Wafer carrying table

Abstract

A wafer placement table 10 is provided with: a ceramic plate 20 having at least a wafer placement section 22 on the upper surface thereof; a cooling plate (30) that is joined to the lower surface of the ceramic plate (20) and that has a refrigerant flow path (32); gas common paths (51b, 52b, 53b) that are provided so as to be more upward than the refrigerant flow path (32); gas introduction paths (51a, 52a, 53a) leading from the lower surface of the cooling plate (30) to each of the gas common paths (51b, 52b, 53b); and a plurality of gas distribution paths (51e, 52e, 53e) provided to each of the gas common paths (51b, 52b, 53b). A gas distribution path (53e) disposed on the outermost periphery of the ceramic plate (20) is provided at a position that does not overlap the refrigerant flow path (32) in plan view.

Description

Technical Field This invention relates to a wafer mounting stage. Background Technology Conventionally, wafer mounting stages are known to include: a ceramic plate having a wafer mounting section on its upper surface; a cooling plate joined to the lower surface of the ceramic plate; and a refrigerant flow path disposed on the cooling plate. For example, in the wafer mounting stage of Patent Document 1, gas introduced from the lower surface of the cooling plate is supplied to the upper surface of the ceramic plate via a gas general path that is C-shaped in plan view and disposed above the refrigerant flow path, through a gas distribution path that runs vertically through the ceramic plate via multiple gas branches extending radially outward from the gas general path. Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-141116 Summary of the Invention However, when using a wafer stage, significant stress can sometimes occur in the gas distribution path located at the outermost periphery of the stage. Patent Document 1 does not consider this, so cracks may form in the wafer stage. In particular, such cracks are more likely to occur when processing wafers using high-power plasma. The present invention was implemented to solve the above-mentioned problems, and its main purpose is to prevent cracks from forming on the wafer stage.

[0001] The wafer stage of the present invention includes: A ceramic plate, the upper surface of which has at least a wafer mounting portion; and A cooling plate, which is joined to the lower surface of the ceramic plate, and has a refrigerant flow path. The wafer stage is characterized by having: A general gas path is located inside the wafer stage, above the refrigerant flow path. A gas inlet path, which extends from the lower surface of the cooling plate to the general gas path; and A gas distribution path, wherein multiple gas distribution paths are provided relative to one general gas path, and extending from the general gas path to the upper surface of the ceramic plate. The outermost gas distribution path in the gas distribution path is located at the outermost periphery of the ceramic plate and is positioned so as not to overlap with the refrigerant flow path when viewed from above. In this wafer stage, the outermost gas distribution path, located at the outermost periphery of the ceramic plate, is positioned so as not to overlap with the refrigerant flow path when viewed from above. During use, the outermost periphery of the wafer stage is prone to significant stress. If the outermost gas distribution path overlaps with the refrigerant flow path when viewed from above, the thinner layer directly above the refrigerant flow path is more susceptible to deformation, making cracks more likely to form near the outermost gas distribution path. However, here, because the outermost gas distribution path is positioned so as not to overlap with the refrigerant flow path when viewed from above, the stress near the outermost gas distribution path is reduced, preventing crack formation. It should be noted that in this specification, terms such as up and down, left and right, and front and back are sometimes used to describe the invention. However, these terms are merely relative positional relationships. Therefore, when the orientation of the wafer stage is changed, sometimes up and down becomes left and right, or left and right becomes up and down, and such situations are also included within the scope of this invention.

[0002] In the aforementioned wafer stage (the wafer stage described in [1] above), the gas distribution path can be connected to the general gas path via a gas branch. Accordingly, for example, when viewed from above, the gas branch crosses the refrigerant flow path from the general gas path and reaches a position that does not overlap with the refrigerant flow path, making it easier to position the gas distribution path in a position that does not overlap with the refrigerant flow path.

[0003] In the aforementioned wafer stage (the wafer stage described in [1] or [2] above), multiple gas general paths can be arranged in a concentric circle manner, and the outermost gas distribution path can be connected to the outermost gas general path among the multiple gas general paths. Accordingly, the number of gas distribution paths that are open on the upper surface of the ceramic plate can be increased. In addition, the gas distribution path connected to the outermost gas general path is prone to generating large stress, therefore, the application of the present invention is of great significance.

[0004] In the aforementioned wafer stage (the wafer stage described in any of [1] to [3] above), the width of at least the portion of the gas distribution path connected to the gas common path may be wider than the width of the gas common path. In this case, the wider portion of the gas distribution path connected to the gas common path is prone to generating greater stress, therefore, the application of the present invention is of great significance.

