Wafer mounting table

Abstract

A wafer mounting table 10 includes: a ceramic substrate 20 including a wafer mounting surface 20a on an upper surface; an electrode 22 built in the ceramic substrate 20; and a conductive electrode extraction part 23 built in the ceramic substrate 20 and electrically connected to the electrode 22. The electrode extraction part 23 has a higher volume fraction of the same ceramic material as the main component of the ceramic substrate 20 than the electrode 22.

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 base having a wafer mounting surface, an electrode embedded in the ceramic base, and a power supply member for supplying power to the electrode. Patent Document 1 discloses that an electrode terminal, which is a part of the electrode, is exposed on the surface of the ceramic base opposite the wafer mounting surface, and the power supply member is electrically connected to the electrode terminal. It also discloses that the electrode is made of a conductive material or a mixture of a conductive material and the material of the ceramic base.

[0003] Japanese Patent Application Laid-Open No. 2012-216786

[0004] However, if the difference in thermal expansion coefficient between the electrode terminal (electrode lead-out portion) and the ceramic base is large, stress is applied to the electrode from the electrode terminal due to temperature changes, which may cause the electrode to peel off or crack. As described in Patent Document 1, the difference in thermal expansion coefficient between the electrode and the ceramic base can be reduced by including the material of the ceramic base in the electrode and electrode terminal. However, if the electrode includes a large amount of the material of the ceramic base, the resistance value of the electrode increases, which is not preferable.

[0005] The present invention has been made to solve such problems, and its main object is to suppress the stress acting on the electrodes due to temperature changes while suppressing an increase in the resistance value of the electrodes.

[0006] In order to achieve the above-mentioned main object, the present invention employs the following means.

[0007] [1] The wafer mounting table of the present invention comprises a ceramic base having a wafer mounting surface on its upper surface, an electrode built into the ceramic base, and a conductive electrode lead-out portion built into the ceramic base and electrically connected to the electrode, wherein the electrode lead-out portion has a higher volume content of the same ceramic material as the main component of the ceramic base compared to the electrode.

[0008] In this wafer mounting table, the electrode lead-out portion has a higher volumetric content of the ceramic material that is the main component of the ceramic base than the electrode. This allows the difference in thermal expansion coefficient between the electrode lead-out portion and the ceramic base to be reduced. This prevents the electrode from peeling or cracking due to stress acting on the electrode from the electrode lead-out portion due to temperature changes. Meanwhile, the electrode has a lower volumetric content of the ceramic material that is the main component of the ceramic base than the electrode lead-out portion, preventing problems caused by excessively high electrode resistance. As a result, this wafer mounting table can suppress stress acting on the electrode due to temperature changes while preventing an increase in the electrode resistance.

[0009] [2] In the wafer mounting table described in [1] above, a part of the upper surface of the electrode lead-out portion may be a base bonding region bonded to the ceramic base. In this case, the electrode lead-out portion is in close contact with the ceramic base in the base bonding region, so that even if stress occurs due to a difference in thermal expansion between the electrode lead-out portion and the ceramic base caused by temperature changes, the stress is less likely to act on the electrode.

[0010] [3] In the wafer mounting table described above (the wafer mounting table described in [2] above), the base bonding region may include a portion of the outer periphery of the upper surface of the electrode lead-out portion. Here, stress acting on the electrode due to temperature changes tends to be large, particularly around the outer periphery of the upper surface of the electrode lead-out portion. Therefore, by including a portion of this outer periphery in the base bonding region, stress acting on the electrode due to temperature changes can be further reduced.

[0011] [4] The wafer mounting table (the wafer mounting table according to any one of [1] to [3]) may further include a power supply member arranged to be inserted from the underside of the ceramic base and electrically connected to the electrode lead-out portion, and a plurality of electrode lead-out portions may be provided for each power supply member. This reduces stress caused by the difference in thermal expansion between the electrode lead-out portion and the ceramic base due to temperature changes, compared to when a single electrode lead-out portion having the same volume as the total volume of the plurality of electrode lead-out portions is provided. In this case, a portion of the upper surface of each of the plurality of electrode lead-out portions may have a base bonding region bonded to the ceramic base.

[0012] [5] In the wafer mounting table described above (the wafer mounting table described in any one of [1] to [4] above), the electrode lead-out portion may have a through-hole that passes through the electrode lead-out portion in the vertical direction. In this case, the volume of the electrode lead-out portion is reduced by the amount of the through-hole, and therefore stress caused by the difference in thermal expansion between the electrode lead-out portion and the ceramic base due to temperature changes can be reduced.

[0013] [6] In the wafer mounting table described above (the wafer mounting table described in any one of [1] to [5] above), the electrode lead-out portion may have a thickness in the vertical direction greater than that of the electrode. If the electrode lead-out portion is thicker than the electrode, stress caused by a difference in thermal expansion between the electrode lead-out portion and the ceramic base due to temperature changes is likely to increase, making it highly significant to apply the present invention.

