Susceptor

Abstract

An inexpensive susceptor is provided that has RF functionality and is suitable for suppressing in-plane variations in the distance between the surface of the ceramic plate and an RF electrode. The susceptor includes: a circular ceramic plate having a first surface and a second surface; an internal electrode embedded in the ceramic plate; a metal layer provided as an RF electrode on all or part of the second surface of the ceramic plate; a circular cooling plate provided a predetermined distance from the second surface of the ceramic plate; a heat transfer space that allows heat transfer via gas between the metal layer and the cooling plate; a seal member provided between the ceramic plate and the cooling plate and along the outer peripheries of the ceramic plate and the cooling plate to provide airtightness in the heat transfer space; and an RF conductive member provided between the ceramic plate and the cooling plate, located on the inner periphery of the seal member, for ensuring electrical connection between the metal layer and the cooling plate.

Description

[Technical Field]

[0001] The present disclosure relates to a susceptor. [Background technology]

[0002] Susceptors are used to support wafers in film deposition and etching equipment used in semiconductor manufacturing processes. A widely used susceptor includes a ceramic plate on which the wafer is placed, an RF electrode for inducing high-frequency plasma generation, and a cooling plate. The ceramic plate typically has a ceramic base made of aluminum nitride (AlN) or other materials with excellent heat and corrosion resistance, with internal electrodes such as a heater electrode, an RF electrode, and an electrostatic chuck (ESC) electrode embedded within.

[0003] Patent Document 1 (JP 2023-5203 A) discloses a substrate support that supports a substrate, which has a substrate adsorption portion equipped with an adsorption electrode for holding the substrate, an RF electrode portion to which RF power is supplied, and a substrate temperature adjustment portion equipped with a heater electrode for adjusting the temperature of the substrate, and discloses a stacked structure in which the RF electrode portion is sandwiched between the substrate adsorption portion and the substrate temperature adjustment portion.

[0004] Patent Document 2 (Japanese Patent No. 6884110) discloses an electrostatic pack assembly including an upper pack plate, a lower pack plate joined to the upper pack plate by a first metal bond, a backing plate joined to the bottom surface of the lower pack plate by a second metal bond, and a conductive gasket. The upper pack plate includes AlN or Al2O3 and has a first thermal expansion coefficient. The upper pack plate further includes one or more heating elements and one or more electrodes for electrostatically clamping a substrate. The lower pack plate includes a material having a first or second thermal expansion coefficient. The backing plate is a disk-shaped plate made of AlN or Al2O3 and has a first diameter smaller than the second diameter of the lower pack plate. The conductive gasket is disposed on the bottom surface of the lower pack plate, outside the first diameter of the backing plate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-5203 [Patent Document 2] Patent No. 6884110 Summary of the Invention

[0006] A typical example of an RF electrode in a conventional susceptor is a metal mesh (e.g., molybdenum mesh) embedded in a ceramic plate. In this conventional structure, the metal mesh is prone to undulations due to its flexibility. This makes it difficult to maintain a uniform in-plane distance between the surface of the ceramic plate and the metal mesh, which is crucial for achieving desirable RF functionality. This uneven distribution of the distance results in variations in the concentration of incident ions generated by applying a voltage to the RF electrode. Therefore, a configuration that can easily suppress variations in the in-plane distance between the surface of the ceramic plate and the metal mesh is desirable.

[0007] Furthermore, in semiconductor manufacturing equipment for etching, high heat dissipation capabilities are required for susceptors in order to quickly dissipate heat input from the plasma. However, currently, high-heat dissipation susceptors use expensive joining methods such as metal diffusion bonding (e.g., TCB bonding) to connect the ceramic plate and cooling plate. Therefore, it would be advantageous if the ceramic plate and cooling plate could be connected using a cheaper method.

[0008] The present inventors have now discovered that by sequentially arranging a metal layer as an RF electrode, a heat transfer space sealed with a sealing member, and a cooling plate on the back side of a ceramic plate in which an internal electrode is embedded, and by arranging an RF conductive member in the heat transfer space to electrically connect the metal layer and the cooling plate, it is possible to provide an inexpensive susceptor that is suitable for suppressing in-plane variations in the distance between the surface of the ceramic plate and the RF electrode.

