FILM FORMATION DEVICE FOR METAL FILM

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2022-200268 filed on Dec. 15, 2022, incorporated herein by reference in its entirety.

BACKGROUND
1. Technical Field

The present disclosure relates to a film formation device, and more particularly, to a film formation device for a metal film that is capable of forming a metal film on a surface of a substrate.

2. Description of Related Art

In a film formation technique known in the related art, a metal film is formed on a surface of a substrate by reducing a metal ion contained in a plating solution to deposit metal derived from a metal ion. In recent years, a film formation device that forms the metal film on the surface of the substrate has been used in such a film formation technique. The film formation device includes an anode, an electrolyte membrane disposed between the anode and a substrate that serves as a cathode, a power supply device that applies a voltage between the anode and the substrate (cathode), a housing provided with an accommodation chamber, and a pressurizing device that pressurizes a plating solution. The accommodation chamber accommodates a plating solution containing a metal ion between the anode and the electrolyte membrane. The film formation device reduces the metal ion contained in the electrolyte membrane by applying the voltage between the anode and the substrate while pressing the surface of the substrate by the electrolyte membrane with the fluid pressure of the plating solution. As a result, a metal film is formed on the surface of the substrate.

Among such film formation devices, a film formation device for a metal film in which an insoluble anode is applied as an anode has attracted attention. However, in the film formation device to which the insoluble anode is applied, water of the plating solution is electrolyzed on the surface of the anode in the accommodation chamber, and oxygen gas is generated. As the film formation time elapses, the amount of oxygen gas generated increases, so that the oxygen gas aggregates and stays on the surface of the anode. In a case in which the surface of the substrate is pressed by the electrolyte membrane with the fluid pressure of the plating solution when forming the metal film as described above, there is a possibility that the metal film cannot be uniformly formed. This is because, when the oxygen gas remains in the accommodation chamber, since the oxygen gas is more compressible than the plating solution, it becomes difficult to uniformly press the surface of the substrate with the electrolyte membrane.

In order to cope with such a problem, for example, a film formation device described in Japanese Unexamined Patent Application Publication No. 2020-152987 (JP 2020-152987 A) is proposed. In the film formation device described in JP 2020-152987 A, in a housing, a partition member that partitions an accommodation chamber into a first accommodation chamber on the anode side in which a first electrolytic solution is accommodated and a second accommodation chamber on the electrolyte membrane side in which a second electrolytic solution (plating solution) containing a metal ion is accommodated, is disposed between the anode and the electrolyte membrane. The partition member is a diaphragm in which a porous body is impregnated with a cation exchange resin. An anode insoluble in the first electrolytic solution is accommodated in the first accommodation chamber. The second accommodation chamber forms a sealed space in which the second electrolytic solution is sealed, in the housing with the electrolyte membrane and the partition member. Therefore, at the time of film formation, water contained in the first electrolytic solution is electrolyzed at the surface of the anode in the first accommodation chamber, and even when the oxygen gas is generated, the oxygen gas from the anode is not mixed into the second electrolytic solution (plating solution) in the second accommodation chamber. Therefore, the second electrolytic solution can be pressurized without the oxygen gas remaining in the second accommodation chamber. As a result, the surface of the substrate can be uniformly pressed by the electrolyte membrane that is subjected to the fluid pressure of the second electrolytic solution, and the metal film can be uniformly formed.

SUMMARY

However, for example, in a configuration such as a film formation device described in JP 2020-152987 A, separately from one accommodation chamber in which the plating solution is accommodated, it is necessary to provide another accommodation chamber in which an insoluble anode is accommodated, the other accommodation chamber being partitioned by the diaphragm from the one accommodation chamber. Therefore, there is a limitation in downsizing of the device, and it is difficult to use the device in a configuration in which the distance between the anode and the substrate is a short distance of about several millimeters. Further, when pressurizing the plating solution, when the differential pressure between the one accommodation chamber in which the plating solution is accommodated and the other accommodation chamber in which the insoluble anode is accommodated is increased, the diaphragm may be deformed or broken, and may not function as a diaphragm.

The present disclosure has been made in view of the above issues, and an object of the present disclosure is to provide a film formation device for a metal film that is capable of uniformly forming a metal film and that is able to be downsized.

