Cracking in thin multi-layers with finite-width and periodic architecture

Many applications involve thin multi-layers comprised of repeating patterns of different material sections, notably interconnect–dielectric structures in microelectronics. This paper considers a variety of failure scenarios in systems with periodically arranged features within a single layer. Crack driving forces are presented for (i) debonding between alternating material sections in a thin film (i.e. channel and tunnel cracking at material junctions), and (ii) channel cracking in a thin uniform coating above a layer comprised of alternating sections of different materials. The effects of elastic mismatch, feature spacing, crack spacing and residual stress are illustrated for a wide range of parameters. The results presented here illustrate that residual stresses in intact sections can strongly promote cracking in adjacent layers, which is in contrast to analyses of blanket film multi-layers which predict that residual stress in adjacent layers has no effect. An important finding is that decreasing the relative size of low-modulus sections significantly increases the crack driving force in adjacent layers. The implications of these results are discussed in the contexts of critical feature spacing and the impact of incorporating low elastic-modulus sections (such as polymer dielectrics) on thermo-mechanical reliability.