Thin-film-formation-substrate manufacturing method and thin-film substrate

This method for manufacturing a thin-film-formation substrate includes a substrate preparation step in which a substrate (10) is prepared, a thin-film formation step in which a silicon thin film (13) is formed on top of the substrate (10), and a crystallization step in which the thin film is exposed to a continuous-wave light beam of a prescribed wavelength with the light beam and/or substrate moved so as to implement relative scanning at a prescribed speed, thereby crystallizing at least a prescribed region of the thin film and forming a crystallized region (50). The shape that the light beam forms on the thin film in the crystallization step has a long axis that intersects the direction of the aforementioned relative scanning. The crystallization region is formed so as to contain a band-shaped first region (51), which extends in a direction that intersects the direction of the relative scanning, and a second region (52) adjacent to the band-shaped first region, with the band-shaped first region having a larger mean grain diameter than the second region.