A new masking method for protecting silicon surfaces during anisotropic silicon wet etching

A room-temperature silicon masking approach based on the exposure of silicon to CHF₃-based plasma is explored. This plasma treatment leads to ultra-thin (2-5 nm) films that consist of a fluorocarbon top layer and a sub-oxide lower layer and are appropriate for anisotropic wet etching masks. The mask resistance to anisotropic wet-etchants is studied as a function of film preparation parameters. Defect evolution is examined for two key film preparation conditions. Masks explored compare favourably with common masking materials such as SiO₂ or Si₃N₄ in terms of achievable patterns and processing options compatible with standard silicon integrated circuit technology. In addition, the new masking method can be applied when sidewall-only wet etching of mesa patterns is desired.