Substrate manufacturing method

A substrate manufacturing method for manufacturing a substrate from a workpiece having a first surface and a second surface on an opposite side from the first surface, the substrate manufacturing method comprising:

• a peeling layer forming step of forming a peeling layer by moving (a) a place where a laser beam having a wavelength transmitted through a material constituting the workpiece is condensed and (b) the workpiece relative to each other along a processing feed direction parallel with the first surface in a state in which the laser beam is condensed in the workpiece;
• an indexing feed step of moving (a) the place where the laser beam is condensed and (b) the workpiece relative to each other along an indexing feed direction orthogonal to the processing feed direction and parallel with the first surface by an indexing feed distance;
• and
• a separating step of separating the substrate from the workpiece with the peeling layer as a starting point after repeating the peeling layer forming step and the indexing feed step alternately,
• wherein, in the peeling layer forming step, the laser beam is condensed so as to have a larger length along the indexing feed direction than a length along the processing feed direction
• wherein, in the peeling layer forming step, the workpiece is irradiated with the laser beam having a wave front controlled by a spatial light modulator,
• light rays located on a central side in a direction corresponding to the indexing feed direction in light rays constituting the laser beam entering the spatial light modulator are condensed to both end sides in the indexing feed direction of the place, and
• light rays located on both end sides in the direction corresponding to the indexing feed direction in the light rays constituting the laser beam entering the spatial light modulator are condensed to a central side in the indexing feed direction of the place.