Impact of super-steep-retrograde channel doping profiles on the performance of scaled devices

Super-steep retrograded (SSR) channels were compared to uniformly doped (UD ) channels as devices are scaled down from 250 nm to the 50 nm technology n ode, according to the scheme targeted by the National Technology Roadmap fo r Semiconductors (1997), The comparison was done at the same gate length L- gate and the same off-state leakage current I-off where it was found that S SR profiles always have higher threshold voltages, poorer subthreshold swin gs, higher linear currents, and lower saturation currents than UD profiles. Using a simulation strategy that takes into account the impact of short-ch annel effects on drive current, it was found that the improved short-channe l effect of retrograde profiles is not enough to translate into a higher pe rformance over the UD channels for all technologies. Hence, if the effectiv e gate-dielectric thickness scales linearly with technology, retrograde dop ing will not be useful from a performance point of view. However, if the sc aling of the gate-dielectric is limited to about 2 nm, SSR profiles can giv e higher drive current than UD channels for the end of the roadmap devices, Thus, the suitability of SSR channels over UD channels depends on the gate -dielectric scaling strategy. Simulations using a self-consistent Schroding er-Poisson solver were also used to show that the impact of quantum mechani cal (QM) effects on the long-channel characteristics of SSR and UD MOSFET's will be similar.