Metal film deposition equipment

Abstract

To provide a metal film deposition device which can uniformly deposit the metal film and can be downsized.SOLUTION: A metal film deposition device comprises an anode composed of an insoluble porous material, an electrolyte membrane arranged between the anode and a substrate serving as a cathode, and a housing having a storage chamber which is arranged between the anode and the electrolyte membrane and stores a plating solution containing metal ions. The device reduces the metal ions impregnated into the electrolyte membrane to deposit the metal film on the substrate by applying a voltage to the substrate while pressing the substrate with the electrolyte membrane. The device further comprises a diaphragm which covers the cathode side of the anode and is attached so as to be in contact with the cathode side of the anode. The diaphragm allows water and hydrogen ions to pass through and does not allow an oxygen gas to pass through. The anode is attached in a manner closing an opening on the side opposite to the cathode side of the storage housing so that the cathode side is exposed to the storage chamber through the diaphragm and the side opposite to the cathode side is exposed to the outside of the storage housing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal film forming apparatus, and more particularly to a metal film forming apparatus capable of forming a metal film on the surface of a substrate. [Background technology]

[0002] Conventionally, a film formation technique has been known in which a metal coating is formed on the surface of a substrate by reducing metal ions contained in a plating solution to precipitate a metal derived from the metal ions. In recent years, in such a film formation technique, a film formation device has been used that includes an anode, an electrolyte membrane disposed between a substrate serving as the anode and a cathode, a power supply device that applies a voltage between the anode and the substrate (cathode), a housing having a chamber for accommodating a plating solution containing metal ions between the anode and the electrolyte membrane, and a pressure device that pressurizes the plating solution. The voltage is applied between the anode and the substrate while the electrolyte membrane is pressed against the surface of the substrate by the hydraulic pressure of the plating solution, thereby reducing the metal ions contained in the electrolyte membrane, thereby forming a metal coating on the surface of the substrate.

[0003] Among these film-forming devices, those for forming metal films using an insoluble anode as the anode have attracted attention. However, in film-forming devices using an insoluble anode, water in the plating solution is electrolyzed on the surface of the anode in the chamber, generating oxygen gas. As the film-forming time passes, the amount of oxygen gas generated increases, causing the oxygen gas to aggregate and accumulate on the surface of the anode. When the electrolyte membrane presses against the surface of the substrate using the hydraulic pressure of the plating solution during the formation of the metal film as described above, if oxygen gas remains in the chamber, it may become difficult for the electrolyte membrane to press against the surface of the substrate uniformly because the oxygen gas is more compressible than the plating solution. As a result, it may become difficult to form a uniform metal film.

[0004] To address these problems, for example, a film formation apparatus described in Patent Document 1 has been proposed. In the film formation apparatus described in Patent Document 1, a housing is provided with a first storage chamber on the anode side, which stores a first electrolytic solution, and a second storage chamber on the electrolyte membrane side, which stores a second electrolytic solution (plating solution) containing metal ions. A partition member separating the storage chambers is disposed between the anode and the electrolyte membrane. The partition member is a porous diaphragm impregnated with a cation exchange resin. The first storage chamber stores an anode that is insoluble in the first electrolytic solution. The electrolyte membrane and the partition member form a sealed space in the second storage chamber, in which the second electrolytic solution is sealed. Therefore, even if water contained in the first electrolytic solution is electrolyzed on the surface of the anode in the first storage chamber during film formation, generating oxygen gas, the oxygen gas from the anode does not mix with the second electrolytic solution (plating solution) in the second storage chamber. Therefore, the second electrolytic solution can be pressurized without leaving oxygen gas in the second storage chamber. This allows the electrolyte membrane, acting under the liquid pressure of the second electrolytic solution, to press uniformly against the surface of the substrate, thereby enabling the metal coating to be formed uniformly. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-152987 Summary of the Invention [Problem to be solved by the invention]

