Electrostatic chuck and method of manufacturing the same, and substrate fixation device

Abstract

To provide an electrostatic chuck that has a simple structure and is improved in attracting performance for an attracted object having high insulation properties.SOLUTION: An electrostatic chuck has a base body which has a mount surface where an attracted object is mounted and an electrostatic electrode which is built in the base body, wherein the base body has a flat surface on the opposite side from the mount surface, and the mount surface is convex or concave relative to the flat surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrostatic chuck, a manufacturing method thereof, and a substrate fixing device. [Background technology]

[0002] Conventionally, film deposition apparatuses (e.g., CVD apparatuses, PVD apparatuses, etc.) and plasma etching apparatuses used in manufacturing semiconductor devices such as ICs and LSIs have stages for precisely holding substrates in vacuum processing chambers. For example, a substrate fixing device has been proposed as such a stage, which uses an electrostatic chuck mounted on a base plate to attract and hold a substrate, which is an object to be attracted. Such a stage is required to stably attract any type of substrate to the electrostatic chuck.

[0003] An example of an electrostatic chuck is an electrostatic chuck that includes an electrostatic chuck body for electrostatically attracting a substrate, a support member including a mounting surface on which the electrostatic chuck body is placed, a restraining means for restraining displacement of a first portion of the electrostatic chuck body in a direction perpendicular to the mounting surface, and a driving means for displacing a second portion of the electrostatic chuck body relative to the mounting surface in a direction perpendicular to the mounting surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-205349 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide an electrostatic chuck that has a simple structure and has improved chucking performance for a highly insulating chucking target object. [Means for solving the problem]

[0006] This electrostatic chuck includes a base having a mounting surface on which an object to be attracted is placed, and an electrostatic electrode built into the base, the surface of the base opposite to the mounting surface being flat, and the mounting surface being convex or concave relative to the flat surface. [Effects of the Invention]

[0007] According to the disclosed technique, it is possible to provide an electrostatic chuck that has a simple structure and has improved chucking performance for chucking objects with high insulating properties. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a simplified example of a substrate fixing device according to a first embodiment. [Figure 2] FIG. 2 is a partially enlarged cross-sectional view of the substrate fixing device according to the first embodiment. [Figure 3] 3 is a cross-sectional view illustrating, in a simplified manner, a state in which the substrate fixing device according to the first embodiment sucks and holds a sapphire substrate. FIG. [Figure 4] 10 is a cross-sectional view illustrating, in a simplified manner, a state in which a sapphire substrate is sucked and held by a substrate fixing device according to a comparative example. FIG. [Figure 5] 10 is a diagram illustrating the suction characteristics of the substrate fixing device 1X. FIG. [Figure 6] 10 is a diagram illustrating the suction characteristics of the substrate fixing device 1. FIG. [Figure 7] 5A to 5C are views (part 1) illustrating a manufacturing process of the substrate fixing device according to the first embodiment. [Figure 8] 10A to 10C are views (part 2) illustrating the manufacturing process of the substrate fixing device according to the first embodiment. [Figure 9] FIG. 10 is a simplified diagram illustrating a substrate fixing device according to a first modified example of the first embodiment. [Figure 10] FIG. 10 is a partially enlarged cross-sectional view of a substrate fixing device according to a first modified example of the first embodiment. [Figure 11] 10 is a simplified cross-sectional view illustrating a state in which a sapphire substrate is sucked and held by a substrate fixing device according to a first modified example of the first embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant explanations may be omitted.

[0010] First Embodiment [Structure of the substrate holding device] 1A and 1B are diagrams illustrating a simplified example of a substrate fixing device according to a first embodiment, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line AA in FIG. 1A.

[0011] 1, the substrate fixing device 1 has, as its main components, a base plate 10, an adhesive layer 20, and an electrostatic chuck 30. The substrate fixing device 1 is an apparatus that attracts and holds a substrate, which is an object to be attracted, by the electrostatic chuck 30 mounted on one surface of the base plate 10. The object to be attracted is placed on a mounting surface 31a of a base 31 of the electrostatic chuck 30 and is attracted and held.

