Electromigration Results with Large Sample Size for Dual Damascene Structures in a Copper/CVD Low-k Dielectric Technology

The reliability of a two-level electromigration structure stressed under various conditions is described. The structure consists of Cu dual damascene metallization with SiCOH as the low-k dielectric. A new electromigration test system is implemented to greatly increase the sample size without significantly increasing the hardware requirements. Due to the presence of two failure modes, the statistical behavior is described by a bimodal lognormal failure distribution. Failure analysis indicates that early failures occur in the Cu vias while late failures occur in the Cu lines. Comparable current density exponent and activation energy values are obtained for both failure modes, suggesting similar void formation mechanisms