[0005] In the aforementioned wafer stage (the wafer stage described in any of [1] to [4] above), the cooling plate can be formed of a composite material of metal and ceramic. This composite material is relatively fragile and prone to cracking; therefore, the application of this invention is of great significance.

[0006] In the above-mentioned wafer stage (the wafer stage described in any of [1] to [5] above), a circular wafer placement part and an annular focusing ring placement part surrounding the wafer placement part may be provided on the upper surface of the ceramic plate, and the outermost gas distribution path may be a path from the gas general path to the focusing ring placement part.

[0007] In the above-mentioned wafer placement stage (the wafer placement stage described in any of [1] to [5] above), a circular wafer placement part may be provided on the upper surface of the ceramic plate, and the outermost gas distribution path may be a path from the gas general path to the wafer placement part. Attached Figure Description Figure 1 This is a longitudinal cross-sectional view of the wafer stage 10. Figure 2 yes Figure 1 A-A cross-sectional view. Figure 3 This is a plan view of the chip placement stage 10. Figure 4 yes Figure 3 A magnified view of a portion of the image. Figure 5 This is a three-dimensional view of the gas transfer channel 53d of the cooling plate 30. Figure 6 This is an explanatory diagram of a variation of the gas supply path 53. Figure 7 This is an explanatory diagram of a variation of the gas supply path 53. Figure 8 This is a longitudinal cross-sectional view of the wafer stage 110. Detailed Implementation Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a longitudinal cross-sectional view of the wafer stage 10 (a cross-sectional view of the wafer stage 10 when it is cut along a plane including the central axis of the wafer stage 10). Figure 2 yes Figure 1 A-A cross-sectional view, Figure 3 This is a plan view of the chip stage 10. Figure 4 yes Figure 3 A magnified view of a portion of the image. Figure 5 This is a three-dimensional view of the area near the gas transfer channel 53d of the cooling plate 30. It should be noted that... Figure 2 The diagrams of the components other than the refrigerant flow path 32 are omitted. The wafer stage 10 is a component used for performing CVD, etching, and other processes on the wafer W using plasma. The wafer stage 10 includes a ceramic plate 20, a cooling plate 30, and a metal bonding layer 40. The ceramic plate 20 is formed of ceramic materials such as alumina and aluminum nitride, and has a circular wafer placement portion 22 on its upper surface. A wafer W is placed in the wafer placement portion 22. A sealing strip 22a is formed along the outer edge of the wafer placement portion 22, and multiple small circular protrusions 22b are formed on the entire surface. The sealing strip 22a and the small circular protrusions 22b have the same height, for example, several μm to tens of μm. The electrode 23 is a planar mesh electrode used as an electrostatic electrode, capable of applying a DC voltage. When a DC voltage is applied to the electrode 23, the wafer W is adsorbed and fixed to the wafer placement portion 22 (specifically, the upper surface of the sealing strip 22a and the upper surface of the small circular protrusions 22b) by electrostatic attraction; when the DC voltage is released, the wafer W is released from adsorption and fixation in the wafer placement portion 22. It should be noted that the portion of the wafer placement portion 22 without the sealing strip 22a or the small circular protrusions 22b is referred to as the reference surface 22c. Figure 3 The image shows a small circular protrusion 22b provided in the area surrounded by a single-dot dashed line in the wafer placement section 22. However, in reality, the small circular protrusion 22b is provided on the entire surface of the area surrounded by the sealing strip 22a in the wafer placement section 22. On the upper surface of the ceramic plate 20, in addition to the wafer placement section 22, an annular focusing ring placement section 24 is also provided around the wafer placement section 22. Hereinafter, the focusing ring is sometimes simply referred to as "FR". The FR placement section 24 is one level lower than the wafer placement section 22. An annular focusing ring 60 is placed in the FR placement section 24. A circumferential groove 60a is provided above the inner side of the focusing ring 60 to prevent it from contacting the wafer W. The FR placement section 24 has an annular groove 24a and FR support surfaces 24b provided on the inner and outer circumferential sides of the groove 24a. The depth of the groove 24a is, for example, several μm to tens of μm. The FR support surface 24b is formed into an annular shape and directly contacts the focusing ring 60 to support the focusing ring 60. The cooling plate 30 is a circular plate component made of a brittle, conductive material. The cooling plate 30 has an internal refrigerant flow path 32 for refrigerant circulation. For example... Figure 2 As shown, the refrigerant flow path 32, viewed from top view, is arranged in a single stroke from one end (inlet) to the other end (outlet) across the entire surface of the ceramic plate 20. In this embodiment, the refrigerant flow path 32 is formed in a vortex shape when viewed from top view. For example, the cooling plate 30 can be manufactured with reference to Japanese Patent No. 5666748. Refrigerant is supplied to one end (inlet) of the refrigerant flow path 32 through a refrigerant circulation device (not shown), and after passing through the refrigerant flow path 32, it is discharged from the other end (outlet) of the refrigerant flow path 32, returning to the refrigerant circulation device. The