[0012] The base plate 10 is a member on which the electrostatic chuck 30 is mounted. The thickness of the base plate 10 is, for example, about 20 to 50 mm. The base plate 10 can be made of metal such as aluminum, copper, or titanium. Among these, it is preferable to use aluminum, which is inexpensive and easy to process.

[0013] The base plate 10 can also be used as an electrode for controlling plasma. By supplying a predetermined high-frequency power to the base plate 10, the energy for causing ions in the generated plasma state to collide with the substrate attracted to the electrostatic chuck 30 can be controlled, thereby enabling an effective etching process.

[0014] A gas supply unit 11 is provided inside the base plate 10 to supply gas for cooling the substrate attracted and held by the electrostatic chuck 30. The gas supply unit 11 includes a gas flow path 111 and a gas injection unit 112.

[0015] The gas flow path 111 is, for example, a hole formed in a ring shape inside the base plate 10. The gas inlet unit 112 is a hole having one end connected to the gas flow path 111 and the other end exposed to the outside from the lower surface of the base plate 10, and introduces an inert gas (e.g., He or Ar) into the gas flow path 111 from outside the substrate fixing device 1. The gas flow path 111 reaches the mounting surface 31 a of the electrostatic chuck 30 via the gas outlet unit 33.

[0016] The gas exhaust section 33 is a vertical hole having one end communicating with the gas flow path 111 and the other end exposed to the outside from the upper surface of the base plate 10, penetrating the adhesive layer 20 and the substrate 31, and exhausts the inert gas introduced into the gas flow path 111 to the mounting surface 31a. In a plan view, the gas exhaust sections 33 are scattered across the mounting surface 31a of the substrate 31. In the illustrated example, there are three gas exhaust sections 33, but any required number can be provided appropriately; for example, several tens to several hundreds of gas exhaust sections 33 may be provided.

[0017] Note that a plan view refers to viewing the object from the normal direction of the upper surface of the base plate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface of the base plate 10.

[0018] A flow path may be provided inside the base plate 10. In this case, the flow path is connected to a cooling medium control device provided outside the substrate fixing device 1, and the cooling medium control device introduces and discharges the cooling medium into the flow path. The cooling medium control device circulates the cooling medium through the flow path to cool the base plate 10, thereby cooling the substrate attracted to the electrostatic chuck 30. For example, water or Galden can be used as the cooling medium.

[0019] The electrostatic chuck 30 is mounted on the base plate 10 via an adhesive layer 20. The adhesive layer 20 may be made of, for example, a silicone-based resin. The adhesive layer 20 has a thickness of, for example, about 0.1 to 1.0 mm. The adhesive layer 20 bonds the base plate 10 and the electrostatic chuck 30 together, and also has the effect of reducing stress caused by the difference in thermal expansion coefficient between the ceramic electrostatic chuck 30 and the aluminum base plate 10.

[0020] The electrostatic chuck 30 is a part that attracts and holds a substrate, which is an object to be attracted. The planar shape of the electrostatic chuck 30 can be, for example, circular. The diameter of the substrate, which is an object to be attracted to the electrostatic chuck 30, can be, for example, approximately 6, 8, 12, or 18 inches. The electrostatic chuck 30 is, for example, a Johnsen-Rahbek type electrostatic chuck. However, the electrostatic chuck 30 may also be a Coulomb force type electrostatic chuck.

[0021] The substrate 31 is a dielectric, and may be made of ceramics such as aluminum oxide (Al2O3) or aluminum nitride (AlN). The thickness of the substrate 31 may be, for example, about 1 to 10 mm, and the relative dielectric constant (1 kHz) of the substrate 31 may be, for example, about 9 to 10.

