Reactive ion etching of silicon carbide in SF6 gas: Detection of CF, CF2, and SiF2 etch products

We have detected by laser-induced fluorescence the radicals SiF2, CF, and CF2 produced during the reactive ion etching of SiC substrates in a pure SF6 plasma. Spatially and temporally resolved measurements were used to distinguish between gas phase and etched surface radical production. Whereas CF and CF2 are produced directly at the etched surface, the SiF2 radicals are produced in the gas phase (probably by electron-impact dissociation of SiF4). We attribute this difference to the formation of a carbon-rich layer on the SiC substrate surface, the removal of which produces CFx (x=1,2,3) radicals. The CF2 radical represents up to 20% of the total carbon etch products under our conditions.