Patent Publication Number: US-2022230905-A1

Title: Wafer placement table and method of manufacturing the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wafer placement table and method of manufacturing the same. 
     2. Description of the Related Art 
     A wafer placement table, which uses a metal bonding layer as an electrode to bond ceramic substrates, is conventionally known. For example, PTL 1 discloses an electrostatic chuck that uses a metal bonding layer as an RF electrode. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2018-006737 A 
     SUMMARY OF THE INVENTION 
     Such an electrostatic chuck is manufactured, for example, by the following manner. Specifically, first, a first ceramic substrate having a wafer placement surface, and a second ceramic substrate in which a connection member is embedded are produced. Subsequently, grinding work is performed on one surface of the second ceramic substrate so as to expose one surface of the connection member, and a ground surface is formed. The surface on the opposite side of the wafer placement surface of the first ceramic substrate, and the ground surface of the second ceramic substrate are bonded via a metal bonding layer. Thus, if the adhesion between the second ceramic substrate and the connection member is low, crack may occur in the second ceramic substrate due to a load at the time of the grinding work. In addition, the connection member may come off from the second ceramic substrate due to a load at the time of the grinding work. 
     The present invention has been devised to solve such a problem, and it is a main object to prevent the occurrence of crack in the ceramic substrate at the time of manufacturing so that the connection member is unlikely to come off. 
     A wafer placement table of the present invention includes: a first ceramic substrate having a wafer placement surface on an upper surface; a second ceramic substrate disposed on a lower surface side of the first ceramic substrate; a metal bonding layer that bonds a lower surface of the first ceramic substrate and an upper surface of the second ceramic substrate; a connection member including an upper base and a lower base, the connection member being embedded in the second ceramic substrate with the upper base in contact with the metal bonding layer; and a power supply terminal electrically connected to the lower base of the connection member, wherein the connection member has a portion in which an area of cross section when the connection member is cut by a plane parallel to the upper base increases from a side of the upper base to a side of the lower base. 
     In the wafer placement table, the connection member embedded in the second ceramic substrate has a portion in which the area of cross section when the connection member is cut by a plane parallel to its upper base increases from the upper base to the lower base. Therefore, for example, as compared with the case where the shape of the connection member is cylindrical, the area of the lateral surface of the connection member is larger, thus the contact area between the second ceramic substrate and the connection member is increased, and the adhesion between the second ceramic substrate and the connection member is improved. Thus, even if a step of exposing the upper base of the connection member embedded in the second ceramic substrate by grinding its surface on which a metal bonding layer is formed is included when a wafer placement table is manufactured, crack is unlikely to occur in the second ceramic substrate. In addition, even if a load is applied to the connection member in the step, the lateral surface of the connection member is caught by the second ceramic substrate, thus is unlikely to come off. 
     Note that the “upper”, “lower” in the present specification do not represent an absolute positional relationship but represents a relative positional relationship. Therefore, depending on the orientation of the wafer placement table, the “upper”, “lower” may refer to “lower” “upper”, or refer to “left”, “right”, or refer to “front”, “back”. 
     In the wafer placement table of the present invention, the second ceramic substrate may have a hole for inserting the power supply terminal in the lower surface of the second ceramic substrate, and the lateral surface of the power supply terminal may be bonded to the lateral surface of the hole. In this manner, the lateral surface of the power supply terminal is fixed to the lateral surface of the hole of the second ceramic substrate, thus the connection member together with the power supply terminal can be prevented from coming off from the second ceramic substrate. 
     In the wafer placement table of the present invention, the connection member may be a member in which metal meshes are stacked in multiple stages. In this manner, even when the wafer placement table is heated or cooled, the connection member is likely to expand and contract because it is made of metal mesh, and ceramic enters gaps in the meshes, thus the thermal expansion coefficient becomes closer to that of the second ceramic substrate. Therefore, crack is unlikely to occur in the second ceramic substrate. 
