Fabrication and testing of a complex-shaped mirror constructed with silicon mirror elements

We have fabricated a complex-shaped mirror array and evaluated its fabrication accuracy. The mirror is constructed with 16 mirror elements with an arc-shaped contour and a spherical reflective surface, and is part of an arc-shaped fly-eye mirror for use in an extreme ultraviolet lithography system. All the mirror elements are manufactured individually, using single-crystal silicon as the mirror material, and are then arranged side by side on a base plate by magnetic attraction. The spherical mirror elements are manufactured to have highly accurate and smooth surfaces, although they have a different shape from those of general optics, and are assembled to form the fly-eye mirror. To evaluate the positioning errors of the mirror elements of the assembled fly-eye mirror, an optical testing system using visible rays are developed. From the measured results using this system, the average tilt error of the mirror elements is 69 arcsec, assuming that the system has a collimation error, which we corrected through calculation. Thus, the fly-eye mirror is fabricated with a high accuracy, demonstrating that the fabrication process is useful in realizing complex-shaped mirrors. (c) 2007 Society of Photo-Optical Instrumentation Engineers.