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 an annular first protrusion 152 arranged on the outer periphery of the top surface 111, and a plurality of protrusions 156 arranged inside a second protrusion 154. The first protrusion 152 is arranged in a position overlapping with a wafer 10 in a vertical direction 5. At the inside of the ceramic substrate 110, there are formed a first gas passage 162 and a second gas passage 164 that has a plurality of openings 164a that opens inside the first protrusion 152. The first gas passage 162 and the second gas passage 164 are gas passages independent of each other.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 first annular protrusion disposed on the outer periphery of the upper surface at a position overlapping with the substrate in the up-down direction and protruding upward from the upper surface; a plurality of protrusions disposed inside the first protrusion on the upper surface and protruding upward from the upper surface; a first gas flow path having an opening on the upper surface inside the first protrusion; a second gas flow path having a plurality of openings distributed in an annular shape on the upper surface, the second gas flow path being located outside the opening of the first gas flow path and inside the first protrusion; a second annular protrusion disposed on the upper surface, the second protrusion being located outside the opening of the first gas flow path and inside the plurality of openings of the second gas flow path, and protruding upward from the upper surface; Equipped with The first gas flow path and the second gas flow path are independent of each other. And, a length L1 of the first protrusion from the top surface in the vertical direction is smaller than a length L2 of the plurality of protrusions from the top surface in the vertical direction; The length L3 of the second protrusion from the top surface in the vertical direction is smaller than the length L2 of the plurality of protrusions 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 first gas flow path and the second gas flow path are independent from each other, and therefore can be used for different purposes. For example, the first gas flow path can be used as an exhaust flow path for exhausting gas, and the second gas flow path can be used as a gas flow path for supplying a gas such as a heat transfer gas. By adjusting the flow rate or pressure of the gas such as a heat transfer gas supplied from the second gas flow path, the pressure in the gap surrounded by the first protrusions and the substrate can be set lower than the pressure (external environment) outside the first protrusions. In this case, the substrate can be attracted toward the upper surface of the ceramic substrate due to the pressure difference. This improves adhesion between the substrate and the upper surfaces of the multiple protrusions, thereby efficiently transferring heat from the ceramic heater to the substrate. However, if the pressure in the gap surrounded by the first protrusions and the substrate is lower than the pressure outside the first protrusions, the pressure difference will cause gas outside the first protrusions to enter the gap surrounded by the first protrusions and the substrate. The ceramic heater is provided with a first gas flow path with multiple openings located inside the first protrusions, which can be used as an exhaust flow path. Therefore, gas that has entered the gap surrounded by the first protrusion and the substrate can be exhausted via the first gas flow path, which makes it possible to suppress temperature fluctuations of the wafer 10 caused by gas mixing in from the outside in the region inside the first protrusion 152, and furthermore, when the external environment contains a corrosive gas, it is possible to suppress particle generation due to corrosion of the region inside the first protrusion of the ceramic heater caused by gas mixing in. [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 protrusions 154 is smaller than the height L1 of the first protrusions 152 and the height L2 of the plurality of protrusions 156. In FIG. [Figure 5] FIG. 5 is a schematic explanatory diagram of a ceramic heater 100 in which the height L1 of the first protrusion 152 and the height L3 of the second protrusion 154 are smaller than the height L2 of the plurality of protrusions 156. In FIG. [Figure 6] 6(a) to 6(e) are diagrams showing the flow of a method for manufacturing the ceramic base 110. [Figure 7] 7(a) to 7(d) are diagrams showing the flow of another method for manufacturing the ceramic base 110. In FIG. [Figure 8] FIG. 8 is a view equivalent to FIG. 2 of a ceramic heater 100A of a comparative example. [Figure 9] FIG. 9 is a table summarizing the results of Examples 1 to 5 and the Comparative Example. 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-shaped 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, an annular first protrusion 152 and a plurality of protrusions 156 are provided on the upper surface 111 of the ceramic substrate 110. Note that in FIG. 1, the number of the plurality of protrusions 156 is reduced compared to FIG. 2 for ease of viewing. Also, as shown in FIG. 2, a first gas flow path 162 and a second 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 such as aluminum nitride, alumina, or silicon nitride.

