Wafer mounting 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

Wafer mounting table

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

[0002] Conventionally, a wafer mounting table has been known that includes a ceramic plate having a wafer mounting surface on its upper surface, a cooling plate provided on the lower surface of the ceramic plate, and a refrigerant flow path built into the cooling plate. For example, Patent Document 1 (JP-A-2005-102626) discloses a wafer mounting table in which the cooling plate is formed of a material with high thermal conductivity, such as aluminum, and the distance between the upper surface of the refrigerant flow path and the wafer mounting surface is constant from the inlet to the outlet of the refrigerant flow path, and the cross-sectional shape of the refrigerant flow path varies depending on the position of the refrigerant flow path. Patent Document 1 describes that the cross-sectional area of ​​the refrigerant flow path corresponding to the relatively high-temperature portion of the wafer mounting surface is smaller than the cross-sectional area of ​​the refrigerant flow path corresponding to the relatively low-temperature portion of the wafer mounting surface. It also describes that the width of the upper surface of the refrigerant flow path from the inlet to the outlet is constant, and the height of the refrigerant flow path is shorter at the position corresponding to the relatively high-temperature portion of the wafer mounting surface than at the position corresponding to the relatively low-temperature portion of the wafer mounting surface.

[0003] Japanese Patent Application Laid-Open No. 2021-28961

[0004] However, 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, but 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 such 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.

[0006] [1] The wafer mounting table of the present invention is a wafer mounting table comprising: a ceramic plate having a wafer mounting surface on its upper surface; a cooling plate provided on the lower surface of the ceramic plate; and a refrigerant flow path built into the cooling plate, wherein the cooling plate is formed of a material having a lower thermal conductivity than Al; the length between the upper surface of the refrigerant flow path and the wafer mounting surface is not constant, with some long and some short portions; the cross-sectional area of ​​the refrigerant flow path is not constant, with some small and some large portions; and the aspect ratio, which is the ratio of the vertical length to the horizontal length in the cross-section of the refrigerant flow path, is not constant, with some small and some large portions.

[0007] In this wafer mounting table, the length between the upper surface of the refrigerant flow path and the wafer mounting surface is not constant, with some long and some short. The shorter sections have higher cooling efficiency than the longer sections. Furthermore, the cross-sectional area of ​​the refrigerant flow path is not constant, with some small and some large. The flow velocity is faster in the smaller cross-sectional area of ​​the refrigerant flow path than in the larger cross-sectional area, resulting in higher cooling efficiency. Furthermore, the aspect ratio of the refrigerant flow path (the ratio of the vertical length to the horizontal length of the cross-section of the refrigerant flow path) is not constant, with some small and some large. When the cooling plate is made of a material with a lower thermal conductivity than aluminum, the smaller the aspect ratio, the higher the cooling efficiency, assuming the same cross-sectional area of ​​the refrigerant flow path. Based on the above, in a wafer mounting table whose cooling plate is made of a material with a lower thermal conductivity than aluminum, temperature unevenness on the wafer mounting surface can be suppressed by adjusting 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-section of the refrigerant flow path.

[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 path and the wafer mounting surface, the cross-sectional area of ​​the coolant flow path, and the aspect ratio of the cross-section of the coolant flow path may be set so that the heat exchange efficiency in the outer periphery of the wafer mounting surface is higher than that in the central region of the wafer mounting surface. Generally, the heat input of plasma to the wafer mounting table is greater in the outer periphery of the wafer mounting surface than in the central region. By taking this into consideration, the above-described setting can increase the cooling efficiency in the outer periphery of the wafer mounting surface compared to the central region, thereby effectively suppressing temperature variations in the wafer mounting surface.

[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 flow path cross-sectional area of ​​the refrigerant flow path may be smaller, and the flow path cross-section aspect ratio 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 that is one step lower than 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 overhangs the wafer mounting table, the peripheral region of the wafer mounting surface is likely to reach a higher temperature. Therefore, the application of the present invention is highly significant.

[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 mounting table of the present invention (the wafer mounting table described in [6] above), the aspect ratio of the high aspect ratio portion of the coolant flow path may be equal to or greater than 1. This can increase the difference in coolant efficiency between the low aspect ratio portion and the high aspect ratio portion of the coolant flow path.

[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 warping of the wafer stage.

[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 with a high cooling requirement of the wafer mounting surface has a higher heat exchange efficiency than the area with a low cooling requirement. For example, the area with a high cooling requirement is the peripheral area of ​​the wafer mounting surface, and the area with a low cooling requirement is the central area of ​​the wafer mounting surface.

[0016] 1 is a cross-sectional view of the wafer mounting table 10; a plan view of the wafer mounting table 10; a cross-sectional view taken along line AA in FIG. 1; a partially enlarged view of FIG. 1; a graph showing the relationship between the aspect ratio of the flow path cross section and temperature characteristics; and a cross-sectional view of a coolant flow path 32 with fins 32a.

