Film formation apparatus and film formation method for forming metal film

A film formation apparatus for forming a metal film, comprising:

• an anode;
• a solid electrolyte membrane disposed between the anode and a substrate;
• a power supply that applies a voltage between the anode and the substrate serving as a cathode;
• and
• a liquid reservoir that holds the anode and the solid electrolyte membrane while separating the anode and the solid electrolyte membrane apart from each other, the liquid reservoir storing an electrolyte solution comprising metal ions between the anode and the solid electrolyte membrane,
• the film formation apparatus being configured to apply a voltage between the anode and the substrate while allowing the solid electrolyte membrane to be in contact with the substrate to reduce the metal ions in the solid electrolyte membrane, and form the metal film on a surface of the substrate,
• wherein,
• the solid electrolyte membrane comprises a central portion, which is a portion that comes into contact with the substrate and the electrolyte solution, and an outer edge portion located outside the central portion,
• the film formation apparatus further comprises a membrane tensioning mechanism configured to apply a tensile force from the central portion toward the outer edge portion while storing the electrolyte solution in the liquid reservoir, to elongate the central portion of the solid electrolyte membrane.