Patent ID: 7442986

Claim:
A nonvolatile semiconductor memory device, comprising: over a main surface of a semiconductor substrate, a first insulator and a first gate electrode formed on said first insulator; a first corner portion formed between a sidewall of said first gate electrode and the main surface of said semiconductor substrate; a second insulator formed on the sidewall of said first gate electrode and on the main surface of said semiconductor substrate on one or both sides of said first gate electrode; a third insulator formed on said second insulator at said first corner portion; a fourth insulator formed on said third insulator at said first corner portion; and a second gate electrode formed on a sidewall of said first gate electrode and at a position opposite to the main surface of said semiconductor substrate on one or both sides of said first gate electrode via said second to fourth insulators, wherein a taper angle of said fourth insulator on the side of not having said first gate electrode is within a range of 95 to 180 degrees, exclusive of 180 degrees, and a thickness of a discontinuity of taper at said corner portion of said fourth insulator is 80% or more of that of said fourth insulator on a flat portion.