Patent Publication Number: US-2023151508-A1

Title: Plating apparatus and air bubble removing method

Description:
TECHNICAL FIELD 
     The present invention relates to a plating apparatus and an air bubble removing method. 
     BACKGROUND ART 
     Conventionally, there has been known what is called a cup type plating apparatus as a plating apparatus that can perform a plating process on a substrate (for example, see PTL 1). Such a plating apparatus includes a plating tank that accumulates a plating solution, a substrate holder that holds a substrate as a cathode, a rotation mechanism that rotates the substrate holder, and an elevating mechanism that elevates the substrate holder. 
     Further, conventionally, there has been known, for example, a technique of arranging a porous ionically resistive element inside the plating tank to ensure in-plane uniformity of a film thickness of the plating film (for example, see PTL 2). 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Unexamined Patent Application Publication No. 2008-194% 
         PTL 2: Japanese Unexamined Patent Application Publication No. 2004-363422 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the cup type plating apparatus as exemplified above in PTL 1, for example, in a case where the ionically resistive element as exemplified in PTL 2 is arranged inside the plating tank, air bubbles contained in the plating solution in the plating tank possibly remain on the ionically resistive element (specifically, on a lower surface of the ionically resistive element and in holes of the ionically resistive element). In a case where the plating process is performed on the substrate in a state where the air bubbles remain on the ionically resistive element, the remaining air bubbles may possibly deteriorate a plating quality of the substrate. 
     The present invention has been made in view of the above, and one of the objects of the present invention is to provide a technique that can remove air bubbles that remain on the ionically resistive element. 
     Solution to Problem 
     [Aspect 1] To achieve the above-described object, a plating apparatus according to one aspect of the present invention includes a plating tank, a substrate holder, a rotation mechanism, and an elevating mechanism. The plating tank is configured to accumulate a plating solution and includes a porous ionically resistive element arranged in the plating tank. The substrate holder is arranged above the ionically resistive element and configured to hold a dummy substrate. The rotation mechanism is configured to rotate the substrate holder. The elevating mechanism is configured to elevate the substrate holder. At least one projecting portion is disposed on a lower surface of the dummy substrate, the at least one projecting portion projecting downward from the lower surface. The substrate holder includes a ring projecting below an outer peripheral edge of the lower surface of the dummy substrate. The projecting portion has a lower surface positioned below a lower surface of the ring. The plating apparatus is configured to cause the rotation mechanism to rotate the substrate holder in a state where the elevating mechanism moves down the substrate holder to allow the projecting portion of the dummy substrate to be positioned above the ionically resistive element and the projecting portion to be immersed in the plating solution of the plating tank. 
     With this aspect, in a case where the projecting portion of the dummy substrate immersed in the plating solution rotates, air bubbles on a lower surface and inside holes of the ionically resistive element can be suctioned using a pressure difference generated in a peripheral area of the projecting portion of the dummy substrate. Thus, the air bubbles that remain on the ionically resistive element can be removed. 
     [Aspect 2] In Aspect 1 described above, a space may be formed between the projecting portion and the ring such that the projecting portion does not contact the ring. 
     [Aspect 3] In Aspect 1 or Aspect 2 described above, the projecting portion has a projection height from the lower surface of the dummy substrate, the projecting height may be a value selected within a range of 1 mm or more and 100 mm or less. 
     With this aspect, a difficulty of transferring the dummy substrate due to the projection height of the projecting portion being excessively high can be suppressed, while a decrease of a removal effect of the air bubbles by the dummy substrate due to the projection height of the projecting portion being excessively low can also be suppressed. That is, the air bubbles that remain on the ionically resistive element can be sufficiently removed, while ensuring facilitated transfer of the dummy substrate. 
     [Aspect 4] In any one of Aspects 1 to 3 described above, the projecting portion may extend in a radial direction of the lower surface of the dummy substrate. 
     [Aspect 5] In Aspect 4 described above, the projecting portion may have a curved portion curved in a circumferential direction of the dummy substrate in at least a part of the projecting portion. 
     [Aspect 6] In any one of Aspects 1 to 3 described above, the projecting portion may include a first portion extending in a radial direction of the lower surface of the dummy substrate from a center of the lower surface of the dummy substrate toward the outer peripheral edge of the lower surface of the dummy substrate, and a second portion connected to an end portion on the outer peripheral edge side of the first portion and inclined with respect to the first portion. 
     [Aspect 7] In any one of Aspects 1 to 3 described above, when the lower surface of the dummy substrate is divided by a plurality of virtual concentric circles, at least one projecting portion may be disposed in each region divided by the plurality of virtual concentric circles. 
     [Aspect 8] In any one of Aspects 1 to 7 described above, the substrate holder may be configured to hold a substrate in a plating process to perform a plating process on the substrate and hold the dummy substrate during an air bubble removal to remove air bubbles that remain on the ionically resistive element, and the elevating mechanism may be configured to position the substrate holder during the air bubble removal above a position of the substrate holder in the plating process. 
     With this aspect, the projecting portion of the dummy substrate can be easily ensured to not contact the ionically resistive element during the air bubble removal. 
     [Aspect 9] In any one of Aspects 1 to 8 described above, when the elevating mechanism immerses the projecting portion of the dummy substrate in the plating solution of the plating tank, a part of the lower surface of the dummy substrate where the projecting portion is not disposed may also be immersed in the plating solution of the plating tank. 
     With this aspect, compared with a case where the area of the lower surface of the dummy substrate where the projecting portion is not disposed is not immersed in the plating solution, in a case where the projecting portion rotates according to the rotation of the substrate holder, a cause of wave on a liquid surface of the plating solution in the plating tank can be suppressed. Thus, a cause of a liquid splash of the plating solution in the plating tank can be suppressed. 