[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 A-A in Fig. 1, and Fig. 4 is an enlarged view of a portion of Fig. 1.

[0018] The wafer mounting table 10 is used to perform CVD, etching, or the like using plasma on a 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 or aluminum nitride. 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 provided on the upper surface of the ceramic plate 20. A wafer W is mounted on the wafer mounting surface 22. Although not shown, an annular seal band is formed along the outer edge of the wafer mounting surface 22, and multiple small circular protrusions are formed over the entire area surrounded by the seal band. The seal band and the small circular protrusions have the same height, e.g., several μm to several tens of μm. The wafer mounting surface 22 has an area that is prone to high temperatures (an area requiring high cooling) and an area that is less prone to high temperatures (an area requiring low cooling). In this embodiment, when processing a wafer W with plasma, the heat input of the plasma is greater on the outer periphery. Therefore, as shown in FIG. 2 , the outer peripheral area 22a (lightly shaded area) of the wafer mounting surface 22 is an area requiring high cooling, and the central area 22b (darkly shaded area) of the wafer mounting surface 22 is an area requiring low cooling.

[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 surfaces of the seal band and the small circular protrusions) by electrostatic attraction. When the application of the DC voltage is stopped, the wafer W is released from the attraction and fixed state 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 formed in the upper part of the inner surface of the focus ring 60 to prevent it from coming 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 (in an overhanging state).

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

[0024] The conductive material used for the cooling plate 30 preferably has a thermal expansion coefficient close to that of the ceramic plate 20. When the ceramic plate 20 is made of alumina, the cooling plate 30 is preferably made of pure Ti or an α-βTi alloy, because the thermal expansion coefficients of pure Ti and α-βTi are close to that of alumina.

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

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

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

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

[0029] Regarding the aspect ratio (the ratio of the vertical length H to the horizontal length W) H / W of the cross section of the refrigerant flow path 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. If the cooling plate 30 is made of a material with a lower thermal conductivity than Al, the cooling efficiency increases as the aspect ratio H / W decreases, assuming the cross-sectional area of ​​the refrigerant flow path 32 is the same (this point will be described later using FIG. 5 ). Therefore, the cooling efficiency of the portion 32x of the refrigerant flow path 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 and Hx<Hy.

[0030] Next, an example of how the wafer mounting table 10 is used 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 attract the wafer W to the wafer mounting surface 22. At the same time, a thermally conductive gas (e.g., He gas) is supplied to a gas passage (not shown) provided inside the wafer mounting table 10 (a passage extending from the underside of the cooling plate 30 to the wafer mounting surface 22). This fills the space surrounded by the underside of the wafer W and the seal band of the wafer mounting surface 22 with gas, thereby improving thermal conduction between the wafer W and the wafer mounting surface 22. The interior of the chamber is then 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 showerhead provided on the ceiling of the chamber. This generates plasma between the wafer W and the showerhead. The plasma is then utilized to perform CVD film formation or etching on the wafer W.

[0031] When processing the wafer W 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, and therefore the outer peripheral region of the wafer W is more likely to become hotter than the central region. Therefore, to uniformly cool the temperature of the wafer W, it is necessary to cool the outer peripheral region 22a of the wafer mounting surface 22 more efficiently than the central region 22b. Taking this into consideration, 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 portions. The portions with short length D have higher cooling efficiency than the portions with long length D. The cross-sectional area S of the coolant flow path 32 is not constant, but has small and large portions. The portions with small cross-sectional area S of the coolant flow path 32 have a faster flow velocity and higher cooling efficiency than the portions with large cross-sectional area S. The aspect ratio H / W, which is the ratio of the vertical length to the horizontal length in the cross section of the coolant flow path 32, is not constant, but has small and large portions. If the cooling plate 30 is made of a material with a lower thermal conductivity than Al, the cooling efficiency will be higher as the aspect ratio decreases, assuming the same cross-sectional area of ​​the coolant flow path 32. From the above, in the wafer mounting table 10 in which the cooling plate 30 is formed of a material with a lower thermal conductivity than Al, temperature unevenness on 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] Furthermore, the thermal conductivity of the cooling plate 30 is preferably 50 W / mK or less. In this case, assuming the cross-sectional area of ​​the refrigerant 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. Taking this into consideration, the length D, the flow path cross-sectional area S, and the aspect ratio H / W are set so that the heat exchange efficiency in the outer peripheral region 22a of the wafer mounting surface 22 is higher than that in 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 allows the cooling efficiency of the outer peripheral region 22a of the wafer mounting surface 22 to be higher than that of the central region 22b, thereby effectively suppressing temperature variations in 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 wafer mounting surface 22. An annular focus ring 60 having an outer diameter larger than the outer diameters of ceramic plate 20 and cooling plate 30 is mounted on focus ring mounting surface 24. In this case, because focus ring 60 overhangs (extends outside) wafer mounting table 10, an outer peripheral region 22a of wafer mounting surface 22 is likely to reach a higher temperature. For this reason, the application of the present invention is highly significant.

