The deposition of inorganic thin films on polymer substrates by plasma-enhanced chemical vapor deposition

Inorganic thin films were deposited on polymer substrates by plasma-enhanced chemical vapor deposition (PECVD). The inorganic/polymer composites have the flexibility of polymers with the surface properties of inorganic materials and thus have several useful and interesting properties. The coated polymer sheets had drastically reduced oxygen diffusion rates compared to the untreated polymers. The use of PECVD as a deposition method resulted in broad interface regions. These ‘interphase’ regions had compositions and morphologies intermediate between those of the bulk polymers and the final inorganic films.; Silicon nitride films were deposited on poly(ethylene terephthalate) (PET) by capacitively-coupled PECVD (CC-PECVD) and electron-cyclotron resonance PECVD (ECR-PECVD). The films were deposited for varying lengths of time and the evolution of the surface properties was studied. Atomic force microscopy was used to resolve the surface morphology. X-ray photoelectron spectroscopy (XPS) was used to measure the composition of the surface. Oxygen transmission rate measurements determined the barrier properties of the thin films.; For CC-PECVD, it was found that the plasma energy density had a large effect on the final film morphology, as well as the structure and composition of the interphase region. For relatively low-energy depositions, the interphase region lacked the granular structure typical of polycrystalline or amorphous thin films. The interphase region was very thin at low-energy depositions and the film quickly converted to stoichiometric silicon nitride. However, at higher-energy, the interphase was much larger and had a distinct granular morphology.; Films deposited by ECR-PECVD were examined as diffusion barriers. The films were found to be excellent barriers, particularly when the substrate was coated on both sides. The barrier properties of the films indicate that they had a low defect density. At the optimum parameters, the ECR-PECVD resulted in films with a high nucleation density and tightly packed grain structure. XPS revealed that these films actually contained a large amount of oxygen and carbon, and that the silicon was in an oxynitride state.