Heater

Abstract

To provide a heater capable of reducing thermal stress acting on a shaft.SOLUTION: The heater includes a mounting plate, a heating element, and a shaft. The shaft has a cylindrical main body and a connecting portion disposed between the main body and the mounting plate. The connection outer peripheral surface of the connection portion has a first enlarged diameter portion connected to the placement plate and a second enlarged diameter portion disposed between the first enlarged diameter portion and the main body portion. The outer diameter of the first enlarged diameter portion is larger than the outer diameter of the second enlarged diameter portion, and the outer diameter of the second enlarged diameter portion is larger than the outer diameter of the main body portion. The first connecting portion connecting the first enlarged diameter portion and the second enlarged diameter portion has a curved surface, a first tapered surface, and a curved surface provided in order from the first enlarged diameter portion toward the second enlarged diameter portion. The second connection portion connecting the second enlarged diameter portion and the main body portion has a curved surface, a second tapered surface, and a curved surface provided in order from the second enlarged diameter portion toward the main body portion.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a substrate holding structure including a substrate holding table having an upper surface on which a substrate to be processed is placed, a heating mechanism disposed inside the substrate holding table, and a support pillar supporting the substrate holding table. The support pillar has a cylindrical main body and a flange between the substrate holding table and the main body. The outer circumferential surface of the portion connecting the flange and the main body is formed by a curved surface with a uniform radius of curvature. In the following description, the substrate holding table is referred to as the mounting plate, the support pillar as the shaft, the flange as the connecting portion, and the substrate holding structure as the heater. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-123582 Summary of the Invention [Problem to be solved by the invention]

[0004] In the heater, the outer peripheral surface of the portion connecting the connecting portion and the main body is configured as a curved surface with a uniform radius of curvature, thereby reducing the thermal stress acting on the shaft due to the heat generated by the heating mechanism heating the mounting plate. Further reduction of the thermal stress is desired, especially at high temperatures.

[0005] One object of the present disclosure is to provide a heater that can reduce thermal stress acting on a shaft. [Means for solving the problem]

[0006] The heater disclosed herein includes a mounting plate having an upper surface on which a wafer is placed, a heating element disposed inside the mounting plate, and a shaft supporting the mounting plate. The shaft has a cylindrical main body and a connecting portion disposed between the main body and the mounting plate. The connecting portion has a connecting inner circumferential surface, a connecting outer circumferential surface, and a connecting end surface with the lower surface of the mounting plate. The connecting outer circumferential surface has a first enlarged diameter portion connected to the mounting plate and a second enlarged diameter portion disposed between the first enlarged diameter portion and the main body. The outer diameter of the first enlarged diameter portion is larger than the outer diameter of the second enlarged diameter portion, and the outer diameter of the second enlarged diameter portion is larger than the outer diameter of the main body. A first connecting portion connecting the first enlarged diameter portion and the second enlarged diameter portion has a first upper curved surface, a first tapered surface, and a first lower curved surface, which are arranged in this order from the first enlarged diameter portion toward the second enlarged diameter portion. The second connecting portion connecting the second enlarged diameter portion and the main body portion has a second upper curved surface, a second tapered surface, and a second lower curved surface provided in that order from the second enlarged diameter portion toward the main body portion. [Effects of the Invention]

[0007] The heater of the present disclosure can reduce thermal stress acting on the shaft. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a side view showing an outline of the heater of the first embodiment. [Figure 2] FIG. 2 is an enlarged view of area A1 in FIG. [Figure 3] FIG. 3 is an enlarged view of area A2 in FIG. [Figure 4] FIG. 4 is a vertical cross-sectional view of the heater of FIG. [Figure 5] FIG. 5 is an enlarged view of area A3 in FIG. [Figure 6] FIG. 6 is an enlarged view of area A4 in FIG. [Figure 7] FIG. 7 is a vertical cross-sectional view of the heater of the second embodiment. [Figure 8] FIG. 8 is a vertical cross-sectional view of the heater of the third embodiment. [Figure 9]FIG. 9 is a vertical cross-sectional view of the heater of the fourth embodiment. [Figure 10] FIG. 10 is a vertical cross-sectional view of the heater of the fifth embodiment. [Figure 11] FIG. 11 is an enlarged view of area A5 in FIG. [Figure 12] FIG. 12 is a vertical cross-sectional view of the heater of the sixth embodiment. [Figure 13] FIG. 13 is a graph showing the relationship between the angle of the tapered surface and the maximum principal stress. [Figure 14] FIG. 14 is a vertical cross-sectional view of the heater of sample No. 101. [Figure 15] FIG. 15 is a vertical cross-sectional view of the heater of sample No. 102. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0010] (1) A heater according to one aspect of the present disclosure includes a mounting plate having an upper surface on which a wafer is placed, a heating element disposed inside the mounting plate, and a shaft supporting the mounting plate. The shaft has a cylindrical main body and a connecting portion disposed between the main body and the mounting plate. The connecting portion has a connecting inner circumferential surface, a connecting outer circumferential surface, and a connecting end surface with the lower surface of the mounting plate. The connecting outer circumferential surface has a first enlarged diameter portion connected to the mounting plate and a second enlarged diameter portion disposed between the first enlarged diameter portion and the main body. The outer diameter of the first enlarged diameter portion is larger than the outer diameter of the second enlarged diameter portion, and the outer diameter of the second enlarged diameter portion is larger than the outer diameter of the main body. A first connecting portion connecting the first enlarged diameter portion and the second enlarged diameter portion has a first upper curved surface, a first tapered surface, and a first lower curved surface, which are arranged in this order from the first enlarged diameter portion toward the second enlarged diameter portion. The second connecting portion connecting the second enlarged diameter portion and the main body portion has a second upper curved surface, a second tapered surface, and a second lower curved surface provided in that order from the second enlarged diameter portion toward the main body portion.

[0011] The heater of (1) above can disperse the concentrated areas of thermal stress, and therefore the thermal stress acting on the shaft can be easily reduced.

[0012] (2) In the heater of (1) above, the angle between a plane perpendicular to the inner circumferential surface of the main body and the first tapered surface, and the angle between a plane perpendicular to the inner circumferential surface of the main body and the second tapered surface may both be 44 degrees or more and 72 degrees or less.

[0013] The heater (2) above is more likely to reduce the thermal stress acting on the shaft than when the angle is less than 44 degrees or when the angle is more than 72 degrees.

