Patent Publication Number: US-2023142358-A1

Title: Structural body and heating apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to a structural body and a heating apparatus. 
     BACKGROUND ART 
     A substrate composed of a ceramic has excellent thermal resistance compared to metal and resin, or the like. For example, an aluminum nitride ceramic has high thermal conductivity and may be used as a structural body for placing or holding an object to be treated, such as various elements, components, or the like, when performing heat treatment of the object to be treated. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: JP 2003-40686 A 
     SUMMARY OF INVENTION 
     A structural body according to one aspect of the present disclosure includes a base, a first electrode layer, a second electrode layer, a first via conductor, a second via conductor, and a connection conductor. The base is composed of a ceramic. The first electrode layer and the second electrode layer are located inside the base. The first via conductor and the second via conductor are located inside the base and connect the first electrode layer and the second electrode layer. The connection conductor is located inside the base and connects the first via conductor and the second via conductor. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic perspective view of a wafer placement apparatus according to an embodiment. 
         FIG.  2    is a schematic cross-sectional view of a structural body according to the embodiment. 
         FIG.  3    is a schematic enlarged view of an H portion illustrated in  FIG.  2   . 
         FIG.  4    is a schematic cross-sectional view of a structural body according to a first modification example. 
         FIG.  5    is a schematic cross-sectional view of a structural body according to a second modification example. 
         FIG.  6    is a schematic cross-sectional view of a structural body according to a third modification example. 
         FIG.  7    is a schematic cross-sectional view of a structural body according to a fourth modification example. 
         FIG.  8    is a schematic cross-sectional view of a structural body according to a fifth modification example. 
         FIG.  9    is a schematic cross-sectional view of a structural body according to a sixth modification example. 
         FIG.  10    is a schematic diagram illustrating an aspect example of inclinations of the first via conductor and the second via conductor. 
         FIG.  11    is a schematic diagram illustrating an aspect example of inclinations of the first via conductor and the second via conductor. 
         FIG.  12    is a schematic diagram illustrating an aspect example of inclinations of the first via conductor and the second via conductor. 
         FIG.  13    is a schematic diagram illustrating an aspect example of inclinations of the first via conductor and the second via conductor. 
         FIG.  14    is a schematic cross-sectional view for illustrating an example of a method of manufacturing the structural body according to the sixth modification example. 
         FIG.  15    is a schematic cross-sectional view for illustrating an example of a method of manufacturing the structural body according to the sixth modification example. 
         FIG.  16    is a schematic cross-sectional view illustrating an example of a method of manufacturing the structural body according to the sixth modification example. 
         FIG.  17    is a schematic cross-sectional view of a structural body according to a seventh modification example. 
         FIG.  18    is a schematic cross-sectional view of a structural body according to the seventh modification example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following is a detailed description of a structural body and a heating apparatus according to the present disclosure (hereinafter referred to as “embodiments”) with reference to the drawings. It should be noted that the structural body and the heating apparatus according to the present disclosure are not limited by the embodiments. In addition, embodiments can be appropriately combined so as not to contradict each other in terms of processing content. In the following embodiments, the same portions are denoted by the same reference signs, and overlapping explanations are omitted. 
     In the embodiments described below, expressions such as “constant”, “orthogonal”, “vertical”, and “parallel” may be used, but these expressions do not need to be exactly “constant”, “orthogonal”, “vertical”, and “parallel”. In other words, it is assumed that the above expressions allow deviations in manufacturing accuracy, installation accuracy, or the like. 
     In each of the drawings referred to below, the vertical upward direction is defined as the Z axis direction in order to make the description easier to understand. 
     Overall Configuration of Wafer Placement Apparatus 
     First, a configuration of a wafer placement apparatus according to an embodiment will be described with reference to  FIG.  1   .  FIG.  1    is a schematic perspective view of a wafer placement apparatus  1  according to an embodiment. 
     The wafer placement apparatus  1  according to an embodiment illustrated in  FIG.  1    is an apparatus for placing a semiconductor wafer, a crystal wafer, or other wafer (hereinafter simply referred to as “wafer”). The wafer placement apparatus  1  has a heating function for heating the placed wafer, and is mounted, for example, in a substrate processing apparatus for performing plasma treatment or the like on the wafer. 
     As illustrated in  FIG.  1   , the wafer placement apparatus  1  includes a structural body  2 , a wiring portion  4 , a power supply unit  5 , and a controller  6 . 
     The structural body  2  includes a base  10  having a disc shape with a thickness in the vertical direction (Z axis direction) and a shaft  20  having a tubular shape connected to the base  10 . A wafer is placed on an upper surface  101  of the base  10 . Further, the shaft  20  is connected to a lower surface  102  of the base  10 . The upper surface  101  and the lower surface  102  of the base  10  have substantially the same shape and are both larger in diameter than the wafer. An electrode layer (not illustrated here) as a heating element is located inside the base  10 . 
