JP2011061049A - Electrostatic chuck - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic chuck that can enhance the flatness of a suction surface and the parallelism of the suction surface to the surface of a metal base by equalizing the thickness of an adhesive layer. <P>SOLUTION: The electrostatic chuck 1 has a ceramic insulating plate 10 and a metal base 30 where the metal base 30 is joined to the ceramic insulating plate 10 through an adhesive layer 20. The electrostatic chuck 1 sucks a sucked object to a first principal plane 11 of the ceramic insulating plate 10 using an electrostatic attraction force generated when a voltage is applied to a suction electrode layer 51. Furthermore, in the adhesive layer 20, two or more ceramic balls 21 are arranged that contact with a second principal plane 12 of the ceramic insulating plate 10 and first surface 31 of the metal base 30 to keep the thickness of the adhesive layer 20. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrostatic chuck used for fixing a semiconductor wafer, correcting the flatness of the semiconductor wafer, transporting the semiconductor wafer, and the like.

  Conventionally, in a semiconductor manufacturing apparatus, a process such as dry etching is performed on a semiconductor wafer (for example, a silicon wafer). In order to increase the accuracy of dry etching, it is necessary to securely fix the semiconductor wafer. Therefore, an electrostatic chuck for fixing the semiconductor wafer by electrostatic attraction has been proposed as a fixing means for fixing the semiconductor wafer.

  More specifically, an electrostatic chuck has an adsorption electrode layer inside a ceramic insulating plate, and uses an electrostatic attractive force generated when a voltage is applied to the adsorption electrode layer, to form a semiconductor wafer. Is adsorbed on the adsorption surface of the ceramic insulating plate. The electrostatic chuck is configured by bonding a metal base to a bonding surface of a ceramic insulating plate via an adhesive layer (see, for example, Patent Document 1).

  By the way, as described above, the electrostatic chuck has a main function of adsorbing the semiconductor wafer to the adsorption surface of the ceramic insulating plate when processing such as dry etching is performed. Therefore, when the semiconductor wafer is attracted to the suction surface having a low flatness, the flatness of the surface of the semiconductor wafer is also lowered following the suction surface. For this reason, for example, when a pattern is formed on a semiconductor wafer by dry etching, problems such as variations in the degree of processing and a decrease in yield are likely to occur. Therefore, in this type of electrostatic chuck, high flatness is required for the suction surface of the ceramic insulating plate. In addition, in order to eliminate the variation in the degree of processing, it is also required to increase the parallelism of the suction surface with respect to the surface of the metal base.

JP-A-4-287344 (FIG. 2 etc.)

  However, the electrostatic chuck described in Patent Document 1 has a problem that the flatness and parallelism described above cannot be sufficiently secured. The cause is that the ceramic insulating plate and the metal base are joined using an adhesive layer. That is, even if the adsorption surface and the bonding surface of the ceramic insulating plate and the front and back surfaces of the metal base are finished with high flatness by machining or polishing, a paste-like adhesive is applied to obtain a uniform thickness. This is because it is difficult to form an adhesive layer.

  In view of this, it is conceivable that a spacer formed of a metal material or a resin material is disposed in the adhesive layer to maintain a constant distance between the ceramic insulating plate and the metal base. However, when the spacer is formed of a metal material, the thermal conductivity of the spacer is increased, so that heat is easily transferred between the ceramic insulating plate and the metal base. As a result, the temperature difference between the region directly above the spacer and the region not directly above the adsorption surface becomes large, and there is a problem that the semiconductor wafer adsorbed on the adsorption surface cannot be uniformly heated or cooled. In addition, when the spacer is formed of a resin material, the spacer is crushed when the ceramic insulating plate and the metal base are joined, and thus there is a problem that the thickness of the adhesive layer cannot be maintained uniformly.

  The present invention has been made in view of the above problems, and a first object is to make the thickness of the adhesive layer uniform so that the flatness of the suction surface and the parallelism of the suction surface with respect to the surface of the metal base. It is an object of the present invention to provide an electrostatic chuck capable of enhancing the above. A second object is to provide an electrostatic chuck capable of solving the above-described problems that occur when the spacer is formed of a metal material or a resin material.

  As means for solving the above-mentioned problems, a ceramic insulating plate having a first main surface and a second main surface and having an adsorption electrode layer therein, a first surface and a second surface, and the first surface One surface includes a metal base bonded to the second main surface side of the ceramic insulating plate via an adhesive layer, and using electrostatic attraction generated when a voltage is applied to the adsorption electrode layer In the electrostatic chuck for adsorbing an object to be adsorbed to the first main surface, the adhesive layer is in contact with the second main surface of the ceramic insulating plate and the first surface of the metal base in the adhesive layer. There is an electrostatic chuck characterized in that a plurality of ceramic spheres having a uniform particle diameter for maintaining the thickness of the agent layer are arranged.

  Therefore, according to the electrostatic chuck of the above means, the plurality of ceramic spheres having a uniform particle size are in contact with the second main surface that is the bonding surface of the ceramic insulating plate and the first surface that is the surface of the metal base. As a result, the thickness of the adhesive layer is kept uniform. That is, each ceramic sphere functions as a spacer that keeps a space between the ceramic insulating plate and the metal base. Thereby, since the second main surface and the first surface are parallel, the flatness of the first main surface (adsorption surface of the ceramic insulating plate) located on the opposite side of the second main surface can be increased, The parallelism of the first main surface with respect to the first surface (the surface of the metal base) can be increased. As a result, since the flatness of the surface of the object to be adsorbed adsorbed on the first main surface also increases, the degree of processing is less likely to vary when processing the object to be adsorbed, and the yield of the object to be adsorbed decreases. Can prevent such problems. Here, the “flatness” and “parallelism” measuring methods described in this specification are based on the measuring method using a precision surface plate defined in JIS B7513.

  Moreover, according to the above means, the spacer (ceramic sphere) is formed using a ceramic material having a lower thermal conductivity than the metal material and being harder than the resin material. Thereby, compared with the case where a spacer is formed with a metal material, since the heat conductivity of a spacer can be restrained low, a heat | fever is no longer transmitted between a ceramic insulating board and a metal base. As a result, the temperature difference between the region directly above the spacer and the region not directly above the first main surface can be reduced, and the object to be adsorbed adsorbed on the first main surface can be uniformly heated or cooled. Can do. Compared to the case where the spacer is formed of a resin material, the spacer is less likely to be crushed when the ceramic insulating plate and the metal base are joined by applying pressure in the thickness direction, so the thickness of the adhesive layer is uniform. Can be held in.

