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°C for 5-300 s. Measurements indicate that both the nitrogen concentration near the Si-SiO₂ interface [N]_int and the hydrogen concentration in nitrided oxides [H] increase monotonically as nitridation proceeds. The flat-band voltage shift ΔV_VB and the increase of the midgap interface state density ΔD induced by the constant-current stress were investigated. While ΔV_FB increases monotonically as nitridation proceeds, ΔD 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 ΔV_FB increases in proportion to [H]. Based on the turnaround behavior of ΔD, a two-factor model is proposed in which one factor, [H], increases δD and the other one, [N]_int, reduces it