CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese patent application JP 2019-054747 filed on Mar. 22, 2019, the entire content of which is hereby incorporated by reference into this application.

BACKGROUND

Technical Field

The present disclosure relates to a film forming apparatus for forming a metal film on a surface of a substrate.

Background Art

Conventionally, film forming techniques for forming a metal film on a surface of a substrate by depositing metal ions thereon is used. For example, JP 2014-051701 A proposes a film forming apparatus for forming a metal film on a surface of a substrate by applying a voltage across an anode and the substrate while pressurizing an electrolyte membrane against the substrate and thus reducing metal ions in the electrolyte membrane.

In such a film forming apparatus, a housing chamber, which houses an electrolytic solution containing metal ions, is provided in contact with the anode and the electrolyte membrane. The electrolyte membrane is attached to a housing, which forms the housing chamber, via an elastic body so as to cover an opening of the housing, and the electrolytic solution is hermetically sealed in the housing chamber.

When a metal film is formed, the substrate is pressurized with the electrolyte membrane with a predetermined pressure while the electrolyte membrane is placed in contact with the substrate so that the elastic body is compressively deformed. Through such compressive deformation of the elastic body, the electrolytic solution in the housing chamber is pressurized and the surface of the substrate is thus pressurized with the electrolyte membrane that is subjected to the fluid pressure of the electrolytic solution. With such a pressurized state maintained, a voltage is applied across the anode and the substrate so that a metal film can be formed on the surface of the substrate.

SUMMARY

However, if an insoluble anode is used as the anode of the film forming apparatus of JP 2014-051701 A, electrolysis of water of the electrolytic solution may occur on the surface of the anode, which in turn may generate oxygen gas on the surface of the anode. Then, the amount of oxygen gas generated may increase with the passage of the film forming time, and the increased oxygen gas may aggregate and accumulate in a predetermined portion on the surface of the anode. Such a phenomenon can occur not only when the electrolytic solution used is an aqueous solution containing metal ions but also when the electrolytic solution used is an electrolytic solution obtained by mixing metal ions in a solvent other than water, such as alcohol, as long as even a slight amount of water is mixed in the electrolytic solution while a film is formed.

As described above, when a metal film is formed, the substrate is pressurized with the electrolyte membrane with the fluid pressure of the electrolytic solution, but if oxygen gas remains in the housing chamber, it may be difficult to uniformly pressurize the surface of the substrate with the electrolyte membrane because the residual oxygen gas has higher compressibility than that of the electrolytic solution. Consequently, it is supposed that a uniform metal film may not be able to be formed.

In view of the foregoing, exemplary embodiments of the present disclosure provide a film forming apparatus for forming a metal film, capable of uniformly pressurizing a surface of a substrate with an electrolyte membrane that is subjected to the fluid pressure of an electrolytic solution containing metal ions while the metal film is formed, even when an anode that is insoluble in the electrolytic solution is used.

Accordingly, a film forming apparatus for forming a metal film according to the present disclosure is a film forming apparatus including at least an anode, an electrolyte membrane disposed between the anode and a substrate, the substrate serving as a cathode, a housing having formed therein a housing chamber that houses an electrolytic solution so that the electrolytic solution contacts the anode and the electrolyte membrane, and a power supply unit adapted to apply a voltage across the anode and the substrate, in which a voltage is applied across the anode and the substrate while the electrolyte membrane is pressurized against the substrate so that metal ions contained in the electrolyte membrane are (chemically) reduced on a surface of the substrate and a metal film is thus formed on the surface of the substrate, the electrolyte membrane is attached to the housing so as to cover an opening of the housing communicating with the housing chamber, the housing has disposed therein a partition member between the anode and the electrolyte membrane, the partition member being adapted to partition the housing into a first housing chamber on the side of the anode that houses a first electrolytic solution as the electrolytic solution and a second housing chamber on the side of the electrolyte membrane that houses a second electrolytic solution as the electrolytic solution, the partition member includes a porous body impregnated with cation exchange resin, the first housing chamber houses as the anode an anode that is insoluble in the first electrolytic solution, the second housing chamber has formed therein a hermetically sealed space in which the second electrolytic solution containing the metal ions is hermetically sealed as the electrolytic solution within the housing, by the electrolyte membrane and the partition member, and the film forming apparatus is provided with a pressure unit adapted to pressurize the second electrolytic solution housed in the second housing chamber.

According to the present disclosure, when a voltage is applied across the anode and the substrate while the substrate is pressurized with the electrolyte membrane, metal ions contained in the electrolyte membrane are reduced on the surface of the substrate. Accordingly, a metal film is formed on the surface of the substrate. In the present disclosure, the partition member is disposed between the anode and the electrolyte membrane, and the partition member includes a porous body impregnated with cation exchange resin. Therefore, formation of an electric field in a region of from the anode to the substrate is not hindered even when a voltage is applied across the anode and the substrate within the housing chamber.

Herein, since the film forming apparatus of the present disclosure uses an anode that is insoluble in the first electrolytic solution, water contained in the first electrolytic solution housed in the first housing chamber may possibly be electrically decomposed while a film is formed, which in turn may generate oxygen gas. However, since the first electrolytic solution and the second electrolytic solution are separated by the partition member in the housing chamber, and the second housing chamber has formed therein a hermetically sealed space in which the second electrolytic solution is enclosed, there is no possibility that the oxygen gas from the anode will be mixed into the second electrolytic solution. Thus, the second electrolytic solution in the second housing chamber can be pressurized by the pressure unit. Accordingly, the surface of the substrate can be uniformly pressurized with the electrolyte membrane that is subjected to the fluid pressure of the second electrolytic solution housed in the second housing chamber.

Further, although hydrogen ions in the first housing chamber increase due to the electrical decomposition of water, such hydrogen ions will pass through the cation exchange resin of the partition member and move to the second housing chamber. Therefore, there is no possibility that excessive hydrogen ions may gather around the anode. Therefore, the voltage applied across the anode and the substrate is stable.

In this manner, even when an anode that is insoluble in the first electrolytic solution is used, it is possible to stabilize a voltage applied across the anode and the substrate while maintaining the state in which the substrate is uniformly pressurized with the electrolyte membrane during formation of a metal film. Accordingly, metal ions contained in the second electrolytic solution in the second housing chamber can be reduced on the surface of the substrate, and a uniform metal film can thus be formed on the surface of the substrate.

Herein, the first housing chamber may be formed of a hermetically sealed space in which the first electrolytic solution is enclosed as long as, even when gas generated on the anode has accumulated in the first housing chamber, the accumulated gas does not inhibit the formation of a metal film. However, in some embodiments, the first housing chamber is open to the outside of the film forming apparatus. According to such embodiments, even when oxygen gas is generated from the anode while a film is formed, the generated oxygen gas can be discharged to the outside of the film forming apparatus.

According to the present disclosure, even when an insoluble anode is used as the anode, a surface of a substrate can be uniformly pressurized with an electrolyte membrane that is subjected to the fluid pressure of an electrolytic solution containing metal ions while a film is formed.

