ADHESION IMPROVEMENT OF PLASMA-DEPOSITED SILICA THIN-FILMS ON STAINLESS-STEEL SUBSTRATE STUDIED BY X-RAY PHOTOEMISSION SPECTROSCOPY AND IN-SITU INFRARED ELLIPSOMETRY

Adhesion of plasma-deposited SiO2 on stainless steel is shown to be en hanced after Ar, N-2, and NH3 plasma pretreatments of the substrate. A dhesion is related to the chemical bonding at the interface. Therefore , it is studied by x-ray photoemission spectroscopy (XPS) and in situ IR ellipsometry performed on very thin films (approximate to 30 Angstr om thick). IR ellipsometry reveals the removal of adsorbed hydrocarbon s on the metallic surface by all plasma treatments. XPS measurements s how the removal of NOx species, related to the sample electropolishing , using N-2 and NH3 plasmas; in contrast, Ar has practically no effect in this case. Plasma-induced modifications are not limited to surface cleaning. Some nitrogen is incorporated in the substrate after N-2 an d NH3 plasmas. In particular, nitrogen is found bonded to Si and to Cr after NH3 and N-2 treatments, respectively, we interpret the adhesion enhancement by hardening of the substrate surface region in the case of N-2 plasma, while, in the case of NH3, it may be related to the for mation of silicon nitride. Cr-N-Si linkages between the substrate and the film may also contribute to adhesion improvement. We also observed changes in the early stages of the film growth. A higher sticking coe fficient of dissociated species on the surface is revealed after plasm a pretreatment. Narrowing of the Si 2p peak in XPS spectra observed in pretreated samples is attributed to a better ordered SiO2 structure a t Si sites in terms of bond angles and/or lengths. In contrast, both I R ellipsometry and XPS show no change at O sites. (C) 1998 American Va cuum Society.