Wafer mounting table and method for manufacturing wafer mounting table

Abstract

This wafer mounting table on which a wafer is mounted and fixed comprises: a ceramic substrate having a mounting surface for a wafer; an electrostatic chuck provided with an ESC electrode and a heater electrode each of which is embedded in the ceramic substrate; a metal cooling plate; and a resin adhesive sheet for bonding the electrostatic chuck and the cooling plate. The adhesive surface of the electrostatic chuck to the adhesive sheet has an uneven structure formed from one or a plurality of kinds of unit structures. In the uneven structure, convex portions are provided at a pitch of 100-300 μm.

Description

Wafer mounting table and method of manufacturing the same

[0001] The present invention relates to a wafer mounting table that electrostatically attracts and fixes a workpiece such as a wafer, and more particularly to the adhesion of an electrostatic chuck.

[0002] A wafer mounting table (also referred to as an electrostatic chuck) on which a semiconductor wafer (hereinafter also referred to simply as a wafer) is electrostatically attracted and fixed when the wafer is subjected to a predetermined process such as plasma processing is already known (see, for example, Patent Documents 1 and 2).

[0003] The wafer mounting table generally has a configuration in which a ceramic base (ceramic member) in which an ESC electrode (electrostatic chuck electrode) for electrostatically attracting a wafer and a heater electrode for heating the wafer are embedded, and a cooling plate (also referred to as a base or the like) having a flow path therein through which a refrigerant for cooling the ceramic base flows, are bonded together with an adhesive layer.

[0004] In this wafer mounting table, a wafer is placed on the mounting surface, which is the upper surface of the ceramic base, and a DC voltage is applied to the ESC electrodes to electrostatically attract and fix the wafer. At the same time, by passing a coolant through the flow path inside the cooling plate and energizing the heater electrodes, the wafer is heated to a predetermined temperature distribution (uniform heating distribution).

[0005] In the wafer mounting table described above, a heater electrode is usually provided so as to obtain a heat generation density that matches the heat extraction distribution, thereby ensuring a desired temperature distribution.

[0006] However, due to variations in the shape (cross-sectional area, width, etc.) of the heater electrodes from the time of design, the expected heat generation density may not be achieved. Due to these factors, the temperature distribution on the surface of the wafer fixed to the wafer mounting table may vary from one wafer to another. In some cases, the wafer mounting table may be manufactured without achieving the desired temperature distribution.

[0007] Furthermore, the heat dissipation distribution in the wafer mounting table may differ from one table to another due to variations in the thickness of the adhesive layer, the processing accuracy of the cooling plate, etc. In particular, when an adhesive sheet made of a sheet-like resin is used as the adhesive layer, variations in the thickness of the adhesive sheet may cause a distribution in the thermal resistance, which may deteriorate the thermal uniformity of the wafer mounting table.

[0008] JP 2020-53460 A Patent No. 5891332 A

[0009] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a wafer mounting table having superior thermal uniformity on the mounting surface compared to conventional wafer mounting tables.

[0010] In order to solve the above-described problems, a first aspect of the present invention is a wafer mounting table on which a wafer is mounted and fixed, comprising: a ceramic base having a wafer mounting surface; an electrostatic chuck including an ESC electrode and a heater electrode, each of which is embedded within the ceramic base; a metal cooling plate; and a resin adhesive sheet that bonds the electrostatic chuck and the cooling plate, wherein the adhesive surface of the electrostatic chuck that is bonded to the adhesive sheet has a concave-convex structure made up of one or more types of unit structures, and the convex portions in the concave-convex structure are provided at a pitch of 100 μm or more and 300 μm or less.

[0011] A second aspect of the present invention is a wafer mounting table according to the first aspect, characterized in that, in each of the one or more types of unit structures, the distance between the tip of the convex portion and the cooling plate is uniform.

[0012] A third aspect of the present invention is the wafer mounting table according to the first aspect, characterized in that the adhesive surface of the electrostatic chuck has the plurality of types of unit structures, and the distance between the tip of the convex portion and the cooling plate is different for each of the plurality of types of unit concave-convex structures.

[0013] A fourth aspect of the present invention is a wafer mounting table according to any one of the first to third aspects, characterized in that the uneven structure has convex portions that are linear in plan view and concave portions that are linear in plan view, which are arranged alternately and periodically.

[0014] In a fifth aspect of the present invention, there is provided the wafer mounting table according to the fourth aspect, wherein the adhesive surface of the electrostatic chuck is made up of a plurality of unit areas, the plurality of types of unit structures are first unit structures having first convex portions forming the convex portions and second uneven structures having second convex portions forming the convex portions, a distance between a tip of the first convex portion and the cooling plate is different from a distance between a tip of the second convex portion and the cooling plate, the first unit structures and the second unit structures are mixed in a predetermined ratio in each of the plurality of unit areas, and the predetermined ratio in each of the plurality of unit areas is determined in accordance with a reference temperature distribution generated on the mounting surface when current is applied to the heater electrode of the wafer mounting table having a flat adhesive surface of the electrostatic chuck.

[0015] In a sixth aspect of the present invention, there is provided the wafer mounting table according to the fourth aspect, wherein the adhesive surface of the electrostatic chuck is made up of a plurality of unit areas, and the plurality of types of unit structures include a first unit structure including a first convex portion forming the convex portion and a first concave portion forming the concave portion, a second unit structure including a second convex portion forming the convex portion and a second concave portion forming the concave portion, the second unit structure including a third convex portion having the same distance from the cooling plate as the first convex portion and a third concave portion having a depth greater than that of the first concave portion, and a third .... and a fourth unit structure consisting of a fourth convex portion identical to the second convex portion and a fourth concave portion deeper than the second concave portion, wherein the first to fourth unit structures are mixed in a predetermined ratio in each of the plurality of unit areas, and the predetermined ratio in each of the plurality of unit areas is determined in accordance with a reference temperature distribution that occurs on the mounting surface when current is applied to the heater electrode of the wafer mounting table having a flat adhesive surface of the electrostatic chuck, and a thickness of the adhesive sheet at a location corresponding to each of the plurality of unit areas.

[0016] A seventh aspect of the present invention is a method for manufacturing a wafer mounting table on which a wafer is mounted and fixed, comprising: a preparation step of preparing an electrostatic chuck including a ceramic base having a wafer mounting surface and an ESC electrode and a heater electrode, each of which is embedded within the ceramic base; and a bonding step of bonding the electrostatic chuck to a metal cooling plate with a resin adhesive sheet, wherein the preparation step includes a correction step of providing a concave-convex structure by alternately and periodically providing convex portions and concave portions on the bonding surface of the electrostatic chuck that is bonded to the adhesive sheet, and the correction step is at least one of a first correction step of reducing variations in temperature distribution occurring on the mounting surface and a second correction step of, if there is thickness unevenness in the adhesive sheet, causing the concave portions to absorb the thickness unevenness.

[0017] An eighth aspect of the present invention is a method for manufacturing a wafer mounting table according to the seventh aspect, characterized in that in the correction process, the uneven structure is made to consist of one or more types of unit structures, and the pitch of the convex portions and the concave portions is set to be 100 μm or more and 300 μm or less, respectively.

[0018] A ninth aspect of the present invention is a method for manufacturing a wafer mounting table according to the eighth aspect, characterized in that in the correction process, the distance between the tip of the convex portion and the cooling plate is made uniform for each of the one or more types of unit structures.

[0019] A tenth aspect of the present invention is the method for manufacturing a wafer mounting table according to the eighth aspect, wherein in the correction step, the plurality of types of unit structures are provided on the adhesive surface of the electrostatic chuck, and a distance between a tip of the convex portion and the cooling plate is made different for each of the plurality of types of unit structures.

[0020] An eleventh aspect of the present invention is a method for manufacturing a wafer mounting table according to any one of the eighth to tenth aspects, characterized in that in the correction step, the convex portion and the concave portion are provided in a linear shape.

[0021] A twelfth aspect of the present invention is a method for manufacturing a wafer mounting table according to the eleventh aspect, wherein when the correction step is the first correction step, the bonding surface of the electrostatic chuck is virtually divided into a plurality of unit areas, the plurality of types of unit structures are first unit structures having first convex portions forming the convex portions and second unit structures having second convex portions forming the convex portions, a distance between a tip of the first convex portion and the cooling plate is different from a distance between a tip of the second convex portion and the cooling plate, the first unit structures and the second unit structures are mixed in a predetermined ratio in each of the plurality of unit areas, and the predetermined ratio in each of the plurality of unit areas is set so that a temperature variation in a temperature distribution occurring on the mounting surface when current is applied to the heater electrode is reduced to be smaller than a temperature variation in a previously measured reference temperature distribution occurring on the mounting surface when current is applied to the heater electrode of the wafer mounting table in which the bonding surface of the electrostatic chuck is flat.

[0022] A thirteenth aspect of the present invention is a method for manufacturing a wafer mounting table according to the eleventh aspect, wherein when the correction step is the first and second correction steps, the adhesive surface of the electrostatic chuck is virtually divided into a plurality of unit areas, and the plurality of types of unit structures are divided into a first unit structure including a first convex portion forming the convex portion and a first concave portion forming the concave portion, a second unit structure including a second convex portion forming the convex portion and a second concave portion forming the concave portion, the second unit structure including a third convex portion having a distance from the cooling plate that is the same as that of the first convex portion and a third concave portion having a depth greater than that of the first concave portion, and a fourth unit structure including a fourth convex portion having a distance from the cooling plate that is the same as that of the second convex portion. and a fourth recess having a depth greater than that of the second recess, and the first to fourth unit structures are mixed in a predetermined ratio in each of the plurality of unit areas, and the predetermined ratio in each of the plurality of unit areas is set so that a temperature variation in a temperature distribution occurring on the mounting surface when a current is applied to the heater electrode is reduced to be smaller than a temperature variation in a reference temperature distribution occurring on the mounting surface when a current is applied to the heater electrode of the wafer mounting table having a flat adhesive surface of the electrostatic chuck, and in accordance with a thickness of the adhesive sheet at a location corresponding to each of the plurality of unit areas.

