Emulation of anamorphic imaging on the SHARP EUV mask microscope

Abstract

The SHARP High numerical aperture Actinic Reticle review Project is a synchrotron-based, extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP emulates the illumination and imaging conditions of current EUV lithography scanners and several generations into the future. An anamorphic imaging optic with increased mask side-NA in the horizontal and increased demagnification in the vertical direction has been proposed to overcome limitations of current multilayer coatings and extend EUV lithography beyond 0.33 NA. 1 Zoneplate lenses with an anamorphic 4x/8x NA of 0.55 are fabricated and installed in the SHARP microscope to emulate anamorphic imaging. SHARP's Fourier synthesis illuminator with a range of angles exceeding the collected solid angle of the newly designed elliptical zoneplates can produce arbitrary angular source spectra, matched to anamorphic imaging. A target with anamorphic dense features down to 50-nm critical dimension is fabricated using 40-nm of nickel as the absorber. In a demonstration experiment anamorphic imaging at 0.55 4x/8xNA and 6º central ray angle is compared to conventional imaging at 0.5 4xNA and 8º central ray angle. A significant contrast loss in horizontal features is observed in the conventional images. The anamorphic images show the same image quality in the horizontal and vertical directions.