     In the wafer placement table of the present invention, the shape of the connection member may be such that the area of cross section when the connection member is cut by a plane parallel to its upper base increases from the upper base to the lower base. In this manner, the connection member has a relatively simple shape, thus the connection member can be produced relatively easily. In this case, the shape of the connection member may be a truncated cone shape, a truncated hemisphere shape or a shape having a lateral surface inwardly curved as compared with the truncated cone shape. In this manner, the connection member has a simple shape, thus the connection member can be produced easily. 
     A method of manufacturing a wafer placement table of the present invention includes: (a) a step of preparing a first ceramic substrate having a wafer placement surface on an upper surface, and a second ceramic substrate in which a connection member including an upper base and a lower base is embedded; (b) a step of forming a bonding surface by grinding the second ceramic substrate so as to expose the upper base of the connection member; and (c) a step of metal bonding a lower surface of the first ceramic substrate and the bonding surface of the second ceramic substrate, wherein the connection member embedded in the second ceramic substrate prepared in step (a) has a portion in which an area of cross section when the connection member is cut by a plane parallel to the upper base increases from a side of the upper base to a side of the lower base. 
     In a method of manufacturing the wafer placement table, the connection member embedded in the second ceramic substrate prepared in step (a) has a portion in which the area of cross section when the connection member is cut by a plane parallel to its upper base increases from the upper base side to the lower base side. Therefore, for example, as compared with the case where the shape of the connection member is cylindrical, the area of the lateral surface of the connection member is larger, thus the contact area between the second ceramic substrate and the connection member is increased, and the adhesion between the second ceramic substrate and the connection member is improved. Thus, when a bonding surface is formed by grinding the second ceramic substrate so as to expose the upper base of the connection member in step (b), crack is unlikely to occur in the second ceramic substrate. In addition, even if a load is applied to the connection member in the step (b), the lateral surface of the connection member is caught by the second ceramic substrate, thus is unlikely to come off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an electrostatic chuck  10 . 
         FIG. 2  is a cross sectional view taken along A-A of  FIG. 1 . 
         FIG. 3  is an enlarged view of portion B of  FIG. 2 . 
         FIGS. 4A to 4G  are explanatory diagrams illustrating an example of a method of manufacturing the electrostatic chuck  10 . 
         FIG. 5  is a cross sectional view of a connection member  120 . 
         FIG. 6  is a cross sectional view of a connection member  220 . 
         FIG. 7  is a cross sectional view of a connection member  320 . 
         FIG. 8  is a cross sectional view of a connection member  420 . 
         FIG. 9  is a cross sectional view of a connection member  520 . 
         FIG. 10  is a cross sectional view of a connection member  620 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of the present invention will be described below with reference to the drawings.  FIG. 1  is a perspective view of an electrostatic chuck  10 ,  FIG. 2  is a cross sectional view taken along A-A of  FIG. 1 , and  FIG. 3  is an enlarged view of portion B of  FIG. 2 . 
     The electrostatic chuck  10  is an example of the wafer placement table of the present invention, and includes a first ceramic substrate  11 , a second ceramic substrate  12 , a metal bonding layer  13 , a connection member  20 , and a power supply terminal  30 . 
     The first ceramic substrate  11  is a disk plate having the same diameter as that of a silicon wafer W which undergoes plasma treatment, and made of ceramic (for example, alumina and aluminum nitride). The diameter of the first ceramic substrate  11  is not particularly limited, however, may be 250 to 350 mm, for example. The upper surface of the first ceramic substrate  11  serves as a wafer placement surface  11   a . A resistance heating element  14  is embedded in the first ceramic substrate  11 . The resistance heating element  14  is comprised of a material of a simple substance or a compound (such as a carbide) of W, Mo, Ti, Si, Ni as the main component, a material in a combination of these, or a mixed material of one of these and the raw material for the first ceramic substrate  11 . The resistance heating element  14  is formed in a one-stroke pattern so that the entire surface of the first ceramic substrate  11  is wired. When a voltage is applied to the resistance heating element  14 , it generates heat and the wafer W is heated. The area where the resistance heating element  14  is wired is circular in a plan view, and is provided on a plane parallel to the wafer placement surface  11   a . Note that the “parallel” refers to the case of not completely parallel within a range of tolerance, in addition to the case of completely parallel. 
