Patent Publication Number: US-10760172-B2

Title: Film forming method for metal film and film forming apparatus therefor

Description:
INCORPORATION BY REFERENCE 
     This is a divisional of U.S. application Ser. No. 15/597,811 filed May 17, 2017 (allowed), which claims priority to Japanese Patent Application No. 2016-102703 filed on May 23, 2016, the disclosure of which, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a film forming method of forming a metal film on the surface of a substrate, and a film forming apparatus therefor, and more particularly to a film forming apparatus for a metal film capable of forming a metal film on the surface of a substrate by applying a voltage between an anode and a substrate. 
     2. Description of Related Art 
     A technique for forming a metal film by causing a metal to deposit on the surface of a substrate has been proposed. As such a technique, for example, Japanese Patent Application Publication No. 2014-051701 (JP 2014-051701 A) proposes a film forming apparatus for a metal film including an anode, a solid electrolyte membrane disposed between the anode and a substrate which is a cathode, a power supply which applies a voltage between the anode and the substrate, and a placing table on which the substrate is placed. The film forming apparatus includes a solution accommodation portion which accommodates a metal solution containing metal ions between the anode and the solid electrolyte membrane and a pressurizing portion which pressurizes the metal solution in the solution accommodation portion. 
     According to the film forming apparatus, the solid electrolyte membrane is pressurized by the liquid pressure of the metal solution pressurized by the pressurizing portion, and the surface of the substrate is pressed by the pressurized solid electrolyte membrane. Accordingly, the solid electrolyte membrane conforms to the surface of the substrate. The metal ions contained in the solid electrolyte membrane are reduced at the surface of the substrate by applying a voltage between the anode and the substrate, thereby forming a uniform metal film on the surface of the substrate. 
     SUMMARY 
     However, in the film forming apparatus according to JP 2014-051701 A, when the substrate is pressed by the solid electrolyte membrane, the substrate is interposed between the solid electrolyte membrane and the placing table. At this time, in a case where the substrate undergoes warping or undulation, a gap may be formed between the placing table and the substrate during film formation. Due to the gap, the reaction force from the placing table is not uniformly exerted on the rear surface of the substrate when the substrate is pressed by the solid electrolyte membrane. As a result, there is a possibility that the solid electrolyte membrane may not be uniformly pressed against the surface of the substrate, and a metal film having a uniform thickness may not be formed. 
     The present disclosure provides a film forming method for a metal film and a film forming apparatus therefor capable of forming a metal film having a uniform film thickness on the surface of a substrate by uniformly pressing a solid electrolyte membrane against the surface of the substrate. 
     According to a first aspect of the present disclosure, there is provided a method for forming a metal film on a surface of a substrate by disposing a solid electrolyte membrane between an anode and the substrate which is a cathode and applying a voltage between the anode and the substrate in a state in which the solid electrolyte membrane is brought into contact with the surface of the substrate placed on a placing table so as to cause metal ions contained in the solid electrolyte membrane to be reduced and cause a metal derived from the metal ions to deposit on the surface of the substrate. 
     In the first aspect, a metal solution containing the metal ions is disposed between the anode and the solid electrolyte membrane, and the metal solution is caused to be in a state of being sealed in a first accommodation chamber of a housing with the solid electrolyte membrane so as to cause the metal solution to be disposed on the surface of the substrate via the solid electrolyte membrane. Furthermore, a fluid is caused to be in a state of being sealed in a second accommodation chamber of the placing table with a thin film so as to cause the fluid to be disposed on a rear surface of the substrate positioned on a side opposite to the surface on which a metal film is formed, via the thin film having flexibility. 
     In order to form the metal film, the substrate is caused to be interposed between the solid electrolyte membrane and the thin film by moving the placing table and the housing relative to each other in a state in which the substrate is placed on the placing table, and the solid electrolyte membrane and the thin film are pressed against the substrate interposed therebetween to cause the solid electrolyte membrane and the thin film to conform to the surface and the rear surface of the substrate, thereby forming the metal film. 
     In the first aspect, the solid electrolyte membrane and the thin film may be pressed by increasing a pressure of the metal solution in the first accommodation chamber or a pressure of the fluid in the second accommodation chamber. 
     The first aspect may include restricting relative displacement between the housing and the placing table in the state in which the substrate is interposed between the solid electrolyte membrane and the thin film, wherein the metal film may be formed while pressing the solid electrolyte membrane and the thin film in the state in which the displacement is restricted. 
     In the first aspect, a plurality of first conductor portions on which the metal film is formed may be formed on the surface of the substrate, second conductor portions electrically connected to the first conductor portions may be formed on the rear surface of the substrate or a side surface of the substrate, a thin film in which a surface on which the substrate is placed has conductivity may be used as the thin film, the thin film may be brought into contact with the second conductor portion by pressing the thin film against the rear surface of the substrate, and the metal film may be formed on the first conductor portions by applying the voltage between the thin film and the anode. 
