Electrostatic Chucks and Susceptors

Abstract

In an electrostatic chuck that electrostatically attracts and fixes a workpiece placed on a mounting surface by applying a voltage to an electrode embedded inside, the mounting surface has an uneven structure consisting of a plurality of convex portions two-dimensionally spaced apart at a predetermined pitch and flat concave portions between the convex portions, and each of the convex portions includes a flat portion having a flat surface that is perpendicular to the thickness direction of the electrostatic chuck and has a uniform height, and an inclined portion that is located around the flat portion and whose height decreases from the flat portion toward the concave portion, and the inclination angle of the upper surface of the inclined portion with respect to the thickness direction of the electrostatic chuck is 65 degrees or more and 84 degrees or less.

Description

[Technical field]

[0001] The present invention relates to an electrostatic chuck for electrostatically attracting and fixing a workpiece such as a wafer, and in particular to the shape of its mounting surface. [Background technology]

[0002] Electrostatic chucks that utilize electrostatic attraction to fix a workpiece are widely used in etching devices such as plasma etching devices and film forming devices such as PVD devices, CVD devices, and ion plating devices used in semiconductor manufacturing processes. As such electrostatic chucks, there are already known ones in which the mounting surface on which a plate-like workpiece such as a semiconductor wafer is placed is an uneven surface having a plurality of convex portions (protrusions), the workpiece is supported by the convex portions, and a cooling gas can be flowed through the concave portions (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses an electrostatic chuck in which the convex portion of the mounting surface is columnar, truncated cone, or hemispherical.

[0004] Patent Document 2 also discloses an embodiment in which the protrusion on the mounting surface has a tip portion including a top surface that is located at the tip and rises with a gently curved surface, a column portion whose cross-sectional diameter decreases from the bottom surface toward the tip portion, and a base portion that connects the column portion and the bottom surface with a gently curved surface.

[0005] In electrostatic chucks such as those disclosed in Patent Documents 1 and 2, particles may be generated due to friction between the workpiece and the protrusions on the mounting surface. Since the generation of such particles can cause defects, it is desirable to reduce it as much as possible. The smaller the contact area between the workpiece and the protrusions, the less likely particles are to be generated, but if the contact area is made too small, the chucking force will be insufficient. If the chucking force is insufficient, for example, the wafer may be lifted by the cooling gas flowing through the recesses. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-123843 A [Patent Document 2] JP 2017-191949 A Summary of the Invention

[0007] The present invention has been made in consideration of the above problems, and has an object to provide an electrostatic chuck having an increased adsorptive force with respect to a workpiece without increasing the contact area.

[0008] In order to solve the above-described problems, a first aspect of the present invention is an electrostatic chuck that electrostatically attracts and fixes a workpiece placed on a mounting surface by applying a voltage to ESC electrodes embedded inside, the mounting surface having an uneven structure including a plurality of convex portions two-dimensionally spaced apart at a predetermined pitch and flat concave portions between the convex portions, the convex portions including a flat portion having a flat surface that is perpendicular to a thickness direction of the electrostatic chuck and has a uniform height, and an inclined portion that is located around the flat portion and has a height that decreases from the flat portion to the concave portion, and an inclination angle of an upper surface of the inclined portion with respect to the thickness direction of the electrostatic chuck is equal to or greater than 65 degrees and equal to or less than 84 degrees.

[0009] A second aspect of the present invention is the electrostatic chuck according to the first aspect, characterized in that the protrusion has a tapered shape in a cross-sectional view.

[0010] A third aspect of the present invention is the electrostatic chuck according to the second aspect, characterized in that the convex portion is continuous with at least one of the flat portion and the concave portion via a curved surface.

[0011] A fourth aspect of the present invention is an electrostatic chuck according to any one of the first to third aspects, characterized in that the flat surface is circular in plan view, and the inclined portion is annular in plan view.

[0012] A fifth aspect of the present invention is an electrostatic chuck according to any one of the first to fourth aspects, characterized in that a height of the flat surface from the recess is 10 μm to 50 μm.

