Prevention of dopant out-diffusion during silicidation and junction formation

Abstract

High integrity cobalt silicide contacts are formed with shallow source/drain junctions. Embodiments include depositing a layer of cobalt on a substrate above intended source/drain regions, followed by silicidation and diffusing impurities from a doped film during or after silicidation in an environment which discourages out-diffusion of the impurities to the environment. The resulting source/drain junctions are self-aligned to the cobalt silicide/silicon substrate interface, thereby preventing junction leakage while advantageously enabling forming the cobalt silicide contacts at optimum thickness to avoid parasitic series resistances. The formation of self-aligned source/drain junctions to the cobalt silicide/silicon substrate interface facilitates reliable device scaling, while the avoidance of unwanted diffusion of impurities to the environment assures adequate doping of the source/drain regions.