The present invention provides a production method for a halftone phase mask which has an SiO2 substrate, an overlying refractory metal SixNy 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 SixNy 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.