[0013] A sixth aspect of the present invention is a susceptor comprising: an electrostatic chuck according to any one of the first to fifth aspects; a heater electrode embedded in the electrostatic chuck; and a cooling plate joined to the electrostatic chuck and capable of cooling the workpiece by circulating a coolant through a flow path provided therein.

[0014] A seventh aspect of the present invention is a susceptor comprising: an electrostatic chuck according to any one of the first to fifth aspects; a heater electrode embedded inside the electrostatic chuck; and a hollow shaft attached to the electrostatic chuck.

[0015] According to the first to seventh aspects of the present invention, the electrostatic adsorption force of the electrostatic chuck can be increased without increasing the contact area between the workpiece and the electrostatic chuck. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view showing a configuration of a wafer mounting table 10 equipped with an electrostatic chuck 20. FIG. [Diagram 2] 2 is a schematic cross-sectional view showing a detailed structure of a mounting surface 20a of the electrostatic chuck 20. FIG. [Diagram 3] 2 is an enlarged cross-sectional view of the vicinity of an inclined portion 25 of an embossment 23. FIG. [Figure 4] 13 is a diagram showing an embossment 23 according to a modified example. FIG. [Diagram 5] FIG. 2 is a diagram showing another embodiment of the electrostatic chuck 20. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Wafer placement table> 1 is a schematic cross-sectional view showing the configuration of a wafer mounting table 10 equipped with an electrostatic chuck 20 according to an embodiment of the present invention, taken along the thickness direction of the electrostatic chuck 20. The wafer mounting table 10 is also called a susceptor, and is used to fix a semiconductor wafer (wafer), which is one type of workpiece, to the electrostatic chuck 20 when the wafer is subjected to a predetermined process, such as a plasma process.

[0018] The wafer mounting table 10 generally has a configuration in which the electrostatic chuck 20 and the cooling plate 30 are bonded to each other by a bonding layer 40, so that the electrostatic chuck 20 and the cooling plate 30 are stacked together.

[0019] The electrostatic chuck 20 is a plate-shaped (e.g., disk-shaped) member made of insulating ceramics such as Al2O3 and AlN, in which an ESC electrode (electrostatic chuck electrode) 21 for electrostatically attracting a wafer is embedded. The electrostatic chuck 20 shown in FIG. 1 further has a heater electrode 22 for heating the wafer embedded therein. Such an electrostatic chuck 20 is also called an electrostatic chuck heater. In the electrostatic chuck 20 shown in FIG. 1, the ESC electrode 21 is embedded closer to the mounting surface 20a than the heater electrode 22. In the electrostatic chuck 20, the main surface opposite to the bonding surface with the bonding layer 40 serves as the mounting surface 20a on which the wafer is mounted.

[0020] Examples of materials for the ESC electrodes 21 and the heater electrodes 22 include metals such as W, Mo, Ti, Si, and Ru, or carbides or nitrides thereof.

[0021] The cooling plate 30 has a flow passage 31 therein, and is a portion for cooling the electrostatic chuck 20 and further the wafer electrostatically attracted and fixed to the mounting surface 20a thereof by introducing a coolant (e.g., water) from the outside into the flow passage 31. In a preferred example, the flow passage 31 has one continuous groove portion formed in a spiral shape in a plan view so that substantially the entire area of ​​the electrostatic chuck 20 is cooled. Alternatively, the flow passage 31 may have a plurality of independent open ring-shaped groove portions formed in a concentric shape in a plan view.

[0022] 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.

[0023] A fin 32 may be provided protruding from at least one location of the flow path 31. The fin 32 has the effect of increasing the flow rate of the refrigerant at the location where it is disposed, thereby locally enhancing the cooling efficiency. The shape and size of the fin 32 are appropriately determined according to the cooling conditions required at the location where it is disposed. The fin 32 may be provided from the same material as the cooling plate 30, or from a material different from that of the cooling plate 30. Note that a configuration in which the fin 32 is not provided is also possible.

