Effect of a contact and protective seal on aluminum electromigration

Abstract The electromigration characteristics of Al-0.5%Cu films deposited by a new Varian electron gun were evaluated. Their electromigration resistance is an order of magnitude worse than that previously reported for similarly evaporated films. Such a degradation in properties has been correlated with a more heterogenous grain structure and a loss of 〈111〉 fiber texture in the present films. An encapsulating layer partially restores the electromigration lifetimes, with the degree of improvement proportional to the mechanical rigidity of the overlying layer. Thus, a trimethylmethoxysilane contact and protective seal (CAPS) enhances conductor reliability by a factor of 2, whereas silicon nitride (SiN) increases the electromigration resistance by a factor of 9. These results suggest that the present design criterion of a d.c. current density of 1×10 5 A cm -2 in aluminum interconnects, based on data on uncovered lines, is somewhat conservative. To enhance layout density, this value may be increased to as much as 2.5×10 5 A cm -2 , depending on the CAPS layer, without compromising chip reliability.