Method for manufacturing semiconductor memory device

摘要

A method for manufacturing a semiconductor memory device, including the steps of: forming a plurality of stripes comprising a first floating gate material film and a ion implantation protective film, covering one longitudinal side wall of the stripes with a resist pattern; removing a given width of the other side wall of the first floating gate material film by an isotropic etching in use of the resist pattern as a mask; forming an impurity region of low concentration by implanting impurity ions of a second conductivity type into the semiconductor substrate of the first conductivity type in use of the ion implantation protective film as a mask in a tilted direction after removing the resist pattern; and forming asymmetrical impurity regions on both sides of the stripe like first floating gate material film as viewed in the cross section along the direction perpendicular to the longitudinal direction of the stripes. According to the above-mentioned method, without using a side wall spacer, a semiconductor memory device provided with asymmetrical impurity regions having precisely desired forms can be obtained.