[0024] The joining of the electrostatic chuck 20 and the cooling plate 30 by the joining layer 40 is achieved, for example, by performing heat and pressure joining on a laminate obtained by bonding a ceramic plate-like member constituting the electrostatic chuck 20 and a member constituting the cooling plate 30 with an adhesive layer such as a resin adhesive or an adhesive sheet, a metal brazing material, or a ceramic bond, while heating and pressurizing the laminate at a predetermined temperature.

[0025] In addition, the wafer mounting table 10 further includes a first power supply unit 50 which is in charge of supplying power to the ESC electrodes 21, and a second power supply unit 60 which is in charge of supplying power to the heater electrode 22.

[0026] 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 electrodes 21. The first power supply unit 50 is inserted into the through hole 33, and is exposed to the outside at the other end side. Then, at the other end side, the power supply terminal 51 is electrically connected to an ESC power supply 70 provided outside.

[0027] In the wafer mounting table 10, with a wafer placed on the mounting surface 20 a of the electrostatic chuck 20, a DC voltage is applied from the ESC power supply 70 to the ESC electrodes 21 through the power supply terminals 51 and the connection parts 53, so that the wafer is electrostatically attracted to the mounting surface 20 a.

[0028] The second power supply unit 60 includes a power supply terminal 61, an insulating member (sleeve) 62 surrounding the power supply terminal 61, and a connection unit 63 provided at one end of the power supply terminal 61 and connected to the heater electrode 22. The second power supply unit 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 a heater power source 80 provided outside.

[0029] In the wafer mounting table 10, electricity is applied to the heater electrode 22 from the heater power source 80 through the power supply terminal 61 and the connection portion 63, thereby heating the wafer mounting table 10 and the wafer.

[0030] Also, cooling plate 30 In the designated position , style A refrigerant inlet / outlet 35 communicating with the passage 31 passes through the passage 31. Although only one refrigerant inlet / outlet 35 is shown in Fig. 1 for simplicity of illustration, in reality, one refrigerant inlet / outlet 35 is provided at each end of the groove portion constituting the passage 31. Each refrigerant inlet / outlet 35 is connected to a chiller unit 90 that circulates and supplies a refrigerant to the passage 31.

[0031] In the wafer mounting table 10 having the above-mentioned configuration, while the wafer mounted on the mounting surface 20 a is electrostatically attracted and fixed by applying a voltage to the ESC electrodes 21, heating by energizing the heater electrodes 22 and circulating and supplying a coolant to the flow paths 31 are performed in parallel, thereby balancing heating and cooling, so that the wafer can be heated with a predetermined temperature distribution.

[0032] The wafer mounting table 10 can be manufactured, for example, by preparing the electrostatic chuck 20 in which the ESC electrodes 21 and the heater electrode 22 are embedded, and the cooling plate 30, and then bonding the electrostatic chuck 20 and the cooling plate 30 with the bonding layer 40, and subsequently embedding the first power supply part 50 and the second power supply part 60.

[0033] The electrostatic chuck 20 can be manufactured by, for example, laminating and adhering a plurality of ceramic green sheets including a ceramic green sheet on which an electrode pattern for the ESC electrodes 21 is printed and a ceramic green sheet on which an electrode pattern for the heater electrode 22 is printed and formed, and hot-pressing and firing a green sheet molded body.

[0034] However, in this embodiment, the mounting surface 20a of the electrostatic chuck 20 after the hot press sintering is subjected to an embossing process (uneven processing) described later, so that a large number of convex portions (projections) are formed.

[0035] The cooling plate 30 can also be fabricated by cutting a bulk metal, gel casting or other casting techniques.

[0036] <Details of the mounting surface> 2 is a schematic cross-sectional view taken along the thickness direction of the electrostatic chuck 20, showing a detailed structure of the mounting surface 20a of the electrostatic chuck 20. Note that Fig. 2 also shows how the wafer 100 is mounted on the mounting surface 20a.

