Cryogenic nanoscale etching of silicon nitride selectively to silicon by alternating SiF4/O2 and Ar plasmas

This article first presents quasi-in situ XPS measurements on Si3N4 and a-Si samples after exposure to an SiF4/O2 plasma at different cryogenic temperatures. A different behavior is observed between the two materials at −65 °C, which has led to the development of a time-multiplexed process for nanoscale etching. This study clearly shows the possibility to switch from a deposition regime to an etching regime by decreasing the temperature. The threshold temperature between these regimes being different for both materials, it was possible to perform selective etching of Si3N4 over a-Si by wisely choosing the temperature.