Ceramic heater

Abstract

To provide a ceramic heater capable of suppressing heat from escaping from a ceramic base material to a shaft.SOLUTION: The ceramic heater 100 includes a ceramic substrate 110, an electrode foil 120, and a shaft 130. In a region where the groove 114 is formed on the side surface of the bonded portion 113 of the ceramic base material 110, a first position 113a, a second position P1, and a third position P2 are arranged in order upward from the bonded surface P3, and a line width L1 of the bonded portion 113 in the first position P1, a line width L2 of the bonded portion 113 in the second position P2, and a line width P3 of the bonded portion 113 in the third position satisfy a relationship of <. L3 L2 L1, in addition, there are a first position L2, a second position L3, and a third position 2LS satisfying P1 <P2 <P3.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a ceramic heater with a shaft, which includes a ceramic substrate on whose upper surface an object to be heated is placed, a heating resistor embedded in the ceramic substrate, and a support member (shaft) that supports the ceramic substrate. The support member has a substantially cylindrical tubular portion and an extension portion located at the upper end of the tubular portion and having an outer diameter larger than that of the tubular portion. The upper surface of the extension portion is joined to the lower surface of the ceramic substrate. Furthermore, a recess is formed on the lower surface of the extension portion at the boundary between the tubular portion and the extension portion, surrounding the tubular portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-220554 Summary of the Invention [Problem to be solved by the invention]

[0004] A recess is formed on the underside of the extension portion at the boundary between the cylindrical portion and the extension portion, which prevents heat that has flowed from the ceramic base into the extension portion from escaping back to the cylindrical portion. However, it is not possible to prevent heat from escaping from the ceramic base to the support member (shaft) at the joint between the ceramic base and the support member (shaft).

[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 prevent heat from escaping from the ceramic substrate to the shaft. [Means for solving the problem]

[0006] According to an aspect of the present invention, there is provided a ceramic substrate having an upper surface on which an object to be heated is placed, a lower surface facing the upper surface in the vertical direction, and a joint portion protruding downward from the lower surface in the vertical direction and having a joint surface parallel to the upper surface, a heating element embedded in the ceramic substrate, a cylindrical shaft having an upper surface joined to the joint surface and a lower surface facing the upper surface in the vertical direction, the outer diameter of the upper surface being the same as the outer diameter of the joint surface of the joint portion, and the outer diameter of the opening of the upper surface being smaller than the outer diameter of the opening of the lower surface, the side surface of the joint portion of the ceramic substrate has a first position, a second position, and a third position arranged in order upward from the joint surface in the vertical direction, let the width in the horizontal direction perpendicular to the vertical direction of the joint portion at the first position be L1, let the width in the horizontal direction of the joint portion at the second position be L2, let the width in the horizontal direction of the joint portion at the third position be L3, when the width in the horizontal direction of the shaft on the upper surface is LS, L1>L2 and L2<L3<2LS A ceramic heater is provided which has a first position, a second position, and a third position that satisfy the above conditions.

Advantages of the Invention

[0007] In the above aspect, on the side surface of the joint portion of the ceramic substrate, there exist a first position, a second position, and a third position such that L2<L1 and L2<L3<2LS. In this case, at least at the second position, a constriction is formed where the cross-sectional area of the joint portion temporarily becomes narrow. Thereby, the flow of heat flowing from the ceramic substrate to the shaft can be suppressed.

Brief Description of the Drawings

[0008] [Figure 1]FIG. 1 is a schematic diagram of a ceramic heater 100. As shown in FIG. [Figure 2] FIG. 2 is a schematic diagram of the electrode foil 120. [Figure 3] FIG. 3 is an explanatory diagram for explaining the ceramic heater 100. As shown in FIG. [Figure 4] 4(a) to 4(e) are diagrams showing the flow of a method for manufacturing the ceramic base 110. [Figure 5] 5(a) to 5(e) are diagrams showing the flow of another method for manufacturing the ceramic base 110. In FIG. [Figure 6] 6(a) to 6(c) are diagrams showing the flow of a method for manufacturing the ceramic heater 100. [Figure 7] 7(a) and (b) are diagrams showing the flow of a manufacturing method for the ceramic heater 100A. [Figure 8] 8(a) and 8(b) are diagrams showing the flow of a manufacturing method for the ceramic heater 100B. [Figure 9] FIG. 9 is a view of the ceramic heater 100 of the first embodiment, which corresponds to FIG. [Figure 10] FIG. 10 is a view equivalent to FIG. 3 of the ceramic heater 100 of the second embodiment. [Figure 11] FIG. 11 is a view equivalent to FIG. 3 of a ceramic heater 100 according to a third embodiment. [Figure 12] FIG. 12 is a view equivalent to FIG. 3 of a ceramic heater 100B according to a fifth embodiment. [Figure 13] FIG. 13 is a view equivalent to FIG. 3 of a ceramic heater 100C of a comparative example. [Figure 14] 1 is a table summarizing the results of Examples 1 to 5 and a 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 Figure 1. The ceramic heater 100 is 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 foil 120, a shaft 130, and a power supply line 140.

