Electromigration resistant alternatives to aluminum-copper

Electromigration performance of a wide range of Al-based conductors has been investigated with two ends in view: (1) an alternative to Al/Cu without the disadvantages associated with Cu; and (2) a conductor with enhanced electromigration resistance. Al/Si/Ti or Al/Ti alloys may furnish the former, though care is required in the use of high (0.8-1%) Ti content as it leads to greatly enhanced whisker growth implying very early short-circuit failure. With system interactions or process compatibility also in view, simple two-layer and three-layer structures involving AlCu are shown to provide the optimum metal for four-layer metal at 3-4- mu m pitch, with TiW or CVD W as an underlayer, Al/Cu or possibly other alloys as main conductor, and Ti, W, or TiW as a cap. The effect of various passivation options has also been investigated. The present work was undertaken as part of the Esprit project Advanced Interconnect for VLSI.<>