Enhancing SiN Selectivity over SiO in Low-RF Power NF-O Reactive Ion Etching: The Effect of NO Surface Reaction.

Highly selective etching of silicon nitride (SiN) and silicon dioxide (SiO) has received considerable attention from the semiconductor community owing to its precise patterning and cost efficiency. We investigated the etching selectivity of SiN and SiO in an NF/O radio-frequency glow discharge. The etch rate linearly depended on the source and bias powers, whereas the etch selectivity was affected by the power and ratio of the gas mixture. We found that the selectivity can be controlled by lowering the power with a suitable gas ratio, which affects the surface reaction during the etching process. X-ray photoelectron spectroscopy of the SiN and QMS measurements support the effect of surface reaction on the selectivity change by surface oxidation and nitrogen reduction with the increasing flow of O. We suggest that the creation of SiON bonds on the surface by NO oxidation is the key mechanism to change the etch selectivity of SiN over SiO.