[0023] According to the first to thirteenth aspects of the present invention, a wafer stage having superior heat transfer properties compared to a stage not having a concave-convex structure is realized.

[0024] In particular, according to the first to sixth and eighth to thirteenth aspects, heat transfer from the convex portions becomes dominant in the heat transfer from the electrostatic chuck to the cooling plate, and a wafer mounting table is realized in which heat transfer from the electrostatic chuck to the cooling plate occurs more efficiently than in the case where the uneven structure is not provided.

[0025] In particular, according to the second, third, ninth, and tenth aspects, a wafer mounting table is realized in which heat transfer from the electrostatic chuck to the cooling plate via the adhesive sheet is made uniform.

[0026] In particular, according to the third and tenth aspects, a wafer mounting table can be realized in which the degree of heat transfer from the electrostatic chuck to the cooling plate via the adhesive sheet varies depending on the location.

[0027] In particular, according to the fifth and sixth aspects, it is possible to realize a wafer mounting table in which the temperature variation on the mounting surface is improved compared to the reference temperature distribution.

[0028] Furthermore, according to the sixth aspect, even when the adhesive sheet has uneven thickness, it is possible to realize a wafer mounting table in which the temperature variation on the mounting surface is improved compared to the reference temperature distribution.

[0029] Furthermore, according to the twelfth and thirteenth aspects, the formation mode of the uneven structure is changed depending on the reference temperature distribution, thereby making it possible to correct temperature variations on the mounting surface of the wafer mounting table.

[0030] Furthermore, according to the thirteenth aspect, by adjusting the depth of the recess in accordance with the uneven thickness of the adhesive sheet, it is possible to correct the temperature variation of the support surface of the wafer support table even when the adhesive sheet has uneven thickness.

[0031] 1 is a schematic cross-sectional view taken along the thickness direction of the wafer mounting table 10; FIG. 2 is a schematic diagram for explaining the detailed structure of the adhesion portion between the electrostatic chuck 20 and the adhesive sheet 40; FIG. 3 is a diagram illustrating two types of uneven structures 25 having different shapes of convex portions 23 and concave portions 24; FIG. 4 is a diagram for explaining temperature variation correction; FIG. 5 is a diagram showing a measured cross-sectional shape profile of the electrostatic chuck 20; FIG. 6 is a diagram for explaining specific details of temperature variation correction; FIG. 7 is a diagram showing a temperature distribution image IM2 on the mounting surface 20a of the wafer mounting table 10 configured using the electrostatic chuck 20 to be corrected; FIG. 8 is a diagram showing how a high rib structure 25H is formed; FIG. 9 is a diagram showing how a low rib structure 25L is formed; FIG. 10 is a diagram showing a wafer mounting table 10 having thickness unevenness in the adhesive sheet 40; FIG. 11 is a diagram showing a wafer mounting table 10 including an electrostatic chuck 20 having an uneven structure 25 corresponding to the thickness unevenness of the adhesive sheet 40; FIG. 12 is a diagram for explaining a thickness-absorbing high rib structure 25H; and FIG. 13 is a diagram for explaining a thickness-absorbing low rib structure 25L.

[0032] 1 is a schematic cross-sectional view of a wafer mounting table 10 according to an embodiment of the present invention, taken along the thickness direction of the wafer mounting table 10. The wafer mounting table 10 generally has a stacked configuration in which an electrostatic chuck 20 and a cooling plate 30 are bonded to each other by an adhesive sheet 40. The wafer mounting table 10 is also referred to as a susceptor, and is used to fix a semiconductor wafer (wafer), which is one type of workpiece, to the electrostatic chuck 20 when performing a predetermined process such as plasma processing on the wafer.

[0033] The electrostatic chuck 20 is made of Al ２ O ３ The electrostatic chuck 20 has an ESC electrode (electrostatic chuck electrode) 21 embedded in a plate-shaped (e.g., disc-shaped) ceramic base made of insulating ceramic such as AlN or the like for electrostatically attracting a wafer. The electrostatic chuck 20 shown in FIG. 1 also has a heater electrode 22 embedded therein for heating the wafer. Such an electrostatic chuck 20 is also referred to as an electrostatic chuck heater. In the electrostatic chuck 20 shown in FIG. 1, the ESC electrode 21 is embedded closer to a mounting surface 20a than the heater electrode 22. The main surface of the electrostatic chuck 20 opposite the bonding surface 20b to which the adhesive sheet 40 is attached serves as the mounting surface 20a on which the wafer is mounted.

[0034] Examples of materials for the ESC electrode 21 and the heater electrode 22 include metals such as W, Mo, Ti, Si, and Ru, or carbides or nitrides thereof.

[0035] The cooling plate 30 has an internal flow path 31, and is a portion that cools the electrostatic chuck 20 and the wafer electrostatically attracted and fixed to the mounting surface 20 a of the electrostatic chuck 20 by introducing a coolant (e.g., water) from the outside into the flow path 31. In one preferred example, the flow path 31 has one continuous groove that is spirally formed in a plan view so that substantially the entire area of ​​the electrostatic chuck 20 is cooled. Alternatively, the flow path 31 may have a plurality of independent open-ring grooves that are concentrically formed in a plan view.

[0036] The cooling plate 30 is preferably made of a metal material such as aluminum, but may be made of ceramics or a composite material of metal and ceramics.

[0037] Fins 32 may be provided protruding from at least one location of the flow path 31. The fins 32 have the effect of increasing the flow rate of the refrigerant at the location where they are provided, thereby locally enhancing the cooling efficiency. The shape and size of the fins 32 are determined appropriately depending on the cooling conditions required at the location where they are provided. The fins 32 may be made of the same material as the cooling plate 30, or may be made of a different material from the cooling plate 30. Note that a configuration in which the fins 32 are not provided is also possible.

[0038] The adhesive sheet 40 is an adhesive sheet made of a resin such as a thermosetting epoxy resin. The electrostatic chuck 20 and the cooling plate 30 are joined using the adhesive sheet 40 by, for example, performing heat and pressure joining, in which a laminate in which the adhesive sheet 40 is sandwiched between the electrostatic chuck 20 and the cooling plate 30 is heated and pressurized at a predetermined temperature. The thickness of the adhesive sheet 40 is preferably at least 100 μm to 300 μm before bonding.

[0039] The wafer stage 10 further includes a first power supply unit 50 that supplies power to the ESC electrode 21 and a second power supply unit 60 that supplies power to the heater electrode 22 .

[0040] The first power supply unit 50 is provided along the stacking direction of the electrostatic chuck 20 and the cooling plate 30, and includes a power supply terminal 51, an insulating member (sleeve) 52 surrounding the power supply terminal 51, and a connection portion 53 provided at one end of the power supply terminal 51 and connected to the ESC electrode 21. The first power supply unit 50 is inserted into the through hole 33 and is exposed to the outside at the other end. The power supply terminal 51 is electrically connected to an external ESC power supply 70 at the other end.

[0041] In the wafer mounting table 10, with a wafer placed on the mounting surface 20a of the electrostatic chuck 20, a DC voltage is applied from the ESC power supply 70 to the ESC electrode 21 via the power supply terminal 51 and the connection part 53, thereby electrostatically attracting the wafer to the mounting surface 20a.

[0042] The second power supply part 60 includes a power supply terminal 61, an insulating member (sleeve) 62 surrounding the power supply terminal 61, and a connection part 63 provided at one end of the power supply terminal 61 and connected to the heater electrode 22. The second power supply part 60 is inserted into a through hole 34 provided in the cooling plate 30, and the other end side is exposed to the outside. The power supply terminal 61 at the other end side is electrically connected to an external heater power supply 80.

[0043] In the wafer mounting table 10, electricity is applied to the heater electrode 22 from the heater power supply 80 via the power supply terminal 61 and the connection portion 63, thereby heating the wafer mounting table 10 and the wafer.

[0044] Further, refrigerant inlets 35 communicating with the flow paths 31 penetrate the cooling plate 30. Although only one refrigerant inlet 35 is shown in Fig. 1 for simplicity of illustration, in reality, one refrigerant inlet 35 is provided at each end of the groove that constitutes the flow path 31. Each refrigerant inlet 35 is connected to a chiller unit 90 that circulates and supplies refrigerant to the flow paths 31.

[0045] In the wafer mounting table 10 having the above-described configuration, a wafer placed on the mounting surface 20 a is electrostatically attracted and fixed by applying a voltage to the ESC electrode 21. In this state, heating is performed by passing current through the heater electrode 22 and a refrigerant is circulated and supplied to the flow path 31 in parallel, thereby balancing heating and cooling and enabling the wafer to be heated with a predetermined temperature distribution.

[0046] The wafer mounting table 10 can be manufactured, for example, by preparing an electrostatic chuck 20 having an ESC electrode 21 and a heater electrode 22 embedded therein, and a cooling plate 30, and then bonding the electrostatic chuck 20 and the cooling plate 30 together with an adhesive sheet 40, and then embedding the first power supply part 50 and the second power supply part 60.

