Ceramic susceptor

Abstract

The present invention provides a ceramic susceptor that, desirably, makes it possible to reduce impedance of an RF rod for suppressing an increase in heat generation that accompanies an increase in frequency. This ceramic susceptor comprises: a disc-shaped ceramic plate which has a first surface and a second surface and in which an RF electrode and a heater electrode are embedded; a cylindrical ceramic shaft which is attached to the second surface of the ceramic plate and which has an internal space; an RF rod, one end of which is directly or indirectly connected to the RF electrode, the other end of which protrudes from the second surface and extends through the internal space; and a heater rod, one end of which is directly or indirectly connected to the heater electrode, the other end of which protrudes from the second surface and extends through the internal space. The RF rod includes: a base part which includes an end part that is fitted in a terminal hole formed in the second surface of the ceramic plate; a core part which extends from the base part in a direction away from the second surface; and an outer peripheral part which covers the outer periphery of the core part and is made of a non-magnetic material.

Description

Ceramic Susceptor

[0001] The present disclosure relates to ceramic susceptors.

[0002] In semiconductor manufacturing processes, susceptors are used to support wafers in film deposition and etching equipment. A widely used susceptor includes a ceramic plate on which the wafer is placed and a cylindrical ceramic shaft attached to the ceramic plate. The ceramic plate typically has a ceramic base made of aluminum nitride (AlN) or other material with excellent heat and corrosion resistance, with internal electrodes embedded therein, such as heater electrodes, RF electrodes, and electrostatic chuck (ESC) electrodes.

[0003] A ceramic susceptor having a ceramic plate in which an RF electrode and a heater electrode are embedded is used in a plasma CVD process. FIGS. 12 and 13 schematically show examples of conventional film formation apparatuses 100, 100′ equipped with such a ceramic susceptor 110. The film formation apparatuses 100, 100′ include a ceramic plate 112 in which an RF electrode 114 and a heater electrode 116 are embedded, and a plasma upper electrode 104, both of which are located within a chamber 102. A wafer W is placed on the ceramic plate 112, and a ceramic shaft 118 is provided on the backside of the ceramic plate 112. In the film formation apparatus 100 shown in FIG. 12, the plasma upper electrode 104 is connected to an RF power supply 106, while the RF electrode 114 is connected to ground 108 via an RF rod 120. In this configuration, RF is applied from the plasma upper electrode 104 to generate plasma, as indicated by the arrows in FIG. 12, and RF current flows to ground 108 through the RF rod 120. 13, the plasma upper electrode 104 is connected to the ground 108, while the RF electrode 114 is connected to the RF power supply 106 via the RF rod 120. In this configuration, RF is applied from the RF electrode 114 to generate plasma, as represented by the arrows in FIG. 13, and RF current flows from the RF electrode 114 to the plasma upper electrode 104 via the RF rod 120.

[0004] For such ceramic susceptors equipped with RF electrodes and heater electrodes, RF rods of various configurations have been proposed.

[0005] Patent Document 1 (Japanese Patent No. 7129587) discloses a wafer support table including a ceramic base in which an RF electrode and a heater electrode are embedded, a hole formed from one surface of the ceramic base toward the RF electrode, and an RF rod joined to the RF electrode exposed at the bottom of the hole. This 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 (between the tip and base end), and a second rod member made of a non-magnetic material such as tungsten that forms a region of the RF rod from the predetermined position to the base end.

[0006] Patent Document 2 (Japanese Patent No. 6586259) discloses a wafer support table including a ceramic base in which an RF electrode and a heater electrode are embedded, a hole formed from one surface of the ceramic base toward the RF electrode, a Ni or Kovar (Kovar (registered trademark) rod joined to the RF electrode exposed at the bottom of the hole, and a copper group element thin film formed on a predetermined region of the outer circumferential surface of the rod. The copper group element thin film is formed on a region of the outer circumferential surface of the rod from the base end of the rod to a predetermined position not inserted into the hole. Specifically, this document discloses an RF terminal in which an Au thin film (Au plating) is formed on a portion of the outer circumferential surface of a Ni rod.

[0007] Patent No. 7129587 Patent No. 6586259

[0008] In recent years, the RF power required for plasma CVD has increased, leading to an increase in RF current. For example, RF currents have been increasing from 13.56 MHz to 27.12 MHz and even 40 MHz. Furthermore, the RF rod impedance continues to increase due to the skin effect, which becomes more pronounced with increasing RF frequencies. Furthermore, applied plasma power has increased to 1 kW and even 3 kW in recent years, causing RF rods to heat up due to the RF current, resulting in poor process results and deterioration of connected parts (melting, burning, alteration, etc.). Therefore, reducing the RF rod impedance is considered as a way to suppress the heat generated by the RF current. However, it has been found that various problems arise when existing configurations designed to achieve low RF rod impedance are adopted.

[0009] The present inventors have now discovered that by employing an RF rod that has, in addition to a base portion and a core portion, an outer peripheral portion made of a non-magnetic material that covers the outer periphery of the core portion, it is possible to provide a ceramic susceptor that can desirably achieve low impedance for the RF rod in order to suppress the increase in heat generation that accompanies higher frequencies.

[0010] Therefore, an object of the present invention is to provide a ceramic susceptor that can desirably achieve low impedance of an RF rod in order to suppress an increase in heat generation that accompanies higher frequencies.