[0014] [7] In the wafer stage described above (the wafer stage described in any one of [1] to [6] above), the ceramic material may be alumina or aluminum nitride.

[0015] 2. A cross-sectional view showing a schematic configuration of a wafer mounting table 10. A partial enlarged view of FIG. 1. An enlarged view of the periphery of the electrode lead-out portion 23 of FIG. 2. A partial top view of the electrode 22 and the electrode lead-out portion 23. An explanatory diagram of a manufacturing process of the ceramic base 20 and a process of joining a power supply member 50 to the electrode lead-out portion 23. An enlarged view of the periphery of the electrode lead-out portion 23 of a modified example. An enlarged view of the periphery of the electrode lead-out portion 23 of a modified example. A partial top view of the electrode 22 and the electrode lead-out portion 23 of a modified example. An enlarged view of the periphery of the electrode lead-out portion 323 of a modified example. A partial top view of the electrode 22 and the electrode lead-out portion 323 of a modified example. An enlarged view of the periphery of the electrode lead-out portion 423 of a modified example. A partial top view of the electrode 22 and the electrode lead-out portion 423 of a modified example.

[0016] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing a schematic configuration of a wafer mounting table 10 of this embodiment (a cross-sectional view when the wafer mounting table 10 is cut at a plane including the central axis of the wafer mounting table 10), Fig. 2 is a partial enlarged view of Fig. 1 (an enlarged view of the area within the frame indicated by the two-dot chain line in Fig. 1), Fig. 3 is an enlarged view of the periphery of the electrode lead-out portion 23 in Fig. 2, and Fig. 4 is a partial top view of the electrode 22 and the electrode lead-out portion 23 (a top view of the periphery of the electrode lead-out portion 23). In Fig. 4, the area where the electrode 22 is present is hatched to make it easier to understand the positional relationship between the electrode 22 and the electrode lead-out portion 23.

[0017] As shown in FIG. 1, the wafer mounting table 10 includes a ceramic base 20, a cooling plate 30, a bonding layer 40, and a power supply member 50.

[0018] The ceramic base 20 is a disk-shaped member having a wafer mounting surface 20a on its upper surface. The ceramic base 20 is formed of a ceramic-containing material. The ceramic-containing material is a material whose main component is a ceramic material, and may contain, in addition to the ceramic material, components derived from sintering aids (e.g., rare earth elements) and unavoidable components. The main component refers to a volume content of 50% or more of the total. The volume content of the ceramic material, which is the main component of the ceramic base 20, may be 80% or more, or even 90% or more, by volume. Examples of ceramic materials include alumina and aluminum nitride. In this embodiment, the main component of the ceramic base 20 is alumina.

[0019] The ceramic substrate 20 incorporates an electrode 22 and an electrode lead-out portion 23. The electrode 22 and the electrode lead-out portion 23 are conductive. The electrode 22 is a flat, monopolar electrode. In this embodiment, the electrode 22 is a disc-shaped electrode. The electrode lead-out portion 23 is a member having a spherical trapezoid shape (a shape obtained by cutting a sphere along two horizontal planes). The electrode lead-out portion 23 is electrically connected to the electrode 22. The electrode lead-out portion 23 is disposed below the electrode 22, and a portion of its upper surface contacts the lower surface of the electrode 22. The lower surface of the electrode lead-out portion 23 is exposed at the bottom surface of the power supply member insertion hole 28 and contacts a brazing material layer 29 disposed on the bottom surface of the power supply member insertion hole 28. The electrode lead-out portion 23 has a greater vertical thickness than the electrode 22. That is, as shown in FIG. 3 , the thickness T2 of the electrode lead-out portion 23 is greater than the thickness T1 of the electrode 22. The thickness T2 is, for example, 0.1 mm or more and 1 mm or less. The thickness T1 is, for example, 0.01 mm or more and 0.03 mm or less. The thickness T2 may be 10 times or more, or 20 times or more, the thickness T1. In this embodiment, the electrode 22 is used as an electrostatic electrode. The layer of the ceramic base 20 above the electrode 22 functions as a dielectric layer. A power supply 62, which is a DC power supply for electrostatic attraction, is connected to the electrode 22 via a power supply member 50.

[0020] A portion of the upper surface of the electrode lead-out portion 23 forms a base bonding region 24 that is bonded to the ceramic base 20. In this embodiment, a circular through-hole 22a is formed in the electrode 22 at a position that overlaps with the electrode lead-out portion 23 when viewed virtually from above ( FIG. 4 ), and the portion of the upper surface of the electrode lead-out portion 23 that is located directly below this through-hole 22a forms the base bonding region 24. When viewed virtually from above, the through-hole 22a overlaps with the center of the electrode lead-out portion 23. When viewed from above, the through-hole 22a is provided concentrically with the electrode lead-out portion 23, and the diameter of the through-hole 22a is smaller than the diameter of the electrode lead-out portion 23. Therefore, when viewed virtually from above, the entire through-hole 22a is included in the electrode lead-out portion 23, and the entire through-hole 22a coincides with the base bonding region 24. Since the through-hole 22 a exists directly above the base bonding region 24 , the electrode 22 does not exist directly above the base bonding region 24 .

