Soft X-ray reduction optical system design for 0.1.MU.m lithography.

Abstract

A two-mirror telecentric optics has been designed for soft X-ray reduction lithography with high throughput. A resolution of 0.1μm is achieved at a wavelength of 130Å with a 20×20mm field using a ring-field scanning method. In the design, aberrations including distortion are reduced using aspherical concave and convex mirrors at a numerical aperture of 0.07. The designed optics achieves a square wave modulation transfer function (MTF) value of over 50% at a spatial frequency of 5000 lines/mm and is capable of resolving 0.1-μm lines and spaces. The depth of focus is ±1μm. The distortion is less than 0.01μm in the 12.5-mm-radius ring image field. Furthermore, uniform ring shaped illumination for the ring field is achieved by using focusing toroidal mirrors.