Mechanical properties of plasma-deposited SiOxNy coatings on polymer substrates using low load carrying capacity techniques

Amorphous hydrogenated silicon oxynitride thin films were deposited on polycarbonate by plasma-enhanced chemical vapour deposition (PECVD) using a dual mode microwave/radio frequency (MW/RF) plasma system. The film composition was adjusted by varying the nature of the silicon gas precursor (silane or hexamethyl–disiloxane), and the flow rate ratio of nitrous oxide (N2O) and ammonia (NH3). The mechanical properties of the film (residual stress, hardness and scratch resistance) were determined by means of curvature method and by low load techniques (0.1–10 mN), such as depth sensing indentation and cantilever microscratch testing. Adequate contact conditions were evaluated using a simple analytical model of stress field distribution. Coating-specific properties were determined by using a low contact load (1 mN) and a sharp indenter (2 μm tip radius). The highest scratch resistance is obtained for hard coatings possessing low internal stress.