A Study on Characteristics of column fails in DDI DRAM

In dual-polycide-gate structure with butting contact, net doping concentration of polysilicon was decreased due to overlap between and and lateral dopant diffusion in silicide/polysilicon layers. The generation of parasitic Schottky diode in butting contact region is attributed both to the -loss due to agglomeration and to the decrease in net doping concentration of polysilicon layer. Parasitic Schottky diode reduces noise margin of sense amplifier in DDI DRAM, which causes column fail. The column fail could be reduced by physical isolation of polysilicon junction or suppressing agglomeration by using nitrogen implantation into polysilicon before formation.