Patent Publication Number: US-2023141651-A1

Title: Structure and heating device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a structure and a heating device. 
     BACKGROUND ART 
     Substrates made of ceramics have superior heat resistance compared to metals and resins. For example, aluminum nitride-based ceramics have a high thermal conductivity, and thus may be used as a structure for placing or holding workpieces such as various elements and components during thermal treatment of the workpieces. 
     When a structure is used as a heater for thermal treatment of a workpiece, a power supply terminal is connected to an electrode layer in order to connect the electrode layer embedded inside the structure to a power supply. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Document 1: JP 2003-40686 A 
       
    
     SUMMARY OF INVENTION 
     A structure according to one aspect of the present disclosure includes a base, an electrode layer, and a terminal. The base is made of a ceramic. The electrode layer is located inside the base. The terminal is electrically connected to the electrode layer at a tip portion of the terminal. In addition, the terminal is in contact with the electrode layer at a tip surface and a side surface of the terminal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic perspective view of a wafer placement device according to an embodiment. 
         FIG.  2    is a schematic cross-sectional view of a structure 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 for describing an example of a manufacturing method for a base according to the embodiment. 
         FIG.  5    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the embodiment. 
         FIG.  6    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the embodiment. 
         FIG.  7    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the embodiment. 
         FIG.  8    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the embodiment. 
         FIG.  9    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the embodiment. 
         FIG.  10    is a schematic cross-sectional view of a structure according to a first modification example. 
         FIG.  11    is a schematic cross-sectional view for describing an example of a manufacturing method for a base according to the first modification example. 
         FIG.  12    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the first modification example. 
         FIG.  13    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the first modification example. 
         FIG.  14    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the first modification example. 
         FIG.  15    is a schematic cross-sectional view for describing the example of the manufacturing method for the base according to the first modification example. 
         FIG.  16    is a schematic cross-sectional view of a structure according to a second modification example. 
         FIG.  17    is a schematic cross-sectional view of a structure according to a third modification example. 
         FIG.  18    is a schematic cross-sectional view of a structure according to a fourth modification example. 
         FIG.  19    is a schematic cross-sectional view of a structure according to a fifth modification example. 
         FIG.  20    is a schematic cross-sectional view of a structure according to a sixth modification example. 
         FIG.  21    is a schematic cross-sectional view of a structure according to a seventh modification example. 
         FIG.  22    is a schematic cross-sectional view of a structure according to an eighth modification example. 
         FIG.  23    is a schematic cross-sectional view of a structure according to a ninth modification example. 
         FIG.  24    is a schematic cross-sectional view of a structure according to a 10th modification example. 
         FIG.  25    is a schematic cross-sectional view of a structure according to an 11th modification example. 
         FIG.  26    is a schematic cross-sectional view of a structure according to a 12th modification example. 
         FIG.  27    is a schematic cross-sectional view of a structure according to a 13th modification example. 
         FIG.  28    is a schematic cross-sectional view of a structure according to a 14th modification example. 
         FIG.  29    is a schematic cross-sectional view of a structure according to a 15th modification example. 
         FIG.  30    is a schematic cross-sectional view of a structure according to a 16th modification example. 
         FIG.  31    is a schematic cross-sectional view of a structure according to a 17th modification example. 
         FIG.  32    is a schematic top view of a terminal according to the 17th modification example. 
         FIG.  33    is a schematic cross-sectional view of a structure according to an 18th modification example. 
         FIG.  34    is a schematic top view of a terminal according to the 18th modification example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of a structure and a heating device according to the present disclosure (hereinafter, referred to as “embodiments”) will be described in detail below with reference to the accompanying drawings. Note that the embodiments described below are not intended to limit the structure and the heating device according to the present disclosure. Each of the embodiments can be appropriately combined within a range in which the processing contents do not contradict each other. In each of the embodiments below, the same reference numerals are assigned to the same portions, and redundant descriptions thereof will be 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, each of the above-described expressions allows for deviations in, for example, manufacturing accuracy, positioning accuracy, and the like. 
     Further, in each of the drawings referred to below, for ease of explanation, the vertical upward direction is defined as a Z axis direction. 
     Overall Configuration of Wafer Placement Device 
     First, a configuration of a wafer placement device according to an embodiment will be described with reference to  FIG.  1   .  FIG.  1    is a schematic perspective view illustrating a wafer placement device  1  according to the embodiment. 
     The wafer placement device  1  according to the embodiment illustrated in  FIG.  1    is a device for placing a semiconductor wafer, a crystal wafer, or another wafer (hereinafter, simply referred to as “wafer”). The wafer placement device  1  has a heating function for heating the placed wafer, and is mounted on, for example, a substrate processing device that performs plasma treatment or the like on the wafer. 
     As illustrated in  FIG.  1   , the wafer placement device  1  includes a structure  2 , a wiring portion  4 , an electric power supply unit  5 , and a controller  6 . 
     The structure  2  includes a base  10  that is disc-shaped and has a thickness in an up-down (Z axis) direction, and a cylindrical shaft  20  connected to the base  10 . The 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 both have a larger 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 electric power supply unit  5  located outside the base  10 . The electric power supply unit  5  is electrically connected to the electrode layer via the wiring portion  4 , and supplies electric power to the electrode layer via the wiring portion  4 . The electric power supply unit  5  includes a power supply circuit that converts electric power supplied from a power supply (not illustrated) to an appropriate voltage. The controller  6  controls the supply of electric power in the electric power supply unit  5 . 
