Method of patterning narrow gate electrode

Abstract

A process is described for forming very narrow polysilicon gate lines for use as gate electrodes in FETs. The process uses a consumable hard mask of silicon oxynitride covered by a thin layer of silicon oxide during the etching of the polysilicon. The thicknesses of the two layers that make up the hard mask are chosen so that the structure also serves as an ARC for the photoresist coating immediately above it. A relatively thin layer of the latter is used in order to improve resolution. After the photoresist has been patterned it may be trimmed or it may be removed and re-formed, since the silicon oxide layer provides protection for the underlying silicon oxynitride. After the hard mask has been formed, all photoresist is removed and the polysilicon is etched. During etching there is simultaneous removal of the silicon oxide layer and part of the silicon oxynitride as well.