An Optimized and Reliable LDD Structure for 1-/spl mu/m NMOSFET Based on Substrate Current Analysis

Abstract
Optimization of the n/sup -/ region concentration for n-channel MOSFET's with a lightly doped drain (LDD) structure was investigated, based on an analysis of the substrate current characteristics. When a substrate current tailing is observed, which is peculiar to the LDDFET with a low-concentration n-region, a gate current is not observed, which suggests strong resistance against hot-carrier injection. This was confirmed by a bias stress test. The optimized surface concentration for the n/sup -/ region ranges from 1 x 10/sup18/ cm/sup -3/ to 2.5 X 10/sup 18/ cm/sup -3/ under negligible V/sub TH/ shift and less than 25-percent driving capability degradation, compared to values for a conventional MOSFET.