CHARACTERIZATION OF CHARGE TRAPPING AND HIGH-FIELD ENDURANCE FOR 15-NM THERMALLY NITRIDED OXIDES

Device-quality gate oxides have been nitrided using both rapid thermal processing and conventional furnace treatment. Charge trapping and high-field endurance including breakdown field and time-dependent dielectric breakdown have been investigated in details. It is found that proper nitridation can elminate positive charge accumulation in oxides, increase charge to breakdown, suppress high-field injection-induced interface state generation, and decrease the dependence of breakdown field on gate area as a result of the reduced density of microdefects. Experimental results show that although both the density and capture cross section of the bulk electron traps are increased by nitridation, the combined effects of bulk and interface traps induced by high-field injection can improve the stability of flat-band voltage. Besides, for lightly nitrided oxides, trap generation rate is greatly decreased as compared with the as-grown oxide. Not only are the density and capture cross section of the traps affected by nitridation, but also the locations of the trapped-charge centroids are changed. Depending on nitridation level and injection polarity, the centroid can move from 40 to 90-110 angstrom off the cathode. It is shown that under high-field injection, both the charge to breakdown and the interface state increase are strongly dependent on injection polarity. This observation can be explained by a physical model which takes both charge trapping and its location into account. The experimental results for post-nitridation annealing suggest that these property modifications most likely result from nitridation-induced structural changes rather than hydrogenation alone.