electrostatic chuck

Abstract

This invention provides a technology for suppressing deformation of a substrate placed in an electrostatic chuck. [Solution] The electrostatic chuck 100 comprises a ceramic substrate 110 and a metal electrostatic adsorption electrode 126 embedded in the ceramic substrate 110. The upper surface 111 of the ceramic substrate 110 has a plurality of first protrusions 156 and a plurality of second protrusions 158 that project upward from the upper surface 111. The upper surfaces 156a of the plurality of first protrusions 156 are located above the upper surfaces 158a of the plurality of second protrusions 158.

Description

Technical Field

[0001] The present invention relates to an electrostatic chuck.

Background Art

[0002] Conventionally, there has been known an electrostatic chuck in which an electrostatic chucking electrode made of a metal (such as W, Mo, or alloys thereof) having a predetermined size is embedded in a ceramic sintered body (ceramic base material) such as AlN ceramics (see, for example, Patent Document 1). In the electrostatic chuck described in Patent Document 1, a plurality of convex portions (pins) are formed on a substrate placement surface, and a substrate such as a silicon wafer is supported in contact with the upper surfaces of the convex portions. In order to suppress electrostatic adsorption force around the convex portions on the substrate placement surface and thereby suppress deformation of the substrate around the convex portions, grooves are formed around the convex portions on the substrate placement surface.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] According to the findings of the inventors, merely forming grooves around the convex portions on the substrate placement surface makes it difficult to suppress deformation of the substrate caused by adsorption of the substrate onto the substrate placement surface when, for example, the height of the convex portions is low.

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide a technique for suppressing deformation of a placed substrate in an electrostatic chuck.

Means for Solving the Problem

[0006] According to an aspect of the present invention, there is provided a plate-shaped ceramic member having a first main surface and a second main surface vertically opposed to the first main surface, and The ceramic member comprises an electrostatic adsorption electrode embedded in the ceramic member, The ceramic member has a plurality of first protrusions and a plurality of second protrusions that project upward from the first main surface, An electrostatic chuck is provided, characterized in that the upper surfaces of the plurality of first protrusions are located above the upper surfaces of the plurality of second protrusions. [Effects of the Invention]

[0007] Since the upper surfaces of the multiple first protrusions are located above the upper surfaces of the multiple second protrusions, the placed substrate comes into contact with the upper surfaces of the multiple first protrusions. Even if the substrate is deflected by electrostatic attraction, the substrate will come into contact with the upper surfaces of the second protrusions, thereby suppressing substrate distortion and preventing the substrate from coming into contact with the upper surface of the ceramic substrate. For example, even when heat transfer is performed by sealing a heat transfer gas in the gap between the substrate and the ceramic substrate, the height of the second protrusions is lower than the height of the first protrusions, so the placed substrate does not necessarily come into contact with the upper surfaces of all of the second protrusions. This prevents the contact area between the heat transfer gas and the substrate from becoming too small when heat transfer is performed by sealing a heat transfer gas in the gap between the substrate and the ceramic substrate, thereby improving the heat transfer effect. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of the electrostatic chuck 100. [Figure 2] Figure 2 is a schematic diagram illustrating the deformation of the wafer 10 when it is placed on the ceramic substrate 110. [Figure 3] Figure 3 is a schematic diagram illustrating the shapes of the multiple first protrusions 156 and second protrusions 158. [Figure 4] Figure 4 is a schematic diagram illustrating the shape of the electrostatic adsorption electrode 126. [Figure 5] Figure 5 is a schematic diagram illustrating the shape of the heater electrode 122. [Figure 6]Figures (a) to (e) show the flow of the manufacturing method for the ceramic substrate 110. [Figure 7] Figures (a) to (d) show the flow of another method for manufacturing the ceramic substrate 110. [Figure 8] (a) is a schematic diagram illustrating the shape of the second protrusion 258 in a top view, (b) is a schematic diagram illustrating the shape of the second protrusion 258 in a side view, and (c) is a schematic diagram illustrating the shape of the second protrusion 258 in a front view. [Figure 9] (a) is a schematic diagram illustrating the shape of the second protrusion 358 when viewed from above, (b) is a schematic diagram illustrating the shape of the second protrusion 358 when its upper surface is a horizontal plane, and (c) is a schematic diagram illustrating the shape of the second protrusion 358 when its upper surface is a curved surface. [Figure 10] Figure 10 is a schematic diagram illustrating the shape of the two-stage protrusion 450. [Figure 11] Figure 11 is a schematic diagram illustrating the first region 111A, the second region 111B, and the third region 111C of the upper surface 111 of the ceramic substrate 110. [Figure 12] Figure 12 is a diagram equivalent to Figure 11, in which the second protrusion 158 is not provided. [Figure 13] Figure 13 is a schematic diagram illustrating the ceramic substrate 110 and the susceptor 150. [Modes for carrying out the invention]

