Interfacial sliding and plasticity in back-end interconnect structures of microelectronic devices

Abstract

Interconnect structures at the back-end of microelectronic devices can deform via unusual, scale-sensitive phenomena due to thermo-mechanical loads sustained during processing, or during service as part of a microelectronic package. Although small, these effects can have a pronounced effect on component reliability. Here, we present results of atomic force microscopy (AFM) studies on Cu-low k dielectric (LKD) back-end interconnect structures (BEIS) to demonstrate these effects, which include creep/plasticity of interconnect lines, and diffusionally accommodated sliding at Cu-LKD interfaces. A previously reported shear-lag based model, which incorporates a constitutive interfacial sliding law developed by us earlier, is utilized to rationalize the observed strain incompatibilites, which are likely to be of concern during back-end processing. We then present a micro-mechanical model to capture the combined effects of in-plane shear and normal plasticity of interconnect lines, accommodated by in-plane interfacial sliding, when a microelectronic device is thermo-mechanically cycled as part of a package. The results are used to rationalize observations of permanent shear deformation of Cu interconnects via in-situ hot-stage AFM studies on the cross-section of back-end structures under conditions of package-induced thermomechanical cycling.