SEMICONDUCTOR MEMORY UNIT

摘要

PURPOSE:To improve functional degradation resulting from repeated erasing and writing without degradation of memory characteristics by producing films of nonmetallic element excess composition and those of metallic element excess composition on the side where an insulating layer comes in contact with an oxide layer. CONSTITUTION:A gate insulator 5 is composed of two or more different types of insulating films which are of different chemical composition ratio or chemical composition one another for a semiconductor memory unit consisting of MIOS type IGFET's. The insulator 5 is of nitride or oxide of a metallic element and has at least both types films of nonmetallic element excess composition 6 and of metallic element excess composition 7 on the side contacting with the oxide film 4. It is possible by such features to improve characteristic of anti-degradation resulting from repeated erasure without degradation of memory characteristics.