[0011] The present disclosure provides the following aspects: [Aspect 1] A ceramic susceptor comprising: a disk-shaped ceramic plate having a first surface and a second surface, and in which an RF electrode and a heater electrode are embedded; a cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space; an RF rod having one end connected directly or indirectly to the RF electrode and the other end extending from the second surface and extending through the internal space; and a heater rod having one end connected directly or indirectly to the heater electrode and the other end extending from the second surface and extending through the internal space, wherein the RF rod comprises: a root portion including an end that is fitted into a terminal hole formed in the second surface of the ceramic plate; a core portion extending from the root portion in a direction away from the second surface; and an outer peripheral portion made of a non-magnetic material that covers the outer periphery of the core portion. [Aspect 2] The ceramic susceptor according to Aspect 1, wherein the non-magnetic material constituting the outer periphery comprises at least one selected from the group consisting of brass, titanium, stainless steel, chromium, tungsten, molybdenum, and gold. [Aspect 3] The ceramic susceptor according to Aspect 1 or 2, wherein the surface of the outer periphery is plated with gold and / or chromium. [Aspect 4] The ceramic susceptor according to any one of Aspects 1 to 3, wherein the outer periphery comprises: a tubular portion composed of a tubular member and / or a mesh member formed into a cylindrical shape; and a cap portion closing the end of the tubular portion opposite the base portion. [Aspect 5] The ceramic susceptor according to any one of Aspects 1 to 4, wherein the core portion and the base portion comprise nickel or titanium. [Aspect 6] The ceramic susceptor according to any one of Aspects 1 to 5, wherein the core portion comprises a rod-shaped member, a cable-shaped member, or a combination thereof. [Aspect 7] The ceramic susceptor according to any one of Aspects 1 to 6, wherein the core portion comprises: a first rod-shaped member constituting a portion of the core portion on the root side; a second rod-shaped member constituting a tip portion of the core portion on the opposite side to the root; and a cable-shaped member interposed between the first rod-shaped member and the second rod-shaped member.[Aspect 8] The ceramic susceptor according to any one of Aspects 1 to 6, wherein the core portion is formed of a single rod-shaped member. [Aspect 9] The ceramic susceptor according to any one of Aspects 1 to 8, wherein the ceramic susceptor includes a plurality of the RF rods, and the plurality of RF rods are connected in the internal space by a connecting member made of a non-magnetic material and having at least one form selected from the group consisting of a mesh, a foil, and a plate. [Aspect 10] The ceramic susceptor according to Aspect 9, wherein the non-magnetic material constituting the connecting member includes at least one selected from the group consisting of brass, titanium, stainless steel, chromium, tungsten, and molybdenum. [Aspect 11] The ceramic susceptor according to any one of Aspects 1 to 10, wherein the RF electrode also functions as an ESC electrode.

[0012] 5 is a schematic top view showing an example of a ceramic susceptor according to the present disclosure. FIG. 6 is a schematic cross-sectional view showing a cross section of the ceramic susceptor shown in FIG. 1 taken along line 2-2 in an orientation during use. FIG. 7 is a schematic cross-sectional view showing a cross section of the ceramic susceptor shown in FIG. 1 taken along line 2-2 in an orientation during manufacturing. FIG. 8 is a schematic cross-sectional view of an RF rod shown in FIGS. 1 to 3. FIG. 9 is a schematic cross-sectional view showing another example of a ceramic susceptor according to the present disclosure. FIG. 10 is a schematic cross-sectional view of an RF rod shown in FIG. 5. FIG. 11 is a plan view schematically showing another example of a ceramic susceptor according to the present disclosure. FIG. 12 is a schematic cross-sectional view of an RF rod and a connecting member shown in FIG. 7. FIG. 13 is a schematic top view of an RF rod and a connecting member shown in FIGS. 7 and 8. FIG. 14 is a schematic cross-sectional view of an RF rod in another example of a ceramic susceptor according to the present disclosure. FIG. 15 is a schematic cross-sectional view showing an example of a terminal connection structure in a ceramic susceptor according to the present disclosure. FIG. 16 is a schematic cross-sectional view showing an example of a conventional film formation apparatus. FIG. 17 is a schematic cross-sectional view showing another example of a conventional film formation apparatus.

[0013] The ceramic susceptor according to the present invention is a ceramic platform for supporting a wafer in a semiconductor manufacturing apparatus. Preferably, the ceramic susceptor according to the present invention is a ceramic heater for a semiconductor film formation apparatus. Typical examples of film formation apparatuses include CVD (chemical vapor deposition) apparatuses (e.g., thermal CVD apparatuses, plasma CVD apparatuses, photo CVD apparatuses, and MOCVD apparatuses) and PVD (physical vapor deposition) apparatuses, with plasma CVD apparatuses being particularly preferred.

[0014] 1 to 3 show an example of a ceramic susceptor 10, while FIG. 4 shows an example of an RF rod 20 included in the ceramic susceptor 10. The ceramic susceptor 10 includes a ceramic plate 12, a ceramic shaft 18, an RF rod 20, and a heater rod 22. An RF electrode 14 and a heater electrode 16 are embedded in the ceramic plate 12. The ceramic plate 12 is disk-shaped and has a first surface 12a on which a wafer (not shown) is placed and a second surface 12b opposite the first surface 12a. A cylindrical ceramic shaft 18 is attached to the second surface 12b of the ceramic plate 12. The ceramic shaft 18 is cylindrical and has an internal space S. The RF rod 20 is provided such that one end of the RF rod 20 is directly or indirectly connected to the RF electrode 14 and the other end of the RF rod 20 extends from the second surface 12b and passes through the internal space S. The heater rod 22 is provided such that one end of the heater rod 22 is directly or indirectly connected to the heater electrode 16 and the other end of the heater rod 22 extends from the second surface 12b and through the internal space S. The RF rod 20 includes a root portion 24, a core portion 26, and an outer periphery 28. The root portion 24 includes an end that is fitted into a terminal hole 12c formed in the second surface 12b of the ceramic plate 12. The core portion 26 extends from the root portion 24 in a direction away from the second surface 12b. The outer periphery 28 is made of a nonmagnetic material and is provided to cover the outer periphery of the core portion 26. By employing an RF rod 20 that includes not only the root portion 24 and the core portion 26 but also the outer periphery 28 made of a nonmagnetic material that covers the outer periphery of the core portion 26, it is possible to provide a ceramic susceptor 10 that can desirably achieve low impedance of the RF rod to suppress increases in heat generation associated with higher frequencies.

