Method of manufacturing vibration element

A method of manufacturing a vibration element comprising a crystal substrate and including

• a first vibration arm and a second vibration arm extending along a first direction and arranged side by side along a second direction intersecting the first direction,
• the first vibration arm and the second vibration arm each having a first surface and a second surface in a front and back relationship that are arranged side by side in a third direction intersecting the first direction and the second direction, and a bottomed groove opening to the first surface, and
• electrodes provided on each of the first vibration arm and the second vibration arm that through application of a drive signal thereto cause the first vibration arm and the second vibration arm to vibrate,
• the method comprising:
• providing the crystal substrate having a first substrate surface and a second substrate surface in a front and back relationship;
• forming a protective film on the first substrate surface;
• and
• dry-etching the protective film and the first substrate surface of the crystal substrate in a single dry-etching step, simultaneously forming the first surface, the bottomed groove, and outer shapes of the first vibration arm and the second vibration arm,
• wherein the forming of the protective film includes applying a protective material to the first substrate surface, exposing the protective material, and developing the protective material such that T1<T2<T3, and
• the forming of the protective film such that T1<T2<T3 is satisfied is conducted before the single dry-etching step of the first substrate surface of the crystal substrate,
• wherein T1 is a thickness of the protective film along the third direction in an inter-arm region positioned between a first vibration arm forming region in which the first vibration arm is formed and a second vibration arm forming region in which the second vibration arm is formed,
• T2 is a thickness of the protective film along the third direction in a groove forming region in which the groove is formed, and
• T3 is a thickness of the protective film along the third direction in a region of the first vibration arm forming region and the second vibration arm forming region excluding the groove forming region.