[0009] <Electrostatic Chuck 100> An electrostatic chuck 100 according to an embodiment of the present invention will be described with reference to Figure 1. The electrostatic chuck 100 according to this embodiment is a substrate holding member for adsorbing and holding a semiconductor wafer such as a silicon wafer (hereinafter simply referred to as wafer 10). In the following description, the vertical direction 5 is defined based on the state in which the electrostatic chuck 100 is installed for use (the state in Figure 1). As shown in Figure 1, the electrostatic chuck 100 according to this embodiment mainly comprises a ceramic substrate 110, a heater electrode 122, and an electrostatic adsorption electrode 126. The heater electrode 122 and the electrostatic adsorption electrode 126 are sometimes collectively referred to as the electrode 120.

[0010] The ceramic substrate 110 is a circular, plate-shaped component with a diameter of 12 inches (approximately 300 mm), and the wafer 10 to be held is placed on its upper surface 111. In Figure 1, the wafer 10 and the ceramic substrate 110 are shown separated for clarity. As shown in Figure 1, the upper surface 111 of the ceramic substrate 110 is provided with an annular protrusion 152 (hereinafter simply referred to as the annular protrusion 152) and a plurality of first protrusions 156. In Figure 1, the number of first protrusions 156 is reduced for clarity. Also, as shown in Figure 1, a first gas channel 164, which will be described later, is formed inside the ceramic substrate 110. The ceramic substrate 110 can be formed from, for example, a ceramic sintered body of aluminum nitride, silicon carbide, alumina, silicon nitride, etc.

[0011] As shown in Figure 1, the annular projection 152 is an annular projection located on the outer periphery (outer edge) of the upper surface 111 of the ceramic substrate 110, and protrudes upward from the upper surface 111. As shown in Figure 2, when the wafer 10 is placed on the ceramic substrate 110, the upper surface 152a of the annular projection 152 abuts against the lower surface of the wafer 10. In other words, when the wafer 10 is placed on the ceramic substrate 110, the annular projection 152 is positioned to overlap with the wafer 10 in the vertical direction 5. On the upper surface 111 of the ceramic substrate 110, inside the annular projection 152, there are a plurality of first projections 156 and a plurality of second projections 158. The plurality of first projections 156 are an example of the first projection of the present invention, and the plurality of second projections 158 are an example of the second projection of the present invention.

[0012] Each of the plurality of first convex portions 156 and second convex portions 158 has a columnar shape (cylindrical shape or truncated conical shape). That is, the shape of the top surface 156a of each of the plurality of first convex portions 156 is circular, and the shape of the top surface 158a of each of the plurality of second convex portions 158 is circular. The outer diameter of the first convex portion 156 is Φ0.1 mm to 1.5 mm. The outer diameter of the second convex portion 158 can be the same as the outer diameter of the first convex portion 156. Alternatively, the outer diameter of the second convex portion 158 can be made smaller than the outer diameter of the first convex portion 156. In FIG. 2, in order to simplify the drawing, one of the plurality of first convex portions 156 is arranged at the approximate center of the top surface 111, and the remaining first convex portions 156 are illustrated as being arranged on the circumferences of four concentric circles arranged at equal intervals. A plurality of the second convex portions 158 are arranged so as to be dispersed among the plurality of first convex portions 156. What is shown in FIG. 1 is merely an example, and the positions, shapes, and / or the number of the first convex portions 156 and the second convex portions 158 are appropriately set according to the application, action, and function. For example, the first convex portions 156 can be arranged at lattice points of an equilateral triangle or a regular square. In this case, the interval (pitch) between adjacent first convex portions 156 can be set to 1 mm to 20 mm. If the pitch is too small, when heat transfer is performed by the heat transfer gas with the heat transfer gas sealed in the gap between the wafer 10 and the ceramic base material 110, the contact area between the heat transfer gas and the wafer 10 becomes too small, and there is a possibility that a sufficient heat transfer effect cannot be obtained. In contrast, if the pitch is too large, when the wafer 10 is deflected by the electrostatic adsorption force, the wafer 10 comes into contact with the top surface 111 of the ceramic base material 110, and there is a possibility that the uniformity of the temperature distribution of the wafer 10 is impaired. Therefore, in the present embodiment, the plurality of second convex portions 158 are arranged so as to be dispersed among the plurality of first convex portions 156. As shown in FIG. 1, by arranging the plurality of second convex portions 158 to be dispersed among the plurality of first convex portions 156, distortion of the wafer 10 can be suppressed, and contact of the wafer 10 with the top surface 111 of the ceramic base material 110 can be suppressed. Thereby, impairment of the uniformity of the temperature distribution of the wafer 10 can be suppressed.

