Fracture in confined thin films: A discrete dislocation study

The fracture toughness of thin metal films confined between elastic layers is studied using a two-dimensional discrete dislocation (DD) method. Fracture along the metal/substrate interface is permitted through the use of a cohesive zone model. The predicted fracture toughness versus film thickness is in good agreement with experimental data for the Cu/TaN/SiO2/Si system. The predicted 0.2%-offset yield stress also agrees with values derived by fitting a continuum plasticity model to the experimental fracture data. The effects of intrinsic interface fracture energy, mode mixity of the loading, and fracture away from the metal/substrate interface are investigated to capture effects present in the experiments. Overall, the results show that the contribution of plastic dissipation to interfacial fracture toughness may be qualitatively predicted using the DD framework and that the DD framework can rationalize experimentally observed size effects under different loading conditions with no ad hoc assumption of the constitutive behavior.