Enhanced negative substrate bias degradation in nMOSFETs with ultrathin plasma nitrided oxide

The degradation induced by substrate hot electron (SHE) injection in 0.13-μm nMOSFETs with ultrathin (∼2.0 - nm) plasma nitrided gate dielectric was studied. Compared to the conventional thermal oxide, the ultrathin nitrided gate dielectric is found to be more vulnerable to SHE stress, resulting in enhanced threshold voltage (V _t ) shift and transconductance (G _m ) reduction. The severity of the enhanced degradation increases with increasing nitrogen content in gate dielectric with prolonged nitridation time. While the SHE-induced degradation is found to be strongly related to the injected electron energy for both conventional oxide [1], [2] and plasma-nitrided oxide, dramatic degradation in threshold voltage shift for nitrided oxide is found to occur at a lower substrate bias magnitude (∼ -1 V), compared to thermal oxide (∼ -1.5 V). This enhanced degradation by negative substrate bias in nMOSFETs with plasma-nitrided gate dielectric is attributed to a higher concentration of paramagnetic electron trap precursors introduced during plasma nitridation [3].