[0021] The electrode 22 and the electrode lead-out portion 23 contain a conductive material such as W, Mo, WC, MoC, Ru, or TiN. The conductive material used for the electrode 22 and the electrode lead-out portion 23 preferably has a thermal expansion coefficient close to that of the ceramic base 20. The conductive material contained in the electrode 22 and the electrode lead-out portion 23 is preferably the same type as the conductive material contained in the electrode 22. The conductive material contained in the electrode 22 and the electrode lead-out portion 23 may be a plurality of types of materials. The electrode 22 and the electrode lead-out portion 23 contain the same ceramic material (alumina in this embodiment) as the main component of the ceramic base 20. This allows the thermal expansion coefficients of the electrode 22 and the electrode lead-out portion 23 to be close to that of the ceramic base 20. The electrode 22 does not necessarily have to contain the same ceramic material as the main component of the ceramic base 20. In addition to the conductive material and ceramic material, the electrode 22 and the electrode lead-out portion 23 may contain components derived from sintering aids (e.g., rare earth elements) and unavoidable components. Furthermore, if the volume contents of the ceramic material in the electrode 22 and the electrode lead-out portion 23 that is the same as the main component of the ceramic base 20 are denoted by C1 and C2 [vol %], respectively, the volume content C2 is higher than the volume content C1. For example, the volume content C1 in the electrode 22 may be 0 vol % or more, 10 vol % or more, or 30 vol % or more. The volume content C1 may be 50 vol % or less. The volume content C2 in the electrode lead-out portion 23 may be 30 vol % or more, 50 vol % or more, or 70 vol % or more. The volume content C2 may be 90 vol % or less, or 80 vol % or less. The difference D (=C2-C1) between the volume content C1 and the volume content C2 may be, for example, 5 volume % or more, 10 volume % or more, 20 volume % or more, or 30 volume % or more. The higher the volume content C1, the closer the thermal expansion coefficient of the electrode 22 is to that of the ceramic base 20. Similarly, the higher the volume content C2, the closer the thermal expansion coefficient of the electrode lead-out portion 23 is to that of the ceramic base 20. In this embodiment, since C1<C2, the thermal expansion coefficient of the electrode lead-out portion 23 is closer to that of the ceramic base 20 than that of the electrode 22.When the conductive material contained in the electrode 22 and the electrode lead-out portion 23 is a material (e.g., one or more of W, Mo, WC, and MoC) having a lower thermal expansion coefficient than the ceramic material (alumina in this embodiment) that is the main component of the ceramic base 20, the higher the volume content C1, the higher the thermal expansion coefficient of the electrode 22, and the higher the volume content C2, the higher the thermal expansion coefficient of the electrode lead-out portion 23. When the conductive material contained in the electrode 22 and the electrode lead-out portion 23 is a material (e.g., one or more of Ru and TiN) having a higher thermal expansion coefficient than the ceramic material (alumina in this embodiment) that is the main component of the ceramic base 20, the higher the volume content C1, the lower the thermal expansion coefficient of the electrode 22, and the higher the volume content C2, the lower the thermal expansion coefficient of the electrode lead-out portion 23. The electrode 22 may contain, as its conductive material, both a material having a lower thermal expansion coefficient and a material having a higher thermal expansion coefficient than the ceramic material (alumina in this embodiment) that is the main component of the ceramic base 20. In this case, too, if the overall thermal expansion coefficient of the conductive materials (multiple types of materials) contained in the electrode 22 differs from the thermal expansion coefficient of the ceramic material, the thermal expansion coefficient of the electrode 22 will change depending on the volume content C1. The same applies to the electrode lead-out portion 23. If the overall thermal expansion coefficient of the conductive materials (multiple types of materials) contained in the electrode lead-out portion 23 differs from the thermal expansion coefficient of the ceramic material, the thermal expansion coefficient of the electrode lead-out portion 23 will change depending on the volume content C2. If C1 < C2, the thermal expansion coefficient of the electrode lead-out portion 23 will be closer to that of the ceramic base 20 than that of the electrode 22. Regardless of whether one type of conductive material or multiple types of conductive materials are used, it is preferable that the overall thermal expansion coefficient of the conductive materials contained in the electrode lead-out portion 23 be the same as or closer to that of the ceramic material that is the main component of the ceramic base 20.

[0022] The volume content C2 of the electrode lead-out portion 23 is a value calculated as the area percentage of the ceramic material confirmed in an observed image when a representative cross section of the electrode lead-out portion 23 is observed at a magnification of 1000 times using a scanning electron microscope (SEM). The volume content C1 of the electrode 22 and the volume content of the main component in the ceramic base 20 are also values ​​calculated in a similar manner.

