Wafer support table and RF rod

Abstract

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

Description

Technical Field This invention relates to a wafer support stage and an RF rod. Background Technology Conventionally, ceramic wafer supports are known for use in processes such as plasma CVD for wafer deposition. These supports include RF rods connected to RF electrodes embedded in a ceramic substrate. For example, Patent Document 1 discloses a hybrid rod as the RF rod. The hybrid rod consists of a first rod component made of Ni forming the region from the tip to a predetermined position of the RF rod, and a second rod component made of a non-magnetic material (e.g., tungsten) forming the region from the predetermined position to the base. This prevents the temperature of the portion directly above the RF rod from becoming excessively high. Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 7129587 Summary of the Invention However, in oxidizing environments, the surface of the second rod component in a non-magnetic system can sometimes oxidize. If the surface of the second rod component oxidizes, the oxidized portion will peel off, and the second rod component may gradually become thinner and break. The present invention was implemented to solve the above-mentioned problems. Its main purpose is to prevent the temperature of the part directly above the RF rod from becoming specifically high, and to prevent deterioration caused by oxidation even in an oxidizing environment.

[0001] The wafer support stage of the present invention includes: A ceramic substrate having a wafer mounting surface and embedded with RF electrodes and heater electrodes; A hole is provided from a surface in the ceramic substrate opposite to the wafer placement surface toward the RF electrode; and An RF rod that supplies high-frequency power to the RF electrode, and whose front end is engaged with the RF electrode exposed on the bottom surface of the hole or a conductive component connected to the RF electrode. The RF rod is a hybrid rod consisting of a first rod component made of Ni forming a region in the RF rod from the front end to a predetermined position between the front end and the base end, and a second rod component joined to the first rod component and forming a region in the RF rod from the predetermined position to the base end. The second rod component is a component with an oxide-resistant film disposed around a non-magnetic core material. In the wafer support stage of the present invention, the second rod component is a component with an oxide-resistant film surrounding the non-magnetic core material. Therefore, even when high-frequency power is supplied to the RF electrode via the second rod component, it is less likely to generate heat or reach high temperatures compared to the case where the second rod component is made of Ni. Thus, the entire RF rod is less likely to reach high temperatures, and heat dissipation from the ceramic substrate is not hindered. As a result, it is possible to prevent the temperature of the portion directly above the rod connected to the RF electrode in the wafer from becoming excessively high. Furthermore, since the second rod component has an oxide-resistant film formed around it, even in oxidizing environments such as oxidation of the non-magnetic core material, degradation caused by oxidation of the second rod component can be prevented.

[0002] In the wafer support stage of the present invention (the wafer support stage described above [1]), the specified position can be defined as follows: a Ni rod is used instead of the mixing rod, the temperature of the heater electrode is set to Ts [°C] (where Ts exceeds the Curie temperature of Ni), the length of the Ni rod is set to L [cm], the temperature difference between the two ends of the Ni rod is set to ΔT [°C], the length of the Ni rod from the front end to the specified position is set to x [cm], and the temperature at the position of the Ni rod is set to T(x) [°C]. T(x) expressed as T(x) = Ts - (ΔT / L) * x is above the Curie temperature of Ni and below the oxidation temperature of the non-magnetic core material. The region from the front end of the RF rod to the specified position, i.e., the first rod component, is made of Ni and is non-magnetic above the Curie temperature, thus suppressing impedance rise. The region from the specified position to the base end, i.e., the second rod component, is a component with an oxide-resistant film provided around the non-magnetic core material, thus suppressing impedance rise. In addition, since the temperature is below the oxidation temperature of the non-magnetic core material, oxidation of the second rod component can be prevented.

[0003] In the wafer support stage of the present invention (the wafer support stage described in [1] or [2] above), the non-magnetic core material can be a tungsten core material, and the oxide-resistant film can be a tungsten carbide film. Accordingly, the second rod component can be manufactured relatively easily. That is, by performing carburizing treatment or PVD or CVD around the tungsten core material, an oxide-resistant film of tungsten carbide can be formed relatively easily. In addition, tungsten carbide has a higher hardness than tungsten, so even if the number of insertions and removals of the second rod component relative to the external socket is increased, the surface of the second rod component is not easily damaged.