[0047] The electrostatic chuck 20 can be produced, for example, by hot-pressing and firing a green sheet compact formed by stacking and adhering a plurality of ceramic green sheets, including a ceramic green sheet on which an electrode pattern for the ESC electrode 21 is printed and formed and a ceramic green sheet on which an electrode pattern for the heater electrode 22 is printed and formed.

[0048] After the hot press firing, the mounting surface 20a of the electrostatic chuck 20 may be subjected to an embossing process (roughening process) to be described later, thereby forming a large number of convex portions (projections).

[0049] The cooling plate 30 can also be fabricated by cutting bulk metal, mold casting or other casting techniques.

[0050] <Detailed Structure of Electrostatic Chuck> Hereinafter, a detailed structure of the bonding portion between the ceramic electrostatic chuck 20 and the resin adhesive sheet 40 provided in the wafer mounting table 10 according to this embodiment will be described.

[0051] 2A and 2B are schematic diagrams illustrating the detailed structure of the adhesive portion between the electrostatic chuck 20 and the adhesive sheet 40. Fig. 2A is a schematic cross-sectional view of the wafer mounting table 10, and Fig. 2B is a schematic enlarged cross-sectional view of portion A shown in Fig. 2A. Note that the dimensions of each portion shown in Fig. 2 differ from the actual dimensions, and the thickness of the adhesive sheet 40 in particular is exaggerated.

[0052] 2( a) and 1, the interface between the electrostatic chuck 20 and the adhesive sheet 40 is shown as if it were flat, but this is merely a simplified illustration. In reality, as shown in FIG. 2( b), the electrostatic chuck 20 according to this embodiment has an adhesive surface 20 b, which is the interface with the adhesive sheet 40, that has a fine uneven structure 25 in which a large number of protrusions 23 and recesses 24 are provided alternately and periodically.

[0053] More specifically, the individual protrusions 23 are spaced apart from one another at a predetermined pitch p in a first direction, which is a certain direction within a plane, and extend a predetermined length in a second direction, which is perpendicular to the first direction within the plane.

[0054] 2 and the following figures, a right-handed xyz coordinate system is used, in which the first direction is the x-axis direction, the second direction is the y-axis direction, and the direction perpendicular to the x-axis and y-axis is the z-axis direction. The following description will be given on the assumption that the wafer mounting table 10 is configured by stacking the cooling plate 30, the adhesive sheet 40, and the electrostatic chuck 20 in this order in the positive direction of the z-axis, i.e., vertically upward, and that the plane including the x-axis and y-axis (xy plane) is parallel to the horizontal plane.

[0055] In this case, each protrusion 23 protrudes in the negative direction of the z-axis, is spaced apart from one another at a predetermined pitch p in the x-axis direction, and extends linearly for a predetermined length in the y-axis direction, which is perpendicular to the x-axis direction in the horizontal plane.

[0056] The spaces between adjacent convex portions 23 in the x-axis direction form concave portions 24. Like the convex portions 23, the individual concave portions 24 are spaced apart from one another at a predetermined pitch p in the x-axis direction, and extend linearly a predetermined length in the y-axis direction, which is orthogonal to the x-axis direction in the horizontal plane.

[0057] Hereinafter, such a concave-convex structure 25 of the electrostatic chuck 20 will also be referred to as a "rib structure." In the case shown in Figure 2(b) , the height of the tip surface (lowermost end surface in Figure 2(b) ) 23e of each of the convex portions 23 constituting the concave-convex structure (rib structure) 25 is uniform, and the height of the bottom surface (uppermost end surface in Figure 2(b) ) 24e of each of the concave portions 24 farthest from the cooling plate 30 is also uniform. Note that in the case shown in Figure 2(b) , the convex portions 23 have a trapezoidal cross section and their side surface portions 23s are inclined, but this is not a required feature, and the convex portions 23 may have a rectangular cross section.

[0058] When the electrostatic chuck 20 having such a concave-convex structure 25 at its interface is bonded to the cooling plate 30 with the adhesive sheet 40, which is made of resin and therefore elastic, the convex portions 23 penetrate into the adhesive sheet 40, and the adhesive sheet 40 is deformed and penetrates into the concave portions 24. As a result, the concave portions 24 are completely filled with the adhesive sheet 40. The bonding of the electrostatic chuck 20 and the cooling plate 30 with the adhesive sheet 40 can be achieved by heat-pressure bonding, in which the laminate is heated at a predetermined temperature and pressurized.

[0059] 2(b), there is always a concave-convex reference line L for which the following relationship holds: That is, there is always a concave-convex reference line L such that the cross-sectional area of ​​a portion 23a below the concave-convex reference line L (negative side in the z-axis direction) of one convex portion 23 is equal to the cross-sectional area of ​​a portion 24a above the concave-convex reference line L (positive side in the z-axis direction) of one concave portion 24 adjacent to the convex portion 23. In consideration of symmetry, it can also be said that the portion adjacent to the convex portion 23 in the horizontal direction is the portion 24a obtained by dividing the portion above the concave-convex reference line L (positive side in the z-axis direction) of each of the concave portions 24 adjacent to the convex portion 23 into two halves (symmetrically about the yz plane) in the drawing.

[0060] The unevenness reference line L forms part of an unevenness reference plane that is parallel to the XY plane including the unevenness reference line L. The unevenness reference plane is a plane in which the volume of a portion 23a of one convex portion 23 below the unevenness reference plane (negative side in the z-axis direction) is equal to the volume of a portion 24a of a recess 24 adjacent to the convex portion 23 above the unevenness reference line.

[0061] In other words, the uneven structure 25 is provided in a manner that includes such an uneven reference line L. To be clear, the height position of the uneven reference line L is not necessarily the same as the midpoint of the distance h between the tip surface 23 e of the convex portion and the bottom surface 24 e of the concave portion 24 (hereinafter referred to as the uneven height).

[0062] The unevenness reference line L is a line indicating the height corresponding to the lower surface of the electrostatic chuck 20 when the uneven structure 25 is virtually leveled and flattened. When the convex portions 23 and the concave portions 24 are formed based on the preset unevenness reference line L, the resin of the adhesive sheet 40 that is pushed aside by the intrusion of the convex portions 23 below the unevenness reference line L intrudes into the portion of the adjacent concave portion 24 above the unevenness reference line L without excess or deficiency. In other words, above and below the unevenness reference line L, the intrusion of the convex portions 23 into the adhesive sheet 40 and the intrusion of the adhesive sheet 40 into the concave portions 24 are balanced.

[0063] Therefore, from a macroscopic perspective, the adhesion between the electrostatic chuck 20 having the uneven structure 25 and the cooling plate 30 using the adhesive sheet 40 according to this embodiment is substantially equivalent to the adhesion between the electrostatic chuck 20 having no such uneven structure 25 and the cooling plate 30 using the adhesive sheet 40, in which the flat surface corresponding to the uneven reference line L serves as the adhesion surface 20b.

[0064] On the other hand, in the wafer mounting table 10 according to this embodiment, the contact area between the electrostatic chuck 20 and the adhesive sheet 40 is increased compared to when the adhesive surface 20b is a flat surface that does not have the uneven structure 25, and therefore the adhesive strength of the electrostatic chuck 20 is further increased.

[0065] Furthermore, when the electrostatic chuck 20 heats up due to power supply to the heater electrode 22, such as when a wafer placed on the mounting surface 20a is heated, the heat is transferred from the electrostatic chuck 20 to the cooling plate 30 via the adhesive sheet 40. However, when the uneven structure 25 shown in FIG. 2(b) is employed, the ceramic constituting the electrostatic chuck 20 has a higher thermal conductivity than the resin constituting the adhesive sheet 40. Therefore, heat transfer via the protrusions 23 (particularly near the tip surface 23e) is dominant over heat transfer via the portions of the adhesive sheet 40 that extend into the recesses 24 (particularly near the bottom surface 24e). This is because heat transfer is likely to occur not only at the tip surface 23e indicated by the arrow AR1, but also from the side surface 23s near the tip surface 23e. For example, Al, which is an example of a ceramic material constituting the electrostatic chuck 20, is used. ２ O ３ The thermal conductivity of alumina is 35 W / m·K, whereas the thermal conductivity of thermosetting epoxy resin, which is an example of the resin material that constitutes adhesive sheet 40, is 0.2 W / m·K.

[0066] As a result, in an electrostatic chuck 20 having an uneven structure 25 along a certain uneven reference line L, heat transfer occurs more efficiently than in an electrostatic chuck 20 that simply has a flat adhesive surface 20b at a position corresponding to the uneven reference line L.

[0067] Furthermore, if we ignore variations in the thickness of the adhesive sheet 40, in the range where the height of the tip surface 23e of the convex portion 23, which controls heat transfer as described above, is uniform, the distance between the cooling plate 30 and the tip surface 23e of the convex portion 23 is constant regardless of location, and therefore, when viewed over the entire range, a state is achieved in which heat is transferred uniformly from the electrostatic chuck 20 to the cooling plate 30 via the adhesive sheet 40.

[0068] The fact that the electrostatic chuck 20 with the concave-convex structure 25 has superior heat transfer properties compared to the electrostatic chuck 20 without the concave-convex structure 25 also means that, under the same conditions of electrical heating using the heater electrode 22, heat transfer from the wafer occurs more easily and the wafer is cooled more easily when heating is performed by energizing the heater electrode 22 on the wafer mounting table 10 using the former than when similar electrical heating is performed on the wafer mounting table 10 using the latter. In consideration of this, when heating the wafer to the same temperature using electrical heating in the former case, the heater power from the heater power supply 80 can be increased when using the wafer mounting table 10, or a thicker adhesive sheet 40 can be used in advance. In this case, the heat transfer can be made uniform and the wafer can be heated in the same way as when the electrostatic chuck 20 does not have the concave-convex structure 25.

