A STUDY OF SERIES RESISTANCE AND EFFECTIVE CHANNEL MOBILITY IN LDD NMOSFET

Abstract

This project involves the study of the series resistance and effective mobility of lightly-doped drain (LDD) nMOSFETs using the drain-current-conductance method (DCCM). A modification to this technique allows the series resistance to be extracted without a knowledge of the physical geometry of the device. This was used in a proposed effective channel length (Leff) extraction technique by taking the bias-dependent series resistance into account. The Leff extracted closely matches the metallurgical channel length (Lmet) value for devices fabricated using a 0.35 µm design rule or process technology; with Lmet being extracted using another independent technique. Where conventional extraction techniques tend to over-estimate the Leff, the proposed method showed more consistent results. The degradation in the series resistance and effective channel mobility under hot-carrier injection was also studied in detail. Models relating their degradation behaviour to stress conditions were established and a new hot-carrier lifetime model was formulated. This linear drain current drift model can account for the different behaviours observed for long and short channel devices, conventional abrupt junction and LDD devices, as well as the hot-carrier behaviour at different gate bias.