Patent ID: 7808031

Claim:
A non-volatile semiconductor memory device comprising a semiconductor substrate having a main surface provided with an element region and an element isolation region arranged alternately in one direction in memory cell region, comprising: a first trench isolation including a first recess formed at said main surface of said semiconductor substrate, a second recess formed at a portion of a surface of said semiconductor substrate defining a bottom surface of said first recess, and an insulation film filling said first and second recesses to serve as said element isolation region adjacent said element region; a diffusion layer provided in said semiconductor substrate at said element region adjacent to said first trench isolation to extend from said main surface depthwise, said diffusion layer reaching a location deeper than said first recess and also in contact with a side surface of said second recess; a tunnel oxide film on said semiconductor substrate at said element region adjacent to said first recess; and a floating gate on said tunnel oxide film and including two silicon layers, wherein said insulation film filling said first and second recesses includes a first insulation film covering a surface of said semiconductor substrate defining said first recess and a second insulation film provided to continuously cover a surface of said first insulation film and a surface of said semiconductor substrate defining said second recess, and a bird's beak is formed at an end portion of said tunnel oxide film adjacent to said first insulation film.