Method for manufacturing a photomask, and dry etching method

摘要

A photomask is manufactured by providing a photomask blank comprising a transparent substrate, a phase shift film, and a light-shielding film, the phase shift film and the light-shielding film including silicon base material layers, a N+O content in the silicon base material layer of the phase shift film differing from that of the light-shielding film, and chlorine dry etching the blank with oxygen-containing chlorine gas in a selected O/Cl ratio for selectively etching away the silicon base material layer of the light-shielding film.