Effect of Localized Noncircular Deformations on Memory Characteristics of V-NAND Cells

Abstract

Vertical NAND (V-NAND) flash memory devices have gained specific attention because of lts lower bit cost and higer bit per area compared with conventional planar type Flash Memories. For the further scaling, however, it requires more complexity in vertical fabrication proesses. During channel etching processes, abnormal deformation was inevitably occurred. Those deformation can adversely affect the reliability and memory operation in V-NAND memory. Here, variation of electrical characteristics of memory cells with abnormal channel shapes were investigated using Technological computer-aided design (TCAD) simulation. In elliptical channel case, at early ISPP stage the program efficiency increases as the aspect-ratio (AR) decreases while at high ISPP condition the program efficiency decreases due to nonuniform electron trapping in the elliptical channel. In single and multiple crown channel case, at early ISPP stage the program efficiency increases slightly due to the enhancement of local electric field in crown region. At high ISPP regime, degradation of the program efficiency is observed due to increase of channel electron concentration in the crown region. In addition, various crown-shape channels depending on different crown size and the number of crowns were analyzed. These results are expected to provide guidelines of programming condition for VNAND memory applications.