ceramic base material 110 in the circumferential direction 7 while fixing the position of the shaft-mounted grinding wheel 191 in the circumferential direction 7, the shaft-mounted grinding wheel 191 can be rotated in the circumferential direction 7 while fixing the position of the ceramic base material 110 in the circumferential direction 7. Alternatively, the ceramic base material 110 and the shaft-mounted grinding wheel 191 can be rotated simultaneously in the circumferential direction 7.

[0023] As the shaft-mounted grinding wheel 191, an electrodeposited grinding wheel with a mesh number (grit size) of 120 mesh or more (for example, a mesh number of about 120 mesh to 600 mesh) can be used. However, the mesh number of the shaft-mounted grinding wheel 191 is not limited to the above range and can be appropriately changed. Also, by changing the diameter of the shaft-mounted grinding wheel 191, the radius of curvature of the rounded portion 114 of the convex portion 113 of the ceramic substrate 110 and the rounded portion 134 of the shaft 130 can be adjusted.

[0024] In this way, the ceramic heater 100 according to the present embodiment can be manufactured. Generally, when grinding is performed by moving a grinding wheel in a predetermined direction, a plurality of grinding marks (scratch marks) extending along the moving direction of the grinding wheel remain on the grinding surface. The lengths of the respective grinding marks (the lengths along the moving direction of the grinding wheel) vary, but the widths of the respective grinding marks are equal to or less than the particle size of the grinding wheel. For example, when the shaft-mounted grinding wheel 191 with a mesh number of 120 mesh or more is used as described above, grinding marks with a width of about 130 μm or less remain on the grinding surface.

[0025] Although not described above, grinding is also performed on the area of the back surface 112 of the ceramic substrate 110 excluding the convex portions 113 and the rounded portions 114. However, similar to normal grinding, the grinding is performed by pressing a grinding wheel against the back surface 112 while rotating the ceramic substrate 110 in the circumferential direction 7. Since the direction in which the grinding wheel moves relative to the back surface 112 is arbitrarily set and changed in addition to the direction toward the center of the rotating body, no definite directionality is recognized in the direction in which the grinding marks remaining in the area of the back surface 112 of the ceramic substrate 110 excluding the convex portions 113 and the rounded portions 114 extend. On the other hand, as described above, when grinding is performed by moving the shaft-mounted grinding wheel 191 in one direction (the direction along the longitudinal direction 6 of the shaft 130) with the longitudinal direction of the shaft-mounted grinding wheel 191 being orthogonal to the longitudinal direction 6 of the shaft 130, a plurality of grinding marks SM parallel to the longitudinal direction of the shaft 130 remain on the ground surface (see FIG. 6). Generally, the grit size of the grinding wheel used for grinding the joint portion 180 and the rounded portions 114 and 134 is smaller than the grit size of the grinding wheel used for grinding the area of the back surface 112 of the ceramic substrate 110 excluding the convex portions 113 and the rounded portions 114. Therefore, the area of the back surface 112 of the ceramic substrate 110 excluding the convex portions 113 and the rounded portions 114 is distinguishable by visual inspection because it is different from the joint portion 180 and the rounded portions 114 and 134 in terms of color tone and contrast.

[0026] In the joint portion 180 between the convex portion 113 of the ceramic substrate 110 and the pedestal portion 133 of the shaft 130, a stress S acts in the longitudinal direction 6 of the shaft 130 due to the thermal history (see FIG. 6). Suppose that, similar to the back surface 112 of the ceramic substrate 110, grinding is performed by pressing a grinding wheel against the joint portion 180 while rotating the ceramic substrate 110 in the circumferential direction 7. Then, grinding marks along the circumferential direction 7 remain on the ground surface of the joint portion 180. In this case, when a stress S parallel to the longitudinal direction 6 of the shaft 130 as shown in FIG. 6 acts on the joint portion 180, each grinding mark will be pulled in the direction in which the width expands. As a result, there is a risk of cracks entering from the grinding marks.

[0027] In contrast, in the present embodiment, as described above, the grinding marks remaining on the ground surface of the joint portion 180 extend along the longitudinal direction 6 of the shaft 130. Therefore, even when a stress S parallel to the longitudinal direction 6 of the shaft 130 acts on the joint portion 180 as shown in FIG. 6, each grinding mark SM is not pulled in the direction in which the width expands. Therefore, it is possible to suppress cracks from entering from the grinding marks SM. Similarly, the grinding marks SM remaining on the ground surface of the rounded portion 114 of the convex portion 113 and the ground surface of the rounded portion 134 of the shaft 130 also extend along the longitudinal direction 6 of the shaft 130. Therefore, for the same reason as described above, it is possible to suppress cracks from entering from the grinding marks SM, and the strength of the rounded portions 114 and 134 can be increased.

