Nanophotonic identification of defects buried in three-dimensional NAND flash memory devices

Advances in nanophotonics and plasmonics have led to the creation of a variety of innovative optical components and devices. However, the development of powerful practical applications has so far been limited. Here we show that subsurface defects in three-dimensional NAND flash memory devices can be identified by exploiting the inherent hyperbolic metamaterial structure of the devices and associated nanophotonic interactions, such as the epsilon-near-zero effect and hyperbolic Bloch mode formation. By incorporating a hyperspectral imaging scheme into an industrial optical inspection tool, we experimentally demonstrate that a diffraction-assisted volume-plasmonic resonance provides a robust mechanism for identifying subsurface defects at a depth that is around ten times deeper than the conventional optical skin depth limit. Further spectral analysis in the longer-wavelength infrared region shows clear hyperbolic guided-mode-resonance signatures that would potentially allow defect identification over the entire device depth and on the scale of multiple micrometres.