[0023] The cooling plate 30 is a disc-shaped member having a refrigerant flow path 32 therein through which a refrigerant can circulate. The refrigerant flow path 32 is formed in a single stroke from one end to the other so that it spreads across the entire surface of the cooling plate 30 in a plan view. One end of the refrigerant flow path 32 is connected to a refrigerant circulation pump (not shown) that regulates the temperature of the refrigerant. The cooling plate 30 is made of a conductive material containing, for example, a metal. Examples of conductive materials include composite materials and metals. Examples of composite materials include metal composite materials (also known as metal matrix composites (MMCs)). Examples of MMCs include materials containing Si, SiC, and Ti, and materials in which porous SiC is impregnated with Al and / or Si. A material containing Si, SiC, and Ti is called SiSiCTi, a material in which porous SiC is impregnated with Al is called AlSiC, and a material in which porous SiC is impregnated with Si is called SiSiC. Examples of metals include Al, Ti, Mo, and alloys thereof. The conductive material used for the cooling plate 30 preferably has a thermal expansion coefficient close to that of the ceramic substrate 20 .

[0024] The bonding layer 40 bonds the lower surface of the ceramic base 20 and the upper surface of the cooling plate 30. The bonding layer 40 may be, for example, a metal bonding layer formed of solder or a metal brazing material. The metal bonding layer may be formed, for example, by TCB (thermal compression bonding). TCB refers to a known method in which a metal bonding material is sandwiched between two members to be joined and the two members are pressure-bonded while heated to a temperature below the solidus temperature of the metal bonding material. An organic adhesive layer may be used as the bonding layer 40 instead of the metal bonding layer.

[0025] The power supply member 50 is a metal member for supplying power to the electrode 22. The power supply member 50 is, for example, a metal rod. The power supply member 50 is electrically connected to the electrode lead-out portion 23 and the electrode 22. The metal used for the power supply member 50 is, for example, W, Mo, Ni, etc., and it is preferable that the thermal expansion coefficient of the metal is close to that of the ceramic base 20. The power supply member 50 is arranged so as to be inserted from the underside of the ceramic base 20 and is electrically connected to the electrode lead-out portion 23. More specifically, the power supply member 50 is inserted from the underside of the cooling plate 30 through the cooling plate through-hole 34 that vertically penetrates the cooling plate 30 and the bonding layer through-hole 44 that vertically penetrates the bonding layer 40, and then into the power supply member insertion hole 28 provided in the ceramic base 20. The diameter of the bonding layer through-hole 44 is the same as the diameter of the cooling plate through-hole 34. The power supply member 50 passes through the inside of an insulating tube 36 arranged in the cooling plate through-hole 34 and is inserted with some play into the power supply member insertion hole 28. The outer peripheral surface of the insulating tube 36 is bonded to the inner peripheral surface of the cooling plate through-hole 34 via an adhesive layer 35. The upper end surface of the insulating tube 36 is located higher than the upper surface of the cooling plate 30 and below the lower surface of the ceramic base 20. The power supply member insertion hole 28 is a cylindrical hole provided in the ceramic base 20, and is provided so as to extend from the lower surface of the ceramic base 20 to the electrode lead-out portion 23.

[0026] The power supply member 50 is electrically connected to the electrode lead-out portion 23 via a brazing material layer 29. The power supply member 50 is joined to the ceramic base 20 and the electrode lead-out portion 23 by the brazing material layer 29. The brazing material layer 29 is provided in the gap between the bottom surface of the power supply member insertion hole 28 and the tip surface (upper end surface) of the power supply member 50, and in the gap between the side surface of the power supply member insertion hole 28 and the side surface of the power supply member 50. The brazing material layer 29 is formed of a brazing material such as Au-Ge, Al, Ag, or Ag-Cu-Ti.

[0027] Next, an example of how the wafer mounting table 10 is used will be described. First, the wafer mounting table 10 is installed in a vacuum chamber (not shown), and a wafer W is mounted on the wafer mounting surface 20a of the wafer mounting table 10. Then, a voltage is applied to the electrode 22 from the power supply 62 via the power supply member 50. This causes the wafer W to be attracted and fixed to the wafer mounting surface 20a. The vacuum chamber is then set to a vacuum or reduced-pressure atmosphere, and the wafer W is processed within the vacuum chamber. For example, when processing the wafer W with plasma, an upper electrode equipped with a showerhead is placed on the ceiling of the vacuum chamber, and a reactive gas is supplied from the showerhead into the space between the wafer W and the upper electrode while a high-frequency voltage is applied between the upper electrode and the cooling plate 30 to generate plasma. After processing of the wafer W is completed, the voltage application to the electrode 22 is released. This releases the wafer W from its attraction and fixation to the wafer mounting surface 20a. A coolant flows through the coolant flow path 32 when it is necessary to lower the temperature of the wafer W.

[0028] Next, the manufacturing method of the wafer mounting table 10, particularly the manufacturing process of the ceramic base 20 and the process of joining the power supply member 50 to the electrode lead-out portion 23, will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram of these processes.

