According to the folks at Applied Materials, trying to build 3D NAND structures in real life would be like trying to dig a one-kilometer-deep, three-kilometer-long trench with walls exactly three meters apart, through interleaved rock strata — and that’s before we discuss gate trenches or the staircases. Conventional etching systems deal with aspect ratios of 3:1 – 4:1, 3D etching requires an aspect ratio of 20:1 or more — and that’s not easy to pull off.

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