[0015] As mentioned above, the RF current has increased in recent years as the RF power required for plasma CVD has increased. Furthermore, the RF rod impedance has steadily increased due to the skin effect, which becomes more pronounced with increasing frequency. Furthermore, as applied plasma power has also increased in recent years, the RF rod heats up due to the RF current, leading to poor process results and deterioration of connected parts (melting, burning, alteration, etc.). Therefore, reducing the RF rod impedance is considered to suppress the heat generated by the RF current. However, various problems arise when existing configurations for achieving low RF rod impedance are adopted. For example, Patent Document 1 (Japanese Patent No. 7129587) claims to have achieved low RF rod impedance using a W / Ni hybrid rod utilizing a non-magnetic material and Curie temperature. However, due to the low impedance characteristics, the temperature of the nickel portion does not rise quickly at the beginning of the process, which increases the time it takes for the Curie temperature to be reached and the process to stabilize, resulting in a new problem: it takes a long time to achieve the desired characteristics. Furthermore, the tungsten portion oxidizes over long-term use, resulting in aging (so-called "aging"). Furthermore, W / Ni hybrid rods are heavy (approximately three times heavier than conventional rods), and when stress is applied in the lateral direction (i.e., a direction approximately perpendicular to the rod axis), the moment generated at the brazed joint increases in proportion to the weight ratio. This can lead to problems with the brazed joint breaking during transportation and handling. Meanwhile, Patent Document 2 (Japanese Patent No. 6586259) discloses gold plating on Ni rods, as mentioned above. However, it is difficult to plate the entire rod after brazing. Furthermore, if gold is plated on the outer periphery of the rod before brazing, the gold plating melts away during the brazing process between the rod and the ceramic heater. One or more of these various problems can be resolved by the ceramic susceptor 10 of the present invention (particularly the RF rod 20 having a unique configuration).In particular, by constructing the outer periphery 28 of the RF rod 20, through which RF current flows intensively due to the skin effect, from a non-magnetic material and making it a separate component from the core portion 26 and root portion 24 that form the interior and bottom of the RF rod 20, it is possible to suppress an increase in resistance when RF current flows intensively through the outer periphery 28. In other words, unlike ferromagnetic materials, non-magnetic materials have the property of not increasing resistance even when a large amount of RF current flows, so by selectively using a non-magnetic material for the outer periphery 28, it is possible to achieve low impedance and suppress an increase in heat generation that accompanies higher frequencies. At the same time, the core portion 26 and root portion 24 can ensure the role of supporting the RF rod 20.

[0016] The ceramic plate 12 preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride, in its main portion (i.e., the ceramic substrate) other than the embedded members such as the RF electrode 14 and the heater electrode 16, from the viewpoints of excellent thermal conductivity, high electrical insulation, and thermal expansion characteristics similar to those of silicon.

[0017] The ceramic plate 12 is disk-shaped. However, the planar shape of the disk-shaped ceramic plate 12 does not need to be a perfect circle; for example, it may be an incomplete circle with a portion missing, such as an orientation flat. The size of the ceramic plate 12 is not particularly limited and can be determined appropriately depending on the diameter of the wafer to be used. However, when the ceramic plate 12 is circular, the diameter is typically 150 to 450 mm, and particularly for 300 mm silicon wafers, the diameter is typically 320 to 380 mm. The thickness of the ceramic plate 12 is typically 10 to 25 mm.

[0018] The second surface 12b of the ceramic plate 12 is provided with terminal holes 12c for enabling terminal connection to each of the RF electrode 14 and the heater electrode 16, and is configured so that an RF rod 20 and a heater rod 22 can be inserted into the RF electrode 14 and the heater electrode 16, respectively. Additionally, the second surface 12b of the ceramic plate 12 may be provided with a thermocouple hole 12d for inserting a thermocouple (not shown).

[0019] The ceramic shaft 18 is a cylindrical member with an internal space S and may have a configuration similar to that of ceramic shafts used in known ceramic susceptors or ceramic heaters. The internal space S is configured so that terminal rods such as the RF rod 20 and the heater rod 22 pass through it. The ceramic shaft 18 is preferably made of the same ceramic material as the ceramic plate 12. Therefore, the ceramic shaft 18 preferably contains aluminum nitride or aluminum oxide, more preferably aluminum nitride. The upper end surface of the ceramic shaft 18 is preferably joined to the second surface 12b of the ceramic plate 12 by solid-state bonding or diffusion bonding. The outer diameter of the ceramic shaft 18 is not particularly limited, but is preferably 40 to 60 mm. The inner diameter of the ceramic shaft 18 (the diameter of the internal space S) is also not particularly limited, but is preferably 33 to 55 mm.

[0020] The heater electrode 16 is not particularly limited, and may be, for example, a conductive coil wired in a single stroke across the entire surface of the ceramic plate 12. Heater rods 22 are connected directly or indirectly (e.g., via connecting members 17) to both ends of the heater electrode 16 for power supply, and the heater rods 22 extend through the internal space S and are connected to a heater power supply (not shown). When power is supplied from the heater power supply, the heater electrode 16 generates heat and heats the wafer placed on the surface of the ceramic plate 12. The heater electrode 16 is not limited to a coil, and may be, for example, a ribbon (a long, thin plate), a mesh, or a print.

[0021] The RF electrode 14 is an electrode that enables film formation by a plasma CVD process when high frequency is applied to it. The RF electrode 14 is preferably a circular thin-layer electrode with a diameter slightly smaller than that of the ceramic plate 12, and may be, for example, a mesh electrode formed into a sheet by weaving thin metal wires into a net. An RF rod 20 is connected to the RF electrode 14 directly or indirectly (e.g., via a connecting member 15) for power supply. The RF rod 20 extends through the internal space S and is connected to an external power supply (see RF power supply 106 in FIG. 13) or grounded (see ground 108 in FIG. 12).