[0014] (3) In the heater of (1) above, the connection inner circumferential surface may have an inner circumferential expanded portion whose inner diameter is larger than the inner diameter of the main body inner circumferential surface of the main body portion. In a cross section including the central axis of the main body portion, a first length is smaller than a first distance. The first length is the shortest length between the connection inner circumferential surface and the second tapered surface along a direction perpendicular to the second tapered surface. The first distance is the distance along the perpendicular bisector between the second tapered surface and an intersection of a perpendicular bisector of the second tapered surface and an extension of the main body inner circumferential surface.

[0015] The heater of (3) above can disperse the concentrated areas of thermal stress, and therefore the thermal stress acting on the shaft can be easily reduced.

[0016] (4) In the heater of (3) above, the inner circumferential expanded diameter portion may be provided so that the first length is greater than 0.5 times the thickness of the main body portion.

[0017] The heater of (4) above tends to reduce the thermal stress acting on the shaft.

[0018] (5) In the heater of (4) above, the angle between a plane perpendicular to the inner circumferential surface of the main body and the first tapered surface, and the angle between a plane perpendicular to the inner circumferential surface of the main body and the second tapered surface may both be 26 degrees or more and 88 degrees or less.

[0019] The heater of (5) above is more likely to reduce the thermal stress acting on the shaft than when the angle is less than 26 degrees or when the angle is more than 88 degrees.

[0020] (6) In the heater according to any one of (1) to (5), at least one of the first upper curved surface and the first lower curved surface and at least one of the second upper curved surface and the second lower curved surface may be disposed between a first imaginary line and a second imaginary line in a cross section including the central axis of the main body portion. The first imaginary line is an imaginary line connecting a radial center point of the connecting end surface and a radial center point of a boundary between the connecting portion and the main body portion. The second imaginary line is an imaginary line connecting a specific point and an outermost point of the boundary. When the lower surface does not have an outer recess connected to the connecting end surface, the specific point is a connection point between the outer periphery of the connecting end surface and the lower surface. When the lower surface has the outer recess, the specific point is a point of the outer recess that is closest to the outer periphery of the connecting end surface among the uppermost points of the outer recess.

[0021] The heater (6) above is more likely to reduce the thermal stress acting on the shaft compared to when at least one of the first connecting portion and the second connecting portion is not positioned between the first imaginary line and the second imaginary line.

[0022] [Details of the embodiments of the present disclosure] Hereinafter, an embodiment of a heater according to the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same objects. The shapes, sizes, positional relationships, etc. shown in each drawing are depicted for the purpose of clarifying the description and do not necessarily represent the actual shapes, sizes, positional relationships, etc.

[0023] [Embodiment 1] <Heater> A heater 1 according to a first embodiment will be described with reference to FIGS. 1 to 6. The heater 1 according to the first embodiment can be used in a film forming apparatus for forming a thin film on the surface of a wafer. The heater 1 is fixed to a mounting base in a chamber so that the showerhead faces the upper surface 2a of a mounting plate 2 shown in FIG. 1. As shown in FIG. 1, the heater 1 according to the first embodiment includes a mounting plate 2, a heating element 3, and a shaft 4. As shown in FIGS. 1 and 2, the mounting plate 2 has an upper surface 2a on which the wafer is mounted and a lower surface 2b opposite the upper surface 2a. The mounting plate 2 according to this embodiment has a circular shape when viewed from above. The wafer is, for example, a silicon or compound semiconductor wafer. The heating element 3 is disposed inside the mounting plate 2 as shown in FIG. 1. The shaft 4 supports the mounting plate 2. In this embodiment, the shaft 4 is cylindrical. 3, the shaft 4 has a cylindrical main body 41 and a connecting portion 42 disposed between the main body 41 and the lower surface 2b of the mounting plate 2. One of the features of the heater 1 of embodiment 1 is that the connecting outer peripheral surface 44 of the connecting portion 42 has a specific structure. In the following description, the inner diameter and outer diameter at each portion of the mounting plate 2 are lengths extending radially from the center of the lower surface 2b of the mounting plate 2, and the inner diameter and outer diameter at each portion of the shaft 4 are lengths extending radially from the central axis of the shaft 4 in a direction perpendicular to the central axis.

[0024] <Placement plate> As described above, a wafer is placed on the upper surface 2a of the mounting plate 2. A shaft 4 is fixed to the lower surface 2b of the mounting plate 2. The material of the mounting plate 2 is, for example, ceramics. Examples of ceramics include aluminum nitride, aluminum oxide, or silicon carbide. The mounting plate 2 may be formed of a composite material of the ceramics and a metal. Examples of the metal forming the composite material include aluminum, an aluminum alloy, copper, or a copper alloy. The material of the mounting plate 2 in this example is ceramics. As shown in the vertical cross section of FIG. 4, the lower surface 2b of the mounting plate 2 in this example has a connection region 21, an inner region 22, and an outer region 23. The vertical cross section of FIG. 4 is a cross section including the central axis of the main body portion 41.

[0025] [Connection area] The connection region 21 is a region that comes into contact with and connects to the connection end surface 45 of the connection portion 42. The connection region 21 is a ring-shaped region. In this example, the width of the connection region 21, which is the difference between the inner and outer diameters, is the same as the width of the connection end surface 45, which is the difference between the inner and outer diameters. In this example, the outer diameter of the connection region 21 is the same as the outer diameter of the connection end surface 45, and the inner diameter of the connection region 21 is the same as the inner diameter of the connection end surface 45.

[0026] [Inner area] The inner region 22 is a region located more inward than the connection region 21 and is a region that is not connected to the connection end surface 45 of the connection portion 42. In this example, the inner region 22 does not face the connection end surface 45 over its entire area. The inner region 22 is a circular region. In this example, the diameter of the inner region 22 is the same as the inner diameter of the connection end surface 45. In this example, the inner region 22 is located on the same plane as the connection region 21. Unlike embodiment 2, which will be described later, the inner region 22 in this example does not have an inner recess 22h (FIG. 7).

[0027] [Outer area] The outer region 23 is a region outside the connection region 21 and is a region that is not connected to the connection end surface 45 of the connection portion 42. The outer region 23 is a region that does not face the connection end surface 45. The outer region 23 is a ring-shaped region. In this example, the outer region 23 is located on the same plane as the connection region 21. That is, in this example, the inner region 22, the connection region 21, and the outer region 23 are located on the same plane. Unlike embodiment 2, which will be described later, the outer region 23 in this example does not have an outer recess 23h (FIG. 7).

