2-MIRROR TELECENTRIC OPTICS FOR SOFT-X-RAY REDUCTION LITHOGRAPHY

A two-mirror telecentric optic has been designed for soft x-ray reduction lithography with high throughput using synchrotron radiation. A resolution of 0.1-mu-m is achieved at a wavelength of 130 angstrom with a 15-mm ring field. In the design, aberrations, including distortion, are reduced using aspherical concave and convex mirrors with an ellipsoid surface at a numerical aperture of 0.07. Telecentric imaging is obtained by illuminating a reflection mask using focusing toroidal mirrors. The designed optics achieves a modulation transfer function (MTF) value of over 40% at a spatial frequency of 5000 lines/mm capable of resolving 0.1-mu-m lines and spaces. The depth of focus is +/- 1-mu-m. The distortion is < 0.01-mu-m in the image field. The imaging field is a 12.5-mm radius ring field which enables a 15 x 15-mm field exposure by the ring-field scanning method. The reduction ratio is 1/5.