The stress-induced escape of migrating aluminium from silicide interconnects

Abstract

Electromigration of foreign aluminium atoms, arising from contact pads, along polycrystalline molybdenum silicide (MoSi 2 ) metallic interconnect lines has been studied. The MoSi 2 -lines with aluminium contact pads on both ends were exposed to electric direct current with densities of between 10 6 and 10 7 A cm −2 over 2000 h. While mass transport of constituent atoms of the line material was not observed, the atomic migration of aluminium is clearly directed from the cathode side toward the anode. Characteristic hillocking along the interconnect line is observed. This result is in accord with the action of a partially grain-blocked polycrystalline via due to clusters, which are present along the line. Compressive stress in front of blocking silicide grains is found to induce a positive mass flux through the line surface. Scanning electron microscopy micrographs, and energy-dispersive x-ray analyses are applied to identify the chemical nature of the degradation sites. It is found that aluminium from the cathode pad incorporates into the interconnect and migrates under the action of the electron wind.