Process Optimization Based on Analysis of Dynamic and Static Performance Requirements of Ion Beam Figuring Machine Tools for Sub-Nanometer Figuring

Abstract

Extreme ultraviolet lithography objective lenses require surface figure accuracy of approximately sub-nanometer root mean square (RMS). As the key equipment for sub-nanometer accuracy figuring, the dynamic and static performance of ion beam figuring (IBF) machine tools are critical. However, the related research is not sufficient and comprehensive. To this end, a general model of dynamic and static performance requirements on three-axis IBF machine tools was established. The requirements on dynamic and static performance under different figuring process for different surface shape were comprehensively analyzed. Analysis results revealed that the three-axis IBF machine tools require typical motion accuracy better than 100 μm and certain dynamic performance for achieving sub-nanometer accuracy. According to the theoretical and simulation results, a process optimization based on analysis of dynamic and static performance requirements of IBF machine tools for sub-nanometer figuring is proposed. To verify the proposed method, a Φ90 mm mirror with 2.594 nm RMS was figured to 0.251 nm RMS by optimizing the processing parameters to ensure that the IBF machine tool with measured performance (positioning error of 52.74 μm, 53.04 μm, 37.71 μm, and maximum acceleration of 1.0 m/s2, 1.3 m/s2, and 1.5 m/s2 for axes x, y, and z, respectively) meets the performance requirements. The proposed method can promote the application of three-axis IBF machine tools in sub-nanometer accuracy figuring.