A method includes preparing a wafer including a substrate and a semiconductor structure, and irradiating an inner portion of the substrate at a predetermined depth in a thickness direction a plurality of times with laser pulses at a first time interval and a predetermined distance interval between irradiations. Each irradiation performed at the first time intervals in the step of irradiating the substrate with laser pulses includes irradiating the substrate at a first focal position in the thickness direction with a first laser pulse having a first pulse-energy; and after irradiating with the first laser pulse, irradiating the substrate with a second laser pulse performed after a second time interval, the second time interval being shorter than the first time interval and being in a range of 3 ps to 900 ps, and the second laser pulse having a second pulse-energy 0.5 to 1.5 times the first pulse-energy.