[0037] 1, for simplicity of illustration, the mounting surface 20a is shown as being uniformly flat, but in reality, the mounting surface 20a of the electrostatic chuck 20 according to the embodiment of the present invention has an uneven structure consisting of a large number (plurality of) protrusions 23 two-dimensionally spaced apart at a predetermined pitch p and recesses 26 between the protrusions 23. Hereinafter, the protrusions 23 will also be referred to as embossments 23, and the surfaces of the recesses 26 will also be referred to as bottom surfaces 26a. The pitch p is set to about 2 mm to 20 mm.

[0038] The embossment 23 has a flat portion 24 and an inclined portion 25. The flat portion 24 is a portion having a flat surface 24a. The flat surface 24a is substantially perpendicular to the thickness direction of the electrostatic chuck 20, is flat, and has a uniform height (vertical distance from the bottom surface 26a of the recess 26) h. However, the flat surface 24a and the bottom surface 26a of the recess 26 may include minute irregularities that are unavoidably generated during manufacturing. Therefore, the height h may be, for example, the difference between the roughness center lines of the flat surface 24a and the bottom surface 26a. The roughness center lines of the flat surface 24a and the bottom surface 26a may be the average value of measured values ​​at a plurality of points measured by a method specified in JIS B 0601:1994 and JIS B 0031:1994. The height h is about 10 μm to 50 μm.

[0039] The inclined portion 25 is located around the flat portion 24 when the support surface 20a is viewed in a plane, and is a portion whose height (vertical distance from the bottom surface 26a of the recess 26) decreases continuously or intermittently from the flat portion 24 toward the recess 26.

[0040] In a preferred embodiment, the flat surface 24a of each embossment 23 is circular with a diameter d1 at the center of the embossment 23 in plan view, and each embossment 23 itself is circular with a diameter d2 in plan view. Accordingly, the inclined portion 25 is annular with a width w in plan view. The upper surface 25a of the inclined portion 25 is linearly tapered in cross section. The inclined portion 25 with the upper surface 25a tapered linearly in cross section may be particularly referred to as the tapered portion 25. The diameter d1 is about 0.5 mm to 3 mm, similar to a conventional embossment not having the inclined portion 25.

[0041] Since the mounting surface 20a has such an uneven structure, when the wafer 100 is mounted on the electrostatic chuck 20, only the flat portion 24 of the embossment 23 actually comes into contact with the wafer 100 and directly supports the wafer 100 downward. Note that a cooling gas for cooling the wafer 100 may be flowed between the wafer 100 and the inclined portion 25 and the recessed portion 26 that do not come into contact with the wafer 100.

[0042] When the wafer 100 is attracted and fixed to the electrostatic chuck 20, as described above, a DC voltage is applied from the ESC power supply 70 to the ESC electrode 21. As a result, a Johnsen-Rahbek force (hereinafter referred to as JR force) Fj is generated between the wafer 100 and the flat portions 24 of all the embossments 23 in contact with the wafer 100.

[0043] However, the force that contributes to the suction and fixation of the wafer 100 is not only the JR force Fj, but also the spatial Coulomb force Fc from a portion that is not in contact with but is close to the wafer 100. Specifically, the spatial Coulomb force Fc is made up of an inclined portion spatial Coulomb force Ft acting between all of the inclined portions 25 (the upper surfaces 25a) and the wafer 100, and a bottom surface spatial Coulomb force Fb acting between the recessed portions 26 (the entire bottom surfaces 26a) and the wafer 100. Hereinafter, the spatial Coulomb force Fc is also referred to as a total spatial Coulomb force Fc.

[0044] That is, the total attraction force F when the wafer 100 is attracted and fixed to the electrostatic chuck 20 is expressed as follows: F=Fj+Fc=Fj+Ft+Fb It is expressed as:

[0045] In this case, the inclined-portion spatial Coulomb force Ft is inversely proportional to the distance between the inclined portion 25 and the wafer 100, and the bottom surface spatial Coulomb force Fb is inversely proportional to the distance between the bottom surface 26a and the wafer 100. Therefore, when the pitch p of the embossments 23 and the planar size (diameter) d1 and height h of the flat portion 24 are all constant and the warping of the wafer 100 can be ignored, as long as there is always a recess 26 between adjacent embossments 23, the greater the width w of the inclined portion 25, the more sufficiently the value of the inclined-portion spatial Coulomb force Ft becomes larger than the bottom surface spatial Coulomb force Fb, and as a result, the total spatial Coulomb force Fc and thus the entire suction force F increase.

