SiO2/Si selectivity in high density CHF3/CH4 plasmas: Role of the fluorocarbon layer

A new high density plasma SiO"2 etching process based on CHF"3/CH"4 mixture is investigated by means of plasma diagnostics and surface analysis. Selectivity as high as 15 with respect to silicon has been obtained. Besides, a slight decrease of the SiO"2 etch rate is observed as compared to CHF"3. Deposition of a carbon-rich fluorocarbon layer on the SiO"2 is thought to play an important role in the etching mechanism, as generally described for Si.