[0006] However, for example, in a structure such as the film formation apparatus described in Patent Document 1, it is necessary to provide another storage chamber for storing an insoluble anode, which is separated from one storage chamber for storing a plating solution by a diaphragm, which limits the miniaturization of the apparatus and makes it difficult to use in a structure in which the distance between the anode and the substrate is short, on the order of a few millimeters. Furthermore, if the pressure difference between the one storage chamber for storing the plating solution and the other storage chamber for storing the insoluble anode becomes large when the plating solution is pressurized, the diaphragm may be deformed or damaged, and may not be able to function as a diaphragm.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide a metal film deposition apparatus that can deposit a metal film uniformly and can be made compact. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a metal film forming apparatus including an anode, an electrolyte membrane disposed between a substrate serving as the anode and the cathode, a housing having a chamber for accommodating a plating solution containing metal ions between the anode and the electrolyte membrane, a power supply device for applying a voltage between the anode and the substrate, and a pressure device for pressurizing the plating solution accommodated in the chamber, wherein the electrolyte membrane is attached so as to cover an opening of the housing on the cathode side that communicates with the chamber, and the voltage is applied while the electrolyte membrane is pressed against the surface of the substrate, thereby reducing the metal ions impregnated in the electrolyte membrane. a film formation apparatus for forming a metal film on a surface of the substrate, the film formation apparatus further comprising a diaphragm attached to cover the cathode-side surface of the anode and in contact with the cathode-side surface of the anode, the diaphragm being a membrane that is permeable to water and hydrogen ions but impermeable to oxygen gas; the anode is attached to close an opening of the accommodating housing on a side opposite to the cathode side, the opening being connected to the accommodating chamber, such that the cathode-side surface is exposed to the accommodating chamber via the diaphragm and the surface opposite to the cathode side is exposed to the outside of the accommodating housing; and the anode is made of a porous body that is insoluble in the plating solution. [Effects of the Invention]

[0009] According to the present invention, a metal film can be formed uniformly and the device can be made smaller. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a metal film forming apparatus according to one embodiment. [Figure 2]1 is a schematic cross-sectional view illustrating a method for forming a metal film using a metal film forming apparatus according to one embodiment. [Figure 3] 1 is a schematic cross-sectional view for explaining the principle of the action and effect of a metal film forming apparatus according to one embodiment, showing the structure between an anode and a plating solution. FIG. [Figure 4] FIG. 1 is a schematic cross-sectional view showing a test system 1 of a metal film forming apparatus. [Figure 5] FIG. 2 is a schematic cross-sectional view showing a test system 2 of a metal film forming apparatus. [Figure 6] 1 is a graph showing the change in voltage over time at a constant current (10 mA) during deposition of metal films in Reference Examples 1 and 2 and a Comparative Example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the metal film forming apparatus of the present invention will be described. 1 is a schematic cross-sectional view showing a metal film forming apparatus according to one embodiment, which will be described below with reference to FIG.

[0012] As shown in FIG. 1 , a metal film forming apparatus 1 according to one embodiment includes an anode 11, an electrolyte membrane 13 disposed between the anode 11 and a substrate B serving as a cathode, and a housing 15 having a storage chamber 17. The storage chamber 17 stores a plating solution L containing metal ions between the anode 11 and the electrolyte membrane 13. The film forming apparatus 1 includes a power supply device 16 that applies a voltage between the anode 11 and the substrate B (cathode). The film forming apparatus 1 further includes a plating solution supply pump 21 as a pressurizing device that pressurizes the plating solution L stored in the storage chamber 17. In the film forming apparatus 1, the direction in which the anode 11 and the substrate B face each other is parallel to the vertical direction. Hereinafter, the vertical direction will be referred to as the downward direction, and the opposite direction will be referred to as the upward direction.

[0013] The substrate B has a conductor B1, which serves as a cathode, partially provided on the surface of an insulating portion B2. The conductor B1 is made of, for example, copper, nickel, silver, iron, etc. The insulating portion B2 is made of, for example, a polymer resin such as epoxy resin, ceramics, etc.

[0014] The electrolyte membrane 13 covers the cathode-side opening 15hc of the accommodating housing 15, which is in communication with the accommodation chamber 17. The electrolyte membrane 13 is attached to the accommodating housing 15 via a sealant 19, such as an O-ring. The film forming apparatus 1 pressurizes the plating solution L using the discharge pressure of the plating solution supply pump 21. This presses the electrolyte membrane 13 toward the cathode using the liquid pressure of the plating solution L, allowing the electrolyte membrane 13 to press against the surface of the substrate B. While pressing the surface of the substrate B with the electrolyte membrane 13 in this manner, the film forming apparatus 1 applies a voltage between the anode 11 and the substrate B using the power supply device 16. This reduces the metal ions impregnated in the electrolyte membrane 13, causing the metal derived from the metal ions to precipitate, thereby forming a metal coating containing the metal on the surface of the substrate B (the surface of the conductor portion B1).

[0015] The film forming apparatus 1 further includes a diaphragm 18 attached to the housing 15 via a seal member 20 such as an O-ring so as to cover the cathode-side surface 11c of the anode 11 and to be in contact with the cathode-side surface 11c of the anode 11. The diaphragm 18 is a membrane that separates water (HO) and hydrogen ions (H + ) but not oxygen gas (O2).