[0004] In the wafer support stage of the present invention (the wafer support stage described above [3]), the thickness of the tungsten carbide film can 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 effectively prevented. In addition, although the 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 will not have a significant impact on the energization of the second rod component.

[0005] The RF rod of the present invention is a hybrid rod consisting of a first rod component made of Ni forming a region from a front end to a predetermined position between the front end and the base end, and a second rod component joined to the first rod component and forming a region from the predetermined position to the base end. The second rod component is a component with an oxide-resistant film disposed around a non-magnetic core material. The application of this RF rod to the wafer support stage of the present invention (the wafer support stage described in any of [1] to [4] above) is of great significance. Attached Figure Description Figure 1 This is a three-dimensional view of the plasma generator 10. Figure 2 yes Figure 1 A-A cross-sectional view. Figure 3 This is a cross-sectional view of the RF rod 30 when it is cut along its length. Figure 4 yes Figure 1 B-B cross-sectional view. Figure 5 This is an explanatory diagram illustrating the method for setting position 33. Figure 6 This is an explanatory diagram illustrating the method for setting position 33. Figure 7 This is a cross-sectional view showing the engagement of the conductive component 23 and the RF rod 30. Detailed Implementation Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a perspective view of the plasma generator 10. Figure 2 yes Figure 1 A-A cross-sectional view, Figure 3 This is a cross-sectional view of the RF rod 30 when it is cut along its length. Figure 4 yes Figure 1 B-B cross-sectional view. like Figure 1 As shown, the plasma generator 10 includes a wafer support stage 20 and an upper electrode 50. The wafer support stage 20 is used to support and heat the wafer W to be subjected to CVD, etching, etc. using plasma, and is installed inside a semiconductor process chamber (not shown). The wafer support stage 20 includes a ceramic substrate 21 and a hollow ceramic shaft 29. The ceramic substrate 21 is a circular plate-shaped component made of ceramic (in this case, aluminum nitride). This ceramic substrate 21 has a wafer mounting surface 21a for mounting a wafer W. A ceramic shaft 29 is joined to the center of the side (back side) 21b of the ceramic substrate 21 opposite to the wafer mounting surface 21a. For example... Figure 2 As shown, an RF electrode 22 and a heater electrode 27 are separately implanted in the ceramic substrate 21. The RF electrode 22 and the heater electrode 27 are parallel to the wafer mounting surface 21a (including substantially parallel cases, the same applies below), and are implanted sequentially from the side closest to the wafer mounting surface 21a. The ceramic substrate 21 has a hole 21c provided from the back surface 21b toward the RF electrode 22. On the bottom surface of the hole 21c, a conductive component 23 connected to the RF electrode 22 is exposed. The RF electrode 22 is a disc-shaped thin-film electrode with a diameter slightly smaller than that of the ceramic substrate 21. It is formed by braiding fine metal wires, mainly composed of Mo, into a mesh and then forming it into a sheet. A disc-shaped conductive component 23 is electrically connected near the center of the RF electrode 22. The conductive component 23 is exposed on the bottom surface of the hole 21c provided on the back surface 21b of the ceramic substrate 21. The conductive component 23 is made of the same Mo material as the RF electrode 22. The heater electrode 27 is formed by wiring a Mo-based coil across the entire surface of the ceramic substrate 21 using a single-stroke technique. At the two ends 27a and 27b of the heater electrode 27 (see reference...) Figure 4 Each of these components is connected to a heater rod (not shown). These heater rods pass through the hollow interior of the ceramic shaft 29 and are connected to an external power source (not shown). The RF electrode 22, conductive component 23, and heater electrode 27 are made of Mo because their coefficient of thermal expansion is close to that of the ceramic substrate 21 (here, AlN), making it difficult to generate cracks during the manufacturing of the ceramic substrate 21. Regarding the RF electrode 22, conductive component 23, and heater electrode 27, even if the material is not Mo, a conductive material with a coefficient of thermal expansion close to AlN can be used. Furthermore, a thermocouple (not shown) for detecting the temperature of the ceramic substrate 21 is inserted in the area surrounded by the ceramic shaft 29 on the back surface 21b of the ceramic substrate 21. The ceramic shaft 29 is a cylindrical component made of the same ceramic as the ceramic substrate 21. The upper end face of the ceramic shaft 29 is joined to the back surface 21b of the ceramic substrate 21 using diffusion bonding or TCB (Thermal Compression Bonding). TCB refers to a known method of bonding two components by clamping a metal bonding material between them and