  The thickness of the ceramic insulating plate is not particularly limited, but may be 0.5 mm or greater and 7.0 mm or less. If the thickness of the ceramic insulating plate is 1.0 mm or less, the ceramic insulating plate becomes too thin, and the strength of the ceramic insulating plate may be reduced and damaged. On the other hand, if the thickness of the ceramic insulating plate is larger than 6.0 mm, the distance to which heat is transferred (distance from the first main surface of the ceramic insulating plate to the first surface of the metal base) becomes longer, so It becomes difficult for the heat of the plate to escape to the metal base side through the adhesive layer. As a result, temperature controllability may be reduced.

  In addition, as a material which comprises a ceramic insulating board, the sintered compact etc. which have high temperature firing ceramics, such as an alumina, a yttria (yttrium oxide), aluminum nitride, boron nitride, silicon carbide, silicon nitride, etc. are mentioned. Depending on the application, a sintered body mainly composed of a low-temperature fired ceramic such as a glass ceramic obtained by adding an inorganic ceramic filler such as alumina to a borosilicate glass or a lead borosilicate glass may be selected. Alternatively, a sintered body mainly composed of a dielectric ceramic such as barium titanate, lead titanate, or strontium titanate may be selected.

  In each process such as dry etching in semiconductor manufacturing, various techniques using plasma are employed, and in processes using plasma, corrosive gas such as halogen gas is frequently used. For this reason, high corrosion resistance is required for the electrostatic chuck exposed to corrosive gas or plasma. Therefore, the ceramic insulating plate is preferably made of a material having corrosion resistance against corrosive gas or plasma, for example, a material mainly composed of alumina or yttria. In this way, since the corrosion of the first main surface of the ceramic insulating plate can be prevented, the flatness of the first main surface is hardly lowered, and the life of the electrostatic chuck can be extended.

  The ceramic insulating plate has the adsorption electrode layer inside. The material constituting the adsorption electrode layer is not particularly limited, but when the adsorption electrode layer and the ceramic insulating plate are formed by the simultaneous firing method, the metal powder in the adsorption electrode layer is higher than the firing temperature of the ceramic insulating plate. Must have a high melting point. For example, when the ceramic insulating plate is made of a so-called high-temperature fired ceramic (for example, alumina), nickel (Ni), tungsten (W), molybdenum (Mo), manganese (Mn) is used as the metal powder in the adsorption electrode layer. Etc. and their alloys can be selected. When the ceramic insulating plate is made of a so-called low-temperature fired ceramic (for example, glass ceramic), copper (Cu), silver (Ag), or an alloy thereof can be selected as the metal powder in the adsorption electrode layer. When the ceramic insulating plate is made of a high dielectric constant ceramic (for example, barium titanate), nickel (Ni), copper (Cu), silver (Ag), palladium (Pd), platinum (Pt), etc. These alloys can be selected. The adsorption electrode layer is formed by applying a conductive paste containing a metal powder, applying the paste by a conventionally known method, for example, a printing method, and then baking. Furthermore, examples of the material for forming the metal base include copper, aluminum, iron, and titanium.

  Further, the material forming the adhesive layer is preferably a material having a large force for bonding the ceramic insulating plate and the metal base or a force for fixing the plurality of ceramic spheres. For example, a metal material such as indium or a silicone resin A resin material such as an acrylic resin, an epoxy resin, a polyimide resin, a polyamideimide resin, or a polyamide resin can be selected. However, since the difference between the thermal expansion coefficient of the ceramic insulating plate and the thermal expansion coefficient of the metal base is large, the adhesive layer may be an adhesive made of an elastically deformable resin material having a function as a buffer material. Particularly preferred is an adhesive made of a silicone resin. If it does in this way, the thermal stress which generate | occur | produces between a ceramic insulating board and a metal base can be relieve | moderated effectively by the silicone resin which has a high elasticity modulus. Here, the “silicone resin” refers to a polymer compound having a main skeleton formed by a siloxane bond (a bond between silicon and oxygen).

  The thickness of the adhesive layer is not particularly limited, but may be set to, for example, 25 μm or more and 700 μm or less. Incidentally, the metal base has not only a function of holding the ceramic insulating plate but also a function of cooling the object to be adsorbed by releasing heat generated from the object to be adsorbed on the first main surface to the outside. However, since the adhesive layer is likely to be made of a resin material having a thermal conductivity much lower than that of a ceramic material or a metal material, if the thickness of the adhesive layer exceeds 700 μm, the distance between the ceramic insulating plate and the metal base It becomes difficult for heat to be transferred and the heat from the object to be adsorbed is difficult to release to the outside. In addition, when the thickness of the adhesive layer is less than 25 μm, when unevenness occurs on the second main surface of the ceramic insulating plate or the first surface of the metal base, an unbonded portion where the adhesive does not spread easily occurs. Furthermore, it is preferable that the thickness of the adhesive layer is equal to the average particle diameter of the plurality of ceramic spheres. In this way, since each ceramic sphere can be reliably brought into contact with the second main surface and the first surface, it becomes easy to uniformly maintain the thickness of the adhesive layer by each ceramic sphere. .

  A plurality of ceramic spheres having a uniform particle diameter are arranged in the adhesive layer. Here, “uniform particle size” means that the particle size of most ceramic spheres is, for example, (adhesive layer thickness) within ± 10 μm, preferably (adhesive layer thickness) within ± 5 μm. It shall be said that. This is because it is considered that the thickness of the adhesive layer is hardly affected if the particle diameter of the ceramic sphere is within the above range. The “ceramic sphere” refers to a sphere having ceramic as a main component. Examples of the material constituting the ceramic sphere include silicon nitride, alumina, zirconia, silicon oxide, aluminum nitride, silicon carbide, boron nitride, barium titanate, and strontium titanate.

  The thermal conductivity of the ceramic sphere at 200 ° C. or lower is not particularly limited, but may be, for example, 2 W / (m · K) or more and 200 W / (m · K) or less. Here, as the material of the ceramic sphere whose thermal conductivity satisfies the above conditions, silicon nitride (thermal conductivity 28 W / (m · K)), alumina (thermal conductivity 30 W / (m · K)), zirconia ( Thermal conductivity 4W / (m · K)), silicon oxide (thermal conductivity 30W / (m · K)), aluminum nitride (thermal conductivity 170W / (m · K)), silicon carbide (thermal conductivity 170W / (M · K)). When the thermal conductivity of the ceramic sphere at 200 ° C. or lower is less than 2 W / (m · K), the temperature difference between the region directly above the ceramic sphere and the region not directly above the first main surface of the ceramic insulating plate. Therefore, it becomes difficult to uniformly heat or cool the object to be adsorbed on the first main surface. On the other hand, if the thermal conductivity of the ceramic sphere at 200 ° C. or lower is larger than 200 W / (m · K), heat is transferred too much between the ceramic insulating plate and the metal base, so the temperature of the first main surface of the ceramic insulating plate Distribution tends to be non-uniform. In this case, problems such as inability to uniformly heat or cool the object to be adsorbed on the first main surface are likely to occur.

