Influence of film structure and composition on diffusion barrier performance of SiOx thin films deposited by PECVD

This study focuses on the oxygen permeability of SiOx thin films on polyethyleneterephtalate (PET) produced by plasma-enhanced chemical vapor deposition (PECVD) from oxygen-diluted hexamethyldisiloxane (HMDSO). The versatile PECVD set-up, equipped with two plasma sources (remote microwave and direct radio frequency), allows the deposition of films with variable morphologies and compositions. The deposits were analyzed by XPS, ellipsometry, and atomic force microscopy (AFM). Curve fitting of the Si 2p peak in X-ray photoelectron spectra (XPS) provided information about the chemical binding states of the silicon atoms. The results clearly show that the oxygen transmission rate (OTR) depends highly on the film structure, whereas the chemical composition has only little effect.In order to achieve the desired dense and smooth film structure, it is necessary to have a high substrate bias, which promotes ion bombardment of the film surface during growth. OTR values down to 0.2 cm3 (STP) m− 2 day− 1, corresponding to a barrier improvement factor of 500, have been achieved.