refrigerant circulation device can adjust the refrigerant to the desired temperature. The refrigerant is preferably a liquid, and preferably electrically insulating. Examples of electrically insulating liquids include fluorinated inactive liquids. Examples of brittle conductive materials include composites of metals and ceramics. Examples of metal-ceramic composites include metal matrix composites (MMC) and ceramic matrix composites (CMC). Specific examples of such composites include materials containing Si, SiC, and Ti; materials obtained by impregnating Al and / or Si into porous SiC; and composites of Al₂O₃ and TiC. Materials containing Si, SiC, and Ti are referred to as SiSiCTi; materials obtained by impregnating Al into porous SiC are referred to as AlSiC; and materials obtained by impregnating Si into porous SiC are referred to as SiSiC. As the conductive material for the cooling plate 30, a material with a coefficient of thermal expansion close to that of the ceramic plate 20 is preferred. If the ceramic plate 20 is made of alumina, the cooling plate 30 is preferably made of SiSiCTi or AlSiC. This is because the coefficients of thermal expansion of SiSiCTi and AlSiC are approximately the same as those of alumina. For example, a circular plate component made of SiSiCTi can be manufactured as follows: First, silicon carbide, metallic Si, and metallic Ti are mixed to prepare a powder mixture. Next, the obtained powder mixture is uniaxially pressurized to form a circular plate-shaped molded body, which is then hot-pressed and sintered in an inactive atmosphere to obtain a circular plate component made of SiSiCTi. The metal bonding layer 40 bonds the lower surface of the ceramic plate 20 and the upper surface of the cooling plate 30. The metal bonding layer 40 can be, for example, a layer formed of solder or brazing filler metal. For example, the metal bonding layer 40 can be formed using TCB (Thermal Compression Bonding). TCB refers to a known method of pressure bonding two components by sandwiching a metal bonding material between them and heating the materials to a temperature below their solidus temperature. The wafer stage 10 has gas supply paths 51, 52, and 53. Gas supply paths 51 and 52 supply gas to the space surrounded by the wafer W, sealing ring 22a, small circular protrusion 22b, and reference surface 22c. Gas supply path 53 supplies gas to the space surrounded by focusing ring 60 and groove 24a. Gas supply path 51 consists of a gas inlet path 51a, a general gas path 51b, a gas branch 51c, a gas transfer groove 51d, and a gas distribution path 51e. Gas supply path 52 consists of a gas inlet path 52a, a general gas path 52b, a gas branch 52c, a gas transfer groove 52d, and a gas distribution path 52e. Gas supply path 53 consists of a gas inlet path 53a, a general gas path 53b, a gas branch 53c, a gas transfer groove 53d, and a gas distribution path 53e. Gas universal paths 51b, 52b, and 53b are concentric annular paths with different diameters when viewed from above. They are formed inside the wafer stage 10, above the coolant flow path 32. In this embodiment, they are formed at the interface between the cooling plate 30 and the metal bonding layer 40, specifically on the upper surface of the cooling plate 30. Gas universal path 51b is located at the innermost periphery, and gas universal path 53b is located at the outermost periphery. Gas introduction paths 51a, 52a, and 53b are configured to lead from the lower surface of the cooling plate 30 to each gas universal path 51b, 52b, and 53b in a manner that does not intersect with the coolant flow path 32. The outermost gas general path 53b has multiple gas branches 53c extending outward in a radial direction. Each gas branch 53c is connected to a gas distribution path 53e that runs vertically through the ceramic plate 20. The connection between the gas branch 53c and the gas distribution path 53e is a gas transfer groove 53d formed by a circular channel. The diameter (width) of the gas transfer groove 53d is greater than the width of the gas distribution path 53e and the width of the gas general path 53b, for example, 1.5 to 2.5 times their width. Similarly, the innermost gas general path 51b, like the gas general path 53b, is also connected to the gas distribution path 51e via gas branches 51c and the gas transfer groove 51d. Similarly, the gas general path 52b, like the gas general path 53b, is also connected to the gas distribution path 52e via gas branches 52c and the gas transfer groove 52d. like Figure 3 and Figure 4 As shown, among the multiple gas distribution paths 51e, 52e, and 53e, the outermost gas distribution path 53e (outermost gas distribution path) located on the periphery of the ceramic plate 20 is positioned where it does not overlap with the refrigerant flow path 32 when viewed from above. The gas transfer groove 53d is also positioned where it does not overlap with the refrigerant flow path 32 when viewed from above. At this position where it does not overlap with the refrigerant flow path 32 when viewed from above, the cooling plate 30 is thicker. Therefore, even if a gas transfer groove 53d with a larger diameter is provided at this position, the stress generated by the gas transfer groove 53d can be suppressed to a smaller extent. In contrast, at the position where it overlaps with the refrigerant flow path 32 when viewed from above, the cooling plate 30 is thinner. Therefore, if a gas transfer groove 53d is provided at this position, a larger stress is generated in the gas transfer groove 53d. The stress generated in gas transfer channels 51d and 52d is less than the stress generated in the outermost gas transfer channel 53d. Therefore, gas transfer channels 51d and 52d or gas distribution paths 51e and 52e can be located at a position that