Patent ID: 7829411

Claim:
A method for forming a high quality oxide layer of different thickness over a first and a second semiconductor region in one processing step, comprising the steps of: producing a doped gate stack that includes the first semiconductor region by growing a tunnel oxide on the semiconductor, depositing floating gate polysilicon on the tunnel oxide, doping the floating gate polysilicon, thus forming doped floating gate polysilicon, depositing an interlayer dielectric on the doped floating gate polysilicon, and depositing control gate polysilicon on the interlayer dielectric; doping the first semiconductor region, including the control gate polysilicon, with a dopant concentration that is higher than a dopant concentration of the second semiconductor region, and oxidising both the first and the second semiconductor regions during the same processing step at a temperature between 500° C. and 650° C. to form the oxide layer predominantly from portions of the first and second semiconductor regions that are oxidized, the oxide layer having a thickness over the first semiconductor region that is at least two times thicker than a thickness of the oxide layer over the second semiconductor region.