[0028] <Heater> The heating element 3 shown in FIG. 1 is a heat source that heats the wafer placed on the upper surface 2a of the mounting plate 2. The heating element 3 is disposed inside the mounting plate 2. There are no particular limitations on the shape and arrangement of the heating element 3. There are no particular limitations on the material of the heating element 3, as long as it can heat the wafer to the desired temperature. The material of the heating element 3 is a metal suitable for resistance heating. The metal forming the heating element 3 is, for example, one selected from the group consisting of stainless steel, nickel, nickel alloy, silver, silver alloy, tungsten, tungsten alloy, molybdenum, molybdenum alloy, chromium, and chromium alloy. The nickel alloy is, for example, nichrome.

[0029] <Shaft> The shaft 4 supports the mounting plate 2. The shaft 4 is arranged concentrically with the mounting plate 2. That is, the shaft 4 and the mounting plate 2 are connected so that the center of the cylindrical shaft 4 and the center of the disk-shaped mounting plate 2 are coaxial. The material of the shaft 4 is one selected from the ceramic group or one selected from the composite material group described in the section on the material of the mounting plate 2. The material of the shaft 4 may be the same as or different from the material of the mounting plate 2. In this example, the material of the shaft 4 is ceramic. As shown in Figures 3 and 4, the shaft 4 has a main body portion 41 and a connecting portion 42.

[0030] [Connection] The connection portion 42 is disposed between the main body portion 41 and the mounting plate 2. The connection portion 42 has a connection inner peripheral surface 43, a connection outer peripheral surface 44, and a connection end surface 45, as shown in FIG.

[0031] <Connection end face> The connection end surface 45 is the area of ​​the upper end surface of the connection portion 42 that is in contact with the lower surface 2b of the mounting plate 2. The upper end surface of the connection portion 42 is the surface that faces the lower surface 2b of the mounting plate 2. In this example, the entire upper end surface of the connection portion 42 is in contact with the lower surface 2b of the mounting plate 2. In other words, the upper end surface of the connection portion 42 is the connection end surface 45. The connection end surface 45 has an annular shape. The outer peripheral edge of the connection end surface 45 is connected to the boundary between the connection region 21 and the outer region 23. The inner peripheral edge of the connection end surface 45 is connected to the boundary between the connection region 21 and the inner region 22.

[0032] <Connection outer surface> The connecting outer peripheral surface 44 has a first enlarged diameter portion 44a, a first connecting portion 44c, a second enlarged diameter portion 44b, and a second connecting portion 44d arranged in this order from the outer peripheral edge of the connecting end surface 45 toward the main body outer peripheral surface 41b of the main body portion 41.

[0033] 《First enlarged diameter part / Second enlarged diameter part》 The first expanded diameter portion 44a is connected to the lower surface 2b of the mounting plate 2. When the first flat surface 440 shown in FIG. 5 is present, the first expanded diameter portion 44a is the region between the connecting end surface 45 and the first flat surface 440. When the first flat surface 440 is not present, the first expanded diameter portion 44a is the region between the connecting end surface 45 and the upper end of the first upper curved surface 441. The upper end of the first upper curved surface 441 is the inflection point above the first upper curved surface 441.

[0034] In this example, the upper end of the first expanded diameter portion 44a is connected to the boundary between the connection region 21 and the outer region 23. The lower end of the first expanded diameter portion 44a is connected to the upper end of the first connecting portion 44c, which will be described later. In this example, the outer diameter of the first expanded diameter portion 44a is uniform from the upper end to the lower end. In this example, the first expanded diameter portion 44a is a cylindrical surface with a uniform outer diameter. The outer diameter of the first expanded diameter portion 44a is larger than the outer diameter of the second expanded diameter portion 44b. Here, the outer diameter of the first expanded diameter portion 44a refers to the maximum outer diameter of the first expanded diameter portion 44a. The outer diameter of the second expanded diameter portion 44b refers to the maximum outer diameter of the second expanded diameter portion 44b.

[0035] The second expanded diameter portion 44b is provided between the first expanded diameter portion 44a and the main body portion 41. When the second flat surface 444 shown in FIG. 6 is present, the second expanded diameter portion 44b is the region between the second flat surface 444 and the lower end of a first lower curved surface 443, which will be described later with reference to FIG. 5. When the second flat surface 444 is not present, the second expanded diameter portion 44b is the region between the lower end of the first lower curved surface 443 and the upper end of the second upper curved surface 445. The lower end of the first lower curved surface 443 is the lower inflection point of the first lower curved surface 443. The upper end of the second upper curved surface 445 is the upper inflection point of the second upper curved surface 445.

[0036] The upper end of the second expanded diameter portion 44b in this example is connected to the lower end of the first connecting portion 44c. The lower end of the second expanded diameter portion 44b in this example is connected to the upper end of the main body portion 41. The second expanded diameter portion 44b in this example is a cylindrical surface with a uniform outer diameter.

[0037] 《1st connection part / 2nd connection part》 The first connecting portion 44c connects the first expanded diameter portion 44a and the second expanded diameter portion 44b. As shown in FIG. 5, the first connecting portion 44c has a first flat surface 440, a first upper curved surface 441, a first tapered surface 442, and a first lower curved surface 443, which are arranged in this order from the first expanded diameter portion 44a to the second expanded diameter portion 44b. The first flat surface 440 connects to the first expanded diameter portion 44a. The first flat surface 440 is perpendicular to the inner circumferential surface 41a of the main body 41. The first flat surface 440 forms a first corner with the first expanded diameter portion 44a. The first corner may be configured as a C-chamfered inclined surface or a R-chamfered curved surface. The first upper curved surface 441 connects the first flat surface 440 and the first tapered surface 442. The outer diameter of the first upper curved surface 441 decreases from the first flat surface 440 toward the first tapered surface 442. The radius of curvature of the first upper curved surface 441 is uniform. The first tapered surface 442 connects the first upper curved surface 441 and the first lower curved surface 443. The outer diameter of the first tapered surface 442 decreases from the first upper curved surface 441 toward the first lower curved surface 443. The first lower curved surface 443 connects the first tapered surface 442 and the second expanded diameter portion 44b. The outer diameter of the first lower curved surface 443 decreases from the first tapered surface 442 toward the second expanded diameter portion 44b. The radius of curvature of the first lower curved surface 443 is uniform.