[0010] The ceramic substrate 110 is a circular, plate-like member with a diameter of 12 inches (approximately 300 mm), and the wafer 10 to be heated is placed on its upper surface, i.e., the mounting surface 111. Note that in FIG. 1, the wafer 10 and the mounting surface 111 of the ceramic substrate 110 are shown separated from each other for clarity of the drawing. Although not shown in FIG. 1, multiple protrusions (multiple convex portions) are formed on the mounting surface 111 by sandblasting, as described below. Furthermore, as shown in FIG. 3, a bonding portion 113 (an example of a bonding portion of the present invention) that protrudes downward is provided at approximately the center of the back surface 112, i.e., the lower surface of the ceramic substrate 110. The ceramic substrate 110 can be formed from a ceramic sintered body such as aluminum nitride, alumina, or silicon nitride.

[0011] As shown in FIG. 1, an electrode foil 120 (one example of a heating element of the present invention) is embedded within the ceramic substrate 110. As shown in FIG. 2, the electrode foil 120 is a metal foil cut into a strip shape and has a bilaterally symmetrical shape. The outer diameter of the electrode foil 120 is approximately 300 mm. A terminal portion 121 for connection to a power supply line 140 (see FIG. 1) is provided approximately in the center of the electrode foil 120. The electrode foil 120 is formed of a foil of a heat-resistant metal (high-melting point metal) such as tungsten (W) foil, molybdenum (Mo) foil, or a foil of an alloy containing molybdenum and / or tungsten. The purity of the tungsten foil and molybdenum foil is preferably 99% or higher. 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 and reducing the current consumption of the ceramic heater 100, the thickness of the electrode foil 120 is preferably 0.1 mm or less. Furthermore, the width of the electrode foil 120 cut into a strip is preferably 2.5 mm to 20 mm, and more preferably 5 mm to 15 mm. In this 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. 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 110 may be embedded inside the ceramic base 110.

[0012] 3, a convex portion (hereinafter referred to as a joint portion 113) that protrudes downward is provided approximately at the center of the rear surface 112 of the ceramic base material 110. The joint portion 113 has a generally cylindrical shape that extends in the up-down direction 5 (the longitudinal direction 6 of the shaft 130, which will be described later). A groove 114 is formed on the side surface of the joint portion 113, surrounding the joint portion 113 in the circumferential direction.

[0013] A shaft 130 is connected to a joint surface 113a, which is the lower end surface of the joint 113. The shaft 130 has a hollow, approximately cylindrical cylindrical portion 131 and a large-diameter portion 132 (see FIG. 1) provided below the cylindrical portion 131. The large-diameter portion 132 has a diameter larger than that of the cylindrical portion 131. In the following description, the longitudinal direction of the cylindrical portion 131 is defined as the longitudinal direction 6 of the shaft 130. As shown in FIG. 1, when the ceramic heater 100 is in use, the longitudinal direction 6 of the shaft 130 is parallel to the up-down direction 5.

[0014] The upper surface of the cylindrical portion 131 is fixed to the joint portion 113 of the ceramic base 110 with a bonding agent such as ceramic or glass. Alternatively, the cylindrical portion 131 and the shaft 130 may be fixed by diffusion bonding without using a bonding agent. The shaft 130 may be formed of a ceramic sintered body such as alumina, aluminum nitride, or silicon nitride, just like the ceramic base 110. Alternatively, in order to improve heat insulation, the shaft 130 may be formed of a material with lower thermal conductivity than the ceramic base 110.

