The reactive ion etching (RIE) of silicon nitride (Si3N4) films formed by low pressure chemical vapor deposition (LPCVD), has been investigated. Studies were done using plasmas of CHF3, CHF3+O2, and CHF3+CO2gases. Anisotropic profiles with vertical sidewalls and no undercut have been achieved with all three plasmas. The etch rate of the Si3N4films in a pure CHF3plasma was found to decrease as a function of time. This effect is explained via a mass transport limiting mechanism. Constant etch rates were observed with plasmas of CHF3+O2and CHF3+CO2. A selectivity of 10:1 for the etching of Si3N4to the underlying Si substrate has been achieved with a CHF3+CO2plasma.