[0029] First, disk-shaped first and second ceramic compacts 120a and 120b, which are ceramic powder compacts, are fabricated using a tape casting method, and then a spherical hole 121 (shaped like a sphere cut along one horizontal plane) is formed in the top surface of the second ceramic compact 120b by cutting (FIG. 5A). The second ceramic compact 120b may be fabricated as a multi-layer compact.

[0030] Next, a conductive paste is printed in a predetermined pattern on the upper surface of the second ceramic compact 120b ( FIG. 5B ). Specifically, the conductive paste is first printed to fill the holes 121 in the second ceramic compact 120b, forming an electrode lead-out portion precursor 123 that will ultimately become the electrode lead-out portion 23. Next, the conductive paste is printed on the upper surface of the second ceramic compact 120b, forming an electrode precursor 122 that will ultimately become the electrode 22. The electrode precursor 122 is printed in a pattern having through holes 122a that will ultimately become the through holes 22a. This brings the lower surface of the electrode precursor 122 into contact with the upper surface of the electrode lead-out portion precursor 123, and the portion of the upper surface of the electrode lead-out portion precursor 123 directly below the through holes 122a becomes the base bonding region 124. The base bonding region 124 is the region that will ultimately become the base bonding region 24. The conductive paste may be, for example, a paste containing particles of the conductive material used for the electrodes 22 and the electrode lead-out portions 23 described above and particles of the same ceramic material as the main component of the ceramic base 20. The conductive paste may contain a sintering aid. The volume contents C1 and C2 described above can be adjusted by adjusting the content ratio of the ceramic material in the conductive paste.

[0031] Next, the first and second ceramic compacts 120a, 120b are stacked and pressure is applied from above and below to obtain a laminate 120 ( FIG. 5C ). Due to the pressure from above and below, a portion of the first ceramic compact 120a penetrates into the through-hole 122a and contacts the base bonding region 124 of the electrode lead-out portion precursor 123. This laminate 120 is hot-press fired and then cooled to room temperature. The power supply member insertion hole 28 is formed by cutting, and appropriate contour and thickness processing is performed to obtain a ceramic base 20 ( FIG. 5D ). The electrode precursor 122 with the through-hole 122a becomes the electrode 22 with the through-hole 22a after hot-press firing. The electrode lead-out portion precursor 123 with the base bonding region 124 becomes the electrode lead-out portion 23 with the base bonding region 24 after hot-press firing and the formation of the power supply member insertion hole 28. The power supply member insertion hole 28 can be formed, for example, by countersinking. The power supply member insertion hole 28 is formed to a depth such that the electrode lead-out portion precursor 123 is exposed at the bottom of the power supply member insertion hole 28. As a result of the countersinking process at this time, a portion of the lower side of the electrode lead-out portion precursor 123 is cut away to form the electrode lead-out portion 23. The hot-press firing causes the electrode lead-out portion 23 to be tightly bonded to the ceramic particles of the ceramic base 20 surrounding the electrode lead-out portion 23. Therefore, the base bonding region 24 of the electrode lead-out portion 23 is tightly bonded to the ceramic particles of the ceramic base 20 that are present directly above the base bonding region 24 (here, the ceramic particles in the through-holes 122 a), and is bonded to the ceramic base 20.

[0032] Next, the power supply member 50 and the electrode lead-out portion 23 are joined and electrically connected. Specifically, a brazing sheet that will eventually become the brazing layer 29 is placed on the bottom surface of the power supply member insertion hole 28, and the power supply member 50 is inserted from the underside of the ceramic base 20. That is, the brazing sheet is sandwiched between the bottom surface of the power supply member insertion hole 28 (including the portion of the electrode lead-out portion 23 that is exposed on the bottom surface) and the tip surface of the power supply member 50. In this state, the brazing material is heated and melted, and then cooled and solidified to form the brazing layer 29 ( FIG. 5E ). As a result, the power supply member 50 and the electrode lead-out portion 23 are joined and electrically connected via the brazing layer 29.

[0033] In parallel with these steps, the cooling plate 30 is fabricated by a known method, and the insulating tube 36 is attached to the cooling plate 30 via an adhesive layer 35. Then, the cooling plate 30 is bonded to the ceramic base 20 after the above-described steps via a bonding layer 40 to obtain the wafer mounting table 10. The step of bonding the power supply member 50 to the electrode lead-out portion 23 ( FIG. 5E ) may be performed before or after bonding the cooling plate 30 to the ceramic base 20.

