Investigation of Nitrogen-Originated NBTI Mechanism in SiON with High-Nitrogen Concentration

We have investigated the nitrogen-originated NBT degradation mechanism of SiON films by using SiON with high nitrogen concentration. It was found that, threshold voltage shift (DeltaV_th) under NBT stress is degraded with increasing nitrogen concentration in bulk rather than that at interface. Furthermore, NBTI exponents strongly correlate with the nitrogen concentration in bulk and pre-stressed flat-band voltage shift (AV_fb ⁱⁿⁱ). From these experimental results, we interpret that there is an additional NBT degradation mechanism with small NBTI exponents (beta > 0.25) and this is originated by pre-existing defects due to nitrogen incorporation. Finally, from the reliability viewpoint, we propose that decreasing the defect in bulk introduced during nitridation is indispensable for the fabrication process of high nitrogen concentration SiON maintaining high reliability