Fabrication of Ultra Precision Optics by Numerically Controlled Local Wet Etching

In this paper, the author presents a novel noncontact subaperture deterministic figuring method, named numerically controlled local wet etching (NC-LWE), for fabricating ultraprecision optics or finishing functional materials. In this method, a localized wet etching area is formed using a combined nozzle that is composed of a coaxially arranged supply part and a suction part for the etchant. In the system, the removal volume at any point on the workpiece surface is determined by the dwelling time of the nozzle. The author applied this method to finish a photomask substrate made of synthetic quartz glass (6 inches), and achieved 56 nm peak to valley flatness with 0.15 nm rms roughness.