[0012] As shown in FIGS. 1 and 2, the annular first protrusion 152 (hereinafter simply referred to as the first protrusion 152) is an annular protrusion arranged on the outer periphery (outer edge) of the upper surface 111 of the ceramic base 110, and protrudes upward from the upper surface 111. As shown in FIG. 2, when the wafer 10 is placed on the ceramic base 110, the upper surface 152a of the first protrusion 152 abuts against the lower surface of the wafer 10. In other words, the first protrusion 152 is arranged at a position that overlaps with the wafer 10 in the up-down direction when the wafer 10 is placed on the ceramic base 110. A plurality of protrusions 156 are provided inside the first protrusion 152. Each of the plurality of protrusions 156 has a cylindrical shape. One of the plurality of protrusions 156 is arranged approximately at the center of the upper surface 111. The remaining protrusions 156 are arranged on the circumference of three equally spaced concentric circles. The convex portions 156 are arranged at equal intervals on the circumference of each concentric circle. The arrangement positions and number of the convex portions 156 are appropriately determined depending on the application, action, and function.

[0013] The height L1 of the first protrusion 152 (the length in the vertical direction from the upper surface 111) and the height L2 of the plurality of protrusions 156 can both be set in the range of 5 μm to 2 mm.

[0014] The width of the first protrusions 152 is desirably constant and can be set to 0.1 mm to 10 mm. The surface roughness Ra of the upper surfaces 152a of the first protrusions 152 can be set to 0.4 μm or less. The surface roughness Ra of the upper surfaces 152a of the first protrusions 152 is preferably 0.2 μm or less, and more preferably 0.1 μm or less.

[0015] The upper surfaces 156a of the plurality of protrusions 156 are preferably circular with a diameter of 1 mm to 5 mm. The distance between each of the plurality of protrusions 156 can be set within a range of 1.5 mm to 30 mm.

[0016] 2, a plurality of openings 162a (eight in this embodiment) of the first gas flow path 162 are formed in the inner region between the first convex portions 152 of the upper surface 111. The plurality of openings 162a are arranged adjacent to the inner side of the first convex portions 162. In other words, the plurality of openings 162a are arranged in an annular shape along the inner circumference of the first convex portion 152. The plurality of openings 162a are arranged outside all of the plurality of convex portions 152.

[0017] The first gas flow path 162 is a gas flow path including a plurality of openings 162a and is formed inside the ceramic base 110. As shown in FIG. 2, the first gas flow path 162 extends downward from each opening 162a and then extends horizontally toward the center of the ceramic base 110. The flow paths from each opening 162a merge via a merging path (not shown) and then extend further downward (see FIG. 2). As will be described later, the lower end of the first gas flow path 162 is joined to the upper end of a third gas flow path 166 formed inside the shaft 130.

[0018] As described above, on the upper surface 111, the plurality of protrusions 156 are arranged on the circumference of three concentric circles. As shown in FIG. 2, an opening 164a of a second gas flow path 164 is formed between the innermost concentric circle on which the plurality of protrusions 156 are arranged and the second innermost concentric circle on the upper surface 111. The second gas flow path 164 is a gas flow path having the opening 164a, and is formed inside the ceramic base 110. The second gas flow path 164 extends downward from the opening 164a. As described below, the lower end of the second gas flow path 164 is joined to the upper end of a fourth gas flow path 168 formed inside the shaft 130.

[0019] The first gas flow path 162 and the second gas flow path 164 are flow paths for supplying or discharging a heat transfer gas for heat transfer between the wafer 10 and the ceramic base 110 to or from a space (gap) defined by the upper surface 111 of the ceramic base 110 and the lower surface of the wafer 10. Examples of the heat transfer gas that can be used include an inert gas such as helium, argon, or a mixture of helium and argon, or nitrogen gas. The heat transfer gas is supplied through the first gas flow path 162 and the second gas flow path 164 at a pressure set within a 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 wire 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 perspective of increasing the resistance of the electrode 120 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 may be provided on the upper surface of the cylindrical portion 131.

