The entire article appears to be publicly available: https://spectrum.ieee.org/chip-x-ray .
Quick summary is that the authors are using a form of scanning X-ray diffraction, to image the internal structure of integrated circuits.
Caption from a video in the online article says
A fly-though of the top layers of an Intel 22-nanometer processor reconstructed from X-ray scans.
The video is 36 seconds, at https://www.youtube.com/watch?v=h_gbDn5Te70 .
Wikipedia has an extensive article about the wider class of techniques: https://en.wikipedia.org/wiki/Ptychography .
--Rik