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 the 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 angstrom and also does not change much from the surface to the interface. For the thinner wet oxide of thickness 40 angstrom, 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 angstrom whereas for the N₂O annealed wet oxide of 51 angstrom the distortion was small. With increasing stressing time, hole trap is followed by electron trapping for the wet oxide of 98 angstrom whereas for the N₂O annealed wet oxide of 51 angstrom, 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 angstrom compared to 98 angstrom. 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.