[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, two gas flow paths (a third gas flow path 166 and a fourth 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 third gas flow path 166 is connected to the lower end of the first gas flow path 162, and the upper end of the fourth gas flow path 168 is connected to the lower end of the second 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. 6(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. 6(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. 6(c), granulated powder P is further poured into the bed-type mold 501 so as to cover the electrode 120, and is pressed and molded with a punch 502. Next, as shown in FIG. 6(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. 6(e), blind holes are drilled down to the electrode 120 to form the terminal 121. If a pellet is embedded, it is sufficient to drill blind holes down to the pellet. Furthermore, through holes are formed to become part of the first gas flow path 162 and the second gas flow path 164, and a groove is formed on the underside of the fired body to become part of the first gas flow path 162.

[0028] Next, although not shown, the steps shown in FIGS. 6(a) to 6(d) are repeated without embedding the electrode 120 to produce another sintered body. Through holes that will become part of the first gas flow path 162 and the second gas flow path 164 are formed in the other sintered body (see FIG. 6(e)). These two sintered bodies are then bonded by diffusion bonding in a stacked state. This makes it possible to produce a ceramic base 110 having the first gas flow path 162 and the second gas flow path 164 formed therein.

[0029] The ceramic base material 110 can also be manufactured by the following method. As shown in Fig. 7(a), a binder is added to aluminum nitride granulated powder P, which is then CIP molded and processed into a disk shape to produce an aluminum nitride compact 510. Next, as shown in Fig. 7(b), the compact 510 is degreased to remove the binder.

[0030] As shown in FIG. 7( 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. 7( 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 gas flow path 162 and the second gas flow path 164 are formed in the fired body, but through-holes and grooves constituting the first gas flow path 162 and the second gas flow path 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 156, annular first convex portions 152, and annular second convex portions 154 on the upper surface 111. Note that sandblasting is a suitable processing method for forming the plurality of convex portions 156, annular first convex portions 152, and annular second convex portions 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 aluminum nitride powder P containing several wt % of binder is molded under hydrostatic pressure (approximately 1 MPa) to form a green body 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 third gas flow path 166 and the fourth gas flow path 168 are formed in the green body. The green body is then fired in a nitrogen atmosphere. For example, the firing is performed at a temperature of 1900°C for two hours. After firing, 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 base 110 is preferably 0.4 μm or less, and more preferably 0.2 μm or less. Alternatively, the upper surface of the cylindrical portion 131 and the lower surface 113 of the ceramic base 110 can be bonded together 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 a thickness of 15 μm at the interface between the upper surface of the cylindrical portion 131 and the lower surface 113 of the ceramic base 110, and the bonding can be achieved by applying a force of 5 kPa in a direction perpendicular to the upper surface 111 (the longitudinal direction 6 of the shaft 130) and heating at a temperature of 1700°C for one hour. Alternatively, the upper surface of the cylindrical portion 131 and the lower surface 113 of the ceramic base 110 can be fixed together by screwing, brazing, or the like.

[0033] In the above description, the ceramic substrate 110 included the first convex portion 152. As another aspect, as shown in FIG. 4, the ceramic substrate 110A may include an annular second convex portion 154 (hereinafter simply referred to as the second convex portion 154) in addition to the first convex portion 152. The second convex portion 154 is an annular convex portion disposed inside the first convex portion 152 and outside the plurality of convex portions 156, and protrudes upward from the upper surface 111 similarly to the first convex portion 152. The first convex portion 152 and the second convex portion 154 are arranged concentrically. The plurality of openings 162a of the first gas flow path 162 are disposed in a region of the upper surface 111 between the first convex portion 152 and the second convex portion 154. In the ceramic substrate 110A shown in FIG. 4, the height L1 of the first convex portion 152 is the same as the height L2 of the plurality of convex portions 156 (L1 = L2), and the height L3 of the second convex portion 154 is lower than the height L1 of the first convex portion 152 (the height L2 of the plurality of convex portions 156) (L3 < L1, L3 < L2). Alternatively, as in the ceramic substrate 110B of the ceramic heater 100 shown in FIG. 5, the height L1 of the first convex portion 152 and the height L3 of the second convex portion 154 can be made the same (L1 = L3), and the height L1 of the first convex portion 152 and the height L3 of the second convex portion 154 can be made lower than the height L2 of the plurality of convex portions 156 (L1 < L2, L3 < L2).

