Highly Reliable and Low Resistive Cu/Low-k Dual Damascene Interconnects by Using TaTi Barrier Metal

Abstract

Novel barrier metal of TaTi alloy has been developed for highly reliable Cu/low-k DD interconnects. TaTi barrier metal with higher Ti concentration improved EM performance, however, it showed both step coverage degradation and line resistance increase. Then, control of Ti diffusion amount from the barrier metal into Cu, determined by Ti concentration in the PVD target, was found to be a key to keep both low line resistance and high reliability. Limited Ti content in the TaTi of Ta-2wt%Ti showed good step coverage, adequate barrier property and better wettability to Cu than Ta. Furthermore, Ta-2wt%Ti achieved 10 times longer EM lifetime than Ta without penalty of line resistance. Thus, Ta-2wt%Ti is one of the promising candidates of barrier metal for highly reliable Cu/low-k interconnects without resistance increase in the future generations.