[0046] This means that instead of increasing the planar size (diameter) d1 of the flat portion 24 in each embossing 23 to increase the JR force Fj, the overall adsorption force F can also be increased by providing an inclined portion 25 in each embossing 23 and allowing the inclined portion spatial Coulomb force Ft to act.

[0047] Furthermore, if the planar size d1 of the flat portion 24 is increased, the contact area between the wafer 100 and the electrostatic chuck 20 will increase, making it easier for particles to be generated; however, since the inclined portion 25 does not come into contact with the wafer 100, even if the inclined portion 25 is provided, particles will not be more likely to be generated.

[0048] In other words, by providing the inclined portion 25 on the emboss 23, the electrostatic adsorption force between the wafer 100 and the electrostatic chuck 20 can be improved without making particles more likely to be generated.

[0049] When the upper surface 25a of the inclined portion 25 is tapered, the effect of providing the inclined portion 25 on the embossment 23 can be evaluated based on the angle α between the upper surface 25a and the thickness direction of the electrostatic chuck 20 (hereinafter referred to as the inclination angle).

[0050] Table 1 shows the results of simulating the bottom surface spatial Coulomb force Fb and the inclined portion spatial Coulomb force Ft while varying the inclination angle α (also referred to as the taper angle α) for the electrostatic chuck 20 having the tapered inclined portion 25 in this manner. The results are shown in Table 1 together with the JR force Fj obtained experimentally in advance, the total spatial Coulomb force Fc obtained from the simulation results, the total attracting force F which is the sum of the JR force Fj and the total spatial Coulomb force Fc, the rate of increase of the total attracting force F, and the aspect ratio w / h.

[0051] [Table 1]

[0052] In addition, in the simulation, the planar size (diameter) of the emboss 23d2 is 0.5 mm, the height h of the flat portion 24 of the embossment 23 is 20 μm, a contact area rate of the wafer 100, which is the ratio of the total area of ​​the flat surface 24a of the flat portion 24 of the embossment 23 to the total planar area of ​​the mounting surface 20a, is 3%, and a value of a DC voltage applied by the ESC power supply 70 to the ESC electrodes 21 during electrostatic attraction is 500 V.

[0053] In addition, the total clamping force F (26.2 Torr) and JR force Fj (18 Torr) for the electrostatic chuck 20 in which the emboss 23 does not have the inclined portion 25, i.e., the inclination angle α=0 degrees, which were experimentally obtained in advance, are used. Therefore, strictly speaking, the values ​​of the forces when the inclination angle α=0 degrees in Table 1 are experimental values. The increase rate of the total clamping force F is shown as the increase rate based on the total clamping force F when the inclination angle α=0 degrees.

[0054] As can be seen from Table 1, the increase rate of the total adsorptive force F tends to increase as the inclination angle α increases.

[0055] In this embodiment, the preferred range of the inclination angle α when the inclined portion 25 is provided on the embossment 23 is set to be 65 degrees or more, at which the total adsorptive force increases by 1% or more compared to when the inclined portion 25 is not provided. This is because it is believed that there is a significant increase in the total adsorptive force F compared to when the inclined portion 25 is not provided. Table 1 also shows that even if the inclination angle α is set to, for example, about 30 degrees, there is almost no effect of increasing the adsorptive force.

[0056] However, the inclination angle α is set to 84 degrees or less. If the inclination angle α exceeds 84 degrees, there is a high possibility that the wafer 100 may come into contact with the inclined portion 25 due to bending of the wafer 100 when the wafer 100 is fixed by suction, which is undesirable.