[0022] The RF electrode 14 may also function as an ESC electrode. The ESC electrode is an abbreviation for an electrostatic chuck (ESC) electrode, and is also called an electrostatic electrode. When the RF electrode 14 functions as an ESC electrode, the RF electrode 14 (or the ESC electrode) chucks a wafer placed on the surface of the ceramic plate 12 by the Johnsen-Rahbek force when a voltage is applied from an external power source.

[0023] The RF rod 20 has a root portion 24, a core portion 26, and an outer peripheral portion 28, and has an overall rod shape.

[0024] The base portion 24 includes an end portion 24a that is fitted into a terminal hole 12c formed in the second surface 12b of the ceramic plate 12. Therefore, the end portion 24a has a shape that allows it to be inserted into the terminal hole 12c (or an eyelet 42, which will be described later with reference to FIG. 11 ). The base portion 24 preferably has a flange 24b adjacent to the end portion 24a. The flange 24b is a part that applies a force that presses the RF rod 20 toward the ceramic plate 12 when inserting the RF rod 20 (particularly the end portion 24a) into the terminal hole 12c, and can also play a role in regulating and positioning the end portion of the outer circumferential portion 28.

[0025] The core portion 26 extends from the root portion 24 in a direction away from the second surface 12b. The core portion 26 preferably includes a rod-shaped member, a cable-shaped member, or a combination thereof. The core portion 26, together with the root portion 24, serves as a support for the RF rod 20. Preferably, an end of the core portion 26 adjacent to the root portion 24 expands in diameter to form an engaging portion 27 that can be fitted or screwed onto the tubular portion 30, thereby enabling the outer circumferential portion 28 to be fixed. Alternatively, the engaging portion 27 that can be fitted or screwed onto the tubular portion 30 may be provided as a separate member (from the core portion 26 and the root portion 24) at the end of the core portion 26 adjacent to the root portion 24, thereby enabling the outer circumferential portion 28 to be fixed. Therefore, the engaging portion 27 may be a part of the core portion 26 or a separate member from the core portion 26. In either case, the engaging portion 27 preferably has a diameter equal to the inner diameter of the tubular portion 30.

[0026] The core portion 26 and the root portion 24 preferably contain nickel or titanium, and more preferably are made of nickel or titanium. The core portion 26 and the root portion 24 made of nickel or titanium can maintain low electrical resistance, making them suitable for use as parts through which DC current (used for wafer chucking using an electrostatic chuck) flows. Furthermore, the core portion 26 and the root portion 24 are preferably made of the same type of metallic material.

[0027] According to a preferred embodiment of the present invention, as shown in FIG. 4 , the core portion 26 may include a first rod-shaped member 26 a constituting the portion of the core portion 26 on the root portion 24 side, a second rod-shaped member 26 b constituting the tip portion of the core portion 26 opposite the root portion 24, and a cable-shaped member 26 c interposed between the first rod-shaped member 26 a and the second rod-shaped member 26 b. In this embodiment, the cable-shaped member 26 c can absorb the difference in thermal expansion coefficient between the nonmagnetic material (e.g., brass) constituting the outer periphery 28 and the material (e.g., nickel) constituting the core portion 26 and the root portion 24. That is, the cable-shaped member 26 c can bend due to its own flexibility, thereby absorbing displacement caused by the difference in thermal expansion coefficient during high-temperature use. Alternatively, according to another preferred embodiment of the present invention, as shown in FIGS. 5 , 6 , and 10 , the core portion 26 may be composed of a single rod-shaped member 26 a.

[0028] The outer peripheral portion 28 is made of a non-magnetic material and is a member provided to cover the outer periphery of the core portion 26. As described above, unlike ferromagnetic materials, non-magnetic materials have the property of being less likely to increase in resistance even when a large amount of RF current flows. Therefore, selectively using a non-magnetic material for the outer peripheral portion 28 can achieve low impedance and suppress the increase in heat generation associated with higher frequencies. The non-magnetic material constituting the outer peripheral portion 28 preferably includes at least one selected from the group consisting of brass, titanium, stainless steel, chromium, tungsten, molybdenum, and gold. However, it is more preferable that the main portion of the outer peripheral portion 28 be composed of a non-magnetic material other than gold or chromium, with the gold or chromium applied to the surface of the outer peripheral portion 28 in the form of plating. In other words, the surface of the outer peripheral portion 28 is preferably plated with gold and / or chromium. Gold plating is particularly preferable because it also functions as an anti-oxidation film for the non-magnetic material constituting the outer peripheral portion 28. Furthermore, chromium plating is preferably used in combination with gold plating because it also functions as a gold diffusion prevention layer as a base for gold plating.

[0029] The outer peripheral portion 28 preferably includes a cylindrical portion 30 and a cap portion 32 that closes the end of the cylindrical portion 30 opposite the base portion 24. The cylindrical portion 30 is preferably composed of a tubular member and / or a mesh member formed into a cylindrical shape. Alternatively, the cylindrical portion 30 may be a metal foil rolled into a cylindrical shape. In either case, the cylindrical portion 30 and the cap portion 32 are preferably plated with gold and / or chromium, as described above.

[0030] The outer periphery 28 can be attached to the core portion 26, for example, as follows: First, a rod formed by the core portion 26 and the base portion 24 is brazed to the RF electrode 14 and / or the connecting member 15. Next, the outer periphery 28 (i.e., the cylindrical portion 30 and the cap portion 32), which has been previously plated with gold or the like, is attached to the core portion 26 or the engaging portion 27 by a known method such as screwing or spot welding so as to cover the outer periphery of the core portion 26.

