A method of etching silicon nitride on patterned heterogeneous structures is described and includes a gas phase etch using anhydrous vapor-phase HF. The HF may be combined with one or more of several precursors in the substrate processing region and near the substrate to increase the silicon nitride etch rate and/or the silicon nitride selectivity. The silicon nitride etch selectivity is increased most notably when compared with silicon of various forms. No precursors are excited in any plasma either outside or inside the substrate processing region according to embodiments. The HF may be flowed through one set of channels in a dual-channel showerhead while the other precursor is flowed through a second set of channels in the dual-channel showerhead.