Atomic bonding and properties of Al-Cu alloy with ϑ(Al2Cu)

Atomic bonding of ϑ (Al₂Cu) in an Al-Cu thin-film alloy is calculated by using empirical electron theory (EET) in solids. Results show that the Cu-Cu bond in the ϑ phase is the strongest, while the second strongest bond is the Al-Cu bond. All of these bonds are stronger than the strongest Cu-Cu bond in pure Cu metal. This is the reason that only ϑ precipitation in the Al-Cu thin-film alloy can be found and not ϑ″ and ϑ′ phases. The electromigration lifetime of Al-Cu thin-film alloy for interconnects is influenced by the stronger atomic bonding in ϑ particles, which are dispersed in the matrix of the alloy. The ϑ precipitation in the Al-Cu thin-film alloy can enhance the strength of the alloy by the stronger bond net and increase the electromigration lifetime for interconnects.