Electromigration Induced Shallow Junction Leakage with Al/Poly‐Si Metallization

It is generally accepted that one way to prevent junction spiking during the 450 ° C / H 2 anneal at shallow junction contacts, is to use a composite metallization of Al over n + poly‐Si. We observe that while such a composite can prevent thermally induced Al/Si interpenetration, the devices are still susceptible to failure by junction leakage at positively biased windows, resulting from the electromigration of Si into the overlying metal. The process involves a localized diffusion of poly‐Si into Al, followed by the transport of Si across the metal‐semiconductor interface. The lifetimes exhibit a strong dependence on current, varying as I − N , where N ≈ 10 , indicative of steep temperature gradients in vicinity of the contacts. However, if the contact window current is scaled down in accordance with the established criterion for electromigration in the interconnect (∼ 10 5 Acm −2 ), our results indicate that Al/poly‐Si contacts to shallow junctions will remain electromigration resistant despite a decrease in window dimensions.