[0013] The height of the annular protrusion 152 can be in the range of 5 μm to 50 μm. Similarly, the height of the multiple first protrusions 156 can also be in the range of 5 μm to 50 μm. The height of the annular protrusion 152 and the multiple first protrusions 156 is preferably 5 μm to 15 μm. In contrast, the height of the multiple second protrusions 158 is preferably lower than the height of the multiple first protrusions 156, and is preferably 1 μm to 5 μm. In this specification, the height of the multiple first protrusions 156 is defined as the vertical length from the upper surface 111 of the ceramic substrate 110 to the upper surface 156a of the multiple first protrusions 156. The same applies to the multiple first protrusions 156 and the annular protrusion 152.

[0014] For multiple first protrusions 156, the angle between the upper surface 156a and the side surface 156s is preferably between 90° and 170° (see Figure 3). Similarly for multiple second protrusions 158, the angle between the upper surface 158a and the side surface 158s is preferably between 90° and 170°. For example, when forming multiple first protrusions 156 and second protrusions 158 by machining using a grinding wheel, the angle between the upper surface 156a and the side surface 156s and the angle between the upper surface 158a and the side surface 158s can be made between 91° and 150° by changing the shape of the grinding wheel. Also, when forming multiple first protrusions 156 and second protrusions 158 by sandblasting, the angle between the upper surface 156a and the side surface 156s and the angle between the upper surface 158a and the side surface 158s can be made between 120° and 170°.

[0015] R processing (R10 µm to R50 µm) can be performed between the top surfaces 156a and the side surfaces 156s of the plurality of first protrusions 156. Performing the R processing stabilizes the contact between the top surface 156a of the first protrusion 156 and the wafer 10. When performing R processing, reducing the R dimension can increase the contact area between the top surface 156a and the wafer 10, thereby improving the heat transfer effect. However, if the R dimension is too small, particles constituting the ceramics (having a diameter of about 2 µm to 7 µm) may fall off due to contact with the wafer 10. Therefore, by setting the R dimension larger than the particle diameter of the falling particles (for example, setting the R dimension to 10 µm or more), falling off of ceramic particles caused by contact with the wafer 10 can be suppressed. Similarly, R processing (R10 µm to R50 µm) can also be performed between the top surfaces 158a and the side surfaces 158s of the plurality of second protrusions 158.

[0016] In the present embodiment, the center line average roughness Ra of the top surface 111 of the ceramic base material 110 is 0.1 µm to 3 µm. In contrast, it is preferable that the center line average roughness Ra of the top surfaces 156a of the plurality of first protrusions 156 and the top surfaces 158a of the plurality of second protrusions 158 is 0.01 µm to 2 µm.

[0017] As shown in FIG. 1, an opening 164a of a first gas flow path 164 is opened between the innermost concentric circle where the plurality of first protrusions 156 are arranged and the second concentric circle from the inner side on the top surface 111 of the ceramic base material 110. The first gas flow path 164 is a gas flow path provided with the opening 164a, and is formed inside the ceramic base material 110. The first gas flow path 164 extends downward from the opening 164a.

[0018] The first gas channel 164 can be used as a channel for supplying gas to the space (gap) defined by the upper surface 111 of the ceramic substrate 110 and the lower surface of the wafer 10. For example, it can supply heat transfer gas for heat transfer between the wafer 10 and the ceramic substrate 110. As the heat transfer gas, for example, an inert gas such as helium or argon, or nitrogen gas can be used. The heat transfer gas is supplied through the first gas channel 164 at a pressure set within the range of 100 Pa to 40000 Pa. In addition, if process gas enters the gap inside the annular protrusion 152 from the gap between the upper surface 152a of the annular protrusion 152 and the lower surface of the wafer 10, the gas can be exhausted through the first gas channel 164. In this case, the differential pressure between the pressure outside the gap and the pressure inside the gap can be adjusted by adjusting the exhaust pressure. This makes it possible to adsorb the wafer 10 toward the upper surface of the ceramic substrate 110.

