Shallow junction cobalt silicide contacts with enhanced electromigration resistance

Abstract

Aluminum contacts to shallow junctions in high‐performance silicon integrated circuits suffer from an inhomogeneous Al/Si interaction, which culminates in a destruction of contact and junction integrity. Certain silicides such as CoSi₂, on the other hand, are thermodynamically stable over Si. However, these still require an additional barrier layer between the top Al and the silicide to inhibit thermally induced reactions with Al. This work addresses the question of electromigration at one such proposed contact metallization scheme consisting of Al/TiN/CoSi₂. Results indicate that the TiN provides a suitable barrier to Al/Si interdiffusion under standard device operating conditions. At extremely high currents and temperature, however, the contacts degrade by a localized Al/TiN interaction, which destroy the TiN barrier integrity, followed by Al/CoSi₂ reaction and Si electromigration from the substrate. In contrast, Al/CoSi₂ contacts are highly susceptible to junction leakage, with junction lifetimes controlled by the kinetics of Si diffusion through CoSi₂.