Metrology Challenges in 3D NAND Flash Technical Development and Manufacturing

Abstract

: 3D NAND technical development and manufacturing face many challenges to scale down their devices, and metrology stands out as much more difficult at each turn. Unlike planar NAND, 3D NAND has a three-dimensional vertical structure with high-aspect ratio. Obviously top-down images is not enough for process control, instead inner structure control becomes much more important than before, e.g. channel hole profiles. Besides, multi-layers, special materials and YMTC unique X-Tacking technology also bring other metrology challenges: high wafer bow, stress induced overlay, opaque film measurement. Technical development can adopt some destructive methodology (TEM, etch-back SEM), while manufacturing can only use non-destructive method. These drive some new metrology development, including X-Ray, mass measure and Mid-IR spectroscopy. As 3D NAND suppliers move to >150 layers devices, the existing metrology tools will be pushed to the limits. Still, the metrology must innovate.