Furthermore, the thermal expansion coefficient of the ceramic sphere is not particularly limited, but may be, for example, 1.0 × 10 ⁻⁶ / K or more and 15 × 10 ⁻⁶ / K or less. Here, as the material of the ceramic sphere whose thermal expansion coefficient satisfies the above conditions, silicon nitride (thermal expansion coefficient 2.8 × 10 ⁻⁶ / K), alumina (thermal expansion coefficient 7.7 × 10 ⁻⁶ / K) ), Zirconia (thermal expansion coefficient 10 × 10 ⁻⁶ / K), silicon oxide (thermal expansion coefficient 3 × 10 ⁻⁶ / K), aluminum nitride (thermal expansion coefficient 4.4 × 10 ⁻⁶ / K), silicon carbide (Thermal expansion coefficient 4.1 × 10 ⁻⁶ / K) and the like. When the thermal expansion coefficient of the ceramic sphere is less than 1.0 × 10 ⁻⁶ / K, the difference in thermal expansion coefficient from the ceramic insulating plate becomes very large. As a result, when exposed to a heat cycle of heating and cooling, the adhesive layer may be peeled off from the ceramic insulating plate, leading to a decrease in reliability. On the other hand, if the thermal expansion coefficient of the ceramic sphere becomes larger than 15 × 10 ⁻⁶ / K, the size of the ceramic sphere is likely to change with a change in temperature, so even if a plurality of ceramic spheres are arranged in the adhesive layer. There is a possibility that problems such as easy cracking in the adhesive layer and peeling of the adhesive layer may occur.

  The plurality of ceramic spheres are preferably made of a material harder than the ceramic insulating plate and the metal base. In this way, when the ceramic insulating plate and the metal base are joined, the ceramic sphere may be crushed even if a pressing force is applied in the thickness direction to the laminate composed of the ceramic insulating plate and the metal base. Becomes smaller. Therefore, it becomes easy to keep the thickness of the adhesive layer uniform by the ceramic balls. Here, as the material of the ceramic sphere which becomes harder than the ceramic insulator and the metal base, silicon nitride (Vickers hardness (HV) is 1500), alumina (Vickers hardness (HV) is 1000 to 1500), zirconia (Vickers) Hardness (HV) is 1300), aluminum nitride (Vickers hardness (HV) is 1100 to 1600), silicon carbide (Vickers hardness (HV) is 2400), and the like.

  Further, the sphericity of the ceramic sphere is not particularly limited, but may be 2 μm or less, for example. If the sphericity of the ceramic sphere is larger than 2 μm, the variation in the particle size of the ceramic sphere will increase, so even if a plurality of ceramic spheres are arranged in the adhesive layer, the thickness of the adhesive layer should be uniform. May not be retained. In this case, the flatness of the ceramic insulating plate and the parallelism of the first main surface with respect to the first surface of the metal base may be reduced.

  In addition, although the method of arrange | positioning a ceramic sphere is not specifically limited, For example, the said ceramic sphere may be arrange | positioned in the ratio of one piece for every area | region of 20 mm square or more and 60 mm square or less in the said adhesive bond layer. In this case, since the ceramic spheres are arranged uniformly along the planar direction of the adhesive layer, the thickness of the adhesive layer can be more uniformly maintained by each ceramic sphere. If the ceramic spheres are arranged at a ratio of one for each area of less than 20 mm square in the adhesive layer, a large number of ceramic spheres must be arranged in the adhesive layer. Will rise. Moreover, since the thermal conductivity of the ceramic sphere is different from the thermal conductivity of the adhesive layer, as described above, the ceramic sphere is arranged in a ratio of one for each area of less than 20 mm square in the adhesive layer. (That is, when the ceramic balls are densely arranged), the temperature distribution on the first main surface of the ceramic insulating plate tends to be non-uniform. On the other hand, if the ceramic spheres are arranged at a ratio of one for each region wider than 60 mm square in the adhesive layer, the ceramic spheres arranged in the adhesive layer are reduced, and thus a plurality of ceramics are included in the adhesive layer. Even if the spheres are arranged, there is a possibility that the thickness of the adhesive layer cannot be kept uniform. In order to make the thickness of the adhesive layer uniform (in other words, to keep the second main surface of the ceramic insulating plate and the first surface of the metal base parallel to each other) It is preferable to arrange three or more ceramic spheres.

1 is a perspective view showing a partially broken electrostatic chuck according to an embodiment of the present invention. The schematic sectional drawing which shows an electrostatic chuck. Explanatory drawing which shows the arrangement | positioning aspect of a ceramic ball | bowl. Explanatory drawing which shows the manufacturing method of an electrostatic chuck. Explanatory drawing which shows the manufacturing method of an electrostatic chuck. Explanatory drawing which shows the manufacturing method of an electrostatic chuck. Explanatory drawing which shows the manufacturing method of an electrostatic chuck. Explanatory drawing which shows the manufacturing method of an electrostatic chuck.

  Hereinafter, an embodiment embodying the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the electrostatic chuck 1 of the present embodiment is an apparatus for adsorbing a semiconductor wafer 2 (adsorbed object) to an adsorption surface 11. The electrostatic chuck 1 includes a ceramic insulating plate 10 and a metal base 30 bonded to the bonding surface 12 side of the ceramic insulating plate 10 via an adhesive layer 20.

As shown in FIGS. 1 and 2, the ceramic insulating plate 10 has a substantially disk shape with a diameter of 300 mm and a thickness of 3.0 mm. The ceramic insulating plate 10 has a suction surface 11 that is a first main surface and a bonding surface 12 that is a second main surface. In the present embodiment, the suction surface 11 and the bonding surface 12 are arranged in parallel to each other, and the flatness of each of the suction surface 11 and the bonding surface 12 is 30 μm or less. The ceramic insulating plate 10 is made of a sintered body mainly composed of alumina, and has a structure in which first to sixth ceramic layers (not shown) are laminated. In this embodiment, the ceramic insulating plate 10 has a thermal conductivity of 32 W / (m · K) and a thermal expansion coefficient of 7.7 ppm / ° C. (= 7.7 × 10 ⁻⁶ / K). In addition, the thermal expansion coefficient of the ceramic insulating board 10 says the average value of the measured value between 30 degreeC-250 degreeC. Further, the ceramic insulating plate 10 has a Vickers hardness (HV) of 1000.

