Plasticity contributions to interface adhesion in thin-film interconnect structures

The effects of plasticity in thin copper layers on the interface fracture r esistance in thin-film interconnect structures were explored using experime nts and multiscale simulations. Particular attention was given to the relat ionship between the intrinsic work of adhesion, G(o), and the measured macr oscopic fracture energy, G(c). Specifically, the TaN/SiO2, interface fractu re energy was measured in thin-film Cu/TaN/SiO2, structures in which the Cu layer was varied over a wide range of thickness. A continuum/FEM model wit h cohesive surface elements was employed to calculate the macroscopic fract ure energy of the layered structure. Published yield properties together wi th a plastic flow model for the metal layers were used to predict the plast icity contribution to interface fracture resistance where the film thicknes s (0.25-2.5 mum) dominated deformation behavior. For thicker metal layers, a transition region was identified in which the plastic deformation and ass ociated plastic energy contributions to G(c), were no longer dominated by t he film thickness. The effects of other salient interface parameters includ ing peak cohesive stress and G(o), are explored.