| 摘要 |
PROBLEM TO BE SOLVED: To obtain a nonvolatile semiconductor storage device in which data can be written highly efficiently. SOLUTION: A nonvolatile semiconductor storage device uses a semiconductor substrate 1 the surface of which contains a first surface region 11 at a first level, a second surface region 12 at a second level lower than the first level, and a stepped side face region 13 connecting the first and second surface regions 11 and 12 to each other. A floating gate 4 is partially faced to the side face region 13 through a first insulating film 3, and the other part of the gate 4 is partially faced to the second surface region 12 through the insulating film 3. A control gate 6 is partially extended onto the first surface region 11 while being insulated from the surface region 11. Therefore, a powerful electric field is formed near the corner section between the side face region 13 and second surface region 12 and, the same time, a local powerful electric field is formed in a channel region due to the potential difference between the floating gate 4 and control gate 6. Consequently, the electron injecting efficiency into the floating gate 4 from the side face region 13 and second surface 2 is remarkably improved and the data writing speed is improved noticeably.
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