Significance of Charge Sharing in Causing Threshold Voltage Roll-Off in Highly Doped 0.1-µ m Si Metal Oxide Semiconductor Field Effect Transistors and its Suppression by Atomic Layer Doping

Abstract

An investigation into the influence of substrate doping concentration on the short channel effects in 0.1-µm nMOSFETs (n-channel metal oxide semiconductor field effect transistors) has shown that, when substrate dopant concentration is higher than 1×1018 cm-3, threshold voltage (V th) roll-off is not improved by heavier doping in the substrate, although punchthrough is suppressed. Furthermore, it was found that threshold voltage roll-off is characterized by a reduction in subthreshold swing. Experimental results suggest that the threshold voltage roll-off is heavily influenced by the effect of the two-dimensional shape of the drain depletion region, namely the charge sharing mechanism. As a candidate device for suppressing charge sharing, the ALD (atomic-layer doped) MOSFET was considered. Its excellent scalability was demonstrated by device simulation.