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Discrete dislocation studies of thin film interfacial fracture

Date: 17.09.2008
Place: ICAMS, Raum 1103

Audrey Chng, IHCP, Singapore, Singapore

Micrometre-thick metal films present in a variety of electronic and micromechanical systems often fail at the interfaces, motivating much work on understanding interfacial toughness of known critical interfaces in these systems. The mechanical behaviour of these thin metal films differs significantly from that of bulk metals, indicating the existence of length-scale effects. Conventional plasticity theories do not involve a length scale and so the plastic deformation of micrometer-sized specimens requires new constitutive models or explicit modelling of the discrete dislocations that cause plasticity. Relevant discrete dislocation (DD) studies will be briefly reviewed before the computational model of a thin metal film confined between elastic layers is described. Fracture along the metal/substrate interface is permitted through use of a cohesive zone model. The predicted fracture toughness versus film thickness is in good agreement with experimental data on the Cu/TaN/SiO2/Si system. In addition, the DD model also predicts behaviour previously unobserved in studies involving length-scale independent continuum plasticity. Overall, the results show that the DD framework is able to model simultaneous size effects associated with boundary constraints and crack tip fields solely through the evolution of the dislocation structures, and that the DD method is a valuable tool for understanding the complex interplay of dislocation plasticity with small-scale boundary conditions, decohering surfaces, and crack tips, all of which interact to control fracture in thin films and other micro-scale structures.

Supporting information:

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