JP2009176569A - Ceramic heater and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic heater capable of suppressing the degradation of strength of a joint part caused by heating. <P>SOLUTION: The ceramic heater includes a plate part 10 formed of a first ceramic sintered body for placing a heated object on the upper face, and a shaft part 12 jointed to the lower face of the plate part 10. The shaft part 12 has a first member 14 joined at one end to the lower face of the plate part 10 and formed of a ceramic sintered body of the same composition as the first ceramic sintered body, and a second member 16 joined to the other end of the first member 14 and formed of a second ceramic sintered body lower in heat conductivity than the plate part 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ceramic heater used in an electronic device manufacturing apparatus and a manufacturing method thereof.

  High temperature processing such as chemical vapor deposition (CVD) and surface modification is used in the manufacturing process of electronic devices such as semiconductor devices and liquid crystal devices. For example, in CVD, a substrate to be processed is placed on a ceramic heater provided in a reaction chamber of a CVD apparatus. The substrate is heated to a high temperature of about 500 ° C. or higher by a ceramic heater, and a semiconductor film or an insulating film is formed on the substrate.

  The ceramic heater is manufactured by joining a cylindrical shaft portion to the lower surface of a flat plate portion made of aluminum nitride (AlN) (see Patent Document 1). A heating element is embedded in the plate portion. The upper surface of the plate portion becomes the mounting surface of the substrate. The ceramic heater is fixed to the reaction chamber by a shaft portion.

  For the plate portion, a material having high thermal conductivity in which an additive is added to AlN is used in order to improve the thermal uniformity. On the other hand, in the ceramic heater, the heat of the plate portion is transmitted through the shaft portion and escapes. Therefore, a cool spot is formed in the vicinity of the region where the shaft portion is joined, and the heat uniformity on the upper surface of the plate portion is deteriorated. In order to prevent heat dissipation through the shaft portion, the shaft portion uses high-purity aluminum nitride having a lower thermal conductivity than the plate portion as a material.

As described above, by using AlN having different purity for the plate portion and the shaft portion, heat radiation through the shaft portion can be reduced, and deterioration of the heat uniformity on the upper surface of the plate portion can be prevented.
Japanese Patent No. 2783980

  Recently, there is an increasing demand for using a ceramic heater in a harsh situation for a long time at a higher temperature than before. However, when such a ceramic heater is used at a high temperature for a long time, the strength in the vicinity of the joint between the plate portion and the shaft portion is lowered. As a result, it has been found that the durability of the ceramic heater deteriorates and may be damaged when an excessive load is applied.

  The objective of this invention is providing the ceramic heater which can suppress such deterioration of intensity | strength, and its manufacturing method.

  According to the first aspect of the present invention, (a) a plate portion made of a first ceramic sintered body on which an object to be heated is placed on the upper surface, and (b) a shaft portion joined to the lower surface of the plate portion. (C) a first member made of a ceramic sintered body having the same composition as that of the first ceramic sintered body, and (c) the shaft portion having one end bonded to the lower surface of the plate portion; A ceramic heater having a second member made of a second ceramic sintered body that is bonded to the other end of one member and has a lower thermal conductivity than the plate portion is provided.

  According to the second aspect of the present invention, (a) a step of forming a plate portion made of a first ceramic sintered body on which an object to be heated is placed, and (b) the same as the first ceramic sintered body. A step of forming a cylindrical first member made of a ceramic sintered body of the composition, and (c) a step of forming a cylindrical second member made of the second ceramic sintered body having a lower thermal conductivity than the plate portion. (2) a step of joining one end of the second member to the other end of the first member by hot pressing; and (e) joining one end of the first member to the lower surface of the plate portion after joining the first and second members. There is provided a method for manufacturing a ceramic heater including a step of bonding by hot pressing.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the ceramic heater which can suppress the deterioration of the intensity | strength of the junction part by heating, and its manufacturing method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  As shown in FIGS. 1 and 2, the ceramic heater according to the embodiment of the present invention includes a plate portion 10, a shaft portion 12, a heating element 18, and the like. A heating element 18 is embedded in the plate portion 10. The shaft portion 12 includes a first member 14 and a second member 16.