overlaps with the refrigerant flow path 32 when viewed from above; however, it is preferable to locate them at a position that does not overlap with the refrigerant flow path 32. Additionally, the widths of the gas general paths 51b, 52b, and 53b are relatively narrow; therefore, they can be located at a position that overlaps with the refrigerant flow path 32 when viewed from above; however, it is preferable to locate them at a position that does not overlap with the refrigerant flow path 32. Next, an example of using the wafer stage 10 will be described. The wafer stage 10 is fixed inside a semiconductor process chamber (not shown). A focusing ring 60 is placed in the FR placement section 24, and a wafer W is placed in the wafer placement section 22. In this state, a DC voltage is applied to the electrode 23, causing the wafer W to adhere to the wafer placement section 22. At the same time, gas (here, a heat-conducting gas such as He) is supplied to the gas supply paths 51, 52, and 53. As a result, heat conduction between the wafer W and the upper surface of the ceramic plate 20, and between the focusing ring 60 and the upper surface of the ceramic plate 20, becomes good. Then, the interior of the chamber is set to a predetermined vacuum atmosphere (or reduced pressure atmosphere), and while supplying process gas from a nozzle located at the top of the chamber, an RF voltage is applied to the cooling plate 30. Plasma is then generated between the wafer W and the nozzle. Then, CVD film deposition or etching is performed on the wafer W using this plasma. It should be noted that the focusing ring 60 is also consumed during the plasma processing of wafer W. However, the focusing ring 60 is thicker than wafer W. Therefore, the focusing ring 60 is replaced after processing multiple wafers W. When processing wafer W using high-power plasma, efficient cooling of wafer W is required. In the wafer stage 10, a metal bonding layer 40 with high thermal conductivity is used as the bonding layer between the ceramic plate 20 and the cooling plate 30 instead of a resin layer with low thermal conductivity. Therefore, the ability to remove heat from wafer W (heat removal capacity) is high. In addition, since the difference in thermal expansion between the ceramic plate 20 and the cooling plate 30 is small, even if the stress relief of the metal bonding layer 40 is low, it is less likely to cause obstruction. Furthermore, since the upper surface of the ceramic plate 20 becomes high-temperature and the lower surface is cooled to a low-temperature, the upper surface of the ceramic plate 20 is prone to stretching, and the wafer stage 10 tends to convex upwards. Therefore, at the outermost periphery of the wafer stage 10, deformation increases and stress is easily generated. In this embodiment, the outermost gas distribution path 53e is provided at a position that does not overlap with the refrigerant flow path 32 when viewed from above (the position where the thickness of the cooling plate 32 is thicker), so the stress near the gas distribution path 53e is reduced. In the wafer stage 10 described above, the gas distribution path 53e disposed on the outermost periphery of the ceramic plate 20 is positioned so as not to overlap with the refrigerant flow path 32 when viewed from above. During use, the outermost periphery of the wafer stage 10 is prone to significant stress. When the outermost gas distribution path 53e overlaps with the refrigerant flow path 32 when viewed from above, the cooling plate 30 directly above the refrigerant flow path 32 is relatively thin and easily deformed, thus cracks are prone to form near the gas distribution path 53e. However, in this embodiment, since the gas distribution path 53e is positioned so as not to overlap with the refrigerant flow path 32 when viewed from above (where the cooling plate 30 is relatively thick), the stress near the gas distribution path 53e is reduced, preventing crack formation. Furthermore, the diameter (width) of the gas transfer groove 53d, which connects to the gas branch 53c of the general gas path 53b in the outermost gas distribution path 53e, is greater than the width of both the general gas path 53b and the gas branch 53c. Therefore, relatively large stresses are easily generated in the gas transfer groove 53d; however, by applying this invention, the stress can be suppressed to a lesser extent. Furthermore, the outermost gas distribution path 53e is connected to the general gas path 53b via a gas branch 53c extending radially. Therefore, even if a refrigerant flow path 32 is provided near the general gas path 53b, the gas distribution path 53e and the gas transfer channel 53d can be easily positioned in a location that does not overlap with the refrigerant flow path 32, by having the gas branch 53c traverse the refrigerant flow path 32 when viewed from above and reaching a position where it does not overlap with the refrigerant flow path 32. Furthermore, the gas general paths 51b, 52b, and 53b are arranged in a concentric circle and are connected to multiple gas distribution paths 51e, 52e, and 53e, respectively. Therefore, gas can be supplied from many locations on the upper surface of the ceramic plate 20. In addition, since the gas distribution path 53e, which is connected to the outermost gas general path 53b, is prone to generating large stress, the application of this invention is of great significance. Furthermore, the cooling plate 30 is formed of a composite material of metal and ceramic. This composite material is relatively fragile and prone to cracking; therefore, the application of this invention is of great significance. Furthermore, a circular wafer placement section 22 and an annular FR placement section 24 surrounding the wafer placement section 22 are provided on the upper surface of the ceramic plate 20, and the outermost gas distribution path 53e is the path from the gas general path 53b to the FR placement section 24. In this ceramic plate 20 equipped with the FR placement section 24, the path for supplying gas to the FR placement section 24 is located at the outermost periphery. 