The effects of fluorine on ultrathin gate oxide and oxynitride (∼40 Å) have been studied. The incorporation of fluorine was done by fluorine ion implantation into polycrystalline silicon (polysilicon) gate followed by a high-temperature drive-in step. It has been found that the integrity of oxide has been improved with the incorporation of fluorine as demonstrated by the reduction of stress-induced leakage current and interface trap generation. Furthermore, unlike thicker dielectrics (>100 Å) for which the charge-to-breakdown (QBD)values decrease with increasing fluorine concentration,QBD’s remain the same as those of the control samples for the ultrathin thickness regime. The mechanism for oxide quality improvement by F will also be discussed in the letter. ©1997 American Institute of Physics.