[0022] The electrostatic electrode 32 is a thin-film electrode and is built into the base 31. The electrostatic electrode 32 is connected to a power source provided outside the substrate fixing device 1, and when a predetermined voltage is applied from the power source, an electrostatic attraction force is generated between the electrostatic electrode 32 and the substrate. This allows the substrate to be attracted and held on the mounting surface 31a of the base 31 of the electrostatic chuck 30. The attraction and holding force becomes stronger as the voltage applied to the electrostatic electrode 32 increases. The electrostatic electrode 32 may be unipolar or bipolar. Examples of materials that can be used for the electrostatic electrode 32 include tungsten and molybdenum.

[0023] A heating element may be provided inside the base 31, which generates heat when a voltage is applied from the outside of the substrate fixing device 1, and heats the mounting surface 31a of the base 31 to a predetermined temperature. The heating element can be disposed, for example, below the electrostatic electrode 32 (on the base plate 10 side).

[0024] The object to be attracted by the electrostatic chuck 30 is a silicon substrate or a sapphire substrate. A sapphire substrate has high insulating properties, so it is more difficult to attract and hold it on the base 31 than a silicon substrate. In particular, if the sapphire substrate is thick and has a large warp, it is difficult to attract and hold it. Therefore, the electrostatic chuck 30 has a mounting surface 31a shaped to match the warped shape of the sapphire substrate. In this application, high insulating properties means that the resistivity is 10 14 Ωcm or more (25℃).

[0025] In the first embodiment, a sapphire substrate warped in a convex shape is assumed, and therefore the mounting surface 31a has a convex shape. Specifically, as shown in FIG. 1(b), the lower surface opposite the mounting surface 31a, which is the upper surface of the base 31, is a flat surface 31b, and the mounting surface 31a has a convex shape relative to the flat surface 31b. The mounting surface 31a side of the base 31 is, for example, dome-shaped. In other words, the height of the mounting surface 31a from the flat surface 31b is highest at the center and decreases toward the periphery. However, the base 31 may have a region with a constant thickness in some areas.

[0026] 2A and 2B are enlarged cross-sectional views of a portion of the substrate fixing device according to the first embodiment, with FIG. 2A showing an enlarged view of part A in FIG. 1B and FIG. 2B showing an enlarged view of part B in FIG. 1B. The enlargement ratios of FIGS. 2A and 2B are the same. As shown in FIGS. 1 and 2B, the mounting surface 31a may include a circular region 311 located at the center and a plurality of annular regions 312 located on the outer periphery of the circular region 311 in a plan view.

[0027] In the example of Fig. 1(a), the mounting surface 31a includes thirteen annular regions 312. As shown in Fig. 1(a), in a plan view, the outer edges of the annular regions 312 can be arranged, for example, concentrically with the center of the circular region 311. Furthermore, as shown in Fig. 2(a) and Fig. 2(b), in a cross-sectional view, the circular region 311 and each annular region 312 can be formed in a stepped shape, with the height of each step decreasing toward the periphery.

[0028] When the annular regions 312 are stepped, the upper surface of each annular region 312 may be parallel to the upper surface of the base plate 10 or may be inclined relative to the upper surface of the base plate 10. Furthermore, the upper surface of each annular region 312 may be flat or curved, or may be a mixture of flat and curved surfaces.

[0029] 3 is a simplified cross-sectional view illustrating a state in which the substrate fixing device according to the first embodiment holds a sapphire substrate by suction. In FIG. 3, the sapphire substrate 100A is warped in a convex shape. The degree of warping varies depending on the diameter, thickness, production lot, etc. of the sapphire substrate. For example, a sapphire substrate with a diameter of 6 inches and a thickness of 1.5 mm may have a warping of approximately 130 μm. In other words, the difference in height between the center and the outermost periphery may be approximately 130 μm.

[0030] Once the diameter, thickness, and production lot of the sapphire substrate 100A to be chucked are determined, a sample can be extracted from the substrate and its warpage measured, thereby determining the warpage tendency. Once the warpage tendency is known, the mounting surface 31a can be processed accordingly, thereby increasing the contact area between the mounting surface 31a and the sapphire substrate 100A and achieving good chuckiness, as shown in FIG. 3. The chuckiness of the sapphire substrate 100A will be described in more detail below based on specific data.