[0069] Preferably, the pitch p of the convex portions 23 is 100 μm or more and 300 μm or less. Furthermore, in the case of a rib structure 25 as shown in FIG. 2( b), the concave portions 24 also have the same pitch p. Setting the pitch p of the convex portions 23 to less than 100 μm is not preferred because it is not easy to ensure the processing precision, including the formation of the concave portions 24, and it is not easy to obtain the desired concave-convex structure 25. Setting the pitch p of the convex portions 23 to more than 300 μm is also not preferred because the resin constituting the adhesive sheet 40 must move (displace or deform) significantly in order for the adhesive sheet 40 to enter the concave portions 24 during bonding, which leaves residual stress after bonding.

[0070] More preferably, the pitch p of the protrusions 23 is set to 150 μm or more. In this case, the desired uneven structure 25 can be formed relatively easily and reliably, and the effect of improving the efficiency of heat transfer can also be obtained favorably.

[0071] However, the shapes of the convex portions 23 and the concave portions 24 corresponding to a certain concave-convex reference line L are not limited to one type. Fig. 3 is a diagram illustrating two types of concave-convex structures 25 (25H, 25L) that share the same concave-convex reference line L but have different shapes of the convex portions 23 and the concave portions 24.

[0072] 3, the cross section of the convex portion 23 (23H) has a vertically elongated shape in the drawing that is narrow in the horizontal direction (x-axis direction), while the cross section of the concave portion 24 (24H) is wider in the horizontal direction than the convex portion 23 (23H). However, although the distance from the concave-convex reference line L to the tip surface 23e of the convex portion 23 is greater than the distance from the concave-convex reference line L to the bottom surface 24e of the concave portion 24, the cross-sectional areas of the portion 23a below the concave-convex reference line L and the portion 24a above the concave-convex reference line L are equal.

[0073] 3, the cross-sectional shapes of the convex portion 23 (23L) and the concave portion 24 (24L) are the same. In this structure, too, the cross-sectional areas of the portion 23a below the concave-convex reference line L and the portion 24a above it are equal.

[0074] Comparing the uneven structure 25H and the uneven structure 25L, the uneven reference line L is common, and the distance from the tip surface 23e of the convex portion 23 to the cooling plate 30 is constant within the range of each structure, while the distance from the uneven reference line L to the tip surface 23e of the convex portion 23H in the uneven structure 25H is larger than the distance from the uneven reference line L to the tip surface 23e of the convex portion 23L in the uneven structure 25L, and therefore the distance to the cooling plate 30 of the convex portion 23H is shorter than that of the convex portion 23L.

[0075] Hereinafter, the uneven structure 25H in which the tip surfaces 23e of the convex portions 23 are relatively far from the uneven reference line L will also be referred to as a high rib structure (or H rib) 25H, and the uneven structure 25L in which the tip surfaces 23e of the convex portions 23 are relatively close to the uneven reference line L will also be referred to as a low rib structure (or L rib) 25L. Note that the high rib structure 25H and the low rib structure 25L shown in Fig. 3 are merely schematic examples, and the specific shapes are not limited to these.

[0076] Such a difference in the uneven structure 25 is related to the magnitude of heat transfer from the electrostatic chuck 20 to the cooling plate 30 via the adhesive sheet 40 .

[0077] That is, the shorter the distance from the tip surface 23e to the cooling plate 30, the smaller the thermal resistance of the adhesive sheet 40 and the greater the amount of heat transfer. Conversely, the greater the distance from the tip surface 23e to the cooling plate 30, the greater the thermal resistance of the adhesive sheet 40 and the smaller the amount of heat transfer. Therefore, in the case shown in Figure 3, the heat transfer from the tip surface 23e of the convex portion 23 is greater for the high rib structure 25H than for the low rib structure 25L shown on the right. In other words, when the conditions for electrical heating using the heater electrode 22 are the same, the area with the high rib structure 25H is more easily cooled than the area with the low rib structure 25L.

[0078] In the present embodiment, the relationship between the distance from the tip surface 23 e of the protrusion 23 to the cooling plate 30 and the thermal resistance of the adhesive sheet 40 as described above is utilized to correct the variation in heat generation distribution on the mounting surface 20 a of the electrostatic chuck 20. In principle, the higher the temperature is compared to a certain reference temperature, the closer the tip surface 23 e of the protrusion 23 to the cooling plate 125 in the uneven structure 25 provided on the opposite surface, and the lower the temperature is compared to the reference temperature, the farther the tip surface 23 e of the protrusion 23 is from the cooling plate 125. This makes it possible to reduce the variation in temperature (or heat generation density) on the mounting surface 20 a (to make the mounting surface 20 a uniform temperature) compared to when no correction is performed.

[0079] Note that such correction is intended only to reduce temperature variations relative to a certain reference temperature, and absolute temperature adjustments, such as matching the temperature of a specific location on the mounting surface 20a to the reference temperature, are performed by adjusting the heater power input to the heater power supply 80 when the wafer mounting table 10 is in use, or by adjusting the thickness of the adhesive sheet 40 to be used in advance.

[0080] 4 is a diagram for explaining the correction of temperature (or heat generation density) variations performed in this embodiment. In this embodiment, the electrostatic chuck 20 is virtually divided into a plurality of unit regions RE in a plan view, and the mixing ratio (planar area ratio) of the high rib structures 25H and the low rib structures 25L in each unit region RE is changed according to the temperature before correction, so that the temperature (or heat generation density) is corrected for each unit region RE. Hereinafter, the region of the unit region RE where the high rib structures 25H are provided will be referred to as a sub-region RE1, and the region where the low rib structures 25L are provided will be referred to as a sub-region RE2.

[0081] More specifically, utilizing the relationship that the more high rib structures 25H there are, the more likely a temperature drop occurs, and the more low rib structures 25L there are, the less likely a temperature drop occurs, the correspondence between the planar area ratio of sub-regions RE1 and RE2 and the amount of temperature (or heat generation density) correction is experimentally determined in advance. Then, based on the actual heat generation distribution, the area ratio to be applied to each unit region RE is set, and each unit region is provided with a concavo-convex structure 25 corresponding to that area ratio. The combination of high rib structures 25H and low rib structures 25L that gives such a planar area ratio between sub-regions RE1 and RE2 is also referred to as a rib pattern.

[0082] The high rib structure 25H and the low rib structure 25L are also referred to as the first unit structure and the second unit structure, respectively. In other words, the rib pattern is a mixture of one or more types of unit structures in a predetermined ratio. Furthermore, the convex portion 23H and the concave portion 24H of the high rib structure 25H are also referred to as the first convex portion and the first concave portion, respectively, and the convex portion 23L and the concave portion 24L of the low rib structure 25L are also referred to as the second convex portion and the second concave portion, respectively.

[0083] 4 illustrates an example in which the area ratio between the sub-region RE1 of the high rib structure 25H consisting of two partial sub-regions RE1a and RE1b and the sub-region RE2 of the low rib structure 25L between the two regions is 2:1. Note that the sub-region RE2 may have partial sub-regions, and the number of partial sub-regions in the sub-regions RE1 and RE2 is not particularly limited. However, it is preferable that the sub-regions RE1 and RE2 are periodically arranged at least within the unit region RE.

[0084] 5 is a diagram showing the measured cross-sectional shape profile of the electrostatic chuck 20 when the ratio of the high rib structure 25H having a pitch p of 150 μm and a concave-convex height h of 50 μm to the low rib structure 25L having a pitch p of 150 μm and a concave-convex height h of 20 μm is varied in four different ways in a unit area RE having a planar size of 37.5 mm × 37.5 mm. The reference temperature is set to 97.7° C.

[0085] 5A shows the profile of a rib pattern having only the high rib structure 25H. Experiments have confirmed that this rib pattern enables temperature correction, reducing the temperature difference between the reference temperature and the temperature on the mounting surface 20a that is higher than the reference temperature by 1°C. This is because, during bonding, the protrusions 23H of the high rib structure 25H penetrate into the adhesive sheet 40, bringing the tip surfaces 23e of the protrusions 23H closer to the cooling plate 30 than when no correction is performed (when bonding is performed on the flat adhesive surface 20b), thereby increasing the amount of heat transfer from the mounting surface 20a.

[0086] 5(d) shows the profile of a rib pattern having only low rib structures 25L. Experiments have confirmed that this rib pattern enables temperature correction, reducing the temperature difference between the reference temperature and the low rib structure 25L on the mounting surface 20a, which is lower than the reference temperature, by 1°C. This is because, even though the protrusions 23L of the low rib structure 25L penetrate into the adhesive sheet 40 during bonding, the distance between the tip surfaces 23e of the protrusions 23L and the cooling plate 30 is larger than when no correction is performed (when bonding is performed on the flat adhesive surface 20b), thereby reducing the amount of heat transfer from the mounting surface 20a.

[0087] In the following, the correction using the former rib pattern will also be referred to as a correction with a temperature correction amount of −1° C., and the correction using the latter rib pattern will be referred to as a correction with a temperature correction amount of +1° C.

[0088] Furthermore, Figure 5(b) shows the profile of a rib pattern in which the high rib structure 25H and the low rib structure 25L are arranged in a 2:1 ratio. Meanwhile, Figure 5(c) shows the profile of a rib pattern in which the high rib structure 25H and the low rib structure 25L are arranged in a 1:2 ratio. It has also been confirmed that when these rib patterns are employed, the temperature correction amounts on the mounting surface 20a are -0.33°C and +0.33°C, respectively. This means that the temperature correction amount when a rib pattern in which both the high rib structure 25H and the low rib structure 25L are employed is an intermediate value between the temperature correction amount of a rib pattern in which only one of the high rib structure 25H and the low rib structure 25L is provided.