[0038] As shown in FIG. 4, the second connecting portion 44d connects the second expanded diameter portion 44b and the main body portion 41. As shown in FIG. 6, the second connecting portion 44d has a second flat surface 444, a second upper curved surface 445, a second tapered surface 446, and a second lower curved surface 447, which are arranged in this order from the second expanded diameter portion 44b toward the main body portion 41. The second flat surface 444 is perpendicular to the main body inner circumferential surface 41a. The second flat surface 444 forms a second corner with the second expanded diameter portion 44b. The second corner may be configured as a C-chamfered inclined surface or a R-chamfered curved surface. The second upper curved surface 445 connects the second flat surface 444 and the second tapered surface 446. The outer diameter of the second upper curved surface 445 decreases from the second flat surface 444 toward the second tapered surface 446. The radius of curvature of the second upper curved surface 445 is uniform. The second tapered surface 446 connects the second upper curved surface 445 and the second lower curved surface 447. The outer diameter of the second tapered surface 446 decreases from the second upper curved surface 445 toward the second lower curved surface 447. The second lower curved surface 447 connects the second tapered surface 446 and the main body portion 41. The outer diameter of the second lower curved surface 447 decreases from the second tapered surface 446 toward the main body portion 41. The radius of curvature of the second lower curved surface 447 is uniform.

[0039] In this example, the radius of curvature of the first upper curved surface 441 shown in FIG. 5 is, for example, 3.0 mm or more and 7.0 mm or less. The angle θ1 of the first tapered surface 442 is, for example, 44 degrees or more and 72 degrees or less. The angle θ1 is the angle between the first tapered surface 442 and a plane perpendicular to the main body inner circumferential surface 41a. The radius of curvature of the first lower curved surface 443 is, for example, 3.0 mm or more and 7.0 mm or less. The radii of curvature of the first upper curved surface 441 and the first lower curved surface 443 may be the same or different within the above range. The radius of curvature of the second upper curved surface 445 shown in FIG. 6 is, for example, 1.0 mm or more and 5.0 mm or less. The angle θ2 of the second tapered surface 446 is, for example, 44 degrees or more and 72 degrees or less. The angle θ2 is the angle between the second tapered surface 446 and a plane perpendicular to the main body inner circumferential surface 41a. The radius of curvature of the second lower curved surface 447 is, for example, 1.0 mm or more and 5.0 mm or less. The radius of curvature of the second upper curved surface 445 and the radius of curvature of the second lower curved surface 447 may be the same or different within the above range. The angles θ1 and θ2 may be the same or different within the above range. When the radius of curvature of the first upper curved surface 441, the angle θ1 of the first tapered surface 442, the radius of curvature of the first lower curved surface 443, the radius of curvature of the second upper curved surface 445, the angle θ2 of the second tapered surface 446, and the radius of curvature of the second lower curved surface 447 each satisfy the above range, thermal stress acting on the shaft 4 is likely to be reduced.

[0040] The radius of curvature of first upper curved surface 441 may be 0.1 mm or more and 8.0 mm or less. Angle θ1 may be 20 degrees or more and 88 degrees or less. The radius of curvature of first lower curved surface 443 may be 0.1 mm or more and 8.0 mm or less, or 1.0 mm or more and 6.0 mm or less. The radius of curvature of second upper curved surface 445 may be 0.1 mm or more and 8.0 mm or less. Angle θ2 may be 20 degrees or more and 88 degrees or less. The radius of curvature of second lower curved surface 447 may be 0.1 mm or more and 8.0 mm or less, or 1.0 mm or more and 6.0 mm or less.

[0041] As shown in Fig. 4, at least one of the first upper curved surface 441 and the first lower curved surface 443 and at least one of the second upper curved surface 445 and the second lower curved surface 447 are disposed between the first virtual line L1 and the second virtual line L2. "At least one of the first upper curved surface 441 and the first lower curved surface 443 being disposed between the first virtual line L1 and the second virtual line L2" means that at least one of the entire first upper curved surface 441 and the entire first lower curved surface 443 is disposed between the first virtual line L1 and the second virtual line L2. In other words, even if at least one of only a portion of the first upper curved surface 441 and only a portion of the first lower curved surface 443 is disposed between the first virtual line L1 and the second virtual line L2, this does not mean that at least one of the first upper curved surface 441 and the first lower curved surface 443 is disposed between the first virtual line L1 and the second virtual line L2. The fact that at least one of the second upper curved surface 445 and the second lower curved surface 447 is positioned between the first virtual line L1 and the second virtual line L2 has the same meaning as the explanation for the first upper curved surface 441 and the first lower curved surface 443 above.

[0042] The first virtual line L1 is a virtual line connecting a radial center point P1 of the connection end surface 45 and a radial center point P2 at the boundary between the connection portion 42 and the main body portion 41. The second virtual line L2 is a virtual line connecting a specific point P3 and an outermost point P4 at the boundary between the connection portion 42 and the main body portion 41. When the outer region 23 does not have an outer recess 23h (FIG. 7) as in this example, the specific point P3 is the connection point between the outer peripheral edge of the connection end surface 45 and the lower surface 2b, i.e., the boundary between the connection region 21 and the outer region 23. When the outer region 23 has an outer recess 23h (FIG. 7) unlike this example, the specific point P3 will be described later. The boundary between the connection portion 42 and the main body portion 41 is the lower end of the second lower curved surface 447 of the second coupling portion 44d.

[0043] At least one of the first upper curved surface 441 and the first lower curved surface 443 and at least one of the second upper curved surface 445 and the second lower curved surface 447 are arranged between the first virtual line L1 and the second virtual line L2, which makes it easier to reduce thermal stress acting on the shaft 4 compared to a case where none of the first upper curved surface 441, the first lower curved surface 443, the second upper curved surface 445, and the second lower curved surface 447 are arranged between the first virtual line L1 and the second virtual line L2. In this example, the first lower curved surface 443 and the second lower curved surface 447 are arranged between the first virtual line L1 and the second virtual line L2.

[0044] Unlike this example, the number of enlarged diameter portions and connecting portions may be three or more. Connecting portions are provided between the enlarged diameter portions and between the lowermost enlarged diameter portion and the main body. Each connecting portion has a curved surface, a tapered surface, and another curved surface arranged in order from top to bottom.

