Multilayer coating and test of the optics for two new 10× Microstepper extreme-ultraviolet lithography cameras

Two new sets of projection and condenser optics for our prototype 10× reduction extremeultraviolet lithography (EUVL) system were coated with Mo/Si multilayers. The coating thickness was graded across the optics by using shadow masks to ensure maximum throughput at all incidence angles in the camera. The overall deviation of the (normalized) wavelength response across the clear aperture of each mirror is negligible, i.e., below 0.005% root mean square for each optic. However, the wavelength mismatch between two optics coated in different runs is up to 0.07 nm. Nevertheless, this is still within the allowed tolerances, and the predicted optical throughput loss in the camera due to such wavelength mismatch is about 4%. EUV reflectances of 63% and 65% were measured around 13.40 nm for the two secondary optics, which is in good agreement with the expected reflectance based on the substrate finish as measured with atomic force microscopy.