Method of manufacturing a photomask and photomask substrate

The present invention is provided to obtain a method for manufacturing a photomask capable of forming a translation pattern with high dimensional accuracy. The method for manufacturing the photomask comprises: a process of preparing a resist-attached photomask substrate in which an optical film, a reflective thin film, and a resist film are layered on a transparent substrate; a process of forming a resist pattern; a thin film etching process of forming a pattern of the reflective thin film; a process of removing the resist pattern; a measuring process of measuring the size of the reflective thin film pattern; an optical film etching process of performing wet etching of the optical film, using the reflective thin film pattern as a mask, based on the etching time for the optical film which is determined according to the measured size; and a process of removing the reflective thin film. With respect to the measuring process, the size is measured by emitting an examination light onto a measurement unit of the ref