[0034] In the ceramic substrates 110A and 110B, the surface roughness Ra of the upper surface 154a of the second convex portion 154 and the upper surfaces 156a of the plurality of convex portions 156 can be 1.6 μm or less. Note that the surface roughness Ra of the upper surface 154a of the second convex portion 154 and the upper surfaces 156a of the plurality of convex portions 156 is preferably 0.4 μm or less, and more preferably 0.2 μm or less.

Example

[0035] Hereinafter, the present invention will be further described using examples and comparative examples. However, the present invention is not limited to the examples and comparative examples described below.

[0036] [Example 1] As shown in FIG. 2, in the ceramic heater 100 of Example 1, the height L1 of the first protrusion 152 and the height L2 of the multiple protrusions 156 are all the same. Although not shown in FIG. 2, a molybdenum mesh (wire diameter 0.1 mm, mesh size #50, plain weave) was cut into the shape shown in FIG. 3 to form the electrode 120. A ceramic base 110 having a diameter of 310 mm and a thickness of 25 mm and having such an electrode 120 embedded therein was then fabricated. A first protrusion 152 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. Furthermore, a plurality of cylindrical protrusions 156 having a diameter of 2 mm and a height of 150 μm from the upper surface 111 were formed on the upper surface 111 of the ceramic base 110. The surface roughness Ra of each of the upper surface 152a of the first protrusion 152 and the upper surface 156a of the protrusion 156 was set to 0.4 μm.

[0037] The diameter of the opening 162a of the first gas flow path 162 is 3 mm. Eight openings 162a are arranged at equal intervals in a circular ring shape along the inner side of the first protrusion 152 on the upper surface 111 of the ceramic base 110. The center of each opening 162a is located 289 mm from the center of the ceramic base 110. The diameter of the opening 164a of the second gas flow path 164 is 3 mm. The center of the opening 164a is located 30 mm from the center of the ceramic base 110.

[0038] 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 164. An exhaust pump (not shown) was connected to the first gas flow path 162, 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 162. At this time, the pressure at the port of the exhaust pump was 133 Pa (1 Torr) or less.

[0039] 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 290 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 second 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 378.5° C., and the average value of the temperature distribution in the second temperature measurement was 378.6° C. The gas flow rate of the argon gas supplied to the second gas flow path 164 was 280 sccm.

[0040] [Example 2] As shown in FIG. 4 , the ceramic heater 100 of Example 2 includes a second protrusion 154 that is lower than the first protrusion 152 and the multiple protrusions 156. The ceramic heater 100 of Example 2 is similar to the ceramic heater 100 of Example 1, except for the second protrusion 154. The second protrusion 154 has an inner diameter of 280 mm, an outer diameter of 286 mm, a width of 3 mm, and a height L3 of 147 μm from the upper surface 111. The surface roughness Ra of the upper surface of the second protrusion 154 is 0.4 μm. In Example 2, argon gas and process gas were supplied at the same pressure as in Example 1. In Example 2, 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 164 was 13 sccm.

[0041] [Example 3] As shown in FIG. 5 , the ceramic heater 100 of Example 3 has second protrusions 154 that are the same height as the first protrusions 152 but lower than the multiple protrusions 156. The ceramic heater 100 of Example 3 is similar to the ceramic heater 100 of Example 2, except that the height L1 of the first protrusions 152 is 147 μm. In Example 3, argon gas and process gas were supplied at the same pressure as in Examples 1 and 2. In Example 3, 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 first gas flow path 162 was 51 sccm.

[0042] [Example 4] As shown in FIG. 5 , the ceramic heater 100 of Example 4 has second protrusions 154 that are the same height as the first protrusions 152 and lower than the multiple protrusions 156. The ceramic heater 100 of Example 4 is similar to the ceramic heater 100 of Example 3, except that the height L1 of the first protrusions 152 and the height L3 of the second protrusions 154 are both 140 μm. In Example 4, argon gas and process gas were supplied at the same pressures as in Examples 1 to 3. 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 first gas flow path 162 was 490 sccm.