     In the first aspect, recesses may be formed on the rear surface of the substrate, and the second conductor portions may be formed at bottom surfaces of the recesses. 
     According to a second aspect of the present disclosure, there is provided a film forming apparatus for a metal film, which includes: an anode; a solid electrolyte membrane which is disposed between the anode and a substrate which is a cathode, and contains metal ions; a power supply which applies a voltage between the anode and the substrate; and a placing table on which the substrate is placed, in which by causing a metal derived from the metal ions to deposit on a surface of the substrate which is in contact with the solid electrolyte membrane, a metal film is formed on the surface of the substrate. 
     The film forming apparatus further includes a housing having a first accommodation chamber which accommodates a metal solution containing metal ions, the metal solution is disposed between the anode and the solid electrolyte membrane, the metal solution is sealed in the first accommodation chamber with the solid electrolyte membrane so as to cause the metal solution to be disposed on the surface of the substrate via the solid electrolyte membrane, a second accommodation chamber which accommodates a fluid is formed in the placing table, and the fluid is sealed in the second accommodation chamber with a thin film so as to cause the fluid to be disposed on a rear surface of the substrate positioned on a side opposite to the surface on which the metal film is formed, via the thin film having flexibility. 
     At least one of the housing and the placing table is movable to cause the substrate to be interposed between the solid electrolyte membrane and the thin film, and the film forming apparatus further includes a pressing portion which presses the solid electrolyte membrane and the thin film against the substrate in a state of being interposed between the solid electrolyte membrane and the thin film. 
     In the second aspect, the pressing portion may be a pump which pressurizes the metal solution in the first accommodation chamber or a pump which pressurizes the fluid in the second accommodation chamber. 
     The second aspect may include a restricting section which restricts relative displacement between the housing and the placing table in the state in which the substrate is interposed between the solid electrolyte membrane and the thin film. 
     In the second aspect, the thin film may be a thin film in which a surface on which the substrate is placed has conductivity. 
     According to the film forming method and the film forming apparatus according to the present disclosure, when the metal film is formed, the solid electrolyte membrane and the thin film conform to the surface and the rear surface of the substrate, the surface of the substrate is uniformly pressurized by the metal solution via the solid electrolyte membrane, and the rear surface of the substrate is uniformly pressurized by the fluid via the thin film. In this state, by applying a voltage between the anode and the substrate, the metal ions contained in the solid electrolyte membrane are reduced, the metal derived from the metal ions is deposited on the surface of the substrate, and a metal film having a uniform film thickness can be formed on the surface of the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1A  is a schematic sectional view of a film forming apparatus for a metal film according to a first embodiment; 
         FIG. 1B  is a view for explaining film formation of a metal film on a surface of a substrate using the film forming apparatus illustrated in  FIG. 1A ; 
         FIG. 2A  is a schematic sectional view of a film forming apparatus for a metal film according to a second embodiment; 
         FIG. 2B  is a view for explaining film formation of a metal film on the surface of the substrate using the film forming apparatus illustrated in  FIG. 2A ; 
         FIG. 3A  is a schematic sectional view of a film forming apparatus for a metal film according to a third embodiment; 
         FIG. 3B  is a view for explaining film formation of a metal film on the surface of the substrate using the film forming apparatus illustrated in  FIG. 3A ; 
         FIG. 4A  is a schematic sectional view of a film forming apparatus for a metal film according to a fourth embodiment; 
         FIG. 4B  is a schematic sectional view of a substrate formed in the fourth embodiment; 
         FIG. 4C  is a view for explaining film formation of a metal film on a surface of the substrate using the film forming apparatus illustrated in  FIG. 4A ; 
         FIG. 4D  is a partial enlarged view of the vicinity of the surface and a rear surface of the substrate illustrated in  FIG. 4C  during the film formation of the metal film; and 
         FIG. 4E  is a partial enlarged view of the vicinity of a side surface of the substrate during the film formation of the metal film according to a modification example corresponding to  FIG. 4D . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to  FIGS. 1A to 4E . 
     1. Film Forming Apparatus  1 A 
       FIG. 1A  is a schematic sectional view of a film forming apparatus  1 A for a metal film according to a first embodiment of the present disclosure. The film forming apparatus  1 A according to this embodiment is an apparatus that causes metal ions to be reduced so that a metal is deposited and a metal film from the deposited metal is formed on the surface of a substrate B. 
     The substrate B is not particularly limited as long as the surface on which the film is formed functions as a cathode (that is, a surface having conductivity). In this embodiment, the substrate B is a metal plate made of aluminum, iron, or the like. Alternatively, the substrate B may be a substrate in which the entirety or a part of the surface made of a polymer resin such as an epoxy resin or ceramics is coated with a metal layer made of copper, nickel, silver, iron, or the like, and the metal layer functions as a cathode. 
     The film forming apparatus  1 A includes a anode  11  made of a metal, a solid electrolyte membrane  13  disposed between the anode  11  and the substrate B (cathode), a power supply  16  which applies a voltage between the anode  11  and the substrate B, and a placing table  40  on which the substrate B is placed. 