[0016] The anode 11 is attached to the accommodating housing 15 so as to close an opening 15ha on the side opposite the cathode side of the accommodating housing 15 that is in communication with the accommodating chamber 17. The cathode-side surface 11c of the anode 11 is exposed to the accommodating chamber 17 via a diaphragm 18, and the surface 11a opposite the cathode side is exposed to the outside of the accommodating housing 15. The anode 11 is made of a flat mesh member (porous body) that is insoluble in the plating solution L. The mesh member is permeable to oxygen gas.

[0017] The storage chamber 17 contains the plating solution L so that the plating solution L comes into contact with the diaphragm 18 and the electrolyte membrane 13. The storage chamber 17 is sealed by the storage housing 15, the diaphragm 18, and the electrolyte membrane 13 so that the plating solution L can be stably pressurized when forming a metal film. The material of the storage housing 15 is not particularly limited as long as it is corrosion-resistant to the plating solution L, and examples of the material include metal materials such as stainless steel.

[0018] The plating solution L is an acidic aqueous solution containing metal ions and is a conductive electrolyte. When a voltage is applied between the anode 11 and the substrate B (cathode), an electric field for film formation is formed in the plating solution L from the anode 11 toward the substrate B. That is, electric field lines start from the cathode-side surface 11c of the anode 11, move toward the substrate B, and reach the surface of the substrate B (the surface of the conductor portion B1).

[0019] The film forming apparatus 1 further includes a pressure reducing device 30. The pressure reducing device 30 has a pressure reducing housing 31. The pressure reducing housing 31 covers the opening 15ha on the side opposite to the cathode side of the housing 15 from the outside of the housing 15, forming a pressure reducing chamber 33 outside the housing 15. The pressure reducing device 30 further includes an exhaust pipe 35 provided on the top of the pressure reducing housing 31 and a vacuum pump 37 (pressure reducing pump) provided in the exhaust pipe 35. The pressure reducing chamber 33 is sealed by the pressure reducing housing 31, the housing 15, and the diaphragm 18 so that the pressure can be reduced stably during the formation of the metal coating. The flow path within the exhaust pipe 35 is connected to the pressure reducing chamber 33. The vacuum pump 37 can reduce the pressure in the pressure reducing chamber 33 by exhausting air through the flow path of the exhaust pipe 35.

[0020] The film forming apparatus 1 further includes a metal mounting table 40 on which the substrate B is placed. The mounting table 40 is connected to the negative pole of a power supply unit 16, and the anode 11 is connected to the positive pole of the power supply unit 16. The mounting table 40 and the conductor portion B1 of the substrate B on which the film is formed are electrically connected. This allows the conductor portion B1 of the substrate B to function as a cathode.

[0021] The film forming apparatus 1 further includes a supply source 22 that supplies the plating solution L and is provided upstream of the plating solution supply pump 21, a supply pipe 23 that connects the supply source 22 and the plating solution supply pump 21, and a communication pipe 24 that connects the plating solution supply pump 21 and the storage chamber 17. The film forming apparatus 1 further includes a drain pipe 26 that is connected to the storage chamber 17 and drains the plating solution L from the storage chamber 17, and a pressure adjustment valve 27 that is provided in the drain pipe 26.

[0022] In the film forming apparatus 1, the liquid pressure in the storage chamber 17 can be adjusted by the pressure regulating valve 27. Note that the film forming apparatus 1 may be provided with an on-off valve instead of the pressure regulating valve 27. The liquid pressure of the plating solution L in the storage chamber 17 may be controlled by adjusting the discharge pressure of the plating solution supply pump 21 with the on-off valve closed. The drain pipe 26 may be connected to the supply source 22. In this case, the plating solution L used in the storage chamber 17 can be returned to the supply source 22 via the drain pipe 26 and reused during film formation.

[0023] The film formation apparatus 1 further includes an elevating device 28 that elevates and lowers the electrolyte membrane 13 together with the accommodating housing 15 and the anode 11 in the vertical direction in which the anode 11 and the substrate B face each other, thereby positioning the electrolyte membrane 13. The elevating device 28 has a main body 28b and a movable part 28m. The main body 28b is fixed to an upper fixed part 50. The upper side of the movable part 28m is connected to the main body 28b and is movable in the vertical direction relative to the main body 28b. The lower end of the movable part 28m is mechanically connected to the accommodating housing 15. During film formation, the elevating device 28 moves the movable part 28m downward relative to the main body 28b, thereby lowering the electrolyte membrane 13 together with the accommodating housing 15, the anode 11, etc. from the standby position shown in FIG. 1 to a film formation position shown in FIG. 2, which will be described later, and bringing the electrolyte membrane 13 into contact with the surface of the substrate B. Then, by stopping the movable part 28m when the electrolyte membrane 13 comes into contact with the surface of the substrate B, the electrolyte membrane 13 is positioned in the vertical direction and the vertical position of the electrolyte membrane 13 is fixed. In this manner, the electrolyte membrane 13 is brought into contact with the surface of the substrate B, and in this state, a metal coating is formed on the surface of the substrate B. After the film formation, the movable part 28m is moved upward relative to the main body part 28b, thereby raising the electrolyte membrane 13 together with the accommodating housing 15, the anode 11, etc. from the film formation position shown in FIG. 2 to the standby position shown in FIG. 1, and separating the electrolyte membrane 13 from the surface of the substrate B.

