High numerical aperture designs for EUV projection lithography

Several different projection optics concepts currently exist for extreme ultraviolet (EUV) projection lithography. Typically, these ring field systems have a numerical aperture at the image/wafer of 0.1 and will resolve 0.1 µm features at 13.4 nm. These systems are unobscured three or four mirror anastigmats.

Since the designs were conceived to satisfy a resolution requirement of 0.1 µm, the forms do not exploit the full resolution potential of the extreme ultraviolet wavelengths between 11.3 and 13.5 nm. Higher numerical aperture optical designs are needed to take advantage of these short wavelengths.