Wafer supporting platform and RF rod

Abstract

A wafer supporting platform 20 is provided with: a ceramic substrate 21 which has a wafer placement surface 21a and in which an RF electrode 22 and a heater electrode 27 are embedded; a hole 21c provided from a surface of the ceramic substrate 21 on the opposite side to the wafer placement surface 21a toward the RF electrode 22; and an RF rod 30 which supplies high-frequency electric power to the RF electrode 22, and which has a tip 30a joined to 23 that is connected to the RF electrode 22 exposed on a bottom surface of the hole 21c. The RF rod 30 is a hybrid rod composed of a first rod member 32 and a second rod member 34. The first rod member 32 is made of Ni, and forms a region of the RF rod 30 from the tip 30a to a predetermined position 33. The second rod member 34 is a member provided with an oxidation-resistant film 34d around a core material 34c made of a non-magnetic material, and forms a region of the RF rod 30 from the predetermined position 33 to a base end 30b.

Description

Wafer support and RF rod

[0001] The present invention relates to a wafer support and an RF rod.

[0002] Conventionally, a ceramic wafer support table used when performing a film formation process on a wafer using plasma CVD or the like, which includes an RF rod connected to an RF electrode embedded in a ceramic base, has been known. For example, Patent Document 1 discloses a hybrid rod as an example of the RF rod. The hybrid rod is composed of a first rod member made of Ni that forms a region from the tip of the RF rod to a predetermined position, and a second rod member made of a non-magnetic material (e.g., tungsten) that forms a region from the predetermined position to the base end. This prevents the temperature directly above the RF rod from becoming excessively high.

[0003] Patent No. 7129587

[0004] However, in an oxidizing environment, the surface of the second rod member, which is made of a non-magnetic material, can oxidize. When the surface of the second rod member oxidizes, the oxidized portion peels off, gradually reducing the thickness of the second rod member and potentially causing damage.

[0005] The present invention has been made to solve these problems, and its main object is to prevent the temperature directly above the RF rod from becoming particularly high, and to prevent deterioration due to oxidation even in an oxidizing environment.

[0006] [1] A wafer support table of the present invention comprises: a ceramic base having a wafer mounting surface and in which an RF electrode and a heater electrode are embedded; a hole formed in the ceramic base from a surface opposite the wafer mounting surface toward the RF electrode; and an RF rod that supplies high-frequency power to the RF electrode and has a tip joined to the RF electrode, the tip of which is exposed at the bottom of the hole, or to a conductive member connected to the RF electrode, wherein the RF rod is a hybrid rod composed of a first rod member made of Ni that forms a region of the RF rod from the tip to a predetermined position located between the tip and a base end, and a second rod member joined to the first rod member and that forms a region of the RF rod from the predetermined position to the base end, and the second rod member is a member having an oxidation-resistant film provided around a non-magnetic core material.

[0007] In the wafer support table of the present invention, the second rod member is a member having an oxidation-resistant film formed around a non-magnetic core material. Therefore, even when high-frequency power is supplied to the RF electrode through the second rod member, the second rod member is less likely to generate heat and reach high temperatures than when the second rod member is made of Ni. Therefore, the entire RF rod is less likely to reach high temperatures, and heat dissipation from the ceramic substrate is not hindered. As a result, the temperature of the portion of the wafer directly above the rod connected to the RF electrode can be prevented from reaching a specific high temperature. Furthermore, because the oxidation-resistant film is formed around the second rod member, deterioration due to oxidation of the second rod member can be prevented, even in an oxidizing environment in which the non-magnetic core material oxidizes.

[0008] [2] In the wafer support table of the present invention (the wafer support table described in [1] above), the predetermined position may be determined such that T(x) is equal to or higher than the Curie temperature of Ni and equal to or lower than the oxidation temperature of the non-magnetic core material, where T(x) is expressed as T(x) = Ts - (ΔT / L) * x, where T(x) is equal to or higher than the Curie temperature of Ni and equal to or lower than the oxidation temperature of the non-magnetic core material, and x is the length of the Ni rod from the tip of the RF rod to the predetermined position. The region from the tip of the RF rod to the predetermined position, i.e., the first rod member, is made of Ni and is not magnetic above the Curie temperature, thereby suppressing an increase in impedance. The region from the predetermined position to the base end, i.e., the second rod member, is a member with an oxidation-resistant film provided around the non-magnetic core material, which can suppress an increase in impedance. Furthermore, since the temperature is below the oxidation temperature of the non-magnetic core material, oxidation of the second rod member can be prevented.

