Impact of the lateral source/drain abruptness on MOSFET characteristics and transport properties

Abstract

The impact of the lateral doping abruptness (LA) of the source/drain extension still remains a polemic issue in CMOS transistor engineering. Based on dedicated simulations, it is shown that the maximum gain in on current achieved with steep profiles does not exceed 3%. Moreover, a suited analytical modeling indicates that the influence of the LA mostly resides in changing the effective channel length (Leff). Subsequently, the impact of the gate overlap is critically reviewed and actually appears to be mostly related to the analytical definition of the simulated device. Eventually, relying on a clear physical background, the analysis is carried out further to investigate the modulation of source injection properties in the framework of the backscattering theory and Monte Carlo (MC) simulations. We propose an additional injection effect that emerges at the source end potential barrier when the junction becomes very abrupt. This effect incorporated within the theory of Lundstrom enables further interpretation and understanding of the MC on-state current calculations.