Novel Negative $Vt$ Shift Phenomenon of Program–Inhibit Cell in $hbox{2}X{-}hbox{3}Xhbox{-}hbox{nm}$ Self-Aligned STI nand Flash Memory

摘要

A novel program–inhibit phenomenon of “negative” cell $Vt$ shift has been investigated for the first time in $ hbox{2}X{-}breakhbox{3}Xhbox{-}hbox{nm}$ self-aligned shallow trench isolation nand Flash memory cells. The negative $Vt$ shift is caused in an inhibit cell when along-word-line adjacent cell is programming. The magnitude of the negative shift becomes larger in the case of higher program voltage $(V_{rm PGM})$, lower field oxide height, slower program speed of the adjacent cell, and high $Vt$ of victim cell. The experimental results suggest that the mechanism of negative $Vt$ shift is attributed to hot holes that are generated by FN electron injection from channel/junction to the control gate. This phenomenon will become worse with cell size scaling since hot hole generation is increased by increasing the electron injection due to narrower floating gate space. Therefore, this negative $Vt$ shift phenomenon is one of the new scaling limiters of nand Flash memory cell, which needs to be managed for 2 and 3 b/cell in $hbox{2}X$ nm and beyond nand Flash memories.