Stepped current electromigration test of multilevel aluminum metallizations on wafer level

Abstract

Electromigration is the phenomenon of electron flux induced mass transport resulting in damage of metal lines and interconnect structures of microelectronic devices. The drift process in aluminum metallizations is studied in order to specify quality and to predict reliability of multilevel systems for application in integrated circuits. In contrast to conventional constant current electromigration experiments, stepped current tests are used to investigate the mechanisms of resistance variations of aluminum lines and via chains. In the experiment which is performed on wafer level, aluminum filled via interconnects are compared to tungsten plugs. The measurements are interpreted using a basic model of mass flux including the influence of Joule heating. Activation energies of the dominating diffusion processes are determined and explained considering effects of short length, near-bamboo crystal structure, copper alloying and interfacial barrier layers.