The effect of nitrogen (N14) implant into dual-doped polysilicon gates was investigated. The electrical characteristics of sub-0.25-μm dual-gate transistors (both p- and n-channel), MOS capacitor quasi-static C-V curve, SIMS profile, poly-Si gate Rs, and oxide Qbd were compared at different nitrogen dose levels. A nitrogen dose of 5 × 1015 cm-2 is the optimum choice at an implant energy of 40 KeV in terms of the overall performance of both p- and n-MOSFET's and the oxide Qbd. 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 × 1016 cm-2) results in poly depletion and increase of sheet resistance in both unsilicided and suicided p+ 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.