[0031] 4 is a simplified cross-sectional view illustrating a state in which a substrate fixing device according to a comparative example suction-holds a sapphire substrate. In the substrate fixing device 1X according to the comparative example, the mounting surface 31a is flat and is substantially parallel to the flat surface 31b, which is the lower surface of the base 31. In other words, the base 31 has a constant thickness, and the thickness at the center is the same as the thickness at the outermost periphery. As a result, the contact area between the mounting surface 31a and the sapphire substrate 100A is reduced.

[0032] FIG. 5 is a diagram illustrating the suction characteristics of the substrate fixing device 1X. A helium leak tester was used to measure the suction characteristics. The object to be measured was a sapphire substrate with a diameter of 6 inches, a thickness of 1.5 mm, and a convex warpage of 130 μm. As a reference, a silicon substrate with a diameter of 6 inches, a thickness of 0.625 mm, and almost no warpage was also measured. The specific measurement method is as follows.

[0033] First, the substrate holding device 1X was attached to a helium leak rate tester placed in a chamber, and the chamber was evacuated to 20 Pa or less. A sapphire substrate was placed on the mounting surface 31a of the substrate holding device 1X, and a voltage was applied to the electrostatic electrode 32 to adsorb the sapphire substrate. Helium gas, set to a pressure of 2660 Pa (20 Torr), was supplied to the mounting surface 31a via the gas supply unit 11 and the gas exhaust unit 33. The leakage rate of the helium gas was then measured when the value of the leakage rate became constant. This test was performed while varying the applied voltage to the electrostatic electrode 32, and the results are plotted in Figure 5. Next, the sapphire substrate was replaced with a silicon substrate, and the same measurement was performed. The results are also plotted in Figure 5. In Figure 5, if the leakage rate of helium gas is 2 sccm or less, it can be determined that the object to be measured is sufficiently adsorbed to the mounting surface 31a.

[0034] As shown in Figure 5, for the reference silicon substrate, the leakage rate of helium gas was 2 sccm or less when the applied voltage was ±500V, and it was determined that the substrate was sufficiently adsorbed to the mounting surface 31a at this point. In contrast, for the sapphire substrate, even when the applied voltage was increased to ±2500V, the leakage rate of helium gas was 3.2 sccm, which was not 2 sccm or less. In other words, even when the applied voltage was increased to ±2500V, the sapphire substrate was not sufficiently adsorbed to the mounting surface 31a. In other words, the substrate fixing device 1X, which has a flat mounting surface 31a, cannot adsorb a sapphire substrate with a warp of 130 μm.

[0035] Fig. 6 is a diagram illustrating the chucking characteristics of the substrate fixing device 1. That is, Fig. 6 plots the results of measurements similar to those described above, with the substrate fixing device 1X replaced with the substrate fixing device 1. The specifications of the sapphire substrate and silicon substrate to be chucked are also similar to those described above.

[0036] As shown in Figure 6, similar to Figure 5, for the reference silicon substrate, the leakage rate of helium gas was 2 sccm or less when the applied voltage was ±500V, and at this point it can be determined that the substrate was sufficiently adsorbed to the mounting surface 31a. In contrast, for the sapphire substrate, the leakage rate of helium gas was 1.2 sccm, or 2 sccm or less, when the applied voltage was increased to ±2000V. In other words, with the substrate fixing device 1, if the applied voltage was increased to ±2000V, a sapphire substrate with a convex warp of 130 μm could be sufficiently adsorbed to the convex mounting surface 31a.

[0037] 5 and 6, it can be said that even if the sapphire substrate, which has high insulating properties and is difficult to adsorb, is significantly warped, sufficient adsorption force can be obtained by adjusting the applied voltage and matching the shape of the mounting surface 31a to the shape of the warp of the sapphire substrate. Note that the reason that sufficient adsorption force can be obtained by matching the shape of the mounting surface 31a to the shape of the warp of the sapphire substrate is thought to be because the contact area between the mounting surface 31a and the sapphire substrate increases.