[0031] 5 and 6 , the cylindrical portion 30 may include a first tubular member 30a constituting the portion of the cylindrical portion 30 on the base portion 24 side, a second tubular member 30b constituting the tip portion of the cylindrical portion 30 opposite the base portion 24, and a mesh member 30c interposed between the first tubular member 30a and the second tubular member 30b. In this embodiment, the mesh member 30c can absorb the difference in thermal expansion coefficient between the nonmagnetic material (e.g., titanium) constituting the cylindrical portion 30 and the material (e.g., nickel) constituting the cylindrical portion 30 and the base portion 24. In other words, the mesh member 30c can bend due to its own flexibility, thereby absorbing displacement caused by the difference in thermal expansion coefficient during high-temperature use. Because the first tubular member 30a, the second tubular member 30b, and the mesh member 30c are components of the cylindrical portion 30, they are preferably made of a non-magnetic material, similar to the constituent material of the cylindrical portion 30 described above, and their surfaces are preferably plated with gold and / or chromium. Examples of preferred mesh members 30c include meshes made of titanium, tungsten, or molybdenum with gold plating on the surface. Alternatively, according to another preferred embodiment of the present invention, as shown in Figures 1 to 4 and 10, the cylindrical portion 30 may be composed of a single tubular member 30a. Examples of preferred tubular members 30a include tubular members made of brass or titanium with gold plating on the surface.

[0032] 7 to 9 , the ceramic susceptor 10 may include a plurality of RF rods 20. In this case, the plurality of RF rods 20 are preferably connected in the internal space S by a connecting member 36 made of a non-magnetic material in at least one form selected from the group consisting of a mesh, a foil, and a plate. Mesh, foil, and plate shapes allow the RF rods 20 to be connected by a non-magnetic material in any of these forms with a planar expansion, thereby further reducing the impedance of the RF rods 20. The non-magnetic material constituting the connecting member 36 preferably includes at least one selected from the group consisting of brass, titanium, stainless steel, chromium, tungsten, and molybdenum.

[0033] The heater rod 22 may have the same configuration as a heater rod used in a known ceramic susceptor or ceramic heater. Therefore, the heater rod 22 may be made of the same material (e.g., nickel or titanium) as the core portion 26 and the base portion 24 of the RF rod 20, and is not particularly limited.

[0034] As described above, the RF rod 20 is connected directly or indirectly to the RF electrode 14, while the heater rod 22 is connected directly or indirectly to the heater electrode 16. The RF rod 20 and the heater rod 22 may be directly joined to the RF electrode 14 and the heater electrode 16, respectively, by brazing or the like, or may be brazed via connecting members 15 and 17 containing a metal member such as Mo, as shown in Figures 2, 3, 5, and 7. The connecting members 15 and 17 are not particularly limited and may have a known connecting structure containing a metal member such as Mo.

[0035] 11 shows a preferred example of the connecting members 15 and 17. The connecting members 15 and 17 shown in FIG.

[0036] The metal member 40 is a member interposed between the RF rod 20 and the RF electrode 14 and / or between the heater rod 22 and the heater electrode 16 to assist in ensuring electrical connection, and its configuration is not particularly limited. A preferred metal member 40 includes a tablet 40a and / or a buffer material 40b, and more preferably includes both the tablet 40a and the buffer material 40b. The tablet 40a is a block-shaped metal member (e.g., configured in a mesh shape) that facilitates ensuring electrical connection between the RF rod 20 and the RF electrode 14, and is provided on the RF electrode 14 side. Similarly, a tablet 40a may also be provided on the heater electrode 16 side to ensure electrical connection between the heater rod 22 and the heater electrode 16. This ensures a sufficient contact area for brazing the RF rod 20, heater rod 22, and / or the buffer material 40b. Preferred examples of the metal constituting the tablet 40a include Mo, W, and a W-Mo alloy, with Mo being preferred. The buffer material 40b is a metal member provided as a buffer to mitigate the difference in thermal expansion between the tablet 40a and the RF rod 20 and / or the difference in thermal expansion between the tablet 40a and the heater rod 22, and is provided between the tablet 40a and the RF rod 20 and / or the tablet 40a and the heater rod 22. A preferred example of the metal constituting the buffer material 40b is an alloy such as Kovar (registered trademark) (Fe-Ni-Co alloy). When the metal member 40 includes the tablet 40a and the buffer material 40b, it is preferable to braze the RF rod 20, the buffer material 40b, and the tablet 40a together using a brazing material 44 (e.g., Au). Similarly, it is preferable to braze the heater rod 22, the buffer material 40b, and the tablet 40a together using a brazing material 44 (e.g., Au).

[0037] The eyelet 42 is a metallic cylindrical member that fits into the terminal hole 12c. The eyelet 42 serves to guide the RF rod 20 or the heater rod 22 for smooth insertion into the terminal hole 12c. The eyelet 42 may be threaded. In this case, the RF rod 20 or the heater rod 22 may also be threaded, allowing the RF rod 20 or the heater rod 22 to be inserted while threaded into the eyelet 42. The metal constituting the eyelet 42 is not particularly limited, but preferred examples include Ni, W, Mo, and W-Mo alloys, with Ni being preferred. Furthermore, the eyelet 42 may have a male thread on its outer periphery. By providing a threaded portion, the eyelet 42 can be threaded into the terminal hole 12c.

[0038] Hereinafter, various embodiments employing various RF rods 20 will be described with reference to the drawings.

[0039] First Embodiment The first embodiment employs an RF rod 20 having a gold-plated brass tube for the outer peripheral portion 28 and a nickel cable-like member for the core portion 26. This embodiment corresponds to the configurations of the ceramic susceptor 10 and RF rod 20 shown in FIGS. 1 to 4 . Accordingly, in the first embodiment, the core portion 26 includes the first rod-shaped member 26 a, the second rod-shaped member 26 b, and the cable-like member 26 c interposed therebetween, as described above. Furthermore, the outer peripheral portion 28 includes the cylindrical portion 30 and the cap portion 32, as described above, and the cylindrical portion 30 is composed of a single tubular member 30 a. Hereinafter, in this embodiment, a member in which the base portion 24, the first rod-shaped member 26 a, the cable-like member 26 c, and the second rod-shaped member 26 b are connected in this order will be referred to as a “Ni cable rod.” The specifications of the RF rod 20 in the first embodiment are as follows: <Ni cable rod> Root portion 24: Nickel member having end 24a and flange 24b First rod-shaped member 26a: Nickel rod (having an engaging portion 27 with an expanded diameter at the end) Second rod-shaped member 26b: Nickel rod Cable-shaped member 26c: Nickel cable <Outer circumferential portion 28> Cylindrical portion 30: Brass tube with gold-plated outer surface (thickness of gold plating: approximately 10 μm) Cap portion 32: Brass cap portion with gold-plated outer surface (thickness of gold plating: approximately 10 μm), having a cap shape that closes one end of the cylindrical portion 30. *Stainless steel (SUS316) may be used instead of brass for the cylindrical portion 30 and cap portion 32.

