Annealing of total dose damage: redistribution of interface state density on [100], [110] and [111] orientation silicon

The annealing of interface states after an X-ray dose of 10 Mrad (SiO₂) under 1-MV/cm bias is studied on [100], [110], and [111] silicon. During annealing the bias is 1 MV/cm. Annealing times range from under an hour to hundreds of hours, and the temperature ranges from 75 to 175 degrees C. Using charge pumping, the energy distribution of interface states within the bandgap is determined. After annealing, the shape of the interface-state density curve implies that one or more defects other than P_b0 and P_b1 are present. Comparison of the interface-state density curves before and after annealing shows that a redistribution of interface-state density occurs over a large portion of the time-temperature range studied. The density near 0.4 eV above the valence band decreases and the density near 0.7 eV increases although the average density does not significantly change. Based upon the time scale and activation energy of the redistribution, a model is proposed in which the rate-limiting step is water diffusion within the gate oxide to the interface. This model provides a framework for a transformation among interface defects that accounts for the observed redistribution. Further tests for this model are discussed.