[0034] In the wafer mounting table 10 of this embodiment described above, the electrode lead-out portion 23 has a higher volume content of the same ceramic material as the main component of the ceramic base 20 than the electrode 22. That is, the volume content C2 is higher than the volume content C1. This reduces the difference in thermal expansion coefficient between the electrode lead-out portion 23 and the ceramic base 20. This prevents the electrode 22 from peeling or cracking due to stress acting on the electrode 22 from the electrode lead-out portion 23 due to temperature changes. For example, if the electrode lead-out portion 23 has a lower thermal expansion coefficient than the ceramic base 20, and the difference in thermal expansion coefficients between the electrode lead-out portion 23 and the ceramic base 20 is large, when the laminate 120 is cooled to room temperature after hot-press firing in the manufacturing process of the ceramic base 20, the electrode lead-out portion 23 (more precisely, the electrode lead-out portion precursor 123) shrinks less due to temperature changes during cooling than the ceramic base 20. Furthermore, if the electrode lead-out portion 23 has a higher thermal expansion coefficient than the ceramic base 20, the large difference in the thermal expansion coefficients between them results in a larger shrinkage of the electrode lead-out portion 23 (more precisely, the electrode lead-out portion precursor 123) due to temperature changes during cooling than the ceramic base 20. This causes stress to be generated in the electrode lead-out portion 23, which in turn applies stress to the electrode 22 directly above the electrode lead-out portion 23, potentially causing peeling or cracking of the electrode 22. This stress is particularly likely to be large around the outer periphery of the upper surface of the electrode lead-out portion 23. For example, peeling or cracking of the electrode 22 is likely to occur in the regions indicated by the two dashed circles in FIG. 3 . Furthermore, stress may be applied to the electrode 22 not only during cooling after firing of the laminate 120 but also during cooling after use of the wafer mounting table 10. In contrast, in this embodiment, the volume content C2 is higher than the volume content C1, thereby suppressing the stress acting on the electrode 22 from the electrode lead-out portion 23 and thereby preventing peeling or cracking of the electrode 22. Furthermore, if the volume content C1 of the electrode 22 is increased in addition to the volume content C2 of the electrode lead-out portion 23, there is a concern that the resistance value of the electrode 22 will become too high, resulting in problems (e.g., a decrease in the function as an electrostatic electrode). In contrast, in this embodiment, the volume content C1 is lower than the volume content C2, so problems caused by the resistance value of the electrode 22 becoming too high can be suppressed.Note that the electrode lead-out portion 23 does not need to function as an electrostatic electrode like the electrode 22, and therefore, even if the resistance value increases, it is less likely to cause problems than the electrode 22. As described above, the wafer mounting table 10 of this embodiment can suppress an increase in the resistance value of the electrode 22 while suppressing stress acting on the electrode 22 due to temperature changes.

[0035] Furthermore, a portion of the upper surface of the electrode lead-out portion 23 forms a base bonding region 24 that is bonded to the ceramic base 20. As a result, the electrode lead-out portion 23 is in close contact with the ceramic base 20 in the base bonding region 24, and the stress generated in the electrode lead-out portion 23 described above can be suppressed by the adhesive force between the base bonding region 24 and the ceramic base 20. As a result, even if stress is generated due to a difference in thermal expansion between the electrode lead-out portion 23 and the ceramic base 20 caused by a temperature change, the stress is less likely to act on the electrode 22.

[0036] Furthermore, the electrode lead-out portion 23 has a greater thickness in the vertical direction than the electrode 22. When the electrode lead-out portion 23 is thicker than the electrode 22, that is, when the volume of the electrode lead-out portion 23 is greater than when the electrode lead-out portion 23 has the same thickness as the electrode 22, stress caused by the difference in thermal expansion between the electrode lead-out portion 23 and the ceramic base 20 due to temperature changes is likely to increase, and therefore, the significance of applying the present invention is great. Note that, since the electrode lead-out portion 23 is thicker than the electrode 22, cutting of not only the electrode lead-out portion 23 but also the electrode 22 can be prevented when forming the power supply member insertion hole 28.

[0037] 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.

[0038] For example, in the above-described embodiment, the electrode lead-out portion 23 has the base bonding region 24, but it may not have the base bonding region 24 as shown in Fig. 6. In Fig. 6, the electrode 22 does not have a through-hole 22a, and the electrode 22 is present directly above the entire upper surface of the electrode lead-out portion 23, so the upper surface of the electrode lead-out portion 23 does not have the base bonding region 24. Even in this case, since the volume content C2 is higher than the volume content C1, it is possible to suppress an increase in the resistance value of the electrode 22 and suppress stress acting on the electrode 22 due to temperature changes.

