In-situ Monitoring of Anodic Oxidation of p-type Si(100) by Electrochemical Impedance Techniques in Nonaqueous and Aqueous Solutions

Electrochemical oxidation of silicon (p-type Si(100)) at room temperature in ethylene glycol and in aqueous solutions has been performed by applying constant low current densities for the preparation of thin SiO2 layers. In-situ ac impedance spectroscopic methods have been employed to characterize the interfaces of electrolyte/ oxide/semiconductor and to estimate the thickness of the oxide layer. The thicknesses of SiO2 layers calculated from the capacitive impedance were in the range of 25-100 Å depending on the experimental conditions. The anodic polarization resistance parallel with the oxide layer capacitance increased continuously to a very large value in ethylene glycol solution. However, it decreased above 4 V in aqueous solutions, where oxygen evolved through the oxidation of water. Interstitially dissolved oxygen molecules in SiO2 layer at above the oxygen evo-lution potential were expected to facilitate the formation of SiO2 at the interfaces. Thin SiO2 films grew effi-ciently at a controlled rate during the application of low anodization currents in aqueous solutions