     The wiring portion  4  electrically connects the electrode layer located inside the base  10  to the power supply unit  5  located outside the base  10 . The power supply unit  5  is electrically connected to the electrode layer through the wiring portion  4  and supplies power to the electrode layer through the wiring portion  4 . The power supply unit  5  includes a power supply circuit for converting power supplied from a power supply (not illustrated) into an appropriate voltage. The controller  6  controls the power supply in the power supply unit  5 . 
     The wafer placement apparatus  1  is configured as described above, and heats a wafer placed on the wafer placement surface  101  by heating the electrode layer inside the base  10  using power supplied from the power supply unit  5 . 
     Configuration of Structural Body 
     Next, the configuration of the structural body  2  will be described with reference to  FIG.  2   .  FIG.  2    is a schematic cross-sectional view of the structural body  2  according to the embodiment.  FIG.  2    illustrates a schematic cross-sectional view taken along the line II-II in  FIG.  1   . 
     Base 
     The base  10  is composed of a ceramic. The ceramic constituting the base  10  includes as a main component, for example, aluminum nitride (AlN), aluminum oxide (Al 2 O 3 , alumina), silicon carbide (SiC), silicon nitride (Si 3 N 4 ), or the like. The main component of a material means here, for example, a component that accounts for 50 mass % or more or 80 mass % or more of the material. The base  10  may include, for example, a sintering aid in addition to the above ceramic. As the sintering aid, for example, a mixture of calcium oxide (CaO) and yttrium oxide (Y 2 O 3 ) is used. 
     As illustrated in  FIG.  2   , the electrode layer  11  is located inside the base  10 . In the present embodiment, the electrode layer  11  includes a first electrode layer  111  and a second electrode layer  112 . The first electrode layer  111  is an electrode layer located relative to the lower surface  102  side of the base  10 . The second electrode layer  112  is an electrode layer located relative to the first electrode layer  111  on the upper surface  101  (which may be described as “wafer placement surface  101 ” hereinafter) side of the base  10 . The first electrode layer  111  and the second electrode layer  112  are, for example, composed of a metal such as Ni, W, Mo and Pt, or an alloy including at least one of the aforementioned metals. 
     The first electrode layer  111  and the second electrode layer  112  extend along the wafer placement surface  101 . Specifically, the first electrode layer  111  and the second electrode layer  112  are spread over substantially the entire surface of the wafer placement surface  101  while drawing a predetermined pattern such as a spiral pattern or a meandering pattern. The thicknesses of the first electrode layer  111  and the second electrode layer  112  are each, by way of example, from 30 μm to 120 μm. 
     The first electrode layer  111  and the second electrode layer  112  are electrically connected through a conductor portion  13 . The specific configuration of the conductor portion  13  will be described later. 
     The upper surface  101  (wafer placement surface  101 ) of the base  10  is parallel to the lower surface  102 . Additionally, the shape of the base  10  is arbitrary. For example, in the embodiment, the shape of the base  10  is circular in plan view, but it is not limited thereto, and may be elliptical, rectangular, trapezoidal or another shape in plan view. For example, the dimension of the base  10  is 20 cm to 35 cm in diameter and 4 mm to 30 mm in thickness. 
     Shaft 
     The shaft  20  is tubular in shape with the upper end of the shaft  20  joined to the lower surface center of the base  10 . In one aspect, the shaft  20  is joined (bonded) to the lower surface  102  of the base  10  by an adhesive. In another aspect, the shaft  20  may be joined to the base  10  by solid phase joining. The shape of the shaft  20  is arbitrary. In one aspect, the shape of the shaft  20  is cylindrical. In another aspect, the shape of the shaft  20  may be, for example, a square cylinder. The material of shaft  20  is arbitrary. In one aspect, the material of the shaft  20  is an insulating ceramic. In another aspect, the material of the shaft  20  may be, for example, an electrically conductive material (metal). 
     The shaft  20  having a tubular shape includes an upper surface  21  joined to the lower surface  102  of the base  10 , a lower surface  22  located opposite to the upper surface  21 , an inner surface  23  connecting the upper surface  21  and the lower surface  22  and constituting the inside of the shaft  20 , and an outer surface  24  connecting the upper surface  21  and the lower surface  22  and constituting the outside of the shaft  20 . 
     In the illustrated example, the inner surface  23  is provided parallel to the outer surface  24  along the direction in which the shaft  20  extends. From another viewpoint, the inner surface  23  is provided parallel to a line parallel to the thickness direction of the base  10 . However, the inner surface  23  may be inclined such that the inner diameter of the shaft  20  decreases downward, or may be inclined such that the inner diameter of the shaft  20  increases downward. The outer surface  24  may have a similar configuration. Thus, at least one of the inner diameter and the outer diameter can be made different in the shaft  20  from the upper end to the lower end. 
