Electromigration in multilayer metallization: Drift-controlled degradation and the electromigration threshold of Al-Si-Cu/TiN<i>x</i>O<i>y</i>/TiSi2 contacts

Abstract

Metallizations that incorporate a conductive layer beneath an Al alloy (multilayers) are necessary for the improvement in electromigration performance required by the continued feature size reduction and increased integration of microelectronic devices. Degradation of contact structures that utilize multilayer metallization will result from electromigration-induced voiding of the Al layer. A detailed understanding of the mechanisms of voiding is required for the accurate prediction of contact reliability. We have examined electromigration voiding in Al-Si-Cu/TiNxOy/TiSi2 multilayer contacts. Accelerated testing reveals that a TiNxOy/TiSi2 layer formed by rapid thermal anneal of Ti is an effective Si diffusion barrier at operating temperatures (&amp;lt;125 °C) and eliminates electromigration-induced leakage failures. Contact degradation occurs by increased resistance due to voiding of the Al-Si-Cu layer. Voiding involves drift-controlled edge displacement where the Al-Si-Cu layer migrates out of positively biased contacts, leaving the TiNxOy/TiSi2 layer intact. For 1-μm-diam contacts, the drift velocity has a significant lattice diffusion component and failure times are expected to far exceed operation lifetimes of devices. Additionally, evidence is presented for an electromigation threshold that eliminates voiding degradation for contacts connected by stripes.