     [Aspect 10] To achieve the above-described object, an air bubble removing method according to one aspect of the present invention is an air bubble removing method of removing air bubbles that remain on a porous ionically resistive element of a plating tank configured to accumulate a plating solution and including the ionically resistive element arranged in the plating tank. The air bubble removing method includes causing a substrate holder to hold a dummy substrate having a lower surface provided with at least one projecting portion projecting downward, moving down the substrate holder holding the dummy substrate and immersing the projecting portion in the plating solution of the plating tank in a state where the projecting portion is positioned above the ionically resistive element, and rotating the substrate holder in a state where the projecting portion of the dummy substrate is positioned above the ionically resistive element and is immersed in the plating solution of the plating tank. The substrate holder includes a ring projecting below an outer peripheral edge of the lower surface of the dummy substrate, and the lower surface of the projecting portion is positioned below a lower surface of the ring. 
     With this aspect, the air bubbles that remain on the ionically resistive element can be removed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view illustrating an overall configuration of a plating apparatus according to this embodiment. 
         FIG.  2    is a plan view illustrating the overall configuration of the plating apparatus according to this embodiment. 
         FIG.  3    is a schematic diagram illustrating a configuration of a plating module in the plating apparatus according to this embodiment. 
         FIG.  4    is a schematic cross-sectional view illustrating a state where a dummy substrate is immersed in a plating solution during an air bubble removal according to this embodiment. 
         FIG.  5    is a cross-sectional view schematically illustrating a state where a substrate holder according to this embodiment holds a substrate as a cathode. 
         FIG.  6    is a schematic bottom view of a dummy substrate according to this embodiment. 
         FIG.  7    is a flowchart illustrating an exemplary air bubble removing method according to this embodiment. 
         FIG.  8    is an enlarged schematic cross-sectional view illustrating a part of a peripheral configuration of a projecting portion during an air bubble removal of the plating apparatus according to Modification 1 of this embodiment. 
         FIG.  9    is a schematic bottom view of a dummy substrate according to Modification 2 of this embodiment. 
         FIG.  10    is a schematic bottom view of a dummy substrate according to Modification 3 of this embodiment. 
         FIG.  11    is a schematic bottom view of a dummy substrate according to Modification 4 of this embodiment. 
         FIG.  12    is a schematic bottom view of a dummy substrate according to Modification 5 of this embodiment. 
         FIG.  13    is a schematic bottom view of a dummy substrate according to Modification 6 of this embodiment. 
         FIG.  14    is a schematic bottom view of a dummy substrate according to Modification 7 of this embodiment. 
         FIG.  15    is a schematic cross-sectional view of a peripheral configuration of a plating tank of a plating apparatus according to Modification 8 of this embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     [Embodiment] The following will describe an embodiment of the present invention with reference to the drawings. Note that, in the following embodiment and modifications of the embodiment, identical reference signs are assigned for identical or corresponding configurations, and their descriptions may be appropriately omitted. Further, the drawings are schematically illustrated to facilitate understanding of the features of constituent elements, and dimensional proportions and the like of each constituent element are not necessarily the same as the actual ones. Further, in some drawings, orthogonal coordinates of X-Y-Z are illustrated for reference. Of the orthogonal coordinates, the Z direction corresponds to an upper side, and the −Z direction corresponds to a lower side (direction in which gravity acts). 
       FIG.  1    is a perspective view illustrating the overall configuration of a plating apparatus  1000  of this embodiment.  FIG.  2    is a plan view illustrating the overall configuration of the plating apparatus  1000  of this embodiment. As illustrated in  FIGS.  1  and  2   , the plating apparatus  1000  includes load ports  100 , a transfer robot  110 , aligners  120 , pre-wet modules  200 , pre-soak modules  300 , plating modules  400 , cleaning modules  500 , spin rinse dryers  600 , a transfer device  700 , and a control module  800 . 
     The load port  100  is a module for loading a substrate housed in a cassette, such as a FOUP, (not illustrated) to the plating apparatus  1000  and unloading the substrate from the plating apparatus  1000  to the cassette. While the four load ports  100  are arranged in the horizontal direction in this embodiment, the number of load ports  100  and arrangement of the load ports  100  are arbitrary. The transfer robot  110  is a robot for transferring the substrate that is configured to grip or release the substrate between the load port  100 , the aligner  120 , and the transfer device  700 . The transfer robot  110  and the transfer device  700  can perform delivery and receipt of the substrate via a temporary placement table (not illustrated) to grip or release the substrate between the transfer robot  110  and the transfer device  700 . 
     The aligner  120  is a module for adjusting a position of an orientation flat, a notch, and the like of the substrate in a predetermined direction. While the two aligners  120  are disposed to be arranged in the horizontal direction in this embodiment, the number of aligners  120  and arrangement of the aligners  120  are arbitrary. The pre-wet module  200  wets a surface to be plated of the substrate before a plating process with a process liquid, such as pure water or deaerated water, to replace air inside a pattern formed on the surface of the substrate with the process liquid. The pre-wet module  200  is configured to perform a pre-wet process to facilitate supplying the plating solution to the inside of the pattern by replacing the process liquid inside the pattern with a plating solution during plating. While the two pre-wet modules  200  are disposed to be arranged in the vertical direction in this embodiment, the number of pre-wet modules  200  and arrangement of the pre-wet modules  200  are arbitrary. 
     For example, the pre-soak module  300  is configured to remove an oxidized film having a large electrical resistance present on a surface of a seed layer formed on the surface to be plated of the substrate before the plating process by etching with a process liquid, such as sulfuric acid and hydrochloric acid, and perform a pre-soak process that cleans or activates a surface of a plating base layer. While the two pre-soak modules  300  are disposed to be arranged in the vertical direction in this embodiment, the number of pre-soak modules  300  and arrangement of the pre-soak modules  300  are arbitrary. The plating module  400  performs the plating process on the substrate. There are two sets of the 12 plating modules  400  arranged by three in the vertical direction and by four in the horizontal direction, and the total 24 plating modules  400  are disposed in this embodiment, but the number of plating modules  400  and arrangement of the plating modules  400  are arbitrary. 
