Hole and Hillock Formation in Gold Metallizations at Elevated Temperatures Deposited on Titanium, Vanadium, and Other Barrier Layers

Gold thin films are potentially important as thin metallizations in microelectronic devices because of their superior electromigration resistance. Gold thin films require, however, an intermediate layer which serves as a diffusion barrier between metallization and device, and which should improve the bondability to the substrate and the stability against hole formation at elevated temperatures. This study presents the effects of Ti and V underlays on the stability of gold films during annealing. Both barrier metals prevent hole formation in gold films during annealing but promote the growth of gold hillocks on the free gold surface. Grain growth in the gold/titanium composite film is negligible during annealing while underlays of V cause the gold grains to grow under similar conditions. Gold films on both underlays have a (111) preferred orientation parallel to the substrate. The properties of these and underlays of In, Cu, and Ni are compared. It is shown that underlays of Sn or In (and to a certain extent also of Ti) are preferable to Cu, Ni and V layers.