Ceramic heater

Abstract

To provide a ceramic heater which is capable of sucking and holding a substrate by depressurizing an air gap between the substrate and a top surface of the ceramic heater, and also capable of suppressing the intrusion of gas from the outside into the air gap between the substrate and the top surface of the ceramic heater.SOLUTION: A ceramic heater 100 includes a ceramic substrate 110 and a metal electrode 120 embedded in the ceramic substrate 110. On a top surface 111 of the ceramic substrate 110, there are provided annular protrusions 151-154, and a plurality of protrusions 155. The height of the annular protrusions 152-154 is lower than the height of the plurality of protrusions 155. At the inside of the ceramic substrate 110, there are formed a first gas passage 161, a second gas passage 162, a third gas passage 163 and a fourth gas passage 164.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a vacuum suction member that suctions and holds substrates such as wafers. The vacuum suction member described in Patent Document 1 includes a base body on which the substrate is placed, a plurality of protrusions that protrude from the upper surface of the base body to support the substrate, and a plurality of annular protrusions that protrude in an annular shape from the upper surface of the outer periphery of the base body to support the substrate. An air passage connected to a vacuum suction device is opened between the outermost annular protrusion and the inner annular protrusion. Similarly, an air passage connected to a vacuum suction device is opened inside the inner annular protrusion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-18945 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the vacuum suction member described in Patent Document 1, the air passage between the two annular protrusions and the air passage inside the inner annular protrusion are connected to the same vacuum suction device. Therefore, when the vacuum suction device is driven to suck the substrate, gas is sucked from the gap between the substrate and the base of the vacuum suction member via these air passages.

[0005] In the semiconductor manufacturing process, ceramic heaters that have the function of sucking and holding substrates such as wafers are mainly used in chambers filled with process gas. If the vacuum suction member described in Patent Document 1 is used in a chamber filled with process gas, there is a risk that the process gas will enter the gap between the substrate and the base of the vacuum suction member when the vacuum suction device is operated to suck the substrate.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a ceramic heater that is capable of reducing the pressure in the gap between the substrate and the upper surface of the ceramic heater to hold the substrate by suction, and that is also capable of preventing gas from entering the gap between the substrate and the upper surface of the ceramic heater from the outside. [Means for solving the problem]

[0007] According to an aspect of the present invention, there is provided a ceramic substrate having an upper surface and a lower surface facing the upper surface in a vertical direction; a heating element embedded in the ceramic substrate, The ceramic substrate is a plurality of annular protrusions arranged concentrically on the upper surface at positions overlapping with the substrate in the up-down direction, each protruding upward from the upper surface; a plurality of convex portions disposed on the upper surface inside an outermost peripheral annular convex portion among the plurality of annular convex portions and protruding upward from the upper surface; a plurality of gas flow paths having openings on the upper surface between the plurality of annular protrusions and inside an innermost annular protrusion among the plurality of annular protrusions, The length of each of the plurality of annular protrusions in the vertical direction from the top surface, except for the outermost annular protrusion, is smaller than the length of each of the plurality of protrusions in the vertical direction from the top surface. Ku, The length of the outermost annular convex portion from the top surface in the vertical direction is the same as the length of each of the plurality of convex portions from the top surface in the vertical direction. A ceramic heater characterized by the above features is provided. [Effects of the Invention]

[0008] In the above-described embodiment, the ceramic heater includes multiple concentrically arranged annular protrusions, multiple protrusions arranged inside the outermost annular protrusion, and multiple gas flow paths. The multiple gas flow paths have openings between the multiple annular protrusions and an opening inside the innermost annular protrusion among the multiple annular protrusions. For example, the pressure of the gas supplied to the gas flow path that opens outermost among the multiple gas flow paths can be adjusted to be approximately the same as the pressure of the external environment, and the pressure of the gas supplied to the other gas flow paths can be adjusted to be lower than the pressure of the external environment. Alternatively, the gas flow path that opens outermost among the multiple gas flow paths can be used as an exhaust gas flow path. In either case, the substrate can be attracted toward the upper surface of the ceramic heater while preventing gas from entering the gap between the substrate and the upper surface of the ceramic heater. Furthermore, the height (vertical length) of all annular protrusions excluding the outermost annular protrusion is smaller than the height of the multiple protrusions. Therefore, the substrate does not come into contact with the upper surfaces of the annular protrusions excluding the outermost annular protrusion. This can prevent localized heat spots from occurring due to contact between the substrate and the upper surfaces of the annular convex portions excluding the outermost annular convex portion, and can also prevent particles generated from the upper surfaces of the annular convex portions from adhering to the substrate due to contact between the substrate and the upper surfaces of the annular convex portions excluding the outermost annular convex portion. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a ceramic heater 100. FIG. [Figure 2] FIG. 2 is a schematic explanatory diagram of the ceramic heater 100. As shown in FIG. [Figure 3] FIG. 3 is a schematic diagram illustrating the electrode 120. As shown in FIG. [Figure 4] FIG. 4 is a schematic explanatory diagram of a ceramic heater 100 in which the height L3 of the second protrusion 154 is smaller than the height L1 of the outermost annular protrusion 151 and the height L2 of the plurality of protrusions 155. [Figure 5] 5(a) to 5(e) are diagrams showing the flow of a method for manufacturing the ceramic base 110. [Figure 6] 6(a) to 6(d) are diagrams showing the flow of another method for manufacturing the ceramic base 110. In FIG. [Figure 7] FIG. 7 is a view equivalent to FIG. 2 of a ceramic heater 100A of a comparative example. [Figure 8] FIG. 8 is a table summarizing the results of Examples 1 to 4 and the Comparative Example. [Figure 9] FIG. 9 is a view corresponding to FIG. 2, showing an example in which four gas flow paths 165A to 168A are provided in the through-hole of the shaft . DETAILED DESCRIPTION OF THE INVENTION

[0010] <Ceramic heater 100> A ceramic heater 100 according to an embodiment of the present invention will be described with reference to Figures 1 and 2. The ceramic heater 100 is used to heat semiconductor wafers such as silicon wafers (hereinafter simply referred to as wafers 10). In the following description, the up-down direction 5 is defined based on the state in which the ceramic heater 100 is installed and ready for use (the state shown in Figure 1). As shown in Figure 1, the ceramic heater 100 according to this embodiment comprises a ceramic substrate 110, an electrode 120, a shaft 130, and a power supply line 140.

