Study of Retention Characteristics and Program Speed Enhancement Using Plasma Nitridation on Interpoly Dielectric

Abstract

The interpoly dielectric in floating gate NAND flash memory, as it is used to bolster both programming speed and data retention, has been extensively investigated in studies examining plasma nitridation technologies. The bird’s beak, as found on an interpoly dielectric edge, likely contributes to a degradation program/erase performance and reliability in cell operation and is abnormally increased above 12 Å during gate sidewall oxidation. This phenomenon can be effectively reduced to less than 1.5 Å through the application of nitrogen plasma nitridation on the floating gate and on the top oxide of the interpoly dielectric. In terms of control gate coupling capability and program voltage, both the physical and electrical properties of the interpoly dielectric can improve by 6% and 1.2 V, respectively. Nevertheless, this study found that data retention problems resulting from plasma nitridation, a process which induces the oxynitride remaining in shallow trench isolation, are the source of electron leakage through the word line. To reduce charging loss and sustain the coupling capabilities of the control gate, selective oxynitride removal with diluted HF is proposed. This interpoly dielectric can enhance memory characteristics and also extends the functional limitation of the NAND flash memory to the 40 nm generation.