  The plate part 10 has a disk shape, for example, if the object to be heated is a circular semiconductor substrate. The object to be heated is placed on the upper surface of the plate portion 10 and heated by the heating element 18 embedded in the plate portion 10. An electrode terminal (not shown) is connected to the heating element 18. The ceramic heater is not limited to a disk shape, and may be a polygonal shape, for example.

  The ceramic heater is fixed to a reaction chamber (not shown) such as a CVD apparatus by a cylindrical shaft portion 12. A flange 20 for joining the first member 14 to the lower surface of the plate portion 10 is provided at one end of the first member 14 of the shaft portion 12. A flange 22 to which the second member 16 is joined is provided at the other end of the first member 14. The first member 14 has a convex curvature in the cylindrical radial direction between the flange 20 at one end and the flange 22 at the other end, and the diameter decreases from the flange 20 toward the flange 22. Has a shape. A flange 24 joined to the flange 22 is provided at one end of the second member 16. At the other end of the second member 16, a flange 26 for fixing to the reaction chamber (not shown) is provided. The second member 16 has a cylindrical shape having substantially the same diameter from the flange 24 at one end toward the flange 26 at the other end.

  The diameter of the plate part 10 is, for example, 200 mm to 300 mm. The height of the shaft portion 12 is 200 mm. A distance between both ends of the first member 14 is a height H. The outer diameter Da on the flange 20 side of the first member 14 is, for example, 60 mm. The outer diameter Db of the flange 22 and the outer diameter Dc of the flange 24 are substantially the same. An inner diameter Dd and an outer diameter De at the center of the second member 16 are 36 mm and 45 mm, respectively. The dimensions of the first and second members 14 and 16 are not limited and can be changed as appropriate.

As the plate portion 10 and the shaft portion 12, an AlN ceramic sintered body having the same composition is used. For example, the plate part 10 and the first member 14 are AlN ceramics sintered bodies (secondary) containing 2 wt% to 10 wt%, preferably 4 wt% to 6 wt% of yttria (Y ₂ O ₃ ) as an additive. 1 ceramic sintered body) is used. Incidentally, as an _{additive, Sm 2 O 3, CeO 2} , Yb 2 O 3, MgO, may be used generally metal oxides used as sintering aids AlN such CaO. For the second member 16, an AlN ceramic sintered body (second ceramic sintered body) having a purity of 99% or more is used.

  As the heating element 18, a conductive material such as a refractory metal such as tungsten (W), molybdenum (Mo), niobium (Nb), or a refractory metal carbide such as tungsten carbide (WC) is used. The heating element 18 has a coil shape, a planar shape such as a mesh, a screen printing body, or a foil.

For example, the thermal conductivity of AlN containing 5% by weight of Y ₂ O ₃ and AlN having a purity of 99% are 170 W / (m · K) and 50 W / (m · K), respectively. Since the plate portion 10 uses a ceramic sintered body having a high thermal conductivity, it is possible to improve the thermal uniformity. On the other hand, since the second member 16 uses a ceramic sintered body having a low thermal conductivity, heat dissipation through the shaft portion 12 can be suppressed. As a result, the thermal uniformity of the plate portion 10 is comparable to the conventional ceramic heater.

The first member 14 is made of an AlN ceramic sintered body containing Y ₂ O _{3 in the same} manner as the plate portion 10. During the high temperature treatment at 600 ° C. or higher such as CVD, the vicinity of the joint between the plate portion 10 and the flange 20 is exposed to a high temperature. Since there is no concentration gradient in the region near the junction, diffusion of Y ₂ O ₃ can be suppressed. Further, the flanges 22 and 24, which are the joint portions of the first and second members 14 and 16, are located away from the plate portion 10, and are kept at a relatively low temperature even during high temperature processing. As a result, the diffusion of Y ₂ O ₃ from the first member 14 to the second member 16 can be suppressed, and the strength of the joint can be prevented from deteriorating.
→ This part has a sudden impression. ⇒This is a partial disclosure of the effects of the present invention, so I think there is no problem.

  Next, a method for manufacturing the ceramic heater shown in FIGS. 1 and 2 will be described with reference to FIGS.