     The cleaning module  500  is configured to perform a cleaning process on the substrate to remove the plating solution or the like left on the substrate after the plating process. While the two cleaning modules  500  are disposed to be arranged in the vertical direction in this embodiment, the number of cleaning modules  500  and arrangement of the cleaning modules  500  are arbitrary. The spin rinse dryer  600  is a module for rotating the substrate after the cleaning process at high speed and drying the substrate. While the two spin rinse dryers  600  are disposed to be arranged in the vertical direction in this embodiment, the number of spin rinse dryers  600  and arrangement of the spin rinse dryers  600  are arbitrary. The transfer device  700  is a device for transferring the substrate between the plurality of modules inside the plating apparatus  1000 . The control module  800  is configured to control the plurality of modules in the plating apparatus  1000  and can be configured of, for example, a general computer including input/output interfaces with an operator or a dedicated computer. 
     An example of a sequence of the plating processes by the plating apparatus  1000  will be described. First, the substrate housed in the cassette is loaded on the load port  100 . Subsequently, the transfer robot  110  grips the substrate from the cassette at the load port  100  and transfers the substrate to the aligners  120 . The aligner  120  adjusts the position of the orientation flat, the notch, or the like of the substrate in the predetermined direction. The transfer robot  110  grips or releases the substrate whose direction is adjusted with the aligners  120  to the transfer device  700 . 
     The transfer device  700  transfers the substrate received from the transfer robot  110  to the pre-wet module  200 . The pre-wet module  200  performs the pre-wet process on the substrate. The transfer device  700  transfers the substrate on which the pre-wet process has been performed to the pre-soak module  300 . The pre-soak module  300  performs the pre-soak process on the substrate. The transfer device  700  transfers the substrate on which the pre-soak process has been performed to the plating module  400 . The plating module  400  performs the plating process on the substrate. 
     The transfer device  700  transfers the substrate on which the plating process has been performed to the cleaning module  500 . The cleaning module  500  performs the cleaning process on the substrate. The transfer device  700  transfers the substrate on which the cleaning process has been performed to the spin rinse dryer  600 . The spin rinse dryer  600  performs the drying process on the substrate. The transfer device  700  grips or releases the substrate on which the drying process has been performed to the transfer robot  110 . The transfer robot  110  transfers the substrate received from the transfer device  700  to the cassette at the load port  100 . Finally, the cassette housing the substrate is unloaded from the load port  100 . 
     Note that the configuration of the plating apparatus  1000  described in  FIG.  1    and  FIG.  2    is merely an example, and the configuration of the plating apparatus  1000  is not limited to the configuration in  FIG.  1    and  FIG.  2   . 
     Subsequently, the plating modules  400  will be described. Since the plurality of plating modules  400  included in the plating apparatus  1000  according to this embodiment have the identical configuration, one of the plating modules  400  will be described. 
       FIG.  3    is a schematic diagram illustrating the configuration of the plating module  400  in the plating apparatus  1000  of this embodiment. Specifically,  FIG.  3    schematically illustrates the plating module  400  in a state before the air bubble removal described later is performed. The plating apparatus  1000  according to this embodiment is a cup type plating apparatus. The plating module  400  of the plating apparatus  1000  includes a plating tank  10 , an overflow tank  20 , a substrate holder  30 , a rotation mechanism  40 , and an elevating mechanism  50 . 
     The plating tank  10  according to this embodiment is configured of a container with a bottom having an opening on an upper side. Specifically, the plating tank  10  has a bottom wall  10   a  and an outer peripheral wall  10   b  extending upward from an outer peripheral edge of the bottom wall  10   a , and an upper portion of the outer peripheral wall  10   b  is open. Note that, although the shape of the outer peripheral wall  10   b  of the plating tank  10  is not particularly limited, the outer peripheral wall  10   b  according to this embodiment has a cylindrical shape as an example. Inside of the plating tank  10 , a plating solution Ps is accumulated. Furthermore, the plating tank  10  includes a supply port (not illustrated) for supplying the plating solution Ps to the plating tank  10 . 
     It is only necessary for the plating solution Ps to be a solution including an ion of a metallic element constituting a plating film, and a specific example of the plating solution Ps is not particularly limited. In this embodiment, a copper plating process is used as an example of the plating process, and a copper sulfate solution is used as an example of the plating solution Ps. Further, in this embodiment, a predetermined additive is included in the plating solution Ps. However, the configuration of the plating solution Ps is not limited to this, and the plating solution Ps can be configured not to include an additive. 
     In the inside of the plating tank  10 , an anode  11  is arranged. Specifically, the anode  11  according to this embodiment is arranged on the bottom wall  10   a  of the plating tank  10  as an example. The specific type of the anode  11  is not particularly limited, and the anode  11  may be an insoluble anode or may be a soluble anode. In this embodiment, the insoluble anode is used as an example of the anode  11 . The specific type of the insoluble anode is not particularly limited, and platinum, iridium oxide, and the like can be used. 
     In the inside of the plating tank  10 , a porous ionically resistive element  12  is arranged above the anode  11 . Specifically, the ionically resistive element  12  is configured of a porous plate member having a plurality of holes  12   a  (pores) (Note that the reference numeral of the hole  12   a  is illustrated in  FIG.  4    described later). The holes  12   a  of the ionically resistive element  12  according to this embodiment are through-holes disposed to communicate the lower surface and the upper surface of the ionically resistive element  12 . The ionically resistive element  12  is a member disposed for ensuring homogenization of an electric field formed between the anode  11  and the substrate Wf as a cathode (the reference numeral is illustrated in  FIG.  5    described later). Thus, by arranging the ionically resistive element  12  in the plating tank  10 , homogenization of a film thickness of the plating film (plated layer) formed on the substrate Wf can be easily ensured. 
     The overflow tank  20  is configured of a container with a bottom arranged outside the plating tank  10 . The overflow tank  20  is a tank disposed for temporarily accumulating the plating solution Ps exceeding an upper end of the outer peripheral wall  10   b  of the plating tank  10  (that is, the plating solution Ps overflowing from the plating tank  10 ). The plating solution Ps temporarily accumulated in the overflow tank  20  is discharged from a discharge port (not illustrated) for the overflow tank  20 , and afterwards, is temporarily accumulated in a reservoir tank (not illustrated) for the overflow tank  20 . The plating solution Ps accumulated in the reservoir tank is then pressure fed by a pump (not illustrated) and circulated to the plating tank  10  again from the supply port for the plating solution. 