[0009] [3] In the wafer support table of the present invention (the wafer support table described in [1] or [2] above), the non-magnetic core material may be a tungsten core material, and the oxidation-resistant film may be a tungsten carbide film. This allows the second rod member to be manufactured relatively easily. That is, by applying a carburizing treatment or PVD or CVD to the periphery of the tungsten core material, the oxidation-resistant film of tungsten carbide can be formed relatively easily. Furthermore, because the hardness of tungsten carbide is greater than that of tungsten, the surface of the second rod member is less likely to be scratched even if the number of times the second rod member is inserted into and removed from an external socket increases.

[0010] [4] In the wafer support table of the present invention (the wafer support table described in [3] above), the thickness of the tungsten carbide film may be 0.1 μm or more and 5 μm or less. If the thickness of the tungsten carbide film is 0.1 μm or more, oxidation and damage to the tungsten core material can be sufficiently prevented. Furthermore, although the electrical resistivity of tungsten carbide is greater than that of tungsten, if the thickness of the tungsten carbide film is 5 μm or less, the tungsten carbide film does not significantly affect the conduction of electricity through the second rod member.

[0011] [5] The RF rod of the present invention is a hybrid rod composed of a first rod member made of Ni that forms a region from the tip to a predetermined position located between the tip and the base end, and a second rod member that is joined to the first rod member and forms a region from the predetermined position to the base end, wherein the second rod member is a member having an oxidation-resistant film provided around a non-magnetic core material.

[0012] This RF rod is highly significant when applied to the wafer support table of the present invention (the wafer support table described in any one of [1] to [4] above).

[0013] A perspective view of the plasma generator 10. An A-A cross-sectional view of Fig. 1. A cross-sectional view of the RF rod 30 cut along the longitudinal direction. A B-B cross-sectional view of Fig. 1. An explanatory diagram of a method for setting a predetermined position 33. An explanatory diagram of a method for setting a predetermined position 33. A cross-sectional view showing a state in which the conductive member 23 and the RF rod 30 are joined.

[0014] A preferred embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a perspective view of a plasma generator 10, Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1, Fig. 3 is a cross-sectional view of an RF rod 30 cut along the longitudinal direction, and Fig. 4 is a cross-sectional view taken along line B-B in Fig. 1.

[0015] As shown in FIG. 1, the plasma generating apparatus 10 includes a wafer support table 20 and an upper electrode 50 .

[0016] The wafer support 20 is used to support and heat a wafer W that is to undergo CVD, etching, or the like using plasma, and is attached inside a semiconductor process chamber (not shown). The wafer support 20 includes a ceramic base 21 and a hollow ceramic shaft 29.

[0017] The ceramic base 21 is a disk-shaped member made of ceramic (here, aluminum nitride). The ceramic base 21 has a wafer mounting surface 21a on which a wafer W can be mounted. A ceramic shaft 29 is bonded to the center of the surface (back surface) 21b of the ceramic base 21 opposite the wafer mounting surface 21a. As shown in FIG. 2, an RF electrode 22 and a heater electrode 27 are embedded in the ceramic base 21 while being spaced apart from each other. The RF electrode 22 and the heater electrode 27 are parallel to the wafer mounting surface 21a (including the case where they are substantially parallel, the same applies below) and are embedded in this order starting from the side closest to the wafer mounting surface 21a. The ceramic base 21 has a hole 21c extending from the back surface 21b toward the RF electrode 22. A conductive member 23 connected to the RF electrode 22 is exposed at the bottom of the hole 21c.

[0018] The RF electrode 22 is a disk-shaped thin-layer electrode slightly smaller in diameter than the ceramic base 21, and is formed from a mesh sheet made of thin metal wires whose main component is Mo. A disk-shaped conductive member 23 is electrically connected to the center of the RF electrode 22. The conductive member 23 is exposed at the bottom of a hole 21c formed in the back surface 21b of the ceramic base 21. The material of the conductive member 23 is Mo, the same as that of the RF electrode 22.

[0019] The heater electrode 27 is a coil made mainly of Mo that is wired in a single stroke across the entire surface of the ceramic substrate 21. Heater rods (not shown) are connected to both ends 27a, 27b (see FIG. 4) of the heater electrode 27. These heater rods are connected to an external power source (not shown) through the hollow interior of the ceramic shaft 29.

