Boron Transport Through Surface Channel pMOS Using W-poly Metal Gate Electrode

Abstract

This work considers boron transport through surface channel p-metal oxide semiconductors ͑pMOSs͒ using tungsten-poly metal gate electrode as a function of poly doping conditions and nitric oxide treatment by analyzing quasi-static capacitance-voltage curves and time-dependent dielectric breakdown characteristics obtained after applying the full thermal budget, especially including selective oxidation to prohibit tungsten oxidation. From the result obtained when nitrogen was implanted into undoped amorphous Si ͑␣-Si͒, it can be recognized that out-diffusion of boron into tungsten and its nitride is negligible. Mixed implantations into undoped ␣-Si aggravates the gate depletion, whereas it has little relationship with boron penetration into the pMOS channel. The abundance of dose in undoped ␣-Si facilitates the boron penetration, leading to gate oxide degradation and variation of the flatband voltage within the wafer as well as to the improvement of the gate depletion. From the comparison of the capacitance-voltage curve and the flatband voltage uniformity among experimental splits, it is found that the nitric oxide treatment retards the boron penetration into the pMOS channel effectively without significant degradation of the gate depletion.