On the time-dependent degradation of LDD n-MOSFETs under hot-carrier stress

摘要

A unified model for hot-carrier-induced degradation in LDD N-MOSFETs is presented. A novel oxide spacer charge pumping method enables interface trap generation in the spacer and overlap/channel regions to be distinctly separated. An excellent correlation between trap generation in the spacer region and linear drain current degradation at high gate voltage is observed. Moreover, trap geneation in the overlap/channel region is found to correlate well with linear drain current degradation at low gate voltage. The results point undambiguously to a twomechanism degradation model invlving drain resistance increase by trap generation in the spacer region, and carrier mobility reduciton by trap generation in the overlap/channel region. The combined effect of a timeindependent lateral electron temperature profile and a finite density of interface trap precursors within the LDD region leads to a self-limiting degraation behavior. This insight forms the basis of a time-dependent trap generation model, which indicates the existence of a single degradation curve. The fact that the degradation curves at different stress drain voltages fall onto a time-scale version of th esingl degradation curve provides strong support for the model. This also offers a straightforward and yet accurate means by which the hot-carrier lifetime corresponding to a specific failure criterion may be extracted. Finally, a power-law relationship between hot-carrier lifetime and substrate current is also observed for the LDD devices, thus preserving the physical essence based on which earlier lifetime models forco