[0043] [Example 5] As shown in FIG. 5 , the ceramic heater 100 of Example 5 has second protrusions 154 that are the same height as the first protrusions 152 and lower than the multiple protrusions 156. The ceramic heater 100 of Example 5 is similar to the ceramic heater 100 of Example 4, except that the height L1 of the first protrusions 152 and the height L3 of the second protrusions 154 are both 135 μm. In Example 5, argon gas and process gas were supplied at the same pressure as in Examples 1 to 4. In Example 5, 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 376.1°C. The flow rate of argon gas supplied to the second gas flow path 164 was greater than 1000 sccm.

[0044] [Comparative Example] As shown in FIG. 8, the ceramic heater 100A of the comparative example is similar to the ceramic heater 100 of Example 1, except that the ceramic substrate 110 does not have a first gas flow path 162. 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 second 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. Furthermore, the gas flow rate of the argon gas supplied to the second gas flow path 164 was less than 0.2 sccm.

[0045] <Summary of Examples and Comparative Examples> FIG. 9 shows a table summarizing the results of the above-mentioned Examples 1 to 5 and Comparative Example.

[0046] As shown in FIGS. 2, 4, and 5, the ceramic heater 100 of Examples 1 to 5 includes a first protrusion 152, a first gas flow path 162 having a plurality of openings 162a arranged along the inner periphery of the first protrusion 152, and a second gas flow path 164 having an opening 164a that opens to the inside of the plurality of openings 162a. The first gas flow path 162 and the second gas flow path 164 are independent of each other. As in Examples 1 to 5, a heat transfer gas (e.g., argon gas) can be supplied through the second gas flow path 164 to the gap surrounded by the first protrusion 152 and the second protrusion wafer 10. Furthermore, the pressure of the heat transfer gas is set lower than the pressure of the process gas in the process chamber (6650 Pa in Examples 1 to 5), 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 156a of the multiple protrusions 156, allowing heat from the ceramic heater 100 to be transferred to the wafer 10 efficiently. However, at the same time, a portion of the process gas in the process chamber enters the gap between the first protrusions 152 and the wafer 10 due to the pressure difference. The ceramic heater 100 is provided with a first gas flow path 162 having multiple openings 162a arranged along the inner circumference of the first protrusions 152, so that the process gas that has entered the gap between the first protrusions 152 and the wafer 10 can be exhausted via the first gas flow path 162. This prevents fluctuations in the temperature of the wafer 10 due to fluctuations in the heat transfer coefficient of the heat transfer gas caused by the process gas being mixed into the heat transfer gas in the area surrounded by the first protrusions 152 and the wafer 10.

[0047] In contrast, as shown in FIG. 8 , the ceramic heater 100A of the comparative example does not have a first gas flow path 162. Therefore, if the pressure in the gap surrounded by the first protrusions 152 and the wafer 10 is set lower than the process gas pressure in the process chamber in order to attract the wafer 10 toward the upper surface 111 of the ceramic substrate 110, the process gas easily enters the gap surrounded by the first protrusions 152 and the wafer 10 due to the pressure difference. This is thought to have caused the process gas to mix with the heat transfer gas in the region inside the first protrusions 152, resulting in a change in the heat transfer coefficient of the heat transfer gas and a change in the temperature of the wafer 10. Note that in the comparative example, the heat transfer coefficient is increased due to the mixing of helium gas contained in the process gas with the heat transfer gas (argon gas), which is thought to have caused the temperature of the wafer 10 to be higher than in Examples 1 to 5.

[0048] Comparing Example 1 and Example 2, in Example 2, by providing the second convex portion 154, it is possible to suppress the heat transfer gas supplied through the second gas flow path 164 from flowing from the inside of the second convex portion 154 toward the multiple openings 162a. This suppresses the gas flow rate through the second gas flow path 164. Furthermore, by providing the second convex portion 154, a pressure difference occurs between the inside and outside of the second convex portion, so that the process gas that has entered from the outside of the first convex portion 152 is suppressed from entering the region inside the second convex portion 154. This suppresses changes in the composition and pressure of the heat transfer gas in the region inside the second convex portion 154, and suppresses temperature changes of the wafer 10.

