Morphology and crystallography of electromigration induced transgranular slit failures in aluminum alloy interconnects

Abstract

Microstructural and crystallographic characterization of electromigration induced voiding and damage in Al and Al-2% Cu interconnects are presented. Scanning electron and focussed ion beam micrographs show that extended voiding in wide lines and transgranular slit voids in near bamboo lines are the preferred failure morphologies. Electron back scattered diffraction analysis of transgranular slit failure sites show a preferred <110> slit void orientation. Estimates of stresses required for stress assisted void growth in unpassivated interconnects are shown to be reasonably close to measured stress levels in films and interconnects. The transgranular void process is shown to be preferred over boundary voiding based on usual estimates for the variation of surface energy and random boundary energies in Al. Finally, line edge void growth into transgranular slit failures at favorably stressed and crystallographically orineted grain sites is presented as an empirical model for the observed electromigration induced failures in near bamboo interconnects lines.