     The anode  11  may be in the form of a block or a flat plate or may be made of a porous body or a mesh (mesh-like member) as long as the anode  11  has a size that covers a region where the substrate B is formed. The material of the anode  11  is the same as the material of a metal film to be formed, and is preferably an anode which is soluble in a metal solution L containing metal ions, which will be described later. Accordingly, the deposition rate of the metal film can be increased. For example, in a case where the metal film is a copper film, it is preferable to use an oxygen-free copper plate as the material of the anode  11 . Since the metal solution L before film formation contains metal ions, the anode  11  may also be an anode which is insoluble in the metal solution L. 
     The solid electrolyte membrane  13  can be impregnated with (contain) the metal ions by being brought into contact with the metal solution L and is not particularly limited as long as the metal ions are reduced at the surface of the substrate B and a metal derived from the metal ions are deposited when a voltage is applied. In this embodiment, the solid electrolyte membrane  13  has flexibility and has a film thickness and a hardness to conform to a surface Ba of the substrate B when pressed during film formation. 
     The film thickness of the solid electrolyte membrane  13  is preferably 100 to 200 μm. Examples of the material of the solid electrolyte membrane include a fluorine-based resin such as NAFION (registered trademark) manufactured by DuPont, a hydrocarbon-based resin, a polyamic acid resin, and a resin having a cation-exchange function such as SELEMION (CMV, CMD, and CMF series) manufactured by Asahi Glass Co., Ltd. 
     The metal solution L is a liquid (electrolyte solution) containing the metal of the metal film to be formed in the state of ions as described above. As the metal, for example, at least one or two or more selected from the group consisting of nickel, zinc, copper, chromium, tin, silver, and lead may be used. The metal solution L is an aqueous solution obtained by dissolving (ionizing) the metal with an acid such as nitric acid, phosphoric acid, succinic acid, nickel sulfate, or pyrophosphoric acid. 
     In this embodiment, the film forming apparatus  1 A further includes a housing  20 . In the housing  20 , the metal solution L is disposed between the anode  11  and the solid electrolyte membrane  13 , and a first accommodation chamber  21  which accommodates the metal solution L to cause the metal solution L to be disposed on the surface Ba of the substrate B via the metal solution L during film formation is formed. 
     In the first accommodation chamber  21 , the anode  11  is disposed at a position opposing the solid electrolyte membrane  13 , and the metal solution L accommodated in the first accommodation chamber  21  is in contact with the solid electrolyte membrane  13  and the anode  11 . In the first accommodation chamber  21 , a first opening  22  which has a size greater than that of the surface Ba of the substrate B on a side where the metal film is to be formed is formed. In the first accommodation chamber  21 , the first opening  22  is covered with the solid electrolyte membrane  13  in the state in which the metal solution L is accommodated between the anode  11  and the solid electrolyte membrane  13 , and the metal solution L is sealed in the first accommodation chamber  21  in a flowing state. 
     As described above, in this embodiment, during film formation, the metal solution L is disposed on the surface Ba of the substrate B via the solid electrolyte membrane  13 , and the solid electrolyte membrane  13  conforms to the surface Ba of the substrate B by the liquid pressure of the metal solution L. As the material of the housing  20 , a metal material such as aluminum or stainless steel or the like may be employed, and the material thereof is not particularly limited as long as the housing  20  is not excessively deformed (rigid body) by a pressing portion  30 A. 
     In this embodiment, the film forming apparatus  1 A is provided with the placing table  40  made of a metal, on which the substrate B is placed. The material of the placing table  40  is a metal material such as aluminum or stainless steel. However, the material thereof is not particularly limited as long as the placing table  40  is not excessively deformed (rigid body) by the pressing portion  30 A. 
     In the placing table  40 , a second accommodation chamber  41  which accommodates a fluid  45  to cause the fluid  45  to be disposed on the rear surface Bb of the substrate B positioned on the side opposite to the surface Ba on which the metal film is formed via a thin film  43  is formed. Specifically, in the second accommodation chamber  41 , a second opening  42  which has a size greater than that of the rear surface Bb of the substrate B is formed. By covering the second opening  42  with the thin film  43  (film) the fluid  45  is sealed in the second accommodation chamber  41  in a flowing state. 
     Here, the fluid  45  is a material having fluidity, for example, a gas, a liquid, or a gel, and is not particularly limited as long as the material has a property of being cushioned from the substrate B when coming into contact with the substrate B via the thin film  43 . For example, the gas includes air and an inert gas such as nitrogen gas. The liquid includes water and an oil. The gel includes a polymer gel such as polystyrene. 
     In this embodiment, the material of the thin film  43  includes a resin, a metal, or a laminate of these materials in a layer form, and the thin film  43  has flexibility. In this embodiment, the material and the thickness of the thin film  43  are not limited as long as the thin film  43  conforms to the rear surface Bb of the substrate B when pressed during film formation and the strength thereof is secured when pressed. The film thickness of the thin film  43  is preferably in a range of 0.1 to 10 μm. 
     The negative electrode of the power supply  16  is connected to the substrate B, and the positive electrode of the power supply  16  is connected to the anode  11 . In a case where a metal layer is formed as the cathode on a part of the surface Ba of the substrate B, the metal layer is electrically connected to the negative electrode of the power supply  16 , for example, via a conductor jig (not illustrated). 
