Method of manufacturing substrate

A method of manufacturing a substrate from a workpiece made of gallium oxide such that the substrate is thinner than the workpiece, the method comprising:

• a separation layer forming step of moving the workpiece and a focused spot of a laser beam having a wavelength transmittable through the gallium oxide and a repetitively pulsed power output relatively to each other perpendicularly to thicknesswise directions of the workpiece while positioning the focused spot within the workpiece, thereby forming in the workpiece a separation layer including a plurality of modified regions arrayed in a direction along which the focused spot travels in the workpiece and cracks developed from each of the plurality of modified regions;
• and
• after the separation layer forming step, a cleaving step of cleaving the workpiece along the separation layer, thereby manufacturing the substrate from the workpiece, wherein
• a value calculated by dividing a center-to-center spacing of an adjacent pair of modified regions in the direction along which the focused spot travels among the plurality of modified regions by a length of modified region of each of the adjacent pair in the direction along which the focused spot travels is in a range of 1.63 to 2.73.