The momentum exchange between lattice atoms and conduction electrons together with the stress gradient along the metal wire embedded into the rigid confinement are two major driving forces for electromigration-induced evolution of stress and vacancy concentration. The growth of mechanical stress causes an evolution of a variety of defects that are inevitably present in the metal, leading to void formation. It affects the electrical properties of the interconnect. In order to estimate the time to failure caused by voiding, the kinetics of stress evolution should be resolved until the first void is nucleated. Then the analysis of the void size evolution should be performed in order to trace changes in resistances of individual voided lines and vias. In this chapter, we review the major results that have been achieved with the 1D phenomenological EM model. We demonstrate its capability to predict the transient and steady-state distributions of the vacancy concentration and the hydrostatic stress, a void nucleation, and its growth, and also a drift of small voids along a metal wire. Despite its simplified nature, the 1D model is capable of addressing the confinement effect of ILD/IMD dielectric on EM-induced degradation, and also the effect of metal grain structure.

Previous chapters have mainly concerned the elastic behaviour of composites. Among the assumptions made in most of these treatments is that the interfacial bond is ‘perfect’. This means that there is no local plasticity, debonding, cracking or sliding – in fact, no elastic or inelastic processes of any description. In practice, such phenomena may take place at or close to the interface, depending on its structure and the stresses generated there. These processes can influence the onset and nature of subsequent failure. Before treating the strength and fracture of composites (Chapters 8 and 9), it is helpful to consider the interface region in detail and examine how its response can be characterised and influenced. The meaning and measurement of bond strength are therefore outlined here. This is followed by information about the formation of interfacial bonding in various systems and the scope for its control.