Wafer placement table

Abstract

A wafer mounting table 10 comprises a ceramic plate 20 having a wafer mounting surface 22 on the upper surface, and a cooling plate provided on the lower surface of the ceramic plate 20. The cooling plate is formed of a material having a thermal conductivity lower than that of Al. The length between the upper surface of a refrigerant flow path 32 and the wafer mounting surface 22 is irregular, having long locations and short locations. The flow path cross section area of the refrigerant flow path 32 is irregular, having small locations and large locations. The aspect ratio of the refrigerant flow path 32, which is the ratio of the longitudinal length to the lateral length in the flow path cross section, is irregular, having small locations and large locations.

Description

[Technical field]

[0001] The present invention relates to a wafer stage. [Background technology]

[0002] Conventionally, a wafer mounting table is known that includes a ceramic plate having a wafer mounting surface on the upper surface, a cooling plate provided on the lower surface of the ceramic plate, and a coolant flow path built into the cooling plate. For example, Patent Document 1 discloses a wafer mounting table in which the cooling plate is formed of a material with high thermal conductivity such as Al, in which the distance between the upper surface of the coolant flow path and the wafer mounting surface is constant from the inlet to the outlet of the coolant flow path, and the cross-sectional shape of the coolant flow path varies depending on the position of the coolant flow path. Patent Document 1 describes that the cross-sectional area of ​​the flow path corresponding to the relatively high temperature part of the wafer mounting surface is smaller than the cross-sectional area of ​​the flow path corresponding to the relatively low temperature part of the wafer mounting surface. It also describes that the width of the upper surface of the coolant flow path from the inlet to the outlet of the coolant flow path is constant, and the length of the coolant flow path in the height direction is shorter at the position corresponding to the relatively high temperature part of the wafer mounting surface than at the position corresponding to the relatively low temperature part of the wafer mounting surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-28961 Summary of the Invention [Problem to be solved by the invention]

[0004] However, while the configuration of Patent Document 1 can suppress uneven heat dissipation in the refrigerant flow path when the cooling plate is made of a material with good thermal conductivity such as Al, it cannot sufficiently suppress uneven heat dissipation when the cooling plate is made of a material with lower thermal conductivity than Al.

[0005] The present invention has been made to solve these problems, and its main object is to suppress temperature unevenness on the wafer mounting surface of a wafer mounting table whose cooling plate is made of a material with a lower thermal conductivity than Al. [Means for solving the problem]

[0006] [1] The wafer mounting table of the present invention comprises: a ceramic plate having a wafer mounting surface on an upper surface thereof; a cooling plate provided on a lower surface of the ceramic plate; A refrigerant flow path built into the cooling plate; A wafer mounting table comprising: The cooling plate is made of a material having a lower thermal conductivity than Al, The length between the upper surface of the coolant flow path and the wafer placement surface is not constant, but has long and short portions. The cross-sectional area of ​​the refrigerant flow path is not constant but has small and large areas. The aspect ratio, which is the ratio of the vertical length to the horizontal length in the flow passage cross section of the refrigerant flow passage, is not constant and has small parts and large parts. It is something.

[0007] In this wafer mounting table, the length between the upper surface of the coolant flow path and the wafer mounting surface is not constant, and there are long and short parts. The short parts have a higher cooling efficiency than the long parts. In addition, the cross-sectional area of ​​the coolant flow path is not constant, and there are small and large parts. The flow rate is faster in the small cross-sectional area of ​​the coolant flow path than in the large cross-sectional area, and the cooling efficiency is higher. In addition, the aspect ratio of the coolant flow path (the ratio of the vertical length to the horizontal length in the cross-sectional area of ​​the coolant flow path) is not constant, and there are small and large parts. When the cooling plate is made of a material with a lower thermal conductivity than Al, the cooling efficiency is higher as the aspect ratio is smaller, assuming that the cross-sectional area of ​​the coolant flow path is the same. From the above, in a wafer mounting table in which the cooling plate is made of a material with a lower thermal conductivity than Al, the temperature unevenness of the wafer mounting surface can be suppressed by adjusting the length between the upper surface of the coolant flow path and the wafer mounting surface, the cross-sectional area of ​​the coolant flow path, and the aspect ratio of the cross-sectional area.