[0011] The ceramic substrate 110 is a circular plate-like member with a diameter of 12 inches (approximately 300 mm), and the wafer 10 to be heated is placed on the ceramic substrate 110. Note that in FIG. 1, the wafer 10 and the ceramic substrate 110 are shown separated from each other for ease of viewing. As shown in FIG. 1, four annular protrusions 151 to 154 and a plurality of protrusions 155 are provided on the upper surface 111 of the ceramic substrate 110. Note that in FIG. 1, the number of the plurality of protrusions 155 is reduced compared to FIG. 2 for ease of viewing. Also, as shown in FIG. 2, a first gas flow path 161, a second gas flow path 162, a third gas flow path 163, and a fourth gas flow path 164, which will be described later, are formed inside the ceramic substrate 110. The ceramic substrate 110 can be formed of a ceramic sintered body made of, for example, aluminum nitride, alumina, silicon nitride, or the like.

[0012] As shown in FIGS. 1 and 2, the four annular protrusions 151 to 154 are annular protrusions arranged concentrically on the upper surface 111 of the ceramic base 110 and protrude upward from the upper surface 111. The annular protrusion 151 is arranged on the outermost side and is arranged along the outer edge of the upper surface 111 of the ceramic base 110. In the following description, the annular protrusion 151 may be referred to as the outermost annular protrusion 151. The annular protrusion 152 is arranged inside the outermost annular protrusion 151, the annular protrusion 153 is arranged inside the annular protrusion 152, and the annular protrusion 154 is arranged inside the annular protrusion 153. As shown in FIG. 2, when the wafer 10 is placed on the ceramic base 110, the upper surface 151a of the outermost annular protrusion 151 abuts or overlaps with the lower surface of the wafer 10. That is, the outermost annular protrusion 151 is positioned so as to overlap the wafer 10 in the vertical direction when the wafer 10 is placed on the ceramic base 110. A plurality of protrusions 155 are provided between the annular protrusion 152 and the annular protrusion 153, between the annular protrusion 153 and the annular protrusion 154, and inside the annular protrusion 154. Each of the plurality of protrusions 155 has a cylindrical shape. One of the plurality of protrusions 155 is disposed approximately at the center of the upper surface 111. The remaining protrusions 155 are arranged on the circumference of three equally spaced concentric circles. The protrusions 155 arranged on the circumference of the outermost concentric circle are arranged between the annular protrusion 152 and the annular protrusion 153. The protrusions 155 arranged on the circumference of the second outermost concentric circle are arranged between the annular protrusion 153 and the annular protrusion 154. The convex portions 155 arranged on the circumference of the innermost concentric circle are arranged inside the annular convex portion 154. Furthermore, the convex portions 155 are arranged at equal intervals on the circumference of each concentric circle. The arrangement positions and number of the convex portions 155 are set appropriately depending on the application, action, and function.

[0013] The height L1 (length in the vertical direction from the upper surface 111) of the outermost annular protrusion 151 and the height L2 of the plurality of protrusions 155 can both be in the range of 5 μm to 2 mm. As shown in FIG. 2, the height L1 of the outermost annular protrusion 151 and the height L2 of the plurality of protrusions 155 can be the same. In this case, the wafer 10 abuts against the upper surface 151a of the outermost annular protrusion 151, thereby preventing the wafer 10 from warping and maintaining the flatness of the wafer 10. Also, as shown in FIG. 4, the height L1 of the outermost annular protrusion 151 can be lower than the height L2 of the plurality of protrusions 155. In either case, the height L3 of the annular protrusions 152 to 154 excluding the outermost annular protrusion 151 is lower than the height L2 of the plurality of protrusions 155. It is preferable that the height L3 of the annular protrusions 152 to 154 be 1 μm to 10 μm lower than the height L2 of the plurality of protrusions 155. Generally, the height of the plurality of convex portions 155 can be calculated by extracting and measuring convex portions 155 at a plurality of locations (for example, about 4 to 100 locations) and averaging the measurements. For example, in the case where the plurality of convex portions 155 are arranged on a circumference as described above, the heights of eight convex portions 155 are extracted at 45° intervals, measured, and averaged to calculate the heights of the plurality of convex portions 155.

[0014] The width of the annular convex portions 151 to 154 is preferably constant and can be set to 0.1 mm to 10 mm. The surface roughness Ra of the upper surfaces 151a to 154a of the annular convex portions 151 to 154 can be set to 0.4 μm or less. The surface roughness Ra of the upper surface 151a of the annular convex portion 151 is preferably 0.2 μm or less, and more preferably 0.1 μm or less. As will be described later, from the viewpoint of preventing the intrusion of process gas, it is preferable to widen the width of the outermost annular convex portion 151 and to reduce the surface roughness.

[0015] The upper surfaces 155a of the plurality of protrusions 155 are preferably circular with a diameter of 1 mm to 5 mm. The distance between each of the plurality of protrusions 155 can be set within a range of 1.5 mm to 30 mm.

[0016] 2 and 4, a plurality of openings 161a (eight in this embodiment) of a first gas flow path 161 are formed in an annular region of the upper surface 111 between the outermost annular protrusion 151 and the annular protrusion 152. The openings 161a are arranged adjacent to the inner side of the outermost annular protrusion 151. In other words, the openings 161a are arranged in an annular shape along the inner circumference of the outermost annular protrusion 151. The openings 161a are arranged outside all of the protrusions 155. An opening 162a of a second gas flow path 162 is formed between the annular protrusion 152 and the annular protrusion 153 of the upper surface 111, an opening 163a of a third gas flow path 163 is formed between the annular protrusion 153 and the annular protrusion 154, and an opening 164a of a fourth gas flow path 164 is formed inside the annular protrusion 154. One each of the openings 162a, 163a, and 164a is provided, but a plurality of each of the openings 162a, 163a, and 164a may be provided.

[0017] The first gas flow path 161 is a gas flow path including a plurality of openings 161a provided in an annular region between the outermost annular convex portion 151 and the annular convex portion 152, and is formed inside the ceramic base 110. As shown in FIGS. 2 and 4, the first gas flow path 161 extends downward from each opening 161a and then extends horizontally toward the center of the ceramic base 110. The flow paths from each opening 161a then merge via a merging path (not shown) and continue to extend downward (see FIG. 2). As will be described later, the lower end of the first gas flow path 161 is joined to the upper end of a fifth gas flow path 165 formed inside the shaft 130.