[0038] Furthermore, if the sapphire substrate is etched without sufficient adhesion, it becomes impossible to uniformly control the temperature within the surface of the sapphire substrate, and the etching is affected by the temperature during etching, resulting in a loss of etching quality. By adjusting the shape of the mounting surface 31a to the shape of the warpage of the sapphire substrate to obtain sufficient adhesion, such problems can be avoided. Furthermore, if the mounting surface 31a of the substrate fixing device 1 has a stepped structure like a staircase, helium gas can flow more easily over the entire mounting surface 31a.

[0039] In order to increase the contact area between the mounting surface 31a and the sapphire substrate, it is necessary to match the shape of the mounting surface 31a to the shape of the object to be attached as closely as possible. Generally, warpage of the object to be attached is relatively small near the center and increases toward the periphery. Therefore, in order to match the warpage tendency of the object to be attached, in the example of FIGS. 1 and 2, the radius W1 of the circular region 311 is wider than the width of each annular region 312 in a plan view. In addition, in the example of FIGS. 1 and 2, the multiple annular regions 312 include annular regions 312 with different widths, and the wider annular regions 312 are positioned closer to the circular region 311 than the narrower annular regions 312.

[0040] When the size of the mounting surface 31a is 6 inches, the radius W1 of the circular region 311 can be, for example, about 12 mm to 14 mm. The width W2 of the annular region 312 closest to the circular region 311 can be, for example, about 8.5 mm to 10.5 mm. The width W3 of the annular region 312 farthest from the circular region 311 can be, for example, about 1.5 mm to 3.5 mm. Some of the annular regions 312 may have the same width.

[0041] Furthermore, when a sapphire substrate with a convex warp of 130 μm is used as the object to be adsorbed and the circular region 311 and the annular region 312 are stepped, the number of steps can be set to about 13 and the difference in height between adjacent steps can be set to about 10 μm, for example. This allows the convex shape of the mounting surface 31a to approximately match the warp of the sapphire substrate.

[0042] [Manufacturing method of substrate fixing device] 7 and 8 are views illustrating the manufacturing process of the substrate fixing device according to the first embodiment. Fig. 7(a) is a plan view, and Fig. 7(b) is a cross-sectional view taken along line BB in Fig. 7(a). Figs. 8(a) to 8(d) are cross-sectional views corresponding to Fig. 7(b).

[0043] 7, a substrate fixing device 1M is fabricated by disposing an electrostatic chuck 30, the upper and lower surfaces of which are flat, on a base plate 10 via an adhesive layer 20. Then, a mask 200 having a plurality of notches 200x formed concentrically in a plan view is disposed so as to cover the entire upper surface of the base 31.

[0044] Specifically, a base 31 incorporating an electrostatic electrode 32 is fabricated by a well-known manufacturing method including, for example, the steps of drilling vias in a green sheet, filling the vias with conductive paste, forming a pattern to become an electrostatic electrode, stacking and firing other green sheets, and flattening the surface. Then, a gas exhaust section 33 is formed so as to penetrate the base 31. The gas exhaust section 33 is formed, for example, by drilling. Next, a base plate 10 is prepared, on which a gas supply section 11, a cooling mechanism, etc. are formed in advance, and an adhesive layer 20 (uncured) is formed on the base plate 10. Then, the base 31 is placed on the base plate 10 with the adhesive layer 20 interposed therebetween, and the adhesive layer 20 is cured. This completes the substrate holding device 1M. The substrate holding device 1M has the same shape as the substrate holding device 1, except that the upper surface, i.e., the mounting surface 31a, is flat.