     In this embodiment, the film forming apparatus  1 A further includes the pressing portion  30 A above the housing  20 . In this embodiment, the housing  20  is movable (can be raised or lowered) by the pressing portion  30 A so that the substrate B can be interposed between the solid electrolyte membrane  13  and the thin film  43 . In this embodiment, the pressing portion  30 A has (1) a function of moving (raising or lowering) the housing  20  with respect to the placing table  40  to cause the substrate B to be interposed between the solid electrolyte membrane  13  and the thin film  43 , and (2) a function of pressing the solid electrolyte membrane  13  and the thin film  43  against the substrate B interposed between the solid electrolyte membrane  13  and the thin film  43 . 
     In this embodiment, the housing  20  is movable with respect to the fixed placing table  40  by the pressing portion  30 A. However, for example, by providing a pressing portion for the placing table  40 , the placing table  40  can be moved with respect to the housing  20  while the housing  20  is fixed. 
     The pressing portion  30 A is not particularly limited as long as the pressing portion  30 A has the functions described in (1) and (2), and for example, a hydraulic or pneumatic cylinder may be employed. Otherwise, the pressing portion  30 A may be a motor with a linear guide or the like. As described above, while causing the substrate B to be interposed between the solid electrolyte membrane  13  and the thin film  43  and pressing the substrate B against the solid electrolyte membrane  13  and the thin film  43  using the pressing portion  30 A, a metal film can be formed. 
     2. Film Forming Method using Film Forming Apparatus  1 A 
     Hereinafter, a film forming method using the film forming apparatus  1 A according to this embodiment will be described.  FIG. 1B  is a view for explaining film formation of a metal film F on the surface Ba of the substrate B using the film forming apparatus  1 A illustrated in  FIG. 1A . 
     First, as illustrated in  FIG. 1A , the substrate B is disposed on the placing table  40  so that the surface Ba on which a metal film is to be formed faces the solid electrolyte membrane  13 . Specifically, the substrate B is placed on the thin film  43  of the placing table  40   43  so that the entirety of the rear surface Bb of the substrate B is disposed on the fluid  45  accommodated in the second accommodation chamber  41  of the placing table  40  via the thin film  43 . 
     As described above, the metal solution L is sealed in the first accommodation chamber  21  of the housing  20  with the solid electrolyte membrane  13  so that the metal solution L is disposed between the anode  11  and the solid electrolyte membrane  13 . Furthermore, the fluid  45  is sealed in the second accommodation chamber  41  of the placing table  40  with the thin film  43  so that the fluid  45  is disposed on the rear surface Bb of the substrate B via the thin film  43 . A metal film is formed on the surface Ba of the substrate B by using the housing  20  and the placing table  40  described above. 
     Specifically, as illustrated in  FIG. 1B , in a state where the substrate B is placed on the placing table  40 , the placing table  40  and the housing  20  are moved relative to each other so that the substrate B is interposed between the solid electrolyte membrane  13  and the thin film  43 . Specifically, the housing  20  is lowered toward the placing table  40  by the pressing portion  30 A to cause the metal solution L to be disposed on the surface Ba of the substrate B via the solid electrolyte membrane  13 . More specifically, the part of the solid electrolyte membrane  13  positioned in the first opening  22  formed in the first accommodation chamber  21  is brought into contact with the surface Ba of the substrate B. 
     Furthermore, by pressurizing the substrate B from the solid electrolyte membrane  13  side by the pressing portion  30 A, the solid electrolyte membrane  13  and the thin film  43  are pressed against the substrate B in the state of being interposed between the solid electrolyte membrane  13  and the thin film  43 . Accordingly, the solid electrolyte membrane  13  and the thin film  43  can conform to the surface Ba and the rear surface Bb of the substrate B. Here, if a pressure gauge (not illustrated) for measuring the pressure of the metal solution L is provided in the first accommodation chamber  21 , the substrate B can be pressed at a predetermined pressure while checking the measured pressure. 
     In this state, a voltage is applied between the anode  11  and the substrate B by the power supply  16  to reduce the metal ions contained in the solid electrolyte membrane  13 , thereby causing a metal derived from the metal ions to deposit on the surface Ba of the substrate B. Accordingly, the metal film F is formed on the surface Ba of the substrate B. 
     As described above, when the metal film F is formed, the solid electrolyte membrane  13  and the thin film  43  conform to the surface Ba and the rear surface Bb of the substrate B, the surface Ba of the substrate B is uniformly pressurized by the metal solution L via the solid electrolyte membrane  13 , and the rear surface Bb of the substrate B is uniformly pressurized by the fluid  45  via the thin film  43 . Accordingly, the solid electrolyte membrane  13  and the thin film  43  can be uniformly pressed against the substrate B without forming a gap from the surface Ba and the rear surface Bb of the substrate B. In this state, by applying a voltage between the anode  11  and the substrate B, the metal ions contained in the solid electrolyte membrane  13  are reduced, the metal derived from the metal ions is deposited on the surface Ba of the substrate B, and the metal film F having a uniform film thickness can be formed on the surface Ba of the substrate B. 
     Second Embodiment 
       FIG. 2A  is a schematic sectional view of a film forming apparatus  1 B for a metal film according to a second embodiment of the present disclosure. The film forming apparatus  1 B according to the second embodiment is different from the first embodiment in the configuration of the pressing portion. Therefore, in the second embodiment, like configurations similar to those of the film forming apparatus  1 A of the first embodiment are denoted by like reference numerals, and the detailed description thereof will be omitted. 