[0018] The second gas flow path 162 is a gas flow path having an opening 162a provided between the annular convex portion 152 and the annular convex portion 153, and is formed inside the ceramic base 110. The third gas flow path 163 is a gas flow path having an opening 163a provided between the annular convex portion 153 and the annular convex portion 154, and is formed inside the ceramic base 110. The fourth gas flow path 164 is a gas flow path having an opening 164a provided inside the annular convex portion 153, and is formed inside the ceramic base 110. As shown in FIGS. 2 and 4 , the second gas flow path 162 and the third gas flow path 163 extend downward from the openings 162a and 163a, respectively, and then extend horizontally toward the center of the ceramic base 110 and further extend downward. The fourth gas flow path 164 extends downward from the opening 164a (see FIG. 2 ). As will be described later, the lower end of the first gas flow path 161 is joined to the upper end of a fifth gas flow path 165 formed inside the shaft 130. The lower end of the second gas flow path 162 is joined to the upper end of a sixth gas flow path 166 formed inside the shaft 130. The lower end of the third gas flow path 163 is joined to the upper end of a seventh gas flow path 167 formed inside the shaft 130. The lower end of the fourth gas flow path 164 is joined to the upper end of an eighth gas flow path 168 formed inside the shaft 130.

[0019] As described above, the second gas flow path 162 to the fourth gas flow path 164 are independent of each other. Therefore, the first gas flow path 161 to the fourth gas flow path 164 can be used for different purposes. For example, the first gas flow path 161 can be used as an exhaust flow path for exhausting gas, and the second gas flow path 162 to the fourth gas flow path 164 can be used as gas flow paths for supplying a heat transfer gas. Alternatively, the first gas flow path 161 and the second gas flow path 162 to the fourth gas flow path 164 can all be used as gas flow paths for supplying a heat transfer gas. In this case, the gas flow rates of the first gas flow path 161 and the second gas flow path 162 to the fourth gas flow path 164 can be individually adjusted. Note that, for example, an inert gas such as helium, argon, or a mixture of helium and argon, or nitrogen gas, can be used as the heat transfer gas. The heat transfer gas is supplied through the first gas flow passage 161 and / or the second to fourth gas flow passages 162 to 164 at a pressure set within the range of 100 Pa to 40,000 Pa.

[0020] As shown in FIGS. 1 and 2, an electrode 120 (one example of a heating element of the present invention) is embedded within the ceramic substrate 110. As shown in FIG. 3, the electrode 120 is a metal mesh or foil cut into a strip shape and has a bilaterally symmetrical shape. The outer diameter of the electrode 120 is approximately 300 mm. A terminal 121 connected to a power supply line 140 (see FIG. 1) is provided approximately at the center of the electrode 120. The electrode 120 is formed of a heat-resistant metal (high-melting-point metal) such as a mesh or foil of tungsten (W), molybdenum (Mo), or an alloy containing molybdenum and / or tungsten. The purity of the tungsten or molybdenum is preferably 99% or higher. The thickness of the electrode 120 is 0.15 mm or less. From the viewpoint of increasing the resistance of the electrode and reducing the current consumption of the ceramic heater 100, it is preferable that the wire diameter be 0.1 mm or less, and the thickness of the electrode 120 be 0.1 mm or less. Furthermore, the width of the strip-shaped electrode 120 is preferably 2.5 mm to 20 mm, and more preferably 5 mm to 15 mm. In this embodiment, the electrode 120 is cut into the shape shown in FIG. 3, but the shape of the electrode 120 is not limited to this and can be changed as appropriate. In addition to the electrode 120, at least one of an electrostatic chuck electrode for attracting the wafer 10 to the upper surface 111 by the Johnsen-Rahbek force and a plasma electrode for generating plasma above the ceramic base 110 may be embedded inside the ceramic base 110.

[0021] 1 and 2, a shaft 130 is connected to the lower surface 113 of the ceramic base 110. The shaft 130 has a hollow, approximately cylindrical cylindrical portion 131 and a large-diameter portion 132 (see FIG. 1) provided below the cylindrical portion 131. The large-diameter portion 132 has a diameter larger than that of the cylindrical portion 131. In the following description, the longitudinal direction of the cylindrical portion 131 is defined as the longitudinal direction 6 of the shaft 130. As shown in FIG. 1, when the ceramic heater 100 is in use, the longitudinal direction 6 of the shaft 130 is parallel to the up-down direction 5.

[0022] The upper surface of the cylindrical portion 131 is fixed to the lower surface 113 of the ceramic base 110. The shaft 130 may be made of a ceramic sintered body such as alumina, aluminum nitride, or silicon nitride, like the ceramic base 110. Alternatively, to improve heat insulation, the shaft 130 may be made of a material with a lower thermal conductivity than the ceramic base 110. An enlarged diameter portion similar to the large diameter portion 132 provided below the upper surface of the cylindrical portion 131 may be provided.

[0023] As shown in FIG. 2, the shaft 130 has a hollow cylindrical shape, and a through-hole extending in the longitudinal direction 6 is formed inside the shaft 130 (the region inside the inner diameter). A power supply line 140 for supplying power to the electrode 120 is arranged in the hollow portion (through-hole) of the shaft 130. The upper end of the power supply line 140 is electrically connected to a terminal portion 121 (see FIG. 3) arranged in the center of the electrode 120. A power supply terminal is provided at the lower end of the power supply line 140, and is connected to a heater power supply (not shown). As a result, power is supplied to the electrode 120 via the power supply line 140.

[0024] 2 and 4, four gas flow paths (a fifth gas flow path 165, a sixth gas flow path 166, a seventh gas flow path 167, and an eighth gas flow path 168) extending in the vertical direction are formed in the cylindrical portion 131 of the shaft 130. As described above, the upper end of the fifth gas flow path 165 is connected to the lower end of the first gas flow path 161, the upper end of the sixth gas flow path 166 is connected to the lower end of the second gas flow path 162, the upper end of the seventh gas flow path 167 is connected to the lower end of the third gas flow path 163, and the upper end of the eighth gas flow path 168 is connected to the lower end of the fourth gas flow path 164.

[0025] Next, a method for manufacturing the ceramic heater 100 will be described. In the following, an example will be described in which the ceramic base 110 and the shaft 130 are made of aluminum nitride.

[0026] First, a method for manufacturing the ceramic substrate 110 will be described. As shown in FIG. 5(a), granulated powder P, primarily composed of aluminum nitride (AlN) powder, is placed in a carbon mold with a bed 501 and pre-pressed with a punch 502. The granulated powder P preferably contains 5 wt% or less of a sintering aid (e.g., Y2O3). Next, as shown in FIG. 5(b), an electrode 120 cut to a predetermined shape is placed on the pre-pressed granulated powder P. The electrode 120 is placed parallel to a plane perpendicular to the pressure direction (the bottom surface of the mold with a bed 501). At this time, a W pellet or a Mo pellet may be embedded at the position of the terminal 121 of the electrode 120.

