Cracking and loss of adhesion of Si3N4 and SiO2:P films deposited on Al substrates

Tensile tests in a scanning electron microscope have been performed to study the mechanical stability of different film/substrate systems consisting of films of Si₃N₄ and SiO₂ :4.5 wt% P deposited on Al substrates. Successive stages of crack development were observed: transverse through-thickness cracking of the film precedes its loss of adhesion and buckling, induced by the transverse contraction of the substrate. It was observed that the presence of a thermally grown Al₂O₃ interlayer improved the adhesion of the films by delaying the de-adhesion process. The influence of roughness on the interfacial strength was analysed from the observation of the de-adhesion of a SiO₂ :4.5 wt% P film deposited on a scratched Al substrate. The critical strain for the through-thickness cracking of each film was calculated. Then the multiple film cracking was analysed through the evolution of the crack density with the longitudinal strain. Finally, by using the point at which the film de-adhered, an interfacial fracture energy was calculated for each system.