Aspect ratio-dependent leaning of a block array in 3D NAND flash memory

Abstract

This paper presents an analysis of the leaning angle in relation to the aspect ratio of the block array in 3D NAND flash memory with a high aspect ratio using TCAD simulation. The simulation data were validated through cross-verification with the Stoney equation, a standard tool for diagnosing film stress. The study confirmed a linear relationship between intrinsic stress and film deformation in single-layer structures. In multi-layer structures, the deformation of the film changes according to the intrinsic stress of the most recently deposited layer. TCAD simulation used a block array structure comprising nine strings between each common source line and a layer range of 10 to 70. The residual stress from the mold stacking process leads to leaning because of stress relaxation after slit etching. Because of the accumulation of lateral stress at each deposition stage, the maximum lateral stress increases with the number of layers.