Methods for etching molybdenum

A substrate processing method including: providing a substrate containing an etch mask over a metallic molybdenum layer in a recessed feature; exposing the substrate to a plasma-excited deposition gas that forms an etch protection layer on a sidewall of the recessed feature; and exposing the substrate to a plasma-excited etching gas that etches the metallic molybdenum layer according to the etch mask, where the exposing steps are alternatingly performed a plurality of times.