[0045] <Connection inner surface> In this example, the inner diameter of the connecting inner circumferential surface 43 is the same as the inner diameter of the main body inner circumferential surface 41 a. The connecting inner circumferential surface 43 connects the inner peripheral edge of the connecting end surface 45 and the main body inner circumferential surface 41 a. Unlike the second embodiment, the connecting inner circumferential surface 43 in this example does not have an inner expanded diameter portion 43 b ( FIG. 10 ).

[0046] <Inner corner> In this example, as shown in FIG. 4 , the inner peripheral corner 46 between the upper end surface of the connecting portion 42 and the connecting inner peripheral surface 43 is configured as an inclined surface. Because the inner peripheral corner 46 is configured as an inclined surface, thermal stress is less likely to concentrate on the inner peripheral corner 46 than if it were not configured as an inclined surface. Therefore, thermal stress acting on the shaft 4 is more likely to be reduced. Unlike this example, the inner peripheral corner 46 may be configured as a curved surface. The inclined surface in this example connects the upper end surface of the connecting portion 42 and the connecting inner peripheral surface 43. The length of the inclined surface in the vertical direction is, for example, 0.1 to 1 times the length of the first expanded diameter portion 44a in the vertical direction. The angle between the inclined surface and a plane perpendicular to the main body inner peripheral surface 41a is, for example, 20 to 88 degrees.

[0047] [Main body] The main body 41 has a cylindrical shape. The main body 41 has uniform inner and outer diameters. The upper end of the main body 41 is connected to the lower end of the connecting portion 42. The lower end of the main body 41 is directly or indirectly connected to a mounting base to which the shaft 4 (not shown) is fixed.

[0048] [Embodiment 2] <Heater> As shown in Fig. 7, the heater 1 of the second embodiment differs from the heater 1 of the first embodiment in that the mounting plate 2 has at least one of an inner recess 22h and an outer recess 23h. In the heater 1 of this example, the mounting plate 2 has both an inner recess 22h and an outer recess 23h. The following description will focus on the above differences. This also applies to the third and subsequent embodiments.

[0049] [Connection area] In the mounting plate 2 of this example, the width, which is the difference between the inner diameter and the outer diameter of the connection region 21, is smaller than the width, which is the difference between the inner diameter and the outer diameter of the upper end surface of the connection portion 42. The outer diameter of the connection region 21 of this example is the same as the outer diameter of the upper end surface of the connection portion 42, and the inner diameter of the connection region 21 of this example is larger than the inner diameter of the upper end surface of the connection portion 42.

[0050] [Inner area] The inner region 22 has an inner recess 22h. The inner recess 22h reduces thermal stress acting on the boundary between the connection region 21 and the connection end face 45. The inner recess 22h is circular. The diameter of the inner recess 22h is larger than the inner diameter of the upper end face of the connection portion 42 and smaller than the outer diameter of the upper end face of the connection portion 42, i.e., the outer diameter of the connection end face 45. The inner region 22 in this example has a first inner region 221 and a second inner region 222 located inside the first inner region 221. The first inner region 221 is an annular region. The first inner region 221 faces a region of the upper end face of the connection portion 42 that is inside the connection end face 45 without contacting it. The second inner region 222 is a circular region. The second inner region 222 is a region located inside the inner periphery of the upper end face of the connection portion 42 and does not face the upper end face of the connection portion 42.

[0051] [Outer area] The outer region 23 has an outer recess 23h. The outer recess 23h reduces thermal stress acting on the boundary between the connection region 21 and the connection end face 45. The outer recess 23h is annular. The outer recess 23h is provided at a position where the inner peripheral edge of the outer recess 23h connects to the outer peripheral edge of the connection region 21. In other words, the inner diameter of the inner peripheral edge of the outer recess 23h is the same as the outer diameter of the connection region 21. In this example, the cross-sectional shape of the outer recess 23h is U-shaped. The cross-section of the outer recess 23h is a cross section that includes the central axis of the main body portion 41.

[0052] The outer recess 23h is composed of an inner circumferential wall surface, an outer circumferential wall surface, and a bottom surface. The inner circumferential wall surface is connected to the connection region 21. In this example, the inner circumferential wall surface is a cylindrical surface that is flush with the first expanded diameter portion 44a. The outer circumferential wall surface faces the inner circumferential wall surface. In this example, the outer circumferential wall surface is a cylindrical surface parallel to the inner circumferential wall surface. The bottom surface is a surface that connects the inner circumferential wall surface and the outer circumferential wall surface. In this example, the bottom surface is a plane parallel to the connection region 21. When the outer region 23 has the outer recess 23h as in this example, the specific point P3 is the uppermost point of the outer recess 23h that is closest to the outer circumferential edge of the connection end face 45. In this example, the specific point P3 is the boundary between the inner circumferential wall surface and the bottom surface.

[0053] 《1st connection part / 2nd connection part》 In this example, the first downward curved surface 443 of the first connecting portion 44c and the second downward curved surface 447 of the second connecting portion 44d are disposed between the first imaginary line L1 and the second imaginary line L2, which makes it easier to reduce thermal stress acting on the shaft 4.

[0054] [Embodiment 3] <Heater> As shown in FIG. 8, the heater 1 of embodiment 3 differs from the heater 1 of embodiment 2 in that the first expansion portion 44a is composed of a first surface and a second surface, and the cross-sectional shape of the outer recess 23h is V-shaped.

[0055] 《First enlarged diameter part》 The first and second surfaces of the first expanded diameter portion 44a in this example are aligned in order from the top to the bottom of the first expanded diameter portion 44a. The first surface of the first expanded diameter portion 44a in this example is configured as an inclined surface whose outer diameter decreases from the top to the second surface. The second surface of the first expanded diameter portion 44a is a cylindrical surface with a uniform outer diameter.

[0056] [Outer area] The outer recess 23h is composed of an inner wall surface connected to the connection region 21 and an outer wall surface facing the inner wall surface. The upper ends of the inner wall surface and the outer wall surface are connected. The inner wall surface is composed of an inclined surface that slopes away from the center of the mounting plate 2 from bottom to top. In this example, the inner wall surface is an inclined surface that is flush with the first surface of the first expanded diameter portion 44a. The angle between the inner wall surface and a plane perpendicular to the main body inner wall surface 41a is the same as the angle between the first surface of the first expanded diameter portion 44a and a plane perpendicular to the main body inner wall surface 41a. The outer wall surface is composed of an inclined surface that slopes toward the center of the mounting plate 2 from bottom to top. In this example, the specific point P3 is the boundary between the inner wall surface and the outer wall surface.

