Semiconductor device including a multilayered interelectrode insulating film

A semiconductor device comprising:

• a semiconductor substrate;
• an element isolation region defined in the semiconductor substrate and having an element isolation insulating film formed therein;
• an active region defined in the semiconductor substrate delineated by the element isolation region;
• a gate insulating film formed in the active region;
• a charge storage layer formed above the gate insulating film;
• a multilayered interelectrode insulating film formed in a first region above an upper surface portion of the element isolation insulating film, a second region along a sidewall portion of the charge storage layer, and a third region above an upper surface portion of the charge storage layer, the interelectrode insulating film including a stack of a first silicon oxide film, a first silicon nitride film, a second silicon oxide film, and a second silicon nitride film;
• and
• a control electrode layer formed above the interelectrode insulating film;
• wherein the second silicon oxide film is thinner in the first region than in the third region.