Patent ID: 8735770

Claim:
A laser processing method of irradiating a planar object to be processed attached to an expandable sheet stretched over an annular frame with processing laser light while locating a converging point within the object with a converging lens, so as to form a modified region to become a cutting start point within the object along a line to cut the object, the method comprising the steps of: setting a processing region having an outer shape between the object and the frame; obtaining coordinates of one intersection between a line including the line to cut and the outer shape of the processing region and coordinates of the other intersection between the line and the outer shape of the processing region; and adjustment information acquiring step of relatively moving at least one of the converging lens and object along the line including the line to cut and, while converging measuring laser light toward the processing region with the converging lens when the converging lens is positioned on the processing region, in the period from when the converging lens reaches the one intersection between the line and the outer shape of the processing region to when the converging lens reaches the other intersection between the line and the outer shape of the processing region, and detecting a reflected light component of the measuring laser light reflected by a laser light irradiation surface of the object, so as to adjust a distance between the laser light irradiation surface and the converging lens such that the converging point of the converging lens is located at a predetermined position with reference to the laser light irradiation surface, converging the processing laser light toward the object with the converging lens, so as to form the modified region within the object, wherein in the step of forming the modified region within the object at least one of step (i) and step (ii) is performed, (i) starting emission of the measuring laser light when the converging lens reaches the one intersection between the line and the outer shape of the processing region, and stopping the emission of the measuring laser light when the converging lens reaches the other intersection between the line and the outer shape of the processing region; (ii) starting an arithmetic operation based on a quantity of the reflected light component of the measuring laser light when the converging lens reaches the one intersection between the line and the outer shape of the processing region, and stopping the arithmetic operation when the converging lens reaches the other intersection between the line and the outer shape of the processing region wherein the arithmetic operation is a focusing operation of the converging lens.