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.