[0057] 《1st connection part / 2nd connection part》 In this example, both the first upper curved surface 441 and the first lower curved surface 443 of the first connecting portion 44c and the second lower curved surface 447 of the second connecting portion 44d are disposed between the first imaginary line L1 and the second imaginary line L2, which makes it easy to reduce thermal stress acting on the shaft 4.

[0058] [Embodiment 4] <Heater> As shown in FIG. 9, the heater 1 of embodiment 4 differs from the heater 1 of embodiment 2 in that the first expanded diameter portion 44a is composed of a first surface and a second surface, and the cross-sectional shape of the outer recess 23h is C-shaped.

[0059] 《First enlarged diameter part》 In this example, the first and second surfaces of the first expanded diameter portion 44a are aligned in order from the upper end to the lower end of the first expanded diameter portion 44a. The first surface of the first expanded diameter portion 44a in this example is configured as a curved surface whose outer diameter decreases from the upper end to the second surface. In this example, the radius of curvature of the first surface is uniform. The second surface of the first expanded diameter portion 44a is a cylindrical surface with a uniform outer diameter.

[0060] [Outer area] The radius of curvature of the outer recess 23h in this example is the same as the radius of curvature of the first surface of the first expanded diameter portion 44a. The specific point P3 in this example is the center of the outer recess 23h.

[0061] 《1st connection part / 2nd connection part》 In this example, both the first upper curved surface 441 and the first lower curved surface 443 of the first connecting portion 44c and the second lower curved surface 447 of the second connecting portion 44d are disposed between the first imaginary line L1 and the second imaginary line L2, which makes it easy to reduce thermal stress acting on the shaft 4.

[0062] [Embodiment 5] <Heater> 10 and 11, the heater 1 of the fifth embodiment differs from the heater 1 of the first embodiment mainly in that the inner circumferential connection surface 43 of the connection portion 42 has an inner circumferential expanded diameter portion 43b. The following description will focus on the differences from the first embodiment. Descriptions of the same configurations and effects as those of the first embodiment may be omitted.

[0063] 《1st connection part / 2nd connection part》 The radii of curvature of the first upper curved surface 441, the first lower curved surface 443, the second upper curved surface 445, and the second lower curved surface 447 in this example are the same as those in the first embodiment. The angle θ1 of the first tapered surface 442 in this example is, for example, 26 degrees or more and 88 degrees or less. The angle θ2 of the second tapered surface 446 in this example is, for example, 26 degrees or more and 88 degrees or less. When the radii of curvature of the first upper curved surface 441, the angle θ1 of the first tapered surface 442, the first lower curved surface 443, the second upper curved surface 445, the angle θ2 of the second tapered surface 446, and the second lower curved surface 447 each satisfy the above ranges, thermal stress acting on the shaft 4 is likely to be reduced.

[0064] The angle θ1 of the first tapered surface 442 may be 30 degrees or more and 80 degrees or less, 40 degrees or more and 75 degrees or less, 44 degrees or more and 72 degrees or less, or 45 degrees or more and 70 degrees or less. The angle θ2 of the second tapered surface 446 may be 30 degrees or more and 80 degrees or less, 40 degrees or more and 75 degrees or less, 44 degrees or more and 72 degrees or less, or 45 degrees or more and 70 degrees or less.

[0065] In this example, the first downward curved surface 443 of the first connecting portion 44c and the second downward curved surface 447 of the second connecting portion 44d are disposed between the first imaginary line L1 and the second imaginary line L2, which makes it easier to reduce thermal stress acting on the shaft 4.

[0066] <Connection inner surface> As shown in Figure 10, the connecting inner circumferential surface 43 of this example has a base portion 43a and an inner circumferential expanded diameter portion 43b. The base portion 43a has an inner diameter that is the same as the inner diameter of the main body portion 41. The inner circumferential expanded diameter portion 43b has an inner diameter that is larger than the inner diameter of the base portion 43a, i.e., the inner diameter of the main body portion 41. The connecting inner circumferential surface 43 of this example has the inner circumferential expanded diameter portion 43b and the base portion 43a, which are arranged in order from the upper end to the lower end. The base portion 43a of this example connects the main body portion 41 and the inner circumferential expanded diameter portion 43b.

[0067] <Inner diameter expansion section> As shown in FIG. 11 , the inner circumferential expanded diameter portion 43b is formed so that the first length D1 is smaller than the first distance D2. The first length D1 is the shortest length between the connecting inner circumferential surface 43 and the second tapered surface 446 along a direction perpendicular to the second tapered surface 446. The first distance D2 is the distance along the perpendicular bisector L3 between the second tapered surface 446 and an intersection P5 between the perpendicular bisector L3 of the second tapered surface 446 and an extension line L4 of the main body inner circumferential surface 41a. By forming the inner circumferential expanded diameter portion 43b so that the first length D1 is smaller than the first distance D2, thermal stress acting on the shaft 4 is likely to be reduced. The inner circumferential expanded diameter portion 43b may be formed so that the first length D1 is greater than 0.5 times the thickness D3 of the main body portion 41. By providing the inner peripheral expanded diameter portion 43b so that the first length D1 is greater than 0.5 times the thickness D3, the thermal stress acting on the shaft 4 is likely to be reduced.

[0068] 10, the upper end of the inner circumferential expanded portion 43b is connected to the inner peripheral edge of the connecting end face 45. The lower end of the inner circumferential expanded portion 43b is connected to the upper end of the base portion 43a. In this example, the lower end of the inner circumferential expanded portion 43b is located at a position corresponding to the second upper curved surface 445. In this example, the inner circumferential expanded portion 43b is provided from the connecting end face 45 to a position corresponding to the second upper curved surface 445.

[0069] As shown in FIG. 11, the portion of the inner circumferential expanded portion 43b connected to the base 43a in this example has a curved surface and a flat surface aligned in order toward the base 43a. The inner diameter of the curved surface decreases toward the base 43a. The radius of curvature of the curved surface is uniform. The flat surface is perpendicular to the main body inner circumferential surface 41a. The flat surface forms a corner with the base 43a. This corner may be composed of an inclined surface or a curved surface.

[0070] Unlike this example, connecting inner circumferential surface 43 may have base portion 43a, inner circumferential expanded diameter portion 43b, and base portion 43a arranged in this order from the upper end to the lower end. The upper end of inner circumferential expanded diameter portion 43b may be located at a position corresponding to second expanded diameter portion 44b, and the lower end of inner circumferential expanded diameter portion 43b may be located at a position corresponding to second upper curved surface 445.

