Method for producing nonvolatile semiconductor memory device

Abstract

A second polysilicon layer (218) and an ONO insulator film (216) are etched using mask insulator films (220a and 220b) as masks to form a control gate (218a), a second gate electrode (218b) and intergate insulator films (216a and 216b). Then, a resist mask (224) for a first gate electrode (214b) is formed in a peripheral transistor forming region or a selecting transistor forming region. Subsequently, a first polysilicon layer (214) is etched using the resist mask and the mask insulating films (220a and 220b) as masks to form a floating gate (214a) and a first gate electrode (214b). Thus, the mask insulator film (220b) has no difference in level, so that the surface of an interlayer insulator film (228) can be flattened.

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