Intermetallic compounds of Al and transitions metals: Effect of electromigration in 1-2-μm-wide lines

This paper describes a method to improve the electromigration capacity of Al-Cu or Al thin-film interconnection metallurgy by incorporating a layer of intermetallic compounds of Al and transition metals. The improvement in lifetime can be 100 times greater than comparable Al-Cu structures tested under the same conditions. Certain structural properties of the intermetallic compounds have been related qualitatively to the failure mode and electromigration lifetime. Results are discussed in an attempt to clarify the mechanisms by which an ordered phase (compound layer) can improve electromigration lifetime. Life-test data obtained from the thin-film metallurgy with Al-transition-metal compound structures indicate that improvements can be achieved by one or a combination of the following factors: (a) blocking void propagation through the film, (b) reducing the rate of mass transport by electromigration, and (c) eliminating divergent damage sites by increasing the degree of preferred grain orientation. In many cases, the thickness of the intermetallic layer can be adjusted to yield a significant improvement in lifetime with only a small increase in stripe resistance.