Abstract: A method for improving profile control during an etch of a nitride layer disposed above a silicon substrate is disclosed. The nitride layer 106 is disposed below a photoresist mask 108A. The method includes positioning the substrate, including the nitride layer and the photoresist mask, in a plasma processing chamber. There is also included flowing a chlorine-containing etchant source gas into the plasma processing chamber. Further, there is included igniting a plasma out of the chlorine-containing etchant source gas to form a chlorine-based plasma within the plasma processing chamber. Additionally, there is included treating, using a chlorine-based plasma, the photoresist mask in the plasma processing chamber. The treatment of the photoresist is configured to etch at least a portion of the photoresist mask and to deposit passivation polymer on vertical sidewalls of the photoresist mask without etching through the nitride layer.