[0019] As shown in Figure 1, a heater electrode 122 and an electrostatic adsorption electrode 126 are embedded inside the ceramic substrate 110. The heater electrode 122 and the electrostatic adsorption electrode 126 can be formed from a mesh, foil, or plate material woven from wires of tungsten (W), molybdenum (Mo), or an alloy containing molybdenum and / or tungsten. As shown in Figure 4, the electrostatic adsorption electrode 126 has two semicircular electrodes 126a and 126b arranged opposite each other at a predetermined distance apart, and has an overall substantially circular shape. For example, the outer diameter of the electrostatic adsorption electrode 126 can be 298 mm. By applying a predetermined voltage (e.g., ±500 V) to electrodes 126a and 126b via terminal 126T, the wafer 10 can be electrostatically adsorbed. Furthermore, if the electrostatic adsorption electrode 126 is formed from a mesh or a foil or plate material (perforated plate) having multiple openings 128 (see Figure 4), the electrostatic adsorption force can be adjusted by adjusting the ratio of openings.

[0020] As shown in Figure 5, the heater electrode 122 is formed from a metal mesh or foil cut into strips. The heater electrode 122 is made of a heat-resistant metal (high melting point metal) such as tungsten (W), molybdenum (Mo), or an alloy containing molybdenum and / or tungsten. The outer diameter of the heater electrode 122 is 298 mm. The heater electrode 120 is not exposed from the side surface of the ceramic substrate 110. A terminal portion 122T, which is connected to a power supply line (not shown), is provided approximately in the center of the heater electrode 122. The thickness of the heater electrode 122 is 0.15 mm or less. When the heater electrode 122 is formed from mesh, the thickness refers to the value excluding the wire intersections. From the viewpoint of increasing the resistance of the heater electrode 122 and reducing the current consumption of the ceramic heater 100, it is preferable to make the wire diameter 0.1 mm or less and the thickness of the heater electrode 122 0.1 mm or less, excluding the wire intersections. In particular, it is preferable that the wire diameter be 0.03 mm or more and 0.05 mm or less. Furthermore, the width of the strip-shaped heater electrode 122 is preferably 2.5 mm to 20 mm, and more preferably 5 mm to 15 mm. In this embodiment, the heater electrode 122 is cut into the shape shown in Figure 5, but the shape of the heater electrode 122 is not limited to this and can be changed as appropriate.

[0021] Next, the manufacturing method of the electrostatic chuck 100 will be described. In the following explanation, we will use the case where the ceramic substrate 110 is made of aluminum nitride as an example. Also, for the sake of simplicity, we will assume that only the electrostatic adsorption electrode 126 is embedded in the ceramic substrate 110.

[0022] First, the method for manufacturing the ceramic substrate 110 will be described. As shown in Figure 6(a), granulated powder Q, mainly composed of aluminum nitride (AlN) powder, is placed in a carbon bed mold 601 and pre-pressed with a punch 602. Preferably, the granulated powder Q contains 5 wt% or less of a sintering aid (for example, Y2O3). A foil or plate of Mo with a thickness of 0.05 mm or more is prepared as the electrostatic adsorption electrode 126. Multiple through holes 128 are formed in the electrostatic adsorption electrode 126 by etching or the like. Alternatively, the electrostatic adsorption electrode 126 can be formed from a mesh woven with Mo wire having a predetermined aperture ratio. Next, as shown in Figure 6(b), the electrostatic adsorption electrode 126, cut to a predetermined shape, is placed on top of the pre-pressed granulated powder Q. The electrostatic adsorption electrode 126 is positioned parallel to the surface perpendicular to the pressing direction (the bottom surface of the bed mold 601). At this time, W pellets or Mo pellets may be embedded at the position of terminal 126T (see Figure 4) of the electrostatic adsorption electrode 126.

[0023] As shown in Figure 6(c), granulated powder Q is further added to the bed mold 601 so as to cover the electrostatic adsorption electrode 126, and then pressed and molded with a punch 602. At this time, the amount of granulated powder Q covering the electrostatic adsorption electrode 126 can be adjusted so that the electrostatic adsorption electrode 126 is embedded at a depth of 0.3 mm or more. Next, as shown in Figure 6(d), the granulated powder Q with the embedded electrostatic adsorption electrode 126 is fired in a pressed state. The pressure applied during firing is preferably 1 MPa or more. It is also preferable to fire at a temperature of 1800°C or higher. Multiple firings can also be performed. Next, as shown in Figure 6(e), blind holes are machined up to the electrostatic adsorption electrode 126 in order to form the terminal 126T. If pellets are embedded, blind holes should be machined up to the pellets. Furthermore, if necessary, through holes may be formed to form gas flow channels 164. This makes it possible to produce a ceramic substrate 110 with gas flow channels 164 formed inside. Furthermore, the through-hole is insulated from the heater electrode 122 and the electrostatic adsorption electrode 126 as needed. Insulation means that the electrodes are not exposed in the through-hole, or by means such as inserting an insulating sleeve into the through-hole.

