Ultraprecision 5-axis control machining of fly-eye mirror in EUV lithography

The study deals with the manufacture of fly-eye mirrors for EUVL by means of ultraprecision 5-axis control milling. The mirrors consist of many small spherical mirror elements with many steps among them. In the present study, two new methods for manufacturing the mirrors using a single-crystal diamond tool are proposed. One method uses a sphere type tool with a circular arc cutting edge. Though the method is theoretically efficient, it is found that it is not practical due to the difficulty of manufacturing the tool accurately. The other one uses a cylinder type tool with aright-angled cutting edge. The tool enables the manufacturing of spherical surfaces with any radius and supports practical use because the efficiency of this method is independent of tool form accuracy. The fly-eye mirror was machined by the latter method to have an array of four spherical mirror elements with the required steps and without any burrs.