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The effect of nitrogen (N/sub 14/)implant into dual-doped polysilicon gates was investigated. The electrical characteristics of sub-0.25-/spl mu/m dual-gate transistors (both p- and n-channel), MOS capacitor quasi-static C-V curve, SIMS profile, poly-Si gate R/sub s/, and oxide Q/sub bd/ were compared at different nitrogen dose levels. A nitrogen dose of 5/spl times/10/sup 15/ cm/sup -2/ is the optimum choice at an implant energy of 40 KeV in terms of the overall performance of both p- and n-MOSFETs and the oxide Q/sub bd/. The suppression of boron penetration is confirmed by the SIMS profiles to be attributed to the retardation effect in bulk polysilicon with the presence of nitrogen. High nitrogen dose (1/spl times/10/sup 16/ cm/sup -2/) results in poly depletion and increase of sheet resistance in both unsilicided and silicided p/sup +/ poly, degrading the transistor performance. Under optimum design, nitrogen implantation into poly-Si gate is effective in suppressing boron penetration without degrading performance of either p- or n-channel transistors.