[0024] 2 is a schematic cross-sectional view for explaining a method for forming a metal film using a metal film forming apparatus according to one embodiment. Hereinafter, a method for forming a metal film using a metal film forming apparatus according to one embodiment (hereinafter, abbreviated as a method for forming a metal film according to one embodiment) will be explained with reference to FIGS.

[0025] In one embodiment of the method for forming a metal film, first, as shown in FIG. 1, in one embodiment of the metal film forming apparatus 1, the substrate B is placed on a mounting table 40 so that the surface of the substrate B (the surface of the conductor portion B1) faces the electrolyte membrane 13.

[0026] 2, the elevator device 28 is used to move the movable part 28m downward relative to the main body part 28b, thereby lowering the electrolyte membrane 13 together with the accommodating housing 15, the anode 11, etc. toward the mounting table 40, thereby bringing the electrolyte membrane 13 into contact with the surface of the substrate B (the surface of the conductor part B1). Then, by stopping the movable part 28m when the electrolyte membrane 13 comes into contact with the surface of the substrate B, the electrolyte membrane 13 is positioned in the vertical direction and the vertical position of the electrolyte membrane 13 is fixed. In this way, the electrolyte membrane 13 is brought into contact with the surface of the substrate B.

[0027] Next, the plating solution L contained in the storage chamber 17 is pressurized by the discharge pressure of the plating solution supply pump 21. In this case, the pressure of the plating solution L contained in the storage chamber 17 is increased to the pressure set by the pressure adjustment valve 27. The operation of the plating solution supply pump 21 may be stopped when the pressure of the plating solution L contained in the storage chamber 17 is increased to the pressure set by the pressure adjustment valve 27. On the other hand, if the operation of the plating solution supply pump 21 is continued after the pressure of the plating solution L contained in the storage chamber 17 is increased to the pressure set by the pressure adjustment valve 27, the plating solution L continues to be supplied from the supply source 22 to the storage chamber 17, and the pressure of the plating solution L contained in the storage chamber 17 is maintained at the pressure set by the pressure adjustment valve 27. Furthermore, when pressurizing the plating solution L, the pressure in the decompression chamber 33 is decompressed by the decompression device 30.

[0028] As described above, with the electrolyte membrane 13 in contact with the surface of the substrate B, the plating solution L is pressurized, and the liquid pressure of the plating solution L presses the electrolyte membrane 13 toward the cathode side. This allows the electrolyte membrane 13 to uniformly press against the surface of the substrate B. At this time, metal ions contained in the plating solution L can be impregnated into the electrolyte membrane 13. Furthermore, by pressurizing the plating solution L and pressing the diaphragm 18 toward the anode 11 with the liquid pressure of the plating solution L, and simultaneously reducing the pressure in the decompression chamber 33 and sucking the diaphragm 18 toward the anode 11, the diaphragm 18 can be brought into close contact with the cathode-side surface 11c of the anode 11.

[0029] Next, while the electrolyte membrane 13 is pressed against the surface of the substrate B and the diaphragm 18 is in close contact with the cathode-side surface 11c of the anode 11, a voltage is applied between the anode 11 and the substrate B (cathode) by the power supply device 16, thereby reducing the metal ions impregnated in the electrolyte membrane 13. This causes the metal derived from the metal ions to precipitate, forming a metal coating F on the surface of the substrate B (the surface of the conductor portion B1).

[0030] 3 is a schematic cross-sectional view for explaining the principle of the function and effect of the metal coating deposition apparatus according to one embodiment, showing the structure between the anode and the plating solution. The function and effect of the metal coating deposition apparatus 1 according to one embodiment will be described below.

[0031] In the metal film forming apparatus 1 according to one embodiment, the anode 11 is insoluble in the plating solution L. Therefore, during the formation of the metal film F, water contained in the plating solution L is electrolyzed at the interface between the diaphragm 18 and the anode 11 (the cathode-side surface 11c of the anode 11), and an electrolytic reaction (2H2O → 4H2O) occurs. + +O2+4e - ) generates oxygen gas. If the generated oxygen gas is mixed into the plating solution L and remains in the storage chamber 17, problems may occur. That is, since oxygen gas is more compressible than the plating solution L, pressurizing the plating solution L makes it difficult for the electrolyte membrane 13 to pressurize the surface of the substrate B uniformly with the liquid pressure of the plating solution L. As a result, it may not be possible to form the metal coating F uniformly.

