Hot-carrier degradation for 90nm gate length LDD-NMOSFET with ultra-thin gate oxide under low gate voltage stress

The hot-carrier degradation for 90~nm gate length lightly-doped drain(LDD) NMOSFET with ultra-thin (1.4~nm) gate oxide under the low gatevoltage (LGV) (at V_g=V_th, where V_th is thethreshold voltage) stress has been investigated. It is found that thedrain current decreases and the threshold voltage increases after theLGV (V_g=V_th stress. The results are opposite to thedegradation phenomena of conventional NMOSFET for the case of thisstress. By analysing the gate-induced drain leakage (GIDL) currentbefore and after stresses, it is confirmed that under the LGV stressin ultra-short gate LDD-NMOSFET with ultra-thin gate oxide, the hotholes are trapped at interface in the LDD region and cannot shortenthe channel to mask the influence of interface states as those inconventional NMOSFET do, which leads to the different degradation phenomena from those of theconventional NMOS devices. This paper also discusses the degradation in the90~nm gate length LDD-NMOSFET with 1.4~nm gate oxide under the LGV stress atV_g=V_th with various drain biases. Experimental results show thatthe degradation slopes (n) range from 0.21 to 0.41. The value ofn isless than that of conventional MOSFET (0.5-0.6) and also that of the long gatelength LDD MOSFET (sim0.8).