(The) improvement of cell properties and the channel potential through applying the low-k macaroni oxide in V-NAND Flash memory

Abstract

For around 39 years since the introduction of planar NAND flash memory for cost-effective storage with high performance, it has been successfully scaled-down through the development in technologies of device, process, and architecture for the enhanced electrical and lithographic property. However, planar NAND flash memory has been faced with fundamental limitations on scaling mainly originating from lithography and electrical characteristics. V-NAND flash memory known as 3-D V-NAND flash memory has been replaced to overcome the fundamental problems such as lithography and electrical characteristics. Due to the emergence of new technology, there have been many materials and structural changes, such as polycrystal-line silicon (poly-Si) instead of single-crystal silicon as the material of the cell channel, the floated string body such as the gate-all-around (GAA) and the macaroni filler made of the oxide, and the charge trap nitride in-stead of the floating gate silicon. Since the introduction of the macaroni oxide filler in V-NAND flash memory, the study of the relationship between the macaroni oxide filler and properties of the cells, such as the channel potential during the self-boosting operation, the subthreshold swing and the initial threshold volt-age distribution of cells, have never been paid to attention. In this paper, the low-$k$ macaroni oxide filler in V-NAND flash memory is proposed for improving the cell characteristics for the first time. The changes of cell characteristics by the proposed condition were investigated using the CENTAURUS T-CAD simulation with the 8-stacked V-NAND flash memory structure except select transistors on both ends. As a result, the reduction of the macaroni oxide dielectric constant increases the channel potential generated during the self-boosting operation in the string that is not desired to be programmed and improves the subthreshold swing of all cells. In addition, the initial threshold voltage distribution of the cells is narrowed because of the improvement of the channel controllability of the gate. This study suggests a new direction of the process integration to improve cell characteristics of V-NAND flash memory, which is newly introduced and rapidly commercialized.