     The second ceramic substrate  12  is disposed on the surface (the lower surface) side on the opposite side of the wafer placement surface  11   a  of the first ceramic substrate  11 . The second ceramic substrate  12  has the same shape as the first ceramic substrate  11 , and is formed of ceramic which is the same material as for the first ceramic substrate  11 . The second ceramic substrate  12  includes the connection member  20  embedded therein. 
     The metal bonding layer  13  bonds the lower surface of the first ceramic substrate  11  and the upper surface of the second ceramic substrate  12 . Thus, the lower surface of the first ceramic substrate  11  is referred to as a bonding surface  11   b , and the upper surface of the second ceramic substrate  12  is referred to as a bonding surface  12   a . The metal bonding layer  13  is comprised of, for example, an Al containing material, such as an Al—Si—Mg based or Al—Mg based material. The thickness of the metal bonding layer  13  is not particularly limited, however, is preferably 1 to 300 μm, and more preferably 50 to 150 μm. In addition, the outer circumference of the metal bonding layer  13  preferably does not protrude from the outer circumference of the first ceramic substrate  11 . The metal bonding layer  13  is formed by TCB (thermal compression bonding), for example. Here, TCB is a publicly known method by which a metal bonding material is inserted between two members to be bonded, and the two members are pressure-bonded with the members heated to a temperature lower than or equal to the solidus temperature of the metal bonding material. The metal bonding layer  13  is used as an electrostatic electrode in the present embodiment. The area (the entirety of the first ceramic substrate  11 ) from the bonding surface  11   b  to the wafer placement surface  11   a  of the first ceramic substrate  11  functions as a dielectric layer  28 . When a DC voltage is applied to the metal bonding layer  13 , the wafer W placed on the wafer placement surface  11   a  is adsorbed and fixed to the wafer placement surface  11   a , and when application of the DC voltage is stopped, adsorbing and fixing of the wafer W to the wafer placement surface  11   a  is stopped. 
     The connection member  20  includes an upper base  20   a  and a lower base  20   b , and is embedded in the second ceramic substrate  12  with the upper base  20   a  in contact with the metal bonding layer  13 . The shape of the connection member  20  has a portion in which the area of cross section when the connection member  20  is cut by a plane parallel to the upper base  20   a  increases from the upper base  20   a  side to the lower base  20   b  side. In the present embodiment, the shape of the connection member  20  is such that the area of cross section increases from the upper base  20   a  to the lower base  20   b , and specifically is a truncated cone shape. The connection member  20  is a bulk body (massive body) produced with, for example, a mixed material obtained by adding ruthenium alloy (for example, RuAl) to tungsten carbide, or metal such as Mo. The surface area of the upper base  20   a  of the connection member  20  is preferably 50% or more and 98% or less of the surface area of the lower base  20   b.    
     One end face  30   t  of the power supply terminal  30  is electrically connected to the lower base  20   b  of the connection member  20 , and the other end face is connected to an external DC power supply which is not illustrated. The power supply terminal  30  is formed of, for example, metal such as Ni or Mo, and is inserted in a hole  33  (see  FIGS. 4A to 4G ) formed in the lower surface  12   b  of the second ceramic substrate  12 . The end face  30   t  of the power supply terminal  30  is bonded to the lower base  20   b  of the connection member  20  by a terminal end face bonding layer  31 . The terminal end face bonding layer  31  is a layer which includes ceramic particles and a metal wax material, and in which the metal wax material is inserted in gaps between the ceramic particles. Alumina ceramic particles and aluminum nitride ceramic particles are preferable as the ceramic particles. The metal wax materials are filled in gaps between the ceramic particles in the terminal end face bonding layer  31 , which thus electrically connects the power supply terminal  30  and the connection member  20 . A lateral surface  30   s  of the power supply terminal  30  is bonded to a lateral surface  33   s  of the hole  33  by a terminal lateral surface bonding layer  32 . The terminal lateral surface bonding layer  32  is a layer formed of a metal wax material. For example, an Au—Ni wax material, an Al wax material, and an Ag wax material are preferable as the metal wax material. 
