Processing efficiency of elastic emission machining for low-thermal-expansion material

Extreme ultraviolet (EUV) lithography is currently being developed as a next‐generation lithography system. In this system, light at a wavelength of 13.4 nm is used, allowing the patterning of lines with dimensions of less than 40 nm. To focus the light, high‐precision optical mirrors are required with a surface roughness of 0.1 nm. In addition, mirror substrates must be low‐thermal‐expansion materials because EUV light is easily absorbed in matter, accordingly converted to heat. ULE (Corning Inc.) and Zerodur (SCHOTT AG) are well‐known examples of such materials. To achieve these requirements for EUV lithography, a high‐performance machining method is needed. In previous studies, the machining performance of elastic emission machining (EEM) for the above materials was examined from the viewpoint of roughness improvement. As a result, we considered that EEM has sufficient figuring and smoothing capability for the fabrication of EUV optics. We next evaluate the processing efficiency of EEM. In this study, the processing efficiency of EEM for a low‐thermal‐expansion material was examined from the viewpoint of the removal rate. As a result of this investigation, the conditions under which the efficiency of EEM is increased were clarified. We analyzed and discussed these conditions. Copyright © 2008 John Wiley & Sons, Ltd.