Formation of Slit-Like Voids at Trench Corners of Damascene Cu Interconnects

Abstract

Stress voiding was investigated in damascene Cu lines embedded in Ta/TaN/SiO₂/Si. Microstructure was observed before and after heat treatment at 723 K using a focused ion beam (FIB) technique. The distribution of thermal stress was calculated using a three-dimensional finite element method (FEM). FIB observation revealed that slit-like voids were formed at trench shoulders both before and after heat treatment. FEM calculation indicated that a large shear stress concentration occurred at the voided sites. The coincidence between the FIB observation and the FEM calculation suggests that the slit-like voids were formed by shear-mode delamination of Cu from the Ta/TaN barrier layer.