[0015] As shown in FIG. 3, shaft 130 has a hollow cylindrical shape, and a through-hole extending in longitudinal direction 6 is formed inside shaft 130. As shown in FIG. 1, a power supply line 140 for supplying power to electrode foil 120 is arranged in the hollow portion (through-hole) of shaft 130. The upper end of power supply line 140 is electrically connected to terminal portion 121 (see FIG. 2) arranged in the center of electrode foil 120. A power supply terminal is provided at the lower end of power supply line 140, and is connected to a heater power supply (not shown). As a result, power is supplied to electrode foil 120 via power supply line 140.

[0016] 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.

[0017] First, a method for manufacturing the ceramic substrate 110 will be described. As shown in FIG. 4(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 mold with a bed 501 has a recess for forming the joint 113. The granulated powder P preferably contains 5 wt% or less of a sintering aid (e.g., Y2O3). Next, as shown in FIG. 4(b), an electrode foil 120 cut to a predetermined shape is placed on the pre-pressed granulated powder P. The electrode foil 120 is placed parallel to a plane perpendicular to the pressure direction (the bottom surface of the mold with a bed 501). At this time, W pellets or Mo pellets may be embedded in the electrode foil 120 at the positions of the terminals 121.

[0018] As shown in FIG. 4(c), granulated powder P is further poured into bed-type mold 501 so as to cover electrode foil 120, and is pressed and molded with punch 502. Next, as shown in FIG. 4(d), granulated powder P with electrode foil 120 embedded therein is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. Also, firing is preferably performed at a temperature of 1800°C or more. Next, as shown in FIG. 4(e), necessary processing is performed to form terminals 121, such as drilling blind holes down to electrode foil 120, to form ceramic substrate 110. If pellets are embedded, it is sufficient to drill blind holes down to the pellets.

[0019] The ceramic base material 110 can also be manufactured by the following method. As shown in Fig. 5(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. 5(b), the compact 510 is degreased to remove the binder.

[0020] As shown in FIG. 5(c), a recess 511 for embedding an electrode foil 120 is formed in a degreased molded body 510. An electrode foil 120 is placed in the recess 511 of the molded body 510, and another molded body 510 is stacked on top of it. Next, as shown in FIG. 5(d), the stacked molded bodies 510 are pressed together with the electrode foil 120 sandwiched between them and fired. The pressure applied during firing is preferably 1 MPa or more. Furthermore, firing is preferably performed at a temperature of 1800°C or higher. Next, as shown in FIG. 5(e), necessary processing is performed to form terminals 121, such as drilling blind holes down to the electrode foil 120, to form a ceramic base 110.

[0021] The upper surface (mounting surface 111) of the ceramic base 110 thus formed is subjected to surface grinding and lapping (mirror polishing). Furthermore, the mounting surface 111 is subjected to sandblasting to form a plurality of protrusions (a plurality of convex portions) (not shown) on the mounting surface 111. Note that sandblasting is a suitable processing method for forming a plurality of protrusions on the mounting surface 111, but other processing methods may also be used.

[0022] Furthermore, as shown in FIG. 6(a), the lower surface (rear surface 112) of the ceramic base 110 is machined to form a joint 113 in approximately the center of the rear surface 112. The outer diameter of the joint 113 is preferably the same as the outer diameter of the cylindrical portion 131 of the shaft 130 to be joined later. The outer diameter (diameter) of the joint 113 is preferably 100 mm or less. The height (length in the vertical direction 5) of the joint 113 is preferably 2 mm or more, and more preferably 5 mm or more. There is no upper limit to the height of the joint 113, but considering ease of manufacture, it is preferably 20 mm or less. Furthermore, the joint surface 113a of the joint 113 is parallel to the mounting surface 111. The surface roughness Ra of the joint surface 113a of the joint 113 is preferably 1.6 μm or less.

[0023] As shown in FIG. 6(b), the cylindrical portion 131 of the shaft 130 is fixed to the joining surface 113a of the joining portion 113. The length of the cylindrical portion 131 of the shaft 130 can be, for example, 50 mm to 500 mm. The shaft 130 can be formed as follows. First, granulated powder P of aluminum nitride to which several wt % of binder has been added is formed under hydrostatic pressure (approximately 1 MPa), and the formed body is processed into a predetermined shape. Thereafter, the formed body is fired in a nitrogen atmosphere. For example, the firing is performed at a temperature of 1900°C for two hours. Then, the sintered body is processed into a predetermined shape after firing, thereby forming the shaft 130. The upper surface of the cylindrical portion 131 and the joining surface 113a of the joining portion 113 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 surface roughness Ra of the bonding surface 113a of the bonding portion 113 is preferably 0.4 μm or less, and more preferably 0.2 μm or less. The upper surface of the cylindrical portion 131 and the bonding surface 113a of the bonding portion 113 of the ceramic base 110 can also 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 bonding surface 113a of the bonding portion 113 of the ceramic base 110 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 mounting surface 111 (the longitudinal direction 6 of the shaft 130). Alternatively, the upper surface of the cylindrical portion 131 and the bonding surface 113a of the bonding portion 113 of the ceramic base 110 can be fixed by screwing, brazing, or the like.

