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/sub 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/SiO/sub 2/ 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/sub BD/-distribution tails in Weibull plots, while maintaining both Si/SiO/sub 2/ interface characteristics and average Q/sub 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 gateoxide film. In addition, the results of infrared (IR) absorption analysis indicated that the strain of SiO/sub 2/ structures is reduced with increasing fluorine doses. We proposed that both strain release and restructuring of the SiO/sub 2/ network by fluorine incorporation are responsible for improving the Q/sub BD/ of weaker oxide films.