  Further, the ceramic insulating plate 10 has a cooling gas passage 41 inside. In the cooling gas channel 41, helium gas (cooling gas) for cooling the semiconductor wafer 2 adsorbed on the adsorption surface 11 flows. The cooling gas flow path 41 includes a plurality of lateral holes 42 extending in the planar direction of the ceramic insulating plate 10 in the third ceramic layer. Each lateral hole 42 has a rectangular cross section, and the length of the ceramic insulating plate 10 in the thickness direction is set to 0.5 mm or more and 1.0 mm or less (1.0 mm in this embodiment). The length in the plane direction is set to 0.5 to 2.0 mm. The lateral holes 42 are arranged at equal angular intervals (60 °) with respect to the central portion C1 (see FIG. 3) of the ceramic insulating plate 10, and extend radially from the central portion C1 toward the outer peripheral portion.

  The cooling gas flow path 41 shown in FIG. 1 includes a pair of annular gas flow paths (not shown) in the first ceramic layer. Both annular gas flow paths are arranged concentrically in a plan view with respect to the center portion C1. The annular gas channel on the outer peripheral side is provided with a plurality of gas jets (not shown) that open at the adsorption surface 11. Each gas ejection port has a circular shape and is arranged at equiangular intervals with respect to the center portion C1.

  Further, as shown in FIG. 1, the cooling gas passage 41 further includes vertical holes 47 and 48 having a diameter of 0.1 to 1.0 mm extending in the thickness direction of the ceramic insulating plate 10. The vertical hole 47 on the inner peripheral side communicates with the horizontal hole 42 at the center, and the end on the adsorption surface 11 side communicates with the annular gas channel on the inner peripheral side, while the end on the bonding surface 12 side has the bonding surface. 12 is open. Further, the vertical hole 48 on the outer peripheral side communicates with the end portion on the adsorption surface 11 side to the annular gas flow path on the outer peripheral side, while the end portion on the bonding surface 12 side communicates with the horizontal hole 42.

  As shown in FIGS. 1 and 2, the ceramic insulating plate 10 has an adsorption electrode layer 51 inside. The adsorption electrode layer 51 is a layer formed with tungsten as a main component, and in the ceramic insulating plate 10, on the adsorption surface 11 side (specifically, on the ceramic layer of the third layer) with respect to the lateral hole 42. Has been placed. The adsorption electrode layer 51 is electrically connected to the upper end surface of a via-hole conductor (not shown) that penetrates the third to fifth ceramic layers, and the lower end surface of the via-hole conductor is the fifth layer ceramic. It is electrically connected to a first pad (not shown) formed on the lower surface of the layer. Further, a first opening (not shown) for exposing the first pad is formed at a predetermined position of the sixth ceramic layer, and a first terminal pin (not shown) is formed on the surface of the first pad. Joined by brazing, soldering, conductive adhesive or the like. The first terminal pin is accommodated in a first recess (not shown) provided in the metal base 30. A voltage is applied to the first terminal pin with an external terminal (not shown) being joined.

  As shown in FIGS. 1 and 2, the ceramic insulating plate 10 has a plurality of heater electrode layers 61 for heating the ceramic insulating plate 10 therein. Each heater electrode layer 61 is a layer formed with tungsten as a main component, and in the ceramic insulating plate 10, closer to the bonding surface 12 than the lateral hole 42 (specifically, on the sixth ceramic layer). Has been placed. Each heater electrode layer 61 is arranged so as to circulate in a spiral shape with respect to the central portion C1. As a result, each heater electrode layer 61 intersects the horizontal hole 42, so that it hardly overlaps the horizontal hole 42 when the ceramic insulating plate 10 is viewed from the thickness direction. The heater electrode layer 61 is electrically connected to a second pad (not shown) formed on the lower surface of the fifth ceramic layer. Further, a second opening (not shown) for exposing the second pad is formed at a predetermined position of the sixth ceramic layer, and a second terminal pin (not shown) is formed on the surface of the second pad. Joined by brazing, soldering, conductive adhesive or the like. The second terminal pin is accommodated in a second recess (not shown) provided in the metal base 30. A voltage is applied to the second terminal pin in a state where an external terminal (not shown) is joined.

As shown in FIGS. 1 and 2, the metal base 30 is made of a material mainly composed of aluminum. In this embodiment, the metal base 30 has a thermal conductivity of 236 W / (m · K) and a thermal expansion coefficient of about 23 ppm / ° C. (= about 23 × 10 ⁻⁶ / K). In addition, the thermal expansion coefficient of the metal base 30 means the average value of the measured value between 0 degreeC and glass transition temperature (Tg). Further, the Vickers hardness (HV) of the metal base 30 is 50. The metal base 30 has a substantially disc shape with a diameter of 340 mm and a thickness of 30 mm. That is, the diameter of the metal base 30 is set larger than the diameter (300 mm) of the ceramic insulating plate 10. The metal base 30 has a first surface 31 to which the ceramic insulating plate 10 is joined, and a second surface 32 located on the opposite side of the first surface 31. In the present embodiment, the first surface 31 and the second surface 32 are arranged in parallel to each other, and the flatness of the first surface 31 and the second surface 32 is 30 μm or less.

  The metal base 30 has cooling fluid flow paths 71 and 72 inside. Cooling water (cooling fluid) for cooling the ceramic insulating plate 10 flows through the cooling fluid flow paths 71 and 72. Each of the cooling fluid flow paths 71 and 72 is disposed so as to spiral around the center C1. The cooling fluid flow path 71 on the inner peripheral side is provided with a plurality of cooling water passages 73 that open at the second surface 32. Further, the cooling fluid passage 72 on the outer peripheral side extends to the outer peripheral side from the ceramic insulating plate 10 when the ceramic insulating plate 10 and the metal base 30 are viewed from the thickness direction.

