Effects of Complex Alloy Additions on Electromigration in Aluminum Thin Films

Electromigration failure times in thin film aluminum conducting stripes, such as those used in planar semiconductor devices and integrated circuits, have in the past been shown to increase with certain binary alloy additions. While the addition of copper has been the object of many studies, other additives increase the failure time as much as or even more than copper. These additions, however, also increase the electrical resistivity of the stripes, which is often undesirable. Magnesium additions, for example, may give a failure time which is ten times that of comparable stripes with copper additions but the increase in resistivity is about 100%. Investigations were carried out with ternary and quaternary alloy additions. The additive elements selected were individually known to be effective against electromigration failures. Typical examples of such ternary and quaternary alloys would be Al-Cu-Mg and Al-Cu-Ni-Mg. It has been found possible to obtain large improvements in failure times combined with relatively low resistivity increments through the use of ternary and quaternary alloy additions.