Patent ID: 7615721

Claim:
A laser processing method comprising: a first step of irradiating an object to be processed with laser light while locating a light converging point of the laser light therewithin, and pulsing the laser light such that each pulse of the laser light forms a modified spot, and the pulsing of the laser light forms a plurality of modified spots which form a modified region caused by multiphoton absorption within said object along a predetermined line in said object without intentionally exposing the modified region in at least a laser light entrance surface of the object to which the laser light is irradiated and without forming grooves in the laser light entrance surface, the formed modified regions having a maximum length in a thickness direction of the object and a length of the modified regions formed in a direction along the predetermined line being larger than any length of the modified region in a direction perpendicular to the direction extending along the predetermined line, and a modified spot formed by a pulse of the laser light has a maximum length in the thickness direction, and a length of said modified spot formed in the direction along the predetermined line is larger than a length of the modified spot in a direction parallel to the surface of the object and perpendicular to the direction extending along the predetermined line; and a second step of irradiating said object with laser light which is transparent through an unmodified region of said object but is more absorbable by said modified region than by said unmodified region to change the modified region formed in the first step and having a function as a cutting start point, into a modified region which easily causes a crack in comparison with the modified region formed in the first step so as to generate a stress at a part where said object is cut along said predetermined line after said first step.