Analytical Model for Cu Interconnect Lifetimes Under Combined Thermomigration and Electromigration Stress

Abstract

The combined effect of thermomigration (TM) and electromigration (EM) on the reliability of Cu interconnects is investigated. Package-level EM+TM tests were conducted to understand the impact of temperature gradients on void nucleation and void growth in the presence of electrical currents. Through failure analysis, void nucleation at the via bottom followed by subsequent void growth toward adjacent vias is confirmed. An analytical model is developed to quantify the impact of temperature gradients on EM lifetime. Results indicate that thermal gradients have a more pronounced impact at lower ambient temperatures, reducing EM lifetime by approximately 50% at 100 °C, compared to a 42% reduction at 300 °C. This work enhances the understanding of EM+TM coupling mechanisms and provides a practical model for predicting Cu interconnect reliability under combined stress conditions.