Oxide etch process with high selectivity to nitride suitable for use on surfaces of uneven topography

Abstract

A plasma etch process is described for the etching of oxide with a high selectivity to nitride, including nitride formed on uneven surfaces of a substrate, e.g., on sidewalls of steps on an integrated circuit structure. The addition of one or more hydrogen-containing gases, preferably one or more hydrofluorocarbon gases, to one or more fluorine-substituted hydrocarbon etch gases and a scavenger for fluorine, in a plasma etch process for etching oxide in preference to nitride, results in a high selectivity to nitride which is preserved regardless of the topography of the nitride portions of the substrate surface. In a preferred embodiment, one or more oxygen-bearing gases are also added to reduce the overall rate of polymer deposition on the chamber surfaces and on the surfaces to be etched, which can otherwise reduce the etch rate and cause excessive polymer deposition on the chamber surfaces. The fluorine scavenger is preferably an electrically grounded silicon electrode associated with the plasma.