[0089] In this way, by changing the rib pattern in each unit area RE of the mounting surface 20a depending on the temperature before correction, an electrostatic chuck 20 can be obtained with improved thermal uniformity compared to when no correction is performed.

[0090] <Specific Example of Temperature Variation Correction> Next, a specific example of temperature variation correction on the mounting surface 20a performed by changing the rib pattern, in other words, by changing the area ratio between the sub-region RE1 and the sub-region RE2, will be described. Figure 6 is a diagram for explaining the specific content of temperature variation correction.

[0091] In order to correct the variations, the wafer mounting table 10 should be constructed using a pre-correction electrostatic chuck 20 that does not have the uneven structure 25 (hereinafter referred to as an uneven electrostatic chuck), the electrostatic chuck 20 should be heated by passing current through the heater electrode 22, and the uneven structure 25 should be formed on the electrostatic chuck 20 based on the temperature distribution on the mounting surface 20 a obtained thereby. However, in this case, the electrostatic chuck 20 without the uneven structure 25 that has been bonded to the cooling plate 30 with the adhesive sheet 40 should be separated to form the uneven structure 25. However, such re-separation is not easy. Moreover, if the uneven structure 25 is formed on the separated electrostatic chuck 20 and then the electrostatic chuck 20 is re-bonded, the bonding state may change. Therefore, this configuration is not necessarily practical.

[0092] On the other hand, for example, if a large number of electrostatic chucks without unevenness are manufactured under the same manufacturing conditions, it is highly likely that the temperature distributions in each of the electrostatic chucks without unevenness will be approximately the same. Therefore, in this embodiment, under this assumption, the temperature distribution of the mounting surface 20 a as shown in FIG. 6( a) is measured for a wafer mounting table 10 constructed using one of such a large number of electrostatic chucks without unevenness, and the result is considered to be the temperature distribution before correction. Temperature variations in other electrostatic chucks 20 manufactured under the same conditions are corrected as part of a pre-bonding preparation process. That is, the uneven structure 25 is provided in each unit region RE of the electrostatic chuck 20 in the same manufacturing lot as the electrostatic chuck 20 for which the temperature distribution measurement was performed, using a common rib pattern based on the temperature distribution before correction.

[0093] In this case, the electrostatic chuck 20 without irregularities that provides the temperature distribution of the mounting surface 20a before correction is referred to as the reference electrostatic chuck 20, and the electrostatic chuck 20 in which the temperature variation correction is performed by providing an irregularity structure 25 based on the temperature distribution before correction is referred to as the electrostatic chuck 20 to be corrected.

[0094] FIG. 6A shows that the ceramic member of the electrostatic chuck 20 is made of alumina (Al ２ O ３1 is a diagram showing a temperature distribution image (thermography image) IM1 on the mounting surface 20a of the reference electrostatic chuck 20 when current is applied to the heater electrode 22 of the reference electrostatic chuck 20 in a wafer mounting table 10 in which the adhesive sheet 40 is made of a thermosetting epoxy resin. In the temperature distribution image IM1, areas closer to white indicate relatively higher temperatures, and areas closer to black indicate relatively lower temperatures. In the temperature distribution image IM1, high-temperature regions exist on the left and right sides of the upper side, while a low-temperature region extends over a wide area except for the vicinity of the center of the lower half. The difference between the maximum and minimum temperatures was 3.1°C.

[0095] 6A, a square mesh M with a side length of 37.5 mm is virtually superimposed on the temperature distribution image IM1. The mesh M is made up of a total of 64 (8×8) square unit meshes Mu. Each unit mesh Mu corresponds to the above-mentioned unit area RE, and a temperature correction amount for the unit area RE of the correction target electrostatic chuck 20 corresponding to the unit mesh Mu is determined based on the temperature distribution within each unit mesh Mu in the temperature distribution image IM1. On the bonding surface 20b of the correction target electrostatic chuck 20, a concavo-convex structure 25 (rib pattern) corresponding to the determined temperature correction amount is formed for each unit area RE.

[0096] In this correction example, one of the five rib patterns A to E shown in Table 1 was applied to perform temperature correction for each unit region RE. In this case, the correction was performed so that the intermediate temperature between the maximum and minimum temperatures described above became the reference temperature. Note that in Table 1, an area ratio of 0 for L ribs or H ribs means that only H ribs (high rib structure 25H) or L ribs (low rib structure 25L) are formed.

[0097]

[0098] Table 1 shows that, for example, for a unit region RE where it is determined that the temperature of the mounting surface 20a should be lowered by 1°C compared to before correction based on the temperature distribution in the unit mesh Mu, a rib pattern A consisting only of a high rib structure 25H is applied. Similarly, for unit regions RE where it is determined that the temperature of the support surface 20a should be lowered by 0.33°C compared to before correction, rib pattern B, in which the high rib structures 25H and the low rib structures 25L are arranged in a ratio of 4:2 (=2:1), is applied. For unit regions RE where it is determined that the temperature is close to the reference temperature and should be maintained at the pre-correction temperature, rib pattern C, in which the high rib structures 25H and the low rib structures 25L are arranged in a ratio of 3:3 (=1:1), is applied. For unit regions RE where it is determined that the temperature of the support surface 20a should be increased by 0.33°C compared to before correction, rib pattern D, in which the high rib structures 25H and the low rib structures 25L are arranged in a ratio of 2:4 (=1:2), is applied. For unit regions RE where it is determined that the temperature of the support surface 20a should be increased by 1°C compared to before correction, rib pattern E, consisting only of the low rib structures 25L, is applied. Note that the rib pattern settings are not limited to those shown in Table 1 and may be set appropriately depending on the obtained temperature distribution image.

[0099] 6B is a diagram showing a rib pattern applied to a unit area RE corresponding to each unit mesh Mu, which is set based on the temperature distribution image IM1, in correspondence with the mesh M in FIG. 6A. Based on the rib pattern, a concavo-convex structure 25 is provided in each unit area RE of the electrostatic chuck 20 to be corrected.

[0100] 7 is a diagram showing a temperature distribution image IM2 on the mounting surface 20 a of the wafer mounting table 10 configured using the electrostatic chuck 20 to be corrected that is from the same manufacturing lot as the reference electrostatic chuck 20 from which the temperature distribution image IM1 in FIG. 6A was obtained. The temperature scale based on shading is the same as that of the temperature distribution image IM1.

[0101] Comparing the temperature distribution image IM2 with the temperature distribution image IM1, it can be seen that the temperature distribution image IM2 has eliminated any significant high temperature areas and reduced low temperature areas. The difference between the maximum and minimum temperatures was 2.2°C.

[0102] These results show that the temperature variation correction according to this embodiment is an effective solution.

[0103] <Method of forming concave-convex structure> Next, one embodiment of a method of forming the concave-convex structure 25 as a preparatory step before bonding will be described. Specifically, an embodiment in which the convex portions 23 and the concave portions 24 form a rib structure having a trapezoidal cross-sectional shape by laser processing will be described. Fig. 8 is a diagram showing how the high rib structure 25H is formed, and Fig. 9 is a diagram showing how the low rib structure 25L is formed. Note that in Figs. 8 and 9, the electrostatic chuck 20 is upside down compared to Fig. 2 and the like.

[0104] The formation of both rib structures is common in that a recess 24 is formed at the irradiation position of the laser light LB by repeatedly irradiating the processing target surface 20s (the surface opposite the mounting surface 20a) of the electrostatic chuck 20 with laser light LB along the y-axis direction before processing (before correction), but the specific irradiation manner is different.

[0105] 8(a) and 9(a), in the concave-convex structure 25 (high rib structure 25H or low rib structure 25L) to be formed with a pitch p, the width of the tip surface 23e of the convex portion 23 is w1, the width of the bottom surface 24e of the concave portion 24 is w2, the concave-convex height (the distance between the tip surface 23e of the convex portion 23 and the bottom surface 24e of the concave portion 24) is h, and the maximum opening width of the concave portion 24 (the width at the same height as the tip surface 23e of the convex portion 23) is w0. Furthermore, the concave portion 24 is formed so that the zx cross section perpendicular to the y-axis direction, which is its extension direction, is symmetrical with respect to the central axis C extending in the vertical direction (z-axis direction).

[0106] In such cases, although the specific numerical values ​​are different, both the high rib structure 25H and the low rib structure 25L shown in Figures 8(a) and 9(a) have a structure in which a convex portion 23 having a width of w1 and a height of h at the tip surface 23e and extending in the y-axis direction, and a concave portion 24 having a width of w2 at the bottom surface 24e and a maximum opening width of w0 and also extending in the y-axis direction, are alternately adjacent to each other in the x-axis direction.

[0107] From the viewpoint of ensuring good heat transfer from the electrostatic chuck 20 to the adhesive sheet 40, the width w1 of the tip surface 23e of the convex portion 23 is desirably 40 μm or more, and from the viewpoint of being less susceptible to the effects of processing variations, the width w1 of the tip surface 23e of the convex portion 23 is desirably 40 μm or more. Furthermore, if the inclination of the side surface 23s of the convex portion 23 with respect to the horizontal plane (xy plane) is 45° or less and the width w2 of the bottom surface 24e of the concave portion 24 is 10 μm or more, the adhesiveness of the adhesive sheet 40 is more sufficiently ensured.

