A technique to probe defects buried inside extreme ultraviolet EUV masks has been implemented
using a dark-field microscopy detection setup. Specific samples have been fabricated to evaluate the
sensitivity of this technique. They consist of silicon oxide gratings of a few nanometers height,
coated with 40 layer pairs of molybdenum–silicon. We observed images with a good contrast on
samples with defects as low as 3 nm. However, the imaging mechanism of scanning dark-field
microscopy is not linear and can produce image distortions. Conditions of correct imaging have
been analyzed, and simulations have been performed that show good agreement with the
experimental data. This work opens the way for a better understanding of the capability of
at-wavelength inspection technique for EUV mask.