[0057] That is, in this embodiment, when the surface of the electrostatic chuck 20 is provided with unevenness by a large number of embossments 23, an inclined portion 25 is provided around the flat portion 24 of each embossment 23 so as to form an inclination angle α of 65 degrees or more and 84 degrees or less with respect to the thickness direction of the electrostatic chuck 20, thereby increasing the electrostatic adsorption force of the wafer 100 to the electrostatic chuck 20 without increasing the contact area with the wafer 100. Note that this range of the inclination angle α of 65 degrees or more and 84 degrees or less roughly corresponds to the range in which the aspect ratio w / h, which corresponds to the tangent (tan) of the inclination angle α, is 2.1 or more and 9.5 or less.

[0058] The effect of increasing the electrostatic adsorption force by using the electrostatic chuck 20 can be obtained in the same manner when a workpiece other than the wafer 100 is placed on the electrostatic chuck 20.

[0059] In addition, by providing the inclined portion 25 to the embossment 23, it is possible to increase the suction force without increasing the area of ​​the flat surface 24a of the flat portion 24, in other words, without increasing the contact area with the wafer 100 compared to when the inclined portion 25 is not provided. From another perspective, by providing the inclined portion 25 while reducing the area of ​​the flat surface 24a, it is possible to reduce the contact area with the wafer 100 while providing the same level of suction force as when the inclined portion 25 is not provided. of It also means that it is possible to obtain it.

[0060] <Example of fine shape of inclined part> FIG. 3 is a schematic enlarged cross-sectional view of the vicinity of an inclined portion 25 of one of the embossments 23 along the thickness direction of the electrostatic chuck 20. As shown in FIG.

[0061] 2 shows how upper surface 25a of inclined portion 25, which is linear in cross section, is continuous with flat surface 24a of flat portion 24 and bottom surface 26a of recess 26. However, when actual inclined portion 25 is viewed microscopically, as shown in FIG. 3, upper surface 25a may be composed of central portion 250, which is a flat inclined surface and linear in cross section, and curved surface portions 251 and 252 at both ends, where curved surface portion 251 is smoothly continuous with bottom surface 26a of recess 26, and curved surface portion 252 is smoothly continuous with flat surface 24a of flat portion 24.

[0062] When the curved surface portion 251 is formed, particles are less likely to remain at the boundary between the embossment 23 and the recess 26. Furthermore, when the curved surface portion 252 is formed, the embossment 23 is less likely to be scraped and scraped when the wafer 100 comes into contact with it.

[0063] However, since the formation range of the curved portions 251 and 252 is usually a very small range at both ends of the inclined portion 25, the imaginary extension surfaces of the central portion 250 of the upper surface 25a, the bottom surface 26a of the recess 26, and the flat surface 24a of the flat portion 24 can be regarded as the upper surface 25a of the inclined portion 25, the bottom surface 26a of the recess 26, and the flat surface 24a of the flat portion 24 in Figure 2, respectively.

[0064] In the cross-sectional view of FIG. 3, the straight line L0 corresponds to the imaginary extension of the central portion 250, the straight line L1 corresponds to the imaginary extension of the bottom surface 26a, and the straight line L2 corresponds to the imaginary extension of the flat surface 24a. The vertical distance and the horizontal distance between the intersection point P1 of the straight line L0 and the straight line L1 and the intersection point P2 of the straight line L0 and the straight line L2 can be regarded as the height h and the width w, respectively. More specifically, the intersection point P1 corresponds to the cross section of the intersection line of the imaginary extension of the central portion 250 and the imaginary extension of the bottom surface 26a, and the intersection point P2 corresponds to the cross section of the intersection line of the imaginary extension of the central portion 250 and the imaginary extension of the flat surface 24a. The angle between the thickness direction of the electrostatic chuck 20 and the straight line L0 can be regarded as the inclination angle α.

[0065] All or some of the embossments 23 provided on the electrostatic chuck 20 may have an inclined portion 25 as shown in Fig. 3. Alternatively, there may be an embossment 23 having only one of the curved portion 251 or the curved portion 252.

