| 摘要 |
An object is to provide a nonvolatile semiconductor memory device which is superior in writing property and charge holding property. A semiconductor substrate in which a channel formation region is formed between a pair of impurity regions is provided, and a first insulating layer, a floating gate electrode, a second insulating layer, and a control gate electrode are provided over the semiconductor substrate. The floating gate electrode includes at least two layers. It is preferable that a band gap of a first floating gate electrode, which is in contact with the first insulating layer, be smaller than that of the semiconductor substrate. It is also preferable that a second floating gate electrode be formed of a metal material, an alloy material, or a metal compound material. This is because, by lowering the bottom energy level of a conduction band of the floating gate electrode than that of the channel formation region in the semiconductor substrate, a carrier injecting property and a charge holding property can be improved.
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