[0024] The ceramic substrate 110 can also be manufactured by the following method. As shown in Figure 7(a), a binder is added to aluminum nitride granules Q and then CIP molding is performed to process it into a disc shape to produce an aluminum nitride molded body 610. Next, as shown in Figure 7(b), the molded body 610 is degreased to remove the binder.

[0025] As shown in Figure 7(c), a recess 611 for embedding the electrostatic adsorption electrode 126 is formed in the degreased molded body 610. The recess 611 may be formed in the molded body 610 in advance. As described above, a foil or plate of Mo with a thickness of 0.05 mm or more is prepared as the electrostatic adsorption electrode 126, and multiple through holes 128 are formed in the electrostatic adsorption electrode 126 by etching or punching. Alternatively, the electrostatic adsorption electrode 126 is formed from a mesh woven from Mo wires having a predetermined aperture ratio. The electrostatic adsorption electrode 126 is placed in the recess 611 of the molded body 610, and another molded body 610 is laminated on top. At this time, the thickness of the other molded body 610 can be adjusted so that the electrostatic adsorption electrode 126 is embedded at a depth of 0.3 mm or more. Next, as shown in Figure 7(d), the molded bodies 610 laminated with the electrostatic adsorption electrode 126 sandwiched in between are fired in a pressed state to produce a fired body. The pressure applied during firing is preferably 1 MPa or higher. Furthermore, firing at a temperature of 1800°C or higher is preferable. Multiple firings can also be performed. The process after the firing of the body is the same as described above, so the explanation is omitted.

[0026] The upper surface 111 of the ceramic substrate 110 formed in this manner is ground and polished. This allows adjustment of the vertical distance 5 from the upper surface 111 of the ceramic substrate 110 to the electrostatic adsorption electrode 126. For example, the vertical distance 5 from the upper surface 111 of the ceramic substrate 110 to the electrostatic adsorption electrode 126 can be adjusted to 0.3 mm or more. Furthermore, by sandblasting the upper surface 111, a plurality of first protrusions 156, second protrusions 158, and annular protrusions 152 are formed on the upper surface 111. While sandblasting is preferred as the processing method for forming the plurality of first protrusions 156, second protrusions 158, and annular protrusions 152, other processing methods can also be used.

[0027] <Effects of the Embodiment> In the above embodiment, the electrostatic chuck 100 comprises a ceramic substrate 110 and a metal electrostatic adsorption electrode 126 embedded in the ceramic substrate 110. The upper surface 111 of the ceramic substrate 110 has a plurality of first protrusions 156 and a plurality of second protrusions 158 that project upward from the upper surface 111. The upper surfaces 156a of the plurality of first protrusions 156 are located above the upper surfaces 158a of the plurality of second protrusions 158.

[0028] Since the upper surfaces 156a of the multiple first protrusions 156 are located above the upper surfaces 158a of the multiple second protrusions 158, the placed wafer 10 comes into contact with the upper surfaces 156a of the multiple protrusions 156. In the above embodiment, the multiple second protrusions 158 are arranged to be dispersed between the multiple first protrusions 156. As a result, even if the wafer 10 is bent due to electrostatic attraction force, the wafer 10 comes into contact with the upper surfaces 158a of the second protrusions 158, thereby suppressing distortion of the wafer 10 and preventing the wafer 10 from coming into contact with the upper surface 111 of the ceramic substrate 110. This prevents the uniformity of the temperature distribution of the wafer 10 from being compromised. If the sole purpose is to prevent the wafer 10 from coming into contact with the upper surface 111 of the ceramic substrate 110, then reducing the pitch of the multiple first protrusions 156 is a possible solution. However, if the pitch of the multiple first protrusions 156 becomes too small, when heat transfer is performed by sealing a heat transfer gas in the gap between the wafer 10 and the ceramic substrate 110, the contact area between the heat transfer gas and the wafer 10 may become too small, and a sufficient heat transfer effect may not be obtained. In contrast, in the above embodiment, multiple second protrusions 158 are arranged to be dispersed among the multiple first protrusions 156. Furthermore, since the height of the second protrusions 158 is lower than the height of the first protrusions 156, the placed wafer 10 does not necessarily come into contact with the upper surface 158a of all the second protrusions 158. This prevents the contact area between the heat transfer gas and the wafer 10 from becoming too small when heat transfer is performed by sealing a heat transfer gas in the gap between the wafer 10 and the ceramic substrate 110.