[0008] [2] In the wafer stage of the present invention (the wafer stage described in [1] above), the thermal conductivity of the cooling plate may be 50 W / mK or less. In this case, assuming that the cross-sectional area of ​​the coolant flow path is the same, the smaller the aspect ratio, the more significantly the cooling efficiency increases.

[0009] [3] In the wafer mounting table of the present invention (the wafer mounting table described in [1] or [2] above), the length between the upper surface of the coolant flow passage and the wafer mounting surface, the flow passage cross-sectional area of ​​the coolant flow passage, and the aspect ratio of the flow passage cross-section of the coolant flow passage may be set so that the heat exchange efficiency of the outer periphery region of the wafer mounting surface is higher than that of the central region of the wafer mounting surface. In general, the heat input of plasma to the wafer mounting surface is greater in the outer periphery region than in the central region. Taking this into consideration, by setting as described above, the cooling efficiency of the outer periphery region of the wafer mounting surface can be made higher than that of the central region, and thus temperature unevenness of the wafer mounting surface can be effectively suppressed.

[0010] [4] In the wafer mounting table of the present invention (the wafer mounting table described in [3] above), the length between the upper surface of the refrigerant flow path and the wafer mounting surface may be shorter in the peripheral region of the wafer mounting surface than in the central region of the wafer mounting surface, the cross-sectional area of ​​the refrigerant flow path may be smaller, and the aspect ratio of the cross-section of the refrigerant flow path may be smaller.

[0011] [5] In the wafer mounting table of the present invention (the wafer mounting table described in [3] or [4] above), the ceramic plate may have an annular focus ring mounting surface around the wafer mounting surface, the focus ring mounting surface being one step lower than the height of the wafer mounting surface, and an annular focus ring having an outer diameter larger than the outer diameter of the ceramic plate and the outer diameter of the cooling plate may be mounted on the focus ring mounting surface. In this case, since the focus ring protrudes outside the wafer mounting table (overhangs), the peripheral region of the wafer mounting surface is likely to become hotter. For this reason, it is highly meaningful to apply the present invention.

[0012] [6] In the wafer stage of the present invention (the wafer stage according to any one of [1] to [5] above), the aspect ratio of the low aspect ratio portion of the coolant flow path may be 0.5 or less. This increases the cooling efficiency of the low aspect ratio portion of the coolant flow path.

[0013] [7] In the wafer stage of the present invention (the wafer stage described in [6] above), the aspect ratio of the coolant flow path at the portion where the aspect ratio is high may be 1 or more. In this way, the aspect ratio of the coolant flow path at the portion where the aspect ratio is low and the portion where the aspect ratio is high may be 1 or more. cooling The efficiency difference can be large.

[0014] [8] In the wafer stage of the present invention (the wafer stage according to any one of [1] to [7] above), the ceramic plate may be made of alumina, and the cooling plate may be made of Ti or a Ti alloy. This reduces the difference in thermal expansion between the ceramic plate and the cooling plate, thereby preventing the wafer stage from warping.

[0015] [9] In the wafer mounting table of the present invention (the wafer mounting table according to any one of [1] to [8] above), the wafer mounting surface may have an area with a high cooling requirement and an area with a low cooling requirement, and the length between the upper surface of the refrigerant flow path and the wafer mounting surface, the cross-sectional area of ​​the refrigerant flow path, and the aspect ratio of the cross-sectional area of ​​the refrigerant flow path may be set so that the area of ​​the wafer mounting surface with a high cooling requirement has a higher heat exchange efficiency than the area with a low cooling requirement. For example, the area with a high cooling requirement is a peripheral area of ​​the wafer mounting surface, and the area with a low cooling requirement is a central area of ​​the wafer mounting surface. [Brief description of the drawings]