In order to solve the above problems, a film formation device for a metal film according to the present disclosure includes: an anode; an electrolyte membrane disposed between the anode and a substrate, the substrate serving as a cathode; an accommodation housing provided with an accommodation chamber that accommodates a plating solution containing a metal ion between the anode and the electrolyte membrane; a power supply device that applies a voltage between the anode and the substrate; and a pressurizing device that pressurizes the plating solution accommodated in the accommodation chamber. The electrolyte membrane is attached so as to cover an opening of the accommodation housing on the cathode side, the opening communicating with the accommodation chamber. The film formation device forms the metal film on a surface of the substrate by reducing the metal ion impregnated in the electrolyte membrane by applying the voltage while pressing the surface of the substrate with the electrolyte membrane. The film formation device further includes a diaphragm that is attached so as to cover a surface of the anode on the cathode side and contact the surface of the anode on the cathode side. The diaphragm is a membrane that is permeable to water and a hydrogen ion, and impermeable to oxygen gas. The anode is attached so as to close an opening of the accommodation housing on a side opposite to the cathode side in such a manner that the surface of the anode on the cathode side is exposed to the accommodation chamber via the diaphragm, and a surface of the anode on a side opposite to the cathode side is exposed to an outside of the accommodation housing, the opening communicating with the accommodation chamber. The anode is made of a porous body insoluble in the plating solution.

According to the present disclosure, the metal film can be uniformly formed, and the device can be downsized.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein:

FIG. 1 is a schematic cross-sectional view illustrating a film formation device for a metal film according to an embodiment;

FIG. 2 is a schematic cross-sectional view for explaining a film forming method for forming a metal film using a film formation device for a metal film according to an embodiment;

FIG. 4 is a schematic cross-sectional view showing a test system 1 of a film formation device for a metal film;

FIG. 5 is a schematic cross-sectional view showing a test system 2 of a film formation device for a metal film; and

FIG. 6 is a graph showing a time-dependent change in voltage at a constant current (10 mA) at the time of film formation of a metal film in Reference Examples 1 and 2 and Comparative Examples.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of a film formation device for a metal film of the present disclosure will be described. FIG. 1 is a schematic cross-sectional view illustrating a film formation device for a metal film according to an embodiment. Hereinafter, a film formation device for a metal film according to an embodiment will be described with reference to FIG. 1.

As illustrated in FIG. 1, a film formation device 1 for a metal film according to an embodiment includes an anode 11, an electrolyte membrane 13 disposed between the anode 11 and a substrate B serving as a cathode, and an accommodation housing 15 provided with an accommodation chamber 17. The accommodation chamber 17 stores a plating solution L containing metal ions between the anode 11 and the electrolyte membrane 13. The film formation device 1 includes a power supply device 16 that applies a voltage between the anode 11 and the substrate B (cathode). The film formation device 1 further includes a plating solution supply pump 21 as a pressurizing device that pressurizes the plating solution L stored in the accommodation chamber 17. In the film formation device 1, the opposite direction in which the anode 11 and the substrate B face each other is parallel to the vertical direction. In the following description, the vertical direction is defined as a downward direction, and the opposite direction is defined as an upward direction.

In the substrate B, a conductive portion B1 serving as a cathode is partially provided on the insulating portion B2. The conductive portion B1 is made of copper, nickel, silver, iron, or the like, for example. The insulating portion B2 is made of, for example, a polymer resin such as an epoxy resin, a ceramic, or the like.

The electrolyte membrane 13 covers the cathode-side opening 15hc of the accommodation housing 15 that communicates with the accommodation chamber 17. The electrolyte membrane 13 is attached to the accommodation housing 15 via a sealing material 19 such as an O-ring. The film formation device 1 pressurizes the plating solution L by the discharge pressure of the plating solution supply pump 21. As a result, the electrolyte membrane 13 is pressed toward the cathode side by the liquid pressure of the plating solution L, and the surface of the substrate B is pressed by the electrolyte membrane 13. The film formation device 1 applies a voltage between the anode 11 and the substrate B by the power supply device 16 while pressing the surface of the substrate B with the electrolyte membrane 13 in this manner. As a result, the metal ions impregnated in the electrolyte membrane 13 are reduced, thereby precipitating the metal derived from the metal ions. Consequently, a metal film containing the metal is formed on the surface (the surface on the conductive portion B1) of the substrate B.

The film formation device 1 further includes a diaphragm 18. The diaphragm 18 covers the surface 11c of the anode 11 on the cathode side, and is attached to the accommodation housing 15 via a sealing material 20 such as an O-ring so as to be contacted with the surface 11c of the anode 11 on the cathode side. The diaphragm 18 is a cation-exchange membrane that transmits water (H₂O) and hydrogen ions (H⁺) and does not transmit oxygen gases (O₂).

