The detection of damages at optics for the extreme ultraviolett (EUV) requires precise tools for at-wavelength-metrology.
Excellent stability of the probe radiation is a precondition for precise measurements. As an EUV-source
we use an electron-based microfocus EUV-tube. This EUV-source is debris-free, and it provides a output
of up to 300&mgr;W at 13.5 nm. The metrology setup benefits from the very good long-time stability and spatial
stability of this tube. Optical samples were characterized in reflectivity and transmission. Optical defects of
EUV-optics were analyzed at-wavelength. The incidence angle of the EUV-radiation was varied from grazing
incidence to nearly normal incidence. Our reflectivity measurements were compared with a calibrated synchrotron
measurement at the German national metrology institute (PTB). The absolute accuracy of the reflectivity
measurement was found to be better than 3% for any incidence angle. The reproducibility of the measurement
was found to be better than 0.5%. Investigations are performed to further improve the reproducibility and
absolute accuracy. The metrology setup is flexible, thus it can be fit to different types of measurement for
different applications. The concept of the metrology setup is discussed and recent results are presented. The
devices can be purchased from the Laser Zentrum Hannover e.V.