[0016] [Figure 1] FIG. [Diagram 2] FIG. [Diagram 3] Cross section AA of Figure 1. [Figure 4] A partially enlarged view of Figure 1. [Diagram 5] 6 is a graph showing the relationship between the aspect ratio of a flow channel cross section and temperature characteristics. [Figure 6] FIG. 3 is a cross-sectional view of a refrigerant flow path 32 with fins 32a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Next, preferred embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view of a wafer mounting table 10 (a cross-sectional view of the wafer mounting table 10 cut along a plane including the central axis of the wafer mounting table 10), Fig. 2 is a plan view of the wafer mounting table 10, Fig. 3 is a cross-sectional view taken along the line AA in Fig. 1, and Fig. 4 is a partially enlarged view of Fig. 1.

[0018] The wafer mounting table 10 is used for performing CVD, etching, or the like by utilizing plasma on the wafer W. The wafer mounting table 10 includes a ceramic plate 20, a cooling plate 30, and a bonding layer 40.

[0019] Ceramic plate 20 is made of a ceramic material such as alumina, aluminum nitride, etc. Ceramic plate 20 has a wafer mounting surface 22, an electrostatic electrode 23, and a focus ring mounting surface 24. Hereinafter, the focus ring may be abbreviated as "FR."

[0020] The wafer mounting surface 22 is a circular surface and is provided on the upper surface of the ceramic plate 20. The wafer W is mounted on the wafer mounting surface 22. Although not shown, the wafer mounting surface 22 has an annular seal band formed along the outer edge, and a plurality of circular small protrusions are formed on the entire surface of the area surrounded by the seal band. The seal band and the circular small protrusions have the same height, for example, several μm to several tens of μm. The wafer mounting surface 22 has an area that is likely to become hot (area with high cooling requirements) and an area that is not likely to become hot (area with low cooling requirements). In this embodiment, when the wafer W is processed with plasma, the heat input of the plasma is greater on the outer periphery side, so that as shown in FIG. 2, the outer periphery area 22a (lightly shaded area) of the wafer mounting surface 22 is an area with high cooling requirements, and the central area 22b (darkly shaded area) of the wafer mounting surface 22 is an area with low cooling requirements.

[0021] The electrostatic electrode 23 is a flat mesh electrode or plate electrode to which a DC voltage can be applied. When a DC voltage is applied to the electrostatic electrode 23, the wafer W is attracted and fixed to the wafer mounting surface 22 (specifically, the upper surface of the seal band and the upper surfaces of the small circular protrusions) by electrostatic attraction, and when the application of the DC voltage is stopped, the wafer W is released from the attraction and fixation to the wafer mounting surface 22.

[0022] The FR mounting surface 24 is provided in an annular shape around the wafer mounting surface 22. The height of the FR mounting surface 24 is one step lower than the height of the wafer mounting surface 22. An annular focus ring 60 is mounted on the FR mounting surface 24. The focus ring 60 is made of, for example, Si. A circumferential groove 62 is provided on the upper part of the inner surface of the focus ring 60 so as not to come into contact with the wafer W. The outer diameter of the focus ring 60 is larger than the outer diameter of the ceramic plate 20 and the outer diameter of the cooling plate 30. Therefore, the focus ring 60 is mounted on the FR mounting surface 24 in a state where it protrudes outside the wafer mounting table 10 (overhanging state).

[0023] The cooling plate 30 is made of a material having a lower thermal conductivity than Al. Examples of such materials include Ti-containing materials. The cooling plate 30 includes a refrigerant flow path 32 in which a refrigerant can circulate. As shown in FIG. 3, the refrigerant flow path 32 is provided so as to cover the entire surface of the ceramic plate 20 from one end (inlet 32in) to the other end (outlet 32out) in a single stroke in a plan view. In this embodiment, the refrigerant flow path 32 is formed in a spiral shape in a plan view. Such a cooling plate 30 can be manufactured, for example, by diffusion bonding a plurality of layered members. The refrigerant is supplied to the inlet 32in of the refrigerant flow path 32 from a refrigerant circulation device (not shown), passes through the refrigerant flow path 32, and is discharged from the outlet 32out of the refrigerant flow path 32 and returns to the refrigerant circulation device. The refrigerant circulation device can adjust the refrigerant to a desired temperature. The refrigerant is preferably a liquid, and is preferably electrically insulating. Examples of electrically insulating liquids include fluorine-based inert liquids.