[0029] <Change form> The embodiments described above are merely illustrative and can be modified as appropriate. For example, the shape, size, and thickness of the heater electrode 122 and the electrostatic adsorption electrode 126 are not limited to those of the embodiments described above and can be modified as appropriate. Furthermore, the heater electrode 122 does not necessarily have to be provided.

[0030] Furthermore, the shape and thickness of the ceramic substrate 110 can be changed as appropriate. Also, the height, width, and other dimensions of the annular protrusion 152, and the shape of the upper surface 152a of the annular protrusion 152 can be changed as appropriate. The height and shape of the upper surfaces 156a of the multiple first protrusions 156 can be changed as appropriate. For example, the shape of the upper surfaces 156a of the multiple first protrusions 156 does not necessarily have to be circular, and can be any appropriate shape, such as a square.

[0031] In the above embodiment, the second protrusion 158 had a cylindrical or frustoconical shape. However, the present invention is not limited to such embodiments. For example, as shown in Figures 8(a) to 8(c), a plurality of second protrusions 258 can be formed that extend radially around the first protrusion 156. Each second protrusion 258 has a semi-cylindrical shape, like a cylinder cut in half. That is, as shown in Figure 8(c), it has a semi-circular shape when viewed from the direction in which the second protrusion 258 extends, and as shown in Figures 8(a) and 8(b), each second protrusion 258 has a rectangular shape when viewed from above and from the side. The height of each second protrusion 258 is 1 μm to 5 μm, similar to the height of the second protrusion 158 in the above embodiment, and is lower than the height of the first protrusion 156. Therefore, by providing multiple second protrusions 258 that extend radially so as to surround each of the multiple first protrusions 156, the same technical effects as those of the second protrusions 158 in the above embodiment can be obtained. In other words, even when the wafer 10 is bent due to electrostatic adsorption force, the wafer 10 can contact the upper surface 258a of the second protrusions 258, thereby suppressing distortion of the wafer 10 and preventing the wafer 10 from contacting the upper surface 111 of the ceramic substrate 110. This makes it possible to suppress the loss of uniformity in the temperature distribution of the wafer 10.

[0032] As shown in Figure 9(a), multiple annular second protrusions 358 of different diameters can be arranged concentrically around each first protrusion 156. Note that "concentric" simply means that the multiple annular second protrusions 358 of different diameters surround the first protrusion 156 in multiple layers; it does not mean that the centers of the multiple annular second protrusions 358 are perfectly aligned. Alternatively, as shown in Figure 9(b), the radial cross-section of the second protrusion 358 may be rectangular, and the upper surface 358a of the second protrusion 358 may be a horizontal surface (i.e., a surface parallel to the upper surface 111 of the ceramic substrate 110). Or, as shown in Figure 9(c), the radial cross-section of the second protrusion 358 may be semicircular, and the upper surface 358a of the second protrusion 358 may be an upwardly convex curved surface. The height of each second protrusion 358 is 1 μm to 5 μm, similar to the height of the second protrusion 158 in the above embodiment, and is lower than the height of the first protrusion 156. Therefore, by providing a plurality of annular second protrusions 358 arranged concentrically so as to surround each of the plurality of first protrusions 156, the same technical effects as those of the second protrusions 158 in the above embodiment can be obtained. In other words, even when the wafer 10 is bent due to electrostatic adsorption force, the wafer 10 can contact the upper surface 358a of the second protrusion 358, thereby suppressing distortion of the wafer 10 and preventing the wafer 10 from contacting the upper surface 111 of the ceramic substrate 110. This makes it possible to suppress the loss of uniformity in the temperature distribution of the wafer 10.

[0033] As shown in Figure 10, some of the multiple first protrusions 156 can be made into two-stage protrusions 450, which are described below. The two-stage protrusion 450 has a first protrusion 456 and a second protrusion 458 which has a larger diameter than the first protrusion 456, and the first protrusion 456 is positioned on the upper surface 458a of the second protrusion 458. Therefore, the height of the first protrusion 456 (the vertical distance from the upper surface 111 of the ceramic substrate 110 to the upper surface 456a of the first protrusion 456) is greater than the height of the second protrusion 458 (the vertical distance from the upper surface 111 of the ceramic substrate 110 to the upper surface 458a of the second protrusion 456). The height of each first protrusion 456 is the same as the height of the first protrusion 156, and the height of the second protrusion 458 is 5 μm lower than the height of the first protrusion 456. The height difference between the first protrusion 456 and the second protrusion 458 can be 3 μm to 7 μm. Since the height of the second protrusion 458 is lower than the height of the first protrusion 456, the same technical effects as the second protrusion 158 in the above embodiment can be obtained by providing the above-mentioned two-stage protrusion 450 in place of some or all of the first protrusion 156. In other words, even when the wafer 10 is bent due to electrostatic adsorption force, the wafer 10 can contact the upper surface 458a of the second protrusion 458, thereby suppressing distortion of the wafer 10 and preventing the wafer 10 from contacting the upper surface 111 of the ceramic substrate 110. This prevents the uniformity of the temperature distribution of the wafer 10 from being impaired. Note that the electrostatic adsorption force in the central region of the upper surface 111 of the ceramic substrate 110 is stronger than the electrostatic adsorption force in the outer peripheral region. Therefore, when replacing some of the multiple first protrusions 156 with two-stage protrusions 450, it is preferable to replace the multiple first protrusions 156 located in the central region, which is a region with strong electrostatic attraction force, with two-stage protrusions 450.