pressing them together at a temperature below the solidus temperature of the metal bonding material. The RF rod 30 is a cylindrical hybrid rod consisting of a first rod member 32 forming a region from the front end 30a to a predetermined position 33 located between the front end 30a and the base end 30b, and a second rod member 34 joined to the first rod member 32 and forming a region from the predetermined position 33 to the base end 30b. The method for setting the predetermined position 33 will be described below. The first rod member 32 is a rod-shaped member made of Ni. The second rod member 34 is a member having an oxide-resistant film 34d disposed around a non-magnetic core material 34c with a impedance lower than Ni. The oxide-resistant film 34d is not disposed on the mating surface 34a of the second rod member 34, but is disposed 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 tungsten rod-shaped member, and the oxide-resistant film 34d is a tungsten carbide film. The tungsten carbide film can be formed by carburizing or PVD on the tungsten rod-shaped member. The resistivity of tungsten is 5.28 × 10⁻⁶. -8 The resistivity of tungsten carbide is 1.92 × 10⁻⁶ Ω·m. -7 The Mohs hardness of tungsten is 7.5 Ω·m, and that of tungsten carbide is 9 Ω·m. The mating surface 32b of the first rod component 32 and the mating surface 34a of the second rod component 34 can be welded or joined by brazing filler metal. For example, butt welding can be used as welding, and for brazing filler metal, Ni brazing filler metal can be used. like Figure 2As shown, the front end 30a of the RF rod 30 (i.e., the front end 32a of the first rod component 32) is joined to the conductive component 23 of the RF electrode 22 via the solder joint 24. The base end 30b of the RF rod 30 (i.e., the base end 34b of the second rod component 34) is connected to the RF power supply 40 via the socket 60 and the cable 64. The 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 narrowed central portion. The diameters of the upper and lower portions of the spring 62 are the same as the diameter of the internal space of the socket 60, while the diameter of the central portion of the spring 62 is smaller than the diameter of the internal space of the socket 60. Multiple slits extending in the vertical direction are provided on the side of the spring 62. The diameter of the second rod component 34 of the RF rod 30 is smaller than the diameter of the upper part of the spring 62, but larger than the diameter of the central part of the spring 62. Therefore, when the second rod component 34 is inserted into the spring 62, the side of the spring 62 undergoes elastic deformation and comes into strong contact with the second rod component 34. like Figure 1 As shown, the upper electrode 50 is fixed above the wafer placement surface 21a of the ceramic substrate 21 (e.g., the top surface of a chamber not shown). This upper electrode 50 is grounded. Here, position 33 is specified as follows. That is, as... Figure 5 As shown, a Ni rod 42 is installed in the wafer support stage 20 to replace the RF rod 30 (hybrid rod). The temperature of the heater electrode 27 is set to Ts [°C] (where Ts is a temperature exceeding the Curie temperature of Ni), the length of the Ni rod 42 is set to L [cm], the difference between the temperature Ta of the front end 42a and the temperature Tb of the base end 42b of the Ni rod 42 is set to ΔT (=Ta-Tb) [°C], the length of the Ni rod 42 from the front end 42a (the connection portion with the RF electrode 22) to the designated position 33 is set to x [cm], and the temperature at the designated position 33 of the Ni rod 42 is set to T(x) [°C]. Here, T(x) is defined as a temperature above the Curie temperature of Ni (360°C) and below the oxidation temperature of tungsten (400°C), as expressed by the following formula (1). Specifically, at the designated position 33, as shown... Figure 6 The length x [cm] between the first position 42c, where the temperature of the Ni rod 42 reaches the Curie temperature of Ni (360°C), and the second position 42o, where the temperature of the Ni rod 42 reaches the oxidation temperature of tungsten (400°C), is defined from the tip 42a. It should be noted that the temperature Ta of the tip 42a of the Ni rod 42 can be considered substantially the same as the temperature Ts of the heater electrode 27. T(x)=Ts-(ΔT / L)*x…(1) Next, an example of using the plasma generator 10 will be described. The plasma generator 10 is arranged in a chamber (not shown), and the 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., 13-30 MHz) is supplied to the RF electrode 22 from the RF power supply 40. This generates plasma between parallel plate electrodes formed by the upper electrode 50 and the RF electrode 22 embedded in the ceramic substrate 21. Using this plasma, CVD film deposition or etching is performed on the wafer W. Furthermore, based on the detection signal from a thermocouple (not shown), the temperature of the wafer W is determined, and the voltage applied to the heater electrode 27 is controlled to reach a set temperature (e.g., 450°C, 500°C, or 550°C). Regarding the RF rod 30, the core material 34c of the second rod member 34 is a tungsten core material, and the