       FIG.  4    is a schematic cross-sectional view illustrating a state where the dummy substrate Wfx described later is immersed in the plating solution Ps during the air bubble removal.  FIG.  5    is a cross-sectional view schematically illustrating a state where the substrate holder  30  holds the substrate Wf as the cathode. With reference to  FIG.  3   ,  FIG.  4   , and  FIG.  5   , the substrate holder  30  is disposed above the ionically resistive element  12 . 
     As illustrated in  FIG.  5   , in the “plating process” to perform a plating process on the substrate Wf, the substrate holder  30  holds the substrate Wf (that is, the substrate Wf on which the plating process is performed) such that the lower surface (surface to be plated) of the substrate Wf is opposed to the ionically resistive element  12 . 
     Meanwhile, as illustrated in  FIG.  3    and  FIG.  4   , in the “air bubble removal” to remove the air bubbles that remain on the ionically resistive element  12 , the substrate holder  30  holds, instead of the substrate Wf, the dummy substrate Wfx such that the lower surface Wfa of the dummy substrate Wfx on which the plating process is not performed is opposed to the ionically resistive element  12 . That is, the substrate holder  30  according to this embodiment is configured to selectively hold the substrate Wf on which the plating process is performed and the dummy substrate Wfx on which the plating process is not performed. 
     With reference to particularly the enlarged view of the A 1  part in  FIG.  3   , the substrate holder  30  according to this embodiment includes a ring  31  disposed to be projected below the outer peripheral edge of the lower surface Wfa (and the lower surface of the substrate Wf) of the dummy substrate Wfx. This ring  31  has a ring shape in a bottom view. 
     Note that a sealing member for suppressing an invasion of the plating solution Ps into a gap between the substrate holder  30  and the dummy substrate Wfx may be disposed between the substrate holder  30  and the dummy substrate Wfx. That is, in this case, the substrate holder  30  holds the dummy substrate Wfx via the sealing member. Examples of the material of the sealing member include fluorine-containing rubber (FKM), or the like. 
     With reference to  FIG.  3   , the substrate holder  30  is connected to the rotation mechanism  40 . The rotation mechanism  40  is a mechanism for rotating the substrate holder  30 . “R 1 ” exemplified in  FIG.  3    is an exemplary rotation direction of the substrate holder  30 . For the rotation mechanism  40 , a known mechanism can be used, such as a rotation motor. The elevating mechanism  50  is supported by a spindle  51  extending in a vertical direction. The elevating mechanism  50  is a mechanism for moving up and down the substrate holder  30  and the rotation mechanism  40 . For the elevating mechanism  50 , a known elevating mechanism can be used, such as a linear motion type actuator. 
     An operation of the plating module  400  is controlled by the control module  800 . The control module  800  includes a microcomputer. The microcomputer includes a Central Processing Unit (CPU)  801  as a processor, a storage device  802  as a non-transitory storage medium, and the like. The control module  800  controls an operation of a controlled unit of the plating module  400  (such as the rotation mechanism  40  and the elevating mechanism  50 ) according to the CPU  801  operating as a processor based on commands of a program stored in a storage device  802 . 
     Incidentally, in the plating apparatus  1000 , for some reason, air bubbles (Bu) are generated in the plating solution Ps of the plating tank  10  in some cases. Specifically, in a case where the insoluble anode is used as the anode  11  as in this embodiment, oxygen (O 2 ) is generated in the plating solution Ps based on the following reaction equation in a plating process of the substrate Wf (that is, when applying current). In this case, the generated oxygen possibly becomes the air bubbles. 
       2H 2 O→O 2 +4H + +4 e   − 
 
     Further, in a case where the soluble anode is provisionally used as the anode  11 , a reaction equation as described above does not occur. However, for example, when the plating solution Ps is first introduced into the plating tank  10 , air may possibly flow into the plating tank  10  together with the plating solution Ps. Accordingly, even in a case where the soluble anode is used as the anode  11 , air bubbles may possibly be generated in the plating solution Ps of the plating tank  10 . 
     As described above, in a case where air bubbles are generated in the plating solution Ps of the plating tank  10 , the air bubbles sometimes remain on the lower surface of the ionically resistive element  12  and in the holes  12   a  of the ionically resistive element  12 . When the plating process is performed on the substrate Wf in the above state, a plating quality of the substrate Wf may possibly deteriorate due to the remaining air bubbles. Therefore, in this embodiment, the following technique is used to deal with the problem. 
     First, a description will be given of the dummy substrate Wfx.  FIG.  6    is a schematic bottom view illustrating a state of the dummy substrate Wfx viewed from a lower side. With reference to  FIG.  3    and  FIG.  6   , the dummy substrate Wfx is a substrate held by the substrate holder  30  instead of the substrate Wf during the air bubble removal. In this embodiment, an outer peripheral edge of the lower surface Wfa of the dummy substrate Wfx has a circular shape. 
     At least one projecting portion  60  projecting downward from the lower surface Wfa is disposed on the lower surface Wfa of the dummy substrate Wfx. That is, a number of the projecting portion  60  may be one or may be plural. This embodiment includes one projecting portion  60  as an example. 
     The projecting portion  60  is configured to suction the air bubbles (that is, air bubbles that remain on the ionically resistive element  12 ) on the lower surface and inside the holes  12   a  of the ionically resistive element  12  using a pressure difference generated in a peripheral area of the projecting portion  60  of the dummy substrate Wfx while the substrate holder  30  rotates in a state where the projecting portion  60  is immersed in the plating solution Ps. Specifically, in a case where the substrate holder  30  rotates in a state where the projecting portion  60  is immersed in the plating solution Ps, a back side in a rotation direction (that is, a side opposite to the rotation direction) of the projecting portion  60  becomes negative pressure. By using this negative pressure, the air bubbles that remain on the ionically resistive element  12  can be suctioned upward. 
     Specifically, the projecting portion  60  according to this embodiment is configured to extend in a predetermined direction along the lower surface Wfa of the dummy substrate Wfx More specifically, the projecting portion  60  according to the embodiment extends in a radial direction of the lower surface Wfa of the dummy substrate Wfx. 