     The wafer placement device  1  is configured as described above, and heats the wafer placed on the wafer placement surface  101  by generating heat in the electrode layer inside the base  10  using the electric power supplied from the electric power supply unit  5 . 
     Configuration of Structure 
     Next, a configuration of the structure  2  will be described with reference to  FIG.  2   .  FIG.  2    is a schematic cross-sectional view of the structure  2  according to the embodiment. Note that  FIG.  2    illustrates a schematic cross-sectional view taken along a line II-II illustrated in  FIG.  1   . 
     Base 
     As illustrated in  FIG.  2   , an 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 upper surface  101  (hereinafter, may be referred to as “wafer placement surface  101 ”) side of the base  10  in relation to the first electrode layer  111 . The first electrode layer  111  and the second electrode layer  112  are made of, for example, a metal such as Ni, W, Mo, or Pt, or an alloy containing at least one of the above 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 arranged 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 thickness of the first electrode layer  111  and the second electrode layer  112  is, for example, 30 μm to 120 μm. 
     The first electrode layer  111  and the second electrode layer  112  are electrically connected to each other through a via conductor  113 . Note that the electrode layer  11  does not necessarily have to include two layers, but may include at least one layer (e.g., the first electrode layer  111 ). 
     The base  10  is made of a ceramic. A main component of the ceramic constituting the base  10  is, for example, aluminum nitride (AlN), aluminum oxide (Al 2 O 3 , alumina), silicon carbide (SiC), or silicon nitride (Si 3 N 4 ). The main component here is, for example, a material that occupies 50 mass % or more or 80 mass % or more of the material. 
     Note that in addition to the ceramic described above, the base  10  may contain, for example, a sintering aid. Examples of the sintering aid include a mixture of calcium oxide (CaO) and yttrium oxide (Y 2 O 3 ). 
     The upper surface  101  (wafer placement surface  101 ) and the lower surface  102  of the base  10  are parallel to each other. Further, the shape of the base  10  is not limited to any particular shape. For example, in the embodiment, the shape of the base  10  is a circular shape in a plan view, but the shape of the base  10  is not limited thereto, and may be an elliptical shape, a rectangular shape, a trapezoidal shape, or the like in a plan view. Dimensions of the base  10 , as an example, are 20 cm to 35 cm in diameter and 4 mm to 30 mm in thickness. 
     Shaft 
     The shaft  20  has a cylindrical shape, and an upper end thereof is bonded to a central portion of the lower surface of the base  10 . As one specific method, the shaft  20  is bonded (adhered) to the lower surface  102  of the base  10  by an adhesive. As another specific method, the shaft  20  may be bonded to the base  10  by solid-phase bonding. The shape of the shaft  20  is not limited to any particular shape. As one specific shape, the shaft  20  has a cylindrical shape. As another specific shape, the shaft  20  may have, for example, a square cylinder shape. The material of the shaft  20  is not limited to any particular material. As one specific material, the material of the shaft  20  is a ceramic having insulating properties. As another specific material, the material of the shaft  20  may be, for example, a conductive material (metal). 
     The cylindrical shaft  20  has an upper surface  21  that is bonded to the lower surface  102  of the base  10 , a lower surface  22  that is located opposite to the upper surface  21 , an inner surface  23  that connects the upper surface  21  and the lower surface  22  and constitutes an inner side of the shaft  20 , and an outer surface  24  that connects the upper surface  21  and the lower surface  22  and constitutes an outer side 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. In another perspective, the inner surface  23  is provided parallel to a straight line parallel to the thickness direction of the base  10 . However, the inner surface  23  may be inclined so that the inner diameter of the shaft  20  decreases downward, or may be inclined so that the inner diameter of the shaft  20  increases downward. Note that the outer surface  24  can be similarly configured. This allows the shaft  20  to be continuously different in at least one of the inner and outer diameters from the upper end to the lower end. 
     Wiring Portion 
     The wiring portion  4  includes a terminal  41  and lead wires  42 . The terminal  41  is a metal (bulk material) having some length in the up-down direction. An upper end portion of the terminal  41  is located inside the base  10 , and a lower end portion of the terminal  41  is located outside the base  10 . In the illustrated example, the terminal  41  is electrically connected to the first electrode layer  111 . The terminal  41  is also electrically connected to the second electrode layer  112  through the via conductor  113 . The shape of the terminal  41  is not limited to any particular shape. In one specific example, the terminal  41  has a cylindrical shape. The terminal  41  is made of, for example, a metal such as Ni, W, Mo, or Pt, or an alloy containing at least one of the above metals. 
     Internal Configuration of Base 
     Next, an 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 terminal  41  is electrically connected to the electrode layer  11  (here, the first electrode layer  111 ) at a tip portion  410  thereof. Specifically, the terminal  41  is in contact with the first electrode layer  111  at a tip surface  411  thereof and a side surface  412  thereof. 
     When a structure made of a ceramic is used as a heater for thermal treatment of a workpiece, a power supply terminal is connected to an electrode layer in order to connect the electrode layer embedded inside the structure with a power supply. In the related art, there is room for further improvement in such a structure in terms of improving the bonding strength between the terminal and the electrode layer. 
