Radiation-induced leakage current of ultra-thin gate oxide under X-ray lithography conditions

The effect of X-ray radiation on the reliability of ultra-thin gate oxide has been studied under normal X-ray lithography conditions. A large increase in leakage current was observed on the irradiated oxides. The current-voltage characteristics of this radiation-induced leakage current (RILC) were found to be very similar to the electrical stress-induced leakage currents (SILC). Both currents comprise a DC component due to trap-assisted tunneling, and a transient component attributed to the tunnel charge/discharging of carriers. A further component, related to the redistribution and trapping of generated holes in the oxide bulk, is observed in the RILC, but only for thicker oxides. Therefore, the RILC and the SILC have the same degradation mechanism in ultra-thin oxides of around 45 Å or less. An experimental relationship between the total X-ray dose and the equivalent charge fluence that induces the same amount of degradation, has been established. The oxide thickness dependence of the relationship was also obtained