PURPOSE: To make it possible to form roughly an even distorted field as a whole even in case the distribution of the intensity of the beam of an excimer laser is uneven by a method wherein adjacent linear damages in the direction vertical to linear damages to be inflicted are formed in such a way that they are shifted from each other along the damages.

CONSTITUTION: Linear damages 2 having an inclination θ to a direction 3 of movement of a silicon wafer 1 are formed. Adjacent linear damages in a direction 7 vertical to the damages 2 are shifted from each other in a lengthwise direction 6 of the damages 2 by the amount Δd of shift. As a result, even if a distribution of an intensity of a beam of an excimer laser is uneven, an even distorted field can be formed as a whole by a method wherein a part 2b of the weak intensity of the beam and a part 2a of the strong intensity of the beam are overlapped each other in the direction 7 vertical to the damages 2 and the amount Δd of shift is properly selected. The inclination θ to the direction 3 of movement of the wafer 1 is give in tan θ=D/Δd to the amount Δd of shift. Provided that, the D is proper intervals (μm) between the damages 2 and the unit of the Δd is μm.