     The terminal  41  according to the embodiment is in contact with the first electrode layer  111  at the tip surface  411  thereof and the side surface  412  thereof. Thus, the bonding strength between the terminal  41  and the first electrode layer  111  can be improved compared to a case in which, for example, the terminal  41  is in contact with the first electrode layer  111  only at the tip surface  411  thereof or only at the side surface  412  thereof. 
     The terminal  41  and the first electrode layer  111  are bonded, for example, by heat-shrinking the first electrode layer  111  to adhere to the terminal  41  in a manufacturing process of the base  10 . Further, the terminal  41  and the first electrode layer  111  may also be bonded by interposing a sealant (not illustrated) in a minute gap between the terminal  41  and the first electrode layer  111 . The sealant contains, for example, aluminum oxide (Al 2 O 3 ) as a main component, and calcium oxide (CaO) and yttrium oxide (Y 2 O 3 ). 
     The first electrode layer  111  to be connected to the terminal  41  has a contact portion  15  at a portion in contact with the terminal  41 . The contact portion  15  is a part of the first electrode layer  111 , and a thickness (width in the up-down direction) thereof is thicker than that of other portions in the first electrode layer  111 . Specifically, the contact portion  15  protrudes toward the lower surface  102  side, that is, toward the opposite side of the wafer placement surface  101 , compared to the other portions of the first electrode layer  111 . As an example, the thickness of the contact portion  15  (maximum thickness excluding a recessed portion  151  described later) is 0.4 mm to 3 mm, preferably 0.6 mm to 2 mm. 
     In this way, by making the contact portion  15 , which is the contact portion with the terminal  41 , thicker than the other portions, the contact area with the side surface  412  of the terminal  41  can be made larger. Thus, the bonding strength between the terminal  41  and the first electrode layer  111  can be further improved. In addition, as will be described in detail later, when forming a recessed portion for housing the tip portion  410  of the terminal  41  using a drill or the like in the first electrode layer  111  in the manufacturing process of the base  10 , it is possible to reduce the likelihood of the drill or the like accidentally passing through the first electrode layer  111 . That is, the manufacturing process of the base  10  can be facilitated. 
     Further, the base  10  has a space  17  around the contact portion  15 . The space  17  extends to a side of the contact portion  15 , and surrounds the entire circumference of the contact portion  15 . By providing the space  17  around the contact portion  15  in this manner, it is possible to suppress the heat transfer to the opposite side of the wafer placement surface  101  due to the insulating effect of the space  17 . Thus, it is possible to efficiently heat the wafer placed on the wafer placement surface  101 . 
     Manufacturing Method for Base According to Embodiment 
     Next, an example of a manufacturing method for the base  10  will be described with reference to  FIGS.  4  to  9   .  FIGS.  4  to  9    are schematic cross-sectional views for describing the example of the manufacturing method for the base  10  according to the embodiment. 
     As illustrated in  FIG.  4   , first, a plurality of ceramic green sheets  201  containing aluminum nitride (AlN) or the like as a main component are layered on one another. On top of that, one (or a plurality of) metal sheet  202  made of a metal or alloy such as tungsten (W), which constitutes the first electrode layer  111 , is layered, and then a plurality of ceramic green sheets  201  are further layered thereon. The plurality of ceramic green sheets  201  layered on the metal sheet  202  are preliminarily formed with an opening  203  for positioning the contact portion  15  described above. 
     Subsequently, as illustrated in  FIG.  5   , the opening  203  is filled with tungsten carbide (WC) paste  204 . Note that the paste  204  may be one that is eventually integrated with the first electrode layer  111 , and does not necessarily have to be tungsten carbide. The paste  204  filled in the opening  203  is dried in the opening  203 . Subsequently, as illustrated in  FIG.  6   , a plurality of ceramic green sheets  201  are further layered thereon. 
     Subsequently, the laminate is then fired at a temperature of 1700 to 1800° C., for example, under a nitrogen atmosphere. As a result, as illustrated in  FIG.  7   , the paste  204  is integrated with the first electrode layer  111  to form the contact portion  15 . In addition, the space  17  is formed on the side of the contact portion  15  due to the shrinkage of the paste  204 . 
     Subsequently, as illustrated in  FIG.  8   , an opening  205  is formed in the base  10 . The opening  205  is formed by using, for example, a drill or the like so as to extend in the up-down direction from the lower surface  102  toward the wafer placement surface  101  (see  FIG.  2   , etc.) of the base  10 . At this time, a part of the contact portion  15  is also drilled by the drill or the like as well as the base  10 . This forms a recessed portion  151  in a part of the contact portion  15  that is recessed in the thickness direction of the contact portion  15 . 
     Subsequently, as illustrated in  FIG.  9   , the terminal  41  is inserted into the opening  205  (see  FIG.  8   ). This positions the tip portion  410  of the terminal  41  inside the recessed portion  151  of the contact portion  15 . Subsequently, a sealant  206  is applied around the terminal  41 . Thereafter, the base  10  is thermally treated, for example, at 1550° C. in a vacuum. This allows the sealant  206  to enter a gap between the terminal  41  and the opening  205  by capillary action, thereby sealing the gap between the terminal  41  and the opening  205 . Further, the terminal  41  and the first electrode layer  111  are bonded to each other. 