[0024] Next, as shown in FIG. 6(c), a cutting or grinding process is performed on the side surface of the joint portion 113 of the ceramic substrate 110 to form a groove 114. In the present embodiment, the cross-section of the groove 114 is substantially semi-circular. The groove 114 is formed so as to surround the side surface of the joint portion 113. In the present embodiment, the upper end of the groove 114 does not contact the back surface 112 of the ceramic substrate 110, and there is a gap in the vertical direction 5 between the upper end of the groove 114 and the back surface 112 of the ceramic substrate 110. In the following description, the outer diameter (horizontal width) of the shaft 130 on the surface joined to the joint surface 113a of the joint portion 113 is referred to as the outer diameter LS of the upper surface of the shaft 130. As shown in FIG. 6(c), in the region of the side surface of the joint portion 113 where the groove 114 is formed, there are three positions (first position P1, second position P2, third position P3) arranged in order from the joint surface 113a upward, and the width (horizontal length) L1 of the joint portion 113 at the first position P1, the width (horizontal length) L2 of the joint portion 113 at the second position P2, and the width (horizontal length) L3 of the joint portion 113 at the third position P3 are such that L2 < L1 and L2 < L3 < 2LS, and there exist the first position P1 to the third position P3. In the example shown in FIG. 6(c), the lower end of the groove 114 corresponds to the first position P1, the center in the vertical direction of the groove 114 corresponds to the second position P2, and the upper end of the groove 114 corresponds to the third position P3.

[0025] In the above description, after fixing the cylindrical portion 131 of the shaft 130 to the joint surface 113a of the joint portion 113, the groove 114 was formed on the side surface of the joint portion 113 of the ceramic substrate 110. However, it is also possible to first form the groove 114 on the side surface of the joint portion 113 of the ceramic substrate 110 and then fix the cylindrical portion 131 of the shaft 130 to the joint surface 113a of the joint portion 113.

[0026] Consider the case where the joining portion 113 of the ceramic substrate 110 is subjected to cutting or grinding before the cylindrical portion 131 of the shaft 130 is fixed to the joining surface 113a of the joining portion 113. In this case, instead of the ceramic heater 100 having grooves 114, the corners of the joining surface 113a of the joining portion 113 may be chamfered along the circumferential direction, as in the ceramic heater 100A shown in FIG. 7(a). This forms chamfered recesses 115 at the corners of the joining surface 113a of the joining portion 113. The cross-sectional shape of the recesses 115 is curved with a radius of curvature of 1 mm or more. After the recesses 115 are formed in the joining surface 113a of the joining portion 113, the cylindrical portion 131 of the shaft 130 is fixed to the joining surface 113a of the joining portion 113, as shown in FIG. 7(b). The fixing method is the same as that described above. The outer diameter (horizontal width) Lb of the joint surface 113a of the joint 113 is smaller than the outer diameter (horizontal width) LS of the upper surface of the flange 133. The surface roughness Ra of the recess 115 is preferably 0.1 μm or less.

[0027] Alternatively, as in the ceramic heater 100B shown in FIG. 8(a), cutting or grinding can be performed to form a tapered shape on the side of the joint 113 toward the joint surface 113a. The cross-sectional shape of the joint 113 is a curved shape with a curvature radius of 1 mm or more. As shown in FIG. 8(a), a flange 133 having a larger outer diameter than the cylindrical portion 131 is provided at the upper end of the shaft 130. Then, as shown in FIG. 8(b), the flange 133 of the shaft 130 is fixed to the joint surface 113a of the joint 113. The outer diameter (horizontal width) Lb of the joint surface 113a of the joint 113 is smaller than the outer diameter (horizontal width) LS of the upper surface of the flange 133. The surface roughness Ra of the tapered side of the joint 113 is preferably 0.1 μm or less.

