AES analysis of failures in Cu based electromigration test samples

Failures occurring in electromigration test of copper interconnects have been characterized by electron backscatter diffraction (EBSD) and scanning Auger microscopy (SAM). The Cu interconnects were 2 μm wide and 500 nm thick stripes on a Ta/TaN barrier. They are imbedded in trenches in a SiO2 layer on Si. The failure manifests as the appearance of voids with lateral dimension of some micrometers. By EBSD mapping, it could be verified that no sidewall texture in the interconnect exist. Auger analysis clearly showed that the Ta/TaN barrier layer has not been destroyed at the site of electromigration failure. The interaction of the electron beam with small particles (≈0.5 μm) was modelled to understand the contribution of electron scattering in the voids to the lateral resolution.