[0032] However, in the film forming apparatus 1, water (H2O) and hydrogen ions (H +A diaphragm 18, which is permeable to oxygen gas (O) but not to oxygen gas (O), covers the cathode-side surface 11c of the anode 11 and is attached so as to be in contact with the cathode-side surface 11c of the anode 11. The anode 11 is attached so as to close an opening 15ha on the side opposite the cathode side of the accommodating housing 15, which is in communication with the accommodating chamber 17. As a result, the cathode-side surface 11c of the anode 11 is exposed to the accommodating chamber 17 via the diaphragm 18, and the surface 11a opposite the cathode side is exposed to the outside of the accommodating housing 15. The anode 11 is made of a mesh member that is permeable to oxygen gas. Furthermore, in the film forming apparatus 1, the diaphragm 18 is brought into close contact with the cathode-side surface 11c of the anode 11 during the formation of the metal coating F.

[0033] Therefore, in the film-forming apparatus 1, during the formation of the metal coating F, as shown in FIG. 3 , water, one of the components of the plating solution L, can permeate the diaphragm 18 and is sequentially supplied to the cathode-side surface 11c of the anode 11. Consequently, oxygen gas is generated by the electrolysis reaction of water on the cathode-side surface 11c of the anode 11. However, the oxygen gas cannot permeate the diaphragm 18, which is in close contact with the cathode-side surface 11c of the anode 11. Therefore, the oxygen gas passes through the holes in the mesh member of the anode 11 and is discharged to the outside of the housing 15. This prevents oxygen gas from remaining in the accommodating chamber 17 and prevents oxygen gas from accumulating at the interface between the diaphragm 18 and the anode 11. This allows the electrolyte membrane 13 to uniformly press against the surface of the substrate B, resulting in the formation of a uniform metal coating. Furthermore, resistance at the interface between the diaphragm 18 and the anode 11 is suppressed. In addition, hydrogen ions generated simultaneously by the electrolysis reaction can permeate the diaphragm 18 and diffuse into the plating solution L. This prevents excess hydrogen ions from forming around the anode 11. This allows the voltage applied between the anode 11 and the substrate B to be stabilized.

[0034] The plating solution L may contain additives such as organic additive components in addition to metal ions, but the additives cannot permeate the diaphragm 18 (cation exchange membrane). Therefore, the additives do not come into direct contact with the anode 11, and decomposition of the additives at the anode 11 due to oxidation or the like can be reduced. This allows the plating solution L to have a longer life. In addition, the electrons (e - ) flows through the anode 11 to the positive terminal of the power supply 16.

[0035] Furthermore, in the structure of a conventional film-forming apparatus using an insoluble anode, as described in Patent Document 1, for example, a separate chamber containing an insoluble anode must be provided, separate from the first chamber containing the plating solution, to prevent oxygen gas from remaining in the chamber containing the plating solution and to uniformly form a metal film. In contrast, the metal film-forming apparatus 1 according to one embodiment prevents oxygen gas from remaining in the chamber 17 containing the plating solution L without providing a separate chamber containing the insoluble anode 11, thereby enabling a uniform metal film F to be formed. This allows for a uniform metal film F to be formed and the film-forming apparatus 1 to be miniaturized. The miniaturization of the film-forming apparatus 1 makes it possible to use the apparatus with a structure in which the distance between the anode 11 and the substrate B is short, on the order of a few millimeters. This allows for a uniform distribution of electric field lines on the surface of the substrate B, thereby enabling a more uniform metal film F to be formed. In addition, unlike the structure of the conventional film forming apparatus described above, the pressure difference between one storage chamber and another storage chamber does not become large, and the diaphragm 18 is not deformed or damaged.

[0036] The configuration of the metal film forming apparatus according to the embodiment will be described in further detail below.

[0037] The anode is not particularly limited as long as it is made of a porous body insoluble in the plating solution (a porous body that does not dissolve in the plating solution L). The porous body of the anode is not particularly limited as long as it is insoluble and permeable to oxygen gas, and may be, for example, a mesh member or a porous member other than a mesh member. The porous body of the anode may have grooves on the cathode side of the anode that allow oxygen gas to pass through, and may have holes that penetrate from the inside of the grooves to the surface of the anode opposite the cathode side.

[0038] The material of the porous body of the anode is not particularly limited as long as it makes the anode insoluble, but for example, platinum, iridium oxide, etc. are preferred because they have a low oxygen overvoltage and enable water electrolysis at a low voltage.