[0049] Comparing Example 2 and Example 3, it was found that by making the height L1 of the first protrusion 152 and the height L3 of the second protrusion 154 3 μm lower than the height L2 of the multiple protrusions 156, the gas flow rate in the second 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 first protrusion 152 and the height L3 of the second protrusion 154 were 3 μm lower than the height L2 of the multiple protrusions 156, the temperature change of the wafer 10 could be sufficiently suppressed. Furthermore, because the height L1 of the first protrusion 152 and the height L3 of the second protrusion 154 were lower than the height L2 of the multiple protrusions 156, the lower surface of the wafer 10 did not come into contact with the upper surface 152 a of the first protrusion 152 and the upper surface 154 a of the second protrusion 154. This makes it possible to prevent localized heat spots from occurring due to contact between the wafer 10 and the upper surface 152a of the first protrusion 152 and between the wafer 10 and the upper surface 154a of the second protrusion 154. Furthermore, contact between the wafer 10 and the upper surface 152a of the first protrusion 152 and between the wafer 10 and the upper surface 154a of the second protrusion 154 makes it possible to prevent particles generated from the upper surface 152a of the first protrusion 152 and the upper surface 154a of the second protrusion 154 from adhering to the wafer 10.

[0050] Comparing Example 3 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 first protrusion 152 and the height L3 of the second protrusion 154 10 μm lower than the height L2 of the multiple protrusions 156. However, it was found that even when the height L1 of the first protrusion 152 and the height L3 of the second protrusion 154 are 10 μm lower than the height L2 of the multiple protrusions 156, the temperature change of the wafer 10 can be sufficiently suppressed.

[0051] Comparing Examples 3 and 4 with Example 5, it was found that the gas flow rate in the second gas flow path 164 became excessive and the consumption of the heat transfer gas (argon gas) significantly increased when the height L1 of the first protrusion 152 and the height L3 of the second protrusion 154 were made 15 μm lower than the height L2 of the multiple protrusions 156. However, it was found that the temperature change of the wafer 10 could be sufficiently suppressed even when the height L1 of the first protrusion 152 and the height L3 of the second protrusion 154 were made 15 μm lower than the height L2 of the multiple protrusions 156.

[0052] <Effects of the embodiment> In the above-described embodiments and examples, the ceramic heater 100 includes a ceramic substrate 110 and a metal electrode 120 embedded in the ceramic substrate 110. The upper surface 111 of the ceramic substrate 110 is provided with a first annular protrusion 152 disposed on the outer periphery of the upper surface 111 and protruding upward from the upper surface 111, and a plurality of protrusions 156 disposed inside the first protrusion 152 and protruding upward from the upper surface 111. The first protrusion 152 is disposed at a position overlapping the wafer 10 in the vertical direction 5 when the wafer 10 is placed on the ceramic substrate 110. Furthermore, the ceramic substrate 110 is provided with a first gas flow path 162 having a plurality of openings 162a distributed annularly adjacent to the inside of the first protrusion 152, and a second gas flow path 164 having an opening 164a opening to the inside of the plurality of openings 162a distributed annularly. The first gas flow path 162 and the second gas flow path 164 are gas flow paths independent of each other.

[0053] The first gas flow path 162 and the second gas flow path 164 are independent of each other, and therefore can be used for different purposes. For example, the first gas flow path 162 can be used as an exhaust flow path for exhausting gas, and the second gas flow path 164 can be used as a gas flow path for supplying heat transfer gas. By adjusting the flow rate or pressure of the heat transfer gas supplied from the second gas flow path 164, the pressure in the gap surrounded by the first protrusion 152 and the wafer 10 can be set lower than the pressure outside the first protrusion 152 (external environment). At this time, the differential pressure between these two can attract the wafer 10 toward the upper surface 111 of the ceramic substrate 110. This improves adhesion between the wafer 10 and the upper surfaces 156a of the multiple protrusions 156, allowing heat from the ceramic heater 100 to be efficiently transferred to the wafer 10. However, if the pressure in the gap surrounded by the first protrusion 152 and the wafer 10 is made lower than the pressure outside the first protrusion 152, the pressure difference will cause gas outside the first protrusion 152 to infiltrate the gap surrounded by the first protrusion 152 and the wafer 10. The ceramic heater 100 is provided with a first gas flow path 162 having multiple openings 162a arranged along the inner periphery of the first protrusion 152, and the first gas flow path 162 is connected to an exhaust pump (not shown). Therefore, gas that has infiltrated into the gap surrounded by the first protrusion 152 and the wafer 10 can be exhausted via the first gas flow path 162. This makes it possible to suppress temperature fluctuations of the wafer 10 in the region inside the first protrusion 152 due to the infiltration of gas from outside.

