| A detailed study of the dynamic processes of the interface traps in MOS structures after exposure to ionizing radiation or hot electrons is presented. Among the important results reported here, a two-peaked interface trap distribution is shown to be characteristic in all the samples studied, and has been found to arise from a defect transformation process in which a peak located at {dollar}sim{dollar}E{dollar}sb{lcub}v{rcub}{dollar} + 0.75 eV, which is the only peak observed immediately after irradiation, gradually converts into a second peak located at {dollar}sim{dollar}E{dollar}sb{lcub}v{rcub}{dollar} + 0.35 eV. In general, the time evolution of the interface traps has been found to present a complex behavior involving three competing processes: defect generation, annealing and transformation. These processes depend strongly on the device's processing history and radiation treatments. The incorporation of impurities such as fluorine and chlorine into the oxide drastically affects the susceptibility of these MOS structures to ionizing radiation and hot electrons. If proper amounts of these impurities are present in the oxide, an improvement of about one order of magnitude may be obtained on the interface trap densities generated by ionizing radiation and hot electrons throughout the silicon bandgap. A model based on an intrinsic strain relaxation mechanism is proposed to explain most of the experimental results. The initial, post-irradiation density of interface traps has been found to be a key factor determining their subsequent long term dependence. Strong evidence will be presented which indicates that hot electron induced interface traps behave very similarly to those generated by ionizing radiation. |