[0039] The diaphragm is not particularly limited as long as it is a membrane that allows water and hydrogen ions to permeate but does not allow oxygen gas to permeate. Examples of the diaphragm include a cation exchange membrane and a neutral diaphragm. However, a cation exchange membrane is preferred because it has high hydrogen ion permeability. Nanoscale channels exist in the cation exchange membrane. The cation exchange membrane selectively allows water and hydrogen ions to permeate through the nanoscale channels. A cation exchange membrane with a high water content is preferred, specifically, for example, Nafion (registered trademark) manufactured by DuPont. This is because a large amount of water can be supplied to the anode. A neutral diaphragm is a neutral diaphragm with no ion selectivity. A neutral diaphragm may be used as the diaphragm when there is no problem of additive degradation at the anode, such as when the plating solution does not contain additives or when the additives contained in the plating solution do not permeate the neutral diaphragm due to their molecular weight or other factors. A preferred example of the neutral diaphragm is Y-9207TA manufactured by Yuasa Membrane Systems Co., Ltd. The thickness of the diaphragm is preferably 10 μm to 200 μm, for example. When the plating solution is a strongly alkaline solution containing metal ions, an anion exchange membrane can also be used as the diaphragm.

[0040] The substrate is not particularly limited as long as the surface portion on which the metal coating is formed functions as a cathode (a surface portion having electrical conductivity). For example, the substrate may be one in which a conductor portion serving as a cathode is partially provided on the surface of an insulating portion as in one embodiment, or the substrate may be entirely made of a metal material such as aluminum or iron.

[0041] The electrolyte membrane is not particularly limited as long as it can be impregnated with metal ions contained in the plating solution by contacting it with a plating solution, and can deposit metal derived from the metal ions on the surface of the substrate by applying a voltage between the anode and the substrate. The electrolyte membrane is usually flexible. The thickness of the electrolyte membrane is, for example, 5 μm to 200 μm. Examples of materials for the electrolyte membrane include fluorine-based resins such as Nafion (registered trademark) manufactured by DuPont, hydrocarbon-based resins, polyamic acid resins, and resins with ion exchange function such as Selemion (CMV, CMD, CMF, etc.) manufactured by Asahi Glass Co., Ltd.

[0042] The plating solution is a solution containing metal ions. More specifically, it is a solution containing the metal contained in the metal coating in the form of metal ions. The plating solution is not particularly limited as long as it is a solution containing metal ions, and may contain additives in addition to the metal ions.

[0043] Examples of the metal of the metal ion include copper, nickel, silver, iron, etc. Examples of the plating solution include solutions such as an aqueous solution in which at least one of these metals is dissolved in an acid such as sulfuric acid, nitric acid, phosphoric acid, succinic acid, or pyrophosphoric acid. Specifically, when the metal of the metal ion is nickel, examples of the plating solution include solutions such as an aqueous solution of nickel sulfate, nickel nitrate, nickel phosphate, nickel succinate, or nickel pyrophosphate. The plating solution may be an acidic solution or an alkaline solution.

[0044] The pressurizing device is not particularly limited as long as it can pressurize the plating solution contained in the storage chamber. The pressurizing device may be, for example, a plating solution supply pump or a pressurizing device composed of a cylinder and a piston. The pressurizing device connects the cylinder containing the plating solution to the storage housing so as to communicate with the storage chamber, and can pressurize and depressurize the plating solution in the storage chamber by moving the piston forward and backward within the cylinder.

[0045] The metal coating forming apparatus preferably further includes a device for tightly contacting the diaphragm with the cathode-side surface of the anode. This is because preventing oxygen gas and the like from accumulating at the interface between the diaphragm and the anode and generating resistance allows a stable current to flow between the anode and the substrate (cathode), thereby achieving uniform formation of the metal coating. The device for tightly contacting the diaphragm is not particularly limited as long as it can tightly contact the cathode-side surface of the anode. However, a device that can uniformly press the diaphragm toward the anode is preferred, such as the pressure device described above. The pressure device applies pressure to the plating solution, and the liquid pressure of the plating solution presses the diaphragm toward the anode, thereby tightly contacting the diaphragm with the anode. A preferred device for uniformly pressing the diaphragm toward the anode is, for example, a pressure reducing device that reduces the pressure in the space outside the housing where the surface of the anode opposite the cathode is exposed. The pressure reducing device reduces the pressure in the space and draws the diaphragm toward the anode, thereby tightly contacting the diaphragm with the anode. The pressure reducing device may be, for example, a device that is composed of a pressure reducing housing, an exhaust pipe, and a pressure reducing pump and that reduces the pressure in a pressure reducing chamber. A film forming apparatus that is equipped with both a pressurizing device and a pressure reducing device as a device for bringing the electrodes into contact with each other is preferred. This is because it can sufficiently prevent oxygen gas and the like from accumulating at the interface between the diaphragm and the anode, thereby creating resistance. The device for bringing the electrodes into contact with each other may also be a device that generates a flow from the cathode side to the anode side in the plating solution contained in the containing chamber (for example, a device composed of a propeller and a drive device for rotating the propeller).