     Note that, before inserting the terminal  41  into the opening  205 , a paste containing metal fine particles of Pt (platinum) or Ni (nickel) as a main component may be applied to a tip of the terminal  41  (on a side in contact with the recessed portion  151 ). By applying Pt paste or Ni paste to the tip of the terminal  41  and then inserting the terminal  41  into the opening  205 , the terminal  41  and the recessed portion  151  (contact portion  15 ) are bonded with Pt or Ni interposed therebetween. This increases the bonding strength between the terminal  41  and the contact portion  15 , thereby increasing the reliability of the bonding between the terminal  41  and the contact portion  15 . 
     FIRST MODIFICATION EXAMPLE 
     Next, a modification example of the structure  2  according to the above-described embodiment will be described. First, a structure according to a first modification example will be described with reference to  FIG.  10   .  FIG.  10    is a schematic cross-sectional view of the structure according to the first modification example. 
     As illustrated in  FIG.  10   , a structure  2 A according to the first modification example includes a base  10 A. The base  10 A has a space  17 A larger than the space  17  that the base  10  according to the above-described embodiment has. Specifically, whereas the space  17  that the base  10  according to the above-described embodiment has extends only to the side of the contact portion  15 , the space  17 A extends to the side and also in the protruding direction (here, in the negative direction of the Z axis) of the contact portion  15 . In other words, the space  17 A is interposed between a side surface  152  of the contact portion  15  and the base  10 A, and is also interposed between a protruding surface  153  (an end surface protruding more than other portions of the first electrode layer  111 ) of the contact portion  15  and the base  10 A. 
     As described above, by having the space  17 A around the contact portion  15  that extends to the side and in the protruding direction of the contact portion  15 , it is possible to further suppress heat transfer to the opposite side of the wafer placement surface  101  due to the insulating effect of the space  17 A. In addition, as will be described later, in a manufacturing process of the base  10 A, the work of forming the recessed portion  151  in the contact portion  15  can be facilitated. 
     Manufacturing Method for Base According to First modification Example 
     Next, a manufacturing method for the base  10 A according to the first modification example will be described with reference to  FIGS.  11  to  15   .  FIGS.  11  to  15    are schematic cross-sectional views for describing an example of the manufacturing method for the base  10 A according to the first modification example. 
     As illustrated in  FIG.  11   , after a plurality of ceramic green sheets  201  and the metal sheet  202  are layered in a procedure similar to that for the base  10  according to the above-described embodiment, the opening  203  is filled with the tungsten carbide (WC) paste  204 . The paste  204  fills the opening  203 , leaving some space. Subsequently, after the opening  203  is further filled with a resin  207 , a plurality of ceramic green sheets  201  are further layered thereon as illustrated in  FIG.  12   . 
     Subsequently, the laminate is then fired at a temperature of 1700 to 1800° C., for example, under a nitrogen atmosphere. As a result, as illustrated in  FIG.  13   , the paste  204  is integrated with the first electrode layer  111  to form the contact portion  15 . In addition, in this step, the space  17 A is formed around the contact portion  15  due to the shrinkage of the paste  204  and the burning of the resin  207 . 
     Although it is possible to form the space  17 A without filling the opening  203  (see  FIG.  11   ) with the resin  207 , filling the opening  203  with the resin  207  can suppress the distortion of the base  10 A after firing. Specifically, since the shrinkage rate of the paste  204  is larger than that of others, the region around the paste  204  (contact portion  15 ) is easily distorted by firing, but by filling the opening  203  with the resin  207 , such distortion can be suppressed. 
     Subsequently, as illustrated in  FIG.  14   , the opening  205  is formed in the base  10 A. The opening  205  is formed by using, for example, a drill or the like so as to extend in the up-down direction from the lower surface  102  toward the wafer placement surface  101  (see  FIG.  2   , etc.) of the base  10 A. As a result, first, the outside of the base  10 A and the space  17 A inside the base  10 A communicate with each other through the opening  205 . Subsequently, the protruding surface  153  of the contact portion  15  is drilled by a drill or the like to form the recessed portion  151  in a part of the contact portion  15  that is recessed in the thickness direction of the contact portion  15 . At this time, since the space  17 A is interposed between the opening  205  and the protruding surface  153  of the contact portion  15 , it is easy for the operator to visually confirm the protruding surface  153  of the contact portion  15  through the opening  205 . Thus, positioning of the recessed portion  151  can be easily performed. 
     Subsequently, as illustrated in  FIG.  15   , the terminal  41  is inserted into the opening  205 . This positions the tip portion  410  of the terminal  41  inside the recessed portion  151  of the contact portion  15 . Subsequently, the sealant  206  is applied around the terminal  41 . Thereafter, the base  10  is thermally treated, for example, at 1550° C. in a vacuum. This allows the sealant  206  to enter the gap between the terminal  41  and the opening  205  by capillary action, thereby sealing the gap between the terminal  41  and the opening  205 . Further, the terminal  41  and the first electrode layer  111  are bonded to each other. 
     SECOND MODIFICATION EXAMPLE 
     Next, a structure according to a second modification example will be described with reference to  FIG.  16   .  FIG.  16    is a schematic cross-sectional view of the structure according to the second modification example. Note that in  FIG.  16    and  FIGS.  17  to  27   , which will be described later, only the first electrode layer and the terminal are illustrated, and other configurations are omitted from the figures. 
