A new dry etching technique-development-free vapor photolithography-was used to transfer a pattern onto silicon nitride film. Plasma-enhanced chemical vapor deposition silicon nitride film and thin low pressure chemical vapor deposition silicon nitride film can be etched to Set a positive pattern. The difference in the etching rate between exposed and unexposed areas was attributed to the difference in the concentration of accelerators that was controlled through a photochemical reaction. The reaction mechanism and other phenomena are discussed.