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 CF_x (x=1,2,3) radicals. The CF₂ radical represents up to 20% of the total carbon etch products under our conditions.