     As illustrated in  FIG.  16   , in a structure  2 B according to the second modification example, the terminal  41  is connected at a position offset from a center position of the contact portion  15 . In this way, the terminal  41  does not necessarily have to be connected to the center position of the contact portion  15 . 
     THIRD MODIFICATION EXAMPLE 
     Next, a structure according to a third modification example will be described with reference to  FIG.  17   .  FIG.  17    is a schematic cross-sectional view of the structure according to the third modification example. 
     As illustrated in  FIG.  17   , a structure  2 C according to the third modification example has a first electrode layer  111 C. A contact portion  15 C of the first electrode layer  111 C according to the third modification example has a plurality of protruding surfaces  153   a  and  153   b  having different protruding heights. Thus, the protruding surfaces  153   a  and  153   b  of the contact portion  15 C do not necessarily have to be the same surface. 
     FOURTH MODIFICATION EXAMPLE 
     Next, a structure according to a fourth modification example will be described with reference to  FIG.  18   .  FIG.  18    is a schematic cross-sectional view of the structure according to the fourth modification example. 
     As illustrated in  FIG.  18   , a structure  2 D according to the fourth modification example includes a first electrode layer  111 D. A contact portion  15 D of the first electrode layer  111 D according to the fourth modification example has a curved corner portion  155 D between a side surface  152 D and a protruding surface  153 D. In this way, by making the corner portion  155 D of the contact portion  15 D curved, stress concentration on the contact portion  15 D can be reduced. 
     FIFTH MODIFICATION EXAMPLE 
     Next, a structure according to a fifth modification example will be described with reference to  FIG.  19   .  FIG.  19    is a schematic cross-sectional view of the structure according to the fifth modification example. 
     As illustrated in  FIG.  19   , a structure  2 E according to the fifth modification example includes a first electrode layer  111 D. A contact portion  15 E of the first electrode layer  111 D according to the fifth modification example has a curved corner portion  156 E between a side surface  152 E and another portion of the first electrode layer  111 D. In this way, by making the corner portion  156 E of the contact portion  15 E curved, stress concentration on the contact portion  15 E can be reduced. 
     SIXTH MODIFICATION EXAMPLE 
     Next, a structure according to a sixth modification example will be described with reference to  FIG.  20   .  FIG.  20    is a schematic cross-sectional view of the structure according to the sixth modification example. 
     As illustrated in  FIG.  20   , a structure  2 F according to the sixth modification example includes a first electrode layer  111 F. The first electrode layer  111 F according to the sixth modification example is curved toward the terminal  41  with a contact portion  15 F as the center. In this way, the first electrode layer  111 F is curved toward the terminal  41 , making it easier for the first electrode layer  111 F to resist the pressing force by the terminal  41 . This makes the bond between the terminal  41  and the first electrode layer  111 F more reliable. 
     The first electrode layer  111 F only needs to be curved toward the terminal  41  at least in some region including the contact portion  15 F, and does not necessarily have to be curved on the whole. 
     In addition, although an example in which the first electrode layer  111 F is curved toward the terminal  41  is described here, the first electrode layer  111 F may be curved toward the wafer placement surface  101 , for example. 
     SEVENTH MODIFICATION EXAMPLE 
     Next, a structure according to a seventh modification example will be described with reference to  FIG.  21   .  FIG.  21    is a schematic cross-sectional view of the structure according to the seventh modification example. 
     As illustrated in  FIG.  21   , a structure  2 G according to the seventh modification example includes a terminal  41 G. The terminal  41 G according to the seventh modification example has a reduced diameter portion  413 G that decreases in diameter from a side surface  412 G toward a tip surface  411 G between the tip surface  411 G and the side surface  412 G. For example, the reduced diameter portion  413 G according to the seventh modification example is a chamfered corner portion located between the tip surface  411 G and the side surface  412 G of the terminal  41 G. Here, a case in which the reduced diameter portion  413 G has a chamfered surface is illustrated, but the reduced diameter portion  413 G may have a rounded surface. 
     In this way, by providing the reduced diameter portion  413 G at a tip portion  410 G of the terminal  41 G, the contact area between the tip portion  410 G of the terminal and the contact portion  15  can be increased. Thus, the bonding strength between the terminal  41 G and the first electrode layer  111  can be further improved. 
     EIGHTH MODIFICATION EXAMPLE 
     Next, a structure according to an eighth modification example will be described with reference to  FIG.  22   .  FIG.  22    is a schematic cross-sectional view of the structure according to the eighth modification example. 
     As illustrated in  FIG.  22   , a structure  2 H according to the eighth modification example includes a terminal  41 H. The terminal  41 H according to the eighth modification example has a reduced diameter portion  413 H that decreases in diameter from a side surface  412 H toward a tip surface  411 H. The reduced diameter portion  413 H according to the eighth modification example is a stepped portion located between the tip surface  411 H and the side surface  412 H. 
     In this way, by providing the reduced diameter portion  413 H having a stepped shape at a tip portion  410 H of the terminal  41 H, the bonding strength between the terminal  41 H and the first electrode layer  111  can be further improved. 
     NINTH MODIFICATION EXAMPLE 
     Next, a structure according to a ninth modification example will be described with reference to  FIG.  23   .  FIG.  23    is a schematic cross-sectional view of the structure according to the ninth modification example. 
