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 i n ethylene glycol and in aqueous solutions has been pet-formed 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 thick ness of the oxide layer. The thicknesses of SiO2 layers calculated from the capacitive impedance were in the range of 25-100 Angstrom 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 solut ions, where oxygen evolved through the oxidation of water. Interstitially d issolved oxygen molecules in SiO2 layer at above the oxygen evolution poten tial were expected to facilitate the formation of SiO2 at the interfaces. T hin SiO2 films grew efficiently at a controlled rate during the application of low anodization currents in aqueous solutions.