The anode 11 is attached to the accommodation housing 15 so as to close the opening 15ha of the accommodation housing 15 communicating with the accommodation chamber 17. In the anode 11, the surface 11c on the cathode side is exposed to the accommodation chamber 17 via the diaphragm 18, and the surface 11a on the other side than the cathode side is exposed to the outside of the accommodation housing 15. The anode 11 is formed of a flat plate-like mesh member (porous body) insoluble in the plating solution L. The mesh-like member is configured to be permeable to oxygen gas.

In the accommodation chamber 17, the plating solution L is stored so that the plating solution L comes into contact with the diaphragm 18 and the electrolyte membrane 13. The accommodation chamber 17 is sealed by the accommodation housing 15, the diaphragm 18, and the electrolyte membrane 13 so that the plating solution L can be stably pressurized when the metal film is formed. The material of the accommodation housing 15 is not particularly limited as long as it has corrosion resistance to the plating solution L, and examples thereof include a metal material such as stainless steel.

The plating solution L is an acidic aqueous solution containing metal ions, and is an electrolytic solution having conductivity. 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, the electric field lines start from the surface 11c of the anode 11 on the cathode side, face toward the substrate B side, and reach the surface of the substrate B (the surface of the conductive portion B1).

The film formation device 1 further includes a pressure reduction device 30. The pressure reduction device 30 includes a pressure reduction housing 31. The pressure reduction housing 31 covers the opening 15ha of the accommodation housing 15 opposite to the cathode side from the outside of the accommodation housing 15, and forms a pressure reduction chamber 33 outside the accommodation housing 15. The pressure reduction device 30 further includes an exhaust pipe 35 provided at an upper portion of the pressure reduction housing 31, and a vacuum pump 37 (pressure reducing pump) provided at the exhaust pipe 35. The pressure reduction chamber 33 is sealed by the pressure reduction housing 31, the accommodation housing 15, and the diaphragm 18 so as to be able to stably decompress during the formation of the metal film. In the exhaust pipe 35, a flow path in the pipe communicates with the pressure reduction chamber 33. The vacuum pump 37 can reduce the pressure in the pressure reduction chamber 33 by exhausting the gas through the flow path of the exhaust pipe 35.

The film formation device 1 further includes a metal placing table 40 on which the substrate B is placed. A negative electrode of the power supply device 16 is connected to the mounting table 40. A positive electrode of the power supply device 16 is connected to the anode 11. The mounting table 40 is electrically connected to the conductive portion B1 on which the substrate B is formed. As a result, the conductive portion B1 of the substrate B can function as a cathode.

The film formation device 1 further includes a supply source 22 for supplying the plating solution L, a supply pipe 23 for connecting the supply source 22 and the plating solution supply pump 21, and a communication pipe 24 for communicating the plating solution supply pump 21 and the accommodation chamber 17. The supply source 22 is provided upstream of the plating solution supply pump 21. The film formation device 1 further includes a drain pipe 26 for draining the plating solution L from the accommodation chamber 17, and a pressure regulating valve 27 provided in the drain pipe 26. The drain pipe 26 is connected to the accommodation chamber 17.

In the film formation device 1, the hydraulic pressure in the accommodation chamber 17 can be adjusted by the pressure regulating valve 27. In the film formation device 1, an on-off valve may be provided instead of the pressure regulating valve 27. Then, the film formation device 1 may control the liquid pressure of the plating solution L in the accommodation chamber 17 by adjusting the discharge pressure of the plating solution supply pump 21 in a state in which the on-off valve is closed. The drain pipe 26 may be connected to a supply source 22. In this case, the film formation device 1 returns the plating solution L used in the accommodation chamber 17 to the supply source 22 via the drain pipe 26, and can be reused at the time of film formation.