Example

[0028] Hereinafter, the present invention will be further described using examples and comparative examples. However, the present invention is not limited to the examples and comparative examples described below.

[0029] [Example 1] In Example 1, as the electrode foil 120, a ceramic substrate 110 having a diameter of 320 mm and a thickness of 20 mm with a molybdenum foil having a thickness of 0.1 mm and a diameter of 300 mm embedded therein was produced. The outer diameter of the convex portion 113 was 100 mm. The cylindrical portion 131 of the shaft 130 had an outer diameter of 60 mm and an inner diameter of 50 mm. The pedestal portion 133 of the shaft 130 had an outer diameter of 80 mm. The shaft 130 had a height of 180 mm. The shaft 130 was joined to the convex portion 113 of the ceramic substrate 110 by diffusion bonding. At this time, diffusion bonding by uniaxial pressing at high temperature was performed under the conditions of 1800 ° C. and 1 MPa in a nitrogen atmosphere. Further, using a shaft-mounted grinding wheel 191 of 240 mesh, grinding was performed so that the shapes of the convex portion 113 of the ceramic substrate 110 and the pedestal portion 133 of the shaft 130 became hexagonal when viewed from the longitudinal direction 6 of the shaft 130. The grinding was performed using a machining center. The directions of the grinding marks remaining on the ground surfaces of the joint portion 180 and the rounded portions 114 and 134 were along the longitudinal direction 6 of the shaft 130. The radii of curvature of the rounded portions 114 and 134 were less than 1 mm.

[0030] The airtightness of the ceramic heater 100 was evaluated according to the following procedure. First, the fabricated ceramic heater 100 was placed in a process chamber. Then, an electric current was passed through the ceramic heater 100 from an external power source (not shown), and a temperature cycle of 650°C to 200°C was repeated. For each cycle, visual inspection for damage and leak check using a helium leak detector were performed. In the leak check, after connecting the opening below the shaft 130 to the helium leak detector, helium gas was blown from the outside of the shaft 130, and the presence or absence of helium leak from the joint portion 180 etc. was evaluated. 10 -8 Pa·m 3 When a leak of / s or more was recognized, it was determined that there was a leak. In this example, no leak was recognized even after repeating the temperature cycle 12 times.

[0031] [Example 2] In Example 2, except that the convex portion 113 of the ceramic base material 110 and the pedestal portion 133 of the shaft 130 were ground using a shaft-mounted grinding wheel 191 of 400 mesh count so as to be a dodecagon when viewed from the longitudinal direction 6 of the shaft 130, it was the same as Example 1. In Example 2, no leak was recognized even after repeating the temperature cycle 12 times.

[0032] [Example 3] In Example 3, except that the convex portion 113 of the ceramic base material 110 and the pedestal portion 133 of the shaft 130 were ground using shaft-mounted grinding wheels 191 of 240 mesh count and 600 mesh count so that part of them was a hexagon and part of them was a dodecagon when viewed from the longitudinal direction 6 of the shaft 130, it was the same as Example 1. In Example 3, no leak was recognized even after repeating the temperature cycle 12 times.

[0033] [Example 4] In Example 4, except that a shaft-mounted grinding wheel 191 with a count of 600 mesh was used to perform grinding so that the shapes of the convex portions 113 of the ceramic substrate 110 and the pedestal portions 133 of the shaft 130 were dodecagonal when viewed from the longitudinal direction 6 of the shaft 130, it was the same as Example 1. In Example 4, no leakage occurred even when 12 temperature cycles were repeated.

