Thin film failure using an interface delamination law

Interfacial debonding of multilayer thin film systems in microelectronics can severely affect device functionality and reliability. There is great engineering value in quantitative evaluation of interface adhesion strength to control adhesion quality. It has been known that the formation energy of new crack surfaces along an interface and plastic dissipation occurring in the bulk materials are the two major energy contributions to total interface toughness. The total interface toughness is the only quantity measurable in a fracture experiment to understand interface adhesion strength, and one must separate the two energy contributions to the total toughness. This can be achieved by computational modeling of the failure process. In this paper, a fracture process zone model is used to specify the interface properties, in which the major parameters are work of separation and peak strength. This model is readily incorporated into a finite element analysis which can be used to predict interfacial decohesion and crack advance along the interface. There is no need to introduce an additional failure criterion and this is an attractive feature of this approach. We have analysed interface crack growth in a 4-point bend specimen. Interfacial crack growth occurs under mixed mode. The crack growth resistance and the contribution of plastic dissipation to total interface toughness are calculated for crack growth along one of the interfaces of a ductile thin film joined with two elastic substrates. The effects of ductile layer thickness, peak separation strength and work of separation on the total work and steady-state work of fracture are discussed