The Effect of Post W-Etchback Cleaning Treatments and Implementation of Refractory Metal Buffer Layers on the Electromigration Performance of TiN/AlCu/TiN/Ti Metallization Systems

TiN/Ti films employed as glue layers for a blanket/etchback W plug technology show a significant surface contamination after the W-etchback process. An Al film deposited directly on a contaminated TiN/Ti underlayer exhibits a very weak texture, increasing the susceptibility to electromigration. Reliability tests confirm that the electromigration performance of a TiN/AlCu/TiN/Ti metallization system with a W plug technology, is significantly inferior to interconnecs that do not employ this plug technology. To improve the electromigration performance of this metallization system, several TiN surface cleaning treatments were evaluated. Also, the impact of the implementation of refractory metal buffer layers, before Al deposition was investigated. Analysis was performed by means of several surface analysis techniques, Al texture measurements and wafer-level reliability tests. It has been demonstrated that the contamination needs to be removed completely, or to be covered by a refractory buffer layer in order to restore the Al texture and to recover the proper electromigration resistance.