[0034] [Example 5] In Example 5, it was the same as Example 1 except that the radii of curvature of the rounded portions 114 and 134 were 0.03 mm. In Example 4, no leakage occurred even when 12 temperature cycles were repeated. Also, in Example 5, the temperature of the ceramic heater 100 was evaluated by the following procedure. A current was passed through the ceramic heater 100 from an external power source (not shown), and temperature control was performed at a set temperature of 400°C using a thermocouple (not shown). With the set temperature maintained at 400°C, a silicon wafer for temperature evaluation was placed on the mounting surface 111 of the ceramic substrate 110. Then, the temperature distribution in a region with a diameter of 290 mm of the silicon wafer for temperature evaluation was measured with an infrared camera. The silicon wafer for temperature evaluation is one obtained by coating the upper surface of a silicon wafer with a diameter of 300 mm with a blackbody film having a thickness of 30 μm. A blackbody film is a film having an emissivity of 90% or more, and can be formed, for example, by coating a blackbody paint mainly made of carbon nanotubes. The value obtained by subtracting the minimum temperature from the maximum temperature of the temperature distribution of the silicon wafer for temperature evaluation measured with the infrared camera was taken as the temperature difference Δ. The temperature difference Δ is an index of the variation in the temperature distribution of the mounting surface 111 of the ceramic substrate 110. In Example 5, the temperature difference Δ with respect to the set temperature of 400°C was 3.3°C.

[0035] Example 6 was the same as Example 2 except that the radii of curvature of the rounded portions 114 and 134 were 0.8 mm. In Example 6, no leakage occurred even when 12 temperature cycles were repeated. Also, the temperature of the ceramic heater 100 was evaluated by the same procedure as in Example 5. In Example 6, the temperature difference Δ with respect to the set temperature of 400°C was 3.5°C.

[0036] In Example 7, it is the same as Example 3 except that the radii of curvature of the rounded portions 114 and 134 are 0.8 mm. In Example 7, no leakage occurred even when 12 temperature cycles were repeated. Also, the temperature of the ceramic heater 100 was evaluated in the same procedure as in Example 5. In Example 7, the temperature difference Δ with respect to the set temperature of 400°C was 3.4°C.

[0037] In Example 8, it is the same as Example 1 except that the radii of curvature of the rounded portions 114 and 134 are 3 mm and the shapes of the convex portion 113 of the ceramic base material 110 and the pedestal portion 133 of the shaft 130 are ground to be 36-sided polygons when viewed from the longitudinal direction 6 of the shaft 130 using a 400-mesh grade shaft-mounted grinding wheel 191. In Example 8, no leakage occurred even when 12 temperature cycles were repeated. Also, the temperature of the ceramic heater 100 was evaluated in the same procedure as in Example 5. In Example 8, the temperature difference Δ with respect to the set temperature of 400°C was 4.5°C.

[0038] In Example 9, it is the same as Examples 2 and 6 except that the radii of curvature of the rounded portions 114 and 134 are 10 mm. In Example 9, no leakage occurred even when 12 temperature cycles were repeated. Also, the temperature of the ceramic heater 100 was evaluated in the same procedure as in Example 5. In Example 9, the temperature difference Δ with respect to the set temperature of 400°C was 5.7°C.

[0039] [Comparative Example 1] In Comparative Example 1, after joining the shaft 130 to the ceramic substrate 110 in the same manner as in Example 1, grinding was performed using a cylindrical processing machine so that the shapes of the convex portion 113 of the ceramic substrate 110 and the pedestal portion 133 of the shaft 130 were circular when viewed from the longitudinal direction 6 of the shaft 130. The direction of the grinding marks remaining on the ground surfaces of the joint portion 180 and the rounded portions 114 and 134 was perpendicular to the longitudinal direction 6 of the shaft 130. The radii of curvature of the rounded portions 114 and 134 were the same as in Example 1 (less than 1 mm). In Comparative Example 1, leakage occurred after repeating the temperature cycle twice.

[0040] [Comparative Example 2] In Comparative Example 2, in the same manner as in Comparative Example 1, grinding was performed using a cylindrical processing machine so that the shapes of the convex portion 113 of the ceramic substrate 110 and the pedestal portion 133 of the shaft 130 were circular when viewed from the longitudinal direction 6 of the shaft 130. The direction of the grinding marks remaining on the ground surfaces of the joint portion 180 and the rounded portions 114 and 134 was perpendicular to the longitudinal direction 6 of the shaft 130. The radius of curvature of the rounded portions 114 and 134 was 3 mm. In Comparative Example 2, leakage occurred after repeating the temperature cycle twice.

[0041] [Summary of Examples and Comparative Examples] Figs. 7 and 8 show a table summarizing the results of the above-described Examples 1 to 9 and Comparative Examples 1 and 2.

