Experimental evidence for nonlucky electron model effect in 0.15-μm NMOSFETs

It is shown that in 0.15-μm NMOSFETs the device lifetime under channel hot-carrier (CHC) stress is lower than that under drain avalanche hot-carrier (DAHC) stress and therefore the hot-carrier stress-induced device degradation in 0.15-μm NMOSFETs cannot be explained in the framework of the lucky electron model (LEM). Our investigation suggests that such a "non-LEM effect" may be due to increased interface state generation by the movement of the maximum impact ionization site from the lightly doped drain (LDD) diffusion region to the boundary of the bulk and LDD region beneath the gate oxide. This paper provides experimental evidence for the non-LEM effect by comparing the degradation characteristics and the maximum impact ionization sites as a function of gate oxide thickness and gate length.