Method for manufacturing vibration element

A method for manufacturing a vibration element, that includes a first vibrating arm and a second vibrating arm extending along a first direction and arranged side by side along a second direction intersecting the first direction, the first vibrating arm and the second vibrating arm each having a first surface and a second surface arranged side by side in a third direction intersecting the first direction and the second direction in a front and back relationship, a bottomed first groove opening to the first surface, and a bottomed second groove opening to the second surface, the method comprising steps of:

• providing a quartz crystal substrate having a first substrate surface and a second substrate surface in a front and back relationship, a first vibrating arm forming region in which the first vibrating arm is to be formed, a second vibrating arm forming region in which the second vibrating arm is to be formed, a first groove forming region in which the bottomed first groove is to be formed, a second groove forming region in which the bottomed second groove is to be formed, and an inter-arm region that is located between the first vibrating arm forming region and the second vibrating arm forming region;
• forming a first base film on the first substrate surface in the first vibrating arm forming region and the second vibrating arm forming region;
• forming a first protective film in a region of the first base film excluding the first groove forming region;
• a first dry-etching of the first substrate surface of the quartz crystal substrate through the first base film and the first protective film to simultaneously form the first surfaces, the bottomed first grooves, and outer shapes of the first vibrating arm and the second vibrating arm;
• forming a second base film on the second substrate surface in the first vibrating arm forming region and the second vibrating arm forming region;
• forming a second protective film in a region of the second base film excluding the second groove forming region;
• a second dry-etching of the quartz crystal substrate at the second substrate surface through the second base film and the second protective film to simultaneously form the second surfaces, the bottomed second grooves, and the outer shapes of the first vibrating arm and the second vibrating arm;
• wherein the method for manufacturing the vibration element further comprises:
• forming a third protective film that is thinner than the first protective film in the first groove forming region of the first base film;
• and
• forming a fourth protective film that is thinner than the second protective film in the second groove forming region of the second base film.