oxide-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, oxidation is less likely compared to the case where the second rod member 34 is made of Cu. Furthermore, in the RF rod 30 of this embodiment, the portion reaching the temperature range exceeding the Curie temperature of Ni is composed of a first rod member 32 made of Ni. Therefore, within this temperature range, since the first rod member 32 is non-magnetic, impedance rise can be suppressed. However, if the RF rod 30 is entirely made of tungsten, while impedance rise can be suppressed, oxidation will occur above 400°C. In contrast, in the RF rod 30 of this embodiment, the portion reaching the temperature range below the oxidation temperature of tungsten is composed of a second rod member 34 having a non-magnetic core material 34c. Within this temperature range, the core material 34c of the second rod member 34 will not oxidize, thus suppressing oxidation of the second rod member 34. Furthermore, even in an oxidizing environment where the core material 34c is oxidized, the second rod member 34 has an oxide-resistant film 34d around the core material 34c, thus suppressing oxidation of the second rod member 34. Next, a manufacturing example of the wafer support stage 20 will be described. First, a ceramic molded body with a conductive component 23 and a heater electrode 27 embedded therein, one side of which is in contact with the RF electrode 22, is fabricated using a die casting method. Here, "die casting method" refers to the following method: a ceramic slurry containing ceramic raw material powder and a curing agent is injected into a molding die, and the curing agent undergoes a chemical reaction within the molding die, thereby solidifying the ceramic slurry and obtaining the molded body. Next, the ceramic molded body is hot-pressed to obtain a ceramic substrate 21. Next, by grinding, a hole 21c is formed on the back surface 21b of the ceramic substrate 21, either to expose the side of the conductive component 23 opposite to the side in contact with the RF electrode 22, or to form a hole for inserting a heater rod connected to the heater electrode 27, or to form a hole for inserting a thermocouple. Next, a ceramic shaft 29 is TCB-jointed to the back surface 21b of the ceramic substrate 21 in a manner coaxial with the ceramic substrate 21. Next, the conductive component 23 and the RF rod 30 are soldered together. Then, the heater electrode 27 is joined to the heater rod, or a thermocouple is installed, thereby obtaining the wafer support stage 20. In the wafer support stage 20 described in detail above, the core material 34c of the second rod component 34 is made of tungsten. Therefore, even when high-frequency power is supplied, it is less prone to heating up and reaching high temperatures compared to the case where the second rod component 34 is made of Ni. Thus, the entire RF rod 30 is less likely to reach high temperatures, and heat dissipation from the ceramic substrate 21 is not hindered. As a result, the temperature of the portion of the RF rod 30 directly above the RF electrode 22 in the wafer W is prevented from becoming excessively high. Furthermore, the second rod component 34 is a component with a tungsten carbide oxide-resistant film 34d surrounding the tungsten core material 34c. Therefore, even in an oxidizing environment (e.g., an environment exceeding the oxidation temperature of tungsten), degradation caused by oxidation can be prevented. Furthermore, the specified position 33 is defined as follows: a Ni rod 42 is used instead of the RF rod 30 (hybrid rod); the temperature of the heater electrode 27 is set to Ts [°C] (where Ts exceeds the Curie temperature of Ni); the length of the Ni rod 42 is set to L [cm]; the temperature difference between the two ends of the Ni rod 42 is set to ΔT [°C]; the length of the Ni rod 42 from the front end 42a to the specified position 33 is set to x [cm]; and the temperature at the specified position 33 of the Ni rod 42 is set to T(x) [°C]. T(x), expressed as T(x) = Ts - (ΔT / L) * x, is above the Curie temperature of Ni and below the oxidation temperature of a non-magnetic material (here, tungsten). The region of the RF rod 30 from the front end 30a to the aforementioned specified position 33, i.e., the first rod component 32, is made of Ni and is non-magnetic above the Curie temperature; therefore, impedance rise can be suppressed. The region from the specified position 33 to the base end 30b, i.e., the second rod member 34, is a member in which a tungsten carbide film, serving as an oxide-resistant film 34d, is provided around the tungsten core material 34c, thus suppressing impedance rise. Furthermore, since the temperature is below the oxidation temperature of tungsten, oxidation of the second rod member 34 can be prevented. It should be noted that the length x [cm] of the Ni rod 42 from the front end 42a to the specified position 33 is independent of the length L [cm] of the Ni rod 42, and reaches 2 [cm] or more and 25 [cm] or less. Furthermore, the core material 34c is a tungsten core material, and the oxide-resistant film 34d is a tungsten carbide film. Therefore, the second rod component 34 can be manufactured relatively easily. That is, by performing carburizing treatment or PVD / CVD on the periphery of