     In this embodiment, instead of the pressing portion  30 A described in the first embodiment, an elevating device  31  which raises and lowers the housing  20  is mounted. The elevating device  31  includes a guide  31   a  which is connected to the housing  20 , and a roller  31   b  which is engaged with the guide  31   a  and is rotated to linearly move the guide  31   a . In this embodiment, the solid electrolyte membrane  13  is not pressed against the surface Ba of the substrate B by using the elevating device  31 . 
     In this embodiment, in the housing  20 , a supply passage  26  through which the metal solution L is supplied to the first accommodation chamber  21  and a discharge passage  27  through which the metal solution L is discharged from the first accommodation chamber  21  are formed. A pump  30 B corresponding to the pressing portion is connected to the supply passage  26  to pressurize the metal solution L in the first accommodation chamber  21 , and a pressure regulating valve  33  which regulates the pressure of the metal solution L in the first accommodation chamber  21  is connected to the discharge passage  27 . 
     In this embodiment, by driving the pump  30 B, the metal solution L is pumped to the first accommodation chamber  21  through the supply passage  26  such that the pressure of the metal solution L in the first accommodation chamber  21  can be increased to a pressure set by the pressure regulating valve  33 . The metal solution L in the first accommodation chamber  21  is discharged from the pressure regulating valve  33  so as not to exceed the set pressure, and the discharged metal solution L is supplied to the pump  30 B such that the metal solution L is circulated through the film forming apparatus  1 B. 
     Hereinafter, a film forming method using the film forming apparatus  1 B according to this embodiment will be described.  FIG. 2B  is a view for explaining film formation of the metal film F on the surface Ba of the substrate B using the film forming apparatus  1 B illustrated in  FIG. 2A . First, as in the first embodiment, the substrate B is placed on the placing table  40 . Next, the housing  20  is lowered (moved) with respect to the placing table  40  by using the elevating device  31  to cause the substrate B to be interposed between the solid electrolyte membrane  13  and the thin film  43 . In this state, by stopping the rotation of the roller  31   b , the position of the guide  31   a  is fixed and the position of the housing  20  with respect to the placing table  40  is fixed. 
     Next, in the fixed state, the pump  30 B is driven. Accordingly, the pressure of the metal solution L in the first accommodation chamber  21  increases such that a pressing force to press the solid electrolyte membrane  13  against the surface Ba of the substrate B is generated. Accordingly, on the rear surface Bb side of the substrate B, the reaction force due to the pressing force acts as a pressing force to press the thin film  43  against the rear surface Bb of the substrate B. As described above, by pressing the solid electrolyte membrane  13  and the thin film  43  against the substrate B, the solid electrolyte membrane  13  and the thin film  43  are caused to conform to the surface Ba and the rear surface Bb of the substrate B and the metal film F can be formed. In this embodiment, since the pressing of the solid electrolyte membrane  13  and the thin film  43  is adjusted by the liquid pressure of the metal solution L in the first accommodation chamber  21 , the surface Ba and the rear surface Bb of the substrate B can be simply pressed at a desired pressure. 
     In addition, in this embodiment, the pump  30 B for pressurizing the metal solution L in the first accommodation chamber  21  is provided, and the solid electrolyte membrane  13  and the thin film  43  are pressed by increasing the pressure of the metal solution L in the first accommodation chamber  21  by the pump  30 B. Alternatively, for example, a pump for pressurizing the fluid  45  in the second accommodation chamber  41  is provided, and the solid electrolyte membrane  13  and the thin film  43  may be pressed by increasing the pressure of the fluid  45  in the second accommodation chamber  41  by the pump. Furthermore, the pressure of the metal solution L or the fluid  45  may be increased by connecting the above-described pump to both the first accommodation chamber  21  and the second accommodation chamber  41 . 
     Third Embodiment 
       FIG. 3A  is a schematic sectional view of a film forming apparatus  1 C for a metal film according to a third embodiment of the present disclosure. The film forming apparatus  1 C according to the third embodiment is different from the second embodiment in that a restricting section  50  is newly provided instead of the elevating device  31 . Therefore, in the third embodiment, like configurations similar to those of the film forming apparatus  1 B of the second embodiment are denoted by like reference numerals, and the detailed description thereof will be omitted. 
     In this embodiment, the restricting section  50  which restricts relative displacement between the housing  20  and the placing table  40  in the state in which the substrate B is interposed between the solid electrolyte membrane  13  and the thin film  43  is further provided. Specifically, the restricting section  50  is constituted by female threaded portions  51 A and  51 B attached to the side surfaces of the housing  20  and the placing table  40 , and male threaded portions  52  screwed to the female threaded portions  51 A and  51 B. The restricting section  50  can restrict the relative displacement between the housing  20  and the placing table  40  by fastening the male threaded portions  52  to the female threaded portions  51 A and  51 B. 
     Hereinafter, a film forming method using the film forming apparatus  1 C according to this embodiment will be described.  FIG. 3B  is a view for explaining film formation of the metal film F on the surface Ba of the substrate B using the film forming apparatus  1 C illustrated in  FIG. 3A . First, as in the second embodiment, the substrate B is placed on the placing table  40 . Next, the housing  20  is moved (lowered) toward the placing table  40  to cause the substrate B to be interposed between the solid electrolyte membrane  13  and the thin film  43 . 