[0045] After fabricating the substrate holding device 1M, a mask 200 is placed on the mounting surface 31a. The mask 200 has a circular planar shape with the same diameter as the mounting surface 31a. That is, at this stage, the entire mounting surface 31a is covered with the mask 200, with no exposed portions. The mask 200 has multiple slits 200x formed concentrically in a plan view, and each area partitioned by the slits 200x can be easily peeled off along the slits 200x. The spacing between adjacent slits 200x corresponds to the width of one step of the staircase shown in Figures 2(a) and 2(b). The mask 200 can be made of a material such as polyester or tetron.

[0046] 8(a), the outermost region of the mask 200 defined by the slits 200x is peeled off. That is, the region of the mask 200 outside the slit 200x with the largest diameter is peeled off. This exposes the outermost region of the mounting surface 31a in a ring shape.

[0047] 8(b), a blasting process is performed on the mounting surface 31a, which is the upper surface of the base 31, using the mask 200. As a result, a first ring-shaped annular region 312 is formed on the outermost periphery of the mounting surface 31a. The first annular region 312 is lower than the mounting surface 31a located on the inner side of the first annular region 312 by, for example, about 10 μm.

[0048] Next, the step of peeling off one of the sections of the mask 200 and the step of blasting are repeated to process the placement surface 31a, which is the upper surface of the base 31, to form a convex placement surface 31a on which the object to be adsorbed is placed.

[0049] Specifically, as shown in FIG. 8(c), the mask 200 is peeled off in a region outside the largest-diameter notch 200x. This exposes the inner ring-shaped portion of the annular region 312 on the mounting surface 31a. Next, as shown in FIG. 8(d), the mounting surface 31a is subjected to blasting using the mask 200. This forms a second ring-shaped annular region 312 on the mounting surface 31a, inside the outermost annular region 312. At the same time, the first annular region 312 located on the outermost periphery becomes deeper than in the state shown in FIG. 8(c), and the two adjacent annular regions 312 form a stepped shape. The second annular region 312 is lowered, for example, by about 10 μm relative to the mounting surface 31a located inside the second annular region 312. Furthermore, the first annular region 312 is lowered, for example, by about 10 μm relative to the second annular region 312.

[0050] Thereafter, the process of peeling off the area outside the notch 200x with the largest diameter at that time and performing the blasting process through the mask 200 is repeated in the same manner until the notch 200x is gone. Finally, the circular mask 200 remaining in the center of the mounting surface 31a is peeled off. The portion from which the circular mask 200 has been peeled off becomes the circular area 311.

[0051] As a result, the mounting surface 31a, in a plan view, includes a circular region 311 located at the center and multiple annular regions 312 located on the outer periphery of the circular region 311, and the outer edges of the annular regions 312 are arranged concentrically with respect to the center of the circular region 311 in a plan view. Furthermore, the circular region 311 and each annular region 312 have a stepped shape in a cross-sectional view, with the center being highest and gradually decreasing toward the periphery, resulting in a convex shape overall. In a plan view, the radius of the circular region 311 may be wider than the width of each annular region 312. Furthermore, the multiple annular regions 312 may include annular regions 312 with different widths, and the wider annular regions 312 may be arranged closer to the circular region 311 than the narrower annular regions 312.

[0052] After the mask 200 is completely removed, the edges of each step may be polished with a hand stone or the like to give the entire mounting surface 31a a smooth convex shape.

[0053] <Modification 1 of the First Embodiment> In Modification 1 of the first embodiment, an example of a substrate fixing device having a different shape of the mounting surface from that of Embodiment 1 is shown. Note that in Modification 1 of the first embodiment, the description of the same components as those of the already described embodiments may be omitted.

[0054] 9A and 9B are diagrams illustrating a simplified example of a substrate fixing device according to Modification 1 of the first embodiment, in which Fig. 9A is a plan view and Fig. 9B is a cross-sectional view taken along line CC in Fig. 9A. Referring to Fig. 9A, the substrate fixing device 1A differs from the substrate fixing device 1 in that the mounting surface 31a of the base 31 is concave relative to the flat surface 31b.