     Next, a method of manufacturing the electrostatic chuck  10  will be described with reference to  FIGS. 4A to 4G .  FIGS. 4A to 4G  are explanatory diagrams illustrating an example of a method of manufacturing the electrostatic chuck  10 . 
     First, the first ceramic substrate  11  which has the wafer placement surface  11   a  and in which the resistance heating element  14  is embedded, and the second ceramic substrate  12  in which the connection member  20  is embedded are prepared. Specifically, as illustrated in  FIG. 4A , a disk-shaped first ceramic molded body  51  (a previous body of the first ceramic substrate  11 ) in which the resistance heating element  14  is embedded and a disk-shaped second ceramic molded body  52  (a previous body of the second ceramic substrate  12 ) in which the connection member  20  is embedded are produced. This step is referred to as step ( 1 ). In step ( 1 ), the first ceramic molded body  51  and the second ceramic molded body  52  are produced by a mold casting method or the like. Here, the “mold casting method” is a method of obtaining a molded body by pouring a ceramic slurry containing ceramic raw material powder and a molding agent into a mold, and causing a chemical reaction of the molding agent in the mold to mold the ceramic slurry. For example, an agent which contains isocyanate and polyol, and produces a molded body by a urethane reaction may be used as the molding agent. Subsequently, as illustrated in  FIG. 4B , the first ceramic molded body  51  and the second ceramic molded body  52  are each hot press sintered while applying a pressure thereto in a thickness direction to produce the first ceramic substrate  11  and the second ceramic substrate  12 . This step is referred to as step ( 2 ). These step ( 1 ) and step ( 2 ) correspond to step (a) in the method of manufacturing a wafer placement table of the present invention. 
     Next, as illustrated in  FIG. 4C , the hole  33  is formed in the lower surface  12   b  of the second ceramic substrate  12  so as to expose the lower base  20   b  of the connection member  20  embedded in the second ceramic substrate  12 . This step is referred to as step ( 3 ). In step ( 3 ), the hole  33  is formed by grind processing, cutting processing, or blast processing. Note that in step ( 3 ), the connection member  20  is unlikely to come off from the second ceramic substrate  12  because the load applied to the connection member  20  at the time of forming the hole  33  in the second ceramic substrate  12  is low. 
     Next, the power supply terminal  30  is inserted into the hole  33 . Specifically, as illustrated in  FIG. 4D , the second ceramic substrate  12  is placed so that the hole  33  is directed upward. The power supply terminal  30  is inserted into the hole  33  with ceramic powder  41  and a metal wax material  42  including multiple ceramic particles placed at the lower base  20   b  of the connection member  20 . This step is referred to as step ( 4 ). In step ( 4 ), for example, alumina ceramic and aluminum nitride ceramic can be used as the ceramic powders  41 . Also, in step ( 4 ), an Au—Ni wax material, an Al wax material, and an Ag wax material can be used as the metal wax material  42 . 
     Next, the power supply terminal  30  and the connection member  20  are connected. Specifically, first, the second ceramic substrate  12  is heated so that the temperature of the metal wax material  42  exceeds a melting point, and the metal wax material  42  is melted. The melted metal wax material  42  permeates into the ceramic powder  41  to fill the gaps between the ceramic particles of the ceramic powder  41 , and enters between the lateral surface  30   s  of the power supply terminal  30  and the lateral surface  33   s  of the hole  33 . The metal wax material  42  is then cooled to be solidified. Then, as illustrated in  FIG. 4E , the terminal end face bonding layer  31  with the metal wax material  42  permeated into gaps between the ceramic particles is formed, and the terminal lateral surface bonding layer  32  is formed of the metal wax material  42 . Consequently, the end face  30   t  of the power supply terminal  30  is bonded to the lower base  20   b  of the connection member  20 , and the lateral surface  30   s  of the power supply terminal  30  is bonded to the lateral surface  33   s  of the hole  33 . This step is referred to as step ( 5 ). In step ( 5 ), the lateral surface  30   s  of the power supply terminal  30  is fixed to the lateral surface  33   s  of the hole  33  of the second ceramic substrate  12 . Thus, the connection member  20  together with the power supply terminal  30  can be prevented from coming off from the second ceramic substrate  12 . 