the tungsten core material, an oxide-resistant film of tungsten carbide can be formed relatively easily. In addition, since tungsten carbide is harder than tungsten, even if the number of insertions and withdrawals of the second rod component 34 relative to the socket 60 increases, the surface of the second rod component 34 is less likely to be damaged. Furthermore, the thickness of the tungsten carbide film 34d, which is an oxide-resistant film, 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 or damage to the tungsten core material 34c, which is the core material, can be sufficiently prevented. Additionally, although the 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 will not significantly affect the energization of the second rod component 34. If the thickness of the tungsten carbide film exceeds 5 μm, the tungsten carbide film may heat up when the RF power increases. Furthermore, the application of the RF rod 30 to the chip support stage 20 is of great significance. It should be noted that the present invention is not limited to any of the above embodiments. Of course, as long as it falls within the technical scope of the present invention, it can be implemented in various ways. In the above embodiment, the front end 32a of the first rod component 32 of the RF rod 30 is joined to the conductive component 23 exposed on the bottom surface of the hole 21c, but this is not particularly limited. For example, the conductive component 23 may not be provided, and the RF electrode 22 may be exposed on the bottom surface of the hole 21c, and the exposed RF electrode 22 may be joined to the front end 30a (front end 32a of the first rod component 32) of the RF rod 30. Alternatively, as... Figure 7 As shown, the conductive component 23 and the RF rod 30 can be connected via a low thermal expansion component 507. The low thermal expansion component 507 is made of a component with a thermal expansion coefficient of at least 8.0 × 10⁻⁶ below 400°C. -1 Conductors formed from materials below a certain temperature (°C) can be, for example, molybdenum, tungsten, molybdenum-tungsten alloys, tungsten-copper-nickel alloys, or Kova alloys. In this case, the hole 21c is formed to be wider than the front end 32a, and a cylindrical atmosphere protector 509 is inserted into the hole 21c. The atmosphere protector 509 can be, for example, pure nickel, nickel-based heat-resistant alloys, gold, platinum, silver, and their alloys. In addition, several gaps are provided between the outer surface of the atmosphere protector 509 and the inner surface of the hole 21c. Furthermore, a low thermal expansion member 507 is housed in the inner space of the atmosphere protector 509. Moreover, the low thermal expansion member 507 is bonded to the bottom surface of the hole 21c and to the conductive member 23 through conductive bonding layers 506 and 508, respectively, and the atmosphere protector 509 is bonded to the bottom surface of the hole 21c through conductive bonding layer 506. The conductive bonding layers 506 and 508 can be Au-Ni solder bonding layers. In this case, the conductive component 23 can be a Ni, Mo, W, or Mo-W alloy. In the above embodiment, the RF electrode 22 is shaped as a mesh, but it can also be other shapes. For example, it can be coil-shaped, planar, or made of perforated metal. In the above embodiments, AlN is used as the ceramic material, but it is not particularly limited to this. For example, alumina or the like can be used. In this case, the materials of the RF electrode 22, the conductive component 23, and the heater electrode 27 are preferably materials with a coefficient of thermal expansion close to that of the ceramic. In the above embodiments, the wafer W can be attracted to the wafer mounting surface 21a by applying a DC voltage to the RF electrode 22. Alternatively, the wafer W can be attracted to the wafer mounting surface 21a by further embedding an electrostatic electrode in the ceramic substrate 21 and applying a DC voltage to the electrostatic electrode. In the above embodiments, the core material 34c is formed of tungsten, and the oxide-resistant film 34d is formed of tungsten carbide, but it is not limited to this. For example, in the above embodiments, the core material 34c can be formed of molybdenum, and the oxide-resistant film 34d can be formed of molybdenum carbide. Industrial availability This invention can be used in plasma CVD-based film deposition processes, plasma etching processes, etc., on wafers. Symbol Explanation 10 Plasma generating device, 20 Wafer support stage, 21 Ceramic substrate, 21a Wafer placement surface, 21b Back side, 21c Hole, 22 RF electrode, 23 Conductive component, 24 Joint, 27 Heater electrode, 27a, 27b Ends, 29 Ceramic shaft, 30 RF rod, 30a Front end, 30b Base end, 32 First rod component, 32a Front end, 32b Joint surface, 33 Specified position, 34 Second rod component, 34a Joint surface, 34b Base end, 34c Core material, 34d Oxidation resistant film, 40 RF power supply, 42 Ni rod, 42a Front end, 42b Base end, 42c First position, 42o Second position, 50 Upper electrode, 60 Socket, 60a Internal space, 62 Spring, 64 Cable, 506 Conductive bonding layer, 507 Low thermal expansion component, 508 Conductive bonding layer, 509 Atmosphere protection body.

