Non-destructive high-resolution X-ray imaging of ULSI micro-electronics using keV X-ray microscopy in Zernike phase contrast

Abstract

We report here on non-destructive high-resolution imaging of ULSI microelectronics, using a phase contrast X-ray microscopy technique with Fresnel zone plate lenses that has been developed at a photon energy of 4 keV. In comparison with electron microscopy, keV X-ray microscopy has advantages in terms of ease of sample preparation, since for transmission electron microscopy, thin sections have to be prepared, or in scanning electron microscopy, only surfaces down to a few 10 nm depth can be studied. X-ray microscopy in the multi-keV photon energy range offers unique possibilities to non-destructively study small structures buried in thick dense samples with high spatial (currently 60 nm) resolution. Since the absorption becomes smaller with increasing photon energy, we applied a method for contrast enhancement as first proposed by Zernike for visible light. While the amplitude contrast between copper and silicon dioxide in these samples is only 7%, negative as well as positive Zernike phase contrast were demonstrated with a contrast of 40% and 45%, respectively.