Fabrication of a fly-eye mirror for an extreme ultraviolet lithography illumination system by arranging silicon mirror elements

摘要

A novel EUVL illumination system including two fly-eye mirrors was proposed by Komatsuda. However, these mirrors are difficult to realize because they have a complex-shaped reflective surface constructed from many concave mirror elements. In the present study, we discuss a fabrication process for the fly-eye mirrors, in which all elements are fabricated individually and are then arranged side-by-side to form the fly-eye mirrors. We propose a fabrication method for the mirror elements in which silicon blocks are ground and polished into a spherical surface, and are then cut into the shape of the mirror element using a wire electric-discharge machine. Using the proposed method, we successfully fabricated mirror elements having a flat reflective surface in the preliminary experiment. Moreover, we propose a method of arranging the mirror elements to construct the fly-eye mirrors. In this method, to arrange the elements accurately without any contamination, the elements are fixed to a base plate containing magnets by attraction of their bottom surfaces. The bottom surfaces are plated with metal to enable their attraction to the magnets. The mirror elements were accurately arranged to satisfy the fly-eye mirror specifications by this magnetic method.