Thin ONO thickness control and gradual gate oxidation suppression by b. N. su2 treatment in flash memory

摘要

A method of forming a flash memory cell is disclosed where nitrogen treatment or implantation is employed. Nitrogen introduced into the upper layers of the polysilicon of the floating gate is instrumental in forming an unusually thin layer comprising nitrogen-oxygen-silicon. This N--O--Si layer is formed while growing the bottom oxide layer of the oxide-nitride- oxide, or ONO, the intergate layer between the floating gate and the control gate of the flash memory cell. Nitrogen in the first polysilicon layer provides control for the thickness of the bottom oxide while at the same time suppressing the gradual gate oxidation (GGO) effect in the floating gate. The now augmented ONO composite through the N--O--Si layer provides an enhanced intergate dielectric and hence, a flash memory cell with more precise coupling ratio and better performance.