The film formation device 1 further includes a lifting device 28 for positioning the electrolyte membrane 13. The lifting device 28 raises and lowers the electrolyte membrane 13 together with the accommodation housing 15 and the anode 11 in the vertical direction in which the anode 11 and the substrate B face each other. The lifting device 28 includes a main body portion 28b and a movable portion 28m. The main body portion 28b is fixed to the upper fixing portion 50. The movable portion 28m has an upper side connected to the main body portion 28b and is vertically movable with respect to the main body portion 28b. The lower end of the movable portion 28m is mechanically connected to the accommodation housing 15. In the lifting device 28, the movable portion 28m is moved downward with respect to the main body portion 28b during film formation. As a result, the lifting device 28 lowers the electrolyte membrane 13 from the standby position shown in FIG. 1 together with the accommodation housing 15, the anode 11, and the like to the film formation position shown in FIG. 2, which will be described later, and brings the electrolyte membrane 13 into contact with the surface of the substrate B. Then, the lifting device 28 stops the movable portion 28m when the electrolyte membrane 13 contacts the front surface of the substrate B, thereby positioning the electrolyte membrane 13 in the vertical direction and fixing the position of the electrolyte membrane 13 in the vertical direction. In this way, the film formation device 1 brings the electrolyte membrane 13 into contact with the surface of the substrate B, and forms a metal film on the surface of the substrate B in this state. After the film formation, the lifting device 28 moves the movable portion 28m upward with respect to the main body portion 28b, thereby raising the electrolyte membrane 13 from the film formation position shown in FIG. 2 together with the accommodation housing 15, the anode 11, and the like to the standby position shown in FIG. 1, and separating the electrolyte membrane 13 from the front face of the substrate B.

FIG. 2 is a schematic cross-sectional view for explaining a film forming method of forming a metal film using the film formation device for the metal film according to the embodiment. Hereinafter, a method of forming a metal film using a film formation device for the metal film according to an embodiment will be described with reference to FIG. 1 and FIG. 2. Hereinafter, a method of forming a metal film using a film formation device for the metal film according to an embodiment is abbreviated as a method of forming a metal film according to an embodiment.

In the method for forming a metal film according to one embodiment, first, as shown in FIG. 1, in the film formation device 1 for the metal film according to one embodiment, the substrate B is placed on the mounting table 40 such that the surface of the substrate B (the surface on the conductive portion B1) faces the electrolyte membrane 13.

Next, as shown in FIG. 2, the movable portion 28m is moved downward with respect to the main body portion 28b by the lifting device 28. Accordingly, the electrolyte membrane 13 is lowered toward the mounting table 40 together with the accommodation housing 15, the anode 11, and the like. Consequently, the electrolyte membrane 13 contacts the surface of the substrate B (the surface of the conductive portion B1). Then, when the electrolyte membrane 13 contacts the front surface of the substrate B, the movable portion 28m is stopped, so that the electrolyte membrane 13 is positioned in the up-down direction and the position of the electrolyte membrane 13 in the up-down direction is fixed. In this way, the electrolyte membrane 13 is brought into contact with the surface of the substrate B.

Next, the plating solution L stored in the accommodation 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 stored in the accommodation chamber 17 is increased to the pressure set by the pressure regulating valve 27. When the pressure of the plating solution L stored in the accommodation chamber 17 is increased to the pressure set by the pressure regulating valve 27, the driving of the plating solution supply pump 21 may be stopped. On the other hand, after the time when the pressure of the plating solution L stored in the accommodation chamber 17 is increased to the pressure set by the pressure regulating valve 27, when the driving of the plating solution supply pump 21 is continued, the plating solution L continues to be supplied from the supply source 22 to the accommodation chamber 17, and the pressure of the plating solution L stored in the accommodation chamber 17 is maintained at the pressure set by the pressure regulating valve 27. Further, when the plating solution L is pressurized, the pressure reduction chamber 33 is reduced by the pressure reduction device 30.

As described above, in a state in which the electrolyte membrane 13 is in contact with the surface of the substrate B, the plating solution L is pressurized, and the electrolyte membrane 13 is pressed toward the cathode side by the liquid pressure of the plating solution L. As a result, the surface of the substrate B is uniformly pressed by the electrolyte membrane 13. At this time, the metal ions contained in the plating solution L can impregnate the electrolyte membrane 13. Further, the plating solution L is pressurized, the diaphragm 18 is pressed toward the anode 11 side by the liquid pressure of the plating solution L, the pressure reduction chamber 33 is reduced, the diaphragm 18 is sucked to the anode 11 side, the diaphragm 18 can be brought into close contact with the surface 11c of the anode 11 on the cathode side.

Next, while the surface of the substrate B is pressed by the electrolyte membrane 13 and the diaphragm 18 is in close contact with the surface 11c of the anode 11 on the cathode side, a voltage is applied between the anode 11 and the substrate B (cathode) by the power supply device 16, so that the metal-ion impregnated in the electrolyte membrane 13 is reduced. As a result, the metal film F is formed on the surface of the substrate B (the surface on the conductive portion B1) by depositing the metal derived from the metal ion.