[0009] Therefore, an object of the present invention is to provide a susceptor having an RF function and an inexpensive structure suitable for suppressing in-plane variations in the distance between the surface of the ceramic plate and the RF electrode.

[0010] According to the present disclosure, the following aspects are provided. [Aspect 1] a circular ceramic plate having a first surface and a second surface; an internal electrode embedded in the ceramic plate; a metal layer provided as an RF electrode on all or part of the second surface of the ceramic plate; a disk-shaped cooling plate provided at a predetermined distance from the second surface of the ceramic plate; a heat transfer space that exists between the metal layer and the cooling plate and that allows heat transfer via gas; a sealing member provided between the ceramic plate and the cooling plate along the outer periphery of the ceramic plate and the cooling plate to provide airtightness to the heat transfer space; an RF conductive member provided between the ceramic plate and the cooling plate at a position on the inner circumferential side of the sealing member, the RF conductive member ensuring electrical connection between the metal layer and the cooling plate; A susceptor comprising: [Aspect 2] 2. The susceptor according to aspect 1, wherein the metal layer has a thickness of 3 to 500 μm. [Aspect 3] A susceptor according to aspect 1 or 2, wherein the metal layer is a layer formed by printing or plating, or is a metal sheet. [Aspect 4] A susceptor according to any one of aspects 1 to 3, wherein the ceramic plate comprises aluminum nitride and / or aluminum oxide. [Aspect 5] A susceptor according to any one of aspects 1 to 4, wherein the cooling plate is made of a metal or a metal-based composite material. [Aspect 6] A susceptor according to any one of aspects 1 to 5, wherein the RF conductive member includes a long, spirally wound metal part. [Aspect 7] The susceptor according to any one of aspects 1 to 6, further comprising a terminal rod connected to the internal electrode, the terminal rod traversing the second surface, the metal layer, the heat transfer space, and the cooling plate, and extending in a direction away from the second surface. [Aspect 8] A susceptor as described in aspect 7, wherein the cooling plate has an opening hole for passing the terminal rod therethrough, and the surface of the opening hole is covered with an insulating material, thereby insulating the terminal rod from the cooling plate. [Aspect 9] A susceptor according to any one of aspects 1 to 8, wherein the cooling plate has an internal space for allowing a cooling medium to flow inside the cooling plate. [Aspect 10] The susceptor according to any one of aspects 1 to 9, further comprising a fixing member provided along an outer periphery of the susceptor, the fixing member fixing the ceramic plate, the metal layer, the sealing member, the RF conductive member, and the cooling plate in a direction in which they are in close contact with each other. [Aspect 11] the ceramic plate has a small diameter portion having a relatively small diameter that provides the first surface and a large diameter portion having a relatively large diameter that provides the second surface, whereby the large diameter portion and the small diameter portion form a step portion; 11. The susceptor of claim 10, wherein the fixing member is configured to be engageable with the stepped portion. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view showing an example of a susceptor according to the present disclosure. [Figure 2] FIG. 2 is a schematic plan view of the susceptor shown in FIG. [Figure 3] FIG. 2 is a schematic perspective view showing an example of an RF conductive member. DETAILED DESCRIPTION OF THE INVENTION

[0012] The susceptor according to the present invention is a stage for supporting a wafer and is used in a semiconductor manufacturing apparatus, particularly a film deposition apparatus or etching apparatus for a semiconductor manufacturing process. Preferably, the susceptor according to the present invention includes a ceramic heater for a semiconductor film deposition apparatus. Typical examples of film deposition 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.