     Wiring Portion 
     The wiring portion  4  includes a terminal  41  and a conducting wire  42 . The terminal  41  is a metal (bulk material) having a certain length in the vertical direction. In the terminal  41 , the upper end side is located inside the base  10  and the lower end side is located outside the base  10 . In the illustrated example, the terminal  41  is electrically connected to the first electrode layer  111  and the second electrode layer  112  via the conductor portion  13 . This point will be described later. 
     The shape of the terminal  41  is arbitrary. In one aspect, the terminal  41  is cylindrical in shape. The terminal  41  is, for example, composed of a metal such as Ni, W, Mo and Pt, or an alloy including at least one of the aforementioned metals. 
     Internal Configuration of Base 
     Next, the internal configuration of the base  10  described above will be specifically described with reference to  FIG.  3   .  FIG.  3    is a schematic enlarged view of an H portion illustrated in  FIG.  2   . 
     As illustrated in  FIG.  3   , the conductor portion  13  electrically connecting the first electrode layer  111  and the second electrode layer  112  includes a first via conductor  131 , a second via conductor  132 , and a connection conductor  133 . The first via conductor  131 , the second via conductor  132 , and the connection conductor  133  are composed of, for example, a metal such as Ni, W, Mo, or Pt, or an alloy including at least a portion thereof. 
     The first via conductor  131  and the second via conductor  132  extend inside the base  10  in a direction intersecting the first electrode layer  111  and the second electrode layer  112 . The first via conductor  131  and the second via conductor  132  each penetrate the first electrode layer  111  and the second electrode layer  112 . 
     Although, here, the first via conductor  131  and the second via conductor  132  are illustrated as extending in a direction orthogonal to the first electrode layer  111  and the second electrode layer  112 , that is, along the Z axis direction which is the thickness direction of the base  10 , the first via conductor  131  and the second via conductor  132  may extend diagonally in the thickness direction of the base  10 , for example. Although the first via conductor  131  and the second via conductor  132  are illustrated as extending in parallel, the first via conductor  131  and the second via conductor  132  need not necessarily be parallel. Also, here, although an example is illustrated in which the first via conductor  131  and the second via conductor  132  penetrate the first electrode layer  111  and the second electrode layer  112  respectively, the first via conductor  131  and the second via conductor  132  each need only penetrate at least one of the first electrode layer  111  and the second electrode layer  112 . 
     The connection conductor  133  extends inside the base  10  along the first electrode layer  111  and the second electrode layer  112 . In the embodiment, the connection conductor  133  is located between the first electrode layer  111  and the lower surface  102  of the base  10 , and connects the respective end portions of the first via conductor  131  and the second via conductor  132 , the end portions penetrating the first electrode layer  111 . 
     The structural body composed of a ceramic has room for further improvement in terms of thermal uniformity. 
     Since the conductor portion  13  is located at a place where the first electrode layer  111  and the second electrode layer  112  overlap in plan view, the place tends to become a heat spot having a higher temperature than other places on the base  10 . On the other hand, the conductor portion  13  is mainly composed of a metal and has a higher thermal conductivity than the base  10  composed of a ceramic. In addition, the conductor portion  13  of the embodiment includes the connection conductor  133  extending along the first electrode layer  111  and the second electrode layer  112 . Thus, according to the structural body  2  according to the embodiment, the heat generated in the heat spot can be distributed through the connection conductor  133  in the direction along the first electrode layer  111  and the second electrode layer  112 , in other words, in the in-plane direction of the wafer placement surface  101 . Thus, the structural body  2  according to the embodiment can improve the thermal uniformity. 
     Further, since the structural body  2  according to the embodiment connects the first electrode layer  111  and the second electrode layer  112  using a plurality of via conductors (the first via conductor  131  and the second via conductor  132 ), conduction between the first electrode layer  111  and the second electrode layer  112  can be ensured. 
     Also, when using the structural body  2 , the first electrode layer  111  and the second electrode layer  112  expand or contract in the horizontal direction (direction along the wafer placement surface  101 ) due to temperature changes. Such deformation of the first electrode layer  111  and the second electrode layer  112  may cause cracks in the base  10 . On the other hand, in accordance with the structural body  2  according to the embodiment, since the first electrode layer  111  and the second electrode layer  112  are connected by the first via conductor  131  and the second via conductor  132 , the thermal deformation of the first electrode layer  111  and the second electrode layer  112  can be suitably suppressed by the first via conductor  131  and the second via conductor  132 . Thus, the occurrence of cracks in the base  10  can be suppressed. 