     In more detail, the projecting portion  60  according to the embodiment extends toward one side and another side in a radial direction from a center Ce of the lower surface Wfa of the dummy substrate Wfx (in other words, the projecting portion  60  extends in a diametral direction of the lower surface Wfa of the dummy substrate Wfx). 
     Further, with reference to the enlarged view of an A 1  part in  FIG.  3   , the projecting portion  60  according to the embodiment has a space  70  from an inner peripheral surface of the ring  31  of the substrate holder  30  such that the projecting portion  60  does not contact the ring  31 . 
     A specific value of a length of the space  70 , that is a distance (d 1 ) between the projecting portion  60  and the ring  31 , is not particularly limited. But, as an example of the numerical value, a value selected within a range of larger than 0 mm and 1 mm or less can be used. That is, the distance (d) satisfies 0 mm&lt;d 1 ≤1 mm in the embodiment. 
     With this configuration, compared with a case where the distance (d 1 ) between the projecting portion  60  and the ring  31  is larger than 1 mm, the air bubbles that remain in a proximity of the outer peripheral edge of the ionically resistive element  12  can be effectively suctioned upward, since the projecting portion  60  extends to the proximity of the outer peripheral edge of the lower surface Wfa of the dummy substrate Wfx. 
     Further, with reference to the enlarged view of the A 1  part in  FIG.  3   , a lower surface  60   a  of the projecting portion  60  according to this embodiment is positioned below a lower surface  31   a  of the ring  31 , in a state where the dummy substrate Wfx is held by the substrate holder  30 . In other words, the projecting portion  60  according to the embodiment is projected below the ring  31 . 
     A projection height (h 1 ) of the projecting portion  60  from the lower surface Wfa of the dummy substrate Wfx is not particularly limited, but in this embodiment a value selected within a range of 1 mm or more and 100 mm or less is used. 
     With this configuration, a difficulty of transferring the dummy substrate Wfx due to the projection height (h 1 ) of the projecting portion  60  being excessively high can be suppressed, while a decrease of a removal effect of the air bubbles by the dummy substrate Wfx described later due to the projection height (h 1 ) of the projecting portion  60  being excessively low can also be suppressed. That is, with this configuration, an ease of transfer of the dummy substrate Wfx can be ensured, while the air bubbles that remain on the ionically resistive element  12  can be sufficiently removed. 
     Note that, as a preferred example of the numerical value of the projection height (h 1 ) of the projecting portion  60  described above, a value selected within a range of 3 mm or more and 50 mm or less is preferred. Specifically, a value selected within a range of 5 mm or more and 20 mm or less is more preferred, and 10 mm is even more preferred. In this embodiment, 10 mm is used as a specific example of the projection height (h 1 ). 
     Further, a paddle for agitating the plating solution Ps may be arranged between the projecting portion  60  and the ionically resistive element  12 , and the plating solution Ps may be agitated by the paddle. 
     Materials of the dummy substrate Wfx and the projecting portion  60  are not particularly limited, but for example, resin, metal, glass, silicon, or a combination of these, and the like may be used. 
     Further, in a case where metal is used as the materials of the dummy substrate Wfx and the projecting portion  60 , resin may be coated on the surfaces of the dummy substrate Wfx and the projecting portion  60  made of metal. With this configuration, metal components of the dummy substrate Wfx and the projecting portion  60  dissolve in the plating solution Ps, allowing a contamination of the plating solution Ps to be effectively suppressed. 
     A manufacturing method of the dummy substrate Wfx is not particularly limited, but the following manufacturing method may be used as an example. Specifically, a substrate having a flat lower surface on which the projecting portion  60  is not formed is prepared, and by cutting the lower surface of the prepared substrate, the projecting portion  60  is formed on the lower surface. Accordingly, the dummy substrate Wfx can be manufactured. That is, in this case, the projecting portion  60  and the portion other than the projecting portion  60  (that is, a “main body of the dummy substrate”) of the dummy substrate Wfx are formed integrally in the dummy substrate Wfx by the cutting work. 
     Alternatively, by preparing the projecting portion  60  in advance, and joining the prepared projecting portion  60  to the lower surface of a substrate having a flat lower surface (that is, the main body of the dummy substrate), the dummy substrate Wfx having a projecting portion  60  on the lower surface Wfa can be manufactured. 
       FIG.  7    is a flowchart illustrating an exemplary air bubble removing method of the plating apparatus  1000  according to this embodiment. The flowchart is performed during the air bubble removal of the air bubbles that remain on the ionically resistive element  12 . Note that a specific performance timing of the air bubble removal (that is, a specific timing to perform the flowchart of  FIG.  7   ) is not particularly limited, but for example, the air bubble removal may be performed when the plating solution Ps is first introduced into the plating tank  10 . Alternatively, the air bubble removal may be performed after the plating process is performed on the substrate Wf. As a specific example, the air bubble removal may be performed after the plating process on the substrate Wf has been performed for a predetermined number of times. Alternatively, the air bubble removal may be performed during a maintenance of the plating apparatus  1000  by, for example, a user causing the substrate holder  30  to hold the dummy substrate Wfx. 
     First, in step S 10 , the dummy substrate Wfx is held by the substrate holder  30  such that the lower surface Wfa of the dummy substrate Wfx is opposed to the ionically resistive element  12 . In this case, the dummy substrate Wfx may be transferred to a location of the substrate holder  30  by a method similar to the transfer method of the substrate Wf. Specifically, the dummy substrate Wfx placed in a “predetermined placement location” may be transferred to a location of the substrate holder  30  by a transfer mechanism (which includes the transfer robot  110  and the transfer device  700  described above). 
     Further, in this case, some of the four load ports  100  exemplified in  FIG.  1    and  FIG.  2    may be used as the “predetermined placement location.” Alternatively, a load port exclusive for the dummy substrate Wfx may be disposed separately from the four load ports  100 , and this may be used as the “predetermined placement location.” 
