To investigate the performance of three-dimensional (3D) nanostructures, it is vital to study their internal structure with a methodology that keeps the device fully functional and ready for further integration. To this aim, we introduce here traceless X-ray tomography (TXT) that combines synchrotron X-ray holographic tomography with high X-ray photon energies (17 keV) in order to study nanostructures "as is" on massive silicon substrates. The combined strengths of TXT are a large total sample size to field-of-view ratio and a large penetration depth. We study exemplary 3D photonic band gap crystals made by CMOS-compatible means and obtain real space 3D density distributions with 55 nm spatial resolution. TXT identifies why nanostructures that look similar in electron microscopy have vastly different nanophotonic functionality: One "good" crystal with a broad photonic gap reveals 3D periodicity as designed, a second "bad" structure without gap reveals a buried void, a third "ugly" one without gap is shallow due to fabrication errors. Thus, TXT serves to non-destructively differentiate between the possible reasons of not finding the designed and expected performance and is therefore a powerful tool to critically assess 3D functional nanostructures.

See the nice animation on YouTube made by ESRF staff: https://www.youtube.com/watch?v=1tEZlNl6Sso :-) many thanks!

https://pubs.acs.org/doi/10.1021/acsnano.9b05519

D. A. Grishina, C. A. M. Harteveld, A. Pacureanu, D. Devashish, A. Lagendijk, P. Cloetens, and W. L. Vos

2019

12/2019

ACS Nano

13

13932-13939

10.1021/acsnano.9b05519

3D, CMOS-compatible, functional, nanofabrication, nanophotonics, nanotechnology, non-destructive inspection, photonic crystals, silicon, X-ray imaging