This paper presents a method for determining positional variation and offsets in high aspect ratio etches used in the production of 3D NAND devices. The method uses a 3D fiducial as a positional reference in the field-of-view, which not only allows for high precision tracking of features through the depth of the device, but also aids in the alignment of images when performing 3D reconstructions. The workflow is based on plasma dual beam diagonal milling, which allows users to characterize structures through the device stack at a much higher throughput/slice than conventional methods, enabling enhanced process monitoring and control.

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