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 embodiments, the gas general path 53b and the gas distribution path 53e (gas transfer channel 53d) are connected by a gas branch 53c extending radially outward from the gas general path 53b, but this is not particularly limited to this. For example, such as Figure 6 As shown, the gas general path 53b and the gas distribution path 53e (gas transfer channel 53d) can be connected by a gas branch 53c extending inward from the annular gas general path 53b. In this case, the gas distribution path 53e (gas transfer channel 53d) is also positioned in a location that does not overlap with the refrigerant flow path 32 when viewed from above. Alternatively, as... Figure 7As shown, at least a portion of the circular gas general path 53b, viewed from above, can be positioned in a location that does not overlap with the refrigerant flow path 32, and the gas transfer channel 53d and the gas distribution path 53e are directly connected thereto. Figure 6 and Figure 7 In this document, the same symbols are used to mark the same constituent elements as in the above-described embodiments. The above embodiments illustrate a case where the upper surface of the ceramic plate 20 has a wafer mounting portion 22 and an FR mounting portion 24, but are not particularly limited to this. For example, like... Figure 8 As shown in the wafer stage 110, the upper surface of the ceramic plate 20 may have a wafer placement section 22, but not an FR placement section. The wafer stage 110 has two gas supply paths 51 and 52. Gas supply path 51 is composed of a gas inlet path 51a, a gas general path 51b, a gas branch section 51c, a gas transfer channel 51d, and a gas distribution path 51e, similar to the embodiment described above. Gas supply path 52 is also composed of a gas inlet path 52a, a gas general path 52b, a gas branch section 52c, a gas transfer channel 52d, and a gas distribution path 52e, similar to the embodiment described above. However, here, since the gas distribution path 52e is the outermost gas distribution path, the gas distribution path 52e and the gas transfer channel 52d are positioned so as not to overlap with the refrigerant flow path 32 when viewed from above. Accordingly, cracks can be prevented from forming in the wafer stage 110. Figure 8 In this document, the same symbols are used to mark the same constituent elements as in the above-described embodiments. In the above embodiments, the gas general paths 51b, 52b, 53b, gas branches 51c, 52c, 53c, and gas transfer channels 51d, 52d, 53d are disposed at the interface between the cooling plate 30 and the metal bonding layer 40 (specifically, on the upper surface of the cooling plate 30), but are not particularly limited thereto. For example, the gas general paths 51b, 52b, 53b, gas branches 51c, 52c, 53c, and gas transfer channels 51d, 52d, 53d can be disposed on the metal bonding layer 40, or they can be disposed at the interface between the ceramic plate 20 and the metal bonding layer 40 (specifically, on the lower surface of the ceramic plate 20). In the above embodiments, the gas universal paths 51b, 52b, and 53b are shaped as annular when viewed from above, but are not particularly limited thereto. For example, the gas universal paths 51b, 52b, and 53b can be shaped as an arc (e.g., C-shaped) when viewed from above, or they can be straight, or they can be zigzag (e.g., along the sides of a polygon). In the above embodiments, each of the gas universal paths 51b, 52b, and 53b is connected to one gas introduction path 51a, 52a, and 53a, but this is not particularly limited. For example, multiple gas introduction paths 51a, 52a, and 53a may be connected to each of the gas universal paths 51b, 52b, and 53b. However, this number is preferably less than the number of gas distribution paths connected to one gas universal path. In the above embodiments, the refrigerant flow path 32 is formed in a vortex shape when viewed from above, but it is not particularly limited to this. For example, the refrigerant flow path 32 can be formed in a serrated shape when viewed from above. In the above embodiments, the cooling plate 30 is made of a composite material of metal and ceramic; however, it can be made of other materials (such as aluminum, aluminum alloy, etc.). In the above embodiments, an electrostatic electrode is exemplified as the electrode 23 built into the ceramic plate 20, but it is not particularly limited to this. For example, instead of electrode 23 or other than electrode 23, a heater electrode (resistive heating element) or an RF electrode may be built into the ceramic plate 20. In the above embodiments, the ceramic plate 20 and the cooling plate 30 are joined by a metal bonding layer 40. However, a resin adhesive layer can be used instead of the metal bonding layer 40. Industrial availability The present invention can be used in apparatus for plasma processing, for example, wafers. Symbol Explanation 10, 110 Wafer stage, 20 Ceramic plate, 22 Wafer placement section, 22a Sealing strip, 22b Circular protrusion, 22c Reference surface, 23 Electrode, 24FR placement section, 24a Groove, 24b Focusing ring support surface, 30 Cooling plate, 32 Refrigerant flow path, 40 Metal bonding layer, 51, 52, 53 Gas supply path, 51a, 52a, 53a Gas introduction path, 51b, 52b, 53b Gas general path, 51c, 52c, 53c Gas branch section, 51d, 52d, 53d Gas transfer trench, 51e, 52e, 53e Gas distribution path, 60 Focusing ring, 60a Circumferential groove, W Wafer.