[0024] The conductive material used for the cooling plate 30 is preferably one having a thermal expansion coefficient close to that of the ceramic plate 20. When the material of the ceramic plate 20 is alumina, the material of the cooling plate 30 is preferably pure Ti or an α-β Ti alloy. alloy This is because the thermal expansion coefficient of is close to that of alumina.

[0025] The bonding layer 40 bonds the lower surface of the ceramic plate 20 and the upper surface of the cooling plate 30. The bonding layer 40 may be, for example, a metal layer formed of solder or a metal brazing material, or a resin layer formed of a resin adhesive.

[0026] The coolant flow path 32 will be described in detail. As shown in Fig. 2, the coolant flow path 32 has a portion 32x corresponding to the outer circumferential region 22a (region with high cooling demand) of the wafer mounting surface 22 and a portion 32y corresponding to the central region 22b (region with low cooling demand). The portion 32x of the coolant flow path 32 corresponding to the outer circumferential region 22a is a portion from the inlet 32in of the coolant flow path 32 to a midway position 32mid. The portion 32y of the coolant flow path 32 corresponding to the central region 22b is a portion from the midway position 32mid of the coolant flow path 32 to the outlet 32out.

[0027] 4, the length D of the coolant flow passage 32 between the upper surface and the wafer mounting surface 22 is such that the length Dx of the portion 32x of the coolant flow passage 32 corresponding to the outer circumferential region 22a of the wafer mounting surface 22 is shorter than the length Dy of the portion 32y corresponding to the central region 22b. The shorter the length D, the more efficiently the heat exchange between the wafer mounting surface 22 and the coolant flowing through the coolant flow passage 32 is performed.

[0028] Regarding the flow path cross-sectional area S of the refrigerant flow path 32, the flow path cross-sectional area Sx of the portion 32x corresponding to the outer circumferential region 22a is smaller than the flow path cross-sectional area Sy of the portion 32y corresponding to the central region 22b. The smaller the flow path cross-sectional area S, the faster the flow rate of the refrigerant flowing through the refrigerant flow path 32 becomes, and the higher the cooling efficiency becomes. Note that the flow path cross-sectional area S is the area of ​​a cross section (flow path cross section) when the refrigerant flow path 32 is cut along a plane perpendicular to the longitudinal direction of the refrigerant flow path 32.

[0029] Regarding the aspect ratio (ratio of vertical length H to horizontal length W) H / W in the flow passage cross section of the coolant flow passage 32, the aspect ratio Hx / Wx of the portion 32x corresponding to the outer circumferential region 22a is smaller than the aspect ratio Hy / Wy of the portion 32y corresponding to the central region 22b. When the cooling plate 30 is formed of a material having a lower thermal conductivity than Al, the cooling efficiency increases as the aspect ratio H / W decreases, assuming that the cross-sectional area of ​​the coolant flow passage 32 is the same (this point will be described later with reference to FIG. 5). Therefore, the cooling efficiency of the portion 32x of the coolant flow passage 32 corresponding to the outer circumferential region 22a is higher than that of the portion 32y corresponding to the central region 22b. In this embodiment, Wx <Wy,Hx<Hyである。