  Further, as shown in FIG. 1, the metal base 30 includes a communication hole 33 having a diameter of 2.5 mm extending in the thickness direction of the metal base 30. Helium gas is supplied to the communication hole 33 via an external pipe (not shown). In the communication hole 33, the end on the first surface 31 side communicates with the vertical hole 47, while the end on the second surface 32 side opens in the second surface 32. The communication hole 33 is arranged avoiding the cooling fluid flow paths 71 and 72. Specifically, the communication hole 33 is disposed between the cooling fluid channel 71 and the cooling fluid channel 72.

As shown in FIGS. 1 to 3, the adhesive layer 20 is an adhesive made of a silicone resin, and the thickness of the adhesive layer 20 is set to 300 μm. In the present embodiment, the adhesive layer 20 has a thermal conductivity of 1.0 W / (m · K) and a thermal expansion coefficient of about 200 ppm / ° C. (= about 200 × 10 ⁻⁶ / K). The thermal expansion coefficient of the adhesive layer 20 refers to an average value of measured values between 0 ° C. and the glass transition temperature (Tg).

As shown in FIGS. 2 and 3, a plurality of ceramic spheres 21 having a uniform particle diameter are arranged in the adhesive layer 20. Each ceramic ball 21 is configured to maintain the thickness of the adhesive layer 20 by contacting the joining surface 12 of the ceramic insulating plate 10 and the first surface 31 of the metal base 30. The average particle diameter of each ceramic sphere 21 is equal to the thickness of the adhesive layer 20, and is set to 300 μm in this embodiment. Each ceramic sphere 21 has a substantially spherical shape with a sphericity of 2 μm. Further, each ceramic sphere 21 is made of a sintered body of silicon nitride which is a kind of high-temperature fired ceramic. In this embodiment, the thermal conductivity of the ceramic sphere 21 at 200 ° C. or lower is 28 W / (m · K), and the thermal expansion coefficient is 2.8 × 10 ⁻⁶ / K. The thermal expansion coefficient of the ceramic sphere 21 is an average value of measured values between 0 ° C. and the glass transition temperature (Tg). Further, the Vickers hardness (HV) of the ceramic sphere 21 is 1500. That is, each ceramic ball 21 is made of a material harder than the ceramic insulating plate 10 (Vickers hardness 1000) and the metal base 30 (Vickers hardness 50).

  As shown in FIG. 3, the ceramic spheres 21 are arranged along the planar direction of the adhesive layer 20. More specifically, one ceramic ball 21 is disposed in the adhesive layer 20 at the location that becomes the central portion C1. Further, in the adhesive layer 20, annular ceramic sphere groups 22 and 23 including a plurality of ceramic spheres 21 are arranged. Both ceramic ball groups 22 and 23 are arranged concentrically in a plan view with respect to the center portion C1. The ceramic spheres 21 constituting the inner peripheral ceramic sphere group 22 are arranged at equiangular (45 °) intervals with the central portion C1 as a reference. On the other hand, the ceramic spheres 21 constituting the outer peripheral ceramic sphere group 23 are arranged at equiangular (30 °) intervals with respect to the central portion C1. Each ceramic ball 21 is arranged so as not to overlap the vertical hole 47 and the communication hole 33 when the ceramic insulating plate 10 is viewed from the thickness direction. Further, each ceramic sphere 21 is arranged avoiding the first and second openings and the first and second recesses when the ceramic insulating plate 10 is viewed from the thickness direction. Moreover, the distance (pitch) between the centers of adjacent ceramic balls 21 is set to 40 mm or more and 50 mm or less. And the ceramic ball | bowl 21 is arrange | positioned in the ratio of one for every 42 mm square area | region in the adhesive bond layer 20. As shown in FIG.

  When the electrostatic chuck 1 of this embodiment is used, a voltage of 3 kV is applied to the adsorption electrode layer 51 to generate an electrostatic attractive force, and the semiconductor wafer 2 is attached to the semiconductor wafer 2 using the generated electrostatic attractive force. Adsorbed to the adsorption surface 11. At this time, helium gas flowing through the cooling gas flow path 41 is supplied from the gas outlet between the adsorption surface 11 and the back surface of the semiconductor wafer 2 to cool the semiconductor wafer 2. In addition, by applying a voltage to the heater electrode layer 61 to heat the ceramic insulating plate 10, the semiconductor wafer 2 adsorbed on the adsorption surface 11 is heated.

  Next, a method for manufacturing the electrostatic chuck 1 will be described.

First, a slurry is prepared by the following procedure. By mixing MgO (1% by weight), CaO (1% by weight), SiO ₂ (6% by weight) with alumina powder (92% by weight), wet-grinding with a ball mill for 50 to 80 hours, and then dehydrating and drying. Get powder. Next, methacrylic acid isobutyl ester (3% by weight), butyl ester (3% by weight), nitrocellulose (1% by weight), dioctyl phthalate (0.5% by weight) were added to the obtained powder, and further trichloroethylene, After adding n-butanol as a solvent, wet mixing is performed with a ball mill to obtain a slurry as a starting material for forming an alumina green sheet.

  Next, this slurry is degassed under reduced pressure, and then poured onto a releasable support (not shown) and cooled to evaporate the solvent. As a result, first to sixth layers of alumina green sheets (unsintered ceramic layers to be the first to sixth ceramic layers) having a desired thickness are formed. The second to sixth layers of alumina green sheets are provided with through holes for forming the vertical holes 47, and the second and third layers of alumina green sheets are used to form the vertical holes 48. A through hole is provided. The first layer alumina green sheet is provided with a through hole for forming an annular gas flow path, and the fourth layer alumina green sheet is provided with a through hole for forming a lateral hole 42. . Further, the sixth layer of alumina green sheet is provided with through holes for forming the first and second recesses. The third to fifth layers of alumina green sheets are provided with through holes for forming via-hole conductors. Each through hole is formed by die cutting or machining an alumina green sheet.

  Moreover, tungsten powder is mixed with the powder for alumina green sheets described above. This is made into a slurry by the same method as that for producing the alumina green sheet to obtain a metallized paste.

  Next, a metallized paste to be the adsorption electrode layer 51 is printed and applied on the upper surface of the third layer of alumina green sheet using a conventionally known paste printing apparatus (for example, a screen printing apparatus). Further, a metallized paste to be the heater electrode layer 61 is printed and applied on the upper surface of the sixth layer of alumina green sheet using a paste printing apparatus. Further, a metallized paste to be a via-hole conductor is printed and applied in a through hole provided in the third to fifth alumina green sheets. Further, a metallized paste to be the first pad and the second pad is printed on the lower surface of the sixth layer of alumina green sheet. Thereafter, the printed metallized paste is dried at room temperature.

