Electromigration Induced Failure as a Function of Via Interface

Abstract

Failure of test structures composed of pairs of W vias connected by lengths of Al/0.5%Cu conductor were compared as a function of the position of the via with respect to the conductor link. In one configuration, the current was passed from first level to a conductor link on second level and in the other the current was passed from second level to one on the first. In each case the links were identical in cross section, length and composition. There was a significant difference in the performance with respect to electromigration lifetime between these configurations as well as a difference in the failure mode. In the first level links, where the current passed first through a a 350A thick TiN ARC (Anti-Reflective Coating) layer and then a 150A Ti layer, the lifetime was significantly shorter than that of the second level samples where the current was passed across an interface of Al₃Ti intermetallic compound. In addition, the failure mode was different, the first metal links failing directly under the via whereas in second metal link, the failures were away from the via in the metal link itself.