A Novel Design of Three-Aspherical-Mirror Imaging Optics for Extreme Ultra-Violet Lithography

The demagnifying optics for extreme ultra-violet lithography (EUVL), which consists of three aspherical mirrors and one plane mirror, is proposed. A resolution of 0.1 µ m can be achieved on a ring field of 26 mm×1 mm in size and the blur size owing to the distortion is small. The assembly tolerance such as decentration tolerance and tilt tolerance is investigated for each of the aspherical mirrors. It is clarified that the assembly accuracy requires 0.0015 degree for the proposed optics.