     Next, the second ceramic substrate  12  is placed so that the hole  33  is directed downward, then as illustrated in  FIG. 4F , the bonding surface  12   a  is formed by performing grind processing on the upper surface  12   c  of the second ceramic substrate  12  so as to expose the upper base  20   a  of the connection member  20 . This step is referred to as step ( 6 ). Also, step ( 6 ) corresponds to step (b) in the method of manufacturing a wafer placement table of the present invention. The connection member  20  has a portion in which the area of cross section when the connection member  20  is cut by a plane parallel to the upper base  20   a  increases from the upper base  20   a  side to the lower base  20   b  side. In the present embodiment, the shape of the connection member  20  is such that the area of cross section increases from the upper base  20   a  side to the lower base  20   b  side, and specifically is a truncated cone shape. Therefore, as compared with the case where the shape of the connection member  20  is cylindrical, the contact area between the second ceramic substrate  12  and the connection member  20  is increased, and the adhesion between the second ceramic substrate  12  and the connection member  20  is improved. Thus, in step ( 6 ), crack is unlikely to occur in the second ceramic substrate  12 . In addition, even if a load is applied to the connection member  20  in the step ( 6 ), the lateral surface of the connection member  20  is caught by the second ceramic substrate  12 , thus is unlikely to come off. 
     The bonding surface lib on the opposite side of the wafer placement surface  11   a  of the first ceramic substrate  11 , and the bonding surface  12   a  of the second ceramic substrate  12  are metal bonded. Specifically, first, as illustrated in  FIG. 4G , a flat plate-shaped metal bonding material  53  having the same diameter as that of the second ceramic substrate  12  is placed on the bonding surface  12   a  of the second ceramic substrate  12 , and the first ceramic substrate  11  is placed on the metal bonding material  53  so that the bonding surface  11   b  of the first ceramic substrate  11  is in contact with the metal bonding material  53 . In this manner, a laminated body  70  with the metal bonding material  53  inserted between the first ceramic substrate  11  and the second ceramic substrate  12  is produced. This step is referred to as step ( 7 ). In step ( 7 ), an Al—Mg based bonding material and an Al-Si-Mg based bonding material can be used as the metal bonding material  53 . Subsequently, the laminated body  70  is pressurized at a temperature (for example, a temperature at the solidus temperature minus 20° C. or higher and the solidus temperature or lower) lower than or equal to the solidus temperature of the metal bonding material  53 , and the first ceramic substrate  11  and the second ceramic substrate  12  are TCB bonded, then the temperature is returned to the room temperature. Thus, the metal bonding material  53  turns to the metal bonding layer  13 , and the electrostatic chuck  10  is obtained. This step is referred to as step ( 8 ). These step ( 7 ) and step ( 8 ) correspond to step (c) in the method of manufacturing a wafer placement table of the present invention. 
     Next, an example of use of the electrostatic chuck  10  of the present embodiment will be described. The wafer W is placed on the wafer placement surface  11   a  of the electrostatic chuck  10 , and the wafer W is adsorbed to the wafer placement surface  11   a  by an electrostatic force by applying a voltage across the metal bonding layer  13  and the wafer W. In this state, plasma CVD film formation is performed or plasma etching is performed on the wafer W. Also, the temperature of the wafer W is controlled at a constant by heating the wafer W by application of a voltage to the resistance heating element  14 , and/or cooling the wafer W by circulation of a refrigerant through a refrigerant passage in a cooling plate which is bonded to the electrostatic chuck  10  and not illustrated. 
