Method for forming an etch mask during the manufacture of a semiconductor device

Abstract

A method used during the formation of a semiconductor device comprises the steps of forming a polycrystalline silicon layer over a semiconductor substrate assembly and forming a silicon nitride layer over the polycrystalline silicon layer. A silicon dioxide layer is formed over the silicon nitride layer and the silicon dioxide and silicon nitride layers are patterned using a patterned mask having a width, thereby forming sidewalls in the two layers. The nitride and oxide layers are subjected to an oxygen plasma which treats the sidewalls and leaves a portion of the silicon nitride layer between the sidewalls untreated. The silicon dioxide and the untreated portion of the silicon nitride layer are removed thereby resulting in pillars of treated silicon nitride. Finally, the polycrystalline silicon is etched using the pillars as a mask. The patterned polycrystalline silicon layer thereby comprises features having widths narrower than the width of the original mask.