[0030] Next, an example of using the wafer mounting table 10 will be described. The wafer mounting table 10 is fixed inside a semiconductor process chamber (not shown). A focus ring 60 is placed on the FR mounting surface 24, and a wafer W is placed on the wafer mounting surface 22. In this state, a DC voltage is applied to the electrostatic electrode 23 to adsorb the wafer W to the wafer mounting surface 22. At the same time, a thermally conductive gas (He gas, etc.) is supplied to a gas passage (a passage from the lower surface of the cooling plate 30 to the wafer mounting surface 22) (not shown) provided inside the wafer mounting table 10. As a result, the gas is filled in the space surrounded by the lower surface of the wafer W and the seal band of the wafer mounting surface 22, so that the thermal conduction between the wafer W and the wafer mounting surface 22 is improved. Then, the inside of the chamber is set to a predetermined vacuum atmosphere (or reduced pressure atmosphere), and an RF voltage is applied to the cooling plate 30 while a process gas is supplied from a shower head provided on the ceiling of the chamber. Then, a plasma is generated between the wafer W and the shower head. The plasma is then utilized to perform CVD film formation or etching on the wafer W.

[0031] When the wafer W is processed with plasma in this manner, the heat input from the plasma is greater in the outer peripheral region of the wafer W than in the central region, so the outer peripheral region of the wafer W is more likely to become hotter than the central region. Therefore, in order to make the temperature of the wafer W uniform, it is necessary to cool the outer peripheral region 22a of the wafer mounting surface 22 more efficiently than the central region 22b. In consideration of this point, in this embodiment, the length D between the upper surface of the coolant flow path 32 and the wafer mounting surface 22, the flow path cross-sectional area S of the coolant flow path 32, and the aspect ratio H / W of the flow path cross section of the coolant flow path 32 are adjusted as described above. As a result, the cooling efficiency of the portion 32x of the coolant flow path 32 corresponding to the outer peripheral region 22a is higher than that of the portion 32y corresponding to the central region 22b.

[0032] In the wafer mounting table 10 described above, the length D between the upper surface of the coolant flow path 32 and the wafer mounting surface 22 is not constant, but has long and short parts. The parts with short length D have higher cooling efficiency than the parts with long length D. The flow path cross-sectional area S of the coolant flow path 32 is not constant, but has small and large parts. The parts with small flow path cross-sectional area S of the coolant flow path 32 have a faster flow rate and higher cooling efficiency than the parts with large flow path cross-sectional area S. The aspect ratio H / W, which is the ratio of the vertical length to the horizontal length in the flow path cross section of the coolant flow path 32, is not constant, but has small and large parts. When the cooling plate 30 is made of a material with a lower thermal conductivity than Al, the cooling efficiency is higher as the aspect ratio is smaller, assuming that the cross-sectional area of ​​the coolant flow path 32 is the same. From the above, in the wafer mounting table 10 in which the cooling plate 30 is formed of a material having a lower thermal conductivity than Al, temperature unevenness of the wafer mounting surface 22 can be suppressed by adjusting the length D between the upper surface of the refrigerant flow path 32 and the wafer mounting surface 22, the flow path cross-sectional area S of the refrigerant flow path 32, and the aspect ratio H / W of the flow path cross section.

[0033] Moreover, the thermal conductivity of the cooling plate 30 is preferably 50 W / mK or less. In this case, assuming that the cross-sectional area of ​​the coolant flow path 32 is the same, the smaller the aspect ratio H / W, the more significantly the cooling efficiency increases. If the thermal conductivity of the cooling plate 30 is 5 to 20 W / mK, the effect of the aspect ratio becomes more significant. For example, the thermal conductivity of pure Ti is 17 W / mK, and the thermal conductivity of an α-β Ti alloy is 7.5 W / mK.

[0034] Furthermore, the plasma heat input to the wafer mounting table 10 is generally greater in the outer peripheral region 22a of the wafer mounting surface 22 than in the central region 22b. In consideration of this point, the length D, the flow path cross-sectional area S, and the aspect ratio H / W are set so that the heat exchange efficiency of the outer peripheral region 22a of the wafer mounting surface 22 is higher than that of the central region 22b. In this embodiment, the outer peripheral region 22a of the wafer mounting surface 22 in the wafer mounting table 10 has a shorter length D, a smaller flow path cross-sectional area S, and a smaller aspect ratio H / W than the central region 22b. This makes it possible to make the cooling efficiency of the outer peripheral region 22a of the wafer mounting surface 22 higher than that of the central region 22b, and thus makes it possible to effectively suppress temperature unevenness of the wafer mounting surface 22.

