A 0.54 μm2 self-aligned, HSG floating gate cell (SAHF cell) for 256 Mbit flash memories

A 0.54 μm² self-aligned memory cell with hemispherical-grained (HSG) poly-Si floating gate (SAHF cell) has been developed for 256 Mbit flash memories. Applying hemispherical-grained (HSG) poly-Si to floating gate extends the upper surface area to double that of the floating gate in comparison with the conventional ones. A high capacitive-coupling ratio of 0.8 and buried n⁺ diffusion layers which are self-aligned to the floating gate poly-Si are realized simultaneously with a simple cell structure and fewer process steps