Two new sets of projection optics for our prototype 10X reduction EUV lithography 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 wavelength response across the clear aperture of each mirror is below 0.01 percent RMS. However, the wavelength mismatch between two optics coated in different runs is up to 0.07 nm. Nevertheless, this is till within the allowed tolerances, and the predicted optical throughput loss in the camera due to such wavelength mismatch is about 4 percent. EUV reflectances of 63-65 percent were measured around 13.40 nm for the secondary optics, which is in good agreement with the expected reflectance based on the substrate finish as measured with AFM.
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