     In the structural body  2  according to the embodiment, the connection conductor  133  is located on the lower surface  102  side of the base  10  relative to electrode layers  11  (the first electrode layer  111  and the second electrode layer  112 ). 
     Thus, heat generated in the first electrode layer  111  and the second electrode layer  112  can be efficiently released to the lower surface  102  side of the base  10 . Therefore, according to the structural body  2  according to the embodiment, the thermal uniformity can be further improved. 
     Also, in the structural body  2  according to the embodiment, the terminal  41  is connected to the connection conductor  133 . The thickness (vertical width) of the connection conductor  133  is greater than the respective thicknesses of the first electrode layer  111  and the second electrode layer  112 . Therefore, for example, when a hole for inserting the terminal  41  is formed in the base  10 , it is less likely to penetrate the first electrode layer  111  or the second electrode layer  112 , compared with the case where the terminal  41  is connected to the first electrode layer  111  or the second electrode layer  112 , so that it is easier to connect the terminal  41 . 
     The thickness (width in the horizontal direction) of each of the first via conductor  131  and the second via conductor  132  is substantially the same as the thickness of the connection conductor  133 . That is, as illustrated in  FIG.  3   , when the base  10  is viewed in cross section, the respective thicknesses of the first via conductor  131  and the second via conductor  132  are greater than each of the thicknesses of the first electrode layer  111  and the second electrode layer  112 . Thus, by thickening the first via conductor  131  and the second via conductor  132 , the reliability of the connection between the first electrode layer  111  and the second electrode layer  112 , and the first via conductor  131  and the second via conductor  132 , can be improved. For example, the respective thicknesses of the first electrode layer  111  and the second electrode layer  112  are from 30 μm to 120 μm, and the respective thicknesses of the first via conductor  131  and the second via conductor  132  are from 0.4 mm to 1 mm. 
     Method of Manufacturing Base According to Embodiment 
     In the following, a method of manufacturing the base  10 , in the case where the main component of the base  10  is AlN, the main component of the electrode layer  11  is W (tungsten), the main component of the conductor portion  13  is W (tungsten), and the terminal  41  is composed of metal W, will be described. 
     First, an unfired AlN sheet is prepared. The AlN sheet includes AlN powder as a main component, and includes sintering aid powder such as CaO and Y 2 O 3 , and a binder. The binder is, for example, an acrylic resin, or the like. 
     An electrode layer sheet, a sheet for the first via conductor, a sheet for the second via conductor, and a sheet for the connection conductor, which are all unfired, are prepared. These sheets are composed of W (tungsten) powder and a binder. 
     The AlN sheet to be located on the lower surface  102  is cut into the outer edge shape of the base  10  and placed. On this AlN sheet, the prepared AlN sheet, the electrode layer sheet, the sheet for the first via conductor, the sheet for the second via conductor, and the sheet for the connection conductor are further used and the sheets are cut in a predetermined shape and layered in a manner to have the shape of the structural body illustrated in  FIG.  3    (the shape before firing). The sheets are layered on each other, and then are brought into close contact with each other by pressurizing the whole to produce a green laminate in which the respective sheets are integrated. 
     The obtained green laminate is fired at 1700° C. to 1850° C. in a nitrogen gas atmosphere. The base AlN is sintered by firing, and the first via conductor  131  is joined to the first electrode layer  111  and the second electrode layer  112 , the second via conductor  132  is joined to the first electrode layer  111  and the second electrode layer  112 , and the connection conductor  133  is joined to the first via conductor  131  and the second via conductor  132 . 
     A through hole for attaching the terminal  41  is made on the lower surface  102  side. The terminal  41  is inserted into the through hole, and the connection conductor  133  and the terminal  41  are joined by known brazing, diffusion bonding, or the like. The conducting wire  42  is joined to the terminal  41 . The shaft  20  having a tubular shape is joined to the bottom surface  102  of the base  10 , and the terminal  41  and the conducting wire  42  are housed inside the shaft  20 . 
     FIRST MODIFICATION EXAMPLE 
     Next, a modification example of the structural body  2  according to the above-described embodiment will be described. First, a structural body according to a first modification example will be described with reference to  FIG.  4   .  FIG.  4    is a schematic cross-sectional view of the structural body according to the first modification example. 
     As illustrated in  FIG.  4   , a structural body  2 A according to the first modification example includes a conductor portion  13 A. The conductor portion  13 A according to the first modification example includes protruding portions  135  and  136 . 
     The protruding portion  135  protrudes from the first via conductor  131  in a direction along the first electrode layer  111  and is in contact with the first electrode layer  111 . Further, the protruding portion  136  protrudes from the second via conductor  132  in a direction along the first electrode layer  111  and is in contact with the first electrode layer  111 . 
