A Study of NBTI and Short-Term Threshold Hysteresis of Thin Nitrided and Thick Non-Nitrided Oxides

Negative bias temperature instability (NBTI) degradation and recovery have been investigated for 7-50-nm non-nitrided oxides and compared to thin 1.8- and 2.2-nm nitrided oxides from a dual work function technology. A wide regime of stress fields from 2.5 to 10 MV/cm has been covered. Thermal activation has been studied for temperatures from 25
^deg
C to 200
^deg
C. The NBTI effect for the nitrided oxide is larger than for non-nitrided oxides. The percentage of threshold shift
V

_th
which is ldquolostrdquo during a long measurement delay-which is the quantity leading to curved
V

_th
versus stress-time curves and to errors in extrapolated lifetimes-is about equal for nitrided or thick non-nitrided oxides. The fraction of recovered
V

_th
is strongly dependent on stress time but only weakly dependent on stress field. Recovery in thick oxides leads to exactly the same problems as for non-nitrided oxides, and clearly, a fast measurement method is needed. The effect of short-term threshold shifts has been studied for extremely short stress times down to 200 ns.