[0027] As shown in FIG. 5(c), granulated powder P is further poured into the bed-type mold 501 so as to cover the electrode 120, and pressed with a punch 502 to form a compact. Next, as shown in FIG. 5(d), the granulated powder P with the electrode 120 embedded therein is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. Furthermore, firing is preferably performed at a temperature of 1800°C or more. Next, as shown in FIG. 5(e), blind holes are drilled to the electrode 120 to form the terminals 121. If a pellet is embedded, blind holes are drilled to the pellets. Furthermore, through holes that will become part of the first to fourth gas flow paths 161 to 164 are formed, and grooves that will become part of the first to fourth gas flow paths 161 to 164 are formed on the underside of the fired body. Note that in FIG. 5(e), only some of the grooves that will become part of the first to fourth gas flow paths 161 to 164 are shown to make the drawing easier to understand.

[0028] Next, although not shown, the steps shown in FIGS. 5(a) to 5(d) are repeated without embedding the electrode 120 to produce another plurality of fired bodies. Through holes that will become part of the first gas flow path 161 and the fourth gas flow path 164 are formed in the other fired bodies (see FIG. 5(e)). Then, these multiple fired bodies are stacked and bonded by diffusion bonding. This makes it possible to produce a ceramic base 110 having the first to fourth gas flow paths 161 to 164 formed therein.

[0029] The ceramic base material 110 can also be manufactured by the following method. As shown in Fig. 6(a), a binder is added to aluminum nitride granulated powder P, which is then CIP molded and processed into a disk shape to produce an aluminum nitride molded body 510. Next, as shown in Fig. 6(b), the molded body 510 is degreased to remove the binder.

[0030] As shown in FIG. 6(c), a recess 511 for embedding the electrode 120 is formed in the degreased compact 510. The electrode 120 is placed in the recess 511 of the compact 510, and another compact 510 is stacked on top of it. Note that the recess 511 may be formed in the compact 510 in advance. Next, as shown in FIG. 6(d), the stacked compacts 510, sandwiching the electrode 120 between them, are fired in a pressed state to produce a fired body. The pressure applied during firing is preferably 1 MPa or more. Furthermore, firing is preferably performed at a temperature of 1800°C or more. Since the steps after producing the fired body are similar to those described above, a description thereof will be omitted. Note that in the above description, through-holes and grooves constituting the first to fourth gas flow paths 161 to 164 are formed in the fired body, but through-holes and grooves constituting the first to fourth gas flow paths 161 to 164 may also be formed in the compact 510 and then fired.

[0031] The upper surface 111 of the ceramic base material 110 thus formed is ground and then subjected to lapping (mirror polishing). Furthermore, the upper surface 111 is subjected to sandblasting to form a plurality of convex portions 155 and annular convex portions 151 to 154 on the upper surface 111. Note that sandblasting is a suitable processing method for forming the plurality of convex portions 155 and annular convex portions 151 to 154 on the upper surface 111, but other processing methods may also be used.

[0032] Next, a method for manufacturing the shaft 130 and a method for bonding the shaft 130 to the ceramic base 110 will be described. First, granulated powder P of aluminum nitride to which several wt % of binder has been added is formed under hydrostatic pressure (approximately 1 MPa), and the green body is processed into a predetermined shape. The length of the cylindrical portion 131 of the shaft 130 can be, for example, 50 mm to 500 mm. At this time, through holes that become the fifth gas flow path 165, the sixth gas flow path 166, the seventh gas flow path 167, and the eighth gas flow path 168 are formed in the green body. Thereafter, the green body is fired in a nitrogen atmosphere. For example, the firing is performed at a temperature of 1900°C for two hours. Then, the sintered body is processed into a predetermined shape to form the shaft 130. The upper surface of the cylindrical portion 131 and the lower surface 113 of the ceramic base 110 can be fixed by diffusion bonding at 1600°C or higher and under a uniaxial pressure of 1 MPa or higher. In this case, the surface roughness Ra of the lower surface 113 of the ceramic substrate 110 is preferably 0.4 μm or less, and more preferably 0.2 μm or less. The upper surface of the cylindrical portion 131 and the lower surface 113 of the ceramic substrate 110 can also be bonded using a bonding agent. For example, an AlN bonding material paste containing 10 wt% Y2O3 can be used as the bonding agent. For example, the AlN bonding material paste can be applied to the interface between the upper surface of the cylindrical portion 131 and the lower surface 113 of the ceramic substrate 110 to a thickness of 15 μm, and then heated at 1700°C for 1 hour while applying a force of 5 kPa in a direction perpendicular to the upper surface 111 (the longitudinal direction 6 of the shaft 130). Alternatively, the upper surface of the cylindrical portion 131 and the lower surface 113 of the ceramic substrate 110 can be fixed together by screwing, brazing, or the like. [Example]

[0033] The present invention will be further described below using examples and comparative examples, but the present invention is not limited to the examples and comparative examples described below.

[0034] [Example 1] As shown in FIG. 2, in the ceramic heater 100 of Example 1, the height L1 of the outermost peripheral annular protrusion 151 and the height L2 of the multiple protrusions 155 are the same, and the height L3 of the annular protrusions 152 to 154 is smaller than the height L2 of the multiple protrusions 155. Although not shown in FIG. 2, a molybdenum mesh (wire diameter 0.1 mm, mesh size #50, plain weave) cut into the shape shown in FIG. 3 was fabricated as the electrode 120. Then, a ceramic base 110 having a diameter of 310 mm and a thickness of 25 mm was fabricated with this electrode 120 embedded therein. Specifically, a peripheral outermost annular protrusion 151 having an inner diameter of 292 mm, an outer diameter of 298 mm, a width of 3 mm, and a height of 150 μm from the upper surface 111 was formed on the upper surface 111 of the ceramic base 110. An annular convex portion 152 having an inner diameter of 280 mm, an outer diameter of 286 mm, a width of 3 mm, and a height of 147 μm was formed inside the outermost annular convex portion 151. An annular convex portion 153 having an inner diameter of 172 mm, an outer diameter of 178 mm, a width of 3 mm, and a height of 147 μm was formed inside the annular convex portion 152. An annular convex portion 154 having an inner diameter of 64 mm, an outer diameter of 70 mm, a width of 3 mm, and a height of 147 μm was formed inside the annular convex portion 153. A plurality of cylindrical convex portions 155 having a diameter of 2 mm and a height of 150 μm from the upper surface 111 of the ceramic substrate 110 were formed inside the second annular convex portion 152 on the upper surface 111 of the ceramic substrate 110. The surface roughness Ra of the upper surfaces 151a to 154a of the annular convex portions 151 to 154 and the upper surface 155a of the convex portion 155 was both 0.4 μm.