Claims

1. A wafer support stage, wherein, have: A ceramic substrate having a wafer mounting surface and embedded with RF electrodes and heater electrodes; A hole is provided from a side of the ceramic substrate opposite to the wafer placement surface toward the RF electrode; as well as An RF rod that supplies high-frequency power to the RF electrode, and whose front end is engaged with the RF electrode exposed on the bottom surface of the hole or a conductive component connected to the RF electrode. The RF rod is a hybrid rod consisting of a first rod component made of Ni forming a region in the RF rod from the front end to a predetermined position between the front end and the base end, and a second rod component joined to the first rod component and forming a region in the RF rod from the predetermined position to the base end. The second rod component is a component with an oxide-resistant film disposed around a non-magnetic core material.

2. The wafer support stage according to claim 1, wherein, The specified position is defined as follows: a Ni rod is used instead of the mixing rod; the temperature of the heater electrode is set to Ts [°C]; the length of the Ni rod is set to L [cm]; the temperature difference between the two ends of the Ni rod is set to ΔT [°C]; the length of the Ni rod from the front end to the specified position is set to x [cm]; and the temperature at the specified position of the Ni rod is set to T(x) [°C]. Where Ts exceeds the Curie temperature of Ni, at this time... T(x), expressed as T(x) = Ts - (ΔT / L) * x, is above the Curie temperature of Ni and below the oxidation temperature of the non-magnetic core material.

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

4. The wafer support stage according to claim 3, wherein, The thickness of the tungsten carbide film is greater than 0.1 μm and less than 5 μm.

5. An RF rod comprising a hybrid rod consisting of a first rod component made of Ni forming a region from a front end to a predetermined position between the front end and a base end, and a second rod component joined to the first rod component and forming a region from the predetermined position to the base end. The second rod component is a component with an oxide-resistant film disposed around a non-magnetic core material.

Images