  Next, the alumina green sheets of the first layer to the sixth layer are thermocompression-bonded in a state where the through holes are aligned so that the cooling gas passage 41, the first and second openings, and the via-hole conductor are formed. Then, a green sheet laminate having a thickness of about 5 mm is formed. Further, the green sheet laminate is cut into a predetermined disc shape (in this embodiment, a disc shape having a diameter of 300 mm).

  Next, the green sheet laminate is degreased in the atmosphere at 250 ° C. for 10 hours, and further fired in a reducing atmosphere at 1400 to 1600 ° C. for a predetermined time. As a result, alumina and tungsten are simultaneously sintered, and the ceramic insulating plate 10 having a desired structure is obtained. Since the size is reduced by about 20% by this firing, the thickness of the ceramic insulating plate 10 is about 4 mm. Thereafter, both the front and back surfaces of the ceramic insulating plate 10 are polished so as to make the thickness of the ceramic insulating plate 10 3 mm, and the flatness of the suction surface 11 and the bonding surface 12 is made 30 μm or less.

  Next, nickel plating is applied to the first and second terminal pins, and the first and second terminal pins subjected to nickel plating are brazed to the first and second pads, soldered, conductive adhesive, etc. The ceramic insulating plate 10 is completed by bonding.

  Further, a ceramic sphere 21 is prepared and prepared in advance. The ceramic sphere 21 is produced as follows, for example. First, at least one selected from the group consisting of rare earth elements, titanium group, earth metal, aluminum group, and carbon group elements is added to the silicon nitride powder as 1 to 15 wt%, preferably 2 to 8 wt% as a sintering aid. % Mix. Next, a slurry is obtained by adding an aqueous solvent to the obtained mixture and wet-mixing with a pulverizer such as an attritor. Then, the obtained slurry is dried by spray drying or the like to obtain a raw material powder.

  Next, by combining the first mold (upper mold), the second mold (lower mold), the third mold (left mold), and the fourth mold (right mold) constituting the mold press, the ceramic ball 21 is placed inside. And a cavity having the same shape and volume. In this state, the obtained raw material powder is filled in the cavity. Then, a compact is obtained by applying a pressing force in the vertical direction of the mold press and compressing the raw material powder filled in the cavity. Thereafter, the first mold, the second mold, the third mold, and the fourth mold are separated from each other, and the spherical molded body is taken out.

  In addition, in this embodiment, since the molded object is formed by compressing raw material powder only in one direction, a high density part and a low part will arise in the obtained molded object. Therefore, in the present embodiment, dry CIP (hydrostatic press) is performed using a rubber mold (not shown). Thereby, the density distribution of a molded object becomes substantially constant, and it becomes a dense molded object.

  Next, the obtained molded body is fired to obtain ceramic spheres 21 which are spherical silicon nitride sintered bodies. In the present embodiment, the molded body is fired in three stages: resin-free firing, primary firing, and secondary firing. More specifically, in the primary firing, the molded body is fired for a predetermined time at 1900 ° C. or less in a non-oxidizing atmosphere containing nitrogen and 0.1 MPa to 1.0 MPa. As a result, silicon nitride is sintered, and the sintered body density is 78% or more (preferably 90% or more). In the subsequent secondary firing, the molded body after the primary firing is fired at 1600 to 1950 ° C. for a predetermined time in a non-oxidizing atmosphere containing nitrogen and 1 MPa to 100 MPa. As a result, the silicon nitride is completely sintered and the ceramic sphere 21 is obtained.

  Thereafter, the obtained ceramic sphere 21 is polished using a conventionally known ball polishing machine. Specifically, first, the ceramic balls 21 are supplied between a pair of upper and lower grindstones provided in the ball grinder. Then, by rotating the upper grindstone to circulate the ceramic sphere 21, the surface of the ceramic sphere 21 is polished, and the sphericity of the ceramic sphere 21 becomes 2 μm.

  Next, an adhesive layer 20 having a predetermined thickness is formed on the first surface 31 of the metal base 30 by applying a paste adhesive once or a plurality of times using a conventionally known screen printing apparatus. (See FIG. 5). In addition, since the adhesive agent of this embodiment is an adhesive agent which consists of silicone resins, it contains organic solvents, such as toluene and acetone. Also, the thickness of the adhesive layer 20 (the particle diameter of the ceramic spheres 21) after bonding is considered in consideration of the fact that the thickness of the adhesive layer 20 is compressed when the ceramic insulating plate 10 is bonded to the metal base 30. ) Is set to 1.4 times, for example.

  Next, the plurality of ceramic balls 21 described above are placed on the surface of the adhesive layer 20 (see FIGS. 5 and 6). Specifically, first, a substantially disk-shaped jig 80 (see FIG. 5) comprising a jig body 81 and a bottom plate 82 is prepared. The jig body 81 has a plurality of positioning holes 83 for arranging the ceramic balls 21. Each positioning hole 83 has a circular cross section, and the inner diameter is slightly larger than the average particle diameter (300 μm) of the ceramic sphere 21. Further, the bottom plate 82 has a function of closing each positioning hole 83 from the lower side of the jig body 81. Then, by inserting the ceramic sphere 21 into each positioning hole 83, each ceramic sphere 21 is arranged along the plane direction of the jig 80.

Next, the jig 80 is disposed above the adhesive layer 20. Then, by pulling out the bottom plate 82 in the plane direction of the jig 80 (the direction of the arrow F1 shown in FIG. 5), the ceramic balls 21 in the positioning holes 83 are dropped and placed on the adhesive layer 20 ( (See FIG. 6). At this time, the ceramic sphere 21 is temporarily fixed in a state where the bottom is buried in the adhesive layer 20. Further, the ceramic insulating plate 10 described above is placed on the adhesive layer 20 and the ceramic ball 21 with the adsorption surface 11 facing upward (see FIG. 7). Then, after the weight 84 is placed on the suction surface 11 of the ceramic insulating plate 10 and vacuum deaeration is performed, a pressing force is applied in the vertical direction (the direction of arrow F2 shown in FIG. 8). As a result, the adhesive layer 20 is compressed in the thickness direction, and each ceramic sphere 21 is embedded in the adhesive layer 20, and the bonding surface 12 of the ceramic insulating plate 10 and the first surface 31 of the metal base 30. Both are in contact (see FIG. 8). In addition, although an excess adhesive protrudes from the outer periphery of the junction part of the ceramic insulating board 10 and the metal base 30, what is necessary is just to remove the excess part of an adhesive by grinding etc. after adhesion | attachment. The weight 84 is preferably set to such an extent that the ceramic sphere 21 can be embedded in the adhesive layer 20 and brought into contact with the first surface 31. Specifically, it is preferable to set the weight of the weight 84 to such an extent that, for example, a surface pressure of 35 to 45 g / cm ² can be obtained on the bonding surface 12.