     In the electrostatic chuck  10  of the present embodiment described above, the connection member  20  embedded in the second ceramic substrate  12  has a portion in which the area of cross section when the connection member  20  is cut by a plane parallel to the upper base  20   a  increases from the upper base  20   a  side to the lower base  20   b  side. Therefore, for example, as compared with the case where the shape of the connection member  20  is cylindrical, the area of the lateral surface of the connection member  20  is larger, thus the contact area between the second ceramic substrate  12  and the connection member  20  is increased, and the adhesion between the second ceramic substrate  12  and the connection member  20  is improved. Thus, even if a step of grinding the surface, on which the metal bonding layer  13  is formed, of the second ceramic substrate  12  in which the connection member  20  is embedded and exposing the upper base  20   a  of the connection member  20  is included when the electrostatic chuck  10  is manufactured, crack is unlikely to occur in the second ceramic substrate  12 . In addition, even if a load is applied to the connection member  20  in the step, the lateral surface of the connection member  20  is caught by the second ceramic substrate  12 , thus is unlikely to come off. 
     In addition, the second ceramic substrate  12  includes the hole  33  in the lower surface of the second ceramic substrate  12  for inserting the power supply terminal  30 , and the lateral surface  30   s  of the power supply terminal  30  is bonded to the lateral surface  33   s  of the hole  33 . In this manner, the lateral surface  30   s  of the power supply terminal  30  is fixed to the lateral surface  33   s  of the hole  33  of the second ceramic substrate  12 , thus the connection member  20  together with the power supply terminal  30  can be prevented from coming off from the second ceramic substrate  12 . 
     In addition, the shape of the connection member  20  is such that (here, a truncated cone shape) the area of cross section when the connection member  20  is cut by a plane parallel to the upper base  20   a  increases from the upper base  20   a  to the lower base  20   b , thus the connection member  20  can be easily manufactured. 
     Note that the present invention is not limited to the above-described embodiment at all, and it is needless to say that the invention can be implemented in various aspects as long as it belongs to the technical scope of the present invention. 
     For example, in the embodiment described above, the power supply terminal  30  and the metal bonding layer  13  are connected by utilizing the connection member  20  produced by a bulk body (massive body) made of metal, however, the invention is not limited to this. For example, as illustrated in  FIG. 5 , the power supply terminal  30  and the metal bonding layer  13  may be connected using a connection member  120  which is formed by stacking metal meshes M 1  to M 6  having different diameters in multiple stages (here, six stages) in descending order of diameter from the power supply terminal  30  side. In this manner, even when the electrostatic chuck  10  is heated or cooled, the connection member  20  is likely to expand and contract because it is made of metal mesh, and ceramic enters gaps in the metal meshes M 1  to M 6 , thus the thermal expansion coefficient becomes closer to that of the second ceramic substrate  12 . Therefore, crack is unlikely to occur in the second ceramic substrate  12 . Note that in  FIG. 5 , the same components as in the embodiment described above are labeled with the same symbol, and a description is omitted. 
