We analyze diffusion and segregation kinetics of fluorine atoms in poly-Si/SiO{sub}2/Si structures with gate oxides of 5 nm by means of secondary ion mass spectroscopy. Well defined doses of fluorine were introduced by ion implantation. Our results indicate fluorine segregation at interfaces to the gate oxide. This segregation is diffusion limited with an effective activation energy of 1.4 eV. The accumulation of fluorine influences the intrinsic reliability of thin oxides. The breakdown behavior was studied using constant voltage, constant current, and stepwise increasing constant current stress, respectively. Weibull plots before and after the heat treatments were analyzed. At low fluorine concentrations up to doses of 5 × 10{sup}15 cm{sup}(-2) fluorine segregation is beneficial, improving, for example the tails of the Weibull plots and slightly increasing the breakdown voltage. For fluorine doses higher than 1 ×10{sup}16 cm{sup}(-2), detrimental consequences were found, degrading the charge to breakdown values by about a factor of 5 after long - term thermal treatments.
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