Pulsed-current duty cycle dependence of electromigration-induced stress generation in aluminum conductors

The effect of duty cycle of pulsed dc currents on the critical length-current density product, (jl/sub c/), was measured using the Blech-Kinsbron edge-displacement technique [Thin Solid Films 25, 327 (1975)]. Unencapsulated Al edge-displacement segments mere stressed at various duty cycles and the critical lengths, the so-called "Blech lengths", were measured. It was found that jl/sub c/ increased with decreasing duty cycle. We measured a factor of 2.6 increase in jl/sub c/ for the 25% duty cycle as compared to dc. This duty cycle dependence of Blech length implies that electromigration resistance for an integrated circuit would be increased for small duty cycle operation by increasing the fraction of interconnects which are sub-Blech-length and are not susceptible to EM damage.