Development of MOS Transistors for Radiation-Hardened Large Scale Integrated Circuits and Analysis of Radiation-Induced Degradation

Radiation-hardened MOSFETs were developed, and experimental results on their total dose degradation were collected to evaluate effects of three techniques for radiation hardening. The three techniques are; (1) adding a silicon-nitride layer onto the phospho-silicate glass passivation layer, (2) thinning of the field oxide by increasing resistance of the channel stopper, and (3) annealing the gate oxide at lower temperature. Technique (1) suppressed the leakage current generated by the parasitic MOSFET, because the negative threshold voltage shift of the parasitic MOSFET was compensated by the positive shift due to the interface states generated by hydrogen trapped in the oxide by the silicon nitride deposition. Furthermore, leakage current decreased with technique (2) as well. Technique (3) was not effective because the gate oxide is inherently thin. Results gotten using a linear model for the threshold voltage shift represented well the measured data up to 1.5 kGy(Si) at a dose rate of 5Gy(Si)/h.