Etching Silicon with HF-H₂O₂-Based Mixtures: Reactivity Studies and Surface Investigations

In semiconductor and photovoltaic industries numerous process steps deal with etching and silicon surface modification. The present study focuses on the reactivity of HF-H2O2-based mixtures toward silicon surfaces in a wide range of concentrations. The generally very moderate reactivity is investigated regarding kinetic aspects and the silicon dissolution reactions. The activation energy of silicon dissolution in HF-H2O2 mixtures is determined to be ∼50 kJ/mol, which supports a surface reaction controlled mechanism. This interpretation is checked by oxidation experiments of Si surfaces with HF-free H2O2 solutions. Resulting silicon surfaces were characterized by means of diffuse reflection Fourier transform infrared spectroscopy and photoelectron spectroscopy. Surface properties give hints for an “electrochemical” silicon oxidation. Furthermore, the oxidation behavior of different H2O2 solutions is compared to that of HNO3 solutions. All results suggest kinetically limited silicon dissolution in HF-H2O2 mixtures and hole injection into the silicon surface to be the rate-determining part of the reaction process.