We show that the incorporation of fluorine into the oxide grown on polysilicon (polyoxide) not only improves the electrical characteristics (i.e., lower leakage current, higher electrical breakdown field), but also improves the reliability (lower electron trapping rate, larger Q(bd)). This improvement is believed to be due to the stress relaxation of the polyoxide and smoother polysilicon/polyoxide interface by the fluorine incorporation. The optimum fluorine dose (2x10(14)) shows the best characteristics such as E-bd over 12 MV/cm and Q(bd)similar to 2 C/cm(2). However, excessive fluorination (1x10(15)) seems to result in performance degradation due to the generation of nonbridging oxygen centers. (c) 2007 The Electrochemical Society.