A manufacturing method comprises steps of: forming a metal pattern having a thickness d on a substrate; forming an insulating film layer on the substrate on which the metal pattern is formed, so that the insulating film layer has an overlap region with the metal pattern, an absolute value of a height difference between the overlap region of the insulating film layer and other regions of the insulating film layer being less than the thickness d; and, forming a pattern of a semiconductor layer and a source/drain metal layer on the substrate on which the insulating film layer is formed.