[0040] In the first embodiment, the RF rod 20 can be attached to the ceramic plate 12 as follows. First, the root portion 24 (particularly the end portion 24a) of the Ni cable rod is inserted into the terminal hole 12c of the ceramic plate 12, and the root portion 24 is soldered to the RF electrode 14 via the connecting member 15. The soldering temperature is approximately 1000°C. Pre-plating the Ni cable rod with gold is not possible because any gold plating would melt and peel off during soldering. Next, the cylindrical portion 30, which is a gold-plated brass tube, is positioned to house the Ni cable rod, and the end of the cylindrical portion 30 is screwed into the engaging portion 27 of the Ni cable rod. At this time, the end of the cylindrical portion 30 is positioned by being restricted by the flange 24b. By welding the gold-plated brass tube, which is the cylindrical portion 30, and the gold-plated brass cap portion 32 at the joint 34, it is possible to prevent the cap portion 32 from loosening and slipping off the cylindrical portion 30 and ensure good electrical connection. In this way, an RF rod 20 is obtained, in which the core portion 26 of the Ni cable rod is covered with the outer circumferential portion 28 (the cylindrical portion 30 and the cap portion 32). Although brass and nickel have different thermal expansion coefficients, the difference in thermal expansion coefficient between the brass constituting the outer circumferential portion 28 and the nickel constituting the core portion 26 and the base portion 24 can be absorbed by the cable-like member 26c (nickel cable). For example, a thermal expansion difference of approximately 1 mm occurs between brass and nickel over a length of 300 mm. However, this embodiment can effectively absorb such a difference in thermal expansion coefficient and displacement. Furthermore, in this embodiment, the outer surface of the outer circumferential portion 28 (i.e., the cylindrical portion 30 and the cap portion 32) is gold-plated, the technical significance of which is explained below. First, gold plating on nickel tubes or nickel cable rods should be avoided because gold diffuses and forms an Au-Ni alloy (i.e., gold-plated nickel tubes cannot be used). Also, nickel is a ferromagnetic material, so it cannot be used for the outer periphery 28, which carries high-frequency waves.In this regard, in this embodiment, the outer surface of the brass outer circumferential portion 28 (the cylindrical portion 30 and the cap portion 32) is gold-plated, which advantageously prevents oxidation of the brass that forms the base of the gold plating at operating temperatures up to approximately 700°C, and reduces impedance by using a paramagnetic material.

[0041] Second Embodiment The second embodiment employs an RF rod 20 having a gold-plated titanium tube for the outer periphery 28 and a nickel cable-like member for the core 26. This embodiment also corresponds to the configuration of the ceramic susceptor 10 and RF rod 20 shown in FIGS. 1 to 4 and has the same configuration as the first embodiment, except that titanium is used instead of brass for the outer periphery 28, as described below. <Outer periphery 28> Cylindrical portion 30: Titanium tube with gold-plated outer surface (thickness of gold plating: approximately 10 μm) Cap portion 32: Titanium cap with gold-plated outer surface (thickness of gold plating: approximately 10 μm), having a cap shape that closes one end of the cylindrical portion 30. *Stainless steel (SUS316) may be used instead of titanium for the cylindrical portion 30 and cap portion 32.

[0042] In the second embodiment, the RF rod 20 can be attached to the ceramic plate 12 in the same manner as in the first embodiment, except that titanium is used instead of brass. Titanium and nickel have different thermal expansion coefficients. However, the difference in thermal expansion coefficient between the titanium constituting the outer periphery 28 and the nickel constituting the core portion 26 and root portion 24 can be absorbed by the cable-shaped member 26c (nickel cable). For example, a thermal expansion difference of approximately 0.8 mm occurs between titanium and nickel over a length of 300 mm. However, this embodiment effectively absorbs such a difference in thermal expansion coefficient and displacement. Furthermore, in this embodiment, the outer surface of the outer periphery 28 (i.e., the cylindrical portion 30 and cap portion 32) is gold-plated, the technical significance of which is explained as follows. First, gold plating of nickel diffuses and forms an Au-Ni alloy, so gold plating of nickel tubes and nickel cable rods should be avoided (i.e., gold-plated nickel tubes cannot be used). Furthermore, nickel is a ferromagnetic material and therefore cannot be used for the outer periphery 28, which transmits high-frequency waves. In this regard, in this embodiment, the outer surface of the titanium outer circumferential portion 28 (the cylindrical portion 30 and the cap portion 32) is gold-plated, which advantageously prevents oxidation of the titanium that forms the base of the gold plating at operating temperatures up to approximately 700°C, and reduces impedance by using a paramagnetic material.

