Reliability of Multi-Terminal Copper Dual-Damascene Interconnect Trees
Author(s)Gan, C.L.; Thompson, Carl V.; Pey, Kin Leong; Choi, Wee Kiong
Electromigration tests on different Cu dual-damascene interconnect tree structures consisting of various numbers of straight via-to-via lines connected at the common middle terminal have been carried out. Like Al-based interconnects, the reliability of a segment in a Cu-based interconnect tree strongly depends on the stress conditions of connected segments. The analytic model based on a nodal analysis developed for Al trees gives a conservative estimate of the lifetime of Cu-based interconnect trees. However, there are important differences in the results obtained under similar test conditions for Al-based and Cu-based interconnect trees. These differences are attributed to the variations in the architectural schemes of the two metallization systems. The absence of a conducting electromigration-resistant overlayer in Cu technology and the low critical stress for void nucleation at the Cu/inter-level diffusion barrier (i.e. Si₃N₄) interface leads to different failure modes between Cu and Al interconnects. As a result, the most highly stressed segment in a Cu-based interconnect tree is not always the least reliable. Moreover, the possibility of liner rupture at stressed dual-damascene vias leads to significant differences in tree reliabilities in Cu compared to Al. While an interconnect tree can be treated as a fundamental unit whose reliability is independent of that of other units in Al-based interconnect architectures, interconnect trees can not be treated as fundamental units for circuit-level reliability analyses for Cu-based interconnects.
Advanced Materials for Micro- and Nano-Systems (AMMNS);
copper dual-damascene interconnect trees, electromigration, via-to-via, dotted-I interconnect trees, levels of metallization