Patent ID: 6919147

Claim:
Production method for a halftone phase mask which has an SiO 2 substrate, an overlying refractory metal Si x N y phase shifter layer ( 2 ) and an overlying chromium oxide or chromium mask layer ( 3 ), having the following steps: provision of a mask ( 4 ) on the chromium oxide or chromium mask layer ( 3 ); etching of the chromium oxide or chromium mask layer ( 3 ) for the purpose of forming a hard mask from the chromium oxide or chromium mask layer ( 3 ) in a first etching step; selective etching of the refractory metal Si x N y phase shifter layer ( 2 ) using the hard mask in a plasma with a chlorine-containing and/or hydrogen-chloride-containing main gas in a second etching step with a predetermined cathode power of at least 20 W.