[0108] To form the high rib structure 25H, as shown in FIG. 8( b), the laser beam LB may be sequentially irradiated onto positions spaced apart by a predetermined irradiation pitch Δwa in the x-axis direction within a predetermined width w3 along the x-axis direction on the processing target surface 20s (the surface opposite the mounting surface 20a) of the electrostatic chuck 20 before processing (before correction). The width w3 is set so that its center position in the x-axis direction coincides with the central axis C of the recess 24 to be finally formed. Furthermore, when forming the protrusions 23 and recesses 24 each having a trapezoidal cross-section as shown in FIG. 8( a), the width w3 may be smaller than the maximum opening width w0 of the recess 24 to be formed. The irradiation of the laser beam LB may be repeated a predetermined number of times.

[0109] For example, when using laser light LB with an output of 20 W, a wavelength of 1030 nm, and a frequency of 200 kHz to form a high rib structure 25H in which the pitch p is 150 μm, the width w1 of the tip surface 23e of the convex portion 23 is 40 μm, the width w2 of the bottom surface 24e of the concave portion 24 is 10 μm, the maximum opening width w0 of the concave portion 24 is 140 μm, the unevenness height h is 45 μm, and the distance between the tip surface 23e of the convex portion 23 and the unevenness reference line L is 15 μm, irradiation of laser light LB with a width w3 of 29 μm and an irradiation pitch Δwa of 1 μm (i.e., irradiation at 30 locations) can be repeated three times, centered on the position that will be the central axis C of the concave portion 24 to be formed.

[0110] On the other hand, when forming the low rib structure 25L, first, as shown in FIG. 9B , laser light LB is sequentially irradiated onto positions spaced apart by a predetermined irradiation pitch Δwb in the x-axis direction over the entire area to be formed of the low rib structure 25L on the processing target surface (the surface opposite the mounting surface 20a) 20s of the electrostatic chuck 20 before processing (before correction). As a result, the ceramic member constituting the electrostatic chuck 20 is removed by a predetermined depth d on the processing target surface 20s side. This irradiation of the laser light LB is referred to as primary irradiation. The primary irradiation may be repeated a predetermined number of times.

[0111] 9(c), laser light LB is sequentially irradiated onto positions spaced apart by a pitch p on the surface 20t newly formed by the removal. The irradiation position in the x-axis direction is set so as to coincide with the position of the central axis C of the recess 24 to be finally formed. This irradiation of laser light LB is referred to as secondary irradiation. The secondary irradiation may be repeated a predetermined number of times.

[0112] For example, when using laser light LB with an output of 20 W, a wavelength of 1030 nm, and a frequency of 200 kHz to form a low rib structure 25L having a pitch p of 150 μm, a width w1 of the tip surface 23e of the convex portion 23 of 40 μm, a width w2 of the bottom surface 24e of the concave portion 24 of 10 μm, a maximum opening width w0 of the concave portion 24 of 140 μm, an unevenness height h of 15 μm, and a distance between the tip surface 23e of the convex portion 23 and the unevenness reference line L of 15 μm, a primary irradiation of laser light LB with an irradiation pitch Δwb of 15 μm is performed once, and then secondary irradiation at a pitch of 150 μm is repeated 10 times.

[0113] In addition, for simplicity of illustration in FIGS. 8 and 9, the side surface 23s of the convex portion 23 is shown as being linear in cross section, but may be stepped or curved depending on the processing conditions.

[0114] Furthermore, as described above, the temperature variation is corrected for each unit region RE, but in known laser beam irradiation devices capable of irradiating the laser beam LB with high precision at pitches of several μm to several tens of μm, the scanning distance of the laser beam LB (the linear distance that can be processed in one continuous irradiation) is at most about 70 mm. Therefore, it is desirable that the size of the unit region RE be 70 mm or less, at least in the scanning direction (y-axis direction).

[0115] Furthermore, when correcting for temperature variations, the rib patterns in each unit region RE are usually different, so the combination of high rib structures 25H and low rib structures 25L formed by irradiation with laser light LB as shown in Figures 8 and 9 also depends on the rib pattern applied to each unit region RE. Therefore, high rib structures 25H and low rib structures 25L are provided in multiple unit regions RE, and when forming a desired rib pattern in each unit region RE, all of the high rib structures 25H and low rib structures 25L may be formed individually across the entire processing surface 20s, or the high rib structures 25H and low rib structures 25L may be formed sequentially for each unit region RE according to the rib pattern applied.

[0116] 2B, in the wafer mounting table 10 according to this embodiment, the uneven structure 25 is provided, thereby making the heat transfer from the electrostatic chuck 20 to the cooling plate 30 via the adhesive sheet 40 uniform at locations where the heights of the tip surfaces 23e of the convex portions 23 are the same. Furthermore, as shown in FIGS. 3 and 4, by utilizing the fact that the magnitude of heat transfer differs depending on the distance between the tip surfaces 23e of the convex portions 23 and the cooling plate 30, the temperature variation on the mounting surface 20a of the electrostatic chuck 20 when current is applied to the heater electrode 22 is corrected for each unit area RE based on a rib pattern such as that shown in Table 1.

[0117] However, the intended effect of such correction can only be achieved when there is substantially no unevenness in the thickness of the adhesive sheet 40 before bonding, or when the unevenness can be substantially ignored. For example, as shown in Figure 4, the balance between the penetration of the convex portions 23 into the adhesive sheet 40 and the penetration of the adhesive sheet 40 into the concave portions 24 above and below the unevenness reference line L is based on the premise that the thickness of the adhesive sheet 40 is uniform.

[0118] However, in actual adhesive sheet 40, for example, when the target thickness is 200 μm, thickness variations (deviations from the specified thickness) of up to about 2 μm may exist locally or overall.

[0119] FIG. 10 is a diagram schematically illustrating the state of the wafer table 10 in which the adhesive sheet 40 has uneven thickness.

[0120] More specifically, FIG. 10A shows a wafer mounting table 10 in which the electrostatic chuck 20 and the cooling plate 30 are bonded to each other by an adhesive sheet 40 having an upper surface 40a that is convex upward and serves as the bonding surface for the electrostatic chuck 20. The thickness of the adhesive sheet 40 is assumed to be at most Δt greater than the reference thickness t. Note that, in this embodiment, the reference thickness t does not refer to the thickness that the adhesive sheet 40 should originally have (the thickness assumed during the design of the wafer mounting table 10), but rather refers to the minimum thickness. Therefore, in this embodiment, thickness variations in the adhesive sheet 40 refer to areas that are relatively thicker than other areas. Furthermore, the electrostatic chuck 20 is assumed to be recessed in accordance with the shape of the upper surface 40a of the adhesive sheet to ensure the flatness of the mounting surface 20a.

[0121] Fig. 10(b) shows a schematic profile of the thermal resistance in the x-axis direction of such an adhesive sheet 40. Note that Fig. 10(b) also corresponds to the profile of the temperature distribution on the mounting surface 20a when heating by the heater electrode 22 is performed uniformly.

[0122] The thicker the adhesive sheet 40, the greater the thermal resistance, and therefore the smaller the heat transfer from the electrostatic chuck 20 to the cooling plate 30. That is, in the configuration shown in Fig. 10(a), the difference in thickness of the adhesive sheet 40 is dominant with respect to the heat transfer from the electrostatic chuck 20 to the cooling plate 30, which affects the thermal uniformity.

[0123] 10A illustrates a case where a single protrusion exists over the entire adhesive sheet 40 for the sake of simplicity, but in reality, one or more local thickness variations may exist, and recesses corresponding to the thickness variations may be formed in the electrostatic chuck 20. Even in such a case, the thickness variations directly affect the heat transfer from the electrostatic chuck 20 to the cooling plate 30.

[0124] On the other hand, FIG. 11 is a diagram schematically illustrating a wafer mounting table 10 in which an uneven structure 25 corresponding to uneven thickness of an adhesive sheet 40 is provided on an electrostatic chuck 20 .

[0125] 11(a) shows a wafer mounting table 10 in which an electrostatic chuck 20 having an uneven structure 25 and a cooling plate 30 are bonded together with an adhesive sheet 40 having the same thickness unevenness as that shown in FIG. 10(a). In addition, in FIG. 11(a), the position of an upper surface 40a in FIG. 10(a) is indicated by a dashed line, which shows the surface shape of the adhesive sheet 40 before bonding.

[0126] 11(a) provided on the electrostatic chuck 20, the tip surfaces 23e of the protrusions 23 have a uniform height, as in the case of the electrostatic chuck 20 shown in FIG. 3, while the height of the bottom surfaces 24e of the recesses 24 varies depending on the location. More specifically, the degree of unevenness is small where the thickness variation is small, and the degree of unevenness is large where the thickness variation is large. As a result, the unevenness structure 25 as a whole is aligned with the position of the upper surface 40a.

[0127] In such a case, it is not possible to conceive of a reference line L for the unevenness that extends across the entire electrostatic chuck 20, but locally, it can be said that the penetration of the convex portions 23 into the adhesive sheet 40 above and below the upper surface 40a and the penetration of the adhesive sheet 40 into the concave portions 24 are roughly balanced.

[0128] Fig. 11(b) shows a schematic profile of the thermal resistance in the x-axis direction of the adhesive sheet 40 when the adhesive sheet 40 is bonded in the manner shown in Fig. 11(a). Note that Fig. 11(b) also corresponds to the profile of the temperature distribution on the mounting surface 20a when the heater electrode 22 uniformly heats the mounting surface 20a.

[0129] 11(b), when the uneven structure 25 is provided on the electrostatic chuck 20 in the manner shown in Fig. 11(a), the thermal resistance in the adhesive sheet 40 becomes approximately uniform regardless of location. This is because, similar to the case shown in Fig. 2(b), heat transfer from the protrusions 23 provided at a uniform height becomes dominant.

