In addition to the well-known positive space charge, electron irradiation of MOS capacitors with 25-keV electrons is shown to introduce additional uncharged electron traps into the oxide layer. These traps persist after most of the positively charged defects have been removed by the usual low-temperature (~ 0c) anneals. Their presence after this anneal is determined by injecting hot electrons into the oxide where they are captured by existing defects. The effective trap densities increase with increasing electron fluence and are reduced by forming-gas anneals at temperatures in excess of 500°C. Observed electron-capture cross sections are between 10-15 and 10-18 cm 2 • The residual radiation damage in oxides exposed to 10-4 Ccm-2 of 25-keV electrons and subsequently annealed at 4OQ°C results in an additional neutral density of 5 X 1011 trapscm-2 with cross sections distributed over the above range. Electron-trapping cross sections and effective trap densities associated with this damage are found to be identical at 77 and 295 K. The traps are possibly associated with dipolar defects formed when valence electrons localize around an ion after the bonds are broken.
We report the voltage-dependence of voltage acceleration for ultra-thin oxides from 2.2V to 5V over a range of Tox values from 1.7nm to 5.0 nm. This unique behavior manifest itself as a power-law voltage-dependence for time-to-breakdown (TBD) over a variety of experimental observations. Using the concept of energy-to-breakdown, we explore the possible scenarios such as fractional energy or defect generation probability as a function of voltage to account for the increase in voltage acceleration with decreasing voltages.
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