     By fastening the male threaded portions  52  to the female threaded portions  51 A and  51 B in the state in which the substrate B is interposed between the solid electrolyte membrane  13  and the thin film  43 , the relative displacement between the housing  20  and the placing table  40  is restricted by the restricting section  50 , and the pump  30 B is driven in this state. 
     Accordingly, the pressure of the metal solution L in the first accommodation chamber  21  increases such that a pressing force to press the solid electrolyte membrane  13  against the surface Ba of the substrate B is generated. Accordingly, on the rear surface Bb side of the substrate B, the reaction force due to the pressing force acts as a pressing force to press the thin film  43  against the rear surface Bb of the substrate B. Since the relative displacement between the housing  20  and the placing table  40  is restricted by the restricting section  50 , the housing  20  is not pushed back by the reaction force, and thus the solid electrolyte membrane  13  and the thin film  43  can be uniformly pressed against the substrate B by the liquid pressure of the metal solution L. Accordingly, the solid electrolyte membrane  13  and the thin film  43  are caused to uniformly conform to the surface Ba and the rear surface Bb of the substrate B and the metal film F can be formed. 
     Furthermore, in this embodiment, unlike the first and second embodiments, the metal film can be formed without the use of the pressing portion  30 A and the elevating device  31  formed of a cylinder, and a compact size can be achieved by the film forming apparatus  1 C. 
     Fourth Embodiment 
       FIG. 4A  is a schematic sectional view of a film forming apparatus  1 D for a metal film according to a fourth embodiment of the present disclosure.  FIG. 4B  is a schematic sectional view of a substrate C formed in the fourth embodiment. In the fourth embodiment, the substrate to be formed is different from that of the third embodiment, and the material of the thin film is different. Therefore, in the fourth embodiment, like configurations similar to those of the film forming apparatus  1 C of the third embodiment are denoted by like reference numerals, and the detailed description thereof will be omitted. 
     As illustrated in  FIG. 4B , the substrate C according to this embodiment is a build-up substrate in which an insulating material and a conductor material are laminated, a plurality of first conductor portions c 1  on which a metal film is to be formed are formed separately from each other on a surface Ca of the substrate C which is made of an insulating resin. Furthermore, second conductor portions c 2  which are electrically connected to the respective first conductor portions c 1  through inner conductors ci of the substrate C are formed on a rear surface Cb of the substrate C which is made of an insulating resin. Specifically, recesses cf are formed on the surface Ca and the rear surface Cb of the substrate C, and the first conductor portions c 1  and the second conductor portions c 2  are formed at the bottom surfaces of the recesses cf. 
     Furthermore, in the film forming apparatus  1 D according to this embodiment, the thin film  43  is a thin film made of a metal such as aluminum. The thin film  43  is connected to the negative electrode of the power supply  16  via the placing table  40  made of a metal. In addition, in this embodiment, since the thin film  43  is a thin film made of a metal, it is preferable that the fluid  45  is a liquid or a gel having conductivity. Accordingly, during film formation, current from the power supply  16  can be caused to uniformly flow through the thin film  43  via the fluid  45 . 
     Hereinafter, a film forming method using the film forming apparatus  1 D according to this embodiment will be described.  FIG. 4C  is a view for explaining film formation of a metal film on the surface Ca of the substrate C using the film forming apparatus  1 D illustrated in  FIG. 4A , and  FIG. 4D  is a partial enlarged view of the vicinity of the surface Ca and the rear surface Cb of the substrate C illustrated in  FIG. 4C  during the film formation of the metal film. 
     First, as in the third embodiment, the substrate C is placed on the placing table  40 . Next, the housing  20  is moved toward the placing table  40  to cause the substrate C to be interposed between the solid electrolyte membrane  13  and the thin film  43 . 
     In the state in which the substrate C is interposed between the solid electrolyte membrane  13  and the thin film  43 , the relative displacement between the housing  20  and the placing table  40  is restricted by the restricting section  50 . In this state, the pump  30 B is driven. Accordingly, the pressure of the metal solution L in the first accommodation chamber  21  increases such that a pressing force to press the solid electrolyte membrane  13  against the surface Ca of the substrate C is generated. Accordingly, on the rear surface Cb side of the substrate C, the reaction force due to the pressing force acts as a pressing force to press the thin film  43  against the rear surface Cb of the substrate C. 
     As described above, as illustrated in  FIG. 4D , the solid electrolyte membrane  13  conforms to the surface Ca on which the recesses cf are formed and comes into contact with the first conductor portions c 1 . On the other hand, the thin film  43  conforms to the rear surface Cb on which the recesses cf are formed and comes into contact with the second conductor portions c 2 . The thin film  43  is a thin film made of a metal, and the second conductor portions c 2  that come into contact with the thin film  43  are electrically connected to the first conductor portions c 1  through the inner conductors ci. 
     Here, the plurality of first conductor portions c 1  of the substrate C are disposed separately from each other on the surface Ca of the substrate C, and each of the first conductor portions c 1  is positioned at the bottom surface of the recess cf formed on the surface Ca. Therefore, it is difficult to directly connect the negative electrode of the power supply  16  to each of the first conductor portions c 1  by using a conductor jig or the like. However, according to this embodiment, without the use of the conductor jig, by causing the thin film  43  to conform to the rear surface Cb on which the recesses cf are formed, the negative electrode of the power supply  16  can simply be electrically connected to the plurality of first conductor portions c 1  from the rear surface Cb side of the substrate C. Therefore, the metal film can be simply formed on the first conductor portions c 1  of the substrate C. Particularly, as in this embodiment, even if the second conductor portions c 2  are formed at the bottom surfaces of the recesses cf formed on the rear surface Cb of the substrate C, by causing the thin film  43  to conform to the rear surface Cb, the thin film  43  can be simply brought into contact with the second conductor portions c 2 . 
