The random nature of energy deposition in gate oxides

Data are presented on statistical fluctuations in energy deposition across individual gate oxides at 77 K for 13- to 63-MeV protons. A two-component model based on microdosimetry theory has been developed to describe proton-induced dose fluctuations. The model considers random factors in the energy deposition process for (1) direct proton strikes within the volume of interest and (2) secondary electrons originating outside of and entering the volume of interest. Experiment and theory are in good agreement. For a 25-nm-thick gate oxide the model has accurately predicted, without any adjustable parameters, the dependence of dose fluctuations on radiation type (proton and X-rays), incident proton energy (13 to 63 MeV) and dose. The model also apparently predicts the proper oxide thickness dependence, although small, systematic deviations from experiment were observed in a 105-nm oxide at low incident proton energies