  Thereafter, the adhesive layer 20 is cured by leaving it for a predetermined time (20 to 24 hours). Thereby, the ceramic insulating plate 10 is bonded to the metal base 30 through the adhesive layer 20, and the ceramic balls 21 are fixed to each other and cannot be moved. As a result, the thickness of the adhesive layer 20 is uniform (in this embodiment, the same length as the average particle diameter of the ceramic balls 21), and the bonding surface 12 and the first surface 31 are parallel to each other. Is completed.

  Next, an evaluation method of the electrostatic chuck and the result will be described.

First, a plurality of measurement samples were prepared as follows. The same electrostatic chuck as that of the present embodiment was prepared and used as an example. That is, in the electrostatic chuck of the example, the ceramic sphere 21 is arranged at a ratio of one for each 42 mm square region in the adhesive layer 20, and the thermal conductivity of the ceramic sphere 21 at 200 ° C. or less is 28 W / (m · K), the thermal expansion coefficient was set to 2.8 × 10 ⁻⁶ / K. In addition, an electrostatic chuck in which the ceramic sphere 21 is not disposed in the adhesive layer 20 was prepared, and this was designated as Comparative Example 1. Furthermore, an electrostatic chuck having ceramic spheres 21 arranged at a ratio of one for each 85 mm square region in the adhesive layer 20 was prepared, and this was designated as Comparative Example 2. In addition, an electrostatic chuck in which ceramic spheres having a thermal conductivity of 240 W / (m · K) at 200 ° C. or less were arranged in the adhesive layer 20 was prepared. In addition, an electrostatic chuck in which metal balls having a thermal expansion coefficient of 26 × 10 ⁻⁶ / K in the adhesive layer 20 instead of the ceramic spheres 21 was prepared.

  As a result, in Comparative Example 1, the flatness of the suction surface 11 of the ceramic insulating plate 10 was 50 μm, and in Comparative Example 2, the flatness of the suction surface 11 was 43 μm. On the other hand, in the examples and comparative examples 3 and 4, the flatness of the suction surface 11 was 30 μm. From the above, it was confirmed that the flatness of Examples and Comparative Examples 3 and 4 was smaller than the flatness of Comparative Examples 1 and 2. Therefore, if the ceramic spheres 21 are arranged in the adhesive layer 20 and the ceramic spheres 21 are arranged at a ratio of one for every 42 mm square region in the adhesive layer 20, the flatness of the adsorption surface 11 can be increased. Proven.

  In Comparative Example 3, the temperature difference between the region directly above the ceramic sphere 21 and the region not directly above the adsorption surface 11 was 0.236 ° C. On the other hand, in Example and Comparative Examples 1, 2, and 4, the temperature difference between the region directly above the ceramic sphere 21 and the region not directly above in the adsorption surface 11 was 0.022 ° C. From the above, it was confirmed that the temperature difference between Example and Comparative Examples 1, 2, and 4 was smaller than the temperature difference of Comparative Example 3. Therefore, if the thermal conductivity of the ceramic sphere 21 at 200 ° C. or lower is set to 28 W / (m · K), the temperature difference at the adsorption surface 11 becomes small, and the semiconductor wafer 2 adsorbed on the adsorption surface 11 is heated uniformly. Or proved to be cool.

Furthermore, a heat cycle of 30 ° C. to 100 ° C. was applied 180 times to each measurement sample (Example, Comparative Examples 1 to 4). As a result, in the electrostatic chuck of Comparative Example 4, the adhesive layer 20 peeled off from the ceramic insulating plate 10 and the metal base 30 when the thermal cycle was applied 130 times. On the other hand, in the electrostatic chucks of Examples and Comparative Examples 1 to 3, peeling of the adhesive layer 20 did not occur even after the thermal cycle was applied 180 times. Therefore, if the ceramic balls 21 having a thermal expansion coefficient of 2.8 × 10 ⁻⁶ / K are arranged in the adhesive layer 20 instead of the metal balls having a thermal expansion coefficient of 26 × 10 ⁻⁶ / K, the adhesion is achieved. It has been proved that the reliability of the electrostatic chuck is improved because the agent layer 20 hardly peels off.

  Therefore, according to the present embodiment, the following effects can be obtained.

  (1) According to the electrostatic chuck 1 of the present embodiment, the plurality of ceramic spheres 21 having a uniform particle diameter come into contact with the bonding surface 12 of the ceramic insulating plate 10 and the first surface 31 of the metal base 30. The thickness of the adhesive layer 20 is kept uniform. That is, each ceramic sphere 21 functions as a spacer that holds the ceramic insulating plate 10 and the metal base 30 at a constant interval. In the present embodiment, since the flatness of the bonding surface 12 and the first surface 31 is high (30 μm or less), the bonding surface 12 and the first surface 31 are substantially parallel. For this reason, the flatness of the suction surface 11 located on the opposite side of the bonding surface 12 is increased, and the parallelism of the suction surface 11 with respect to the first surface 31 is increased. As a result, the flatness of the surface of the semiconductor wafer 2 attracted to the attracting surface 11 is also increased. Therefore, when processing is performed on the semiconductor wafer 2, the degree of processing is less likely to vary, and the yield of the semiconductor wafer 2 is reduced. Can prevent problems.

  (2) In this embodiment, the spacer (ceramic sphere 21) is formed using a ceramic material having a lower thermal conductivity than a metal material and harder than a resin material. Thereby, compared with the case where a spacer is formed with a metal material, since the thermal conductivity of the spacer (ceramic ball 21) can be kept low, heat is excessively transferred between the ceramic insulating plate 10 and the metal base 30. It will not be done. As a result, the temperature difference between the region directly above the ceramic sphere 21 and the region not directly above the adsorption surface 11 can be reduced, and the semiconductor wafer 2 adsorbed on the adsorption surface 11 can be uniformly heated or cooled. Can do. In addition, the spacer (ceramic sphere 21) is less likely to be crushed when the ceramic insulating plate 10 and the metal base 30 are joined, compared to the case where the spacer is formed of a resin material. Can be held.