[0035] Furthermore, ceramic plate 20 has an annular focus ring mounting surface 24 around wafer mounting surface 22, which is one step lower than the height of wafer mounting surface 22, and an annular focus ring 60 having an outer diameter larger than the outer diameter of ceramic plate 20 and cooling plate 30 is mounted on focus ring mounting surface 24. In this case, focus ring 60 protrudes (overhangs) outside wafer mounting table 10, and therefore outer peripheral region 22a of wafer mounting surface 22 is likely to reach a higher temperature. For this reason, there is great significance in applying the present invention.

[0036] Furthermore, it is preferable that the aspect ratio H / W at the portion of the coolant flow path 32 where the aspect ratio H / W is low is 0.5 or less. In this way, the cooling efficiency at the portion of the coolant flow path 32 where the aspect ratio H / W is low is further improved. .child At this time, the inside of the refrigerant flow passage 32 ChiaThe aspect ratio H / W at the portion with the high aspect ratio H / W may be equal to or greater than 1. In this way, the aspect ratio H / W at the portions with the low aspect ratio H / W and the portions with the high aspect ratio H / W in the coolant flow passage 32 may be equal to or greater than 1. cooling The efficiency difference can be large.

[0037] It is also preferable that the ceramic plate 20 is made of alumina, and the cooling plate 30 is made of Ti or a Ti alloy, so that the difference in thermal expansion between the ceramic plate 20 and the cooling plate 30 is small, thereby making it possible to suppress warping of the wafer mounting table 10.

[0038] Here, we will explain the results of examining the relationship between the thermal conductivity of the material used in the cooling plate, the aspect ratio of the flow passage cross section, and the cooling efficiency. The materials used for the cooling plate were a first material (e.g., Ti) with a thermal conductivity of 20 W / mK, a second material (e.g., Al) with a thermal conductivity of 100 W / mK, and a third material (e.g., Al) with a thermal conductivity of 200 W / mK. The cross-sectional shape of the coolant flow passage was a cross-sectional area of ​​80 cm. 2 The dimensions were fixed at 0.5, and four quadrangles (rectangles or squares) were used: 6 mm long x 13 mm wide (aspect ratio about 0.5, first shape), 7 mm long x 11.5 mm wide (aspect ratio about 0.6, second shape), 9 mm long x 9 mm wide (aspect ratio 1, third shape), and 11.5 mm long x 7 mm wide (aspect ratio about 1.6, fourth shape). The surface temperature was determined when the refrigerant flow path was formed so that the upper surface of the refrigerant flow path was located at a specified distance within 10 mm from the heat input part inside the cooling plate. The results are shown in the graph in Figure 5. The vertical axis of this graph indicates the difference in temperature from when the cross section of the refrigerant flow path is a square cross section (aspect ratio 1). From this graph, it was found that for the first material with low thermal conductivity, if the cross-sectional area of ​​the refrigerant flow path is the same, the lower the aspect ratio, the higher the cooling efficiency, and especially when the aspect ratio is 0.5 or less, the cooling efficiency is high. In addition, it was found that for the second and third materials with high thermal conductivity, if the cross-sectional area of ​​the refrigerant flow path is the same, the cooling efficiency is high regardless of the aspect ratio, but the cooling efficiency decreases slightly when the aspect ratio is 0.6 or less.

[0039] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms within the technical scope of the present invention.

