Investigation of floating gate depletion effect on NAND FLASH reliability

Abstract

Continuous technology scaling on NAND FLASH results in serious FG poly depletion issue due to Phosphorous out-gassing and degrades the cell reliability. Phosphorous implantation (P-IMP) into in-situ dope poly can improve poly depletion issue, but the FG bending and FG height loss were observed. In this study, we have successfully explored the methods to minimize FG bending and FG height loss issue by adding plasma oxide (PO) as screen oxide and/or changing the rotation times and temperature control of ion implantation. Finally, P-IMP on FG was validated at 36nm NAND FLASH device and shows significantly improvement on FG depletion and cell reliability.