AC electromigration characterization and modeling of multilayered interconnects

The AC electromigration of multilayered interconnect systems consisting of TiW-AlSiCu and CVD W-AlSiCu is studied under stress of repetitive dual-pulse current waveforms at 2 MHz. By using a general AC waveform in which the peak current density of the first pulse j/sub 1/ is fixed and the second is varied from +j/sub 1/ to -j/sub 1/, a continuous electromigration spectrum from DC through pulsed DC to pure AC conditions is obtained. Although an average current model fits the data well, there is a singularity in the median time-to-failure at pure-AC conditions. To avoid this singularity, a modification of the average current model, called the average current recovery model, is developed. It heuristically accounts for the degree of damage recovery during opposite-polarity pulses through a single recovery parameter.<>