[0055] In Modification 1 of the first embodiment, a sapphire substrate warped into a concave shape is assumed, and therefore the mounting surface 31a has a concave shape. Specifically, as shown in FIG. 9(b), the lower surface opposite the mounting surface 31a, which is the upper surface of the base 31, is a flat surface 31b, and the mounting surface 31a is concave relative to the flat surface 31b. The mounting surface 31a side of the base 31 is, for example, bowl-shaped. In other words, the height of the mounting surface 31a from the flat surface 31b is lowest at the center and increases toward the periphery. However, the base 31 may have a region with a constant thickness.

[0056] 10A and 10B are enlarged cross-sectional views of a substrate fixing device according to Modification 1 of the first embodiment, with FIG. 10A showing an enlarged view of part C in FIG. 9B and FIG. 10B showing an enlarged view of part D in FIG. 9B. The enlargement ratios of FIGS. 10A and 10B are the same. As shown in FIGS. 9 and 10B, the mounting surface 31a may include a circular region 311 located at the center and a plurality of annular regions 312 located on the outer periphery of the circular region 311 in a plan view.

[0057] In the example of Fig. 9(a), the mounting surface 31a includes thirteen annular regions 312. As shown in Fig. 9(a), in a plan view, the outer edges of the annular regions 312 can be arranged, for example, concentrically with the center of the circular region 311. Furthermore, as shown in Fig. 10(a) and Fig. 10(b), in a cross-sectional view, the circular region 311 and each annular region 312 can be formed in a stepped shape with the height of each step increasing toward the periphery.

[0058] When the annular regions 312 are stepped, the upper surface of each annular region 312 may be parallel to the upper surface of the base plate 10 or may be inclined relative to the upper surface of the base plate 10. Furthermore, the upper surface of each annular region 312 may be flat or curved, or may be a mixture of flat and curved surfaces.

[0059] 11 is a simplified cross-sectional view illustrating a state in which a substrate fixing device according to Modification 1 of the first embodiment suction-holds a sapphire substrate. In FIG. 11, the sapphire substrate 100B is warped in a concave shape. The degree of warping varies depending on the diameter, thickness, production lot, etc. of the sapphire substrate. For example, a sapphire substrate with a diameter of 6 inches and a thickness of 1.5 mm may have a warping of approximately 130 μm. In other words, the difference in height between the center and the outermost periphery may be approximately 130 μm.

[0060] Once the diameter, thickness, and production lot of the sapphire substrate 100B to be adsorbed are determined, a sample can be extracted from the substrate and measured for warpage, thereby determining the warpage tendency. Once the warpage tendency is known, the mounting surface 31a can be processed to match the warpage tendency, thereby increasing the contact area between the mounting surface 31a and the sapphire substrate 100B and achieving good adsorption, as shown in FIG.

[0061] To form the mounting surface 31a into a concave shape, a mask is placed on the flat mounting surface 31a, as in FIG. 7 of the first embodiment. Then, unlike the first embodiment, the innermost region of the mask 200 defined by the slits 200x is first peeled off, and blasting is performed starting from the center. Thereafter, the region inside the slit 200x with the smallest diameter at that point is peeled off, and the blasting process is performed through the mask. This process is repeated until all the slits are gone. Finally, the mask remaining on the outermost periphery of the mounting surface 31a is peeled off.

[0062] As a result, the mounting surface 31a, in a plan view, includes a circular region 311 located at the center and multiple annular regions 312 located on the outer periphery of the circular region 311, and the outer edges of the annular regions 312 are arranged concentrically with respect to the center of the circular region 311 in a plan view. Furthermore, the circular region 311 and each annular region 312 have a stepped shape in a cross-sectional view, with the lowest point in the center and the height increasing toward the periphery, resulting in an overall concave shape. In a plan view, the radius of the circular region 311 may be wider than the width of each annular region 312. Furthermore, the multiple annular regions 312 may include annular regions 312 with different widths, and the wider annular regions 312 may be arranged closer to the circular region 311 than the narrower annular regions 312.