[0013] 1 and 2 show one embodiment of a susceptor 10. The susceptor 10 shown in FIG. 1 includes a ceramic plate 12, an internal electrode 14, a metal layer 16, a cooling plate 18, a heat transfer space 20, a seal member 22, and an RF conductive member 24. The ceramic plate 12 is circular and has a first surface 12a and a second surface 12b. The internal electrode 14 is embedded within the ceramic plate 12. The metal layer 16 is provided as an RF electrode on all or part of the second surface 12b of the ceramic plate 12. The cooling plate 18 is circular and is provided at a predetermined distance from the second surface 12b of the ceramic plate 12. The heat transfer space 20 is a space that allows heat transfer via gas and exists between the metal layer 16 and the cooling plate 18. The seal member 22 is provided between the ceramic plate 12 and the cooling plate 18 along the outer peripheries of the ceramic plate 12 and the cooling plate 18 to provide airtightness to the heat transfer space 20. The RF conductive member 24 is a member that ensures electrical connection between the metal layer 16 and the cooling plate 18, and is provided between the ceramic plate 12 and the cooling plate 18 at a position on the inner periphery of the seal member 22. By sequentially arranging the metal layer 16 as an RF electrode, the heat transfer space 20 sealed with the seal member 22, and the cooling plate 18 on the second surface 12b of the ceramic plate 12 in which the internal electrode 14 is embedded, and by arranging the RF conductive member 24 that electrically connects the metal layer 16 and the cooling plate 18 in the heat transfer space 20, it is possible to provide an inexpensive susceptor that is suitable for suppressing in-plane variations in the distance between the first surface 12a of the ceramic plate 12 and the metal layer 16 (RF electrode).

[0014] As mentioned above, in conventional structures, the metal mesh is prone to undulation due to its flexibility. This makes it difficult to maintain a uniform in-plane distance between the ceramic plate surface and the metal mesh, which is crucial for achieving desirable RF functionality. This uneven distribution of the distance results in variations in the incident ion concentration generated by applying a voltage to the RF electrode. Since RF functionality is affected by the distance between the ceramic plate surface and the RF electrode, variations in the distance within a product result in variations in the incidence of ions on the wafer, which in turn leads to variations in the characteristics of the wafer surface. For example, when etching a wafer surface by the incidence of ions or radicals, variations in electron density and temperature due to these variations significantly affect product performance. Therefore, a configuration that easily suppresses variations in the distance between the ceramic plate surface and the metal mesh is desirable. In this regard, according to the present invention, instead of embedding an RF electrode such as a metal mesh within the ceramic plate 12, a metal layer 16 is formed on all or part of the second surface 12b of the ceramic plate 12, and this metal layer 16 is used as the RF electrode. In this configuration, after processing the second surface 12b of the ceramic plate 12 to improve its smoothness, the metal layer 16 can be formed by an inexpensive method such as printing, plating, or sheet bonding, and used as an RF electrode. For example, the second surface 12b of the ceramic plate 12 can be given the desired flatness and parallelism (relative to the first surface 12a) by conventional machining or other methods. Then, by forming the metal layer 16 on the second surface 12b of the ceramic plate 12, the surface of the metal layer 16 can be easily parallelized relative to the first surface 12a of the ceramic plate 12. Furthermore, forming the ceramic plate 12 and the metal layer 16 in separate processes can reduce manufacturing costs. This reduces in-plane variation in the distance between the first surface 12a of the ceramic plate 12 and the metal layer 16 (RF electrode), thereby achieving desired RF functionality at low cost.

[0015] Furthermore, in semiconductor manufacturing equipment for etching, a susceptor is required to have high heat dissipation capabilities in order to quickly dissipate heat input from the plasma. However, in susceptors with high heat dissipation capabilities, expensive joining methods such as metal diffusion bonding (e.g., TCB bonding) are currently used to connect the ceramic plate and the cooling plate. Therefore, it would be advantageous to connect the ceramic plate and the cooling plate using a less expensive method. In this regard, according to the present invention, instead of joining the cooling plate to the second surface 12b of the ceramic plate 12 using an expensive joining method, the cooling plate 18 is disposed via a heat transfer space 20 sealed with a seal member 22. This heat transfer space 20 is formed by providing the seal member 22 along the outer periphery of the ceramic plate 12 and the cooling plate 18 to provide airtightness to the heat transfer space 20, enabling heat transfer via gas. Electrical connection between the metal layer 16 serving as an RF electrode and the cooling plate 18 is ensured by an RF conductive member 24 provided on the inner periphery of the seal member 22. These structures can be constructed inexpensively because they do not require expensive joining techniques such as metal diffusion bonding (e.g., TCB bonding). At the same time, heat generated in the ceramic plate 12 can be efficiently removed through the heat transfer space 20 and the adjacent cooling plate 18. Additionally, since the heat transfer space 20 is sealed with the seal member 22, the corrosive gas used for cleaning in the chamber can be prevented from penetrating into the heat transfer space 20, thereby preventing corrosion of the metal layer 16 by the corrosive gas.