[0071] [Embodiment 6] <Heater> As shown in FIG. 12 , the heater 1 of the sixth embodiment differs from the heater 1 of the fifth embodiment in that the mounting plate 2 has at least one of an inner recess 22h and an outer recess 23h and the first expanded diameter portion 44a is composed of a first surface and a second surface. In the heater 1 of this example, the mounting plate 2 has both the inner recess 22h and the outer recess 23h. The inner recess 22h and the outer recess 23h of this example are the same as the inner recess 22h and the outer recess 23h of the fourth embodiment. The first surface and the second surface of the first expanded diameter portion 44a of this example are the same as the first surface and the second surface of the first expanded diameter portion 44a of the fourth embodiment. In this example, both the first upper curved surface 441 and the first lower curved surface 443 of the first connecting portion 44c and the second lower curved surface 447 of the second connecting portion 44d are disposed between the first virtual line L1 and the second virtual line L2. Therefore, the thermal stress acting on the shaft 4 is likely to be reduced.

[0072] [Test Example 1] In Test Example 1, the difference in the magnitude of thermal stress acting on the shaft due to differences in the configuration of the outer circumferential surface of the connecting portion of the shaft was investigated.

[0073] <Model No. 1> The heater of model No. 1 is the heater 1 of embodiment 4 described with reference to FIG. 9. The radius of curvature of the first upper curved surface 441 was 6 mm. The angle θ1 of the first tapered surface 442 was 45 degrees. The radius of curvature of the first lower curved surface 443 was 6 mm. The radius of curvature of the second upper curved surface 445 was 3 mm. The angle θ2 of the second tapered surface 446 was 45 degrees. The radius of curvature of the second lower curved surface 447 was 3 mm.

[0074] <Model No.2> The heater of model No. 2 is the heater 1 of embodiment 6 described with reference to Fig. 12. The heater of model No. 2 differs from the heater of model No. 1 in that it has an inner peripheral expanded diameter portion 43b.

[0075] <Model No. 101> The heater of model No. 101 is the heater 101 shown in FIG. 14. The heater 101 differs from the heater of model No. 1 mainly in that the heater 101 has only one enlarged diameter portion and one connecting portion. The connecting portion 112 connecting the enlarged diameter portion 111 and the main body portion 41 on the connecting outer peripheral surface 44 of the heater 101 is composed of a flat surface 121, an upper curved surface 122, a tapered surface 123, and a lower curved surface 124, which are arranged in this order from the enlarged diameter portion 111 toward the main body portion 41. The radius of curvature of the upper curved surface 122 was 7 mm. The angle θx of the tapered surface 123 was 45 degrees. The radius of curvature of the lower curved surface 124 was 3 mm.

[0076] <Model No. 102> The heater of model No. 102 is the heater 102 shown in FIG. 15. The heater 102 has two expansion sections, a first expansion section 44a and a second expansion section 44b, but differs from the heater of model No. 1 in that the first connecting section 44c and the second connecting section 44d do not have tapered surfaces. The first connecting section 44c is composed of flat and curved surfaces aligned in order from the first expansion section 44a to the second expansion section 44b. The flat surface of the first connecting section 44c is perpendicular to the inner circumferential surface of the main body 41. The curved surface of the first connecting section 44c has a uniform radius of curvature. The second connecting section 44d is composed of flat and curved surfaces aligned in order from the second expansion section 44b to the main body 41. The flat surface of the second connecting section 44d is perpendicular to the inner circumferential surface of the main body 41. The radius of curvature of the curved surface of the second connecting portion 44d is uniform.

[0077] <Model No. 103> Although not shown, the heater of model No. 103 differs from the heater of model No. 101 in that the connecting portion 112 in FIG. 14 does not have a tapered surface 123. The connecting portion 112 is composed of flat and curved surfaces aligned in order from the expanded diameter portion 111 toward the main body portion 41. The flat surfaces are perpendicular to the inner circumferential surface of the main body portion 41. The curved surfaces have a uniform radius of curvature. The flat surfaces and curved surfaces are similar to the flat surfaces and curved surfaces of the second connecting portion 44d in the heater of model No. 102 shown in FIG. 15.

[0078] <Stress analysis> When the temperature of the top surface of the mounting plate was heated to 750°C by a heating element, the maximum principal stress (MPa) acting on the shaft was analyzed using CAE (Computer Aided Engineering). The results are shown in Table 1. Table 1 also shows the locations where the maximum principal stress acted.

[0079] [Table 1]

[0080] As shown in Table 1, the maximum principal stress of the heaters of Models No. 1 and No. 2 was smaller than the maximum principal stress of the heaters of Models No. 101 to 103. The maximum principal stress of the heaters of Models No. 1 and No. 2 was 50 MPa or less.

[0081] [Test Example 2] In Test Example 2, the angles of the tapered surfaces of Models No. 1, No. 2, and No. 101 were changed to examine the difference in the magnitude of the thermal stress acting on the shaft.

[0082] <Model No. 1> In Model No. 1, the angle θ1 of the first tapered surface 442 and the angle θ2 of the second tapered surface 446 were set to 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, and 80 degrees.

[0083] <Model No.2> In model No. 2, the angle θ1 of the first tapered surface 442 and the angle θ2 of the second tapered surface 446 were set to 25 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 80 degrees, and 88 degrees.

[0084] <Model No. 101> In model No. 101, the angle θx of the tapered surface 123 was set to 40 degrees, 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 80 degrees, and 88 degrees.

[0085] The maximum principal stress acting on the shaft was determined in the same manner as in Test Example 1. The results are shown in Table 2 and Figure 13. Table 2 and Figure 13 also show the results of Test Example 1, i.e., the results for a 45-degree angle. The horizontal axis of Figure 13 is the angle of the tapered surface (degrees), and the vertical axis is the maximum principal stress (MPa). In Figure 13, the results of Model No. 1 are shown with crosses, the results of Model No. 2 are shown with black circles, and the results of Model No. 101 are shown with open squares. In Figure 13, adjacent marks are connected by straight lines.

[0086] [Table 2]

[0087] When comparing the same angles, the maximum principal stress of the heaters of Models No. 1 and No. 2 was smaller than the maximum principal stress of the heater of Model No. 101 regardless of the angle θ1 or the angle θ2.