[0043] Third Embodiment The third embodiment employs an RF rod 20 having a gold-plated titanium mesh member for the outer peripheral portion 28 and a nickel rod-shaped member (not including a cable-shaped member) for the core portion 26. This embodiment corresponds to the configurations of the ceramic susceptor 10 and RF rod 20 shown in FIGS. 5 and 6 . Accordingly, in the third embodiment, the core portion 26 comprises a single rod-shaped member 26 a. Furthermore, as described above, the outer peripheral portion 28 includes a cylindrical portion 30 and a cap portion 32, and the cylindrical portion 30 is composed of a first tubular member 30 a, a second tubular member 30 b, and a mesh member 30 c interposed therebetween. Hereinafter, in this embodiment, the integrated body composed of the base portion 24 and the rod-shaped member 26 a will be referred to as a “Ni rod.” The specifications of the RF rod 20 in the third embodiment are as follows: <Ni rod> Base portion 24: Nickel member having end portion 24a and flange 24b Core portion 26 (rod-shaped member 26a): Nickel rod (having engaging portions 27 with expanded diameters at the ends) <Outer circumferential portion 28> First tubular member 30a: Titanium tube having gold-plated outer surface (gold plating thickness: approximately 10 μm) Second tubular member 30b: Titanium tube having gold-plated outer surface (gold plating thickness: approximately 10 μm) Mesh-shaped member 30c: Mesh sleeve made of titanium, tungsten, or molybdenum having gold-plated outer surface (50 mesh (wire diameter 0.12 mm and opening: approximately 0.4 mm) or 24 mesh (wire diameter: 0.35 mm and opening: approximately 0.7 mm) (gold plating thickness: approximately 10 μm)) (*In the case of a tungsten or molybdenum mesh, chrome plating is provided between the mesh and the gold plating. In addition, in the case of a titanium mesh, a TiN layer may be provided between the mesh and the gold plating.) Cap portion 32: A titanium cap portion with a gold-plated outer surface (thickness of gold plating: approximately 10 μm), having a cap shape that closes one end of the cylindrical portion 30.

[0044] In the third embodiment, the RF rod 20 can be attached to the ceramic plate 12 as follows. The following description will be given assuming that a titanium mesh sleeve with a gold-plated outer surface is used as the mesh member 30c. However, the same applies to gold-plated tungsten or molybdenum mesh sleeves. First, the root portion 24 (particularly the end portion 24a) of the Ni rod is inserted into the terminal hole 12c of the ceramic plate 12, and the root portion 24 is soldered to the RF electrode 14 via the connecting member 15. The soldering temperature is approximately 1000°C. Pre-plating the Ni rod with gold is not possible because the gold plating melts and peels off during soldering. Next, the cylindrical portion 30, which is a gold-plated titanium tube / mesh sleeve composite, is positioned to accommodate the Ni rod, and the end of the cylindrical portion 30 is screwed into the engagement portion 27 of the Ni rod. At this time, the end of the cylindrical portion 30 is positioned by being restricted by the flange 24b. By welding the cylindrical portion 30 (particularly the gold-plated titanium tube) arranged in this manner to the gold-plated titanium cap portion 32 at the joint 34, it is possible to prevent the cap portion 32 from loosening and coming off the cylindrical portion 30 and ensure good electrical connection. In this way, an RF rod 20 is obtained, in which the core portion 26 of the Ni rod is covered with the outer circumferential portion 28 (the cylindrical portion 30 and the cap portion 32). Although titanium and nickel have different thermal expansion coefficients, the difference in thermal expansion coefficient between the titanium constituting the outer circumferential portion 28 and the nickel constituting the core portion 26 and the base portion 24 can be absorbed by the mesh-like member 30c (titanium mesh sleeve) (a displacement of about ±1 mm can be absorbed without any problems). Furthermore, in this embodiment, the outer surface of the outer circumferential portion 28 (i.e., the cylindrical portion 30 and the cap portion 32) is gold-plated, the technical significance of which is explained below. First, gold plating on nickel tubes or nickel cable rods should be avoided because gold diffuses and forms an Au-Ni alloy (i.e., gold-plated nickel tubes cannot be used). Also, nickel is a ferromagnetic material and therefore cannot be used for the outer periphery 28 through which high frequency waves flow, whereas titanium is a paramagnetic material and is suitable for the outer periphery 28 through which high frequency waves flow.However, titanium is an active material and easily oxidizes and deteriorates at high temperatures. In this regard, in this embodiment, the outer surface of the titanium outer circumferential portion 28 (the cylindrical portion 30 and the cap portion 32) is gold-plated, which advantageously prevents oxidation of the titanium that forms the base of the gold plating and reduces impedance due to the paramagnetic material at operating temperatures up to approximately 700°C.

[0045] (Fourth Embodiment) In the fourth embodiment, as shown in FIGS. 7 to 9 , multiple RF rods 20 are connected together. That is, as described above, multiple RF rods 20 are connected together by a connecting member 36 made of a nonmagnetic material, thereby further reducing the impedance of the RF rods 20. In this embodiment, two RF rods 20 are connected together by a thin-plate or mesh-like connecting member 36 made of titanium, brass, or stainless steel (SUS316) with a gold-plated surface. As shown in FIGS. 7 to 9 , the connecting member 36 is provided so as to hang from the cylindrical portions 30 of both RF rods 29, and the portions of the connecting member 36 that are wrapped around and fixed to the cylindrical portions 30 form thin-walled pipes 36a with a thickness of 1 mm or less. The thin-walled pipes 36a do not necessarily have to be wrapped around the cylindrical portions 30 of the connecting member 36; they may also be pre-formed into a cylindrical shape so that the cylindrical portions 30 can be inserted therein. 8, it is preferable to arrange the connecting member 36 over substantially the entire length of the tubular portion 30 from the viewpoint of reducing impedance, but the connecting member 36 may be arranged over only a portion of the length of the tubular portion 30. Furthermore, the connecting member 36 is preferably provided so as to hang over the joint 34 between the tubular portion 30 and the cap portion 32, and is preferably configured so that the connecting member 36 can be welded and fixed at the same time as the joint 34 is welded.

[0046] 7 to 9, RF rods 20 having the same configuration as in the first or second embodiment are used, but the present invention is not limited to this, and RF rods 20 of the third embodiment can also be used. Therefore, attachment of multiple RF rods 20 to the ceramic plate 12 can be performed in the same manner as in the first, second, or third embodiment, except for providing the connecting members 36. Then, by simultaneously welding the connecting members 36 when welding the joints 34, the connecting members 36 can be fixed to the RF rods 20.

