A growth substrate is removed from a semiconductor film, and a surface of the semiconductor film exposed by removing the growth substrate is flattened. The semiconductor film along device division lines are partially etched by dry etching to form grooves in a lattice that form streets, not reaching the metal support in the semiconductor film. The surface of the semiconductor film at the bottom of the grooves is flattened. The semiconductor film along the device division lines at the bottom of the grooves are further etched by wet etching to expose the metal support at the bottom of the grooves to finish the streets.