Nonvolatile semiconductor memory device and method for fabricating the same, and semiconductor integrated circuit device

摘要

In a semiconductor substrate having a surface including a first surface region at a first level, a second surface region at a second level lower than the first level, and a step side region linking the first and second surface regions together, a channel region has a triple structure. Thus, a high electric field is formed in a corner portion between the step side region and the second surface region and in the vicinity thereof. A high electric field is also formed in the first surface region. As a result, the efficiency, with which electrons are injected into a floating gate, considerably increases.