     Thus, by providing the protruding portions  135  and  136  in the conductor portion  13 A, the contact surface area between the conductor portion  13 A and the first electrode layer  111  can be increased. Therefore, in accordance with the structural body  2 A according to the first modification example, the electrical connection between the conductor portion  13 A and the first electrode layer  111  can be made more reliable. Further, the joining strength between the conductor portion  13 A and the first electrode layer  111  can be enhanced. 
     Here, an example of a case where both the first via conductor  131  and the second via conductor  132  are provided with the protruding portions  135  and  136  respectively, is illustrated, but the protruding portion  135  or  136  may be provided in at least one of the first via conductor  131  and the second via conductor  132 . 
     In addition, although an example is described in which the protruding portions  135  and  136  protrude outward from the first via conductor  131  and the second via conductor  132  respectively, the protruding portions  135  and  136  may protrude inward from the first via conductor  131  and the second via conductor  132  respectively. That is, the protruding portion  135  may protrude from the first via conductor  131  toward the second via conductor  132 , and the protruding portion  136  may protrude from the second via conductor  132  toward the first via conductor  131 . 
     Here, an example is illustrated in which the protruding portions  135  and  136  are in contact with the first electrode layer  111  on the lower surface (the surface located on the lower surface  102  side of the base  10 ) side of the first electrode layer  111 , but the protruding portions  135  and  136  may be in contact with the first electrode layer  111  on the upper surface (the surface located on the wafer placement surface  101  side of the base  10 ) side of the first electrode layer  111 . In other words, the protruding portions  135  and  136  may be located between the first electrode layer  111  and the second electrode layer  112 . 
     SECOND MODIFICATION EXAMPLE 
     Next, a structural body according to a second modification example will be described with reference to  FIG.  5   .  FIG.  5    is a schematic cross-sectional view of the structural body according to the second modification example. 
     As illustrated in  FIG.  5   , the structural body  2 B according to the second modification example includes a conductor portion  13 B. The conductor portion  13 B according to the second modification example includes the protruding portions  137  and  138 . 
     The protruding portion  137  protrudes from the first via conductor  131  in a direction along the second electrode layer  112  and is in contact with the second electrode layer  112 . The protruding portion  138  protrudes from the second via conductor  132  in a direction along the second electrode layer  112  and is in contact with the second electrode layer  112 . 
     Thus, the protruding portions  137  and  138  may be in contact with the second electrode layer  112 . In this case, since the contact surface area between the conductor portion  13 B and the second electrode layer  112  can be increased, the electrical connection between the conductor portion  13 B and the second electrode layer  112  can be made more reliable. Further, the joining strength between the conductor portion  13 B and the second electrode layer  112  can be enhanced. 
     Here, an example of a case where both the first via conductor  131  and the second via conductor  132  are provided with the protruding portions  137  and  138  respectively, is illustrated, but the protruding portion  137  or  138  may be provided in at least one of the first via conductor  131  and the second via conductor  132 . 
     In addition, although an example is described in which the protruding portions  137  and  138  protrude outward from the first via conductor  131  and the second via conductor  132  respectively, the protruding portions  137  and  138  may protrude inward from the first via conductor  131  and the second via conductor  132  respectively. 
     Here, an example is illustrated in which the protruding portions  137  and  138  are in contact with the second electrode layer  112  on the lower surface side of the second electrode layer  112 , but the protruding portions  137  and  138  may be in contact with the second electrode layer  112  on the upper surface side of the second electrode layer  112 . 
     In addition, the structural body  2 B may further include the protruding portions  135  and  136  according to the first modification example. 
     THIRD MODIFICATION EXAMPLE 
     Next, a structural body according to a third modification example will be described with reference to  FIG.  6   .  FIG.  6    is a schematic cross-sectional view of the structural body according to the third modification example. 
     As illustrated in  FIG.  6   , a structural body  2 C according to the third modification example includes a conductor portion  13 C. In the conductor portion  13 C according to the third modification example, a connection conductor  133  is located between the second electrode layer  112  and the wafer placement surface  101  of the base  10  (see  FIG.  2   ). The connection conductor  133  according to the third modification example connects respective end portions of the first via conductor  131  and the second via conductor  132 , which penetrate the second electrode layer  112 . 
     Thus, the connection conductor  133  may be located on the wafer placement surface  101  side of the base  10  relative to electrode layers  11  (the first electrode layer  111  and the second electrode layer  112 ). 
     In the structural body  2 C according to the third modification example, the terminal  41  is connected to the first via conductor  131 . Specifically, the terminal  41  is connected to an end portion of the first via conductor  131 , which penetrates the first electrode layer  111 . Thus, the terminal  41  may be connected to the first via conductor  131 . The terminal  41  may also be connected to the second via conductor  132 . 