(A) First, the plate part 10 is produced by hot press firing. The ceramic molded bodies of the first and second members 14 and 16 are formed by cold isostatic pressing (CIP) molding and fired. For the plate part 10 and the first member 14, for example, AlN containing 5% by weight of Y ₂ O ₃ as an additive is used. For the second member 16, AlN having a purity of 99% is used.

  (B) As shown in FIG. 3, the flange 24 of the second member 16 is joined to the flange 22 of the first member 14 by hot pressing to form the shaft portion 12. As shown by the arrows in FIG. 3, the hot press is sandwiched between unillustrated graphite jigs with the flange surfaces 22 and 24 aligned with each other under the conditions of a temperature of 1500 ° C. to 2500 ° C. and a pressure of 40 kPa to 60 kPa. It is carried out by pressing.

  (C) As shown in FIG. 4, the flange 20 of the first member 14 is joined to the lower surface of the plate portion 10 by hot pressing. Hot press is performed by pressing the flange 20 and the upper surface of the plate part with a graphite jig (not shown) as shown by arrows in FIG. 4 under conditions of a temperature of 1500 ° C. to 2500 ° C. and a pressure of 40 kPa to 60 kPa. To be implemented. In this way, the ceramic heater shown in FIGS. 1 and 2 is manufactured.

  Changes in the shape of the shaft portion 12 of the manufactured ceramic heater are evaluated by a shape evaluation apparatus. Further, the ceramic heater is subjected to heat treatment at 800 ° C. for 5000 hours in the atmosphere, and the bonding strength is measured by a tensile strength test.

As shown in FIG. 5, a plate portion 10 made of an AlN ceramic molded body containing 5% by weight of Y ₂ O ₃ as an additive and a shaft portion 12a made of an AlN ceramic sintered body having a purity of 99% are provided. A ceramic heater is used as a comparative example. In the comparative example, the shaft portion 12a is an integral sintered body, and includes a first shaft portion 14a having a hook shape having a height H and a second shaft portion 16a having a cylindrical shape. The shaft portion 12 is joined to the plate portion 10 by the flange 20 of the first shaft portion 14a.

In the table of FIG. 6, the results of evaluating the bonding strength of Examples 1 to 5 manufactured by changing the height H of the first member 14 containing Y ₂ O ₃ as an additive in the range of 30 mm to 70 mm are shown. It is shown. In the comparative example including the shaft portion 12a without the ceramic sintered body containing Y ₂ O ₃ as an additive, the initial strength before and after the heating test and the strength after the test are 300 MPa and 100 MPa, respectively.

When the vicinity of the joint deteriorated by the use of the ceramic heater of the comparative example for a long period of time at high temperature was observed in detail, it is considered that the diffusion of Y ₂ O _{3 as} a sintering aid occurred from the plate portion 10 to the shaft portion 12a. Voiding due to mass transfer due to atomic diffusion seems to occur along the grain boundaries in AlN. In particular, since the deterioration is severe in the air, the diffusion of oxygen is considered to have an effect. It is considered that the diffusion occurs because the Y ₂ O ₃ concentrations of the plate portion 10 and the shaft portion 12a are different.

  On the other hand, in Examples 1 to 5 including the first member, the initial strength and post-test strength are in the range of 430 MPa to 460 MPa and 210 MPa to 440 MPa, respectively, and the deterioration rate is significantly smaller than that of the comparative example. In Examples 1-5, although a big difference is not seen in initial strength, strength after a test increases with the increase in height H of the 1st member 14, for example, in Example 5 in which height H is 70 mm, The strength after the test is 440 MPa, which is the same value as the initial strength. That is, it can be seen that increasing the height H of the first member 14 can more effectively prevent the deterioration of the bonding strength due to the heat treatment. However, if the height H of the first member 14 is set to 120 mm or more with respect to the height of the shaft portion of 200 mm, the heat dissipation through the shaft portion 12 increases and the thermal uniformity of the plate portion 10 deteriorates. Therefore, the height H of the first member 14 is desirably in the range of 30 mm to 120 mm, preferably in the range of 50 mm to 70 mm.