FIG. 3 is a schematic cross-sectional view for explaining the principle of the operation and effect of the film formation device for the metal film according to the embodiment, and shows the structure between the anode and the plating solution. Hereinafter, the operation and effect of the film formation device 1 for the metal film according to one embodiment will be described.

In the film formation device 1 for the metal film according to the embodiment, the anode 11 is insoluble in the plating solution L. Therefore, at the time of forming 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 surface 11c of the anode 11 on the cathode side). This electrolysis reaction (2H₂O→4H⁺+O₂+4e⁻) generates oxygen-gas. If the generated oxygen gas is mixed into the plating solution L and remains in the accommodation chamber 17, a problem may occur. That is, since the oxygen gas has higher compressibility than the plating solution L, it is difficult to uniformly press the surface of the substrate B by the electrolyte membrane 13 due to the liquid pressure of the plating solution L by pressurizing the plating solution L. As a result, there is a possibility that the metal film F cannot be uniformly formed.

However, in the film formation device 1, the diaphragm 18 that allows water (H₂O) and hydrogen ions (H⁺) to pass therethrough and does not allow oxygen gas (O₂) to pass therethrough is attached so as to cover the surface 11c of the anode 11 on the cathode side and to be contacted with the surface 11c of the anode 11 on the cathode side. The anode 11 is attached so as to close an opening 15ha of the accommodation housing 15 communicating with the accommodation chamber 17. As a result, in the anode 11, the surface 11c of the cathode side is exposed to the accommodation chamber 17 via the diaphragm 18, and the surface 11a of the anode side is exposed to the outside of the accommodation housing 15. The anode 11 is formed of a mesh-like member that is permeable to oxygen gas. Further, in the film formation device 1, the diaphragm 18 is brought into close contact with the surface 11c of the anode 11 on the cathode side when the metal film F is formed.

Therefore, in the film formation device 1, at the time of forming the metal film F, as shown in FIG. 3, water of the components of the plating solution L can pass through the diaphragm 18, and is sequentially supplied to the surface 11c of the anode 11 on the cathode side. Therefore, oxygen-gas is generated by the electrolysis of water on the surface 11c of the anode 11 on the cathode-side. However, the oxygen-gas cannot pass through the diaphragm 18, and the diaphragm 18 is in close contact with the surface 11c of the anode 11 on the cathode-side. Therefore, the oxygen gas passes through the hole of the mesh-shaped member of the anode 11 and is discharged to the outside of the accommodation housing 15. As a result, it is possible to prevent the oxygen gas from remaining in the accommodation chamber 17 and prevent the oxygen gas from accumulating at the interface between the diaphragm 18 and the anode 11. Therefore, the surface of the substrate B can be uniformly pressed by the electrolyte membrane 13, and the metal film is uniformly formed. Furthermore, resistance is suppressed from occurring at the interface between the diaphragm 18 and the anode 11. In addition, hydrogen ions simultaneously generated by the reaction of electrolysis can pass through the diaphragm 18, and thus diffuse into the plating solution L. Therefore, excessive hydrogen ions around the anode 11 are suppressed. As a result, the voltage applied between the anode 11 and the substrate B is stabilized.

Note that the plating solution L may contain an additive such as an organic additive component in addition to the metal ion, but the additive cannot permeate through the diaphragm 18 (cation exchange membrane). Therefore, the additive does not directly contact the anode 11, and decomposition due to oxidation or the like of the additive at the anode 11 can be reduced. Therefore, it is possible to extend the life of the plating solution L. Electrons (e⁻) generated by the electrolysis flow through the anode 11 to the positive electrode of the power supply device 16.

Further, for example, in the structure of the conventional film formation device to which the insoluble anode described in JP 2020-152987 A is applied, to prevent the oxygen gas remains in the accommodation chamber in which the plating solution is stored, in order to uniformly deposit the metal film, separately from one accommodation chamber in which the plating solution is stored, partitioned by a diaphragm from the one accommodation chamber, insoluble anode it is necessary to be provided. On the other hand, in the film formation device 1 for the metal film according to the embodiment, the oxygen gas is prevented from remaining in the accommodation chamber 17 in which the plating solution L is stored, and the metal film F can be uniformly formed without providing another accommodation chamber in which the insoluble anode 11 is stored. Therefore, the metal film F can be uniformly formed, and the film formation device 1 can be miniaturized. Due to the miniaturization of the film formation device 1, in particular, the apparatus can be used with a configuration in which the distance between the anode 11 and the substrate B is a short distance of about several mm. As a result, the density distribution of the electric field lines on the surface of the substrate B can be made uniform, so that the metal film F can be formed more uniformly. In addition, unlike the structure of the conventional film formation device described above, the differential pressure between one accommodation chamber and another accommodation chamber increases, and the diaphragm 18 is not likely to be deformed or damaged.