[0035] The diameter of the opening 161a of the first gas flow path 161 is 3 mm. Eight openings 161a are equally spaced apart so as to line up in an annular shape on the upper surface 111 of the ceramic base 110 between the outermost annular protrusion 151 and the annular protrusion 152. The center of each opening 161a is located 289 mm from the center of the ceramic base 110. The diameter of the opening 162a of the second gas flow path 162 is 3 mm. The opening 162a is located between the annular protrusion 152 and the annular protrusion 153 on the upper surface 111 of the ceramic base 110. The center of the opening 162a is located 220 mm from the center of the ceramic base 110. The diameter of the opening 163a of the third gas flow path 163 is 3 mm. The opening 163a is located between the annular protrusion 153 and the annular protrusion 154 on the upper surface 111 of the ceramic base 110. The center of the opening 163a is located 160 mm from the center of the ceramic base 110. The diameter of the opening 164a of the fourth gas flow path 164 is 3 mm. The opening 164a is disposed inside the annular protrusion 154 on the upper surface 111 of the ceramic base 110. The center of the opening 164a is located 30 mm from the center of the ceramic base 110.

[0036] The ceramic heater 100 having such a shape was placed in a process chamber. A mixed gas of argon and helium was supplied as a process gas at a pressure of 26,600 Pa (200 Torr) into the process chamber. Furthermore, argon gas was supplied as a heat transfer gas at a pressure of 6,650 Pa (50 Torr) through the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164. Furthermore, an exhaust pump (not shown) was connected to the first gas flow path 161, and the gap between the substrate 10 and the upper surface 111 of the ceramic base 110 was evacuated through the first gas flow path 161. At this time, the pressure at the port of the exhaust pump was 133 Pa (1 Torr) or less.

[0037] The temperature of the ceramic heater 100 was evaluated using the following procedure. First, a silicon wafer for temperature evaluation was placed on the ceramic substrate 110, and 650 W of heater power was supplied to the ceramic heater 100 from an external power supply (not shown). Then, a process gas and argon gas as a heat transfer gas were supplied at the above pressure. The temperature distribution in a 298 mm diameter area of ​​the silicon wafer for temperature evaluation was then measured using an infrared camera. The temperature distribution was measured when the supply of argon gas to the fourth gas flow path 164 began (first measurement) and 10 minutes later (second measurement). The silicon wafer for temperature evaluation was a 300 mm diameter silicon wafer coated with a 30 μm thick blackbody film on its top surface. A blackbody film is a film with an emissivity (radiation rate) of 90% or higher, and can be formed, for example, by coating a blackbody paint whose main ingredient is carbon nanotubes. In Example 1, the average value of the temperature distribution in the first temperature measurement was 377.9° C., and the average value of the temperature distribution in the second temperature measurement was 378.0° C. The gas flow rates of the argon gas supplied to the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 were 12 sccm in total.

[0038] [Example 2] The ceramic heater 100 of Example 2 is similar to the ceramic heater 100 of Example 1. In Example 2, temperature evaluation was performed under the same conditions as in Example 1, except that the pressure of the argon gas supplied to the first gas flow path 161 was set to 26,600 Pa (200 Torr). In Example 2, the average value of the temperature distribution in the first temperature measurement was 377.7°C, and the average value of the temperature distribution in the second temperature measurement was 377.8°C. The gas flow rates of the argon gas supplied to the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 were a total of 11 sccm.

[0039] [Example 3] The ceramic heater 100 of Example 3 is similar to the ceramic heater 100 of Example 1, except that the height L1 of the outermost peripheral annular convex portion 151 is 147 μm. In Example 3, argon gas and process gas were supplied at the same pressure as in Example 2. In Example 3, the average value of the temperature distribution in the first temperature measurement was 377.7°C, and the average value of the temperature distribution in the second temperature measurement was 377.6°C. The gas flow rate of argon gas supplied to the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 was 39 sccm in total.

[0040] [Example 4] The ceramic heater 100 of Example 4 is similar to the ceramic heater 100 of Example 1, except that the height L1 of the outermost peripheral annular convex portion 151 is 140 μm. In Example 4, argon gas and process gas were supplied at the same pressure as in Example 2. In Example 4, the average value of the temperature distribution in the first temperature measurement was 377.9°C, and the average value of the temperature distribution in the second temperature measurement was 378.0°C. The gas flow rate of argon gas supplied to the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 was 42 sccm in total. [Comparative Example] As shown in FIG. 7, the ceramic heater 100A of the comparative example is similar to the ceramic heater 100 of Example 1, except that the ceramic base 110 does not include the first gas flow path 161, the second gas flow path 162, the third gas flow path 163, and the annular protrusions 152-154. In the comparative example, a mixed gas of argon and helium was supplied as a process gas into the process chamber at a pressure of 26,600 Pa (200 Torr). Furthermore, argon gas was supplied through the fourth gas flow path 164 at a pressure of 6,650 Pa (50 Torr). In the comparative example, the average value of the temperature distribution in the first temperature measurement was 377.7°C, and the average value of the temperature distribution in the second temperature measurement was 383.3°C. The gas flow rate of the argon gas supplied to the fourth gas flow path 164 was less than 0.2 sccm.

[0041] <Summary of Examples and Comparative Examples> FIG. 8 shows a table summarizing the results of the above-mentioned Examples 1 to 4 and Comparative Example.

[0042] In Example 1, the pressure of the heat transfer gas supplied to the second gas flow path 162 to the fourth gas flow path 164 is set lower (6650 Pa in Example 1) than the pressure of the process gas in the process chamber, so that the wafer 10 can be attracted toward the upper surface 111 of the ceramic substrate 110 due to the pressure difference. This improves adhesion between the wafer 10 and the upper surfaces 155a of the multiple protrusions 155, allowing heat from the ceramic heater 100 to be efficiently transferred to the wafer 10. However, at the same time, the pressure difference causes some of the process gas in the process chamber to enter the gap between the outermost annular protrusion 151 and the wafer 10. However, the ceramic heater 100 is provided with a first gas flow path 161 having multiple openings 161a arranged along the inner periphery of the outermost annular protrusion 151, so that the process gas that has entered the gap between the outermost annular protrusion 151 and the wafer 10 can be exhausted via the first gas flow path 161. This prevents fluctuations in the temperature of the wafer 10 due to fluctuations in the thermal conductivity of the heat transfer gas caused by mixing of the process gas with the heat transfer gas in the area surrounded by the outermost annular protrusion 151 and the wafer 10. Furthermore, the annular protrusions 152-154 are provided inside the multiple openings 161a of the first gas flow path 161, preventing the process gas that has entered the gap surrounded by the outermost annular protrusion 151 and the wafer 10 from diffusing inward. Furthermore, because the height L3 of each of the annular protrusions 152-154 is smaller than the height L2 of the multiple protrusions 155, the wafer 10 does not come into contact with the upper surfaces 152a-154a of the annular protrusions 152-154. This prevents localized heat spots caused by contact between the wafer 10 and the upper surfaces 152a-154a of the annular protrusions 152-154. Furthermore, the contact between the wafer 10 and the upper surfaces 152a to 154a of the annular protrusions 152 to 154 can prevent particles generated from the upper surfaces 152a to 154a of the annular protrusions 152 to 154 from adhering to the wafer 10.

