Spatially resolved reflectometry for EUV optical components

The introduction of EUV lithography into high volume manufacturing poses new challenges to any optical component in the lithography machines. Particularly the homogeneity of the optical properties is of importance. The present measurement capabilities of PTB using synchrotron radiation are based on a monochromatized, focused beam with a typical footprint on the sample in the order of 1 mm 2 . This, however, is not sufficient to detect small defects of optical coatings, local effects of irradiation and lifetime experiments or the like. We present our new set-ups for the spatially resolved measurement of reflectance and transmittance of optical elements. For the transmittance measurement we prepare a homogeneous almost parallel beam and place a CCD detector close behind the sample. For a sufficiently parallel beam and short enough distance, the resulting resolution is defined by the CCD pixel size, 13.5 μm square. For the spatial resolved reflectance measurement, the illuminated spot on the mirror under investigation is imaged with 10x magnification using a Wolter-type optic onto a CCD. The grazing incidence Wolter optic provides a broad-band transmittance for the optics starting from about 6 nm to longer wavelengths and thus allows measuring spectrally resolved the full reflectance curve of Mo/Si mirrors.