Photomask blank, photomask, and photomask manufacturing method

A method of manufacturing a photomask comprising the steps of:

• preparing a photomask blank having a light-shielding film, the light-shielding film comprising a light-shielding layer and a front-surface antireflection layer on a transparent substrate;
• dry-etching the front-surface antireflection layer with a fluorine-based gas containing no oxygen using, as a first etching mask, a resist film having a transfer pattern;
• and
• dry-etching the light-shielding layer with a chlorine-based gas containing no oxygen using, as a second etching mask, the front-surface antireflection layer being dry-etched using the first etching mask and having the transfer pattern,
• wherein the light-shielding layer is formed in contact with the transparent substrate, the light shielding layer being made of a material consisting of tantalum and nitrogen, and containing 7 at % or more and 51 at % or less nitrogen, the material being capable of being dry-etched with the chlorine-based gas containing no oxygen,
• wherein the front-surface antireflection layer is formed in contact with the light-shielding layer, the front-surface antireflection layer being made of a material consisting of tantalum and oxygen and containing 50 at % or more oxygen, the material not being capable of being dry-etched with the chlorine-based gas and capable of being dry-etched with the fluorine-based gas.