Electromigration degradation of buried power rails considering grain evolution in stacked integration

Electromigration in buried power rail (BPR) structures for sub-5 nm complementary field-effect transistor devices has emerged as a critical reliability concern due to extreme current densities and elevated temperatures. In this work, we develop a coupled multiphysics phase field model to investigate the impact of dynamic grain evolution on electromigration degradation in BPR structures. The framework integrates electrothermal simulation, vacancy transport, stress evolution, and grain boundary migration kinetics. Results reveal that grain coarsening fundamentally alters vacancy transport through modification of grain boundary diffusion pathways. Comparative analysis demonstrates that grain evolution reduces vacancy accumulation at the cathode from approximately 2.5 times to 1.7 times the equilibrium value, while hydrostatic tensile stress decreases. Grain boundary fraction decreases by approximately 60% due to coarsening, accompanied by corresponding reductions in average diffusivity. Furthermore, electrical and thermal conductivities increase due to reduced grain boundary scattering, while representative elastic stiffness components decrease. This study demonstrates that neglecting grain evolution could lead to overestimation of the local physical driving forces for electromigration-induced failure. By accounting for grain dynamics, our framework enables more realistic reliability assessments for advanced power delivery networks.