[0043] In Examples 2 to 4, the pressure of the heat transfer gas supplied to the second gas flow path 162 to the fourth gas flow path 164 is set lower than the pressure of the process gas in the process chamber (6650 Pa in Example 1), so the wafer 10 can be attracted toward the upper surface 111 of the ceramic substrate 110 due to the pressure difference. This improves adhesion between the wafer 10 and the upper surfaces 155a of the multiple protrusions 155, allowing heat from the ceramic heater 100 to be efficiently transferred to the wafer 10. However, at the same time, the pressure difference causes some of the process gas in the process chamber to enter the gap surrounded by the outermost annular protrusion 151 and the wafer 10. However, the ceramic heater 100 is provided with a first gas flow path 161 having multiple openings 161a arranged along the inner periphery of the outermost annular protrusion 151, and the heat transfer gas is supplied through the first gas flow path 161 at a pressure similar to the pressure of the process gas (26600 Pa in Examples 2 to 4). As a result, the pressure of the heat transfer gas in the region between the outermost annular convex portion 151 and the annular convex portion 152 becomes approximately the same as the pressure of the process gas in the process chamber. This reduces the pressure difference between the region between the outermost annular convex portion 151 and the annular convex portion 152 and the interior of the process chamber, thereby preventing the process gas in the process chamber from entering the region between the outermost annular convex portion 151 and the annular convex portion 152. This prevents the temperature of the wafer 10 from fluctuating due to fluctuations in the thermal conductivity of the heat transfer gas caused by the process gas being mixed into the heat transfer gas. Furthermore, as described above, the annular convex portions 152 to 154 are provided inside the multiple openings 161a of the first gas flow path 161, preventing the process gas that has entered the gap surrounded by the outermost annular convex portion 151 and the wafer 10 from diffusing inward.

[0044] In contrast, as shown in FIG. 8 , the ceramic heater 100A of the comparative example does not have the first gas flow path 161 to the third gas flow path 163. Therefore, if the pressure in the gap between the outermost annular protrusion 151 and the wafer 10 is set lower than the process gas pressure in the process chamber to attract the wafer 10 toward the upper surface 111 of the ceramic substrate 110, the process gas easily enters the gap between the outermost annular protrusion 151 and the wafer 10 due to the pressure difference. Furthermore, the ceramic heater 100A of the comparative example does not have the annular protrusions 152 to 154. This is thought to be due to the mixing of the process gas with the heat transfer gas in the region inside the outermost annular protrusion 151, which changes the thermal conductivity of the heat transfer gas and thus the temperature of the wafer 10. Note that in the comparative example, the mixing of helium gas contained in the process gas with the heat transfer gas (argon gas) increases the thermal conductivity, which is thought to be why the temperature of the wafer 10 is higher than in Examples 1 to 4.

[0045] Comparing Example 2 and Example 3, it was found that by making the height L1 of the outermost annular protrusion 151 3 μm lower than the height L2 of the plurality of protrusions 155, the gas flow rate in the fourth gas flow path 164 increased and the consumption of the heat transfer gas (argon gas) increased. However, it was also found that even when the height L1 of the outermost annular protrusion 151 was 3 μm lower than the height L2 of the plurality of protrusions 155, temperature changes in the wafer 10 could be sufficiently suppressed. Furthermore, because the height L1 of the outermost annular protrusion 151 is lower than the height L2 of the plurality of protrusions 155, the lower surface of the wafer 10 does not come into contact with the upper surface 151 a of the outermost annular protrusion 151. This prevents localized heat spots from occurring due to contact between the wafer 10 and the upper surface 151 a of the outermost annular protrusion 151. Furthermore, contact between the wafer 10 and the upper surface 151 a of the outermost annular protrusion 151 prevents particles generated from the upper surface 151 a of the outermost annular protrusion 151 from adhering to the wafer 10.

[0046] Comparing Example 2 and Example 4, it was found that the gas flow rate in the second gas flow path 164 increases and the consumption of the heat transfer gas (argon gas) increases by making the height L1 of the outermost annular convex portion 151 10 μm lower than the height L2 of the plurality of convex portions 155. However, it was found that even when the height L1 of the outermost annular convex portion 151 is 10 μm lower than the height L2 of the plurality of convex portions 155, the temperature change of the wafer 10 can be sufficiently suppressed.

[0047] <Effects of the embodiment> In the above embodiments and examples, the ceramic heater 100 includes a ceramic base 110 and a metal electrode 120 embedded in the ceramic base 110. The ceramic base 110 has an upper surface 111 provided with a plurality of concentrically arranged annular protrusions 151-154 that protrude upward from the upper surface 111, and a plurality of protrusions 155 that are arranged inside the outermost annular protrusion 151 and protrude upward from the upper surface 111. The annular protrusions 151-154 are positioned so as to overlap with the wafer 10 in the vertical direction 5 when the wafer 10 is placed on the ceramic base 110. Furthermore, inside the ceramic base 110, a first gas flow path 161 having a plurality of openings 161a distributed in an annular pattern between the outermost peripheral annular protrusion 151 and the annular protrusion 152 is formed adjacent to the inner side of the outermost peripheral annular protrusion 151, a second gas flow path 162 having openings 162a opening between the annular protrusion 152 and the annular protrusion 153, a third gas flow path 163 having openings 163a opening between the annular protrusion 153 and the annular protrusion 154, and a fourth gas flow path 164 having openings 164a opening to the inner side of the annular protrusion 154. The first to fourth gas flow paths 161 to 164 are independent gas flow paths.

