Cu interconnect lifetime estimation in the presence of thermal gradients

Abstract

Through physical and electrical analysis, the impact of thermal gradients on mass transport in Cu interconnects is studied using a dedicated test structure. The key physical parameter for thermomigration (TM), the heat of transport (Q∗), is evaluated experimentally to be 0.21 eV. Furthermore, an analytical model based on existing 1D physics-based models [M. A. Korhonen et al., J. Appl. Phys. 73, 3790–3799 (1993); H. Zahedmanesh et al., Microelectron. Reliab. 111, 113769 (2020)] is proposed to predict the time to void nucleation, the void growth rate (νgrowth), and the time to failure (TTF) due to TM. Also, their dependence on temperature (T), temperature gradient (dTdx), and second derivative of the temperature (d2Tdx2) is derived. This analytical model calibrated using experimental data predicts a TTF of 38 years for a 1μm wide Cu interconnect under specific stress conditions: an operating temperature of 100°C, a local temperature increase of 67°C, and a d2Tdx2=−2.9°C/μm2 induced by an external heat source.