| 摘要 |
PROBLEM TO BE SOLVED: To improve write and erase speed by forming a thinner tunnel insulting film than a gate insulating film between a part of a drain region and a floating gate electrode, and then by forming a thicker insulating film than the tunnel insulting film between the other part of the drain region and the floating gate electrode. SOLUTION: After removing a resist, a gate insulating film 14 with the film thickness of 1000-2000Åis etched back to form a side wall of a silicon oxide film in the circumference of a first nitride film 12a and a second nitride film 12b. In this case, a thick gate insulating film 14 remains on a source region 4, and only the central part of the gate insulating film is removed from the surface of a drain region 5, and other part of the drain region 5 on the surface of the drain region 5 is covered with the thick gate insulating film 14. Namely, the drain region 5 is divided into a thick region of silicon oxide film and a thin region of silicon oxide film. Next, each part of the first nitride film 12a and the second nitride film 12b is removed to be oxidized entirely. Then, the oxide film adjacent to the central part on the surface of the drain region 5 is removed and region oxidized. In this way, a tunnel oxide film 15 is formed.
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