[0046] The metal coating deposition apparatus may further include a lifting device. The lifting device is not particularly limited as long as it can raise and lower the electrolyte membrane and position the electrolyte membrane in the opposing direction between the anode and the substrate. The lifting device may be, for example, a hydraulic or pneumatic actuator composed of a cylinder and a piston, or an electric actuator that is raised and lowered by a motor or the like. Note that the deposition apparatus does not need to include a lifting device as long as it can raise and lower the electrolyte membrane and position the electrolyte membrane in the opposing direction between the anode and the substrate.

[0047] The metal film forming apparatus is not particularly limited, but may be one in which the components are arranged so that the opposing direction between the anode and the substrate is parallel to the vertical direction. The metal film forming apparatus may be one in which the components are arranged so that the opposing direction between the anode and the substrate is horizontal. The metal film forming apparatus may be one in which the components are arranged so that the opposing direction between the anode and the substrate is inclined with respect to the vertical direction. [Example]

[0048] The metal film forming apparatus according to the embodiment will be described in more detail below with reference to a reference example and a comparative example.

[0049] [Reference example 1] First, a test system 1 for a metal film forming apparatus was constructed. The test system 1 simulates the metal film forming apparatus according to the embodiment. Fig. 4 is a schematic cross-sectional view showing the test system 1 for a metal film forming apparatus.

[0050] In test system 1, as shown in FIG. 4, the internal space of the housing is divided into a storage chamber and a decompression chamber by an anode and a diaphragm. A substrate serving as a cathode is stored in the storage chamber. A plating solution is also stored in the storage chamber. A power supply device is also provided to apply a voltage between the anode and the substrate (cathode). A pressure device (not shown) is also provided to pressurize the plating solution stored in the storage chamber. A pressure reduction device (not shown) is also provided to reduce the pressure in the decompression chamber.

[0051] The diaphragm covers the cathode side surface of the anode and is attached to the housing so as to be in contact with the cathode side surface of the anode. The diaphragm is a cation exchange membrane that is permeable to water and hydrogen ions but not to oxygen gas. The anode is attached to the housing so as to close the communication portion connecting the storage chamber and the decompression chamber, with the cathode side surface exposed to the storage chamber through the diaphragm and the surface opposite the cathode side exposed to the decompression chamber. The anode is made of a flat mesh member that is insoluble in the plating solution. The mesh member is permeable to oxygen gas. The substrate is immersed in and in contact with the plating solution. The substrate is made entirely of a metal material. The plating solution is an acidic aqueous solution containing metal ions and is a conductive electrolyte.

[0052] Next, using test system 1, a metal coating was formed on the surface of the substrate. Specifically, the plating solution contained in the storage chamber was pressurized using a pressure device to maintain a constant liquid pressure for the plating solution. At the same time, the pressure in the decompression chamber was reduced to -0.3 atmospheres relative to atmospheric pressure using a pressure reduction device. While maintaining this state, a constant current (10 mA) was applied between the anode and the substrate (cathode) using a power supply. This reduced the metal ions contained in the plating solution, thereby forming a metal coating on the surface of the substrate.

[0053] [Reference example 2] A metal coating was formed on the surface of a substrate using test system 1 under the same conditions as in Reference Example 1, except that the pressure in the pressure-reducing chamber was not reduced. Specifically, the plating solution contained in the storage chamber was pressurized using a pressure device to maintain a constant liquid pressure in the plating solution. At the same time, the pressure in the pressure-reducing chamber was not reduced, and the pressure was maintained at atmospheric pressure. While maintaining the above conditions, a constant current (10 mA) was applied between the anode and the substrate (cathode) using a power supply. This reduced the metal ions contained in the plating solution, thereby forming a metal coating on the surface of the substrate.

[0054] [Comparative Example] First, a test system 2 for a metal film forming apparatus was constructed. Unlike the embodiment, the test system 2 simulates a metal film forming apparatus that does not have a diaphragm. Fig. 5 is a schematic cross-sectional view showing the test system 2 for a metal film forming apparatus.

[0055] In test system 2, as shown in FIG. 5, the internal space of a housing identical to that of test system 1 is divided into two storage chambers by the same anode as that of test system 1. One storage chamber is identical to that of test system 1 and contains the same substrate as that of test system 1. Both storage chambers contain the same plating solution as that of test system 1. Furthermore, a power supply device is provided to apply a voltage between the anode and the substrate (cathode). A pressure device (not shown) is provided to pressurize the plating solution contained in both storage chambers. The anode is attached to the housing so that the surface on the cathode side is exposed to one storage chamber and the surface opposite the cathode side is exposed to the other storage chamber, blocking the communication part connecting both storage chambers.