[0034] In the above embodiment, the upper surface 111 of the ceramic base material 110 is provided with a plurality of first convex portions 156 and a plurality of second convex portions 158. In the above embodiment, the center line average roughness Ra (0.1 μm < Ra < 3 μm) of the upper surface 111 of the ceramic base material 110 is uniform. However, the present invention is not limited to such an embodiment. For example, as shown in FIG. 11, the center line average roughness Ra1 of a region within a radius of 1.5 mm from the center of each first convex portion 156 on the upper surface 111 of the ceramic base material 110 (hereinafter referred to as a first region 111A) can be made larger than 3 μm (Ra1 > 3 μm). Similarly, the center line average roughness Ra2 of a region within a radius of 1.5 mm from the center of each second convex portion 158 on the upper surface 111 of the ceramic base material 110 (hereinafter referred to as a second region 111B) can be made larger than 3 μm (Ra2 > 3 μm). In this case, the center line average roughness Ra3 of a third region 111C on the upper surface 111 of the ceramic base material 110 excluding the first region 111A and the second region 111B can satisfy 0.1 μm < Ra3 < 3 μm. According to the findings of the inventors, the magnitude of the electrostatic adsorption force on the upper surface 111 of the ceramic base material 110 is smaller in a region having a larger center line average roughness Ra than in a region having a smaller center line average roughness Ra. Therefore, by making the center line average roughness Ra1 and Ra2 of the first region 111A, which is a region within a radius of 1.5 mm from the center of each first convex portion 156 on the upper surface 111 of the ceramic base material 110, and the second region 111B, which is a region within a radius of 1.5 mm from the center of each second convex portion 158, larger than 3 μm, the electrostatic adsorption force of the first region 111A and the second region 111B around the first convex portion 156 and the second convex portion 158 can be reduced compared to the electrostatic adsorption force of the third region 111C. Thereby, distortion of the wafer 10 can be suppressed when the wafer 10 is in contact with the upper surface 156a of the first convex portion 156 and the upper surface 158a of the second convex portion 158.

[0035] In the above description, the center line average roughness Ra2 of the second region 111B, which is a region within a radius of 1.5 mm from the center of the second protrusion 158, is set to be larger than 3 µm. However, the present invention is not limited to such an embodiment. In a case where a plurality of the second protrusions 158 are not provided on the upper surface 111 of the ceramic base material 110, the center line average roughness Ra1 of the first region 111A, which is a region within a radius of 1.5 mm from the center of the plurality of first protrusions 156, is set to be larger than 3 µm (Ra1 > 3 µm), and the center line average roughness Ra of a region other than the first region 111A on the upper surface 111 of the ceramic base material 110 can satisfy 0.1 µm < Ra < 3 µm (see FIG. 12). Even in this case, the electrostatic adsorption force of the first region 111A around the first protrusion 156 can be reduced compared to the electrostatic adsorption force of other regions. Accordingly, distortion of the wafer 10 can be suppressed when the wafer 10 is in contact with the upper surface 156a of the first protrusion 156.

