Atomistic Study of Lateral Charge Diffusion Degradation During Program/Erase Cycling in 3-D NAND Flash Memory

Abstract

Impacts of lateral charge diffusion on the retention characteristics of charge-trapping (CT) 3-D NAND flash memory are comprehensively studied in this paper. Atomistic study through ab initio calculation is carried out to understand the correlations between P/E stress induced shallow trap generations and pre-existing traps in Si 3 N 4. It is shown that more shallow traps will be generated with a combination of electron/hole injections and free hydrogen (H) during P/E cycling. Our results strongly suggest that process optimizations to control free H in Si 3 N 4 CT layer could be a key point for robust retention characteristics. INDEX TERMS Silicon nitride, 3D NAND, charge trapping, lateral charge diffusion, shallow trap.

Impact of hydrogen plasma treatment on fluorine-contained silicon nitride films

“…The SiN charge trapping layer is formed continuously along the channel of the NAND strings, so that electrons trapped in each memory cell can laterally migrate to adjacent memory cells. [12][13][14][15][16] Since the number of electrons trapped in each memory cell significantly affects the threshold voltage of the memory cells, lateral charge migration causes serious problems with data retention characteristics and limits cell size (cell pitch) reduction. Furthermore, Multiple Level Cell (MLC) technology to increase the bit density of 3D flash memory requires tighter control of the number of electrons trapped in each memory cell.…”