     As illustrated in  FIG.  23   , a structure  21  according to the ninth modification example includes a terminal  41 I. The terminal  41 I according to the ninth modification example has a tip surface  411 I having a curved surface. In this way, by making the tip surface  411 I of the terminal  41 I curved, the contact area between a tip portion  410 I of the terminal  41 I and the contact portion  15  can be increased. Thus, the bonding strength between the terminal  41 I and the first electrode layer  111  can be further improved. 
     10TH MODIFICATION EXAMPLE 
     Next, a structure according to a 10th modification example will be described with reference to  FIG.  24   .  FIG.  24    is a schematic cross-sectional view of the structure according to the 10th modification example. 
     As illustrated in  FIG.  24   , a structure  2 J according to the 10th modification example includes a terminal  41 J. The terminal  41 J according to the 10th modification example has a tapered shape in which a side surface  412 J decreases in diameter toward a tip surface  411 J. In this way, by making a tip portion  410 J of the terminal  41 J tapered, the contact area between the tip portion  410 J of the terminal  41 J and the contact portion  15  can be increased. Thus, the bonding strength between the terminal  41 J and the first electrode layer  111  can be further improved. 
     11TH MODIFICATION EXAMPLE 
     Next, a structure according to an 11th modification example will be described with reference to  FIG.  25   .  FIG.  25    is a schematic cross-sectional view of the structure according to the 11th modification example. 
     As illustrated in  FIG.  25   , a structure  2 K according to the 11th modification example includes a terminal  41 K. The terminal  41 K according to the 11th modification example has a reverse tapered shape in which a side surface  412 K increases in diameter toward a tip surface  411 K. In this way, by making a tip portion  410 K of the terminal  41 K have a reverse tapered shape, the contact area between the tip portion  410 K of the terminal  41 K and the contact portion  15  can be increased. Thus, the bonding strength between the terminal  41 K and the first electrode layer  111  can be further improved. In addition, the reverse tapered shape suppresses the separation of the terminal  41 K. 
     12TH MODIFICATION EXAMPLE 
     Next, a structure according to a 12th modification example will be described with reference to  FIG.  26   .  FIG.  26    is a schematic cross-sectional view of the structure according to the 12th modification example. 
     As illustrated in  FIG.  26   , a structure  2 L according to the 12th modification example extends diagonally with respect to the protruding direction of the contact portion  15  (here, the Z axis direction). In this way, a terminal  41 L may extend diagonally with respect to the protruding direction of the contact portion  15 , in other words, the thickness direction of the base (up-down direction). This allows the thermal expansion of the terminal  41 L to be shifted in the right-left direction, thereby suppressing the cracks in the base. 
     13TH MODIFICATION EXAMPLE 
     Next, a structure according to a 13th modification example will be described with reference to  FIG.  27   .  FIG.  27    is a schematic cross-sectional view of the structure according to the 13th modification example. 
     As illustrated in  FIG.  27   , a structure  2 M according to the 13th modification example includes a first electrode layer  111 M. A contact portion  15 M of the first electrode layer  111 M according to the 13th modification example has a gap  208  between a part of a bottom surface  151   a  in the recessed portion  151  and a part of the tip surface  411  in the terminal  41 . In this way, by having the gap  208 , thermal conduction from the first electrode layer  111 M to the terminal  41  can be suppressed. Thus, the heat generated in the first electrode layer  111 M can be efficiently transferred to the wafer. 
     14TH MODIFICATION EXAMPLE 
     Next, a structure according to a 14th modification example will be described with reference to  FIG.  28   .  FIG.  28    is a schematic cross-sectional view of the structure according to the 14th modification example. 
     As illustrated in  FIG.  28   , a structure  2 N according to the 14th modification example includes a first electrode layer  111 N. A contact portion  15 N of the first electrode layer  111 N according to the 14th modification example protrudes toward the wafer placement surface  101  (see  FIG.  2   ) side compared to other portions of the first electrode layer  111 N. In this way, the contact portion  15 N does not need to protrude toward the lower surface  102  of the base  10  like the contact portion  15  illustrated in  FIG.  3   , for example, but may protrude toward the wafer placement surface  101 . 
     15TH MODIFICATION EXAMPLE 
     Next, a structure according to a 15th modification example will be described with reference to  FIG.  29   .  FIG.  29    is a schematic cross-sectional view of the structure according to the 15th modification example. 
     As illustrated in  FIG.  29   , a structure  20  according to the 15th modification example includes a first electrode layer  111 O. A contact portion  15 O of the first electrode layer  111 O according to the 15th modification example protrudes toward the wafer placement surface  101  (see  FIG.  2   ) side of the base  10  as well as toward the lower surface  102  side of the base  10  compared with other portions of the first electrode layer  111 O. In this way, the contact portion  15 O may protrude toward both the wafer placement surface  101  and the lower surface  102 . This makes it possible to increase the contact area between the terminal  41  and the contact portion  15 O. Thus, the bonding strength between the terminal  41  and the first electrode layer  111 O can be further improved. 
     16TH MODIFICATION EXAMPLE 
     Next, a structure according to a 16th modification example will be described with reference to  FIG.  30   .  FIG.  30    is a schematic cross-sectional view of the structure according to the 16th modification example. 
     As illustrated in  FIG.  30   , a structure  2 P according to the 16th modification example includes a first via conductor  113   a  and a second via conductor  113   b.    
