Method of forming tiny silicon nitride spacer for flash eprom by fully wet etching technology

Abstract

A method of forming very small silicon nitride spacers in split-gate flash EPROMs is disclosed which prevent the occurrence of 'write disturb', unwanted reverse tunneling, or erasing. This is accomplished by forming spacers with well-controlled dimensions and well-defined shapes through a judicious use of a fully wet etch technique, including main-etch and over-etch. The use of a phosphoric acid solution in combination with sulfuric acid+hydrogen peroxide widens the process window from a few seconds to several minutes so that the small-dimensioned silicon nitride spacers can be better controlled than it has been possible in the past. In the first embodiment phosphoric solution is used both for main-etch and for over-etch. In the second embodiment, phosphoric solution is used for main-etch only, while the sulfuric+hydrogen peroxide solution is used as an over-etch in forming the tiny silicon nitride spacers of the invention. In the third embodiment, the step of over-etching of the spacers is combined with the step of stripping off of an implant photomask, thus, shortening the manufacturing product cycle.