Ultrahigh-selectivity silicon nitride etch process using an inductively coupled plasma source

A very high-selectivity silicon nitride etch process has been developed on an inductively coupled plasma etching system which uses a $NF3/O2/NH3$ (nonchlorine) chemistry. Etch selectivity of low-pressure chemical vapor deposition nitride to thermal oxide greater than 100:1 was achieved at a nitride etch rate of 500 Å/min. A $NF3/O2$ chemistry was optimized for nitride to oxide selectivity of about 12:1, with a nitride etch rate of 1200 Å/min. The addition of $NH3$ inhibits oxide etching thus enhancing selectivity. The net etch rate for oxide may be reduced to zero while maintaining a reasonably high etch rate for nitride thus resulting in essentially infinite selectivity. The process is stable, repeatable and creates no particles. A split lot test on device wafers against standard wet etch process demonstrates superior process and device performance.