[0056] Next, using test system 2, a metal coating was formed on the surface of the substrate. Specifically, the plating solution contained in both chambers was pressurized using a pressure device to maintain a constant liquid pressure for the plating solution. While maintaining this state, a constant current (10 mA) was applied between the anode and the substrate (cathode) using a power supply. This reduced the metal ions contained in the plating solution, thereby forming a metal coating on the surface of the substrate.

[0057] [evaluation] In Reference Examples 1 and 2 and the Comparative Example, the voltage (cell voltage) between the anode and the substrate was measured during the formation of the metal film, and the change in voltage over time at a constant current (10 mA) during the formation of the metal film was evaluated. Figure 6 is a graph showing the change in voltage over time at a constant current (10 mA) during the formation of the metal film in Reference Examples 1 and 2 and the Comparative Example.

[0058] As shown in FIG. 6 , in Reference Example 1, the voltage increased for a predetermined time after the start of current application and then stabilized, allowing current to flow continuously at a constant voltage. In Reference Example 1, the pressure in the vacuum chamber was reduced, and the diaphragm adhered closely to the anode. As a result, air and oxygen gas generated by electrolysis did not accumulate at the interface between the diaphragm and the anode. Instead, the oxygen gas passed through the pores of the porous anode and was discharged into the vacuum chamber. This is believed to have prevented high resistance from occurring at the interface between the diaphragm and the anode. Therefore, under the conditions of Reference Example 1, the reaction resistance of the anode can be suppressed, allowing a metal coating to be formed at a high speed. On the other hand, in Reference Example 2, the voltage continued to increase at a faster rate than in Reference Example 1 after the start of current application and reached the upper limit of the power supply (20 V). Eventually, the resistance between the anode and the substrate became so high that current could no longer flow. In Reference Example 2, unlike Reference Example 1, the vacuum chamber was not decompressed, and the diaphragm did not adhere sufficiently to the anode, which is thought to have resulted in high resistance due to accumulation of air and oxygen gas at the interface between the diaphragm and the anode. In addition, in the Comparative Example, after the start of current application, the voltage initially increased at a slower rate than in Reference Example 1, then continued to increase at an accelerated rate, and reached the upper limit of the power supply (20 V). In the Comparative Example, it is thought that the anode was continuously covered with oxygen gas, causing the voltage to continue to increase.

[0059] The above describes in detail the metal film forming apparatus according to an embodiment of the present invention, but the present invention is not limited to the above embodiment, and various design modifications can be made within the scope of the spirit of the present invention as set forth in the claims. [Explanation of symbols]

[0060] 1: Metal film forming device, 11: Anode, 13: Electrolyte membrane, 15: Housing, 16: Power supply unit, 17: Storage chamber, 18: Diaphragm, 21: Plating solution supply pump (pressurizing device), B: Substrate, L: Plating solution, F: Metal film

Claims

[Claim 1] an anode; an electrolyte membrane disposed between the anode and cathode substrates; a housing having a chamber between the anode and the electrolyte membrane for accommodating a plating solution containing metal ions; a power supply that applies a voltage between the anode and the substrate; a pressurizing device that pressurizes the plating solution contained in the container; the electrolyte membrane is attached to cover an opening on the cathode side of the accommodating housing that communicates with the accommodating chamber, a film forming apparatus that applies the voltage while pressing the electrolyte membrane against the surface of the substrate, thereby reducing the metal ions impregnated in the electrolyte membrane, thereby forming a metal coating on the surface of the substrate, the film forming apparatus further includes a diaphragm attached to cover the cathode side surface of the anode and in contact with the cathode side surface of the anode; the film forming apparatus further includes a decompression chamber and a decompression device for bringing the diaphragm into close contact with the anode, the diaphragm is a membrane that is permeable to water and hydrogen ions but not permeable to oxygen gas, the anode is attached to close an opening of the accommodating housing that is communicated with the accommodating chamber and that is on an opposite side to the cathode side, such that a surface of the anode on the cathode side is exposed to the accommodating chamber via the diaphragm and a surface of the anode on the opposite side to the cathode side is exposed to an outside of the accommodating housing, the anode is made of a porous body that is insoluble in the plating solution, the decompression chamber is a space outside the accommodating housing to which a surface of the anode opposite to the cathode side is exposed, The metal film forming apparatus is characterized in that the pressure reducing device reduces the pressure in the pressure reducing chamber.

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