Method of manufacturing a semiconductor device

A method of manufacturing a semiconductor memory device, said semiconductor memory device comprising a memory cell and an MISFET for a peripheral circuit, said method comprising steps of:

• providing a semiconductor substrate having a memory cell forming region and a peripheral circuit forming region, with a first gate insulating film formed on said memory cell forming region, a floating gate electrode formed on said first gate insulating film, a second gate insulating film formed on said floating gate electrode, and a control gate electrode formed on said second gate insulating film, and with a third gate insulating film formed on said peripheral circuit forming region, and a first gate electrode of said MISFET formed on said third gate insulating film;
• introducing in said memory cell forming region an impurity substantially in self-alignment with one end portion of said control gate electrode to form a first semiconductor region in said memory cell forming region;
• introducing in said memory cell forming region an impurity substantially in self-alignment with another end portion of said control gate electrode to form a second semiconductor region in said memory cell forming region, wherein said second semiconductor region has a same conductivity type as that of said first semiconductor region, wherein said second semiconductor region extends under said floating gate electrode in such a manner that an overlap area between said second semiconductor region and said floating gate electrode is greater than the overlap area between said first semiconductor region and said floating gate electrode;
• introducing in said peripheral circuit forming region an impurity in self-alignment with said first gate electrode to form a fourth semiconductor region in said peripheral circuit forming region, wherein said fourth semiconductor region has a same conductivity type as said first semiconductor region, and wherein an impurity concentration of said first semiconductor region is higher than an impurity concentration of said fourth semiconductor region;
• after the steps of introducing the impurities to form first, second and fourth semiconductor regions, forming first side wall spacers on both side surfaces of said control and floating gate electrodes in self-alignment with said control and floating gate electrodes, and forming second side wall spacers on both side surfaces of said first gate electrode in self-alignment with said first gate electrode;
• and
• introducing in said peripheral circuit forming region an impurity in self-alignment with said second side wall spacers to form a fifth semiconductor region in said peripheral circuit forming region, wherein said fifth semiconductor region has the same conductivity type as said first semiconductor region, wherein an impurity concentration of said fifth semiconductor region is higher than the impurity concentration of said fourth semiconductor region, and wherein said fourth and fifth semiconductor regions serve as a drain region of said MISFET, and
• wherein carriers stored in said floating gate electrode are transferred from said floating gate electrode to said first semiconductor region by tunneling through said first insulating film.