[0036] As shown in Figure 13, a susceptor 150 can be joined to the lower surface 113 of the ceramic substrate 110. The susceptor 150 has a circular plate shape with a diameter equal to or larger than that of the ceramic substrate 110, and a flow channel 130 is formed inside it. The susceptor 150 can be made of Al, conductive ceramics, ceramics, etc. The ceramic substrate 110 and the susceptor 150 can be joined using hard brazing, soft brazing, adhesives such as silicone bond, etc. Alternatively, a female screw hole and a through hole through which a screw passes can be formed in either the ceramic substrate 110 or the susceptor 150, and they can be fastened with a screw. In this case, it is preferable to form a groove for airtight sealing in either the ceramic substrate 110 or the susceptor 150, and fasten them with an airtight seal (O-ring, etc.) in between. Furthermore, when hard brazing the ceramic substrate 110 and the susceptor 150, for example, aluminum brazing material (A4047, eutectic point 577°C) can be used as the hard brazing material. These hard brazing materials may contain active metals such as Ti, Hf, and Zr. Metal foil such as Al foil can also be used as the hard brazing material. When hard brazing the ceramic substrate 110 and the ceramic susceptor 150, it is preferable to make the centerline average roughness Ra of the joining surface before joining 1.6 μm or less. Furthermore, when soft brazing the ceramic substrate 110 and the susceptor 150, for example, In, Sn, Pb, and alloys thereof (solder) can be used as the soft brazing material. Furthermore, when soft brazing the ceramic substrate 110 and the ceramic susceptor 150, it is preferable to make the centerline average roughness Ra of the joining surface before joining 1.6 μm or less. Alternatively, a thin film of Cr or Ti may be formed on the bonding surface beforehand.

[0037] Although embodiments and modified versions of the invention have been described above, the technical scope of the present invention is not limited to the scope described above. It will be obvious to those skilled in the art that various modifications or improvements can be made to the above embodiments. It is also clear from the claims that such modified or improved forms may be included in the technical scope of the present invention.

[0038] The order in which each process in the manufacturing method shown in the specification and drawings is executed is not specifically defined, and unless the output of a previous process is used in a later process, the processes can be executed in any order. Even if phrases such as "first," and "next," are used for convenience, this does not mean that the processes must be performed in that order. [Explanation of symbols]

[0039] 100 ceramic susceptors 110 Ceramic substrate 122 Heater electrodes 126 Electrodes for electrostatic adsorption 156, 456 First protrusion 158, 258, 358, 458 Second convex section

Claims

1. A plate-shaped ceramic member having a first main surface and a second main surface facing the first main surface in the vertical direction, The ceramic member comprises an electrostatic adsorption electrode embedded in the ceramic member, The ceramic member has a plurality of first protrusions and a plurality of second protrusions that project upward from the first main surface, An electrostatic chuck characterized in that the upper surfaces of the plurality of first protrusions are located above the upper surfaces of the plurality of second protrusions.

2. The electrostatic chuck according to claim 1, wherein the plurality of second protrusions are arranged radially around each of the plurality of first protrusions.

3. The electrostatic chuck according to claim 1, wherein the plurality of second protrusions are arranged concentrically around each of the plurality of first protrusions.

4. The plurality of first protrusions project upward from the upper surface of the plurality of second protrusions. The electrostatic chuck according to claim 1, wherein the outer diameter of the plurality of second protrusions is larger than the outer diameter of the plurality of first protrusions.

5. The plurality of second protrusions are positioned to be distributed in the region of the first main surface where the plurality of first protrusions are not located. The electrostatic chuck according to claim 1, wherein the height of the plurality of second protrusions in the vertical direction from the first main surface is 1 μm to 5 μm.

6. The electrostatic chuck according to any one of claims 1 to 5, wherein the outer diameter of the plurality of first protrusions is Φ0.1 mm to 1.5 mm, and the vertical height of the plurality of first protrusions from the first main surface is 5 μm to 50 μm.

7. The electrostatic chuck according to claim 4 or claim 5, wherein the centerline average roughness Ra1 of the first main surface in a first region with a radius of 1.5 mm or less from the center of the plurality of first protrusions, and in a second region with a radius of 1.5 mm or less from the center of the plurality of second protrusions, is greater than the centerline average roughness Ra2 of the third region of the first main surface excluding the first and second regions.

8. The electrostatic chuck according to claim 7, wherein Ra1 > 3 μm and 0.1 μm < Ra2 < 3 μm.

9. A plate-shaped ceramic member having a first main surface and a second main surface facing the first main surface in the vertical direction, The ceramic member comprises an electrostatic adsorption electrode embedded in the ceramic member, The ceramic member has a plurality of first protrusions and a plurality of second protrusions that project upward from the first main surface, An electrostatic chuck characterized in that the centerline average roughness Ra1 of the first main surface in a first region with a radius of 1.5 mm or less from the center of the plurality of first protrusions, and in a second region with a radius of 1.5 mm or less from the center of the plurality of second protrusions, is greater than the centerline average roughness Ra2 of the third region of the first main surface excluding the first and second regions.

10. The electrostatic chuck according to claim 9, wherein Ra1 > 3 μm and 0.1 μm < Ra2 < 3 μm.

Images