Patent ID: 6066531
Filing Date: 2000-05-23
Classification: H01L

Abstract:
A method for manufacturing a semiconductor memory device, comprising the steps of:forming a gate insulating film, a first floating gate material film and an ion implantation protective film in this order over the surface of a semiconductor substrate of a first conductivity type;forming a first resist pattern on the ion implantation protective film;forming a plurality of stripes comprising the first floating gate material film and the ion implantation protective film, the stripes being spaced apart from each other by a given distance, by etching in use of the first resist pattern as a mask;forming a second resist pattern to cover one longitudinal side wall of the stripes after removing the first resist pattern;removing a given width of the other side wall of the first floating gate material film by an isotropic etching with the second resist pattern used as a mask;forming an impurity region of a low concentration by implanting impurity ions of a second conductivity type into the semiconductor substrate of the first conductivity type with the ion implantation protective film used as a mask in a tilted direction after removing the second resist pattern; andforming 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 by implanting impurity ions of the second conductivity type into the semiconductor substrate of the first conductivity type with the ion implantation protective film used as a mask in the direction perpendicular to the semiconductor substrate to form an impurity region of high concentration.