     FOURTH MODIFICATION EXAMPLE 
     Next, a structural body according to a fourth modification example will be described with reference to  FIG.  7   .  FIG.  7    is a schematic cross-sectional view of the structural body according to the fourth modification example. 
     As illustrated in  FIG.  7   , the structural body  2 D according to the fourth modification example includes a base  10 D. The base  10 D according to the fourth modification example includes a lower surface  102 D at a position where the end portions of the first via conductor  131  and the second via conductor  132 , which penetrate the first electrode layer  111 , are exposed. 
     Thus, the exposure of the respective ends of the first via conductor  131  and the second via conductor  132  to the lower surface  102 D facilitates connection of the terminal  41  to the end portion of the first via conductor  131  or the second via conductor  132 . 
     FIFTH MODIFICATION EXAMPLE 
     Next, a structural body according to a fifth modification example will be described with reference to  FIG.  8   .  FIG.  8    is a schematic cross-sectional view of the structural body according to the fifth modification example. 
     As illustrated in  FIG.  8   , in the structural body  2 E according to the fifth modification example, the terminal  41  is in contact with the first electrode layer  111  at the tip surface  411  and the side surface  412 . Therefore, the joining strength between the terminal  41  and the first electrode layer  111  can be improved as compared with, for example, the case where the terminal  41  contacts the first electrode layer  111  only at the tip surface  411  or the case where the terminal  41  contacts the first electrode layer  111  only at the side surface  412 . 
     The structural body  2 E according to the fifth modification example includes a conductor portion  13 E. The conductor portion  13 E according to the fifth modification example includes a contact portion  139  at a contact location of the connection conductor  133  with the terminal  41 . The contact portion  139  is a portion of the connection conductor  133 , and the thickness of the contact portion  139  (vertical width) is thicker than other portions of the connection conductor  133 . Specifically, the contact portion  139  protrudes toward the lower surface  102  side, that is, toward the side opposite to the wafer placement surface  101 , as compared with other portions of the connection conductor  133 . 
     Thus, by making the contact portion  139 , which is the contact location with the terminal  41 , thicker than the other locations, the contact surface area of the terminal  41  with the side surface  412  can be made larger. Therefore, the joining strength between the terminal  41  and the first electrode layer  111  can be further improved. 
     The base  10 E according to the fifth modification example includes a space  17  around the contact portion  139 . The space  17  extends laterally to the contact portion  139  and surrounds the entire circumference of the contact portion  139 . Thus, by providing the space  17  around the contact portion  139 , heat transfer to the side opposite to the wafer placement surface  101  can be suppressed by the insulating action of the space  17 . Therefore, the wafer placed on the wafer placement surface  101  can be efficiently heated. 
     In the structural body  2 E according to the fifth modification example, the first via conductor  131  and the second via conductor  132  are located on both sides of the contact portion  139 , respectively. Thus, the location of the first via conductor  131  and the second via conductor  132  on both sides of the contact portion  139  can suppress thermal deformation of the first electrode layer  111  and the second electrode layer  112  around the contact portion  139 . Therefore, the joining strength between the terminal  41  and the first electrode layer  111  can be enhanced under the use environment in which the temperature is repeatedly raised and lowered. 
     SIXTH MODIFICATION EXAMPLE 
     Next, a structural body according to a sixth modification example will be described with reference to  FIGS.  9  to  13   .  FIG.  9    is a schematic cross-sectional view of the structural body according to the sixth modification example.  FIGS.  10  to  13    are schematic diagrams illustrating aspect examples of the inclinations of the first via conductor  131 F and the second via conductor  132 F. 
     As illustrated in  FIG.  9   , a structural body  2 F includes a base  10 F and a conductor portion  13 F. The base  10 F includes the space  17  around the contact portion  139 , similar to the base  10 E according to the fifth modification example. 
     The conductor portion  13 F includes a first via conductor  131 F, a second via conductor  132 F, and a connection conductor  133 F. 
     The first via conductor  131 F, the second via conductor  132 F, and the connection conductor  133 F each include a stepped portion  150 . The stepped portion  150  includes a plane (stepped surface) along the first electrode layer  111  or the second electrode layer  112 . In other words, the first via conductor  131 F, the second via conductor  132 F, and the connection conductor  133 F are deviated in a plurality of locations along the first electrode layer  111  or the second electrode layer  112 , and the stepped portion  150  is formed by this deviation. 
       FIG.  9    illustrates an example in which an extending direction D 1  of the first via conductor  131 F and an extending direction D 2  of the second via conductor  132 F both coincide with the vertical direction (Z axis direction). The extending direction D 1  of the first via conductor  131 F may be specified, for example, by the direction of a straight line (the direction from the lower end toward the upper end) connecting the center portion of the lower end (the end portion on the negative side of the Z axis) and the center portion of the upper end (the end portion on the positive side of the Z axis) of the first via conductor  131 F. The same applies to the extending direction D 2  of the second via conductor  132 F. 
