JUNCTION LEAKAGE DUE TO COSI2 FORMATION ON AS-DOPED POLYSILICON

Junction leakage has been observed for shallow diodes that simulate em itter-base junctions in npn bipolar transistors, due to CoSi2 formatio n on As-doped polysilicon. The leakage depends on the Co thickness, th e polysilicon thickness, and the device area, but is relatively indepe ndent of the Co anneal conditions between 600 and 800-degrees-C. Sever e roughness at the CoSi2-polysilicon interface is also observed, espec ially after annealing at 800-degrees-C. The leakage is probably due to CoSi2 protrusions in the substrate that are produced during the initi al silicide formation.