Nonvolatile semiconductor storage device and method of manufacturing the same

A method of manufacturing a nonvolatile semiconductor device comprising:

• dividing a semiconductor substrate into a plurality of element regions by defining a plurality of trenches extending in a first direction into the semiconductor substrate so as to be aligned in a second direction intersecting with the first direction and filling the trenches with an element isolation film;
• exposing an upper surface of the element regions by lowering an upper surface of the element isolation film so as to be lower than an upper surface of the semiconductor substrate;
• forming a silicon oxide film along an upper surface and an upper sidewall of the element regions and along the upper surface of the element isolation film so as to form recesses on an upper side thereof;
• filling the recesses with the first silicon nitride film;
• forming a plurality of diffusion layers in a surface layer of the element regions after filling the recesses with the first silicon nitride film;
• forming a second silicon nitride film thicker than the first silicon nitride film above the first silicon nitride film;
• forming an interlayer insulating film above the second silicon nitride film;
• forming a plurality of holes through the interlayer insulating film using the second silicon nitride film as a stopper;
• extending the holes to expose each of the diffusion layers;
• and
• filling the holes with a contact.