A symmetrical side wall (SSW)-DSA cell for a 64 Mbit flash memory

A 0.4- mu m stacked gate cell for a 64-Mb flash memory has been developed which has the symmetrical side wall diffusion self-aligned (SSW-DSA) structure. Using the proposed SSW-DSA cell with p/sup +/ pockets at both the drain and the source, an adequate punchthrough resistance to scale the gate length down to sub-half-micron has been obtained. It is also demonstrated that the uniform erasing scheme applying negative bias to the gate which is adopted for the SSW-DSA cell shows lower trapped charges after write/erase (W/E) cycles evaluated by a charge pumping technique, and results in better endurance and retention characteristics than nonuniform erasing schemes. This cell will enable the realization of a 64-Mb flash memory with single 5-V supply operation, 10/sup 6/ W/E endurance, and sector erasing scheme.<>