Improvement of charge-to-breakdown distribution by fluorine incorporation into thin gate oxides

This paper reports on the effect of fluorine incorporation on gate-oxide reliability, especially the spatial distribution of charge-to-breakdown (Q_BD). Fluorine atoms were implanted into gate electrodes and introduced into gate-oxide films by annealing. Excess fluorine incorporation increased the oxide thickness and degraded not only the reliability of Si/SiO₂ interfaces but also dielectric-breakdown immunity. However, it was found, for the first time, that appropriate fluorine incorporation into gate-oxide films could dramatically improve Q_BD-distribution tails in Weibull plots, while maintaining both Si/SiO₂ interface characteristics and average Q_BD values. The experimental result for a depth profile of fluorine atoms indicated that fluorine atoms are located dominantly at the two interfaces of the gate-oxide film. In addition, the results of infrared (IR) absorption analysis indicated that the strain of SiO₂ structures is reduced with increasing fluorine doses. We proposed that both strain release and restructuring of the SiO₂ network by fluorine incorporation are responsible for improving the Q_BD of weaker oxide films.