[0039] In the above-described embodiment, the base bonding region 24 is located in the central portion of the upper surface of the electrode lead-out portion 23, but the position of the base bonding region 24 is not limited thereto. For example, as shown in FIGS. 7 and 8 , the base bonding region 24 may include a portion of the outer peripheral edge of the upper surface of the electrode lead-out portion 23. FIG. 7 is a cross-sectional view taken along the line A-A in FIG. 8 . In FIGS. 7 and 8 , the base bonding region 24 of the electrode 22 includes a region 224 a and multiple (six in this example) regions 224 b. As in the above-described embodiment, the region 224 a is located in the central portion of the upper surface of the electrode lead-out portion 23 and is located directly below the through-hole 222 a in the electrode 22. Therefore, the region 224 a is not in contact with the electrode 22 but is bonded to the ceramic base 20. The electrode 22 is provided with a plurality of (six in this example) trapezoidal through-holes 222b, which are provided across the outer peripheral edge of the electrode lead-out portion 23 (the circular outline of the electrode lead-out portion 23 shown in FIG. 8 ) in a top view, from the inside to the outside in the radial direction of the electrode lead-out portion 23. As a result, a region 224b including a part of the outer peripheral edge of the upper surface of the electrode lead-out portion 23 (the part shown by the solid line among the outlines of the electrode lead-out portion 23 in FIG. 8 ) is not in contact with the electrode 22 and forms part of the base bonding region 24 that is bonded to the ceramic base 20. The rest of the upper surface of the electrode lead-out portion 23 other than the base bonding region 24 (regions 224a and 224b) is in contact with the lower surface of the electrode 22 and is electrically connected. As described above, stress acting on the electrode 22 due to temperature changes tends to be large, particularly around the outer peripheral edge of the upper surface of the electrode lead-out portion 23. Therefore, by including a portion of this outer peripheral edge in region 224b of the base bonding region 24, stress acting on the electrode 22 due to temperature changes can be further reduced. If the entire outer peripheral edge of the upper surface of the electrode lead-out portion 23 were included in the base bonding region 24, electrical continuity between the electrode lead-out portion 23 and the electrode 22 would be lost. Therefore, in Figures 7 and 8, only a portion of the outer peripheral edge of the upper surface of the electrode lead-out portion 23 is included in the base bonding region 24, rather than the entire portion. In Figures 7 and 8, the number of regions 224b may be one. In Figures 7 and 8, the base bonding region 24 does not have to include region 224a. In other words, the electrode 22 does not have to have a through-hole 222a.

[0040] In the above-described embodiment, one electrode lead-out portion 23 is provided for one power supply member 50, but this is not limited thereto. Multiple electrode lead-out portions 23 may be provided for one power supply member 50. For example, as shown in FIGS. 9 and 10 , three electrode lead-out portions 323a to 323c may be provided as electrode lead-out portions 323 for one power supply member 50. FIG. 9 is a cross-sectional view taken along the line B-B in FIG. 10 . In FIGS. 9 and 10 , the electrode lead-out portion 323 has three electrode lead-out portions 323a to 323c spaced apart from one another. The base bonding region 324 has regions 324a to 324c that are part of the upper surfaces of the three electrode lead-out portions 323a to 323c. Each of the electrode lead-out portions 323a to 323c is a spherical trapezoid-shaped member, and its lower surface is joined and electrically connected to the power supply member 50 via a brazing layer 29. The electrode 22 has a through hole 322a similar to the through hole 22a. The through hole 322a is provided so as to straddle the outer peripheral edge of each of the electrode lead-out portions 323a to 323c from the inside to the outside in the radial direction when viewed from above. As a result, regions 324a to 324c including a portion of the outer peripheral edge of each of the electrode lead-out portions 323a to 323c (portions indicated by solid lines among the outlines of the electrode lead-out portions 323a to 323c in FIG. 10) are not in contact with the electrode 22 and form a base bonding region 324 that is bonded to the ceramic base 20. The portion of the upper surface of the electrode lead-out portion 323 other than the base bonding region 324 (regions 324a to 324c) is in contact with the lower surface of the electrode 22 and is electrically connected. Because the electrode lead-out portion 323 is divided into multiple electrode lead-out portions 323a-323c, stress caused by the difference in thermal expansion between the electrode lead-out portion 323 and the ceramic base 20 due to temperature changes can be reduced compared to when a single electrode lead-out portion 23 having the same volume as the total volume of the multiple electrode lead-out portions 323a-323c is provided. Furthermore, for each of the multiple electrode lead-out portions 323a-323c, a portion of the outer periphery of the upper surface is included in the base bonding region 324 (regions 324a-324c). Therefore, similar to the electrode lead-out portion 23 shown in FIGS. 7 and 8, stress acting on the electrode 22 from the electrode lead-out portion 323 due to temperature changes can be further reduced. In FIGS. 9 and 10, the electrode 22 may not have a through-hole 322a and the base bonding region 324 may not exist.Furthermore, one or more of the regions 324a to 324c of the electrode lead-out portions 323a to 323c may not include part of the outer periphery of the upper surface of the corresponding electrode lead-out portion 323a to 323c, for example, one or more of the regions 324a to 324c of the electrode lead-out portions 323a to 323c may be located in the center of the corresponding electrode lead-out portion 323a to 323c. Even in these cases, the above-described effect obtained by dividing the electrode lead-out portion 323 into multiple electrode lead-out portions 323a to 323c can be obtained.

