Gate Structure Dependence of Variability in Polycrystalline Silicon Fin-Channel Flash Memories

摘要

Polycrystalline silicon (poly-Si) fin-channel tri-gate (TG)- and double-gate (DG)-type flash memories with a thin n~+-poly-Si floating gate (FG) and different control-gate (CG) lengths (L_CG's) from 76 to 256 nm have been fabricated and their electrical characteristics including statistical threshold voltage (V_t) and subthreshold slope (S-slope) have been comparatively investigated before and after one program/erase (P/E) cycle. It was experimentally found that better short-channel effect (SCE) immunity, a smaller V_t variation, and a higher program speed are obtained in TG-type flash memories than in DG-type memories. The higher performance of TG-type flash memories is contributed by the additional top gate and recessed bottom silicon dioxide (SiO_2) regions, which strengthen the controllability of the channel potential and increase the coupling ratio of the FG to the CG. Therefore, the developed poly-Si fin-channel TG structure is expected to be very useful for the fabrication of high-density and low-cost flash memories.