Stress analysis of encapsulated fine-line aluminum interconnect

Mechanical stresses are known to cause hillock formation and creep voids in aluminum based interconnect on integrated circuits. While the effects of differential thermal expansion between an aluminum film and a silicon substrate are well known, the effects on an encapsulated narrow aluminum line are not. We report here an analysis of the stresses generated in such a line upon cooling from 400 °C after passivation deposition. At 25 °C the principal stresses in the aluminum are all tensile with magnitudes several times the yield strength. The aluminum need not fail, but a high driving force for creep remains. High stresses also are generated in the passivation which could lead to cracking.