[0036] Furthermore, it is preferable that the aspect ratio H / W at the portion of the refrigerant flow path 32 with the low aspect ratio H / W is 0.5 or less. This increases the cooling efficiency at the portion of the refrigerant flow path 32 with the low aspect ratio H / W. In this case, the cooling efficiency at the portion of the refrigerant flow path 32 with the low aspect ratio H / W is also increased. In this case, the aspect ratio H / W at the portion of the refrigerant flow path 32 with the high aspect ratio H / W for cooling requirements may be 1 or more. This increases the difference in cooling efficiency between the portion of the refrigerant flow path 32 with the low aspect ratio H / W and the portion of the refrigerant flow path 32 with the high aspect ratio H / W.

[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 preventing the wafer mounting table 10 from warping.

[0038] Here, we will explain the results of examining the relationship between the thermal conductivity of the material used for the cooling plate, the aspect ratio of the flow path 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 refrigerant flow path was set to a cross-sectional area of ​​80 cm. 2 Four quadrilaterals (rectangles or squares) were used: 6 mm x 13 mm (aspect ratio approximately 0.5, first shape), 7 mm x 11.5 mm (aspect ratio approximately 0.6, second shape), 9 mm x 9 mm (aspect ratio 1, third shape), and 11.5 mm x 7 mm (aspect ratio approximately 1.6, fourth shape). The surface temperature was determined when the refrigerant flow channel was formed inside the cooling plate so that its upper surface was located within a predetermined distance of 10 mm from the heat input. The results are shown in the graph in Figure 5. The vertical axis of this graph represents the temperature difference compared to when the refrigerant flow channel had a square cross section (aspect ratio 1). This graph shows that for a first material with low thermal conductivity, the lower the aspect ratio, the higher the cooling efficiency, given the same cross-sectional area of ​​the refrigerant flow channel. The cooling efficiency was particularly high when the aspect ratio was 0.5 or less. Furthermore, 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 as long as they fall within the technical scope of the present invention.

[0040] In the above-described embodiment, the outer peripheral region 22 a 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 22 b. However, this is not particularly limited. As long as the heat exchange efficiency of the outer peripheral region 22 a of the wafer mounting surface 22 is ultimately higher than that of the central region 22 b, the magnitude relationship between 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 22 a of the wafer mounting surface 22 is ultimately higher than that of the central region 22 b, the outer peripheral region 22 a 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 22 b; a shorter length D, a larger flow path cross-sectional area S, and a smaller aspect ratio H / W than the central region 22 b; or a longer length D, a smaller flow path cross-sectional area S, and a smaller aspect ratio H / W than the central region 22 b. 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 determined as follows. First, a first chiller capable of circulating a refrigerant while controlling the temperature of the refrigerant is connected to the inlet 32 ​​in and outlet 32 ​​out of the refrigerant flow path 32, and a refrigerant at the same temperature as room temperature (e.g., 25°C) is circulated through the refrigerant flow path 32. Simultaneously, a refrigerant at a predetermined temperature (e.g., 80 to 100°C) is prepared in a second chiller. Then, a valve is used to switch from the refrigerant at the same temperature as room temperature to the refrigerant at the predetermined temperature, and the refrigerant at the predetermined temperature is circulated through the refrigerant flow path 32. After a predetermined time (e.g., 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 / second)) is calculated from the temperature distribution, and this temperature rise rate is used as an index of the heat exchange efficiency. For example, when the refrigerant temperature of the wafer mounting table 10 is switched from 25° C. to 80° C., 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 can be seen that the heat exchange efficiency of the outer peripheral region 22a is higher than that of the central region 22b. The temperature rise rate of the boundary between the outer peripheral region 22a and the central region 22b is an intermediate value.

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

[0043] In the above-described embodiment, electrostatic electrode 23 is built into ceramic plate 20 at a position facing wafer mounting surface 22. In addition, an FR adsorption electrode for electrostatically adsorbing focus ring 60 may be provided inside ceramic plate 20 at a position facing 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 to this. 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 outer diameter of the focus ring 60 is 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 this is not limitative. 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-described 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 has the electrostatic electrode 23 built into the ceramic plate 20, but the present invention is not 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 (resistive heating element) or a built-in plasma generating electrode (RF electrode).

[0048] In the above-described embodiment, the wafer mounting table 10 may have a plurality of lift pin holes that penetrate vertically through 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, when the wafer mounting surface 22 is viewed from above, a plurality of lift pin holes are provided at equal intervals along concentric circles of the wafer mounting surface 22.

[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.

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

[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 made 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 but has small parts and large parts, 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 .