[0028] In this manner, the ceramic heaters 100, 100A, and 100B according to this embodiment can be manufactured. As shown in FIG. 6(c), in the case of a ceramic heater 100 in which grooves 114 are formed in the joints 113, the horizontal cross-sectional area at the center of the groove 114 of the joints 113 (where the outer diameter is L2) is smaller than the horizontal cross-sectional areas at the bottom end of the groove 114 (where the outer diameter is L1) and the top end of the groove 114 (where the outer diameter is L3). In other words, a constriction is formed in the region of the joints 113 where the grooves 114 are formed, temporarily narrowing the horizontal cross-sectional area of ​​the joints 113. This makes it possible to suppress the flow of heat from the ceramic base 110 to the shaft 130. In other words, it is possible to suppress the loss of heat from the ceramic base 110 toward the shaft 130.

[0029] In the case of a ceramic heater 100A in which a recess 115 is formed in the joint 113 (see FIGS. 7(a) and 7(b)), or in the case of a ceramic heater 100B in which the side surface of the joint 113 is tapered toward the joint surface 113a (see FIGS. 8(a) and 8(b)), the outer diameter (horizontal width) Lb of the joint 113 at the joint surface 113a is smaller than the outer diameter (horizontal width) LS of the upper surface of the cylindrical portion 131 of the shaft 130. In this case as well, the flow of heat from the ceramic base 110 to the shaft 130 can be suppressed. In other words, the escape of heat from the ceramic base 110 toward the shaft 130 can be suppressed. [Example]

[0030] The present invention will be further described below using examples and comparative examples, but the present invention is not limited to the examples and comparative examples described below.

[0031] [Example 1] FIG. 9 shows the ceramic heater 100 of Example 1. Although not shown in FIG. 9, a molybdenum mesh (wire diameter 0.1 mm, mesh size #50, plain weave) was cut into the shape shown in FIG. 2 to form the electrode foil 120. A ceramic substrate 110 having a diameter of 310 mm and a thickness of 25 mm was then fabricated with this electrode foil 120 embedded therein. A joint 113 having an outer diameter of 70 mm and a height of 10 mm was formed on the back surface 111 of the ceramic substrate 110. The joint surface 113a of the joint 113 was processed to have a surface roughness Ra of 0.2 μm. A shaft 130 having an outer diameter of 70 mm and an inner diameter of 60 mm was also fabricated. The inner diameter of the upper surface of the shaft 130 was 50 mm. The surface roughness of the upper surface of the shaft 130 was 0.2 μm. The upper surface of the shaft 130 and the joining surface 113a of the joining portion 113 were joined by diffusion bonding using the procedure described above. Then, a groove 114 was formed on the side surface of the joining portion 113. The cross section of the groove 114 was approximately rectangular with a width of 6 mm and a depth of 3 mm, and the center of the groove 114 in the width direction (vertical direction) was located 5 mm away from the back surface 111 in the vertical direction. In other words, the vertical distance between the upper end of the groove 114 and the back surface 111 was 2 mm. In the cross section of the groove 114, the radius of curvature (R dimension) of the corner was approximately the same as the R dimension of the corner of the tool (0.3 mm or less). Furthermore, the surface roughness Ra of the inner surface of the groove 114 was 1.0 μm.

[0032] The ceramic heater 100 was evaluated for airtightness using the following procedure. First, the manufactured ceramic heater 100 was placed in a process chamber. Then, a current was passed through the ceramic heater 100 from an external power supply (not shown), and a temperature cycle of set temperatures from 650°C to 200°C was repeated. After each cycle, a visual check for damage and a leak check using a helium leak detector were performed. In the leak check, the lower opening of the shaft 130 was connected to the helium leak detector, and then helium gas was sprayed from the outside of the shaft 130 to evaluate the presence or absence of helium leaks from the joint 180, etc. -8 Pa·m 3 / s or more was observed, it was determined that a leak had occurred. In this example, no leak was observed even after four temperature cycles.

