Electrode reaction and mechanism of silicon anodization

The electrochemical processes occurring during anodization of low resis-tivity silicon were studied to determine the effect of electrolysis conditions on the rate and quality of oxide production. The rate of anodic SiO2 formation vs. water content in N-methylacetamide (NMA) ~- KNO ~ solutions was studied by means of ionic current efficiency, weight and analysis of silicon oxide. Current efficiencies of oxide production up to 3.0 % were observed and the best oxides were formed at the lowest values of 1.6-1.8 % The oxide formed corresponded within experimental error of method (___15%) to SiO2 when Si was anodized in NMA solutions containing from about 0.5-3.5% H20. At higher water content, the film weight increased with respect o stoi-chiometric SiO2 as determined by silicon in oxide analysis. Thermally grown oxides showed a stoichiometric ratio (with some scatter); however, weight measurements of the silicon before and after thermal oxidation indicated that about 12 % of the silicon consumed id not appear in the oxide formed. Th