Embodiments of the present disclosure are directed to selective etching processes. The processes include flowing a precursor comprising one or more of an interhalogen, a halogen-containing species, a pseudohalogen species, a mixture of one or more of the interhalogen, the halogen-containing species, or the pseudohalogen species and an amine or a phosphine, or a mixture of one or more of the interhalogen, the halogen-containing species, or the pseudohalogen species with a sulfur-containing species, into a semiconductor processing chamber containing a substrate, and forming an activated species of the precursor to etch a substrate. The substrate has a plurality of alternating layers of silicon oxide and silicon nitride thereon and a trench formed through the plurality of alternating layers. The silicon nitride layers are selectively etched relative to the silicon oxide layers at an etch selectivity of greater than or equal to 500:1.