Study of hot carrier degradation in NMOSFET's by gate capacitance and charge pumping current

Abstract

Hot carrier degradation in n-channel MOSFET's is studied using gate capacitance and charge pumping current for three gate stress voltages: Vg to approximately Vt, Vd/2, Vd. The application of these two sensitive techniques reveals new information on the types of trap charges and the modes of degradation. At low Vg stress near threshold voltage, the fixed charge is attributed to holes. For high Vg stress, the fixed charge is predominantly electrons. Data for mid Vg stress suggest little net fixed charge trapping. Interface traps are observed for all stress conditions and are demonstrated from differential gate capacitance spectra to exhibit both donor and acceptor trap behavior. Mid Vg stress is shown to result in the highest density of interface traps. These traps can be annealed to a large extent for temperatures up to 300 °C. A post-stress generation of interface trap is observed at low Vg stress, in agreement with recent observation. Further, a linear relation is found to exist between the change in overlap gate capacitance and the increase in peak charge pumping current, and suggests spatial uniformity in the degradation of the interface.