Photomask blank manufacturing method and photomask manufacturing method

摘要

A thin film made of a material containing a metal and silicon is formed on a light-transmissive substrate. Then, a treatment is performed to modify a main surface of the thin film in advance so that when exposure light having a wavelength of 200 nm or less is accumulatively irradiated on a thin film pattern of a photomask to be produced by patterning the thin film, the transfer characteristic of the thin film pattern does not change more than a predetermined degree. This treatment is performed by carrying out, for example, a heat treatment in an atmosphere containing oxygen at 450° C. to 900° C.