Reflection masks for soft x-ray projection lithography

Soft X-ray Project Lithography (SXPL) may be used to fabricate high resolution structures for future integrated circuits. This technique will use a reflection mask which is a substrate coated with an x-ray multilayer mirror and patterned with a thin ({approximately}50 nm) layer of x-ray absorber. Mask patterning processes must not degrade the reflectivity of the x-ray mirror and mask repair techniques must be developed. The technical challenges of conventional reflecting optical imaging system designs are severe and mask technology can have a significant impact on this issue. Specifically, innovative mask designs can reduce the complexity of the optical system by decreasing the number of mirrors and replacing aspheric optical surfaces with spherical surfaces. We have developed a technique, called Encoded Mask Lithography, with which we have designed an optical system which uses only two (spherical) imaging mirrors and has 30 mm diameter field of view.