Effect of barrier process on electromigration reliability of Cu/porous low-k interconnects

Abstract

Electromigration (EM) reliability of Cu/low-k interconnects with a conventional preclean-first process, and an advanced barrier-first process has been investigated. Compared with the preclean-first process, extrinsic early failures were not observed for the barrier-first process. This suggests that process-induced defects, which are the most probable cause for early failures, are significantly reduced for the barrier-first process. Transmission electron microscopy observation demonstrated a more uniform and thicker Ta barrier for the barrier-first process than the preclean-first process. This led to a higher (jL)c product, and prolonged the EM lifetime accordingly. In addition, a predeposited Ta barrier during the barrier-first process protected the mechanically weak low-k dielectrics from plasma etch damage, and a uniform via profile resulted. In contrast, the via opening at the top was found to be larger than that of at the via bottom for the preclean process. The uniform via profile is another advantage of the barrier-first process from the point of view of process control.