TRANSMISSION ELECTRON-MICROSCOPY OF AL-CU INTERCONNECTS DURING IN-SITU ELECTROMIGRATION TESTING

Transmission electron microscopy of 2.1 mu m wide Al-4 wt.% Cu interco nnects during in-situ electromigration stressing shows microstructural evolution and the development of damage, including failure. Voids whi ch develop early stop growing and are not fatal. Hillocking is associa ted with Al-Cu precipitates; voiding which leads to failure is associa ted with copper depletion. Void initiation is at the upstream end of i nclined grain boundaries crossing the lines, which have a near-bamboo microstructure. Heating events occur as damage develops, arising from further voiding or from stress build-up. Open-circuit failure can occu r when the proximity of grain boundaries impairs the stress-driven hea ling. A schematic model for open-circuit failure in bamboo lines is pr oposed. The relative advantages of in-situ and conventional testing ar e discussed.