Patent ID: 8624153

Claim:
A laser processing method, for irradiating an object to be processed with a first laser beam while converging the first laser beam with a lens such that a converging point is positioned within the object, and forming a modified region within the object along a cutting line in the object; the method comprising: a preparatory step of holding the lens at an initial position with respect to a main surface of the object in a vertical direction, the initial position being set so that the converging point is located at a predetermined position within the object; a first processing step of emitting the first laser beam while holding the lens at the initial position, and moving the lens and the object relative to each other along the main surface of the object, thereby forming an initial portion of the modified region in one end part of the cutting line; and a second processing stet of releasing the lens from being held at the initial position after forming the initial portion of the modified region in the one end part, and then moving the lens and the object relative to each other along the main surface while adjusting a gap between the lens and the main surface of the object, thereby forming a remainder portion of the modified region that is different than the initial portion, wherein the method switches from the first processing step to the second processing step during the forming of the modified region, and wherein, in the second processing step, the first laser beam and a second laser beam for measuring a displacement of the main surface are converged by the lens onto the object on the same axis, and the lens is released from being held after the quantity of reflected light of the second laser beam reflected by the main surface exceeds a predetermined threshold.