Micro-scratch analysis and mechanical properties of plasma-deposited silicon-based coatings on polymer substrates

Advanced optical applications require multifunctional coatings with specifi c mechanical properties, such as resistance to damage and good adhesion to different types of substrates, including polymers. In the present study we deposited amorphous hydrogenated silicon nitride (SiN1.3) and oxide (SiO2) films on polycarbonate and on silicon substrates by plasma enhanced chemica l vapor deposition (PECVD), using a dual-mode microwave/radio frequency pla sma system. The film adhesion was determined by the micro-scratch test. Dep th-sensing indentation and substrate curvature measurements were used to ev aluate the microhardness. Young's modulus and residual stresses of the film s. The adhesion strength, represented by the critical load, L-c, when the f ilm starts to delaminate, was determined as a function of the substrate mat erial and the energy of bombarding ions. A direct correlation between the L -c values and the mechanical properties of the films was found. The formati on of different crack patterns in the coatings during the scratch procedure is explained in terms of stress release mechanism depending on the mechani cal properties of the film, the substrate and the interface region. In addi tion, different models applicable to the evaluation of the work of adhesion in the case of hard coatings on soft substrates are critically reviewed. ( C) 1999 Elsevier Science S.A. All rights reserved.