     After the step S 10 , the projecting portion  60  of the dummy substrate Wfx is immersed in the plating solution Ps of the plating tank  10  (step S 11 ). In this embodiment, as exemplified in  FIG.  4   , by moving down the substrate holder  30  using the elevating mechanism  50 , the projecting portion  60  is immersed in the plating solution Ps of the plating tank  10 . Further, at this point, the elevating mechanism  50  immerses the projecting portion  60  in the plating solution Ps in a state where the projecting portion  60  is positioned a predetermined distance above the ionically resistive element  12 , such that the projecting portion  60  of the dummy substrate Wfx does not contact the ionically resistive element  12 . 
     Further, as exemplified in the enlarged view of an A 3  part in  FIG.  4   , when the projecting portion  60  of the dummy substrate Wfx is immersed in the plating solution Ps, the elevating mechanism  50  according to this embodiment immerses not only the projecting portion  60  but also the part of the lower surface Wfa of the dummy substrate Wfx where the projecting portion  60  is not disposed in the plating solution Ps. That is, the part other than the projecting portion  60  of the lower surface Wfa of the dummy substrate Wfx is also positioned below a liquid surface of the plating solution Ps during the air bubble removal of the dummy substrate Wfx according to the embodiment. 
     With this configuration, compared with a case where the part of the lower surface Wfa of the dummy substrate Wfx where the projecting portion  60  is not disposed is not immersed in the plating solution Ps (see  FIG.  8    according to Modification 1 described below), in a case where the projecting portion  60  rotates according to the rotation of the substrate holder  30 , the projecting portion  60  suppresses a cause of wave on the liquid surface of the plating solution Ps of the plating tank  10 . Accordingly, a cause of a liquid splash in the plating solution Ps of the plating tank  10  can be suppressed. 
     Further, the elevating mechanism  50  in this embodiment may position the substrate holder  30  above the position of the substrate holder  30  in the plating process, when immersing the projecting portion  60  in the plating solution Ps during the air bubble removal. That is, in a case where a ground height of the substrate holder  30  in the plating process is a “first predetermined value,” a ground height of the substrate holder  30  during the air bubble removal may be a “second predetermined value” that is higher than the first predetermined value. With this configuration, the projecting portion  60  of the dummy substrate Wfx can be easily suppressed of contacting the ionically resistive element  12  during the air bubble removal. 
     However, it is not limited to the configuration described above. For example, the elevating mechanism  50  may not position the substrate holder  30  above the position of the substrate holder  30  in the plating process when immersing the projecting portion  60  in the plating solution Ps during the air bubble removal. 
     After the step S 11  in  FIG.  7   , step S 12  is performed. In the step S 12 , the rotation mechanism  40  rotates the substrate holder  30  in a state where the projecting portion  60  of the dummy substrate Wfx is positioned above the ionically resistive element  12  and the projecting portion  60  of the dummy substrate Wfx is immersed in the plating solution Ps. 
     Thus, according to the rotation of the substrate holder  30  in the step S 12 , the dummy substrate Wfx held by the substrate holder  30  rotates, and the projecting portion  60  also rotates. Accordingly, the air bubbles on the lower surface of the ionically resistive element  12  and inside the holes  12   a  (that is, the air bubbles that remain on the ionically resistive element  12 ) can be suctioned using the pressure difference generated in the peripheral area of the projecting portion  60  of the lower surface Wfa of the dummy substrate Wfx. Thus, the air bubbles that remain on the ionically resistive element  12  can be removed. 
     Note that, after the step S 12  has been performed (that is, after the air bubble removal has been performed), the rotation mechanism  40  stops the rotation of the substrate holder  30 , and the elevating mechanism  50  moves up the substrate holder  30 , thus positioning the dummy substrate Wfx above the plating solution Ps. Subsequently, the dummy substrate Wfx is removed from the substrate holder  30  (step S 13 ). 
     With the embodiment as described above, the air bubbles that remain on the ionically resistive element  12  of the plating tank  10  can be removed by performing the step S 12  described above. Accordingly, when performing the plating processing on the substrate Wf, the deterioration of the plating quality of the substrate Wf due to the remaining air bubbles can be suppressed. 
     [Modification 1 of Embodiment] Note that, during the air bubble removal of the embodiment described above, the part of the lower surface Wfa of the dummy substrate Wfx where the projecting portion  60  is not disposed is also immersed in the plating solution Ps but the configuration is not limited to this.  FIG.  8    is an enlarged schematic cross-sectional view illustrating a part (A 3  part) of a peripheral configuration of the projecting portion  60  during the air bubble removal of a plating apparatus  1000 A according to Modification 1 of the embodiment. As illustrated in  FIG.  8   , during the air bubble removal, the part of the lower surface Wfa of the dummy substrate Wfx where the projecting portion  60  is not disposed is not necessarily immersed in the plating solution Ps. and only the projecting portion  60  may be immersed in the plating solution Ps. 
     Even in this modification, similarly to the plating apparatus  1000  according to this embodiment described above, the air bubbles that remain on the ionically resistive element  12  can be removed. Accordingly, when performing the plating process on the substrate Wf, the deterioration of the plating quality of the substrate Wf due to the remaining air bubbles can be suppressed. 
     Further, in the embodiment and Modification 1 described above, a shape of the projecting portion  60  is not limited to the shape exemplified in  FIG.  5   . The following describes modifications of the projecting portion  60  (Modification 2 to Modification 6). 
     [Modification 2 of Embodiment]  FIG.  9    is a schematic bottom view of the dummy substrate Wfx of a plating apparatus  1000 B according to Modification 2 of the embodiment. A projecting portion  60 B according to the modification extends only toward one side in the radial direction from the center Ce of the lower surface Wfa (that is, the projecting portion  60 B does not extend toward another side in the radial direction). In other words, the projecting portion  60 B extends only in the radial direction of the lower surface Wfa of the dummy substrate Wfx. Even in this modification, an operational advantage similar to the plating apparatus  1000  according to the embodiment described above can be provided. 
     [Modification 3 of Embodiment]  FIG.  10    is a schematic bottom view of the dummy substrate Wfx of a plating apparatus  1000 C according to Modification 3 of the embodiment. The dummy substrate Wfx according to this modification has a plurality of projecting portions. A number of the plurality of projecting portions is not particularly limited, and it may be two, three, or four or more. This modification has two projecting portions as an example. Specifically, the plurality of projecting portions according to this modification are a projecting portion  60 C- 1  and a projecting portion  60 C- 2 . 