[0016] The ceramic plate 12 preferably contains aluminum nitride and / or aluminum oxide, more preferably aluminum nitride, in its main portion (i.e., the ceramic substrate) other than the embedded members such as the internal electrodes 14, 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 missing portion, 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, if it is circular, the diameter is typically 150 to 450 mm, and particularly for 300 mm silicon wafers, it is typically 320 to 380 mm. The thickness of the ceramic plate 12 is typically 10 to 25 mm.

[0018] The first surface 12a and the second surface 12b of the ceramic plate 12 are preferably flat and parallel. That is, as described above, the second surface 12b of the ceramic plate 12 is given the desired flatness and parallelism (relative to the first surface 12a) by conventional machining or the like. Then, by forming the metal layer 16 on the second surface 12b of the ceramic plate 12, the in-plane variation in the distance between the first surface 12a of the ceramic plate 12 and the metal layer 16 (RF electrode) can be effectively suppressed, thereby achieving the desired RF function at low cost. For example, the flatness of the second surface 12b is preferably 50 μm or less, more preferably 20 μm or less. The parallelism of the second surface 12b relative to the first surface 12a is preferably 50 μm or less, more preferably 20 μm or less. Flatness and parallelism are terms defined in JIS B 0621-1984. That is, flatness is defined as the distance between two geometrically parallel planes when the distance between the two parallel planes is minimum when the planar feature (second surface 12b) is sandwiched between them. Also, the parallelism of the planar feature (second surface 12b) to the datum plane (corresponding to the first surface 12a) is defined as the distance between the two planes when the planar feature (second surface 12b) is sandwiched between two geometrically parallel planes that are parallel to the datum plane (corresponding to the first surface 12a).

[0019] Preferably, the ceramic plate 12 has a small diameter portion 12c having a relatively small diameter that provides the first surface 12a, and a large diameter portion 12d having a relatively large diameter that provides the second surface 12b, whereby the large diameter portion 12d and the small diameter portion 12c form a step portion 12e. A ceramic plate 12 having this shape is advantageous in that it is easy to attach a fixing member 30, which will be described later.

[0020] The internal electrode 14 is an electrode embedded in the ceramic plate 12 and includes a heater electrode, an ESC electrode, or both. The heater electrode is not particularly limited, but may be, for example, a conductive coil wired in a single stroke across the entire surface of the ceramic plate 12. Terminal rods 26 are connected to both ends of the heater electrode for power supply, and the heater electrode is connected to a heater power supply (not shown) via the terminal rods 26. The terminal rods 26 connected to the internal electrode 14 preferably extend in a direction away from the second surface 12b, across the second surface 12b, the metal layer 16, the heat transfer space 20, and the cooling plate 18. When power is supplied from the heater power supply, the heater electrode generates heat and heats a wafer placed on the surface of the ceramic plate 12. The heater electrode is not limited to a coil and may be, for example, a ribbon (a thin, elongated plate), a mesh, or a print. The ESC electrode is an abbreviation for an electrostatic chuck (ESC) electrode and is also called an electrostatic electrode. The ESC electrodes are preferably circular thin-layer electrodes having a diameter slightly smaller than that of the ceramic plate 12. For example, they may be mesh electrodes formed by weaving thin metal wires into a net shape into a sheet. Terminal rods 26 are connected to the ESC electrodes for power supply, and the terminal rods may be connected to an external power supply (not shown). In this case, too, the terminal rods 26 connected to the internal electrodes 14 serving as ESC electrodes preferably extend in a direction away from the second surface 12b, across the second surface 12b, the metal layer 16, the heat transfer space 20, and the cooling plate 18. When a voltage is applied from an external power supply, the ESC electrodes chuck a wafer placed on the surface of the ceramic plate 12 by the Johnsen-Rahbek force. The internal electrode 14 may include both a heater electrode and an ESC electrode. In this case, the heater electrode and the ESC electrode may be embedded at different depths in the ceramic plate 12 as separate internal electrodes 14. Alternatively, only one of the heater electrode and the ESC electrode may be embedded in the ceramic plate 12.