[0130] This suggests that if the height of the tip surface 23e of the convex portion 23 is made uniform while the degree of unevenness in the uneven structure 25 is adjusted according to the unevenness in the thickness of the adhesive sheet 40, it is possible to suitably correct the temperature variation on the mounting surface 20a of the electrostatic chuck 20 even if the adhesive sheet 40 has uneven thickness.

[0131] However, as described above, in reality, temperature (or heat generation density) variations occur randomly and indefinitely depending on the location, so it is not realistic to change the height of the tip surface 23e in a way that faithfully corresponds to such variations. In addition, the degree of thickness unevenness in the adhesive sheet 40 varies from one individual to another, so it is not realistic to faithfully correspond to such thickness unevenness.

[0132] Therefore, prior to bonding, the thickness distribution of the adhesive sheet 40 is measured in advance, and if the adhesive sheet 40 has thickness unevenness, in order to correct the temperature variation on the mounting surface 20a, the rib pattern in each unit region RE is set in the above-described manner based on the temperature distribution on the mounting surface 20a of the reference electrostatic chuck 20. In addition to the normal high rib structure 25H and low rib structure 25L, high rib structures 25H and low rib structures 25L in which the recesses 24 are deeper than the depth determined in relation to the uneven reference line L in order to absorb the thickness unevenness are also used as constituent units of the rib pattern. Hereinafter, the high rib structure 25H and low rib structure 25L in which the recesses 24 are deepened in this way will be referred to as the thickness-absorbing high rib structure 25H and the thickness-absorbing low rib structure 25L, respectively.

[0133] While the normal high rib structure 25H and low rib structure 25L are referred to as the first and second unit structures, respectively, the thickness-absorbing high rib structure 25H and thickness-absorbing low rib structure 25L are also referred to as the third and fourth unit structures, respectively. In other words, when absorbing thickness variations in the adhesive sheet 40 in addition to correcting temperature variations, the rib pattern is a mixture of one or more of these four types of unit structures in a predetermined ratio. Furthermore, the convex portions 23H and concave portions 24H of the thickness-absorbing high rib structure 25H are also referred to as the third convex portions and the third concave portions, respectively, and the convex portions 23L and concave portions 24L of the thickness-absorbing low rib structure 25L are also referred to as the fourth convex portions and the fourth concave portions, respectively.

[0134] 12 is a diagram illustrating a thickness-absorbing high rib structure 25H, and FIG. 13 is a diagram illustrating a thickness-absorbing low rib structure 25L. As shown in FIGS. 12(a) and 13(a), the thickness-absorbing high rib structure 25H and the thickness-absorbing low rib structure 25L have the same convex portions 23 as the normal high rib structure 25H and the normal low rib structure 25L, and are formed in the same manner as the normal convex portions 23 (when thickness unevenness is not taken into consideration). Meanwhile, the recesses 24 are formed so that their bottom surfaces 24f are deeper than the bottom surfaces 24e of the recesses 24 in the normal high rib structure 25H and the normal low rib structure 25L, which are determined according to the position of the unevenness reference line L. This can be achieved by appropriately adjusting the processing conditions during the laser processing described above.

[0135] As a result, as shown in Figures 12(b) and 13(b), in the thickness absorbing high rib structure 25H and the thickness absorbing low rib structure 25L, a range deeper than the recess 24 in the normal high rib structure 25H and the low rib structure 25L becomes the thickness absorbing region 24α.

[0136] When correcting the temperature variation on the mounting surface 20a, the area ratios of the normal high rib structure 25H, the normal low rib structure 25L, the thickness absorbing high rib structure 25H, and the thickness absorbing low rib structure 25L in the rib pattern applied to the unit area RE are changed depending on the amount of temperature correction in each unit area RE identified from the temperature distribution on the mounting surface 20a in the reference electrostatic chuck and the degree of thickness unevenness in the adhesive sheet 40 at the location corresponding to the individual unit area RE, which has been identified in advance.

[0137] That is, in Figures 12 and 13, for the sake of simplicity, a bottom surface 24f is formed at a position deeper than the normal bottom surface 24e in only one recess 24, and a thickness absorption region 24α is provided, but in reality, the area ratio of the thickness absorbing high rib structure 25H and the thickness absorbing low rib structure 25L in each unit region RE is set according to the degree of thickness unevenness at the location corresponding to each unit region RE, in other words, according to the size of the thickness unevenness to be absorbed in each unit region RE.

[0138] In this case, the uneven structure 25 in each unit region RE does not necessarily correspond to the shape of the actual thickness unevenness at the location of the adhesive sheet 40 corresponding to that unit region RE, but the greater the thickness unevenness in the location, the greater the area ratio of the thickness-absorbing high rib structure 25H to the thickness-absorbing low rib structure 25L. In other words, more thickness-absorbing regions 24α are provided. Because the adhesive sheet 40 is elastic, the locations with thickness unevenness are deformed by the intrusion of the protrusions 23 and are therefore able to suitably intrude into the recesses 24 having the thickness-absorbing regions 24α.

[0139] The maximum thickness adjustment amount of the adhesive sheet 40 by providing the thickness-absorbing high rib structure 25H and the thickness-absorbing low rib structure 25L is 2 μm or more. This means that when at least one of the thickness-absorbing high rib structure 25H and the thickness-absorbing low rib structure 25L is provided in the unit region RE, the amount of thickness variation absorption is at least 2 μm. In this case, the thickness variation absorption by the thickness-absorbing region 24α becomes effective.

[0140] Table 2 shows examples of rib patterns set in each unit region RE when temperature variations on the mounting surface 20a are corrected while absorbing thickness variations, and shows the area ratios of a normal high rib structure 25H (H rib), a normal low rib structure 25L (L rib), a thickness-absorbing high rib structure 25H (thickness-absorbing H rib), and a thickness-absorbing low rib structure 25L (thickness-absorbing L rib). In Table 2, the area ratios of each rib structure are designated A, B, C, and D, respectively. An area ratio of 0 means that the corresponding rib structure is not provided.

[0141]

[0142] In the example shown in Table 2, the thermal resistance adjustment amount for temperature variation correction is adjusted to five levels: +1.0° C., +0.5° C., ±0° C., −0.5° C., and −1.0° C. For example, a thermal resistance adjustment amount of +1.0° C. corresponds to performing a temperature correction that reduces the temperature difference between the reference temperature and the mounting surface 20a that is lower than the reference temperature by 1.0° C.

[0143] In the example shown in Table 2, the ratio (A+B) of the sum of the ratios of the normal high rib structure 25H and the thickness-absorbing high rib structure 25H to the sum of the ratios (C+D) of the normal low rib structure 25L and the thickness-absorbing low rib structure 25L is changed to five levels: 8:0, 6:2, 4:4, 2:6, and 0:8, thereby varying the thermal resistance adjustment amount among the five levels. This means that the thickness-absorbing high rib structure 25H and the thickness-absorbing low rib structure 25L function equally to the normal high rib structure 25H and the thickness-absorbing low rib structure 25L in terms of correcting temperature variations on the support surface 20a.

[0144] On the other hand, by changing the ratio of the sum of the ratios of the normal high rib structure 25H and the normal low rib structure 25L (A+C) to the sum of the ratios of the thickness-absorbing high rib structure 25 and the thickness-absorbing low rib structure 25L (B+D) from 8:0, 4:4, and 0:8, the sheet thickness adjustment amount can be changed to three levels: 0 μm, 1 μm, and 2 μm.

[0145] This makes it possible to correct temperature variations on the mounting surface 20a even when the adhesive sheet 40 has thickness variations, by applying one of 15 rib patterns to each unit area RE depending on the temperature distribution on the mounting surface 20a of the reference electrostatic chuck 20 and the distribution of thickness variations on the adhesive sheet 40 that have been specified in advance.

[0146] It has been confirmed that when a rib pattern of A:B:C:D = 8:0:0:0 is applied to a unit area RE where the temperature at the corresponding location on the mounting surface 20a rises by 1°C compared to when there is no thickness unevenness, when a rib pattern of A:B:C:D = 0:8:0:0 is applied, the temperature rise is limited to 0.1°C.

[0147] It has also been confirmed that, while applying a rib pattern of A:B:C:D = 0:0:8:0 causes the temperature at the corresponding location on the mounting surface 20a to rise by 1°C compared to when there is no thickness unevenness, applying a rib pattern of A:B:C:D = 0:0:0:8 limits the temperature rise to only 0.4°C.

[0148] As described above, according to the present embodiment, in a wafer mounting table configured such that an electrostatic chuck and a cooling plate are bonded to each other with an adhesive sheet, by providing an uneven structure on the adhesive surface of the electrostatic chuck that is bonded to the adhesive sheet, a wafer mounting table having superior heat transfer properties compared to a case where such an uneven structure is not provided is realized.

[0149] In other words, heat transfer from the electrostatic chuck to the cooling plate is dominated by heat transfer from the convex portions, so heat can be transferred from the electrostatic chuck to the cooling plate more efficiently than in the case where there is no uneven structure.

[0150] Furthermore, by making the distance between the tip surface of the convex portion and the cooling plate uniform at least within the range of the uneven structure, heat transfer from the electrostatic chuck to the cooling plate via the adhesive sheet can be made uniform.

