Impact of via-line contact on CU interconnect electromigration performance

Damascene processing creates special features for copper interconnect electromigration (EM). Though the fast Cu diffusion path is along the interface between Cu and the top cap layer, the early EM fails are often associated with vias, either by voiding in the via (via depletion), or by voiding underneath the via (line depletion). While most of the early EM fails for via depletion are related to the liner quality in vias, for line depletion EM the contact configuration between the via and the underlying line is critical to the failure characteristics. The contact between the via and the line liner below can effectively prevent or minimize open-circuit type EM failures. Redundant vias can significantly improve the EM performance in both the median failure time (t/sub 50/) and the distribution shape (sigma, /spl sigma/), depending on the arrangement of these vias relative to the line below. This paper presents an EM study of Cu interconnects with various via/line contact configurations. Results from single via and multiple via contacts, with and without redundancy to the underlying lines, are discussed.