     In this way, by connecting the first electrode layer  111  and the second electrode layer  112  using a plurality of via conductors (first via conductor  113   a  and second via conductor  113   b ), it is possible to make the electrical connection between the first electrode layer  111  and the second electrode layer  112  more secure. 
     Further, when the structure  2 P is used, 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 changes in temperature. Such deformation of the first electrode layer  111  and the second electrode layer  112  may cause cracks in the base  10 . In contrast, in the structure  2 P according to the 16th modification example, the first electrode layer  111  and the second electrode layer  112  are connected by the plurality of via conductors (first via conductor  113   a  and second via conductor  113   b ). Thus, according to the structure  2 P according to the 16th modification example, thermal deformation of the first electrode layer  111  and the second electrode layer  112  can be suppressed by the plurality of via conductors. Thus, it is possible to suppress cracks in the base  10 . 
     Moreover, the first via conductor  113   a  and the second via conductor  113   b  are located on both sides of the contact portion  15 , respectively. For example, in the example illustrated in  FIG.  30   , the first via conductor  113   a  is located on the left side of the contact portion  15  on the paper surface, and the second via conductor  113   b  is located on the right side of the contact portion  15  on the paper surface. In this way, by having the first via conductor  113   a  and the second via conductor  113   b  located on both sides of the contact portion  15 , thermal deformation of the first electrode layer  111  and the second electrode layer  112 , especially around the contact portion  15 , can be suppressed. Thus, for example, when the structure  2 P is used, it is possible to suppress separation of the terminal  41  from the first electrode layer  111  due to thermal deformation of the first electrode layer  111  and the second electrode layer  112 . In other words, it is possible to increase the bonding strength between the terminal  41  and the first electrode layer  111  in an operation environment in which the temperature is repeatedly raised and lowered. 
     17TH MODIFICATION EXAMPLE 
     Next, a structure according to a 17th modification example will be described with reference to  FIGS.  31  and  32   .  FIG.  31    is a schematic cross-sectional view of the structure according to the 17th modification example.  FIG.  32    is a schematic top view of a terminal according to the 17th modification example. 
     As illustrated in  FIG.  31   , a structure  2 Q according to the 17th modification example includes a terminal  41 Q. As illustrated in  FIGS.  31  and  32   , the terminal  41 Q has a recessed portion  415  on the side surface  412 . The recessed portion  415  is provided at the tip portion  410  of the terminal  41 Q. Specifically, on the side surface  412  of the terminal  41 Q, the recessed portion  415  is continuously provided from a portion facing the contact portion  15  to a portion facing the base  10 . 
     The sealant  206  enters such a recessed portion  415 . In other words, the recessed portion  415  is filled with the sealant  206 . 
     In this way, by allowing the sealant  206  to enter the recessed portion  415 , the bonding strength between the terminal  41 Q and the base  10  can be improved. In addition, by allowing the sealant  206  to enter the recessed portion  415 , the bonding strength between the terminal  41 Q and the contact portion  15  can be improved. Further, even when more than the required amount of the sealant  206  (e.g., pt (platinum)) is applied in the manufacturing process, the excess sealant  206  accumulates in the recessed portion  415 , thereby suppressing seepage of the sealant  206  from the lower surface  102  of the base  10  during manufacturing, for example. 
     Note that, although a case in which the terminal  41 Q has one recessed portion  415  is illustrated here, the number of recessed portions  415  possessed by the terminal  41 Q may be two or more. In addition, the recessed portion  415  may extend from the tip surface  411  to a base end surface of the terminal  41 Q. 
     18TH MODIFICATION EXAMPLE 
     Next, a structure according to an 18th modification example will be described with reference to  FIGS.  33  and  34   .  FIG.  33    is a schematic cross-sectional view of the structure according to the 18th modification example.  FIG.  34    is a schematic top view of a terminal according to the 18th modification example. 
     As illustrated in  FIG.  33   , a structure  2 R according to the 18th modification example includes a terminal  41 R. As illustrated in  FIGS.  33  and  34   , the terminal  41 R has a recessed portion  416  on the tip surface  411 . The recessed portion  416  is provided at the tip portion  410  of the terminal  41 R. Specifically, the recessed portion  416  is provided on the tip surface  411  of the terminal  41 R. Both ends of the recessed portion  416  reach the side surface  412  of the terminal  41 R. Note that, although a case in which the terminal  41 R has one recessed portion  416  is illustrated here, the terminal  41 R may have a plurality of recessed portions  416 . For example, the terminal  41 R may have two recessed portions  416  that intersect in a cross. The terminal  41 R may further have a recessed portion  415  similar to the recessed portion  415  possessed by the terminal  41 Q according to the 17th modification example. In this case, the recessed portion  415  and the recessed portion  416  may be contiguous. 
     In such a recessed portion  416 , the sealant  206  is entered. In other words, the recessed portion  416  is filled with the sealant  206 . 
     In this way, by allowing the sealant  206  to enter the recessed portion  416 , the bonding strength between the terminal  41 R and the base  10  can be improved. In addition, by allowing the sealant  206  to enter the recessed portion  416 , the bonding strength between the terminal  41 R and the contact portion  15  can be improved. Further, even when more than the required amount of the sealant  206  (e.g., pt (platinum)) is applied in the manufacturing process, the excess sealant  206  accumulates in the recessed portion  416 , thereby suppressing seepage of the sealant  206  from the lower surface  102  of the base  10  during manufacturing, for example. 
