Polarity-dependent oxide breakdown of NFET devices for ultra-thin gate oxide

The polarity-dependent oxide breakdown of NFET devices has been carefully studied for ultra-thin gate oxides. The measurement of charge-to-breakdown, Q_BD, is found to be consistently lower for the gate injection mode than that of the substrate injection mode for the range of oxide thickness investigated here. On the other hand, the time-to-breakdown, T_BD, of the gate and substrate injection modes, shows a crossover behavior as oxide thickness is reduced. The possible mechanisms are discussed to explain the degradation in QBD under the gate injection mode. Because of important implications for SOI technology applications, we have conducted a systematic reliability evaluation of NFET devices under the gate injection mode. Thickness, voltage, and temperature dependences of T_BD(Q_BD) as well as for the Weibull slopes have been extensively characterized. The results of these studies indicate that the trend in these dependencies is very similar to what was previously found for the substrate injection mode, such as the power-law T_BD voltage dependence and temperature-independent voltage acceleration.