     The respective extending directions D 1  and D 2  of the first via conductor  131 F and the second via conductor  132 F are not limited to the example illustrated in  FIG.  9   . For example, as illustrated in  FIG.  10   , the extending directions D 1  and D 2  may be inclined at predetermined angles θ 1  and θ 2  respectively with respect to the positive Z-axis direction (vertically upward). 
     Although  FIG.  10    illustrates an example in which the first via conductor  131 F and the second via conductor  132 F are inclined in the same direction, the inclination directions of the first via conductor  131 F and the second via conductor  132 F are not necessarily the same. For example, as illustrated in  FIG.  11   , the first via conductor  131 F and the second via conductor  132 F may be inclined away from each other from the lower end toward the upper end. As illustrated in  FIG.  12   , the first via conductor  131 F and the second via conductor  132 F may be inclined toward each other from the lower end toward the upper end. 
       FIGS.  9  to  12    illustrate an example in which the extending directions D 1  and D 2  of the first via conductor  131 F and the second via conductor  132 F are constant respectively from the lower end to the upper end, but the respective extending directions D 1  and D 2  do not necessarily need to be constant. For example, as illustrated in  FIG.  13   , the extending direction D 11  in the lower half of the first via conductor  131 F and the extending direction D 12  in the upper half of the first via conductor  131 F may be different. Similarly, the extending direction D 21  in the lower half of the second via conductor  132 F and the extending direction D 22  in the upper half of the second via conductor  132 F may be different. 
     The inclination angles θ 1  and θ 2  of the extending directions D 1  and D 2  are respectively, for example, 2° to 30°. 
     An example of a method of manufacturing the structural body  2 F according to the sixth modification example will be described with reference to  FIGS.  14  to  16   .  FIGS.  14  to  16    are schematic cross-sectional views for explaining an example of the method of manufacturing the structural body  2 F according to the sixth modification example. 
     As illustrated in  FIG.  14   , a plurality of ceramic green sheets  201  mainly composed of aluminum nitride (AlN) and a plurality of metal sheets  202  and  203  mainly composed of tungsten (W) (a plurality of sheets mainly composed of W metal powder) are layered to form a shape (before firing) of the structural body  2 F illustrated in  FIG.  9   . Openings are formed in predetermined locations in the ceramic green sheets  201 , and the metal sheets  202  are positioned in the openings. The sheets are layered on each other, and then are brought into close contact with each other by pressurizing the whole to produce a green laminate in which the respective sheets are integrated. 
     The obtained green laminate is fired at 1700° C. to 1850° C. in a nitrogen gas atmosphere. As a result, as illustrated in  FIG.  15   , AlN as a base  10 F is sintered. Also, the first via conductor  131 F is joined to the first electrode layer  111  and the second electrode layer  112 , the second via conductor  132 F is joined to the first electrode layer  111  and the second electrode layer  112 , and the connection conductor  133 F is joined to the first via conductor  131 F and the second via conductor  132 F. 
     Then, as illustrated in  FIG.  16   , a through hole for attaching the terminal  41  is formed on the lower surface  102  side. Thereafter, a Pt (platinum) paste is applied to a bottom portion of the through hole, and the terminal  41  is inserted into the through hole to perform heat treatment. Thus, the terminal  41  and the contact portion  139  are joined. Further, Pt enters the gap between the terminal  41  and the base  10 F, and the gap between the terminal  41  and the base  10 F is sealed. 
     Subsequently, after a paste of sealant is applied around the terminal  41 , the base  10 F is heat treated, for example, at 1550° C. in a vacuum. Thus, the sealant enters the gap between the terminal  41  and the base  10 F by capillary action, and the gap between the terminal  41  and the base  10 F is further sealed. 
     SEVENTH MODIFICATION EXAMPLE 
     Next, a structural body according to a seventh modification example will be described with reference to  FIG.  17   .  FIG.  17    is a schematic cross-sectional view of the structural body according to the seventh modification example. 
     As illustrated in  FIG.  17   , a structural body  2 G includes a base  10 G and a conductor portion  13 G. The base  10 G includes the space  17  around the contact portion  139 , similar to the base  10 E according to the fifth modification example. 
     The conductor portion  13 G includes a first via conductor  131 G, a second via conductor  132 G, and a connection conductor  133 G. In each of the first via conductor  131 G and the second via conductor  132 G, the diameter K 2  on the upper end side is larger than the diameter K 1  on the lower end side between the first electrode layer  111  and the second electrode layer  112 .  FIG.  17    illustrates an example in which each of the first via conductor  131 G and the second via conductor  132 G gradually increases in diameter from the lower end side toward the upper end side between the first electrode layer  111  and the second electrode layer  112 . 
