레이저 가공 장치의 레이저 발진기는 복수의 서브 펄스로 구성된 각각의 버스트 펄스를 생성한다.
A laser oscillator of a laser processing apparatus generates burst pulses each composed of a plurality of sub-pulses. The plurality of sub-pulses are generated in such a manner that the energy of the sub-pulse sequentially changes from a lower energy to a higher energy, and the burst pulses are applied to a wafer, whereby the wafer is formed therein with shield tunnels extending from the front surface to the back surface of the wafer and each being composed of a minute hole and an amorphous phase surrounding the minute hole.