Dissolution windows for wet chemical processing of silicon and silicon dioxide: Potential-pH diagrams for the Si-F-H2O system

Potential-pH diagrams are presented for the systems Si-H2O and Si-F-H2O. It is shown that the stability field of elemental silicon lies well below the water stability region, indicating that silicon is highly unstable in water relative to oxidation to Si(IV). Thus, the ability to suppress oxide formation must be attributed to kinetic effects. It is shown further that the introduction of HF and F- into the aqueous phase results in a partial displacement by SiF62- of the Si(OH)(4)(aq) and SiO2 stability fields originally present in the Si-H2O system. Under some conditions, the SiF62- stability domain is nested between two SiO2 stability fields. It is suggested that the minimal etching rates observed at relatively low and relatively high pH solutions of HF may be related in part to the presence of the solubility walls in both pH regimes.