[0048] The first gas flow path 161 to the fourth gas flow path 164 are independent of each other, and therefore can be used for different purposes. For example, as in Example 1, the first gas flow path 161 can be used as an exhaust flow path for exhausting gas, and the second gas flow path 162 to the fourth gas flow path 164 can be used as gas flow paths for supplying argon gas, a heat transfer gas. Alternatively, as in Examples 2 to 4, the first gas flow path 161 and the second gas flow path 162 to the fourth gas flow path 164 can all be used as gas flow paths for supplying argon gas, a heat transfer gas. In either case, by adjusting the flow rates of the heat transfer gas supplied to the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164, respectively, the pressure in the gap surrounded by the outermost annular protrusion 151 and the wafer 10 can be set lower than the pressure outside the outermost annular protrusion 151 (external environment). In this case, the wafer 10 can be attracted toward the upper surface 111 of the ceramic substrate 110 due to the pressure difference. Because the adhesion between the wafer 10 and the upper surfaces 155a of the multiple protrusions 155 is improved, heat from the ceramic heater 100 can be efficiently transferred to the wafer 10. However, if the pressure in the gap surrounded by the outermost annular protrusion 151 and the wafer 10 is made lower than the pressure outside the outermost annular protrusion 151, the pressure difference will cause gas outside the outermost annular protrusion 151 to enter the gap surrounded by the outermost annular protrusion 151 and the wafer 10. The ceramic heater 100 is provided with a first gas flow path 161 having multiple openings 161a arranged along the inner circumference of the outermost annular protrusion 151. As in the first embodiment, gas that has entered the gap surrounded by the outermost annular protrusion 151 and the wafer 10 can be exhausted via the first gas flow path 161. Alternatively, as in the second to fourth embodiments, the heat transfer gas can be supplied through the first gas flow path 161 at a pressure similar to that of the process gas, thereby reducing the pressure difference between the area between the outermost annular convex portion 151 and the annular convex portion 152 and the inside of the process chamber.This reduces the pressure difference between the pressure of the heat transfer gas in the region between the outermost annular convex portion 151 and the annular convex portion 152 and the pressure of the process gas in the process chamber, thereby preventing the process gas in the process chamber from entering the region between the outermost annular convex portion 151 and the annular convex portion 152. In either case, it is possible to prevent fluctuations in the temperature of the wafer 10 in the region inside the outermost annular convex portion 151 due to the intrusion of gas from outside.

[0049] As described above, when the first gas flow path 161 is used as an exhaust gas flow path or when the pressure of the gas supplied to the first gas flow path 161 is set higher than the pressure of the gas supplied to the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164, a gas flow occurs between the first gas flow path 161 and the second to fourth gas flow paths 162 to 164. In this embodiment, the annular convex portions 152 to 154 other than the outermost annular convex portion 151 are provided, so that the above-mentioned gas flow can be suppressed and the pressure in the gap between the wafer 10 and the upper surface 111 of the ceramic base 110 can be made nearly uniform.

[0050] Furthermore, the height L3 of each of the annular protrusions 152-154 other than the outermost annular protrusion 151 is smaller than the height L2 of the plurality of protrusions 155. Therefore, the wafer 10 does not come into contact with the upper surfaces 152a-154a of the annular protrusions 152-154. This prevents the occurrence of localized heat spots due to contact between the wafer 10 and the upper surfaces 152a-154a of the annular protrusions 152-154. Furthermore, the contact between the wafer 10 and the upper surfaces 152a-154a of the annular protrusions 152-154 prevents particles generated from the upper surfaces 152a-154a of the annular protrusions 152-154 from adhering to the wafer 10.

[0051] In the above-described embodiments and examples, the height L1 of the outermost peripheral annular convex portion 151 can be made smaller than the height L2 of the plurality of convex portions 155 (L1 < L2). Even in this case, it is possible to suppress the gas outside the outermost peripheral annular convex portion 151 from entering the inside of the outermost peripheral annular convex portion 151, and it is possible to suppress the temperature change of the wafer 10. Further, since the height L1 of the outermost peripheral annular convex portion 151 is lower than the height L2 of the plurality of convex portions 155, the lower surface of the wafer 10 does not contact the upper surface 151a of the outermost peripheral annular convex portion 151. Thereby, generation of local heat spots due to contact between the wafer 10 and the upper surface 151a of the outermost peripheral annular convex portion 151 can be suppressed. Further, it is possible to suppress particles generated from the upper surface 151a of the outermost peripheral annular convex portion 151 from adhering to the wafer 10 due to contact between the wafer 10 and the upper surface 151a of the outermost peripheral annular convex portion 151. As described above, the height L1 of the outermost peripheral annular convex portion 151 and the height L2 of the plurality of convex portions 155 are both defined as the vertical length from the upper surface 111 of the ceramic base material 110.

[0052] In the above-described embodiments and examples, the difference between the height L2 of the plurality of convex portions 155 and the height L3 of the annular convex portions 152 to 154 can be set to 1 μm or more and 10 μm or less (1 μm ≤ L2 - L3 ≤ 10 μm). In this case, since the gap between the annular convex portions 152 to 154 and the lower surface of the wafer 10 can be made 10 μm or less, the process gas that has entered the gap surrounded by the outermost peripheral annular convex portion 151 and the wafer 10 is suppressed from diffusing inward. Further, since the gap between the annular convex portions 152 to 154 and the lower surface of the wafer 10 can be made 1 μm or more, the wafer 10 does not contact the upper surfaces 152a to 154a of the annular convex portions 152 to 154. Thereby, generation of local heat spots due to contact between the wafer 10 and the upper surfaces 152a to 154a of the annular convex portions 152 to 154 can be suppressed. Further, it is possible to suppress particles generated from the upper surfaces 152a to 154a of the annular convex portions 152 to 154 from adhering to the wafer 10 due to contact between the wafer 10 and the upper surfaces 152a to 154a of the annular convex portions 152 to 154.

[0053] In the above-described embodiments and examples, a fifth gas flow path 165, a sixth gas flow path 166, a seventh gas flow path 167, and an eighth gas flow path 168 extending in the vertical direction may be formed in the cylindrical portion 131 of the shaft 130. The upper end of the fifth gas flow path 165 is connected to the lower end of the first gas flow path 161, the upper end of the sixth gas flow path 166 is connected to the lower end of the second gas flow path 162, the upper end of the seventh gas flow path 167 is connected to the lower end of the third gas flow path 163, and the upper end of the eighth gas flow path 168 is connected to the lower end of the fourth gas flow path 164. Four gas flow paths connected to the first gas flow path 161, the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 are formed in the cylindrical portion 131 of the shaft 130, so that gas can be easily exhausted from the first gas flow path 161 through these paths, and gas (for example, heat transfer gas) can be supplied to the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164. Furthermore, these gas flow paths can be used arbitrarily for exhausting or suctioning gas.