[0042] In Examples 1 to 9, the joining portion 180 and the rounded portions 114 and 134 were ground using the shaft-mounted grinding wheel 191 at a machining center. As a result, the direction of the grinding marks remaining on the ground surfaces of the joining portion 180 and the rounded portions 114 and 134 was along the longitudinal direction 6 of the shaft 130. Therefore, as described above, even when the stress S acts in the longitudinal direction 6 of the shaft 130 due to the thermal history, the grinding marks are not pulled in the direction in which the width of the grinding marks expands. Therefore, it is considered that the occurrence of cracks from the grinding marks could be suppressed. As a result, in any of Examples 1 to 9, no leakage was observed in the airtightness test. On the other hand, in Comparative Examples 1 and 2, grinding was performed by pressing a grinding wheel against the joining portion 180 and the rounded portions 114 and 134 while rotating the ceramic substrate 110 in the circumferential direction 7 using a cylindrical processing machine. In this case, the direction of the grinding marks remaining on the ground surfaces of the joining portion 180 and the rounded portions 114 and 134 was perpendicular to the longitudinal direction 6 of the shaft 130. When the stress S acts in the longitudinal direction 6 of the shaft 130 due to the thermal history, the grinding marks are pulled in the direction in which the width of the grinding marks expands, and there is a high possibility that cracks will enter from the grinding marks. In fact, in Comparative Examples 1 and 2, leakage occurred by repeating the above temperature cycle twice.

[0043] As in Examples 8 and 9, when the radius of curvature of the rounded portions 114 and 134 exceeds 1 mm, the temperature difference Δ, which is the value obtained by subtracting the minimum temperature from the maximum temperature of the temperature distribution of the silicon wafer for temperature evaluation, becomes 4°C or more. On the other hand, as in Examples 5 to 7, when the radius of curvature of the rounded portions 114 and 134 is less than 1 mm, the temperature difference Δ could be suppressed to less than 4°C. This is considered to be because when the radius of curvature of the rounded portions 114 and 134 is reduced, the thermal resistance in the rounded portions 114 and 134 becomes higher compared to when the radius of curvature is increased, and the heat transmitted to the shaft 130 and dissipated can be reduced.

[0044] <Operational Effects of the Embodiment> In the above-described embodiment, the ceramic heater 100 includes a ceramic base material 110, a metal electrode foil 120 embedded in the ceramic base material 110, and a shaft 130. A convex portion 113 is provided on the back surface 112 of the ceramic base material 110 facing the mounting surface 111. A rounded portion 114 is provided on the side surface of the convex portion 113, and a rounded portion 134 is provided on the side surface of the pedestal portion 133 of the shaft 130. As described above, the joint portion 180 between the convex portion 113 and the pedestal portion 133 of the shaft 130 and the rounded portions 114 and 134 are all ground surfaces, and a plurality of grinding marks SM parallel to the longitudinal direction 6 of the shaft 130 remain. As described above, even when a stress S parallel to the longitudinal direction 6 of the shaft 130 acts on the joint portion 180, the rounded portions 114 and 134, each grinding mark SM is not pulled in a direction in which the width expands. Therefore, it is possible to suppress the occurrence of cracks from the grinding marks SM.

[0045] In the above-described embodiment and examples, the shapes of the convex portion 113 of the ceramic base material 110 and the pedestal portion 133 of the shaft 130 are polygonal when viewed from the longitudinal direction 6 of the shaft 130. In this case, compared with the case where the shapes of the convex portion 113 and the pedestal portion 133 are circular when viewed from the longitudinal direction 6 of the shaft 130, it is easier to position the ceramic heater 100 in a predetermined chamber. Further, the polygonal shape can be adjusted as appropriate. Thereby, since the wall thickness of the pedestal portion 133 of the shaft 130 can be adjusted, the heat flow flowing through the shaft 130 can be adjusted to improve the heat uniformity of the mounting surface 111 of the ceramic base material 110.

[0046] In the above-described embodiments and examples, the radius of curvature of the rounded portion 114 of the convex portion 113 of the ceramic substrate 110 and the radius of curvature of the rounded portion 134 of the shaft 130 can be made less than 1 mm. In this case, compared with the case where the radius of curvature is increased, the thermal resistance in the rounded portions 114 and 134 can be increased, and the heat transmitted to the shaft 130 and dissipated can be reduced. As a result, it is possible to suppress the deterioration of components such as the O-ring provided on the shaft 130 due to heat, and to extend the life of these components.

