Laser processing method for cutting substrate and laminate part bonded to the substrate

A laser processing method of irradiating a substrate having a front face formed with a laminate part including a plurality of functional devices with laser light while locating a light-converging point of the laser light within the substrate so as to form a modified region which functions as a start point for cutting within the substrate along a cutting line of the substrate,

• the method comprising:
• a first forming step of forming a plurality of rows of first modified regions along the cutting line;
• a second forming step of forming at least one row of a second modified region along the cutting line at a position between the first modified region closest to a rear face of the substrate and the rear face to form a fracture extending along the cutting line from the second modified region to the rear face such that the fracture does not reach the front face of the substrate;
• expanding an expandable film bonded to the rear face of the substrate in a direction that is parallel to the rear face of the substrate to expand the fracture at the rear face to cut the substrate and the laminate part along the cutting line by advancing the fracture from the substrate to the laminate part by way of the first modified regions.