[0021] The metal layer 16 is provided as an RF electrode on all or part of the second surface 12b of the ceramic plate 12. The thickness of the metal layer 16 is preferably 3 to 500 μm, more preferably 20 to 300 μm, and even more preferably 50 to 200 μm. Such a thin metal layer 16 can easily fit the surface shape of the second surface 12b of the ceramic plate 12, thereby reducing the likelihood of deformation such as waviness. This effectively reduces in-plane variations in the distance between the first surface 12a of the ceramic plate 12 and the metal layer 16 (RF electrode). In this sense, the metal layer 16 is preferably a layer formed by printing or plating. Alternatively, the metal layer 16 may be a metal sheet, which can be bonded to the second surface 12b using an inexpensive method such as an adhesive.

[0022] The material of the metal layer 16 is not particularly limited as long as it can function as an RF electrode, but it is preferably made of a metal such as molybdenum, tungsten, or zirconium, or an alloy thereof, whose thermal expansion coefficient is close to that of aluminum nitride or aluminum oxide.

[0023] The cooling plate 18 is a disk-shaped plate provided at a predetermined distance from the second surface 12b of the ceramic plate 12. The cooling plate 18 may have a cooling plate configuration commonly used for ceramic heaters and electrostatic chucks. The cooling plate 18 is preferably made of a metal such as aluminum or an aluminum alloy from the viewpoints of RF supply, heat dissipation, and cost. However, the cooling plate 18 may also be made of a metal matrix composite (MMC) such as SiSiCTi (a composite material containing Si, SiC, and Ti). A typical cooling plate 18 has an internal space that provides a flow path 18a for flowing a coolant within the cooling plate 18. For example, the flow path 18a may be connected to a coolant supply path and a coolant discharge path (not shown), and the coolant discharged from the coolant discharge path may be temperature-adjusted and then returned to the coolant supply path.

[0024] Preferably, the cooling plate 18 has an opening hole for passing the terminal rod 26, and the surface of the opening hole is covered with an insulating member 28, thereby insulating the terminal rod 26 from the cooling plate 18 (made of, for example, metal).

[0025] The heat transfer space 20 is a space that exists between the metal layer 16 and the cooling plate 18 and that allows heat transfer via gas. A typical heat transfer space 20 is an enclosed space surrounded by the ceramic plate 12 having the metal layer 16 on its second surface 12b, the cooling plate 18, and a sealing member 22, and during use, the heat transfer space 20 is filled with a gas for heat transfer. A preferred example of the gas filled in the heat transfer space 20 is helium (He).

[0026] The seal member 22 is provided between the ceramic plate 12 and the cooling plate 18, along the outer peripheries of the ceramic plate 12 and the cooling plate 18, to provide airtightness to the heat transfer space 20. By providing airtightness to the heat transfer space 20 in this manner, it is possible to prevent the corrosive gas used for cleaning in the chamber from entering the heat transfer space 20, thereby preventing corrosion of the metal layer 16 by the corrosive gas. The seal member 22 is not particularly limited as long as it has the heat resistance required for the susceptor 10, and common, inexpensive seal members such as O-rings and metal seals can be used. Therefore, the present invention is also advantageous in terms of cost because it does not require the use of expensive seal parts with special shapes and / or made of special materials as the seal member 22.

[0027] The RF conductive member 24 is a member that ensures electrical connection between the metal layer 16 and the cooling plate 18 and is provided between the ceramic plate 12 and the cooling plate 18, at a position on the inner periphery of the seal member 22. That is, in order for the metal layer 16 to function as an RF electrode, the metal layer 16 needs to be connected to an RF power source (not shown) or grounded. However, because the heat transfer space 20 in the susceptor 10 is located directly below the metal layer 16, a means for supplying RF to the metal layer 16 on the cooling plate 18 side is required. In this regard, the presence of the RF conductive member 24 between the metal layer 16 and the cooling plate 18 ensures electrical connection between the metal layer 16 and the cooling plate 18. Therefore, the metal layer 16 can function as an RF electrode by connecting the cooling plate 18 to an RF power source (not shown) or grounding it.

