A silicon oxide film having at least one opening portion is formed, on a silicon substrate. A structural member formed of a material less prone to be etched by hydrofluoric acid than a silicon oxide film is formed, wherein the structural member is provided on the silicon oxide film and reaches the silicon substrate in the opening portion. Wet etching using hydrofluoric acid is performed, on the silicon substrate on which the silicon oxide film and the structural member are provided. The interface between the silicon oxide film and the structural member is exposed to hydrofluoric acid, in performing the wet etching.