[0066] The uneven structure consisting of the embossments (convex portions) 23 having the inclined portions 25 of a tapered or other shape and the concave portions 26 can be formed, for example, by processing the flat surface of the ceramic plate-like member constituting the electrostatic chuck 20 and the member constituting the cooling plate 30 using various known processing techniques, such as sandblasting, machining, ultrasonic processing, laser processing, and polishing, in an appropriate combination, prior to joining the ceramic plate-like member constituting the electrostatic chuck 20 and the member constituting the cooling plate 30.

[0067] As described above, according to this embodiment, when the surface of an electrostatic chuck that electrostatically attracts and fixes a workpiece, such as a semiconductor wafer, is provided with a large number of embossments to create unevenness in order to reduce the contact area, an inclined portion that forms an angle of 65 degrees or more and 84 degrees or less with respect to the thickness direction of the electrostatic chuck is provided around the flat portion of each embossment, thereby increasing the electrostatic attracting force of the electrostatic chuck without increasing the contact area between the workpiece and the electrostatic chuck.

[0068] <Modification> The inclination angles α of the inclined portions 25 of the individual embossments 23 provided on the mounting surface 20a of the electrostatic chuck 20 do not need to be the same, and may be different depending on the position of the individual embossments 23 when the electrostatic chuck 20 is viewed in a plan view.

[0069] For example, the inclination angle α of the embossments 23 located in the outer periphery may be set to be larger than the inclination angle α of the embossments 23 located in the center. In this case, the embossments 23 in the outer periphery have a stronger suction force than the embossments 23 in the center, so that even if the wafer to be sucked is warped, the wafer can be prevented from separating from the mounting surface 20a in the outer periphery and the wafer can be suitably fixed.

[0070] In the above-described embodiment, the description has been focused mainly on a configuration in which the height of inclined portion 25 continuously decreases from flat portion 24 toward recess 26, and more specifically, a configuration in which inclined portion 25 is tapered has been exemplified. However, as mentioned above, the height of inclined portion 25 may also be changed intermittently.

[0071] FIG. 4 is a diagram showing an embossment 23 according to a modified example having an inclined portion 25 of such a shape. More specifically, FIG. 4 is a schematic enlarged cross-sectional view along the thickness direction of the electrostatic chuck 20 in the vicinity of the inclined portion 25. In the embossment 23 shown in FIG. 4, the inclined portion 25 is provided in a multi-stage shape consisting of a plurality of steps 25s. That is, the height of the inclined portion 25 changes intermittently from the flat portion 24 to the recessed portion 26. In this case, the inclined line 25b passing through the edge portion of each step 25s in the cross section can be treated in the same manner as the straight line formed by the cross section of the upper surface 25a of the tapered inclined portion 25 shown in FIG. 2, for example. That is, the angle formed by the inclined line 25b and the thickness direction of the electrostatic chuck 20 corresponds to the inclination angle α.

[0072] Such an embossment 23 having a multi-stage inclined portion 25 consisting of a plurality of steps 25s can be formed by, for example, laser processing.

[0073] Even in the case of an electrostatic chuck 20 in which an uneven structure is formed on the mounting surface 20a by the embossing 23 having such a multi-stage inclined portion 25, the effect of increasing the electrostatic adsorption force in the electrostatic chuck 20 can be obtained without increasing the contact area between the workpiece and the electrostatic chuck 20.

[0074] <Another aspect of electrostatic chuck> Fig. 5 is a schematic cross-sectional view taken along the thickness direction of an electrostatic chuck 20 of another embodiment different from that shown in Fig. 1. The electrostatic chuck 20 shown in Fig. 5 is generally composed of a plate-shaped (e.g., disk-shaped) ceramic plate 12 made of insulating ceramics similar to the electrostatic chuck 20 shown in Fig. 1, and a hollow ceramic shaft 14 joined to the ceramic plate 12.

