Prompt Radiation Damage and Short Term Annealing in CMOS/SOS Devices

Abstract

The radiation induced damage and the subsequent short term annealing in CMOS/SOS devices have been experimentally investigated. Transient threshold voltage shifts were measured after exposure to prompt ionization pulses. The measurements concentrated on early annealing, within 100 microseconds after the ionization pulse. Longer term annealing, up to 100 seconds after the ionization, was also characterized. The effects of prompt dose-rate, temperature, gate oxide thickness, and the electric field in the gate oxide during the ionization and during the annealing period were examined. The data demonstrate that the threshold shift is independent of dose-rate for prompt (less than 30 nanosecond) ionization. The annealing rate is shown to be a strong function of temperature with no annealing occurring at -195°C and an enhanced annealing rate at +125°C. The data demonstrate that, at room temperature and for zero field in the gate oxide, there is no significant annealing occurring before one microsecond after a prompt pulse. Threshold shift is shown to be proportional to the square of the gate oxide thickness. Threshold shift and annealing rate are shown to be dependent on the magnitude and polarity of the field in the gate oxide. The bias dependence results for p-channel transistors are consistent with those predicted by a stochastic thermal charge-hopping transport model.