The above ceramic heater is described using the first member 14 made of an AlN ceramic sintered body having substantially the same purity as the plate portion 10. However, in the shaft portion 12a made of the integrally sintered body shown in FIG. 5, the first shaft portion 14a in which the purity of AlN is inclined may be used. The purity of the AlN ceramic sintered body of the plate part 10 and the second shaft part 16a is 95% (containing 5% by weight of Y ₂ O ₃ ) and 99%, respectively. The height H of the first shaft portion 14a is set to 70 mm, and in the first shaft portion 14a, the plate portion 10 side is set to 95%, the second shaft portion 16a side is set to 99%, and the gap between them is a step difference of 4% or less. The purity is inclined at regular intervals. The table of FIG. 7 shows the bonding strengths of Examples 6 to 9 in which the purity of the AlN ceramic molded body is inclined at equal intervals of 4%, 2%, 1%, and 0.5%. .

  As shown in FIG. 7, the initial strength and post-test strength of Examples 6 to 9 are increased from 340 MPa to 390 MPa and 300 MPa to 350 MPa, respectively, as compared to the comparative example. The smaller the step size of the purity, the larger the initial strength and the strength after the test. Moreover, the deterioration by a heating test is comparatively small with 40 MPa.

  The table of FIG. 8 shows the bonding strength when the flange outer diameter difference (Db−Dc) between the outer diameter Db of the flange 22 and the outer diameter Dc of the flange 24 shown in FIG. 2 is changed. Flange outer diameter difference (Db-Dc) is -5 mm, -2 mm, 2 mm, and 5 mm. Although lower than Example 5, they are increased from 400 MPa to 370 MPa and 380 MPa to 350 MPa, respectively, as compared with the comparative example. Further, it can be seen that when the outer diameter of the flange 24 of the second member 16 is made smaller than the flange 22 of the first member 14, the reduction in bonding strength is slightly greater. Thus, it is desirable that the difference between the outer diameters of the flanges 22 and 24 is smaller, and it is more desirable that the outer diameter of the flange 24 is not smaller than that of the flange 22.

  The table in FIG. 9 shows the results of evaluating the joining strength and the presence or absence of deformation of the shaft portion 12 by changing the joining order and the pressing place in the hot press process. In Example 5 and 14, the 1st member 14 and the 2nd member 16 are joined previously, and in Example 15 and 16, the plate part 10 and the 1st member 14 are joined previously. Further, in the fifth and fifteenth embodiments, the flange to be bonded is pressed against the target member to be bonded later, and in the fourteenth and sixteenth embodiments, the flange on the end surface facing the flange to be bonded is pressed.

  As shown in FIG. 9, both Examples 5 and 14 to 16 have higher bonding strength than the comparative example. As for the joining order, it can be seen that both the initial strength and the strength after the test are slightly increased when the first member 14 and the second member 16 are joined first. When joining the 1st member 14 and the 2nd member 16 previously, it turns out that it is better to press the flange of joining object. On the other hand, in Examples 15 and 16 in which the plate portion 10 and the first member 14 are joined first, it can be seen that the dependence on the pressing location is small. In Examples 14 and 16, since the end face of the flange 26 is pressed in the hot press process in which the joining order is later, the shaft portion 12 is deformed. In the fifteenth embodiment, when the first member 14 and the second member 16 which are joined later are joined, the plate portion 10 and the flange 24 are used as pressing places, so that the first member 14 having a kettle shape is deformed. Has occurred. Thus, the procedure of joining the first and second members 14 and 16 first is desirable, and the pressing location is desirably the flange to be joined.

  In the above description, the hook-shaped shaft portion 12 shown in FIG. 2 is used, but the shape of the shaft portion is not limited. For example, as shown in FIG. 10, a shaft portion 12 b having a cylindrical shape including a cylindrical first member 14 b and a cylindrical second member 16 may be used. The first member 14 b includes a flange 20 joined to the plate portion 10 and a flange 22 joined to the flange 24 of the second member 16. The thickness of the cylindrical portion of the first and second members 14b, 16 is 4 mm to 5 mm. Moreover, as shown in FIG. 11, you may use the thick-shaped shaft part 12c provided with the thick cylindrical 1st and 2nd members 14c and 16c. The thickness of the first and second members 14c and 16c is, for example, 7 mm to 8 mm, and no flange is provided at both ends. The shaft portion 12c can be provided with a thin through-hole extending from the end surface of the thick cylindrical portion of the first and second members 14c and 16c to the plate portion 10 without damaging the strength, and is suitable for use as a vacuum chuck. Structure.

