Electrochemical impedance spectroscopy as a probe for wet chemical silicon oxide characterization

The kinetics of the chemical growth of silicon oxide in H2O2-containing ammonia solutions and its break-up by dilute ammonia solutions was investigated using electrochemical techniques and more specifically electrochemical impedance spectroscopy. The recording of the open circuit potential (OCP), complemented by successive impedance diagrams, demonstrates clearly the build-up of a silicon oxide passivating layer when hydrophobic Si surfaces are immersed in NH3 + H2O2 solutions. The thickening of the chemical oxide coating mainly results in the decrease of the capacitance value together with the enhancement of the ohmic surface resistance. On the other hand, pure ammonia dilute solutions lead to the progressive destruction of this hydrophilic passivating surface oxide, which is revealed by the simultaneous decay of the real component of the impedance. Finally, we observed the break-up of the passive layer, characterized by a sudden drop of the OCP to a value quite identical to that obtained with a bare Si surface. This process resulted in a dramatic corrosion of the substrate surface.