[0047] <Modification> The above-described embodiments are merely illustrative and can be modified as appropriate. For example, the shapes and dimensions of the ceramic substrate 110 and the shaft 130 are not limited to those of the above-described embodiments and can be modified as appropriate. The shape of the convex portion 113 of the ceramic substrate 110 and the pedestal portion 133 of the shaft 130, as viewed from the longitudinal direction 6 of the shaft 130, can also be an arbitrary polygonal shape. Further, in the above-described embodiments, molybdenum foil, tungsten foil, or a foil of an alloy containing molybdenum and / or tungsten was used as the electrode foil, but the present invention is not limited to such an aspect. For example, a foil of a metal other than molybdenum and tungsten, or a foil of an alloy can also be used.

[0048] In the above-described embodiments and Examples 1 to 9, both the rounded portion 114 of the convex portion 113 of the ceramic substrate 110 and the rounded portion 134 of the shaft 130 were provided, but the present invention is not limited to such an aspect. Either one or both of the rounded portion 114 of the convex portion 113 of the ceramic substrate 110 and the rounded portion 134 of the shaft 130 may not be provided.

[0049] In the above-described embodiments and Examples 1 to 9, the shaft 130 had a pedestal portion 133, and a rounded portion 134 was provided on the side surface of the pedestal portion 133. However, the present invention is not limited to such an aspect. For example, as shown in FIG. 9, at the joint portion 180 between the shaft 130 and the convex portion 113, the shaft 130 and the convex portion 113 may be integrally formed and have a rounded portion 185 (an example of the tapered surface of the present invention) that becomes thinner toward the lower side (one side in the longitudinal direction 6). Even in this case, a plurality of grinding marks SM parallel to the longitudinal direction 6 of the shaft 130 remain on the rounded portion 185, which is a ground surface. As described above, even when a stress S parallel to the longitudinal direction 6 of the shaft 130 acts on the rounded portion 185 of the joint portion 180, each grinding mark SM is not pulled in the direction in which the width expands. Therefore, it is possible to suppress cracks from entering from the grinding marks SM.

[0050] As described above, the embodiments of the invention and their modified forms have been described, but the technical scope of the present invention is not limited to the scope described above. It will be apparent to those skilled in the art that various changes or improvements can be made to the above-described embodiments. It is also apparent from the description of the claims that forms incorporating such changes or improvements can also be included in the technical scope of the present invention.

[0051] In the manufacturing method shown in the specification and drawings, the execution order of each process is not particularly specified, and unless the output of the previous process is used in the subsequent process, it can be executed in any order. For the sake of convenience, even if it is described using "first," "next," etc., it does not mean that it is essential to implement in this order.

Explanation of Reference Numerals

[0052] 100 Ceramic Heater 110 Ceramic Substrate 120 Electrode Foil 130 Shaft 140 Feeder Line

Claims

1. A shaft in the shape of a long cylinder in the longitudinal direction, a ceramic substrate joined to one end of the shaft in one side of the longitudinal direction, the ceramic substrate having a placement surface on which an object to be heated is placed, a back surface facing the placement surface in the longitudinal direction, and a convex portion protruding from the back surface to the other side in the longitudinal direction, a heating element embedded in the ceramic substrate, and a side surface of the convex portion of the ceramic substrate or a joint portion between the convex portion and the shaft is a ground surface, the side surface of the convex portion or the joint portion between the convex portion and the shaft has grinding marks parallel to the longitudinal direction, the joint portion between the convex portion and the shaft has a polygonal shape when viewed from the longitudinal direction, characterized in that it is a ceramic heater.

2. A shaft in the shape of a long cylinder in the longitudinal direction, a ceramic substrate joined to one end of the shaft in one side of the longitudinal direction, the ceramic substrate having a placement surface on which an object to be heated is placed, a back surface facing the placement surface in the longitudinal direction, and a convex portion protruding from the back surface to the other side in the longitudinal direction, a heating element embedded in the ceramic substrate, and a side surface of the convex portion of the ceramic substrate or a joint portion between the convex portion and the shaft is a ground surface, the side surface of the convex portion or the joint portion between the convex portion and the shaft has grinding marks parallel to the longitudinal direction, at the joint portion between the convex portion and the shaft, the shaft has a tapered surface that becomes thinner toward the other side in the longitudinal direction, the tapered surface of the shaft is a ground surface, the tapered surface has grinding marks parallel to the longitudinal direction, characterized in that it is a ceramic heater.

3. The ceramic heater according to Claim 1 or 2, wherein a cross section parallel to the longitudinal direction of a boundary portion between the back surface and the convex portion of the ceramic substrate has a curved portion with a radius of curvature of less than 1 mm.

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