Effect of Al alloy and stacked film composition on linewidth dependence of electromigration lifetime

Al alloy composition and the type of the underlayer are among the process variables which determine the residual stress in VLSI interconnects. The residual stress affects the critical reliability parameter, threshold product. Effect of linewidth on electromigration lifetime is correlated with the linewidth dependence of residual stress and microstructure. The lifetime of submicron lines is limited by stress/microstructure gradients at wide/narrow transitions. Process implications are discussed.