NONVOLATILE SEMICONDUCTOR MEMORY DEVICE AND METHOD OF MANUFACTURING THE SAME

In one embodiment, a nonvolatile semiconductor memory device includes a substrate, and a well of a first conductivity type formed in the substrate. The device further includes a plurality of first isolation layers disposed in parallel to each other in the well, and a second isolation layer disposed in parallel to the first isolation layers in the well, a width of a substrate surface between the second isolation layer and the first isolation layers being set greater than a width of a substrate surface between the first isolation layers. The device further includes a memory cell including a gate insulator, a floating gate, an inter-gate insulator, and a control gate sequentially disposed on the well between the first isolation layers, and a dummy cell including a gate insulator, a floating gate, an inter-gate insulator, and a control gate sequentially disposed on the well between the second isolation layer and one of the first isolation layers. The device further includes a diffusion layer of a second conductivity type formed under the dummy cell in the well between the second isolation layer and the one of the first isolation layers, an upper surface of the diffusion layer being formed at a position higher than bottom surfaces of the first and second isolation layers with the surface of the substrate.