  The table of FIG. 12 shows the results of evaluating the joint strength and the deformation of the shaft portions of Examples 5, 17 and 18 having shaft portions 12, 12b, and 12c having a kettle shape, a torso shape, and a thick shape as shaft types. Show. The pressing place in the hot press processing of Examples 5 and 17 is a flange to be joined. In Example 18, the end surfaces of the first and second members 14c and 16c serve as pressing places.

  As shown in FIG. 12, in any shaft type, the bonding strength is higher than that in the comparative example. As for the shaft type, the strength of the hook shape of Example 5 is the maximum, and the strength is slightly decreased in the order of the cylindrical shape of Example 17 and the thick shape of Example 18. None of Examples 5, 17, and 18 is seen in the deformation of the shaft. In Example 18 in which the end face is used as the pressing place, the first and second members 14c and 16c use thick cylindrical members, so that it is possible to prevent deformation of the shaft portion 12c due to hot pressing.

  Further, when the first and second members 14 and 16 are joined, a taper or a step is provided as a joining shape of the shaft portion 12 in order to prevent displacement between the members, instead of the flanges 22 and 24 that contact in a plane. May be. As shown in FIG. 13, the first and second members 14 and 16 are joined with the joint surface between the flange 22 a of the first member 14 and the flange 24 a of the second member 16 inclined at a taper angle α. As shown in FIG. 14, the second members 14 and 16 are joined by providing a step Sa on the joining surfaces of the flanges 22 b and 24 b so that the inside of the flange 22 b of the first member 14 is recessed from the outside. As shown in FIG. 15, the second members 14 and 16 are joined by providing a step Sb on each joint surface of the flanges 22 c and 24 c so that the outer side of the flange 22 b of the first member 14 is recessed from the inside.

  The table of FIG. 16 shows the evaluation results of the bonding strength for each of Examples 19 to 21 in which the joint shape of the shaft portion 12 is tapered, Example 22 of the step Sa, and Example 23 of the step Sb. . The taper angles α of Examples 19 to 21 are 5 °, 10 °, and 15 °, respectively.

  As shown in FIG. 16, as the taper angle α increases, the bonding strength decreases. In Example 21 in which the taper angle α is 15 °, the initial strength is the same value as that of the comparative example, but it can be seen that the decrease in strength after the test is suppressed as compared with the comparative example. From the results of Examples 22 and 23, it can be seen that the step Sa has higher bonding strength than the step Sb. The bonding strength of Example 5 having a flat bonding shape is the highest. Therefore, when the joint shape of the shaft portion 12 is a taper, it is desirable to reduce the taper angle α, and when the joint shape is a step, it is desirable to reduce the step.

Thus, in the embodiment of the present invention, the AlN ceramic sintered body containing Y ₂ O ₃ as an additive is used for the first member 14 joined to the plate portion 10 and the plate portion 10, and is fixed to the reaction chamber. The second member 16 is made of an AlN ceramic sintered body having a purity of 99% or more. Therefore, when the plate part 10 is heated to a high temperature, even if the joint part between the plate part 10 and the shaft part 12 is exposed to a high temperature, the strength deterioration of the joint part can be prevented. Moreover, since the joint part of the 1st and 2nd members 14 and 16 is hold | maintained at comparatively low temperature, the strength deterioration of a joint part hardly arises. Furthermore, the thermal conductivity of the second member 16 is smaller than that of the plate portion 10 and the first member 14. Therefore, heat dissipation through the shaft portion 12 can be suppressed. As described above, according to the embodiment of the present invention, it is possible to obtain a good temperature uniformity of the ceramic heater, and to prevent deterioration of the strength of the joint due to heating at a high temperature.