Hereinafter, the configuration of the film formation device for the metal film according to the embodiment will be described in more detail.

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 an insoluble body capable of permeating oxygen gas, and may be, for example, a mesh-like member or a porous member other than a mesh-like member. As the porous body of the anode, a groove through which oxygen gas can flow may be provided on the surface of the anode on the cathode side, and a hole penetrating from the inside of the groove to the surface of the anode on the opposite side to the cathode side may be provided.

The material of the porous body of the anode is not particularly limited as long as the anode is an insoluble anode, but is preferably platinum, iridium oxide, or the like, for example. These are because the oxygen overvoltage is low and allows electrolysis of water at low voltages.

The diaphragm is not particularly limited as long as it is a membrane that allows water and hydrogen ions to pass therethrough and does not allow oxygen gas to pass therethrough. Examples of the diaphragm include a neutral diaphragm in addition to a cation exchange membrane (cation exchange membrane), but a cation exchange membrane is preferable. This is because the permeation performance of hydrogen ions is high. There are nanoscale channels in the cation exchange membrane. Cation exchange membranes selectively transmit water and hydrogen ions through nanoscale channels. The cation-exchange membrane preferably has a high water content, and specifically, for example, Nafion (registered trademark) manufactured by Du Pont Co., Ltd. is preferable. This is because a large amount of water can be supplied to the anode. The neutral septum is a neutral septum that is not ion-selective. If the problem of degradation of the additive at the anode does not occur, a neutral diaphragm may be used as the diaphragm. An example of a case where the problem of deterioration of the additive at the anode does not occur is a case where the additive is not included in the plating solution, a case where the additive contained in the plating solution does not permeate through the neutral diaphragm depending on the molecular weight or the like, and the like. The neutral diaphragm is preferably, for example, a Y-9207TA manufactured by Yuasa Membrane Systems Co., Ltd. The thickness of the diaphragm is preferably, for example, 10 μm to 200 μm. When the plating solution is a strongly alkaline solution containing metal ions, an anion exchange membrane (anion exchange membrane) may be used as the diaphragm.

The substrate is not particularly limited as long as the surface portion on which the metal film is formed functions as a cathode (conductive surface portion). The substrate may be, for example, one in which a conductor portion serving as a cathode is partially provided on the surface of the insulating portion as in one embodiment, or a substrate made entirely of a metal material such as aluminum or iron.

The electrolyte membrane is not particularly limited as long as it can be impregnated with metal ions contained in the plating solution by being brought into contact with the plating solution, and can deposit metal ions derived from 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 the electrolyte membrane include fluorine-based resins such as Nafion (registered trademark) manufactured by Du Pont, hydrocarbon-based resins, polyamic acid resins, and resins having an ion-exchange function such as CMV, CMD, CMF manufactured by Asahi Glass Co., Ltd.

The plating solution is a solution containing metal ions. More specifically, it is a solution containing a metal contained in a metal film in the form of a metal ion. The plating solution is not particularly limited as long as it is a solution containing a metal ion, and may contain an additive or the like in addition to the metal ion.

Examples of the metal of the metal ion include copper, nickel, silver, and iron. Examples of the plating solution include an aqueous solution obtained by dissolving at least one of these metals 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 an aqueous solution of nickel sulfate, nickel nitrate, nickel phosphate, nickel succinate, nickel pyrophosphate, and the like. The plating solution may be an acidic solution or an alkaline solution.

The pressurizing device is not particularly limited as long as it can pressurize the plating solution stored in the accommodation chamber. The pressurizing device may be, for example, a plating solution supply pump or a pressurizing device composed of a cylinder and a piston. In the pressurizing device, in a state in which the cylinder in which the plating solution is stored is connected to the accommodation housing so as to communicate with the accommodation chamber, the plating solution in the accommodation chamber can be pressurized and depressurized by advancing and retracting the piston in the cylinder.

