Characterization of charge trapping and high-field endurance for 15-nm thermally nitrided oxides

Abstract

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, are investigated in detail. It is found that proper nitridation can eliminate positive charge accumulation in oxides, increase charge to breakdown, suppress high-field injection-induced interface state generation, and decrease the dependence of the breakdown field on the 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 and interface traps increased by nitridation, the combined effects of bulk and interface traps induced by high-field injection can improve the stability of the flatband voltage. For lightly nitrided oxides, the 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 the nitridation level and injection polarity, the centroid can move from 40 to 90-110 angstrom off the cathode. It is also 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 postnitridation annealing suggest that these property modifications most likely result from nitridation-induced structural changes rather than hydrogenation alone.