Method of forming through-substrate

A method of forming a through-substrate having a first surface and a second surface opposite to the first surface, the method causing the first surface to communicate with the second surface through the substrate, the method comprising:

• a first step that forms a first trench having a protective film on its side surfaces using dry etching from a side of the first surface of the substrate, the dry etching comprising a process that performs etching and forming the protective film;
• and
• a second step that forms a second trench from a side of the second surface of the substrate using dry etching, the second trench communicating with the first trench,
• wherein the dry etching in the second step is performed while the protective film formed in the first step is present on the side surfaces of the first trench,
• wherein the first step comprises:
• a trench formation that etches the substrate, and forms a trench;
• a depth adjustment that adjusts a depth of the trench while forming the protective film on the side surfaces of the trench by the dry etching, and forms the trench as the first trench;
• and
• a protective film adjustment that adjusts a state of the protective film after the depth adjustment, and
• wherein the protective film adjustment comprises forming the protective film on the first surface.