RDF effect induced by source/drain doping in nano-scale UTB SOI MOSFET with nominally un-doped channel

SOI MOSFETs with un-doped channel are generally considered immune to random dopant fluctuation (RDF) effect. However in ultra-small MOSFETs, the lateral extension distribution of source/drain (S/D) impurity can make the “nominally” un-doped channel considerably doped, thus very likely resulting in an unexpected noticeable RDF effect. In this work, we investigate the unexpected RDF effect in UTB SOI MOSFETs with un-doped channel by device simulation. Results show that, for sub-20nm gate length devices, the S/D doping abruptness (δ) is required to be around 1 nm/dec to have an acceptable V_th variation caused by the unexpected RDF effect. This requirement seems too difficult to meet in the present or near future technologies. A new limit to scaling nano-scale SOI devices is thus revealed.