Electrodissolution of p-Si in acidic fluoride media - Modeling of the steady state

With the aim of explaining the dependence of the steady-state electrodissol ution current density (I) of Si in acidic fluoride media on total fluoride concentration (C-F), pH, and mass transfer rate, a kinetic model is propose d. The Si electrode is assumed to be covered by a thin SiO2 layer, formed b y an electrochemical reaction at the Si/oxide interface, which undergoes di ssolution by three parallel chemical reactions. These reactions convert SiO 2 to SiF62-, under the action of HF and HF2- and occur under mixed control; their kinetics is assumed to be of the second order. Fast equilibria betwe en fluoride species and H+ are assumed. The model is compared with experime ntal results obtained by ourselves and with those in the literature. The C- F, pH, and Ohm dependencies of the current density measured at a fixed pote ntial in the electropolishing domain are well reproduced with an appropriat e choice of the rate constants of the dissolution reactions, the only adjus table parameters. It is shown that I depends on the angular speed of the el ectrode (Ohm) in such a way that I-1 vs. Ohm(-1/2) plots are almost linear, resembling traditional Koutecky-Levich behavior. (C) 2000 The Electrochemi cal Society. S0013-4651(99)10-025-9. All rights reserved.