     As described above, the structures (e.g., structures  2 ,  2 A to  2 P) according to the respective embodiments include the respective bases (e.g.,  10 ,  10 A), the respective electrode layers (e.g., first electrode layers  111 ,  111 C,  111 D,  111 F,  111 M,  111 N,  111 O), and the respective terminals (e.g., terminals  41 ,  41 G,  41 H,  41 I,  41 J,  41 K,  41 L). The base is made of a ceramic. The electrode layer is located inside the base. The terminal is electrically connected to the electrode layer at the tip portion of the terminal. Further, the terminals are in contact with the respective electrode layers at the respective tip surfaces (e.g., tip surfaces  411 ,  411 G,  411 H,  411 I,  411 J,  411 K) of the terminals and the respective side surfaces (e.g., side surfaces  412 ,  412 G,  412 H,  412 J,  412 K) of the terminals. Thus, according to the structures according to the respective embodiments, the bonding strength between the terminal and the electrode layer can be improved. 
     The electrode layers may have the respective contact portions (e.g., contact portions  15 ,  15 C,  15 D,  15 E,  15 F,  15 M,  15 N,  15 O) with the respective terminals. In this case, each of the contact portions may be thicker than the other portions in the electrode layer. By making the contact portion, which is the portion in contact with the terminal, thicker than the other portions in the electrode layer, the contact area with the side surface of the terminal can be made larger. Thus, the bonding strength between the terminal and the electrode layer can be further improved. 
     The electrode layer may have the recessed portion (e.g., recessed portion  151 ) in a part of the contact portion that is recessed in the thickness direction of the contact portion. In this case, the tip portion of the terminal may be located inside the recessed portion. Since the contact portion is thickly formed, when the recessed portion is formed in the contact portion using a drill or the like in the manufacturing process of the base, the likelihood of the drill or the like accidentally passing through the electrode layer can be reduced. That is, the manufacturing process of the base can be facilitated. 
     The structure according to the embodiment (e.g., structure  2 M) may have the gap (e.g., gap  208 ) between a part of the bottom surface of the recessed portion and a part of the tip surface of the terminal. This makes it possible to suppress thermal conduction from the electrode layer to the terminal. 
     The electrode layer (e.g., electrode layer  111 F) may be curved toward the terminal at least in the region including the contact portion. This makes it easier for the electrode layer to resist the pressing force by the terminal, thereby ensuring a more secure bond between the terminal and the electrode layer. 
     The bases (e.g., bases  10 ,  10 A) may have the respective spaces (e.g., spaces  17 ,  17 A) around the contact portion. This makes it possible to suppress thermal conduction in the direction in which the space is present due to the insulating effect of the space. 
     The space (e.g., space  17 A) may extend to the side and in the protruding direction of the contact portion. This makes it possible to further suppress thermal conduction in the direction in which the space is present. 
     The terminal (e.g., terminal  41 J) may have a shape that decreases in diameter toward the tip surface (e.g., tip surface  411 J). This makes it possible to increase the contact area between the tip portion of the terminal and the contact portion. Thus, the bonding strength between the terminal and the electrode layer can be further improved. 
     The terminal (e.g., terminal  41 K) may have a shape that increases in diameter toward the tip surface (e.g., tip surface  411 K). This makes it possible to increase the contact area between the tip portion of the terminal and the contact portion. Thus, the bonding strength between the terminal and the electrode layer can be further improved. In addition, the reverse tapered shape suppresses the separation of the terminal. 
     The tip surface (e.g., tip surface  411 I) of the terminal (e.g., terminal  41 I) may be curved. This makes it possible to increase the contact area between the tip portion of the terminal and the contact portion. Thus, the bonding strength between the terminal and the electrode layer can be further improved. 
     In the above-described embodiments, the wafer placement device has been described as an example of the heating device, but the heating device according to the present disclosure is not limited to the wafer placement device as long as heat is generated in the electrode layer inside the base to heat an object (e.g., an object placed on one side of the base). 
     Additional effects and variations can be easily derived by a person skilled in the art. Thus, a wide variety of aspects of the present invention are not limited to the specific details and representative embodiments represented and described above. Accordingly, various changes are possible without departing from the spirit or scope of the general inventive concepts defined by the appended claims and their equivalents. 
     REFERENCE SIGNS LIST 
     
         
           1 : Wafer placement device 
           2 : Structure 
           4 : Wiring portion 
           5 : Electric power supply unit 
           6 : Controller 
           10 : Base 
           11 : Electrode layer 
           15 : Contact portion 
           17 : Space 
           20 : Shaft 
           41 : Terminal 
           42 : Lead wire 
           101 : Upper surface (wafer placement surface) 
           102 : Lower surface 
           111 : First electrode layer 
           112 : Second electrode layer 
           113 : Via conductor 
           113   a:  First via conductor 
           113   b:  Second via conductor 
           151 : Recessed portion 
           152 : Side surface 
           153 : Protruding surface 
           201 : Ceramic green sheet 
           202 : Metal sheet 
           203 : Opening 
           204 : Paste 
           205 : Opening 
           206 : Sealant 
           208 : Gap 
           410 : Tip portion 
           411 : Tip surface 
           412 : Side surface