[0040] In the above-described embodiment, the outer peripheral region 22a of the wafer mounting surface 22 has a shorter length D, a smaller flow path cross-sectional area S, and a smaller aspect ratio H / W than the central region 22b, but is not particularly limited thereto. As long as the heat exchange efficiency of the outer peripheral region 22a of the wafer mounting surface 22 is ultimately higher than that of the central region 22b, the magnitude relationship of the length D, the flow path cross-sectional area S, and the aspect ratio H / W may be set in any manner. For example, as long as the heat exchange efficiency of the outer peripheral region 22a of the wafer mounting surface 22 is ultimately higher than that of the central region 22b, the outer peripheral region 22a of the wafer mounting surface 22 may have a shorter length D, a smaller flow path cross-sectional area S, and a larger aspect ratio H / W than the central region 22b, or may have a shorter length D, a larger flow path cross-sectional area S, and a smaller aspect ratio H / W than the central region 22b. Alternatively, as long as the heat exchange efficiency of the outer peripheral region 22a of the wafer mounting surface 22 is ultimately higher than that of the central region 22b, the outer peripheral region 22a of the wafer mounting surface 22 may have a shorter length D, a larger flow path cross-sectional area S, and a larger aspect ratio H / W than the central region 22b, or may have a longer length D, a smaller flow path cross-sectional area S, and a larger aspect ratio H / W, or may have a longer length D, a larger flow path cross-sectional area S, and a smaller aspect ratio H / W.

[0041] The heat exchange efficiency can be obtained as follows. First, a first chiller capable of circulating a refrigerant while controlling the temperature of the refrigerant is connected to the inlet 32in and the outlet 32out of the refrigerant flow path 32, and a refrigerant having the same temperature as room temperature (for example, 25°C) is circulated through the refrigerant flow path 32. At the same time, a refrigerant having a predetermined temperature (for example, 80 to 100°C) is prepared in the second chiller. Then, a refrigerant having the same temperature as room temperature is switched to a refrigerant having the predetermined temperature by a valve, and the refrigerant having the predetermined temperature is circulated through the refrigerant flow path 32. After a predetermined time (for example, 10 seconds) has elapsed since the refrigerant was switched, the temperature distribution of the wafer mounting surface 22 is measured. The temperature rise rate (amount of temperature rise per unit time (°C / sec)) is calculated from the temperature distribution, and the temperature rise rate is used as an index of the heat exchange efficiency. For example, when a refrigerant of 25°C is switched to a refrigerant of 80°C in the wafer mounting table 10, the temperature rise rate of the outer peripheral region 22a of the wafer mounting surface 22 is 7.5°C / sec or more, and the temperature rise rate of the central region 22b is 5°C / sec or less. Therefore, it is found that the heat exchange efficiency of the outer peripheral region 22a is higher than that of the central region 22b. The temperature rise rate at the boundary between the outer peripheral region 22a and the central region 22b is an intermediate value between the two.

[0042] In the above-described embodiment, the region requiring high cooling is the outer circumferential region 22a of the wafer mounting surface 22, and the region requiring low cooling is the central region 22b of the wafer mounting surface 22, but the present invention is not limited to this.

[0043] In the embodiment described above, the electrostatic electrode 23 is built into the interior of the ceramic plate 20 at a position facing the wafer mounting surface 22. In addition, an FR adsorption electrode for electrostatically adsorbing the focus ring 60 may be provided inside the ceramic plate 20 at a position facing the FR mounting surface 24.

[0044] In the above-described embodiment, the ceramic plate 20 has the wafer mounting surface 22 and the FR mounting surface 24, but is not limited thereto. For example, the ceramic plate 20 may have the wafer mounting surface 22 but not the FR mounting surface 24.

[0045] In the above-described embodiment, the focus ring 60 has an outer diameter larger than the outer diameter of the wafer mounting table 10 (the outer diameter of the ceramic plate 20 and the outer diameter of the cooling plate 30), but is not limited thereto. For example, the outer diameter of the focus ring 60 may be the same as the outer diameter of the wafer mounting table 10.

[0046] In the above embodiment, the coolant flow passage 32 is formed in a spiral shape in a plan view, but is not limited to this. For example, the coolant flow passage 32 may be formed in a zigzag shape in a plan view.

[0047] In the above-described embodiment, the wafer mounting table 10 having the electrostatic electrode 23 built in the ceramic plate 20 has been exemplified, but the present invention is not particularly limited to this. For example, instead of or in addition to the electrostatic electrode 23, the ceramic plate 20 may have a built-in heater electrode (resistance heating element) or a built-in plasma generation electrode (RF electrode).

