Nonvolatile semiconductor memory device and method of manufacturing the same

A nonvolatile semiconductor memory device, comprising:

• a semiconductor substrate;
• element isolation insulating films being along a first direction in the semiconductor substrate with a certain spacing therebetween and reached to a certain depth from a surface of the semiconductor substrate;
• and
• element regions sandwiched by the element isolation insulating films, with MONOS type memory cells disposed on an upper surface thereof,
• each of the MONOS type memory cells comprising:
• a tunnel insulating film disposed on one of the element regions;
• a charge storage film disposed continuously on the element regions and the element isolation insulating films;
• a block insulating film disposed on the charge storage film;
• and
• a control gate electrode disposed on the block insulating film,
• the charge storage film comprising:
• a charge film disposed on the one of the element regions and having a certain charge trapping characteristic;
• and
• a degraded charge film disposed on one of the element isolation insulating films and having a charge trapping characteristic inferior to that of the charge film, and
• the degraded charge film having a length of an upper surface thereof set shorter than a length of a lower surface thereof in a cross-section along the first direction.