INFRARED ELLIPSOMETRY STUDY OF THE OXIDATION MECHANISMS OF HYDROGENATED AMORPHOUS-SILICON

A detailed study of the oxidation of plasma deposited amorphous silicon (a-Si:H) using infrared phase modulated ellipsometry (IRPME) is presented. a-Si:H is found to be resistant against air oxidation confirming previous measurements. A 5-6 angstrom thick oxide layer at the surface of a-Si:H is observed after a few months of exposure to air. The extreme sensitivity of IRPME is emphasized. In particular Si-O-Si and (O(n))Si-H stretching vibrations are identified at the film surface at the submonolayer level. The oxidation mechanisms are discussed. The weak reactivity of a-Si:H with atmosphere is correlated with the presence of a hydrogen rich thin layer at the top surface.