Characterization of defects in PECVD-SiO2 coatings on PET by confocal microscopy

Abstract

Thin, transparent ceramic coatings on polymers are effective barriers against gas and vapor transmission. However, they always display some residual permeation, which can be attributed to defects. The main sources of these defects are dust particles on the polymer surface before deposition, and roughness of the polymer surface due to the presence of so-called antiblock particles. The transparency and extreme thinness of the films (d≈50 nm) render the detection of defects virtually impossible by optical and even by electron microscopies. However, by using a technique based on reactive ion etching (RIE) in oxygen plasma, we are able to render defects visible, even by optical microscopy at relatively low magnification (100×). In the present article we present a confocal microscopy study, which has helped to better understand the effect of RIE at defect sites, as well as the origins of the defects in these coatings.