REDUCTION IN FLUX DIVERGENCE AT VIAS FOR IMPROVED ELECTROMIGRATION INMULTILAYERED ALCU INTERCONNECTS

Using of W-plug vias in AlCu interconnects is known to significantly d egrade electromigration (EM) performance because W is a diffusion barr ier and prevents the depleting species by EM from being replenished at the via. In the present study, we demonstrate that this problem of li mited source for EM migrating species can be dramatically alleviated i n a multilayered metallization of TiN/AlCu/TiN using Al-plug vias. EM lifetime improvements as large as by an order of magnitude are accompl ished by reducing the flux divergence at the Al-plug via. This flux di vergence is critically determined by the effective thickness of some t ransition metal films at the via, which include a Ti/TiN stack for the via barrier and a TiN layer of antireflection coating for the bottom level metal lead. Scanning electron microscopy failure analysis also v erifies that the samples with W-plug vias have the void damages consis tently located at the via. For the samples with Al-plug vias and with the flux divergence at the via being largely reduced, the void failure s locate on the metal lead and no visible damage at or within the via, indicating the reduced flux divergence at the via has become smaller than those generated on the metal lead due to microstructural variatio ns. (C) 1996 American Institute of Physics.