  Modern semiconductor integrated circuits are increasingly fabricated at
untrusted third party foundries. There now exist myriad security threats of
malicious tampering at the hardware level and hence a clear and pressing need
for new tools that enable rapid, robust and low-cost validation of circuit
layouts. Optical backside imaging offers an attractive platform, but its
limited resolution and throughput cannot cope with the nanoscale sizes of
modern circuitry and the need to image over a large area. We propose and
demonstrate a multi-spectral imaging approach to overcome these obstacles by
identifying key circuit elements on the basis of their spectral response. This
obviates the need to directly image the nanoscale components that define them,
thereby relaxing resolution and spatial sampling requirements by 1 and 2 - 4
orders of magnitude respectively. Our results directly address critical
security needs in the integrated circuit supply chain and highlight the
potential of spectroscopic techniques to address fundamental resolution
obstacles caused by the need to image ever shrinking feature sizes in
semiconductor integrated circuits.