[0033] Furthermore, the temperature of the ceramic heater 100 was evaluated using the following procedure. A current was applied to the ceramic heater 100 from an external power supply (not shown), and the temperature was controlled 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. The temperature distribution in a 290 mm diameter area of ​​the silicon wafer for temperature evaluation was measured using an infrared camera. The silicon wafer for temperature evaluation was a 300 mm diameter silicon wafer coated with a 30 μm thick blackbody film on its upper surface. A blackbody film is a film with an emissivity (radiation rate) of 90% or higher and can be formed, for example, by coating a blackbody paint whose main ingredient is carbon nanotubes. The temperature difference Δ was calculated by subtracting the maximum temperature from the minimum temperature in the temperature distribution of the silicon wafer for temperature evaluation measured with the infrared camera. The temperature difference Δ is an index of the temperature distribution variation on the mounting surface 111 of the ceramic substrate 110. In Example 1, the temperature difference Δ relative to the set temperature of 400°C was 3.5°C.

[0034] [Example 2] FIG. 10 shows a ceramic heater 100 of Example 2. The ceramic heater 100 of Example 2 is similar to the ceramic heater 100 of Example 1, except that the cross-sectional shape of the groove 114 is semicircular with a radius of curvature of 3 mm, and the center of the groove 114 in the width direction (vertical direction) is located 3 mm away from the rear surface 111 in the vertical direction. The vertical distance between the upper end of the groove 114 and the rear surface 111 is 0 mm. The surface roughness of the inner surface of the groove 114 was 1.0 μm. In Example 2, no leakage was observed even after 12 temperature cycles. The temperature difference Δ from the set temperature of 400°C was 3.7°C.

[0035] [Example 3] FIG. 11 shows a ceramic heater 100 of Example 3. The ceramic heater 100 of Example 3 is similar to the ceramic heater 100 of Example 1, except that grooves 114 are formed in the ceramic substrate 110, each of which has a constricted shape toward the center. In the cross-sectional shape of the grooves 114, the tips of the grooves 114 in the depth direction have a semicircular shape with a radius of curvature of 3 mm. The distance D between the centers of the radii of curvature is 50 mm. The vertical distance between the center of the radius of curvature and the back surface 111 is 3 mm. The surface roughness Ra of the inner surface of the grooves 114 is 1.0 μm. In Example 3, no leakage was observed even after 12 temperature cycles. The temperature difference Δ from a set temperature of 400°C was 3.3°C.

[0036] [Example 4] The ceramic heater 100 of Example 4 is similar to Example 1, except that the radius of curvature of the corners of the cross-sectional shape of the grooves 114 is 1 mm, and the surface roughness of the inner surface of the grooves 114 is 0.09 μm. In Example 4, no leakage was observed even after 12 temperature cycles. Furthermore, the temperature difference Δ from the set temperature of 400°C was 3.5°C.

[0037] [Example 5] FIG. 12 shows a ceramic heater 100B according to Example 5. The side surface of the joint 113 of the ceramic heater 100 according to Example 5 is a tapered curved surface that tapers toward the joint surface 113a. The height of the joint 113 (the vertical distance from the back surface 112 to the joint surface 113a) is 5 mm, and the cross-sectional shape of the joint 113 is an arc-shaped curve with a radius of curvature of 5 mm. The surface roughness Ra of the side surface of the joint 113 is 0.08 μm. The shaft 130 is provided with a flange 133 at the upper end of the cylindrical portion 131, the flange 133 having an outer diameter larger than that of the cylindrical portion 131. The cylindrical portion 131 has an outer diameter of 60 mm and an inner diameter of 50 mm, while the flange 133 has an outer diameter of 70 mm and an inner diameter of 50 mm. In Example 5, no leakage was observed even after 12 temperature cycles. The temperature difference Δ relative to the set temperature of 400°C was 5.7°C.

[0038] [Comparative Example] FIG. 13 shows a ceramic heater 100C as a comparative example. In this comparative example, the longitudinal cross section of the joint 113 of the ceramic substrate 110 is substantially rectangular and does not have a tapered shape that narrows toward the joint surface 113a. Furthermore, the side surface of the joint 113 does not have a recess or groove that temporarily narrows the outer diameter. The outer diameter of the joint 113 is 90 mm. Furthermore, a flange 133 with a larger outer diameter than the cylindrical portion 131 is provided at the upper end of the cylindrical portion 131 of the shaft 130. The cylindrical portion 131 has an outer diameter of 70 mm and an inner diameter of 50 mm. The flange 133 has an outer diameter of 90 mm, an inner diameter of 60 mm, and a thickness of 15 mm. In this comparative example, leakage was observed after two temperature cycles. Furthermore, the temperature difference Δ from the set temperature of 400°C was 6.1°C.