Claims

1. A wafer loading platform comprising: a ceramic plate having at least a wafer placement portion on its upper surface; and a cooling plate, which is joined to the lower surface of the ceramic plate and has a coolant flow path, The wafer placement table is characterized by comprising: a common gas path provided above the refrigerant flow path within the wafer placement table; a gas introduction path extending from the lower surface of the cooling plate to the gas common path; and a gas distribution path, the gas distribution path being provided in plurality with respect to one gas common path and extending from the gas common path to the upper surface of the ceramic plate; The outermost peripheral gas distribution path arranged at the outermost periphery of the ceramic plate among the gas distribution paths is provided at a position that does not overlap with the coolant flow path in a plan view.

2. The wafer stage according to claim 1, wherein: The gas distribution path is connected to the gas common path via a gas branch portion.

3. The wafer placement table according to claim 1 or 2, wherein: The common gas paths are arranged in a plurality of concentric circles. The outermost peripheral gas distribution path is connected to the outermost gas common path among the plurality of gas common paths.

4. The wafer placement table according to claim 1 or 2, wherein: At least a portion of the gas distribution path connected to the gas common path has a width wider than a width of the gas common path.

5. The wafer placement table according to claim 1 or 2, wherein: The cooling plate is formed of a composite material of metal and ceramic.

6. The wafer placement table according to claim 1 or 2, wherein: A circular wafer placement portion and an annular focus ring placement portion surrounding the wafer placement portion are provided on the upper surface of the ceramic plate. The outermost peripheral gas distribution path is a path from the gas common path to the focus ring mounting portion.

7. The wafer placement table according to claim 1 or 2, wherein: A circular wafer placement portion is provided on the upper surface of the ceramic plate. The outermost peripheral gas distribution path is a path from the gas common path to the wafer placement portion.

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