(Other embodiments)
Although the embodiments of the present invention have been described as described above, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art. It goes without saying that the present invention includes various embodiments not described herein. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a top view which shows an example of the ceramic heater which concerns on embodiment of this invention. It is the schematic which shows the AA cross section of the ceramic heater shown in FIG. It is sectional drawing (the 1) which shows an example of the manufacturing method of the ceramic heater which concerns on embodiment of this invention. It is sectional drawing (the 2) which shows an example of the manufacturing method of the ceramic heater which concerns on embodiment of this invention. It is sectional drawing which shows an example of the ceramic heater by a comparative example. It is a table | surface which shows an example of the evaluation result of the ceramic heater which concerns on embodiment of this invention. It is a table | surface which shows the other example of the evaluation result of the ceramic heater which concerns on embodiment of this invention. It is a table | surface which shows the other example of the evaluation result of the ceramic heater which concerns on embodiment of this invention. It is a table | surface which shows the other example of the evaluation result of the ceramic heater which concerns on embodiment of this invention. It is sectional drawing which shows the other example of the ceramic heater which concerns on embodiment of this invention. It is sectional drawing which shows the other example of the ceramic heater which concerns on embodiment of this invention. It is a table | surface which shows the other example of the evaluation result of the ceramic heater which concerns on embodiment of this invention. It is sectional drawing which shows the other example of the ceramic heater which concerns on embodiment of this invention. It is sectional drawing which shows the other example of the ceramic heater which concerns on embodiment of this invention. It is sectional drawing which shows the other example of the ceramic heater which concerns on embodiment of this invention. It is a table | surface which shows the other example of the evaluation result of the ceramic heater which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Plate part 12 ... Shaft part 14 ... 1st member 16 ... 2nd member 20, 22, 24, 26 ... Flange

Claims (7)

A plate portion made of a first ceramic sintered body on which an object to be heated is placed on the upper surface;
A ceramic heater comprising a shaft portion joined to the lower surface of the plate portion,
The shaft portion is
A cylindrical first member made of a ceramic sintered body having one end bonded to the lower surface of the plate portion and having the same composition as the first ceramic sintered body;
A ceramic heater having a cylindrical second member made of a second ceramic sintered body joined to the other end of the first member and having a thermal conductivity lower than that of the plate portion.   The first member has a convex curvature outward in the cylindrical radial direction between the one end and the other end, and the diameter decreases from the one end toward the other end. The ceramic heater according to claim 1.   A flange for joining the first member to the plate portion by a hot press method is provided at the one end, and a flange for joining the first member to the second member by a hot press method at the other end. The ceramic heater according to claim 1, wherein the ceramic heater is provided.   The ceramic heater according to claim 1, wherein the second member of the first member is a thick cylindrical shape having a thickness of 7 mm to 8 mm.   The first ceramic sintered body is aluminum nitride containing 2% by weight to 10% by weight of yttria as an additive, and the second ceramic sintered body is aluminum nitride having a purity of 99% or more. The ceramic heater according to any one of claims 1 to 4. A plate portion made of a first ceramic sintered body on which an object to be heated is placed on the upper surface;
A cylindrical first shaft portion joined to the lower surface of the plate portion, and a cylindrical second shaft made of a second ceramic sintered body connected to the first shaft portion and having a lower thermal conductivity than the plate portion. A ceramic heater comprising a shaft portion of an integrally sintered body having a portion,
The first ceramic sintered body is aluminum nitride containing 2 wt% to 10 wt% of an additive, the second ceramic sintered body is aluminum nitride having a purity of 99% or more, the plate side and the second Inclining the composition of the first shaft portion from the plate side toward the second shaft portion side so as to have the same composition as the first and second ceramic sintered bodies on each of the shaft portion sides. Characteristic ceramic heater. Forming a plate portion made of a first ceramic sintered body on which an object to be heated is placed;
Forming a cylindrical first member made of a ceramic sintered body having the same composition as the first ceramic sintered body;
Forming a cylindrical second member made of a second ceramic sintered body having a lower thermal conductivity than the plate portion;
Joining one end of the second member to the other end of the first member by hot pressing;
And joining the one end of the first member to the lower surface of the plate portion by hot pressing after joining the first and second members.

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