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

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Abstract
It is generally accepted that one way to prevent junction spiking during the 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 , where , 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 (∼ 105 Acm−2), our results indicate that Al/poly‐Si contacts to shallow junctions will remain electromigration resistant despite a decrease in window dimensions.

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