[0075] One main surface 12a of the ceramic plate 12 is a mounting surface 20a having a number of protrusions (embossments) 23 similar to those in Fig. 2. Although the illustration is simplified in Fig. 5, the embossments 23 on the one main surface 12a also have flat portions 24 and inclined portions 25 as shown in Fig. 2. That is, around the flat portion 24 of each embossment 23, an inclined portion 25 is provided that forms an angle of 65 degrees or more and 84 degrees or less with respect to the thickness direction of the electrostatic chuck. Note that Fig. 5 also shows how the wafer 100 is mounted on the mounting surface 20a.

[0076] The ceramic shaft 14 is preferably made of the same insulating ceramic as the ceramic plate 12, and is joined to the other main surface 12b of the ceramic plate 12 by solid-state bonding or diffusion bonding.

[0077] 1, the ceramic plate 12 has embedded therein an ESC electrode 21 for electrostatically attracting a wafer and a heater electrode 22 for heating the wafer. However, current is applied to the ESC electrodes 21 and the heater electrode 22 through rod-shaped power supply terminals 51 and 61 inserted into the internal space of the hollow ceramic shaft 14. Note that illustration of the sleeves 52 and 62 and the connection portions 53 and 63 is omitted in FIG. The power supply terminal 51 is also referred to as an ESC rod 51, and the power supply terminal 61 is also referred to as a heater rod 61.

[0078] 1, the electrostatic chuck 20 having the above configuration is bonded to the cooling plate 30 by a bonding layer 40 (not shown in FIG. 5) to form the wafer mounting table 10.

[0079] In addition, the ceramic plate 12 shown in Fig. 5 has a plurality of lift pin holes 16 penetrating in the thickness direction. More specifically, the lift pin holes 16 are provided in a manner penetrating the bonding layer 40 and the cooling plate 30, and are holes through which lift pins (not shown) for lifting the wafer 100 placed on the placement surface 20a from below are inserted from below the wafer placement table 10. Although not shown in Fig. 1, the wafer placement table 10 shown in Fig. 1 also has a plurality of lift pin holes.

[0080] In a wafer mounting table equipped with an electrostatic chuck having the configuration shown in FIG. 5, the electrostatic adsorption force of the electrostatic chuck can be increased without increasing the contact area between the workpiece and the electrostatic chuck.

Claims

1. An electrostatic chuck that electrostatically attracts and fixes a workpiece placed on a mounting surface by applying a voltage to an ESC electrode embedded inside, the mounting surface has an uneven structure including a plurality of convex portions spaced apart from each other in a two-dimensional manner at a predetermined pitch and flat concave portions between the convex portions; The convex portion is a flat portion having a flat surface perpendicular to a thickness direction of the electrostatic chuck and having a uniform height; an inclined portion located around the flat portion and having a height decreasing from the flat portion toward the recess; Equipped with an inclination angle of the upper surface of the inclined portion with respect to a thickness direction of the electrostatic chuck is 65 degrees or more and 84 degrees or less; Electrostatic chuck characterized by:

2. 2. The electrostatic chuck of claim 1, The convex portion has a tapered shape in cross section. Electrostatic chuck characterized by:

3. 3. The electrostatic chuck of claim 2, The convex portion is continuous with at least one of the flat portion and the concave portion via a curved surface. Electrostatic chuck characterized by:

4. 4. The electrostatic chuck according to claim 1, The flat surface is circular in plan view, The inclined portion is annular in plan view. Electrostatic chuck characterized by:

5. 4. The electrostatic chuck according to claim 1, The height of the flat surface from the recess is 10 μm to 50 μm. Electrostatic chuck characterized by:

6. An electrostatic chuck according to any one of claims 1 to 3, a heater electrode embedded in the electrostatic chuck; a cooling plate that is joined to the electrostatic chuck and has a flow path provided therein through which a coolant is circulated and supplied, thereby cooling the workpiece; A susceptor comprising:

7. An electrostatic chuck according to any one of claims 1 to 3, a heater electrode embedded in the electrostatic chuck; a hollow shaft attached to the electrostatic chuck; A susceptor comprising:

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