Time dependent annealing of radiation-induced leakage currents in MOS devices

Results are presented showing the radiation response of several unhardened commercial 1.25-μm bulk CMOS processes using LOCOS (local oxidation of silicon) isolation technology. In all cases studied radiation-induced failure is caused by effects in the field oxide, and the radiation-induced ΔV_T in the channel region is usually small at the failure dose. Time-dependent leakage current data for the field oxides are presented and discussed. It is found that the newer 1.25-μm technologies generally survive the higher doses than the older 3-μm processes, probably because they have thinner field oxides. It is also found that a wide variety of annealing responses can be expected for the various field oxides. This fact implies that great care must be taken in predicting leakage current response at doses and dose rates other than those used in testing. Finally, it is found that, qualitatively, the same annealing processes are observed in field and gate oxides, but there are quantitative differences in the important parameters