Patent ID: 8247311

Claim:
A laser processing method of converging laser light within a silicon wafer having a thickness t (500 μm<t) with a condenser lens and thereby forming a plurality of rows of modified regions to become a cutting start point within the silicon wafer along a line to cut the silicon wafer, the method comprising the steps of: forming a first modified region along the line to cut in a first area having a depth of 350 μm to 500 μm from a laser light entrance surface of the silicon wafer; forming a second modified region along the line to cut in a second area having a depth of 0 μm to 250 μm from the laser light entrance surface, wherein a laser light irradiation condition for forming the first modified region is made different from a laser light irradiation condition for forming the second modified region, and the making of the laser light irradiation conditions different corrects a spherical aberration of the laser light in the first area; and suppressing occurrence of twist hackles within an area of the silicon wafer by ensuring that the laser light incident on the condenser lens when forming the first modified region has a divergent angle greater than that of the laser light incident on the condenser lens when forming the second modified region, wherein the divergent angle of the laser light incident on the condenser lens is changed by a beam expander.