The adhesion of SiNx thin layers on silica–acrylate coated polymer substrates

Plasma Enhanced Chemical Vapor Deposition (PECVD) was used to grow 200, 300 and 400 nm thick silicon nitride layers (SiNx) on a high temperature aromatic polyester substrate spin coated with a silica–acrylate hybrid coating (hard coat). Layers deposited without oxygen plasma treatment remained attached to the substrate, while spontaneous buckle delamination of the layer deposited with oxygen plasma treatment was observed directly after layer deposition. This effect was investigated using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM). SIMS analyses showed a considerable increase of silicon oxide by exposing the substrate to oxygen plasma treatment, while AFM showed an increased roughness. Bright-field transmission electron micrographs show the presence of a particulate SiO2 layer. The oxygen plasma treatment thus removes the acrylate from the hard coat layer leaving behind the SiO2 particles leading to lower adhesion and thus to spontaneous buckle delamination.