Method of forming sharp beak of poly by oxygen/fluorine implant to

Abstract

A method is provided for forming a short and sharp gate bird's beak in order to increase the erase speed of a split-gate flash memory. This is accomplished in two embodiments where in the first, fluorine is implanted in the first polysilicon layer to form the floating gate. It is disclosed here that the implanting of fluorine increases the oxidation rate of the polysilicon and because of the faster oxidation, the polygate bird's beak (GBB) that is formed attains a relatively short and sharp shape in comparison with conventional beaks. This has the attendant benefit of forming a relatively small memory cell, and the concomitant increase in the erase speed of the cell. In the second embodiment, oxygen is used with the same favorable results. A third embodiment discloses the structure of a split-gate flash memory cell having a sharp bird's beak.