[0020] The reason why Mo is used as the material for the RF electrode 22, the conductive member 23, and the heater electrode 27 is that it has a thermal expansion coefficient close to that of the material (AlN in this case) of the ceramic base 21, and is therefore less likely to crack during the manufacture of the ceramic base 21. Materials other than Mo can also be used for the RF electrode 22, the conductive member 23, and the heater electrode 27 as long as they are conductive materials with a thermal expansion coefficient close to that of AlN. A thermocouple (not shown) for detecting the temperature of the ceramic base 21 is inserted into a region of the back surface 21b of the ceramic base 21 surrounded by the ceramic shaft 29.

[0021] The ceramic shaft 29 is a cylindrical member made of the same ceramic as the ceramic base 21. The upper end surface of the ceramic shaft 29 is joined to the back surface 21b of the ceramic base 21 by diffusion bonding or thermal compression bonding (TCB). TCB is a known method in which a metal joining material is sandwiched between two members to be joined, and the two members are pressure-joined while being heated to a temperature below the solidus temperature of the metal joining material.

[0022] The RF rod 30 is a cylindrical hybrid rod composed of a first rod member 32 that defines a region of the RF rod 30 from the tip 30a to a predetermined position 33 located between the tip 30a and the base end 30b, and a second rod member 34 that is joined to the first rod member 32 and defines a region of the RF rod 30 from the predetermined position 33 to the base end 30b. A method for setting the predetermined position 33 will be described later. The first rod member 32 is a rod-shaped member made of Ni. The second rod member 34 is a member having an oxidation-resistant film 34d provided around a core material 34c made of a non-magnetic material with an impedance lower than that of Ni. The oxidation-resistant film 34d is not provided on the joint surface 34a of the second rod member 34, but is provided on the base end 34b (the same as the base end 30b of the RF rod 30). In this embodiment, the core material 34c is a rod-shaped member made of tungsten, and the oxidation-resistant film 34d is a tungsten carbide film. The tungsten carbide film can be formed by subjecting a rod-shaped member made of tungsten to carburizing or PVD. The electrical resistivity of tungsten is 5.28×10 -8 Ω m, and the electrical resistivity of tungsten carbide is 1.92 x 10-7 The Mohs hardness of tungsten is 7.5 on the Ω·m scale, and the Mohs hardness of tungsten carbide is 9. The joining surface 32b of the first rod member 32 and the joining surface 34a of the second rod member 34 may be welded or joined with a brazing material. For example, butt welding can be used as the welding, and for example, Ni brazing material can be used as the brazing material.

[0023] As shown in FIG. 2 , the tip 30a of the RF rod 30 (i.e., the tip 32a of the first rod member 32) is joined to the conductive member 23 of the RF electrode 22 via a brazing joint 24. The base end 30b of the RF rod 30 (i.e., the base end 34b of the second rod member 34) is connected to the RF power supply 40 via a socket 60 and a cable 64. High-frequency power from the RF power supply 40 is supplied to the RF electrode 22 via the cable 64, the socket 60, and the RF rod 30. The socket 60 is a conductive, bottomed, cylindrical body. A spring 62 is disposed in the cylindrical internal space 60a of the socket 60. The spring 62 is a cylindrical body with a tapered central portion. The diameters of the upper and lower parts of the spring 62 are the same as the diameter of the internal space of the socket 60, and the diameter of the central part of the spring 62 is smaller than the diameter of the internal space of the socket 60. A plurality of slits extending in the vertical direction are formed on the side of the spring 62. The diameter of the second rod member 34 of the RF rod 30 is smaller than the diameter of the upper part of the spring 62 and larger than the diameter of the central part of the spring 62. Therefore, when the second rod member 34 is inserted into the spring 62, the side surface of the spring 62 is elastically deformed and comes into strong contact with the second rod member 34.

[0024] 1, the upper electrode 50 is fixed to a position above (for example, the ceiling surface of a chamber not shown) that faces the wafer mounting surface 21a of the ceramic base 21. The upper electrode 50 is connected to ground.