[0054] In the above-described embodiments and examples, the height L1 of the first convex portion 152 can be made smaller than the height L2 of the plurality of convex portions 156 (L1 < L2). Even in this case, it is possible to suppress the gas outside the first convex portion 152 from entering the inside of the first convex portion 152, and to suppress the temperature change of the wafer 10. Further, since the height L1 of the first convex portion 152 is lower than the height L2 of the plurality of convex portions 156, the lower surface of the wafer 10 does not contact the upper surface 152a of the first convex portion 152. Thereby, it is possible to suppress the generation of local hot spots due to the contact between the wafer 10 and the upper surface 152a of the first convex portion 152. Further, it is possible to suppress the adhesion of particles generated from the upper surface 152a of the first convex portion 152 to the wafer 10 due to the contact between the wafer 10 and the upper surface 152a of the first convex portion 152. As described above, the height L1 of the first convex portion 152 and the height L2 of the plurality of convex portions 156 are both defined as the vertical length from the upper surface 111 of the ceramic base material 110.

[0055] In the above-described embodiments and examples, in addition to the first convex portion 152, a second convex portion 154 can be provided inside the first convex portion 152. The height L3 of the second convex portion 154 can be made smaller than the height L2 of the plurality of convex portions 156 (L3 < L2). By providing the second convex portion 154, it is possible to suppress the heat transfer gas supplied through the second gas flow path 164 from flowing from the inside of the second convex portion 154 toward the plurality of openings 162a. Thereby, the gas flow rate in the second gas flow path 164 can be suppressed. Further, by providing the second convex portion 154, it is possible to suppress the process gas that has entered from the outside of the first convex portion 152 due to the differential pressure from entering the region inside the second convex portion 154. Thereby, it is possible to suppress changes in the components of the heat transfer gas and changes in the pressure of the heat transfer gas in the region inside the second convex portion 154, and it is possible to suppress temperature changes in the wafer 10. Furthermore, the difference between the height L2 of the plurality of convex portions 156 and the height L3 of the second convex portion 154 can be made greater than 0 μm and 10 μm or less (0 μm < L2 - L3 ≦ 10 μm). In this case, while suppressing the gas flow rate in the second gas flow path 164 from becoming too large, it is possible to suppress the gas outside the first convex portion 152 from entering the inside of the second convex portion 154. Thereby, temperature changes in the wafer 10 can be suppressed.

[0056] In the above-described embodiments and examples, a third gas flow path 166 and a fourth gas flow path 168 extending in the vertical direction can be formed in the cylindrical portion 131 of the shaft 130. The upper end of the third gas flow path 166 is connected to the lower end of the first gas flow path 162, and the upper end of the fourth gas flow path 168 is connected to the lower end of the second gas flow path 164. Since two gas flow paths connected to the first gas flow path 162 and the second gas flow path 164 are formed in the cylindrical portion 131 of the shaft 130, gas can be easily exhausted from the first gas flow path 162 through these, and gas (for example, heat transfer gas) can be supplied to the second gas flow path 164.

[0057] <Modification> The above-described embodiments are merely illustrative and can be modified as appropriate. For example, the shapes and dimensions of the ceramic substrate 110 and the shaft 130 are not limited to those of the above-described embodiments and can be modified as appropriate. The dimensions, shapes, and the surface roughness Ra of the upper surface of the first convex portion 152 and the second convex portion 154 can be modified as appropriate.

