Interface trap and oxide charge generation under negative bias temperature instability of p -channel metal-oxide-semiconductor field-effect transistors with ultrathin plasma-nitrided SiON gate dielectrics

The interface trap generation ( Δ N it ) and fixed oxide charge buildup ( Δ N ot ) under negative bias temperature instability (NBTI) of p -channel metal-oxide-semiconductor field-effect transistors ( p MOSFETs) with ultrathin (2 nm) plasma-nitrided SiON gate dielectrics were studied using a modified direct-current-current-voltage method and a conventional subthreshold characteristic measurement. Different stress time dependences were shown for Δ N it and Δ N ot . At the earlier stress times, Δ N it dominates the threshold voltage shift ( Δ V th ) and Δ N ot is negligible. With increasing stress time, the rate of increase of Δ N it decreases continuously, showing a saturating trend for longer stress times, while Δ N ot still has a power-law dependence on stress time so that the relative contribution of Δ N ot increases. The thermal activation energy of Δ N it and the NBTI lifetime of p MOSFETs, compared at a given stress voltage, are independent of the peak nitrogen concentration of the SiON film. This indicates that plasma nitridation is a more reliable method for incorporating nitrogen in the gate oxide.