[0025] Here, the predetermined position 33 is determined as follows. That is, as shown in FIG. 5 , a Ni rod 42 is attached to the wafer support table 20 in place of the RF rod 30 (hybrid rod). The temperature of the heater electrode 27 is Ts [°C] (where Ts is a temperature exceeding the Curie temperature of Ni), the length of the Ni rod 42 is L [cm], the difference between the temperature Ta of the tip 42a of the Ni rod 42 and the temperature Tb of the base end 42b is ΔT (= Ta - Tb) [°C], the length from the tip 42a of the Ni rod 42 (the connection portion with the RF electrode 22) to the predetermined position 33 is x [cm], and the temperature of the Ni rod 42 at the predetermined position 33 is T(x) [°C]. Here, x [cm] is determined so that T(x) expressed by the following formula (1) is equal to or higher than 360°C, which is the Curie temperature of Ni, and equal to or lower than 400°C, which is the oxidation temperature of tungsten. Specifically, the length x [cm] from the tip 42a is determined so that the predetermined position 33 is located between a first position 42c where the temperature of the Ni rod 42 is the Curie temperature of Ni (360°C) and a second position 42o where the temperature of the Ni rod 42 is the oxidation temperature of tungsten (400°C), as shown in Figure 6. The temperature Ta of the tip 42a of the Ni rod 42 can be considered to be substantially the same as the temperature Ts of the heater electrode 27. T(x) = Ts - (ΔT / L) * x (1)

[0026] Next, an example of how the plasma generator 10 is used will be described. The plasma generator 10 is placed in a chamber (not shown), and a wafer W is placed on the wafer placement surface 21a. Then, a reactive gas is introduced into the chamber, and high-frequency power (e.g., 13 to 30 MHz) is supplied from an RF power supply 40 to the RF electrode 22. This generates plasma between parallel plate electrodes consisting of an upper electrode 50 and the RF electrode 22 embedded in the ceramic substrate 21. This plasma is used to perform CVD film deposition or etching on the wafer W. The temperature of the wafer W is determined based on a detection signal from a thermocouple (not shown), and the voltage applied to the heater electrode 27 is controlled so that the temperature reaches a set temperature (e.g., 450°C, 500°C, or 550°C). In the RF rod 30, the core 34c of the second rod member 34 is a tungsten core material, and the oxidation-resistant film 34d is a tungsten carbide film. Therefore, even if the temperature of the second rod member 34 rises due to heat conduction from the first rod member 32, the second rod member 34 is less likely to oxidize than, for example, when the second rod member 34 is made of Cu.

[0027] Furthermore, in the RF rod 30 of this embodiment, the portion in the temperature range above the Curie temperature of Ni is composed of the first rod member 32 made of Ni. Therefore, in such a temperature range, the first rod member 32 is non-magnetic, and therefore, an increase in impedance can be suppressed. Furthermore, if the RF rod 30 were entirely made of tungsten, an increase in impedance could be suppressed, but oxidation would occur at temperatures above 400°C. In contrast, in the RF rod 30 of this embodiment, the portion in the temperature range below the oxidation temperature of tungsten is composed of the second rod member 34 having a core material 34c made of a non-magnetic material. In such a temperature range, the core material 34c of the second rod member 34 does not oxidize, and therefore oxidation of the second rod member 34 can be suppressed. Furthermore, even in an oxidizing environment in which the core material 34c is oxidized, the second rod member 34 has an oxidation-resistant film 34d around the core material 34c, and therefore oxidation of the second rod member 34 can be suppressed.

[0028] Next, a manufacturing example of the wafer support table 20 will be described. First, a ceramic compact is produced by mold casting, in which a conductive member 23 and a heater electrode 27 are embedded, one side of which is in contact with the RF electrode 22. Here, the "mold casting" refers to a method of obtaining a compact by injecting a ceramic slurry containing a ceramic raw material powder and a molding agent into a mold and then chemically reacting the molding agent in the mold to mold the ceramic slurry. Next, the ceramic compact is hot-press fired to obtain a ceramic base 21. Next, a grinding process is performed to form a hole 21c in the back surface 21b of the ceramic base 21 so that the surface of the conductive member 23 opposite the surface in contact with the RF electrode 22 is exposed. A hole 21c is also formed in the back surface 21b of the ceramic base 21, a hole for inserting a heater rod connected to the heater electrode 27 is formed, and a hole for inserting a thermocouple is also formed. Next, a ceramic shaft 29 is joined to the back surface 21b of the ceramic base 21 by TCB so as to be coaxial with the ceramic base 21. Next, the conductive member 23 and the RF rod 30 are brazed. Then, the heater electrode 27 is joined to the heater rod, and a thermocouple is attached to the heater rod, thereby obtaining the wafer support table 20 .