     In this embodiment, the thin film  43  is a metal thin film. However, for example, if the surface on which the substrate C is placed is a thin film having conductivity, by bringing the thin film  43  into contact with the first conductor portions c 1 , the negative electrode of the power supply  16  can be electrically connected to the first conductor portions c 1  via the thin film  43 . Therefore, the thin film  43  may be a thin film in which a resin layer and a metal layer are laminated as long as the surface on which the substrate C is placed has conductivity. For example, the thin film  43  may be a thin film in which a filler having conductivity is contained in a resin. 
     Furthermore, in the substrate C of this embodiment, the second conductor portions c 2  electrically connected to the first conductor portions c 1  through the inner conductors ci are formed on the rear surface Cb of the substrate C. However, for example, as illustrated in  FIG. 4E  the second conductor portion c 2  which are electrically connected to the first conductor portions c 1  through the inner conductors ci may be formed on a side surface Cd of the substrate C. Even in this case, when the second conductor portions c 2  are brought into contact with the thin film  43  by causing the thin film  43  to conform to the rear surface Cb of the substrate C and a part of the side surface Cd thereof during pressing, the negative electrode of the power supply  16  can simply to electrically connected to the plurality of first conductor portions c 1  from the side surface side of the substrate C. 
     The present disclosure will be described with reference to the following examples. [Example 1] A metal film was formed using the film forming apparatus  1 D illustrated in  FIG. 4A  described above. First, as the substrate, a glass epoxy substrate in which glass fibers are impregnated with an epoxy resin was prepared. The dimensions of the glass epoxy substrate were 40 mm×50 mm×0.8 mm. A resist having a thickness of 20 μm was formed on the surface of the substrate, and 16 copper lands (first conductor portions) having a diameter of 0.6 mm were formed on the surface exposed from the resist. Specifically, the copper lands are formed at the bottom surfaces of the recesses on the surface of the substrate formed by the resist. Furthermore, as illustrated in  FIG. 4B , a plurality of recesses are formed on the rear surface of the substrate made of the glass epoxy resin, and second conductor portions which are electrically connected to the respective copper lands are formed at the bottom surfaces of the recesses. 
     Next, as the metal solution, a 1.0 mol/L copper sulfate aqueous solution was prepared and accommodated in a first accommodation chamber. A mesh made of oxygen-free copper was used as the anode, and a fluororesin-based solid electrolyte membrane (NAFION N117 (registered trademark) manufactured by DuPont) having a film thickness of 50 μm was used as the solid electrolyte membrane. A polystyrene gel (modulus of elasticity: about 5 MPa) was used as the fluid accommodated in the second accommodation chamber of the placing table, and an aluminum thin film was used as the thin film. 
     By driving the pump in a state in which the substrate was interposed between the solid electrolyte membrane and the thin film, the pressure inside the first accommodation chamber was set to 1.0 MPa. Accordingly, while the solid electrolyte membrane was pressed against the surface of the substrate at 1.0 MPa, a voltage was applied between the anode and the placing table for 40 minutes to reach a current density of 50 mA/cm 2 , and a copper film was formed on the surface of the copper land of the substrate. 
     Comparative Example 1 
     In the same manner as in Example 1, a copper film was formed on the substrate. 
     The difference from Example 1 is that the anode in the first accommodation chamber is brought into contact with the solid electrolyte membrane by using the film forming apparatus  1 A illustrated in  FIG. 1A  to cause the anode to be pressed (pressurized) against the substrate via the solid electrolyte membrane, and a titanium plate was disposed in the second accommodation chamber of the placing table of the film forming apparatus without providing a thin film. 
     Comparative Example 2 
     In the same manner as in Example 1, a copper film was formed on the substrate. The difference from Example 1 is that the anode in the first accommodation chamber is brought into contact with the solid electrolyte membrane by using the film forming apparatus  1 A illustrated in  FIG. 1A  to cause the anode to be pressed (pressurized) against the substrate via the solid electrolyte membrane. 
     Comparative Example 3 
     In the same manner as in Example 1, a copper film was formed on the substrate. The difference from Example 1 is that a titanium plate was disposed in the second accommodation chamber of the placing table of the film forming apparatus without providing a thin film. 
     Comparative Example 4 
     In the same manner as in Example 1, a copper film was formed on the substrate. The difference from Example 1 is that a conductive silicone rubber was disposed in the second accommodation chamber of the placing table of the film forming apparatus without providing a thin film. 
     Reference Examples 1 and 2 
     In the same manner as in Example 1, a copper film was formed on the substrate. The difference from Example 1 is that the liquid pressure of the metal solution was set to 0.1 MPa and 0.5 MPa during film formation by adjusting the set pressure of the pressure regulating valve. 
     The film forming conditions of Example 1, Comparative Examples 1 to 4, and Reference Examples 1 and 2 and the number of copper lands on which a copper film was formed are shown in Table 1 below. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Second 
                   