[0088] For heater model No. 1, when angle θ1 and angle θ2 were between 45 degrees and 70 degrees, the maximum principal stress was 50 MPa or less, which was further reduced. For heater model No. 2, when angle θ1 and angle θ2 were between 26 degrees and 88 degrees, the maximum principal stress was 50 MPa or less, which was further reduced.

[0089] [Test Example 3] In test example 3, the differences in the magnitude of thermal stress acting on the shaft were investigated for three heaters, Example 1, Example 2, and Example 3, in which the positions of the first upper curved surface 441, the first lower curved surface 443, the second upper curved surface 445, and the second lower curved surface 447 of Model No. 1 were varied.

[0090] In the first example of Model No. 1, as shown in Fig. 9, the first upper curved surface 441, the first lower curved surface 443, and the second lower curved surface 447 were arranged between the first virtual line L1 and the second virtual line L2. The second upper curved surface 445 was arranged outside the second virtual line L2, i.e., to the right of the second virtual line L2.

[0091] In the second example of model No. 1, although not shown in the figures, the second lower curved surface 447 was disposed between the first imaginary line L1 and the second imaginary line L2 in Fig. 9. The first upper curved surface 441 and the first lower curved surface 443 were disposed inside the first imaginary line L1 in Fig. 9, i.e., on the left side of the first imaginary line L1 in Fig. 9. The second upper curved surface 445 was disposed outside the second imaginary line L2 in Fig. 9.

[0092] In the third example of Model No. 1, although not shown in the drawings, the first lower curved surface 443 and the second lower curved surface 447 were arranged between the first virtual line L1 and the second virtual line L2 in Fig. 9. The first upper curved surface 441 and the second upper curved surface 445 were arranged outside the second virtual line L2.

[0093] The maximum principal stress acting on the shaft was determined in the same manner as in Test Example 1. As a result, the maximum principal stress acting on the shaft in Example 1 was smaller than the maximum principal stress acting on the shaft in Examples 2 and 3. The maximum principal stress acting on the shaft in Example 3 was smaller than the maximum principal stress acting on the shaft in Example 2.

[0094] The present invention is not limited to the configurations shown in the embodiments, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0095] 1, 101, 102 heater 2. Mounting plate 2a Top side 2b Bottom side 21 Connection Area 22 Inner area 22h Inner recess 221 1st inner region 222 Second inner area 23 Outer area 23h Outer recess 3 Heating element 4 shafts 41 Main body 41a Inner surface of main body 41b Main body outer surface 42 Connection 43 Connection inner surface 43a base 43b Inner circumferential expansion part 44 Connection outer surface 44a 1st enlarged diameter section 44b 2nd enlarged diameter section 44c 1st connection part 44d 2nd connection part 440 1st plane 441 1st upward curve 442 First tapered surface 443 1st downward curved surface 444 2nd plane 445 2nd upward curve 446 Second tapered surface 447 2nd downward curved surface 45 Connection end face 46 Inner corner 111 Expanded diameter part 112 Connection section 121 plane 122 Upward curved surface 123 Tapered surface 124 Downward curved surface A1, A2, A3, A4, A5 area D1 First length D2 1st distance D3 Thickness L1 First virtual line L2 Second virtual line L3 perpendicular bisector L4 extension line P1 center point P2 center point P3 specific point P4 Outermost point P5 intersection θ1, θ2, θx angle

Claims

1. a mounting plate having an upper surface on which a wafer is placed; a heating element disposed inside the mounting plate; a shaft supporting the mounting plate, The shaft A cylindrical main body; a connecting portion disposed between the main body portion and the mounting plate, The connection portion is a connecting inner peripheral surface, a connecting outer peripheral surface, and a connecting end surface with the lower surface of the mounting plate; The connecting outer circumferential surface is a first enlarged diameter portion connected to the mounting plate; a second enlarged diameter portion disposed between the first enlarged diameter portion and the main body portion, the outer diameter of the first enlarged diameter portion is larger than the outer diameter of the second enlarged diameter portion, the outer diameter of the second enlarged diameter portion is larger than the outer diameter of the main body portion, a first connecting portion connecting the first expanded diameter portion and the second expanded diameter portion has a first upper curved surface, a first tapered surface, and a first lower curved surface provided in this order from the first expanded diameter portion toward the second expanded diameter portion; a second connecting portion connecting the second enlarged diameter portion and the main body portion, the second connecting portion having a second upper curved surface, a second tapered surface, and a second lower curved surface provided in this order from the second enlarged diameter portion toward the main body portion; heater.

2. 2. The heater of claim 1, wherein an angle formed between a plane perpendicular to the inner circumferential surface of the main body and the first tapered surface, and an angle formed between a plane perpendicular to the inner circumferential surface of the main body and the second tapered surface are both 44 degrees or more and 72 degrees or less.

3. the connecting inner circumferential surface has an inner circumferential expanded portion having an inner diameter larger than an inner diameter of the main body inner circumferential surface of the main body portion, In a cross section including a central axis of the main body, the first length is smaller than the first distance, the first length is the shortest length between the connecting inner circumferential surface and the second tapered surface along a direction perpendicular to the second tapered surface, 2. The heater according to claim 1, wherein the first distance is a distance along the perpendicular bisector between the second tapered surface and an intersection of the perpendicular bisector of the second tapered surface and an extension of the inner circumferential surface of the main body.

4. The heater according to claim 3 , wherein the first length of the inner circumferential expanded diameter portion is greater than 0.5 times the thickness of the main body portion.

5. 5. The heater according to claim 4, wherein an angle formed between a plane perpendicular to the inner peripheral surface of the main body and the first tapered surface, and an angle formed between a plane perpendicular to the inner peripheral surface of the main body and the second tapered surface are both 26 degrees or more and 88 degrees or less.

6. at least one of the first upper curved surface and the first lower curved surface, and at least one of the second upper curved surface and the second lower curved surface are disposed between a first virtual line and a second virtual line in a cross section including a central axis of the main body portion, the first virtual line is a virtual line connecting a radial center point of the connection end surface and a radial center point of a boundary between the connection portion and the main body portion, the second virtual line is a virtual line connecting the specific point and the outermost point on the boundary, The specific point is When the lower surface does not have an outer recess connected to the connecting end surface, the connection point is a connection point between the outer periphery of the connecting end surface and the lower surface, 6. The heater according to claim 1, wherein, when the lower surface has the outer recess, the outer recess is located at the uppermost position of the outer recess and is closest to the outer peripheral edge of the connecting end surface.

Images