Electrochemical impedance spectroscopy as a probe for wet chemical siliconoxide characterization

The kinetics of the chemical growth of silicon oxide in H2O2-containing amm onia solutions and its break-up by dilute ammonia solutions was investigate d using electrochemical techniques and more specifically electrochemical im pedance spectroscopy. The recording of the open circuit potential (OCP), co mplemented by successive impedance diagrams, demonstrates clearly the build -up of a silicon oxide passivating layer when hydrophobic Si surfaces are i mmersed in NH3 + H2O2 solutions. The thickening of the chemical oxide coati ng mainly results in the decrease of the capacitance value together with th e enhancement of the ohmic surface resistance. On the other hand, pure ammo nia dilute solutions lead to the progressive destruction of this hydrophili c 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 qui te identical to that obtained with a bare Si surface. This process resulted in a dramatic corrosion of the substrate surface.