               
               
                   
                 Pressurization 
                 Pressurizing 
                 accommodation 
                 Number 
               
               
                   
                 type 
                 force (MPa) 
                 chamber 
                 (pieces) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 1 
                 Liquid pressure 
                 1.0 
                 Gel + thin film 
                 16 
               
               
                 Comparative 
                 Anode 
                 1.0 
                 Titanium plate 
                 0 
               
               
                 Example 1 
                 pressurization 
               
               
                 Comparative 
                 Anode 
                 1.0 
                 Gel + thin film 
                 0 
               
               
                 Example 2 
                 pressurization 
               
               
                 Comparative 
                 Liquid pressure 
                 1.0 
                 Titanium plate 
                 0 
               
               
                 Example 3 
               
               
                 Comparative 
                 Liquid pressure 
                 1.0 
                 Rubber 
                 14 
               
               
                 Example 4 
               
               
                 Reference 
                 Liquid pressure 
                 0.1 
                 Gel + thin film 
                 8 
               
               
                 Example 1 
               
               
                 Reference 
                 Liquid pressure 
                 0.5 
                 Gel + thin film 
                 14 
               
               
                 Example 2 
               
               
                   
               
            
           
         
       
     
     &lt;Results and Discussion&gt; 
     In Example 1, a copper film was formed on all the copper lands. However, in Comparative Examples 1 to 3, no copper film was formed on the copper lands, and in Comparative Example 4 and Reference Examples 1 and 2, the copper lands with no copper film formed thereon were present. 
     In Example 1, it is thought that during film formation, by causing the solid electrolyte membrane to conform to the surface of the substrate by the liquid pressure generated on the first accommodation chamber side, the solid electrolyte membrane was in contact with all the first conductor portions of the substrate. In addition to this, it is thought that on the rear surface side of the substrate, the gel in the second accommodation chamber had deformed (flowed) due to the reaction force of the liquid pressure on the first accommodation chamber side such that the thin film conformed to the rear surface of the substrate and the thin film was in contact with all the second conductor portions of the substrate. Accordingly, it is thought that the copper film was formed on all the copper lands in Example 1. 
     On the other hand, it is thought that in Comparative Examples 1 and 2, since the solid electrolyte membrane pressed the surface of the substrate by the pressure from the anode in contact with the solid electrolyte membrane during film formation, the solid electrolyte membrane did not conform to the surface of the substrate and the solid electrolyte membrane was not in contact with all the first conductor portions of the substrate. Accordingly, it is thought that no copper film was formed on all the copper lands in Comparative Examples 1 and 2. 
     Furthermore, it is thought that in Comparative Example 3, since the titanium plate was not deformed by the reaction force of the liquid pressure on the first accommodation chamber side on the rear surface side of the substrate, the thin film did not conform to the rear surface of the substrate and the thin film was not in contact with the second conductor portions of the substrate. Accordingly, it is thought that no copper film was formed on all the copper lands in Comparative Example 3. 
     In Comparative Example 4, although the silicone rubber was deformed by the reaction force of the liquid pressure on the first accommodation chamber side on the rear surface side of the substrate, the silicone rubber is not a fluid, the silicone rubber is less likely to deform than the polystyrene gel. Accordingly, it is thought that the thin film did not perfectly conform to the rear surface of the substrate and the thin film was not in contact with a part of the second conductor portions of the substrate. Accordingly, it is thought that in Comparative Example 4, a copper film was not formed on a part of the copper lands. 
     In Reference Examples 1 and 2, it is thought that since the liquid pressure of the metal solution was low, on the rear surface side of the substrate, the flow of the gel in the second accommodation chamber was insufficient due to the reaction force of the liquid pressure on the first accommodation chamber side, the thin film did not perfectly conform to the rear surface of the substrate, and the thin film was not in contact with a part of the second conductor portions of the substrate. Accordingly, it is thought that in Reference Examples 1 and 2, a copper film was not formed on a part of the copper lands. 
     While the embodiments of the present disclosure have been described above in detail, the present disclosure is not limited to the above-described embodiments, and various changes in design may be made without departing from the spirit of the present disclosure described in the appended claims.