[0028] The RF conductive member 24 is not particularly limited as long as it can ensure electrical connection between the metal layer 16 and the cooling plate 18, but preferably includes a spirally wound, elongated metal part as shown in Fig. 3. This elongated metal part may be in the shape of a plate, a rod, or any other shape. It is preferable to use a commercially available spiral spring gasket as the spirally wound, elongated metal part because it is inexpensive.

[0029] The susceptor 10 preferably further includes a fixing member 30 provided along the outer periphery of the susceptor 10. The fixing member 30 is preferably configured to fix the ceramic plate 12, the metal layer 16, the seal member 22, the RF conductive member 24, and the cooling plate 18 in a direction that brings them into close contact with each other. For example, if the ceramic plate 12 has a small-diameter portion 12c and a large-diameter portion 12d, thereby forming a stepped portion 12e, as described above, the fixing member 30 is preferably configured to be engageable with the stepped portion 12e. The fixing member 30 is not particularly limited as long as it can fix the ceramic plate 12, the metal layer 16, the seal member 22, the RF conductive member 24, and the cooling plate 18 in a direction that brings them into close contact with each other. However, known fixing means such as a clamp or a ring-shaped member (provided along the outer periphery of the ceramic plate 12) may be used. In the case of a clamp, the ceramic plate 12 (e.g., the portion extending as the stepped portion 12e of the large-diameter portion 12d), the seal member 22, the cooling plate 18, etc. may be clamped and fixed by the clamp's fixing mechanism. In the case of a ring-shaped member, the ring-shaped member is placed on the ceramic plate 12 (for example, the portion extending as the stepped portion 12e of the large diameter portion 12d), and this ring-shaped member is fixed to the cooling plate 18 or other device component with a fastening means such as a screw so as to press the ring-shaped member toward the cooling plate 18.

Claims

1. a circular ceramic plate having a first surface and a second surface; an internal electrode embedded in the ceramic plate; a metal layer provided as an RF electrode on all or part of the second surface of the ceramic plate; a disk-shaped cooling plate provided at a predetermined distance from the second surface of the ceramic plate; a heat transfer space that exists between the metal layer and the cooling plate and that allows heat transfer via gas; a sealing member provided between the ceramic plate and the cooling plate along the outer periphery of the ceramic plate and the cooling plate to provide airtightness to the heat transfer space; an RF conductive member provided between the ceramic plate and the cooling plate at a position on the inner circumferential side of the sealing member, the RF conductive member ensuring electrical connection between the metal layer and the cooling plate; A susceptor comprising:

2. 2. The susceptor according to claim 1, wherein the metal layer has a thickness of 3 to 500 μm.

3. 3. The susceptor according to claim 1, wherein the metal layer is a layer formed by printing or plating, or is a metal sheet.

4. The susceptor of claim 1 , wherein the ceramic plate comprises aluminum nitride and / or aluminum oxide.

5. 3. The susceptor according to claim 1, wherein the cooling plate is made of a metal or a metal matrix composite material.

6. The susceptor of claim 1 or 2, wherein the RF conductive member comprises an elongated spirally wound metal component.

7. 3. The susceptor according to claim 1, further comprising a terminal rod connected to the internal electrode and extending in a direction away from the second surface across the second surface, the metal layer, the heat transfer space and the cooling plate.

8. 8. The susceptor according to claim 7, wherein the cooling plate has an opening hole for passing the terminal rod therethrough, and the surface of the opening hole is covered with an insulating material, thereby insulating the terminal rod from the cooling plate.

9. The susceptor according to claim 1 or 2, wherein the cooling plate has an internal space for allowing a cooling medium to flow inside the cooling plate.

10. 3. The susceptor according to claim 1, further comprising a fixing member provided along an outer periphery of the susceptor, the fixing member fixing the ceramic plate, the metal layer, the sealing member, the RF conductive member, and the cooling plate in a direction in which they are in close contact with each other.

11. the ceramic plate has a small diameter portion having a relatively small diameter that provides the first surface and a large diameter portion having a relatively large diameter that provides the second surface, whereby the large diameter portion and the small diameter portion form a step portion; The susceptor according to claim 10 , wherein the fixing member is configured to be engageable with the stepped portion.

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