Method of cutting semiconductor substrate via modified region formation and subsequent sheet expansion

A method of cutting a semiconductor substrate, the method comprising the steps of:

• irradiating a semiconductor substrate having a sheet bonded thereto with laser light having a wavelength that enables the laser light to transmit through a laser incident surface of the semiconductor substrate, while locating a light-converging point within the semiconductor substrate, thereby forming a modified region only within the semiconductor substrate along each of a plurality of cutting lines arranged in a matrix with respect to a surface of the semiconductor substrate, wherein each modified region is a molten processed region separated from the laser incident surface in a thickness direction of the semiconductor substrate, and wherein each modified region forms a cutting part of the semiconductor substrate to be cut;
• and
• expanding the sheet, after the cutting parts of the semiconductor substrate are formed by the irradiating step, by pulling peripheral portions of the sheet outwardly, thereby cutting and separating at least the semiconductor substrate along the cutting lines along which the cutting parts have been formed.