     The projecting portion  60 C- 1  has a configuration similar to the projecting portion  60  in  FIG.  6    described above. On the other hand, the projecting portion  60 C- 2  intersects with the projecting portion  60 C- 1  and extends toward one side and another side in a radial direction from the center Ce. That is, the projecting portion  60 C- 2  has a configuration of the projecting portion  60 C- 1  copied and arranged (or copied and rotated) in a circular shape. Note that an angle formed by the projecting portion  60 C- 1  and the projecting portion  60 C- 2  is not particularly limited, but in this modification the angle is 90 degrees as an example. 
     Even in this modification, an operational advantage similar to the plating apparatus  1000  according to the embodiment described above can be provided. Further, since the modification has a plurality of projecting portions, compared with a case where there is only one projecting portion, the air bubbles can be suctioned effectively. Accordingly, the air bubbles that remain on the ionically resistive element  12  can be suppressed effectively. 
     Note that the dummy substrate Wfx according to Modification 2 exemplified in  FIG.  9    described above may have a plurality of the projecting portions  60 B. That is, the dummy substrate Wfx may have a plurality of the projecting portions  60 B extending only toward one side in the radial direction from the center Ce of the lower surface Wfa exemplified in  FIG.  9   . 
     [Modification 4 of Embodiment]  FIG.  11    is a schematic bottom view of the dummy substrate Wfx of a plating apparatus  1000 D according to Modification 4 of the embodiment. A projecting portion  60 D of the dummy substrate Wfx according to this modification is different from the projecting portion  60  in  FIG.  6    in the respect of having a curved portion curved in a circumferential direction of the dummy substrate Wfx in at least a part of the projecting portion  60 D. Specifically, the projecting portion  60 D according to the modification has a curved portion  61   a  and a curved portion  61   b.    
     The curved portion  61   a  is arranged on one side in the radial direction of the lower surface Wfa below the center Ce, and the curved portion  61   b  is arranged on another side in the radial direction of the lower surface Wfa below the center Ce. The curved portion  61   a  and the curved portion  61   b  are curved to project toward the circumferential direction of the lower surface Wfa of the dummy substrate Wfx. 
     Even in this modification, an operational advantage similar to the plating apparatus  1000  according to the embodiment described above can be provided. 
     Note that the dummy substrate Wfx according to this modification may have a plurality of the projecting portions  60 D. 
     [Modification 5 of Embodiment]  FIG.  12    is a schematic bottom view of the dummy substrate Wfx of a plating apparatus  1000 E according to Modification 5 of the embodiment. A projecting portion  60 E of the dummy substrate Wfx according to this modification includes a first portion  62  and second portions (second portion  63   a  and second portion  63   b ). The first portion  62  is a portion extending in a radial direction of the lower surface Wfa from the center Ce of the lower surface Wfa of the dummy substrate Wfx toward the outer peripheral edge of the dummy substrate Wfx. Specifically, the first portion  62  according to this embodiment extends to one side and another side in the radial direction of the lower surface Wfa from the center Ce to the outer peripheral edge of the dummy substrate Wfx. 
     The second portion  63   a  and the second portion  63   b  are portions connected to end portions on the outer peripheral edge side of the first portion  62  and inclined with respect to the first portion  62 . Specifically, regarding the end portions on the outer peripheral edge side of the first portion  62  (end portion  62   a  and end portion  62   b ), the second portion  63   a  is connected to the end portion  62   a  on one side, and the second portion  63   b  is connected to the end portion  62   b  on another side. 
     Note that inclination angles (θ) of the second portion  63   a  and the second portion  63   b  with respect to the first portion  62  are not particularly limited but in this modification the inclination angles are values selected within a range of larger than 0 degree and smaller than 90 degrees. Specifically, the inclination angles are values selected within a range of 10 degrees or more and 45 degrees or less. Further, in this modification, the second portion  63   a  and the second portion  63   b  have the same inclination angle values. However, it is not limited to this configuration, and the inclination angles of the second portion  63   a  and the second portion  63   b  may be different values. 
     Further, in this modification, the projecting portion  60 E includes two second portions (second portion  63   a  and second portion  63   b ) but it is not limited to this configuration. The projecting portion  60 E may include only one of the second portion  63   a  and the second portion  63   b.    
     Even in this modification, an operational advantage similar to the plating apparatus  1000  according to the embodiment described above may be provided. 
     Note that the dummy substrate Wfx according to this modification may have a plurality of the projecting portions  60 E. For example, the dummy substrate Wfx according to Modification 3 described above ( FIG.  10   ) may include the second portion according to this modification. 
     Further, the dummy substrate Wfx according to Modification 2 described above ( FIG.  9   ) may include the second portion according to this modification. Even in this case, the dummy substrate Wfx may have a plurality of projecting portions each including the second portion. 
     [Modification 6 of Embodiment]  FIG.  13    is a schematic bottom view of the dummy substrate Wfx of a plating apparatus  1000 F according to Modification 6 of the embodiment. The dummy substrate Wfx according to this modification has a plurality of projecting portions. Specifically, the plurality of projecting portions according to this modification are a projecting portion  60 F- 1 , a projecting portion  60 F- 2 , a projecting portion  60 F- 3 , a projecting portion  60 F- 4 , and a projecting portion  60 F- 5 . 
     Further, the plurality of projecting portions according to this modification has a configuration in which in a case where the lower surface Wfa of the dummy substrate Wfx is divided by a plurality of virtual concentric circles (virtual concentric circle C 1 , virtual concentric circle C 2 , virtual concentric circle C 3 , and virtual concentric circle C 4 ), at least one projecting portion is disposed to each region divided by the plurality of virtual concentric circles. 
