REMOTE PLASMA-ETCHING OF SILICON-NITRIDE AND SILICON DIOXIDE USING NF3 O-2 GAS-MIXTURES/

The etching of silicon nitride (Si3N4) and silicon dioxide (SiO2) in t he afterglow of NF3 and NF3/O-2 microwave discharges has been characte rized. The etch rates of both materials increase approximately linearl y with the flow of NF3 due to the increased availability of F atoms. T he etch rate of Si3N4 is enhanced significantly upon O-2 injection int o the NF3 discharge for O-2/NF3 ratios of 0.3 and higher, whereas the SiO2 etch rate is less influenced for the same flow ratios. X-ray phot oelectron spectroscopy of processed Si3N4 samples shows that the fluor ine content of the reactive layer, which forms on the Si3N4 surface du ring etching, decreases with the flow of O-2, and instead oxidation an d nitrogen depletion of the surface occur. The oxidation of the reacti ve layer follows the same dependence on the flow of O-2 as the etch ra te. Argon actinometry and quadrupole mass spectrometry are used to ide ntify reactive species in the etching of both materials. The atomic fl uorine density decreases due to dilution as O-2 is added to the discha rge. The mass spectrometer did not detect NFx species (x = 1-3) at any discharge parameter setting, which indicates the near complete dissoc iation of NF,. Nitric oxide (NO) was detected by mass spectrometry, an d the NO density shows the same dependence on O-2 how as the Si3N4 etc h rate and the surface oxidation. Based on this observation, we propos e that the etch rate enhancement for Si3N4 is due to the adsorption of the NO on the Si3N4 surface, followed by the formation of N-2 with a N atom from the surface. The O atom can then attach to the same surfac e site, contributing to the oxidation. (C) 1998 American Vacuum Societ y. [S0734-2101(98)00604-6].