Effects of N distribution on charge trapping and TDDB characteristics of N2O annealed wet oxide

Wet pyrogenic oxide of different thicknesses was annealed in N₂O ambient and the N concentration in the films was studied by using SIMS (secondary ion mass spectroscopy). It was found that for a certain annealing time and temperature, the N concentration (at %) increases with decreasing wet oxide thickness and the location of the peak of N is observed near the interface of nitrided oxide and Si substrate. On the contrary, after nitridation the concentration of H is higher in the thicker wet oxide of thickness 100 Å and also does not change much from the surface to the interface. For the thinner wet oxide of thickness 40 Å, the concentration of H is less and decreases toward the interface. Gate dielectrics were characterized using high-frequency and quasi-static measurements. After a constant current stress, a large distortion was observed for the N₂O annealed wet oxide of 98 Å whereas for the N₂O annealed wet oxide of 51 Å the distortion was small. With increasing stressing time, hole trap is followed by electron trapping for the wet oxide of 98 Å whereas for the N₂O annealed wet oxide of 51 Å, hole trapping increases a little at the beginning and then saturates. From the TDDB characteristics, a longer t_BD was observed for N₂O annealed wet oxide of 51 Å compared to 98 Å. From the experimental results, it can be suggested that the improved reliability of thin gate oxide is due to the large amount of N concentration near the interface only. Hence for the device fabrication process, if the wet oxide is nitrided in N₂O ambient, the reliability of gate oxide will be improved in the ultrathin region