Exposure of plasma deposited silicon nitride to 193 nm ArF excimer laser radiation suppresses the etch rate in buffered HF solution by as much as a factor of 50. Using a contact mask, 0.23 &mgr;m lines and spaces were transferred into silicon nitride by this exposure and etching technique. The mechanism involves transient thermal annealing induced by the 15 ns laser pulses, which reduces the concentration of NH and SiH groups.