It is an object to improve a yield of a step of cutting off a substrate. A substrate is cut off by using an ablation process. An ablation process uses a phenomenon in which a molecular bond in a portion irradiated with a laser beam, that is, a portion which absorbs the laser beam is cut off, photodegraded, and evaporated. In other words, a substrate is irradiated with a laser beam, a molecular bond in a portion of the substrate is cut off, photodegraded, and evaporated; accordingly, a groove is formed in the substrate. A method for cutting the substrate has steps of selectively emitting a laser beam and forming a groove in the substrate, and selectively emitting a laser beam to the groove and cutting off the substrate. Methods for manufacturing a groove in a substrate and cutting off a substrate are used for manufacturing a semiconductor device.