Mechanical stress measurements in damascene copper interconnects and influence on electromigration parameters

Abstract

This paper presents mechanical stress measurements versus temperature in advanced damascene copper lines with various geometries using synchrotron high flux X-rays. Elasto-plastic behaviour versus temperature is evidenced as well as temperature transitions between tensile and compressive stresses. We discuss the theoretical influence of /spl sigma/(T) on electromigration (EM), lifetime (MTF), and current design rule for the two degradation modes of voids and hillocks. We show that EM extrapolations should be reconsidered. While MTF defined by open failure is weakly affected by mechanical stress conditions, hillock mode failure would lead to a reduction of maximum current density design rule J/sub max/. The prospective impact of low k materials relative to mechanical stress is then addressed.