[0041] In the above-described embodiment, the electrode lead-out portion 23 may have a through-hole penetrating the electrode lead-out portion 23 in the vertical direction. For example, as shown in FIGS. 11 and 12, the electrode lead-out portion 423 may have a through-hole 425. FIG. 11 is a cross-sectional view taken along the CC line in FIG. 12. In FIGS. 11 and 12, the electrode lead-out portion 423 has a through-hole 425 penetrating the electrode lead-out portion 423 in the vertical direction, and therefore the ring-shaped region on the upper surface of the electrode lead-out portion 423 located directly below the through-hole 22a serves as the base bonding region 424. The volume of the electrode lead-out portion 423 is reduced by the amount of the through-hole 425, thereby reducing stress caused by the difference in thermal expansion between the electrode lead-out portion 423 and the ceramic base 20 due to temperature changes. In FIGS. 11 and 12, the electrode 22 may not have a through-hole 22a, and the base bonding region 424 may not exist. Even in this case, the above-described effect of the electrode lead-out portion 423 having the through-hole 425 can be obtained. 11 and 12, the through-hole 222b shown in FIGS. 7 and 8 may be added to the electrode 22, and the region 224b shown in FIGS. 7 and 8 may be added as part of the base bonding region 424.

[0042] In the above-described embodiment, the electrode lead-out portion 23 has a spherical trapezoidal shape, but is not limited to this. For example, the electrode lead-out portion 23 may have a cylindrical shape.

[0043] In the above-described embodiment, the electrode 22 is an electrostatic electrode. However, this is not limiting and the electrode 22 may be a heater electrode or an RF electrode (a high-frequency electrode for generating plasma). Even when the electrode 22 is a heater electrode or an RF electrode, there is a concern that problems may occur due to excessively high resistance of the electrode 22, making the application of the present invention highly significant. For example, if the electrode 22 is a heater electrode, excessively high resistance of the electrode 22 may cause problems such as excessively high power supply voltage to be applied to generate the required amount of heat. If the electrode 22 is an RF electrode, excessively high resistance of the electrode 22 may cause the electrode 22 to overheat and break when RF is applied, or may increase the power consumed by the electrode 22, reducing the amount of plasma generated. The application of the present invention can prevent these problems while also preventing peeling and cracking of the electrode 22. In the above-described embodiment, the wafer mounting table 10 may have two or more of an electrostatic electrode, a heater electrode, and an RF electrode built into the ceramic base 20. In this case, the present invention may be applied to at least one of the built-in electrodes.

[0044] In the above-described embodiment, the electrode 22 is a flat electrode, but is not limited thereto and may be, for example, a mesh electrode. In this case, if a part of the upper surface of the electrode lead-out portion 23 is a region directly above which the mesh openings of the electrode 22 are present (i.e., not in contact with the electrode 22) and which is bonded to the ceramic base 20, that region can be called a base bonding region.

[0045] Although not specifically described in the above embodiment, the area of ​​the base bonding region 24 is 1.2 mm 2 When the base bonding region has a plurality of regions as shown in Figures 7 to 10, the area of ​​each of the plurality of regions may be 1.2 mm 2 In addition, each of the plurality of regions may have an area of ​​1.2 mm or more. 2 Not limited to the case where the area is 1.2 mm or more, 2 It may include one or more regions where the above is true.

[0046] In the above-described embodiment, a metal rod is used as the power supply member 50, but the power supply member 50 is not limited to this, and may be, for example, a metal cable.

[0047] The present invention can be used in an apparatus for processing wafers.

[0048] 10 wafer mounting table, 20 ceramic base, 20a wafer mounting surface, 22 electrodes, 22a, 122a, 222a, 222b, 322a through holes, 23, 123, 323, 323a to 323c, 423 electrode lead-out portion, 24, 124, 324, 424 base bonding area, 28 power supply member insertion hole, 29 brazing material layer, 30 cooling plate, 32 refrigerant flow path, 34 cooling plate through hole, 35 adhesive layer, 36 insulating tube, 40 bonding layer, 44 bonding layer through hole, 50 power supply member, 62 power source, 120 laminate, 120a, 120b first and second ceramic molded bodies, 121 hole, 122 electrode precursor, 123 Electrode lead-out portion precursor, 224a, 224b, 324a to 324c regions, 425 through-hole.

Claims

1. A wafer mounting table comprising: a ceramic base having a wafer mounting surface on an upper surface thereof; an electrode built into the ceramic base; and a conductive electrode lead-out portion built into the ceramic base and electrically connected to the electrode, wherein the electrode lead-out portion has a higher volumetric content of the same ceramic material as the main component of the ceramic base compared to the electrode.

2. The wafer mounting table according to claim 1, wherein a portion of an upper surface of said electrode extraction portion is a base bonding region that is bonded to said ceramic base.

3. The wafer mounting table according to claim 2, wherein the base bonding region includes a part of the outer periphery of the upper surface of the electrode extraction portion.

4. The wafer mounting table according to claim 1 or 2, further comprising: a power supply member arranged to be inserted from the underside of the ceramic base and electrically connected to the electrode lead-out portion, wherein a plurality of the electrode lead-out portions are provided for one of the power supply members.

5. The wafer mounting table according to claim 1 or 2, wherein the electrode lead-out portion has a through-hole that passes through the electrode lead-out portion in the vertical direction.

6. The wafer mounting table according to claim 1 or 2, wherein the electrode extraction portion has a thickness in the vertical direction greater than that of the electrode.

7. The wafer stage according to claim 1 or 2, wherein the ceramic material is alumina or aluminum nitride.

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