[0039] <Summary of Examples and Comparative Examples> FIG. 14 shows a table summarizing the results of the above-mentioned Examples 1 to 5 and Comparative Example.

[0040] As shown in FIGS. 9 to 11, in the ceramic heaters 100 of Examples 1 to 4, grooves 114 are formed on the side surfaces of the joint portions 113. In Examples 1 to 4, in the region of the side surface of the joint portion 113 where the grooves 114 are formed, there are three positions (first position P1, second position P2, third position P3) arranged in order upward from the joint surface 113a. The width (horizontal length) L1 of the joint portion 113 at the first position P1, the width (horizontal length) L2 of the joint portion 113 at the second position P2, and the width (horizontal length) L3 of the joint portion 113 at the third position P3 are such that L2 < L1 and L2 < L3 < 2LS. In this case, at least at the second position P2, a constriction is formed where the horizontal cross-sectional area of the joint portion 113 temporarily becomes narrow. Thereby, the flow of heat flowing from the ceramic base material 110 to the shaft 130 can be suppressed. In contrast, in the comparative example (see FIG. 13), such first to third positions P1 to P3 do not exist, and no portion where the horizontal cross-sectional area temporarily becomes narrow is formed in the joint portion 113. Therefore, it is considered that the variation in the temperature distribution of the mounting surface 111 in the ceramic heaters 100 of Examples 1 to 4 can be made smaller than that of the ceramic heater 100C of the comparative example.

[0041] As shown in FIG. 12, in Example 5, the side surface of the joint portion 113 of the ceramic heater 100B has a tapered curved surface that tapers toward the joint surface 113a. The outer diameter (horizontal width) Lb of the joint portion 113 at the joint surface 113a is smaller than the outer diameter (horizontal width) LS of the upper surface of the cylindrical portion 131 of the shaft 130. Thereby, similar to Examples 1 to 4, the flow of heat flowing from the ceramic base material 110 to the shaft 130 can be suppressed. Therefore, it is considered that the variation in the temperature distribution of the mounting surface 111 in the ceramic heater 100B of Example 5 can be made smaller than that of the ceramic heater 100C of the comparative example.

[0042] Comparing Example 1 and Example 4, in the ceramic heater 100 of Example 1, the radius of curvature of the corners of the cross-sectional shape of the grooves 114 is less than 0.3 mm, whereas in the ceramic heater 100 of Example 4, the radius of curvature of the corners of the cross-sectional shape of the grooves 114 is 1 mm. Thus, by making the radius of curvature of the corners of the cross-sectional shape of the grooves 114 1 mm or more, it is possible to alleviate stress generated at the corners and suppress the occurrence of cracks at the corners. This is thought to be why the ceramic heater 100 of Example 4 is less likely to cause leakage than the ceramic heater 100 of Example 1. Furthermore, in Example 1, the surface roughness Ra of the inner surface of the grooves 114 including the corners is 1.0 μm, whereas in Example 4, the surface roughness Ra of the inner surface of the grooves 114 including the corners is 0.09 μm. Thus, it is thought that by making the surface roughness Ra of the inner surface of the grooves 114 including the corners 0.1 μm or less, it is possible to suppress the occurrence of cracks at the corners. This is also thought to be a factor in the ceramic heater 100 of Example 4 being less susceptible to leakage than the ceramic heater 100 of Example 1.

[0043] <Effects of the embodiment> In the above-described embodiments and examples, 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 joint portion 113 is provided on the back surface 112 facing the placement surface 111 of the ceramic base material 110. A groove 114 is provided on the side surface of the joint portion 113. As described above, in the region of the side surface of the joint portion 113 where the groove 114 is formed, there are a first position P1, a second position P2, and a third position P3 arranged in order upward from the joint surface 113a. The width (horizontal length) L1 of the joint portion 113 at the first position P1, the width (horizontal length) L2 of the joint portion 113 at the second position P2, and the width (horizontal length) L3 of the joint portion 113 at the third position P3 satisfy L2 < L1 and L2 < L3 < 2LS. In this case, at least at the second position P2, a constriction is formed in which the horizontal cross-sectional area of the joint portion 113 temporarily becomes narrow. Thereby, the flow of heat flowing from the ceramic base material 110 to the shaft 130 can be suppressed.