  (3) The ceramic sphere 21 of the present embodiment is substantially spherical with a sphericity of 2 μm. Thereby, the outer peripheral surface of the ceramic sphere 21 comes into point contact with the joining surface 12 of the ceramic insulating plate 10 and the first surface 31 of the metal base 30. As a result, the adhesive layer 20 is less likely to be sandwiched between the ceramic sphere 21 and the ceramic insulating plate 10 or between the ceramic sphere 21 and the metal base 30, so that an error is less likely to occur in the thickness of the adhesive layer 20. . Further, when the electrostatic chuck 1 is manufactured, when the ceramic sphere 21 is inserted into the positioning hole 83 of the jig body 81 of the jig 80 (see FIG. 5), the orientation of the ceramic sphere 21 is not considered. It will be over. Furthermore, when the ceramic sphere 21 is placed on the adhesive layer 20 (see FIG. 6), the orientation of the ceramic sphere 21 need not be considered. In addition, when the ceramic sphere 21 is placed on the adhesive layer 20, the outer peripheral surface of the ceramic sphere 21 is in point contact with the surface of the adhesive layer 20, so that the contact area between the ceramic sphere 21 and the adhesive layer 20 is large. The pressure is applied to the adhesive layer 20 from the ceramic sphere 21 is increased. As a result, the ceramic sphere 21 is easily embedded and temporarily fixed in the adhesive layer 20, so that the ceramic sphere 21 is less likely to be displaced. Moreover, the void in the adhesive bond layer 20 can be reduced. Therefore, since the void of the adhesive layer 20 can be reliably generated, for example, the heat of the ceramic insulating plate 10 can be uniformly transmitted through the adhesive layer 20.

  (4) The ceramic insulating plate 10 of the present embodiment is made of a material mainly composed of alumina for which a ceramic green sheet molding technique (that is, a ceramic layer molding technique) has been established. The adsorption electrode layer 51, the heater electrode layer 61, and the like can be easily formed. In addition, since the metal base 30 of the present embodiment is made of a metal material (aluminum in the present embodiment) that can be easily processed, the cooling fluid flow paths 71 and 72 can be easily formed.

  In addition, you may change this embodiment as follows.

  In the manufacturing method of the electrostatic chuck 1 according to the above embodiment, after the adhesive layer 20 is formed on the first surface 31 of the metal base 30, the ceramic balls 21 and the ceramic insulating plate 10 are placed on the adhesive layer 20. In this state, the ceramic balls 21 were embedded in the adhesive layer 20 by applying a pressing force in the vertical direction. However, the manufacturing method of the electrostatic chuck 1 is not limited to the above embodiment. For example, the adhesive layer 20 may be formed on the first surface 31 after fixing the plurality of ceramic balls 21 on the first surface 31 by bonding or the like. Further, after the adhesive layer 20 is formed on the bonding surface 12 of the ceramic insulating plate 10, the ceramic ball 21 and the metal base 30 are placed on the adhesive layer 20 and a pressing force is applied in the vertical direction to apply the ceramic. The sphere 21 may be embedded in the adhesive layer 20.

  In the manufacturing method of the electrostatic chuck 1 according to the above embodiment, the adhesive layer 20 is formed on the first surface 31 of the metal base 30 by printing and applying a paste-like adhesive using a screen printing apparatus. It was. However, the adhesive layer 20 may be formed by joining the ceramic insulating plate 10 and the metal base 30 with a sheet-like adhesive layer interposed therebetween. For example, a plurality of ceramic balls 21 are placed on one side of a sheet-like adhesive layer, and the adhesive layer on which the ceramic balls 21 are placed is sandwiched between the ceramic insulating plate 10 and the metal base 30. Also good.

  In the electrostatic chuck 1 of the above embodiment, the semiconductor wafer 2 is the object to be adsorbed, but another member such as a liquid crystal panel may be the object to be adsorbed.

  Next, the technical ideas grasped by the embodiment described above are listed below.

  (1) A ceramic insulating plate having a first main surface and a second main surface and having an adsorption electrode layer therein; and a first surface and a second surface and the first surface is the first of the ceramic insulating plate. And a metal base bonded to the main surface side through an adhesive layer, and an object to be adsorbed on the first main surface using electrostatic attraction generated when a voltage is applied to the adsorption electrode layer. In the electrostatic chuck to be adsorbed, a particle size in the adhesive layer that maintains the thickness of the adhesive layer in contact with the second main surface of the ceramic insulating plate and the first surface of the metal base An electrostatic chuck comprising a plurality of ceramic spheres arranged in uniform, wherein the plurality of ceramic spheres are made of silicon nitride.

DESCRIPTION OF SYMBOLS 1 ... Electrostatic chuck 2 ... Semiconductor wafer 10 as to-be-adsorbed object ... Ceramic insulating board 11 ... Adsorption surface 12 as 1st main surface ... Joining surface 20 as 2nd main surface ... Adhesive layer 21 ... Ceramic ball | bowl 30 ... Metal base 31 ... first surface 32 ... second surface 51 ... electrode layer for adsorption

Claims (8)

A ceramic insulating plate having a first main surface and a second main surface and having an adsorption electrode layer therein, and a first surface and a second surface, and the first surface is the second main surface of the ceramic insulating plate And a metal base bonded to the first electrode surface using an electrostatic attraction generated when a voltage is applied to the adsorption electrode layer. In the electric chuck,
In the adhesive layer, a plurality of ceramic spheres having a uniform particle size that contact the second main surface of the ceramic insulating plate and the first surface of the metal base to maintain the thickness of the adhesive layer Is an electrostatic chuck.   2. The electrostatic chuck according to claim 1, wherein a thickness of the adhesive layer is 25 μm or more and 700 μm or less, and is equal to an average particle diameter of the plurality of ceramic spheres.   The electrostatic chuck according to claim 1, wherein the adhesive layer is an adhesive made of a silicone resin.   4. The electrostatic chuck according to claim 1, wherein the ceramic spheres are arranged in a ratio of one for each region of 20 mm square to 60 mm square in the adhesive layer. 5. .   5. The static electricity according to claim 1, wherein a thermal conductivity of the ceramic sphere at 200 ° C. or less is 2 W / (m · K) or more and 200 W / (m · K) or less. Electric chuck. 6. The electrostatic chuck according to claim 1, wherein a thermal expansion coefficient of the ceramic sphere is 1.0 × 10 ⁻⁶ / K or more and 15 × 10 ⁻⁶ / K or less. .   The electrostatic chuck according to claim 1, wherein the plurality of ceramic spheres are made of a material harder than the ceramic insulating plate and the metal base.   The electrostatic chuck according to claim 1, wherein the sphericity of the ceramic sphere is 2 μm or less.

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