Design of EUVL camera with large numerical aperture

A design of four-mirror imaging optics is presented for the wavelength of 13.5 nm. The numerical aperture (NA) is 0.15. The reduction ratio is 5:1. The exposure area on wafer is 0.5 mm (width) X 25 mm (chord length). The designed resolution is 50 nm with MTF approximately equals 60%. The distortion is less than 0.01% and the astigmatism is near zero at the designed ring field.