The stoichiometry of metal assisted etching (MAE) of Si in V2O5 + HF and HOOH + HF solutions

The metals Ag, Au, Pd and Pt were deposited as nanoparticles onto H-terminated Si(100) wafers and single crystal Si chunks to act as catalysts for electroless etching induced by the presence of a strong oxidant in HF(aq). This process is known as metal assisted etching (MAE). Aqueous solutions of V2O5 + HF and HOOH + HF were investigated. The stoichiometry of MAE in V2O5 + HF solutions depended on the chemical identity of the metal. The stoichiometry when etching with Ag and Au was the same as previously determined for electroless Si etching in V2O5 + HF solutions in the absence of a metal catalyst. With Pd and Pt nanoparticles the stoichiometry is significantly different, consuming more V2O5 and producing less H2 per mole of Si etched. This indicates that the metal catalyst changes the mechanism of etching, implicating the polarization induced by the metal nanoparticle in the etch mechanism. Etching in V2O5 + HF was well behaved and gave consistently reproducible kinetic results. In contrast, we were unable to obtain well-behaved stoichiometries for HOOH + HF solutions. This is related to heightened sensitivity on reaction conditions compared to the V2O5 system as well as nonlinearities introduced by side reactions.