A photomask blank having a film of at least one layer formed on a substrate is manufactured by forming a film on a substrate and irradiating the film with light from a flash lamp. A photomask is manufactured from the thus manufactured photomask blank by forming a patterned resist on the film on the blank by photolithography, etching away those portions of the film which are not covered with the resist, and removing the resist. The photomask blank and photomask have minimized warpage and improved chemical resistance.