A method of manufacturing a display device that includes: performing a surface treatment on at least one of two opposing surfaces of a carrier substrate and a mother substrate; bonding the carrier substrate and the mother substrate; performing a thin film formation process on the mother substrate; and separating the carrier substrate and the mother substrate. The thin film formation process includes a heat treatment operation, the surface treatment includes using an inorganic acid or an organic acid, and the surface treatment controls a content of —OH, —OH2+, and —O− groups of the at least one treated surface.