Analysis of Mechanical Stress on Fowler-Nordheim Tunneling for Program Operation in 3D NAND Flash Memory

This study investigated the relationship between mechanical stress and program efficiency in three-dimensional (3D) NAND flash memory devices. A stacked memory array transistor (SMArT) 3D NAND flash structure was modeled using a technology computer -aided design (TCAD) simulation. The mechanical stress distribution in the device depended on the deposition temperature (T D ) of the constituent material. In particular, the T D of tungsten (T D,W ) dominated the mechanical stress. The tensile stress on the polycrystalline silicon (poly -Si) channel increased as the T D,W decreased, and the compressive stress on the tunneling oxide (T ox ) decreased. Consequently, the barrier height between T ox and poly -Si, and the effective electron mass decreased as the electric field in the T ox increased. These changes significantly increased the Fowler-Nordheim (FN) tunneling process and program efficiency, indicating the crucial performance of 3D NAND flash. Moreover, the mechanical stress caused by the differences in T D,W improved the program efficiency at a lower program voltage (V PGM ). Therefore, a change in the mechanical stress based on decreasing T D,W improved the program efficiency through a higher FN tunneling process.