     In the electrostatic chuck  10  of the embodiment described above, the connection member  20  in a truncated cone shape is used, however, the invention is not limited to this. For example, as illustrated in  FIG. 6 , the shape of a connection member  220  may be a truncated hemisphere shape (or a shape obtained by cutting a hemisphere by two planes parallel to the bottom surface) in which the area of cross section when the connection member  220  is cut by a plane parallel to its upper base  220   a  increases from an upper base  220   a  side to a lower base  220   b  side. Alternatively, as illustrated in  FIG. 7 , the shape of a connection member  320  may be a konide shape (shape of a truncated cone with a lateral surface inwardly curved) in which the area of cross section when the connection member  320  is cut by a plane parallel to its upper base  320   a  increases from an upper base  320   a  side to a lower base  320   b  side. Alternatively, as illustrated in  FIG. 8 , a connection member  420  may be a barrel shape having a portion  420   c  in which the area of cross section when the connection member  420  is cut by a plane parallel to its upper base  420   a  increases from an upper base  420   a  side to a lower base  420   b  side. Alternatively, as illustrated in  FIG. 9 , a connection member  520  may be a shape (shape of a cylinder with a lateral surface inwardly curved) having a portion  520   c  in which the area of cross section when the connection member  520  is cut by a plane parallel to its upper base  520   a  increases from an upper base  520   a  side to a lower base  520   b  side. Alternatively, as illustrated in  FIG. 10 , a connection member  620  may be a shape (a barrel shape with a lateral surface having a bulged lower portion) having a portion  620   c  in which the area of cross section when the connection member  620  is cut by a plane parallel to its upper base  620   a  increases from an upper base  620   a  side to a lower base  620   b  side. In  FIG. 6  to  FIG. 10 , the same components as in the embodiment described above are labeled with the same symbol, and a description is omitted. The connection members  220 ,  320 ,  420 ,  520 ,  620  each have a larger area of the lateral surface as compared with the case where the shape of each connection member is cylindrical, thus even if a step of exposing the upper bases  220   a ,  320   a ,  420   a ,  520   a ,  620   a  by grinding the lower surface  12   b  of the second ceramic substrate  12  is included, crack is unlikely to occur in the second ceramic substrate  12 . In addition, even if a load is applied to the connection members  220 ,  320 ,  420 ,  520 ,  620  in the step, the lateral surface of each of the connection members  220 ,  320 ,  420 ,  520 ,  620  is caught by the second ceramic substrate  12 , thus is unlikely to come off. 
     In the embodiment described above, the metal bonding layer  13  is used as an electrostatic electrode, however, the invention is not limited to this. For example, the metal bonding layer  13  may be used as a ground electrode. In this case, the metal bonding layer  13  is connected to the ground, and the electrostatic electrode may be embedded in the first ceramic substrate  11  so as to be parallel to the resistance heating element  14 . 
     In the embodiment described above, the end face  30   t  of the power supply terminal  30  and the lower base  20   b  of the connection member  20  are bonded via the terminal lateral surface bonding layer  32  comprised of the ceramic powder  41  and the metal wax material  42 , however, the invention is not limited to this. For example, the terminal lateral surface bonding layer  32  may not include the ceramic powder  41 , and may be comprised of the metal wax material  42 . In this case, in step ( 4 ), it is sufficient that the power supply terminal  30  be inserted in the hole  33  with the ceramic powder  41  not placed but the metal wax material  42  placed on the lower base  20   b  of the connection member  20 , and the metal wax material  42  be melted, then cooled and solidified in the same manner as in the above-described embodiment. 
     In the embodiment described above, when the electrostatic chuck  10  is manufactured, the power supply terminal  30  is connected to the connection member  20 , then the bonding surface  12   a  is formed by grinding the upper surface  12   c  of the second ceramic substrate  12 , and the first ceramic substrate  11  and the second ceramic substrate  12  are bonded, however, the invention is not limited to this. For example, after the bonding surface  12   a  is formed by grinding the upper surface  12   c  of the second ceramic substrate  12 , the lower surface  12   b  may be provided with the hole  33 , the power supply terminal  30  may be connected to the connection member  20 , and the first ceramic substrate  11  and the second ceramic substrate  12  may be metal bonded. Alternatively, after the bonding surface  12   a  is formed by grinding the upper surface  12   c  of the second ceramic substrate  12 , and the first ceramic substrate  11  and the second ceramic substrate  12  are metal bonded, the hole  33  may be formed in the lower surface  12   b , and the power supply terminal  30  may be connected to the connection member  20 . 
     In the embodiment described above, an RF electrode may be embedded in the first ceramic substrate  11  or the second ceramic substrate  12 . The RF electrode is an electrode to be utilized when a plasma is generated. 
     The present application claims priority of Japanese Patent Application No. 2021-007360 filed on Jan. 20, 2021, the entire contents of which are incorporated herein by reference.