A variation in the reactive ion etch (RIE) rate of silicon oxynitride ( SiOxNy) films deposited by plasma‐enhanced chemical vapor deposition was studied by CHF3RIE, CHF3+carbon mono‐oxide (CO) RIE and CF4RIE. The source gas flow rate ratio (R=N2O/SiH4) during the SiOxNyfilm deposition was varied to obtain a film of different atomic composition. Etch rates decreased in the order of CF4RIE, CHF3RIE, and CHF3+CO RIE, and the etch selectivity of SiO2over SiOxNyincreased in the same order also. The fluorocarbon ( CFx) film deposited during a RIE process was analyzed by x‐ray photoelectron spectroscopy measurements. Etch rates are found to be correlated to both thickness and atomic composition of the CFxfilm. Carbon‐rich fluorocarbon films are found to be more resistive against RIE.