Semiconductor device and method of manufacturing the same

A method of manufacturing a semiconductor device, comprising the steps of:

• forming a gate insulating film on a main surface of a semiconductor substrate;
• forming a conducting film for floating gate on the gate insulating film;
• forming a control gate on the conducting film for floating gate with a first insulating film interposed therebetween;
• forming a first sidewall insulating film made of the same material as that of the gate insulating film, so as to cover one sidewall of the control gate on the conducting film for floating gate;
• by selectively removing the conducting film for floating gate with the first sidewall insulating film as a mask, forming a floating gate from the conducting film for floating gate, and exposing a portion of the gate insulating film at the floating gate;
• forming a first nitrogen introduced portion by introducing nitrogen into the exposed portion of the gate insulating film;
• after forming the first nitrogen introduced portion, removing the first sidewall insulating film to expose an upper surface of a lateral protrusion of the floating gate protruding laterally from a region immediately below the control gate;
• and
• forming an erase gate so as to face the upper surface and a side surface of the lateral protrusion.