Empirical model of effective channel length (L eff ) for 0.25-μm LDD nMOSFET

Abstract

ABSTRACT The definition of effective channel length (Leff) 5 different from the metallurgical junction length (Lmet), or mask length (Lk) for lightly—doped-drain (LDD) nMOS devices. Based on the measured data for 0.25 tmnMOSFET, an empirical expression on the deviation of effective channel length from the mask, ALeff wasproposed with fitting parameters extracted, which fits the experimental data very well. The approach involves measuring the intrinsic channel resistance under GCA (graded channel approximation) condition, namely VDS << VGS. By measuring the channel resistance versus different mask lengths under differential variation of gate voltage VGS, the ALeff can be determined. The result predicts that under high gate voltage (VGS), a larger portionof gate overlapping region contributes to the conducting effective channel length (Leff). Keywords: effective channel length measurement, LDD, 0.25 tm technology, source-drain resistance measurement. 1. IntroductionFor deep submicron MOS devices the LDD structure {Fig. 1] becomes standard. The effective