Characterization of Annealing of Co60 Gamma-Ray Damage at the Si/Si02 Interface

The annealing of Co60 gamma-ray damage at the Si/SiO2 interface is a well behaved phenomenon. Based on the characterization of annealing over a temperature range of 25° to 300°C, a physical model is developed. This model suggests that the annealing of the radiation damage occurs in two phases: first, the Qf-like trapped positive charges are converted to acceptor-like fast-states, and second, the fast-states are gradually annihilated. Both of these phases occur at an accelerated rate at a given temperature in presence of hydrogen. The densities of trapped positive charges and fast-states reach saturation levels which depend on the level of radiation (dose rate), and the temperature. The tolerance level of an IC to radiation exposure depends on these saturation levels. The experimental results also indicate that the positive charges are trapped at the Si/SiO2 interface even if a negative gate-bias is applied during irradiation. Furthermore, it is unambiguously observed that once the holes are trapped at the interface, they do not move along the interface even under applied biases, but they move only toward Si where they become acceptor-like fast-states.