Laser processing method

A laser processing method of converging laser light within a silicon wafer having a thickness t (500 μm<t) with a condenser lens so as to form 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 by locating a converging point of the laser light in the first area;
• and
• 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 by locating the converging point in the second area;
• wherein, when forming the first modified region, the laser light is converged within the silicon wafer so as to cancel a spherical aberration to occur in response to a depth from the laser light entrance surface, and thereby an influence of the spherical aberration is reduced.

A laser processing method of converging laser light within a silicon wafer having a thickness t (350 μm<t≦500 μm) with a condenser lens so as to form 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 t μm from a laser light entrance surface of the silicon wafer by locating a converging point of the laser light in the first area;
• and
• 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 by locating the converging point in the second area;
• wherein, when forming the first modified region, the laser light is converged within the silicon wafer so as to cancel a spherical aberration to occur in response to a depth from the laser light entrance surface, and thereby an influence of the spherical aberration is reduced.