A simulation study of charge transfer doping for ultra-shallow source/drain extensions

To improve the performance of extremely scaled MOSFETs, we propose the use of a novel charge transfer-doped source/drain extension (CTE); i.e., a source/drain extension (SDE) consisting of an inversion layer induced by ionized impurities placed immediately above the Si surface. The performance of MOSFETs with CTEs (CTE-MOS) has been compared to that of MOSFETs with conventional SDEs (conv.MOS) for the 45 nm technology node by two-dimensional device simulations. The use of CTEs significantly improves the short-channel characteristics, while degrading the drive current by ∼10% at a fixed gate length Lgate because of their higher resistance than that of conventional SDEs. In the comparison with the conv.MOS assuming that the Lgate fluctuation is ±20% and that the off-state subthreshold leakage current should be lowered to a specified value at Lgate = −20%, the CTE-MOS is found to have 1–1.4 times the drive current at Lgate = +20% and 0.3–0.4 times the threshold voltage roll-off. These better features of the CTE-MOS are attributed to the excellent immunity to the short-channel effects owing to the extreme shallowness of CTEs.