[0058] For example, in the ceramic substrate 110B shown in FIG. 5, the height L1 of the first convex portion 152 and the height L3 of the second convex portion 154 were the same (L1 = L3). However, the present invention is not limited to such an aspect, and either one of the height L1 of the first convex portion 152 and the height L3 of the second convex portion 154 may be higher than the other. Further, in the ceramic substrate 110A shown in FIG. 4, the height L1 of the first convex portion 152 and the height L2 of the plurality of convex portions 156 were the same (L1 = L2), and the height L3 of the second convex portion 154 was lower than the height L1 of the first convex portion 152 and the height L2 of the plurality of convex portions 156 (L3 < L1, L3 < L2). However, the present invention is not limited to such an aspect, and the height L1 of the first convex portion 152, the height L2 of the plurality of convex portions 156, and the height L3 of the second convex portion 154 may all be the same (L1 = L2 = L3).

[0059] The height, the shape of the upper surface 156a, and the surface roughness Ra of the upper surface of the plurality of convex portions 156 can be modified as appropriate. For example, the shape of the upper surface 156a of the plurality of convex portions 156 does not necessarily have to be circular and can be any shape. In that case, it is preferable to have an area comparable to that of the circular upper surface 156 having a diameter of 1 mm to 5 mm. Further, in the above description, the plurality of convex portions 156 were arranged so as to be distributed concentrically, but the present invention is not limited to such an aspect. For example, the plurality of convex portions 156 may be arranged so as to be distributed at random positions. Even in that case, the separation distance between the respective convex portions of the plurality of convex portions 156 is preferably in the range of 1.5 mm to 30 mm.

[0060] 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.

[0061] In the above embodiment, the ceramic heater 100 includes a shaft 130, but the present invention is not limited to this embodiment, and the ceramic heater 100 does not necessarily have to include a shaft 130. Furthermore, even if the ceramic heater 130 includes a shaft 130, the third gas flow path 166 and the fourth 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, instead of the third gas flow path 166 and the fourth gas flow path 168, separate gas piping can be provided in the hollow region of the cylindrical portion 131 (the region where the power supply line 140 is provided).

[0062] 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.

[0063] 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]

[0064] 100 Ceramic heater 110 Ceramic substrate 120 electrodes 130 shaft 140 Feed line 152 First convex part 154 Second convex part 156 Multiple protrusions 162 First gas flow path 164 Second 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 first annular projection disposed on the outer periphery of the upper surface at a position overlapping with the substrate in the up-down direction and projecting upward from the upper surface; a plurality of protrusions disposed inside the first protrusion on the upper surface and protruding upward from the upper surface; a first gas flow path having an opening on the upper surface inside the first protrusion; a second gas flow path having a plurality of openings distributed in an annular pattern on the upper surface, the second gas flow path being located outside the opening of the first gas flow path and inside the first protrusion; a second annular protrusion disposed on the upper surface, the second protrusion being located outside the opening of the first gas flow path and inside the plurality of openings of the second gas flow path, and protruding upward from the upper surface; the first gas flow path and the second gas flow path are independent of each other, a length L1 of the first protrusion from the top surface in the vertical direction is smaller than a length L2 of the plurality of protrusions from the top surface in the vertical direction; a length L3 of the second protrusion from the upper surface in the vertical direction, the length L3 being smaller than a length L2 of each of the plurality of protrusions from the upper surface in the vertical direction.

2. The difference L2-L3 between the length L2 of the plurality of convex portions from the top surface in the vertical direction and the length L3 of the second convex portion from the top surface in the vertical direction is 0μm<L2-L3≦10μm 2. The ceramic heater according to claim 1, wherein the following relationship is satisfied:

3. Further, a cylindrical shaft is joined to the lower surface of the ceramic substrate, the shaft includes two gas passages disposed between an inner surface of the shaft and an outer surface of the shaft; 3. The ceramic heater according to claim 1, wherein one of the two gas flow paths is connected to the first gas flow path, and the other of the two gas flow paths is connected to the second gas flow path.

4. The first gas flow path is a gas flow path for supplying a heat transfer gas, 2. The ceramic heater according to claim 1, wherein the second gas flow path is an exhaust flow path for exhausting gas.

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