Novel negative Vt shift program disturb phenomena in 2X∼3X nm NAND flash memory cells

Abstract

A novel program disturb phenomena of “negative” cell-Vt shift has been investigated for the first time in 2X∼3X nm Self-Aligned STI cell[1,2] of NAND flash memory. The negative Vt shift occurs on an inhibited cell adjacent to a cell being programmed in the WL direction. The magnitude of the shift becomes larger when the programming voltage (VPgm) is higher, thinner field oxide and slower program speed of the adjacent cell. The mechanism of negative Vt shift is attributed to hot holes that are generated by FN electrons, injected from channel / junction to the control gate (CG) along the isolation. This phenomenon will become worse with scaling since hot hole generation is increased by increasing electron injection due to narrower FG space. Therefore, this negative Vt shift phenomenon is one of the new NAND flash memory cell scaling limiter, that needs to be managed for 2bits and 3bits/cell in 2X nm and beyond.