Experimental study of electromigration at bamboo grain boundaries with a new test structure using the single-crystal aluminum interconnection

Electromigration (EM) voids in the bamboo structure interconnect were observed by a new test structure with single-crystal aluminum leads. The new test structure consists of a single grain connected to single-crystal aluminum leads formed by lateral-solid phase epitaxial growth (L-SPE). The grain was formed by suppressing L-SPE of the single-crystal aluminum leads. Since the void nucleation sites were confined to the grain boundaries, the voids were easily located and observed. In addition, the crystal orientation of single-crystal aluminum leads could be controlled by L-SPE, and so the analysis could be performed more accurately than using traditional test structures that have a series of grains with random crystal orientation. The accelerated EM test was carried out under ideal conditions similar to that of real devices, because the temperature gradients around the test site of the bamboo grain boundaries were negligible. In our preliminary experiment, a void was observed in the grain, located next to the positive voltage lead. This seems to be contradictory to general understandings, we think this is because of the grain boundary configuration difference and/or EM induced vacancy fluxes difference.