Charge-trapping properties of ultrathin nitrided oxides prepared by rapid thermal annealing

Ultrathin (8 nm) oxides were nitrided by lamp-heated rapid thermal annealing in ammonia at 900-1150 degrees C for 5-300 s. Measurements indicate that both the nitrogen concentration near the Si-SiO/sub 2/ interface (N)/sub int/ and the hydrogen concentration in nitrided oxides (H) increase monotonically as nitridation proceeds. The flat-band voltage shift Delta V/sub VB/ and the increase of the midgap interface state density Delta D induced by the constant-current stress were investigated. While Delta V/sub FB/ increases monotonically as nitridation proceeds, Delta D is found for the first time to show a turnaround with nitridation time: it increases, reaches a maximum at a certain nitridation time, and then decreases gradually to a value that is lower, in some cases, by more than one order of magnitude than that of a thermal oxide. It is found for the first time that Delta V/sub FB/ increases in proportion to (H). Based on the turnaround behavior of Delta D, a two-factor model is proposed in which one factor, (H), increases delta D and the other one, (N)/sub int/, reduces it.<
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