[0063] After the mask 200 is completely removed, the edges of each step may be polished with a hand stone or the like to give the entire mounting surface 31a a smooth concave shape.

[0064] As described above, a sapphire substrate may warp in a convex shape or a concave shape. Therefore, the tendency of warping of the sapphire substrate is grasped in advance, and the mounting surface 31a is machined into a convex or concave shape according to the shape of the warp. This makes it possible to realize an electrostatic chuck 30 that has a simple structure and improved chucking performance for highly insulating chucking targets. The electrostatic chuck 30 also has the same effect on chucking targets with high insulating properties other than a sapphire substrate.

[0065] The simple structure is, for example, a structure that does not require a driving means for displacing the electrostatic chuck body as described in the prior art documents.

[0066] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0067] For example, the method for machining the mounting surface 31a into a convex or concave shape is not limited to blasting, and it is also possible to use, for example, a horizontal axis rotary grinder, a vertical axis rotary grinder, a machining center, a milling machine, a laser, an electric discharge machine, or the like to machine the mounting surface 31a into a convex or concave shape. [Explanation of symbols]

[0068] 1,1A board fixing device 10 Base Plate 11 Gas supply section 20 Adhesive layer 30 Electrostatic Chuck 31 Base 31a Placement surface 31b flat surface 32 Electrostatic Electrode 33 Gas exhaust section 100A, 100B Sapphire substrate 111 Gas flow path 112 Gas injection section 200 masks 200x notch 311 Circular Area 312 Annular Region

Claims

1. a base having a mounting surface on which an object to be adsorbed is placed; an electrostatic electrode built into the substrate; the surface of the base opposite to the mounting surface is a flat surface, The electrostatic chuck, wherein the mounting surface has a convex or concave shape relative to the flat surface.

2. the mounting surface has a convex shape relative to the flat surface, 2. The electrostatic chuck according to claim 1, wherein the height of the mounting surface from the flat surface is highest at the center and decreases toward the periphery.

3. the mounting surface is concave relative to the flat surface, 2. The electrostatic chuck according to claim 1, wherein the height of the mounting surface from the flat surface is lowest at the center and increases toward the periphery.

4. the mounting surface includes, in a plan view, a circular region located at the center and a plurality of annular regions located on an outer periphery of the circular region; In a plan view, an outer edge of each of the annular regions is arranged concentrically with respect to a center of the circular region, The electrostatic chuck of claim 1 , wherein the circular region and each of the annular regions are stepped in cross section.

5. The electrostatic chuck of claim 4 , wherein, in a plan view, the radius of the circular region is greater than the width of each of the annular regions.

6. the plurality of annular regions include annular regions having different widths, 6. The electrostatic chuck of claim 5, wherein the wider annular region is located closer to the circular region than the narrower annular region.

7. A base plate and A substrate fixing device comprising: an electrostatic chuck according to claim 1 provided on the base plate.

8. A step of placing an electrostatic chuck on a base plate, the upper and lower surfaces of which are flat surfaces of a substrate; a step of placing a mask having a plurality of notches formed concentrically in a plan view so as to cover the entire upper surface; peeling off the innermost or outermost region of the mask defined by the slits; blasting the upper surface through the mask; a step of processing the upper surface by repeating the peeling step and the blasting step to form a mounting surface on which an object to be attracted is placed, the mounting surface includes, in a plan view, a circular region located at a center thereof and a plurality of annular regions located outside the circular region, an outer edge of each of the annular regions being arranged concentrically with respect to a center of the circular region, and the circular region and each of the annular regions having a stepped shape in a cross-sectional view.

9. The method for manufacturing an electrostatic chuck according to claim 8 , wherein, in a plan view, the radius of the circular region is wider than the width of each of the annular regions.

10. the plurality of annular regions include annular regions having different widths, The method of claim 9 , wherein the wider annular region is positioned closer to the circular region than the narrower annular region.

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