Surface etching mechanism of silicon nitride in fluorine and nitric oxide containing plasmas

The etch rate of silicon nitride (Si3N4) in the afterglow of fluorine-conta ining plasmas is strongly enhanced when both nitrogen and oxygen are added to the remote discharge. This effect is attributed to the formation of nitr ic oxide (NO), which we identify as a highly reactive precursor for the etc hing of Si3N4. The Si3N4 etch rate, surface oxidation, and the depletion of the surface of N atoms show a linear dependence on the NO density. In orde r to determine the products of the NO reaction at the Si3N4 surface, mass s pectrometry was performed in immediate proximity to the surface with a spec ially designed movable sampling orifice. Both SiF4 and N-2 are identified a s primary etch products, but a smaller amount of N2O was also detected. Bas ed on our results, we suggest that NO enhances the removal of N from the Si 3N4 surface by the formation of gaseous N-2, and leaving behind an O atom, while the overall surface oxidation remains very low, and the reactive laye rs are very thin. This modified surface reacts more readily with F atoms th an the Si3N4 surface. (C) 2001 American Vacuum Society. [DOI: 10.1116/1.132 9118].