[0029] In the wafer support table 20 described above, the core material 34c of the second rod member 34 is made of tungsten, and therefore, even when high-frequency power is supplied, the second rod member 34 is less likely to generate heat and reach a high temperature than if the second rod member 34 were made of Ni. Therefore, the entire RF rod 30 is less likely to reach a high temperature, and heat dissipation from the ceramic base 21 is not hindered. As a result, the temperature of the portion of the wafer W directly above the RF rod 30 connected to the RF electrode 22 can be prevented from reaching a specific high temperature. Furthermore, the second rod member 34 is a member having a tungsten carbide oxidation-resistant film 34d provided around the tungsten core material 34c, and therefore, deterioration due to oxidation can be prevented even in an oxidizing environment (e.g., an environment exceeding the oxidation temperature of tungsten).

[0030] Furthermore, the predetermined position 33 uses a Ni rod 42 instead of the RF rod 30 (hybrid rod), and is determined such that T(x) (expressed as T(x) = Ts - (ΔT / L) * x) is equal to or higher than the Curie temperature of Ni and equal to or lower than the oxidation temperature of a non-magnetic material (tungsten in this case), where T(x) is equal to or higher than the Curie temperature of Ni and is equal to or lower than the oxidation temperature of a non-magnetic material (tungsten in this case), where T(x) is equal to or higher than the Curie temperature, and x is equal to or lower than the Curie temperature. The region from the tip 30a of the RF rod 30 to the predetermined position 33, i.e., the first rod member 32, is made of Ni and is not magnetic above the Curie temperature, thereby suppressing an increase in impedance. The region from the predetermined position 33 to the base end 30b, i.e., the second rod member 34, is a member in which a tungsten carbide film, which is an oxidation-resistant film 34d, is provided around a tungsten core material, which is a core material 34c, and therefore an increase in impedance can be suppressed. Furthermore, because the temperature is below the oxidation temperature of tungsten, oxidation of the second rod member 34 can be prevented. Note that the length x [cm] from the tip 42a of the Ni rod 42 to the predetermined position 33 is 2 [cm] or more and 25 [cm] or less, regardless of the length L [cm] of the Ni rod 42.

[0031] Furthermore, the core material 34c is a tungsten core material, and the oxidation-resistant film 34d is a tungsten carbide film. Therefore, the second rod member 34 can be manufactured relatively easily. That is, the oxidation-resistant film of tungsten carbide can be formed relatively easily by performing a carburizing treatment or PVD or CVD on the periphery of the tungsten core material. Furthermore, because the hardness of tungsten carbide is greater than that of tungsten, the surface of the second rod member 34 is less likely to be scratched even if the number of times the second rod member 34 is inserted into and removed from the socket 60 increases.

[0032] Furthermore, the thickness of the tungsten carbide film, which is the oxidation-resistant film 34d, is preferably 0.1 μm or more and 5 μm or less. If the thickness of the tungsten carbide film is 0.1 μm or more, oxidation and damage to the tungsten core material, which is the core material 34c, can be sufficiently prevented. Although the electrical resistivity of tungsten carbide is greater than that of tungsten, if the thickness of the tungsten carbide film is 5 μm or less, the tungsten carbide film does not significantly affect the conduction of electricity through the second rod member 34. If the thickness of the tungsten carbide film exceeds 5 μm, there is a risk that the tungsten carbide film will generate heat when the RF power is increased.

[0033] The RF rod 30 is highly advantageous when applied to the wafer support table 20 .

[0034] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

[0035] In the above-described embodiment, the tip 32a of the first rod member 32 of the RF rod 30 is joined to the conductive member 23 exposed on the bottom surface of the hole 21c, but this is not particularly limited. For example, the RF electrode 22 may be exposed on the bottom surface of the hole 21c without providing the conductive member 23, and the exposed RF electrode 22 may be joined to the tip 30a of the RF rod 30 (the tip 32a of the first rod member 32). Alternatively, as shown in FIG. 7 , the conductive member 23 and the RF rod 30 may be connected via a low thermal expansion member 507. The low thermal expansion member 507 has a thermal expansion coefficient of at least 8.0×10 at 400° C. or less. -1 / °C or less, and examples of suitable materials include molybdenum, tungsten, molybdenum-tungsten alloy, tungsten-copper-nickel alloy, and Kovar. In this case, the hole 21c is formed wider than the width of the tip 32a, and a cylindrical atmosphere protector 509 is inserted into the hole 21c. Materials suitable for the atmosphere protector 509 include pure nickel, nickel-based heat-resistant alloy, gold, platinum, silver, and alloys thereof. A small gap is provided between the outer surface of the atmosphere protector 509 and the inner surface of the hole 21c. A low-thermal expansion member 507 is accommodated within the interior space of the atmosphere protector 509. The low-thermal expansion member 507 and the bottom surface of the hole 21c, and the low-thermal expansion member 507 and the conductive member 23, are bonded together by conductive bonding layers 506 and 508, respectively, and the atmosphere protector 509 and the bottom surface of the hole 21c are bonded together by conductive bonding layer 506. The conductive bonding layers 506 and 508 may be Au--Ni brazing bonding layers, in which case the conductive member 23 may be made of Ni, Mo, W, or a Mo--W alloy.

