Patent ID: 8367276

Claim:
A photomask manufacturing method comprising the steps of: preparing a mask blank comprising a transparent substrate, a light-shielding film formed on said transparent substrate and made of a material mainly containing chromium and including an antireflection layer at an upper layer thereof, and having a thickness of 90 nm or less and an optical density which is equal to 2.5 or more with respect to exposure light having a wavelength of 200 nm or less, a mask layer formed on said antireflection layer of said light-shielding film and having a thickness of 5 nm to 20 nm for serving as an etching mask in etching that forms said light-shielding film into a transfer pattern, said mask layer made of a material containing silicon, a chromium nitride-based film formed on said mask layer and containing at least chromium and nitrogen, and an electron beam writing resist film formed on said chromium nitride-based film; applying a pattern writing process and a development process to said electron beam writing resist film to form a resist pattern; dry-etching said chromium nitride-based film by a dry etching gas containing chlorine gas using said resist pattern as an etching mask to form a chromium nitride-based film pattern; dry-etching said mask layer by a dry etching gas containing fluorine gas using said chromium nitride-based film pattern as an etching mask to form a mask layer pattern; dry-etching said light-shielding film by a dry etching gas containing chlorine gas using said mask layer pattern as an etching mask to form a light-shielding film pattern including said antireflection layer at an upper portion thereof and to remove said chromium nitride-based film pattern simultaneously; and removing said mask layer pattern.