Comparative Study of Uniform Versus Supersteep Retrograde MOSFET Channel Doping and Implications for 6-T SRAM Yield

The benefit of supersteep retrograde (SSR) channel doping for suppressing short-channel effects in planar bulk MOSFET performance is studied via technology computer-aided design simulation of devices with gate length L
_g
= 28 nm. It is found that drain-induced barrier lowering is reduced by more than 40%, and variation in saturation threshold voltage (σ V
_T,Sat
), caused by random dopant fluctuation, is reduced by ~50%, with SSR channel doping. However, degraded drive current is observed for SSR channel doping due to enhanced body effect. Estimations of six-transistor static random access memory (SRAM) cell yield indicate that 33% reduction in the minimum operating voltage (V
_MIN,SRAM
) can be achieved with SSR channel doping.