     Specifically, the projecting portion  60 F- 1  is arranged in a region on an inner side of the virtual concentric circle C 1 , and the projecting portion  60 F- 2  is arranged in a region between the virtual concentric circle C 1  and the virtual concentric circle C 2 . Further, the projecting portion  60 F- 3  is arranged in a region between the virtual concentric circle C 2  and the virtual concentric circle C 3 , and the projecting portion  60 F- 4  is arranged in a region between the concentric circle C 3  and the virtual concentric circle C 4 . The projecting portion  60 F- 5  is arranged in a region on an outer side of the concentric circle C 4 . 
     Further, the respective projecting portions disposed in each region extend in the radial direction of the lower surface Wfa of the dummy substrate Wfx. Regarding a pair of regions adjacent to one another, an angle formed by an extending direction of a projecting portion arranged in one region and an extending direction of a projecting portion arranged in another region is 90 degrees as an example. 
     Specifically, an angle formed by the projecting portion  60 F- 1  and the projecting portion  60 F- 2 , an angle formed by the projecting portion  60 F- 2  and the projecting portion  60 F- 3 , an angle formed by the projecting portion  60 F- 3  and the projecting portion  60 F- 4 , and an angle formed by the projecting portion  60 F- 4  and the projecting portion  60 F- 5  are each 90 degrees. 
     Even in this modification, an operational advantage similar to the plating apparatus  1000  according to the embodiment described above can be provided. 
     Note that, in this modification, regarding a pair of regions adjacent to one another, an angle formed by an extending direction of a projecting portion arranged in one region and an extending direction of a projecting portion arranged in another region is not limited to 90 degrees. The angle may be smaller or larger than 90 degrees. Further, in  FIG.  13   , one projecting portion is disposed to each region divided by the plurality of virtual concentric circles but it is not limited to this configuration. Two or more projecting portions may be disposed to each region divided by the plurality of virtual concentric circles. 
     [Modification 7 of Embodiment]  FIG.  14    is a schematic bottom view of the dummy substrate Wfx of a plating apparatus  1000 G according to Modification 7 of the embodiment. The dummy substrate Wfx according to this modification is different from the dummy substrate Wfx according to the embodiment exemplified in  FIG.  6    in the respect of further including an orientation flat ORF and a notch NT. 
     Note that a transfer of the dummy substrate Wfx according to this modification may be performed in a method similar to the transfer of the substrate Wf. That is, the transfer mechanism may transfer the dummy substrate Wfx to the location of the substrate holder  30  after the aligner  120  adjusts the positions of the orientation flat ORF and the notch NT of the dummy substrate Wfx in a predetermined direction. 
     Even in this modification, an operational advantage similar to the plating apparatus  1000  according to the embodiment described above may be provided. 
     Further, the dummy substrate Wfx according to this modification may include only one of the orientation flat ORF and the notch NT. That is, the dummy substrate Wfx may have a configuration in which the orientation flat ORF is included but the notch NT is not included, or have a configuration in which the notch NT is included but the orientation flat ORF is not included. 
     Further, the dummy substrate Wfx according to Modifications 2 to 6 described above may include at least one of the orientation flat ORF and the notch NT. 
     [Modification 8 of Embodiment] In Modifications 1 to 7 described above, whether or not air bubbles exist on the lower surface of the ionically resistive element  12  may be confirmed based on an ultrasonic sound wave transmitted along the lower surface of the ionically resistive element  12  after removing the air bubbles using the dummy substrate Wfx (hereinafter referred to as an “air bubble confirming process”). Specifically, the air bubble confirming process may be performed after the step S 12  in  FIG.  7    is performed and before the step S 13  is performed. The following is a configuration of a plating apparatus  1000 H according to the modification. 
       FIG.  15    is a schematic cross-sectional view illustrating a peripheral configuration of the plating tank  10  of the plating apparatus  1000 H according to this modification. Note that, in  FIG.  15   , illustrations of the overflow tank  20  and the like are omitted. The plating apparatus  1000 H includes a transmitter  80  and a receiver  81  in an area below the ionically resistive element  12  in the outer peripheral wall  10   b  of the plating tank  10 . The transmitter  80  transmits an ultrasonic sound wave (UL) along the lower surface of the ionically resistive element  12 . 
     The receiver  81  is configured to receive an ultrasonic sound wave transmitted by the transmitter  80 . Specifically, the receiver  81  according to the modification is disposed on the outer peripheral wall  10   b  to be opposed to the transmitter  80 . The transmitter  80  and the receiver  81  are controlled by the control module  800 . 
     In the air bubble confirming process (that is, when confirming air bubbles), the transmitter  80  transmits the ultrasonic sound wave along the lower surface of the ionically resistive element  12 . The receiver  81  transmits received information regarding the ultrasonic sound wave to the control module  800 . The control module  800  determines whether or not air bubbles exist on the lower surface of the ionically resistive element  12  based on the ultrasonic sound wave received by the receiver  81 . 
     Specifically, in a case where the ultrasonic sound wave transmitted by the transmitter  80  strikes the air bubbles (air bubbles that exist on the lower surface of the ionically resistive element  12 ), compared with a case where the ultrasonic sound wave transmitted by the transmitter  80  does not strike the air bubbles and is received by the receiver  81 , a strength of the ultrasonic sound wave received by the receiver  81  tends to be weaker. Accordingly, it can be determined whether or not the air bubbles exist on the lower surface of the ionically resistive element  12  based on the strength of the ultrasonic sound wave received by the receiver  81 . 
     Therefore, the control module  800  according to the modification determines whether or not air bubbles exist on the lower surface of the ionically resistive element  12  based on whether the strength of the ultrasonic sound wave received by the receiver  81  is higher or lower than a predetermined value. 
     Although this embodiment and modifications according to the present invention have been described in detail above, the present invention is not limited to such specific embodiment and modifications, and further various kinds of variants and modifications are possible within the scope of the gist of the present invention described in the claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  . . . plating tank 
               11  . . . anode 
               12  . . . ionically resistive element 
               30  . . . substrate holder 
               31  . . . ring 
               40  . . . rotation mechanism 
               50  . . . elevating mechanism 
               60  . . . projecting portion 
               70  . . . space 
               1000  . . . plating apparatus 
             Wf . . . substrate 
             Wfx . . . dummy substrate 
             Ps . . . plating solution 
             Bu . . . air bubble 
             UL . . . ultrasonic sound wave