NONVOLATILE STORAGE DEVICE, ITS DRIVING METHOD, AND ITS MANUFACTURE

摘要

PURPOSE:To reduce the stresses applied to tunnel insulating films so as to increase the number of rewriting times by forming gate insulating films having relatively thick thicknesses and the tunnel insulating films having thicknesses which are thinner than those of the gate insulating films in channel areas generated between adjacent buried impurity diffusion layers. CONSTITUTION:Gate oxide films 15 are formed in the areas 14 generated between each buried impurity diffusion layer 131, 132, and 133 except predetermined parts on drain areas 13b sides. Then tunnel oxide films 16 are formed in predetermined parts of the areas 14 on drain areas 13a sides. Then a trap nitride film 17 which stores charges is formed on the entire surface of this nonvolatile storage device including the films 15 and 16 and a block oxide film 18 which encloses the charges stored in the film 17 in the film 17 for a long time is formed on the film 17.