Uv-enhanced dry stripping of silicon nitride films

Abstract

A UV light-enhanced process for rapidly stripping films of silicon nitride in a dry reaction environment, which may be free of plasma or plasma effluents. This process is carried out in a sealed reactor which allows simultaneous exposure of a substrate wafer to a polyatomic fluorine containing gas which can be photodissociated by UV radiation to produce atomic fluorine and to UV radiation. Silicon nitride stripping rates in excess of 500 .ANG./min are readily obtainable with UV-stimulated fluorine-based processes, while maintaining the bulk wafer temperature below 300.degree. C. Selectivities for silicon nitride-to-silicon oxide etching of greater than 30 can be achieved for the stripping of silicon nitride LOCOS mask layers in the presence of field oxide and pad oxide layers when a chlorine or bromine containing gas which can be photodissociated by UV radiation to produce atomic chlorine or bromine is used in mixture with the fluorine containing gas. Selectivity and etch rate are controlled through UV lamp exposure, substrate temperature, and additions of nitrogen diluent, and photodissociable chlorine or bromine containing gases. The process addresses many of the limitations of plasma-downstream etch tools for dry silicon nitride stripping, including complete elimination of charged particles and sputtered contaminants associated with plasma effluents.