[0044] In the above-described embodiments and examples, the side surfaces of the joint portions 113 of the ceramic heaters 100A and 100B have a tapered curved surface that tapers toward the joint surface 113a. The outer diameter (horizontal width) Lb of the joint portion 113 at the joint surface 113a is smaller than the outer diameter (horizontal width) LS of the upper surface of the cylindrical portion 131 of the shaft 130. Thereby, the flow of heat flowing from the ceramic base material 110 to the shaft 130 can be suppressed.

[0045] In the above embodiments and examples, the cross-sectional shape of the groove 114 of the ceramic heater 100 can have a curved portion with a radius of curvature of 1 mm or more. In particular, the radius of curvature of the corners or other portions of the cross-sectional shape of the groove 114 of the ceramic heater 100 with the smallest radius of curvature can be 1 mm or more. Similarly, the cross-sectional shapes of the ceramic heaters 100A and 100B can have a curved portion with a radius of curvature of 1 mm or more. Stress can be alleviated in curved portions with a radius of curvature of 1 mm or more, and the occurrence of cracks in these portions can be suppressed. This can suppress the occurrence of leaks in the ceramic heaters 100, 100A, and 100B.

[0046] In the above embodiments and examples, the surface roughness Ra of the inner surface of the groove 114 of the ceramic heater 100 can be set to 0.1 μm or less. Similarly, the surface roughness Ra of the tapered curved surface that tapers toward the bonding surface 113a on the side surface of the bonding portion 113 of the ceramic heaters 100A, 100B can be set to 0.1 μm or less. This makes it possible to prevent cracks from occurring in areas with a surface roughness Ra of 0.1 μm or less, and to prevent leaks from occurring in the ceramic heaters 100, 100A, 100B.

[0047] <Modification form> The above-described embodiments are merely illustrative and may 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 may be modified as appropriate. The shape and dimensions of the joint 113 and the cross-sectional shape, width, and other dimensions of the groove 114 may also be modified as appropriate. The shape and dimensions of the tapered curved surface provided on the side of the joint 113 may also be modified as appropriate. In the above-described embodiments, molybdenum foil, tungsten foil, or foil of an alloy containing molybdenum and / or tungsten is used as the electrode foil, but the present invention is not limited to such embodiments. For example, foil of a metal other than molybdenum or tungsten, or foil of an alloy, may also be used.

[0048] In the above embodiment and Examples 1 to 5, when no flange 133 is formed at the upper end of shaft 130, the diameter of the upper surface of shaft 130 and the diameter of joining surface 113a of joining portion 113 are the same, but the present invention is not limited to such an embodiment, and the diameter of the upper surface of shaft 130 and the diameter of joining surface 113a of joining portion 113 can be changed to appropriate sizes.

[0049] 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.

[0050] 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]

[0051] 100 Ceramic heater 110 Ceramic substrate 113 Joint 114 Groove 115 recess 120 Electrode foil 130 shaft 140 Feed line

Claims

1. A ceramic base having an upper surface on which an object to be heated is placed, a lower surface facing the upper surface in the vertical direction, and a joint portion protruding downward in the vertical direction from the lower surface, the joint portion having a joint surface parallel to the upper surface; a heating element embedded in the ceramic substrate; a cylindrical shaft having an upper surface joined to the joining surface and a lower surface facing the upper surface in the up-down direction, the outer diameter of the upper surface being the same as the outer diameter of the joining surface of the joining portion, and the outer diameter of an opening of the upper surface being smaller than the outer diameter of an opening of the lower surface, The side surface of the joining portion of the ceramic base has a first position, a second position, and a third position which are arranged in this order from the joining surface upward in the vertical direction, A width of the joint portion at the first position in a horizontal direction perpendicular to the up-down direction is defined as L1, The horizontal width of the joint at the second position is L2, The horizontal width of the joint at the third position is L3, When the horizontal width of the shaft on the upper surface is LS, L1>L2 and L2<L3<2LS A ceramic heater having a first position, a second position, and a third position that satisfy the following:

2. 2. The ceramic heater according to claim 1, wherein a cross section of the joining portion of the ceramic base, which is parallel to the vertical direction, in a region including the first position, the second position, and the third position, has a curved portion with a radius of curvature of 1 mm or more.

3. 3. The ceramic heater according to claim 1, wherein the surface roughness Ra of the side surface of the joint portion of the ceramic base in a region including the first position, the second position, and the third position is 0.1 μm or less.

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