Strategy against electromigration-induced stress by passivation thickness design

Abstract

This study proposes a strategy to determine an appropriate passivation thickness to prevent electromigration (EM) deterioration. Although it is widely recognized that depositing passivation can effectively saturate the interconnect resistance against EM deterioration, the effect of passivation thickness on the lifetime of interconnections against EM has not been thoroughly investigated. In this study, quantitative models were developed to show direct analytical solutions. First, the effects of passivation thickness on the interconnect resistance against EM were examined through experiments using an Al interconnect coated with tetraethyl orthosilicate passivation. Assuming realistic conditions, the behavior of passivation fracturing as a function of passivation thickness was modeled under elastic, elastic-plastic, and elastic-plastic with plastic zone conditions. The models considered the critical tensile stress in the circumferential direction at the inner wall of a long cylindrical tube subject to internal pressure. These three models explain the saturation mechanism of passivation against EM resistance. Based on these findings, an appropriate passivation thickness for the required resistance against passivation fracture due to EM can be determined. This research provides valuable insights for designing reliable interconnects in microelectronics.