[0054] <Modification form> The above-described embodiment is merely illustrative and may be modified as appropriate. For example, the shapes and dimensions of the ceramic base 110 and the shaft 130 are not limited to those of the above-described embodiment and may be modified as appropriate. The dimensions such as height and width, shape, and surface roughness Ra of the upper surface of the annular protrusions 151-154 may be modified as appropriate. Furthermore, the number of annular protrusions is not limited to four and may be any number equal to or greater than two.

[0055] In the above-described embodiment and example, the heights of the annular protrusions, excluding the outermost annular protrusion, are all the same. However, the present invention is not necessarily limited to this embodiment. For example, the heights of the annular protrusions, excluding the outermost annular protrusion, may be different from each other.

[0056] In the above-described embodiment and examples, the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 each have one opening. However, the present invention is not necessarily limited to this. The second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 may each have multiple openings.

[0057] In the above-described embodiments and examples, the number of independent gas flow paths is four, but the present invention is not limited to such an embodiment. The number of independent gas flow paths can be three or less, or five or more. For example, in the above-described embodiments and examples, the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 are independent of one another. However, the second gas flow path 162, the third gas flow path 163, and the fourth gas flow path 164 can be made into gas flow paths that communicate with one another. In that case, the cylindrical portion 131 of the shaft 130 can also be provided with independent gas flow paths corresponding to the number of these independent gas flow paths.

[0058] The height of the multiple protrusions 155, the shape of the upper surface 155a, and the surface roughness Ra of the upper surface 155a can be changed as appropriate. For example, the shape of the upper surface 155a of the multiple protrusions 155 does not necessarily have to be circular and can be any shape. Even in this case, it is preferable that the upper surface 155a has an area similar to that of a circular upper surface 156 having a diameter of 1 mm to 5 mm. In the above description, the multiple protrusions 155 are arranged so as to be distributed concentrically, but the present invention is not limited to this embodiment. For example, the multiple protrusions 155 may be arranged so as to be distributed at random positions. Even in this case, the distance between each of the multiple protrusions 155 is preferably in the range of 1.5 mm to 30 mm.

[0059] In the above embodiment, molybdenum, tungsten, or an alloy containing molybdenum and / or tungsten is used as the electrode, but the present invention is not limited to such an embodiment. For example, metals other than molybdenum and tungsten, or alloys thereof, may also be used.

[0060] In the above embodiment, the ceramic heater 100 includes the shaft 130, but the present invention is not limited to this configuration, and the ceramic heater 100 does not necessarily have to include the shaft 130. Furthermore, even if the ceramic heater 130 includes the shaft 130, the fifth gas flow path 165, sixth gas flow path 166, seventh gas flow path 167, and eighth gas flow path 168 extending in the vertical direction do not have to be formed in the cylindrical portion 131 of the shaft 130. For example, as shown in FIG. 9 , instead of the fifth gas flow path 165, sixth gas flow path 166, seventh gas flow path 167, and eighth gas flow path 168 provided in the cylindrical portion 131 of the shaft 130, it is also possible to provide separate gas piping in the hollow region inside the inner surface of the cylindrical portion 131 (the region where the power supply line 140 is provided) to form the fifth gas flow path 165A, sixth gas flow path 166A, seventh gas flow path 167A, and eighth gas flow path 168A. The upper end of the fifth gas flow path 165A is connected to the lower end of the first gas flow path 161, the upper end of the sixth gas flow path 166A is connected to the lower end of the second gas flow path 162, the upper end of the seventh gas flow path 167A is connected to the lower end of the third gas flow path 163, and the upper end of the eighth gas flow path 168A is connected to the lower end of the fourth gas flow path 164.

[0061] Although the present invention has been described above using embodiments and modifications thereof, the technical scope of the present invention is not limited to the scope of the above description. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0062] The order of execution of each process in the manufacturing method shown in the specification and drawings is not particularly specified, and the processes may be executed in any order unless the output of a previous process is used in a subsequent process. For convenience, even if a description is made using "first," "next," etc., it does not mean that the processes must be executed in this order. [Explanation of symbols]

[0063] 100 Ceramic heater 110 Ceramic substrate 120 electrodes 130 shaft 140 Feed line 151 Outermost circular convex part 152~154 Annular convex part 155 Multiple protrusions 161 First gas flow path 162 Second gas flow path 163 Third gas flow path 164 4th gas flow path 165, 165A 5th gas flow path 166, 166A 6th gas flow path 167, 167A 7th gas flow path 168, 168A 8th gas flow path

Claims

1. a ceramic substrate having an upper surface and a lower surface facing the upper surface in the vertical direction; a heating element embedded in the ceramic substrate, The ceramic substrate is a plurality of annular protrusions arranged concentrically on the upper surface at positions overlapping the substrate in the up-down direction and each protruding upward from the upper surface; a plurality of convex portions disposed on the upper surface inside an outermost peripheral annular convex portion among the plurality of annular convex portions and protruding upward from the upper surface; a plurality of gas flow paths having openings on the upper surface between the plurality of annular protrusions and inside an innermost annular protrusion among the plurality of annular protrusions, the length of each of the plurality of annular protrusions from the top surface in the vertical direction, excluding the outermost annular protrusion, is smaller than the length of each of the plurality of protrusions from the top surface in the vertical direction, a ceramic heater, wherein the length of the outermost annular convex portion from the upper surface in the vertical direction is the same as the length of each of the plurality of convex portions from the upper surface in the vertical direction.

2. 2. The ceramic heater according to claim 1, wherein the length of the outermost annular protrusion from the top surface in the vertical direction is smaller than the length of each of the plurality of protrusions from the top surface in the vertical direction.

3. 3. The ceramic heater according to claim 1, wherein a difference between a length of the plurality of convex portions from the top surface in the vertical direction and a length of each of the plurality of annular convex portions excluding the outermost peripheral convex portion from the top surface in the vertical direction is 1 μm to 10 μm.

4. Further, a cylindrical shaft is joined to the lower surface of the ceramic base, the shaft includes a plurality of intra-shaft gas passages disposed between an inner surface of the shaft and an outer surface of the shaft; 4. The ceramic heater according to claim 1, wherein the plurality of gas flow paths are connected to the plurality of gas flow paths in the shaft, respectively.

5. Further, a cylindrical shaft is joined to the lower surface of the ceramic base, the shaft includes a plurality of gas lines disposed within an inner surface of the shaft; 4. The ceramic heater according to claim 1, wherein the plurality of gas flow paths are connected to the plurality of gas pipes, respectively.

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