[0151] Furthermore, by varying the distance between the tip surfaces of the convex portions and the cooling plate, the degree of heat transfer from the electrostatic chuck to the cooling plate via the adhesive sheet can be adjusted depending on the location. By utilizing this, it is possible to correct temperature variations on the mounting surface by changing the formation mode of the concave-convex structure depending on the temperature distribution on the mounting surface when no concave-convex structure is provided. By adjusting the depth of the concave-convex structure depending on the uneven thickness of the adhesive sheet, it is possible to correct temperature variations on the mounting surface even when such uneven thickness exists.

[0152] <Modifications> In the above-described embodiment, the uneven structure is assumed to be a rib structure in which the convex portions and concave portions are linear and alternately positioned in a plan view, but the uneven structure for temperature uniformity is not limited to this.

[0153] For example, the convex portions may be arranged in a grid pattern in a plan view, with the spaces between the grids of the convex portions being concave portions, or the convex portions and concave portions in such a grid may be interchanged.

[0154] Alternatively, the configuration may be such that dot-shaped (for example, circular, rectangular, or other polygonal) protrusions are periodically and discretely positioned at lattice point positions in a plan view, and recesses are formed around them.

[0155] In any of these aspects, as long as the convex portions and concave portions are provided in a manner that has the above-mentioned concave-convex reference surfaces, it is possible to obtain the same effects as in the above-mentioned embodiment.

[0156] In the above-described embodiment, the uneven structure is provided to correct temperature variations over the entire mounting surface 20a, which is circular in plan view. Therefore, it is assumed that the heights of the tip surfaces of the convex portions within the ranges of the high rib structure and the low rib structure are uniform, but the range of 10% of the outer periphery of the mounting surface may be excluded from this uniformity.

[0157] Furthermore, from the viewpoint of ensuring uniform heat transfer, it is desirable that the height of the tip surface of the convex portion within each high rib structure and low rib structure is the same, but in practice, as long as a balance is maintained between the penetration of the convex portion into the adhesive sheet and the penetration of the adhesive sheet into the recessed portion, a configuration in which the height of the tip surface of the convex portion varies by up to 5 μm is also acceptable.

[0158] In addition, in the above-described embodiment, the temperature variation of the mounting surface is corrected by combining a high rib structure and a low rib structure with different unevenness heights in the uneven structure, but instead, it is also possible to realize a difference in heat transfer in the adhesive sheet by combining two types of rib structures with the same distance between the tip surface of the convex portion and the cooling plate and different widths of the tip surface. However, even in such a case, for the same reasons as in the above-described embodiment, it is preferable that the pitch of the convex portion is 300 μm or less.

[0159] Furthermore, in the above-described embodiment, the temperature variation of the mounting surface is corrected and the thickness variation of the adhesive sheet is also addressed. However, if the temperature variation of the mounting surface does not need to be corrected, it is possible to address only the thickness variation of the adhesive sheet. For example, a configuration is conceivable in which only the normal low rib structure 25L and the thickness-absorbing low rib structure 25L are mixed in a predetermined ratio depending on the thickness variation of the adhesive sheet 40. In such a case, the temperature of the mounting surface itself can be adjusted by adjusting the heater power.

Claims

1. A wafer mounting table on which a wafer is mounted and fixed, comprising: a ceramic base having a wafer mounting surface; an electrostatic chuck equipped with an ESC electrode and a heater electrode each embedded within the ceramic base; a metal cooling plate; and a resin adhesive sheet that bonds the electrostatic chuck and the cooling plate, wherein the bonding surface of the electrostatic chuck that is bonded to the adhesive sheet has an uneven structure made up of one or more types of unit structures, and in the uneven structure, the convex portions are provided at a pitch of 100 μm or more and 300 μm or less.

2. A wafer mounting table as set forth in claim 1, wherein the distance between the tip of the protrusion and the cooling plate is uniform in each of the one or more types of unit structures.

3. A wafer mounting table as claimed in claim 1, characterized in that the adhesive surface of the electrostatic chuck has the multiple types of unit structures, and the distance between the tip of the convex portion and the cooling plate is different for each of the multiple types of unit uneven structures.

4. A wafer mounting table as described in any one of claims 1 to 3, characterized in that in the uneven structure, the convex portions that are linear in a plan view and the concave portions that are linear in a plan view are alternately and periodically arranged.

5. A wafer mounting table as described in claim 4, wherein the adhesive surface of the electrostatic chuck is composed of a plurality of unit areas, the plurality of types of unit structures are a first unit structure having a first convex portion forming the convex portion, and a second unit structure having a second convex portion forming the convex portion, the distance between the tip of the first convex portion and the cooling plate is different from the distance between the tip of the second convex portion and the cooling plate, and in each of the plurality of unit areas, the first unit structure and the second unit structure are mixed at a predetermined ratio, and the predetermined ratio in each of the plurality of unit areas is determined in accordance with a reference temperature distribution that occurs on the mounting surface when current is passed through the heater electrode of the wafer mounting table in which the adhesive surface of the electrostatic chuck is flat.

6. A wafer mounting table as set forth in claim 4, wherein the adhesive surface of the electrostatic chuck is made up of a plurality of unit areas, and the plurality of types of unit structures are a first unit structure consisting of a first convex portion forming the convex portion and a first concave portion forming the concave portion, a second unit structure consisting of a second convex portion forming the convex portion and a second concave portion forming the concave portion, the second unit structure consisting of a third convex portion whose distance from the cooling plate is the same as that of the first convex portion and a third concave portion whose depth is greater than that of the first concave portion, and a fourth unit structure consisting of a fourth convex portion whose distance from the cooling plate is the same as that of the second convex portion and a fourth concave portion whose depth is greater than that of the second concave portion, and in each of the plurality of unit areas, the first to fourth unit structures are mixed in a predetermined ratio, the predetermined ratio in each of the plurality of unit areas is determined in accordance with a reference temperature distribution that occurs on the mounting surface when current is applied to the heater electrode of the wafer mounting table, the adhesive surface of the electrostatic chuck being flat, and a thickness of the adhesive sheet at a location corresponding to each of the plurality of unit areas.

7. A method for manufacturing a wafer mounting table on which a wafer is mounted and fixed, comprising: a preparation step of preparing an electrostatic chuck including a ceramic base having a wafer mounting surface, and an ESC electrode and a heater electrode each embedded inside the ceramic base; and a bonding step of bonding the electrostatic chuck and a metallic cooling plate with a resin adhesive sheet, wherein the preparation step includes a correction step of providing an uneven structure by alternately and periodically providing convex portions and concave portions on the bonding surface of the electrostatic chuck that is bonded to the adhesive sheet, and the correction step is at least one of a first correction step of reducing variations in temperature distribution occurring on the mounting surface, and a second correction step of, when there are thickness unevenness in the adhesive sheet, causing the concave portions to absorb the thickness unevenness.

8. A method for manufacturing a wafer mounting table as described in claim 7, characterized in that in the correction process, the uneven structure is made to consist of one or more types of unit structures, and the pitches of the convex portions and the concave portions are each set to 100 μm or more and 300 μm or less.

9. A method for manufacturing a wafer mounting table as described in claim 8, characterized in that in the correction process, the distance between the tip of the convex portion and the cooling plate is made uniform for each of the one or more types of unit structures.

10. A method for manufacturing a wafer mounting table as described in claim 8, characterized in that in the correction process, the multiple types of unit structures are provided on the adhesive surface of the electrostatic chuck, and the distance between the tip of the convex portion and the cooling plate is made different for each of the multiple types of unit structures.

11. A method for manufacturing a wafer stage according to any one of claims 8 to 10, wherein in the correction step, the convex portion and the concave portion are provided in a straight line.

12. A method for manufacturing a wafer mounting table as defined in claim 11, wherein when the correction step is the first correction step, the adhesive surface of the electrostatic chuck is virtually divided into a plurality of unit areas, the plurality of types of unit structures are a first unit structure having a first convex portion forming the convex portion and a second unit structure having a second convex portion forming the convex portion, the distance between the tip of the first convex portion and the cooling plate and the distance between the tip of the second convex portion and the cooling plate are made different, the first unit structure and the second unit structure are mixed in a predetermined ratio in each of the plurality of unit areas, and the predetermined ratio in each of the plurality of unit areas is set so that a temperature variation in a temperature distribution occurring on the mounting surface when a current is applied to the heater electrode is reduced to be lower than a temperature variation in a reference temperature distribution occurring on the mounting surface when a current is applied to the heater electrode of the wafer mounting table having a flat adhesive surface of the electrostatic chuck.

13. A method for manufacturing a wafer mounting table as set forth in claim 11, wherein when the correction process is the first and second correction processes, the adhesive surface of the electrostatic chuck is virtually divided into a plurality of unit areas, the plurality of types of unit structures are a first unit structure consisting of a first convex portion forming the convex portion and a first concave portion forming the concave portion, a second unit structure consisting of a second convex portion forming the convex portion and a second concave portion forming the concave portion, the second unit structure consisting of a third convex portion whose distance from the cooling plate is the same as that of the first convex portion and a third concave portion whose depth is greater than that of the first concave portion, and a fourth unit structure consisting of a fourth convex portion whose distance from the cooling plate is the same as that of the second convex portion and a fourth concave portion whose depth is greater than that of the second concave portion, and the first to fourth unit structures are mixed in a predetermined ratio in each of the plurality of unit areas, the predetermined ratio in each of the plurality of unit areas is set so that a temperature variation in a temperature distribution occurring on the mounting surface when current is applied to the heater electrode is reduced to be less than a temperature variation in a reference temperature distribution occurring on the mounting surface when current is applied to the heater electrode of the wafer mounting table having a flat adhesive surface of the electrostatic chuck, the reference temperature distribution being measured in advance, and in accordance with a thickness of the adhesive sheet at a location corresponding to each of the plurality of unit areas.

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