MORPHOLOGY OF ELECTROMIGRATION-INDUCED DAMAGE AND FAILURE IN AL-ALLOY THIN-FILM CONDUCTORS

Distinct morphologies of electromigration-induced voids and failures are shown for Al, Al-2%Cu, and Al-2%Cu-1% Si narrow (1-6 mu-m) unpassivated thin film conductors. SEM and TEM images typically show large non-fatal voids and narrow slit-like open circuit failures for all film conditions and accelerated test conditions. Evidence for transgranular slit failures is shown for 1.33 mu-m wide conductors. A simple model for void growth is presented which accounts for the void morphologies seen. The observed morphologies and the results of void growth modelling suggest that slit voids nucleate after other voids and rapidly produce failure. These conclusions are discussed in terms of 'classical' models for electromigration failure processes and resistance and noise power monitoring techniques.