Observation and restoration of negative electromigration activation energy behavior due to thermo-mechanical effects

An apparent negative activation energy behavior in electromigration lifetime was observed for Cu/low-k single damascene interconnects. We explain this as a result of a fast failure mode by thermo-mechanical damage at low temperatures around 250/spl deg/C. Mechanical strengthening of the via by thickening the sidewall barrier and surrounding it with strong inter-layer dielectric have successfully suppressed the thermo-mechanical failures and restored the activation energy behavior to normal. We show that ensuring thermo-mechanical stability is a key concern for developing reliable high performance interconnects.