Method for manufacturing vibration element

A method for manufacturing a vibration element including a first vibrating arm and a second vibrating arm that extend along a first direction and are arranged side by side along a second direction intersecting the first direction, the first and second vibrating arms each have 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 for manufacturing the vibration element comprising:

• providing a quartz crystal substrate having a first substrate surface and a second substrate surface in a front and back relationship, and having a first vibrating arm forming region, a second vibrating arm forming region, a first groove forming region, a second groove forming region, and a inter-arm region located between the first vibrating arm forming region and the second vibrating arm forming region;
• forming a first protective film on the first substrate surface in a region excluding the first groove forming region where the bottomed first grooves are to be formed from in the first vibrating arm forming region where the first vibrating arm is to be formed and the second vibrating arm forming region where the second vibrating arm is to be formed;
• a first dry-etching of the first substrate surface of the quartz crystal substrate via the first protective film to form the bottomed first grooves and to begin forming outer shapes of the first and second vibrating arms;
• forming a second protective film in the bottomed first grooves that were formed during the first dry-etching;
• a second dry etching of the first substrate surface of the quartz crystal substrate via the second protective film to form the first surface and to continue to form the outer shapes of the first and second vibrating arms;
• forming a third protective film on the second substrate surface in a region excluding the second groove forming region where the bottomed second grooves are to be formed in the first vibrating arm forming region and the second vibrating arm forming region;
• a third dry etching of the second substrate surface the quartz crystal substrate via the third protective film to form the bottomed second grooves and to continue to form the outer shapes of the first and second vibrating arms;
• forming a fourth protective film in the bottomed second grooves;
• and
• a fourth dry etching of the second substrate surface of the quartz crystal substrate via the fourth protective film to form the second surface and to complete formation of the outer shapes of the first and second vibrating arms.