[0048] In the above-described embodiment, the wafer mounting table 10 may have a plurality of lift pin holes that vertically penetrate the wafer mounting table 10. The lift pin holes are holes for inserting lift pins that move the wafer W up and down relative to the wafer mounting surface 22. For example, a plurality of lift pin holes are provided at equal intervals along concentric circles of the wafer mounting surface 22 when the wafer mounting surface 22 is viewed in plan.

[0049] In the above-described embodiment, as shown in Fig. 6, fins 32a (protrusions) may be provided on the ceiling surface of the refrigerant flow path 32. The fins 32a may be provided along the direction of the refrigerant flow path 32 over the entire refrigerant flow path 32 or over a portion of the refrigerant flow path 32. Only one fin 32a may be provided, or two or more fins 32a may be provided. [Industrial Applicability]

[0050] The present invention can be used, for example, in an apparatus for plasma processing a wafer. [Explanation of symbols]

[0051] 10 wafer mounting table, 20 ceramic plate, 22 wafer mounting surface, 22a outer peripheral region, 22b central region, 23 electrostatic electrode, 24 focus ring mounting surface, 30 cooling plate, 32 coolant flow path, 32a fin, 32in inlet, 32mid midway position, 32out outlet, 32x portion corresponding to outer peripheral region, 32y portion corresponding to central region, 40 bonding layer, 60 focus ring, 62 circumferential groove, W wafer.

Claims

1. a ceramic plate having a wafer mounting surface on an upper surface thereof; a cooling plate provided on a lower surface of the ceramic plate; A refrigerant flow path built into the cooling plate; a focus ring mounting surface that is annular and is provided around the wafer mounting surface of the ceramic plate, the focus ring mounting surface being one step lower than the height of the wafer mounting surface; A wafer mounting table comprising: The cooling plate is formed of a material having a thermal conductivity lower than that of Al, The length between the upper surface of the coolant flow path and the wafer placement surface is not constant, but has long and short portions. The cross-sectional area of ​​the refrigerant flow path is not constant but has small and large areas. The aspect ratio, which is the ratio of the vertical length to the horizontal length in the flow passage cross section of the refrigerant flow passage, is not constant and has small and large portions, an aspect ratio of a cross section of the coolant flow passage in a portion corresponding to the focus ring mounting surface is smaller than an aspect ratio of a cross section of the coolant flow passage in a portion corresponding to a central region of the wafer mounting surface; Wafer placement stage.

2. The thermal conductivity of the cooling plate is 50 W / mK or less. The wafer stage according to claim 1 .

3. a length between an upper surface of the refrigerant flow path and the wafer mounting surface, a flow path cross-sectional area of ​​the refrigerant flow path, and an aspect ratio of the flow path cross-section of the refrigerant flow path are set so that a heat exchange efficiency in an outer periphery region of the wafer mounting surface is higher than a heat exchange efficiency in a central region of the wafer mounting surface. The wafer stage according to claim 1 .

4. a peripheral region of the wafer mounting surface has a shorter length between the upper surface of the coolant flow path and the wafer mounting surface, a smaller cross-sectional area of ​​the coolant flow path, and a smaller aspect ratio of the cross-section of the coolant flow path, compared to a central region of the wafer mounting surface; The wafer stage according to claim 3 .

5. An annular focus ring having an outer diameter larger than an outer diameter of the ceramic plate and an outer diameter of the cooling plate is placed on the focus ring mounting surface. The wafer stage according to claim 3 .

6. The aspect ratio at the portion of the refrigerant flow path where the aspect ratio is low is 0.5 or less. The wafer stage according to claim 1 .

7. The aspect ratio at the portion of the refrigerant flow path where the aspect ratio is high is 1 or more. The wafer stage according to claim 6 .

8. the ceramic plate is made of alumina; The cooling plate is made of Ti or a Ti alloy. The wafer stage according to claim 1 .

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