Energy distribution and electrical characteristics of NBTI induced Si/SiON interface states

Evidence from negative-bias temperature stressing of both p- and n-MOSFET employing the ultra-thin (15 Aring) plasma-nitrided gate dielectric shows that stress induced Si/SiON interface states have (1) a bipolar, i.e. both acceptor- and donor-like, characteristic in the upper-half of the Si bandgap and (2) a donor-like characteristic in the lower-half of the Si bandgap. During I_d-V_g measurement of the p-MOSFET, interface states above mid-gap behave like ldquopositive oxide trapped chargerdquo, resulting in a negative shift of the subthreshold I-V curve of the p-MOSFET. On the other hand, a change in charge state from positive-to-negative, during positive gate bias sweep, results in a significant ldquostretch-outrdquo of the n-MOSFET subthreshold I-V curve. As a consequence of this bipolar charge-state transition, stress induced interface state density extracted from subthreshold swing degradation of the n-MOSFET is consistently ~2times that obtained from the increase in the charge pumping current.