Provided is a method and system for increasing etch rate and etch selectivity of a masking layer on a substrate in an etch treatment system, the etch treatment system configured for single substrate processing. The method comprises obtaining a supply of steam water vapor mixture at elevated pressure, obtaining a supply of treatment liquid for selectively etching the masking layer over the silicon or silicon oxide at a set etch selectivity ratio, placing the substrate into the etch processing chamber, combining the treatment liquid and the steam water vapor mixture, and injecting the combined treatment liquid and the steam water vapor mixture into the etch processing chamber, wherein the flow of the combined treatment liquid and the steam water vapor mixture is controlled to maintain a set etch rate and a set etch selectivity ratio of the masking layer to silicon or silicon oxide.