Copper-catalyzed etching of silicon by F2: kinetics and feature morphology

The copper-catalyzed fluorination of silicon is first order in [F2] and in [Cu]s until the coverage reaches ∼4 monolayers. Above ∼4 monolayers the reaction rate is zero order in copper, suggesting a limited number of catalytically active Cu/Si sites. Copper islands form at high coverages, above saturation, and provide a reservoir of catalyst. The limited rate of surface diffusion of copper leads to anisotropic etching and feature size-dependent etch depths. The copper compounds, CuF2 and CuO, and copper silicides, Cu5Si and Cu3Si, all catalyzed the F2-Si reaction which suggests that they are all converted to the same active species. The results can be explained by mechanisms involving copper fluorides or copper silicides as active intermediates.