Formation of junctions by diffusion from a doped amorphous silicon film during silicidation

Abstract

High integrity ultra-shallow source/drain junctions are formed employing cobalt silicide contacts. These are formed by depositing a layer of cobalt on a substrate above intended source/drain regions, and depositing a doped amorphous silicon film on the cobalt. Silicidation, as by rapid thermal annealing, is performed to form a low-resistance cobalt suicide while consuming the amorphous silicon film and diffusing impurities from the doped amorphous silicon film through the cobalt silicide into the substrate. The diffusion of the impurities forms shallow junctions extending into the substrate a substantially constant depth below the cobalt silicide/silicon substrate interface. The consumption of the amorphous silicon film during silicidation, which results in less consumption of substrate silicon, and formation of source/drain junctions self-aligned to the cobalt silicide/silicon substrate interface, enables the formation of ultra-shallow source/drain junctions without junction leakage while allowing the formation of cobalt silicide contacts at optimum thickness, thereby facilitating reliable device scaling.