The film formation device for the metal film preferably further includes a device for bringing the diaphragm into close contact with the surface of the anode on the cathode side. This is because, by suppressing the occurrence of the accumulation resistance of oxygen gas or the like at the interface between the diaphragm and the anode, it is possible to stably flow a current between the anode and the substrate (cathode), so that it is possible to realize uniform film formation of the metal film. The apparatus to be brought into close contact is not particularly limited as long as the diaphragm can be brought into close contact with the surface of the anode on the cathode side. As the apparatus to be brought into close contact with each other, an apparatus capable of uniformly pressing the diaphragm to the anode side is preferable, and for example, the above-described pressurizing device is preferable. The pressurizing device pressurizes the plating solution and presses the diaphragm toward the anode side with the liquid pressure of the plating solution, whereby the diaphragm can be brought into close contact with the anode. As a device capable of uniformly pressing the diaphragm to the anode side, for example, a pressure reduction device that reduces the pressure in a space outside the accommodation housing in which the surface of the anode opposite to the cathode side is exposed is preferable. The pressure reduction device can bring the diaphragm into close contact with the anode by reducing the pressure in the space and sucking the diaphragm to the anode side. Examples of the decompression device include a pressure reduction housing, an exhaust pipe, and a decompression pump, and include a device that decompresses the pressure reduction chamber. As the film formation device, a film formation device including both a pressurizing device and a depressurizing device is preferable as an apparatus to be brought into close contact. This is because it is possible to sufficiently suppress the occurrence of the resistance due to the accumulation of oxygen gas or the like at the interface between the diaphragm and the anode. Note that the apparatus to be brought into close contact may be a device that generates a flow from the cathode side toward the anode side in the plating solution stored in the accommodation chamber (for example, a device including a propeller and a driving device that rotates the propeller).

The film formation device for the metal film may further include a lifting device. The lifting device is not particularly limited as long as the electrolyte membrane can be positioned by raising and lowering the electrolyte membrane in a direction in which the anode and the substrate face each other. The lifting device may be, for example, a hydraulic or pneumatic actuator composed of a cylinder and a piston, or may be, for example, an electric actuator lifted and lowered by a motor or the like. Note that the film formation device does not have to include the lifting device as long as the electrolyte membrane can be positioned by raising and lowering the electrolyte membrane in the opposite direction in which the anode and the substrate face each other.

The film formation device for the metal film is not particularly limited, but may be one in which the constituent elements are arranged such that the opposite direction in which the anode and the substrate face each other is parallel to the vertical direction. As a film formation device for a metal film, the constituent elements may be arranged such that the opposite direction in which the anode and the substrate face each other is the horizontal direction. As a film formation device for a metal film, the constituent elements may be arranged such that the opposite direction in which the anode and the substrate face each other is a direction inclined with respect to the vertical direction.

Hereinafter, a film formation device for a metal film according to an embodiment will be described in more detail with reference to a reference example and a comparative example.

Reference Example 1

First, a test system 1 of a film formation device for a metal film was constructed. The test system 1 simulates the film formation device for a metal film according to the embodiment. FIG. 4 is a schematic cross-sectional view showing a test system 1 of a film formation device for a metal film.

In the test system 1, as shown in FIG. 4, the internal space of the housing is partitioned into an accommodation chamber and a pressure reduction chamber by an anode and a diaphragm. A substrate serving as a cathode is accommodated in the accommodation chamber. In addition, a plating solution is accommodated in the accommodation chamber. Further, a power supply device that applies a voltage between the anode and the substrate (cathode) is provided. A pressurizing device (not shown) for pressurizing the plating solution stored in the accommodation chamber is provided. A decompression device (not shown) for decompressing the pressure reduction chamber is provided.

The diaphragm covers the cathode-side surface of the anode and is attached to the housing so as to contact the cathode-side surface of the anode. The diaphragm is a cation exchange membrane that is permeable to water and hydrogen ions and impermeable to oxygen gas. The anode is attached to the housing such that the surface on the cathode side is exposed to the accommodation chamber via the diaphragm, and the surface on the opposite side to the cathode side is exposed to the pressure reduction chamber, so as to close the communication portion communicating the accommodation chamber and the pressure reduction chamber. The anode is formed of a plate-like mesh member insoluble in the plating solution. The mesh-like 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 metallic material. The plating solution is an acidic aqueous solution containing metal ions, and is an electrolytic solution having conductivity.

Subsequently, a test system 1 was used to deposit a metal coating on the surface of the substrate. Specifically, the plating solution stored in the accommodation chamber is pressurized by the pressurizing device, and the fluid pressure of the plating solution is kept constant. At the same time, the pressure reduction chamber was decompressed at −0.3 atmospheres relative to atmospheric pressure by the decompression device. While the above conditions were maintained, a current was applied at a constant current (10 mA) between the anode and the substrate (cathode) by the power supply device. As a result, the metal ions contained in the plating solution were reduced, so that a metal film was formed on the surface of the substrate.