[0036] In the above-described embodiment, the RF electrode 22 has a mesh shape, but it may have other shapes. For example, it may be coil-shaped or flat, or may be made of punched metal.

[0037] In the above-described embodiment, AlN is used as the ceramic material, but this is not a limitation. For example, alumina may be used. In this case, it is preferable to use materials for the RF electrode 22, the conductive member 23, and the heater electrode 27 that have a thermal expansion coefficient close to that of the ceramic.

[0038] In the above-described embodiment, the wafer W may be attracted to the wafer mounting surface 21 a by applying a DC voltage to the RF electrode 22. Alternatively, an electrostatic electrode may be further embedded in the ceramic base 21, and the wafer W may be attracted to the wafer mounting surface 21 a by applying a DC voltage to the electrostatic electrode.

[0039] In the above-described embodiment, the core material 34c is made of tungsten and the oxidation-resistant film 34d is made of tungsten carbide, but this is not limiting. For example, in the above-described embodiment, the core material 34c may be made of molybdenum and the oxidation-resistant film 34d may be made of molybdenum carbide.

[0040] The present invention can be used when performing a film formation process by plasma CVD, a plasma etching process, or the like on a wafer.

[0041] 10 plasma generating device, 20 wafer support table, 21 ceramic base, 21a wafer mounting surface, 21b back surface, 21c hole, 22 RF electrode, 23 conductive member, 24 joint portion, 27 heater electrode, 27a, 27b end portion, 29 ceramic shaft, 30 RF rod, 30a tip, 30b base end, 32 first rod member, 32a tip, 32b joint surface, 33 predetermined position, 34 second rod member, 34a joint surface, 34b base end, 34c core material, 34d oxidation resistant film, 40 RF power supply, 42 Ni rod, 42a tip, 42b base end, 42c first position, 42o second position, 50 upper electrode, 60 socket, 60a internal space, 62 spring, 64 cable, 506 conductive joint layer, 507 Low thermal expansion member, 508 conductive bonding layer, 509 atmosphere protection body.

Claims

1. A wafer support comprising: a ceramic base having a wafer mounting surface and in which an RF electrode and a heater electrode are embedded; a hole provided in the ceramic base from the surface opposite the wafer mounting surface toward the RF electrode; and an RF rod that supplies high frequency power to the RF electrode and is joined to the RF electrode with a tip exposed at the bottom of the hole or to a conductive member connected to the RF electrode, wherein the RF rod is a hybrid rod composed of a first rod member made of Ni that forms a region of the RF rod from the tip to a predetermined position located between the tip and the base end, and a second rod member joined to the first rod member and that forms a region of the RF rod from the predetermined position to the base end, and the second rod member is a member having an oxidation-resistant film provided around a non-magnetic core material.

2. The wafer support table according to claim 1, wherein the predetermined position is determined such that T(x), expressed by T(x) = Ts - (ΔT / L) * x, is equal to or higher than the Curie temperature of Ni and equal to or lower than the oxidation temperature of the non-magnetic core material, when a Ni rod is used instead of the hybrid rod, the temperature of the heater electrode is Ts [°C] (where Ts is greater than the Curie temperature of Ni), the length of the Ni rod is L [cm], the temperature difference between both ends of the Ni rod is ΔT [°C], the length from the tip of the Ni rod to the predetermined position is x [cm], and the temperature of the Ni rod at the position is T(x) [°C].

3. The wafer support table according to claim 1 or 2, wherein the non-magnetic core material is a tungsten core material, and the oxidation-resistant film is a tungsten carbide film.

4. The wafer support table according to claim 3, wherein the thickness of said tungsten carbide film is 0.1 μm or more and 5 μm or less.

5. An RF rod which is a hybrid rod comprising a first rod member made of Ni which defines a region from the tip to a predetermined position located between the tip and the base end, and a second rod member which is joined to the first rod member and defines a region from the predetermined position to the base end, wherein the second rod member is a member having an oxidation-resistant film provided around a non-magnetic core material.

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