     EIGHTH MODIFICATION EXAMPLE 
     Next, a structural body according to an eighth modification example will be described with reference to  FIG.  18   .  FIG.  18    is a schematic cross-sectional view of the structural body according to the seventh modification example. 
     As illustrated in  FIG.  18   , a structural body  2 H includes a base  10 H and a conductor portion  13 H. The base  10 H includes the space  17  around the contact portion  139 , similar to the base  10 E according to the fifth modification example. 
     The conductor portion  13 H includes a first via conductor  131 H, a second via conductor  132 H, and a connection conductor  133 H. In each of the first via conductor  131 H and the second via conductor  132 H, the diameter K 4  on the upper end side is smaller than the diameter K 3  on the lower end side between the first electrode layer  111  and the second electrode layer  112 .  FIG.  18    illustrates an example in which each of the first via conductor  131 H and the second via conductor  132 H gradually decreases in diameter from the lower end side toward the upper end side between the first electrode layer  111  and the second electrode layer  112 . 
     As described above, the structural body (for example, the structural body  2 ,  2 A to  2 E) according to the embodiments includes the base (for example, the base  10 ,  10 D,  10 E), the first electrode layer (for example, the first electrode layer  111 ), the second electrode layer (for example, the second electrode layer  112 ), the first via conductor (for example, the first via conductor  131 ), the second via conductor (for example, the second via conductor  132 ), and the connection conductor (for example, the connection conductor  133 ). The base is composed of a ceramic. The first electrode layer and the second electrode layer are located inside the base. The first via conductor and the second via conductor are located inside the base and connect the first electrode layer and the second electrode layer. The connection conductor is located inside the base and connects the first via conductor and the second via conductor. 
     Therefore, in accordance with the structural body according to the embodiments, since the heat generated in the heat spot where the first electrode layer and the second electrode layer overlap can be dispersed through the connection portion, the thermal uniformity can be improved. 
     The first via conductor and the second via conductor penetrate the first electrode layer, and the connection conductor connects the respective end portions of the first via conductor and the second via conductor, which penetrate the first electrode layer. The base includes a first surface (for example, the wafer placement surface  101 ) on which an object to be placed (for example, a wafer) is placed and a second surface (for example, the lower surface  102 ) located opposite to the first surface. In this case, the first electrode layer may be located on the second surface side relative to the second electrode layer. 
     Thus, heat generated in the heat spot can be efficiently released to the second surface side of the base. Therefore, in accordance with the structural body according to the embodiments, the thermal uniformity can be further improved. 
     The structural body according to the embodiments may include a terminal (for example, the terminal  41 ) connected to the connection conductor. In this case, the connection conductor may be thicker than each of the first electrode layer and the second electrode layer. Therefore, in accordance with the structural body according to the embodiments, it is easy to connect the terminal. 
     The terminal may contact the connection conductor at a tip surface (for example, the tip surface  411 ) and a side surface (for example, the side surface  412 ) of the terminal. Thus, the joining strength between the terminal and the first electrode layer can be improved as compared with, for example, the case where the terminal contacts the first electrode layer only at the tip surface or the case where the terminal contacts the first electrode layer only at the side surface. 
     The structural body according to the embodiments may include a protruding portion (for example, the protruding portions  135  to  138 ) protruding from at least one of the first via conductor and the second via conductor in a direction along and in contact with the first electrode layer or the second electrode layer Thus, since the contact surface area between the conductor portion and the first electrode layer can be increased, the electrical connection between the conductor portion and the first electrode layer can be made more reliable. 
     Although the above-described embodiments have been described with reference to a wafer placement apparatus as an example of a heating apparatus, the heating apparatus according to the present disclosure may be one that heats an object (e.g., an object to be placed that is placed on one side of the base) by heating the electrode layer inside the base, and is not limited to the wafer placement apparatus. 
     Further effects and modification examples can be readily derived by those skilled in the art. Thus, the broader aspects of the present invention are not limited to the specific details and representative embodiments represented and described above. Accordingly, various changes may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 
     REFERENCE SIGNS LIST 
       1  Wafer placement apparatus
 
 2  Structural body
 
 4  Wiring portion
 
 5  Power supply unit
 
       6  Controller 
       10  Base 
       11  Electrode layer
 
 13  Conductor portion
 
       20  Shaft 
       41  Terminal 
       101  Upper surface (Wafer placement surface)
 
 102  Lower surface
 
 111  First electrode layer
 
 112  Second electrode layer
 
 131  First via conductor
 
 132  Second via conductor
 
 133  Connection conductor
 
 135  to  139  Protruding portion