Non-volatile semiconductor memory device and process of manufacturing the same

A non-volatile semiconductor memory device, comprising:

• a semiconductor substrate having device formation regions defined by device isolation trenches;
• a first gate insulator film formed over said device formation regions;
• a floating gate formed on said first gate insulator film;
• a first device-isolation insulator film formed in said device isolation trenches and having recesses thereon, and contacted with the floating gate;
• a second device-isolation insulator film formed in said recesses;
• a second gate insulator film formed over a surface of said floating gate and said first and second device-isolation insulator films;
• and
• a control gate formed above said floating gate and said first and second device-isolation insulator films via said second gate insulator film, wherein the uppermost portions at both ends of said first device-isolation insulator film are located higher than the uppermost portions at both ends of said second device-isolation insulator film,
• wherein said second device-isolation insulator film is higher in etching rate than said first device-isolation insulator film under a certain etching condition.