[0047] Fifth Embodiment The fifth embodiment employs an RF rod 20 having a gold-plated titanium tube for the outer circumferential portion 28 and a titanium rod-shaped member (not including a cable-shaped member) for the core portion 26. As shown in FIG. 10 , the RF rod 20 according to the fifth embodiment employs the outer circumferential portion 28 of the second embodiment and corresponds to a configuration in which the Ni rod of the third embodiment is replaced with a Ti rod. Therefore, as described above, the core portion 26 includes a single rod-shaped member 26a. Furthermore, as described above, the outer circumferential portion 28 includes a cylindrical portion 30 and a cap portion 32, and the cylindrical portion 30 is composed of a single tubular member 30a. That is, in the fifth embodiment, a member for absorbing thermal expansion differences, such as a cable-shaped member 26c or a mesh-shaped member 30c, is not required. This is because not only the outer circumferential portion 28 but also the base portion 24 and the core portion 26 are made of titanium, and therefore no difference in thermal expansion coefficients occurs. The specifications of the RF rod 20 according to the fifth embodiment are as follows. <Ti rod> Root portion 24: titanium member having end portion 24a and flange 24b Core portion 26 (rod-shaped member 26a): titanium rod (having an engaging portion 27 with an expanded diameter at the end) <Outer portion 28> Cylindrical portion 30: titanium tube with gold-plated outer surface (thickness of gold plating: approximately 10 μm) Cap portion 32: titanium cap portion with gold-plated outer surface (thickness of gold plating: approximately 10 μm), having a cap shape that closes one end of the cylindrical portion 30.

[0048] In the fifth embodiment, the RF rod 20 can be attached to the ceramic plate 12 as follows. First, the root portion 24 of the Ti rod is inserted into the terminal hole 12c of the ceramic plate 12, and the root portion 24 (particularly the end portion 24a) is soldered to the RF electrode 14 via the connecting member 15. The soldering temperature is approximately 1000°C. Pre-gold plating of the Ti rod is not possible because the gold would melt and peel off during soldering. Next, a gold-plated titanium tube, or cylindrical portion 30, is positioned to accommodate the Ti rod, and the end of the cylindrical portion 30 is threaded into the engagement portion 27 of the Ti rod. The end of the cylindrical portion 30 is positioned by being restricted by the flange 24b. The gold-plated titanium tube, or cylindrical portion 30, and the gold-plated titanium cap portion 32 are welded at the joint 34 to prevent the cap portion 32 from loosening and coming off the cylindrical portion 30 and ensure good electrical connection. In this way, an RF rod 20 is obtained, having a structure in which the core portion 26 of the Ti rod is covered with the outer circumferential portion 28 (the cylindrical portion 30 and the cap portion 32). In this embodiment, the outer surface of the outer circumferential portion 28 (i.e., the cylindrical portion 30 and the cap portion 32) is gold-plated, the technical significance of which is explained as follows. First, titanium is a paramagnetic material and is suitable for the outer circumferential portion 28 through which high frequency waves flow. However, titanium is an active material and quickly oxidizes and deteriorates at high temperatures. In this regard, in this embodiment, gold plating of the outer surface of the titanium outer circumferential portion 28 (the cylindrical portion 30 and the cap portion 32) can advantageously prevent oxidation of the titanium that forms the gold-plated base and reduce impedance due to the paramagnetic material at operating temperatures up to approximately 700°C.

Claims

1. A ceramic susceptor comprising: A disc-shaped ceramic plate having a first surface and a second surface, with an RF electrode and a heater electrode embedded therein; A cylindrical ceramic shaft attached to the second surface of the ceramic plate and having an internal space; An RF rod having one end directly or indirectly connected to the RF electrode, the other end extending from the second surface and extending through the internal space; A heater rod having one end directly or indirectly connected to the heater electrode, the other end extending from the second surface and extending through the internal space; wherein the RF rod includes: A root portion including an end fitted into a terminal hole formed in the second surface of the ceramic plate; A core portion extending in a direction away from the second surface from the root portion; An outer peripheral portion made of a non-magnetic material covering the outer periphery of the core portion.

2. The ceramic susceptor according to claim 1, wherein the non-magnetic material constituting the outer peripheral portion includes at least one selected from the group consisting of brass, titanium, stainless steel, chromium, tungsten, molybdenum, and gold.

3. The ceramic susceptor according to claim 1 or 2, wherein the surface of the outer peripheral portion is plated with gold and / or chromium.

4. The ceramic susceptor according to claim 1 or 2, wherein the outer peripheral portion includes: A tubular portion constituted by a tubular member and / or a mesh-shaped member formed in a cylindrical shape; A cap portion closing an end portion of the tubular portion opposite to the root portion.

5. The ceramic susceptor according to claim 1 or 2, wherein the core portion and the root portion contain nickel or titanium.

6. The ceramic susceptor according to claim 1 or 2, wherein the core portion includes a rod-shaped member, a cable-shaped member, or a combination thereof.

7. The ceramic susceptor according to claim 1 or 2, wherein the core portion includes: A first rod-shaped member constituting a portion of the core portion on the root portion side; A second rod-shaped member constituting a tip portion of the core portion opposite to the root portion; A cable-shaped member interposed between the first rod-shaped member and the second rod-shaped member.

8. The ceramic susceptor according to claim 1 or 2, wherein the core portion is composed of a single rod-shaped member.

9. The ceramic susceptor according to claim 1 or 2, wherein the ceramic susceptor includes a plurality of the RF rods, and the plurality of the RF rods are connected by a connecting member made of a non-magnetic material in at least one form selected from the group consisting of a mesh form, a foil form, and a plate form in the internal space.

10. The ceramic susceptor according to claim 9, wherein the non-magnetic material constituting the connecting member includes at least one selected from the group consisting of brass, titanium, stainless steel, chromium, tungsten, and molybdenum.

11. The ceramic susceptor according to claim 1 or 2, wherein the RF electrode also functions as an ESC electrode.

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