Reference Example 2

The test system 1 was used under the same conditions as in Reference Example 1 except that the decompression of the pressure reduction chamber was not performed, and a metal film was formed on the surface of the substrate. Specifically, the plating solution stored in the accommodation chamber is pressurized by the pressurizing device, and the fluid pressure of the plating solution is kept constant. At the same time, the pressure reduction chamber was left at atmospheric pressure without decompression. While the above conditions were maintained, a current was applied at a constant current (10 mA) between the anode and the substrate (cathode) by the power supply device. As a result, the metal ions contained in the plating solution were reduced, so that a metal film was formed on the surface of the substrate.

Comparative Example

First, a test system 2 of a film formation device for a metal film was constructed. Unlike the embodiment, the test system 2 simulates a film formation device for a metal film that does not include a diaphragm. FIG. 5 is a schematic cross-sectional view showing a test system 2 of a film formation device for a metal film.

In the test system 2, as shown in FIG. 5, the internal space of the same housing as the test system 1 is partitioned into two accommodation chambers by the same anode as the test system 1. One of the accommodation chambers is the same as the accommodation chamber of the test system 1, and the same substrate as the test system 1 is stored. Both chambers contain the same plating solution as the test system 1. Further, a power supply device that applies a voltage between the anode and the substrate (cathode) is provided. A pressurizing device (not shown) for pressurizing the plating solution accommodated in both accommodation chambers is provided. The anode is attached to the housing so as to close the communication portion that communicates with both the accommodation chambers such that the surface on the cathode side is exposed to one accommodation chamber and the surface on the opposite side to the cathode side is exposed to the other accommodation chamber.

Subsequently, a test system 2 was used to deposit a metal coating on the surface of the substrate. Specifically, the plating solution stored in both the accommodation chambers is pressurized by the pressurizing device, and the fluid pressure of the plating solution is kept constant. While this condition was maintained, a constant current (10 mA) was applied between the anode and the substrate (cathode) by the power supply device. As a result, the metal ions contained in the plating solution were reduced, so that a metal film was formed on the surface of the substrate.

EVALUATION

In Reference Examples 1 and 2 and Comparative Examples, the voltage (bath voltage) between the anode and the substrate was measured at the time of forming the metal film, and the time-dependent change in the voltage at the constant current (10 mA) at the time of forming the metal film was evaluated. FIG. 6 is a graph showing a time-dependent change in voltage at a constant current (10 mA) at the time of film formation of a metal film in Reference Examples 1 and 2 and Comparative Examples.

As shown in FIG. 6, in the reference example 1, the voltage is constant after the voltage rises until a predetermined time elapses from the start of the application of the current, and the current can continuously flow at a constant voltage. In Reference Example 1, the pressure reduction chamber is depressurized, as a result of the diaphragm is sufficiently close contact with the anode, without oxygen gas generated by air or electrolysis at the interface between the diaphragm and the anode accumulates, oxygen gas passes through the pores of the anode of the porous body, it is considered that discharged to the pressure reduction chamber. Thus, it is considered that the occurrence of high resistance at the interface between the diaphragm and the anode can be suppressed. Therefore, under the conditions of Reference Example 1, the reaction resistance of the anode can be suppressed, it is considered that the metal film can be formed at high speed. On the other hand, in Reference Example 2, the voltage continued to increase at a higher speed than in Reference Example 1 after the application of the current started, and reached the upper limit (20 V) of the power supply. Eventually, the resistance between the anode and the substrate became high and no current was applied. In Reference Example 2, unlike Reference Example 1, as a result of the diaphragm is not sufficiently adhered to the anode because the pressure reduction chamber was not depressurized, air and oxygen gas at the interface between the diaphragm and the anode accumulated, it is considered that high resistance occurred. Further, in the comparative example, after the application of the current was started, the voltage initially increased at a gentler speed than in the reference example 1, and continued to increase while increasing the speed, and reached the upper limit (20 V) of the power supply. In the comparative example, it is considered that the anode is continuously covered with oxygen gas and the voltage is continuously increased.

Although the film formation device for a metal film according to the embodiment of the present disclosure has been described in detail above, the present disclosure is not limited to the above-described embodiment, and various design changes can be made without departing from the spirit of the present disclosure described in the claims.

FILM FORMATION DEVICE FOR METAL FILM

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