Abstract
Numerically controlled local wet etching (NC-LWE) has been developed as a novel noncontact subaperture deterministic figuring method for fabricating ultraprecision optics or for finishing functional materials. In this method, a localized wet etching area is formed using a combined nozzle that is constructed by coaxially arranging the supply part and the suction part of the etchant. The removal volume anywhere on the workpiece surface is determined by the convolution of the removal function and the dwelling time distribution of the nozzle. The machining properties of this method are insensitive to external disturbances, such as vibration or thermal deformation, because the removal process is performed under a noncontact condition.I applied NC-LWE to finish a 6 in photomask substrate made of synthesized quartz glass having size of 6 in, and improved the flatness of the substrate from 260 to 69 nm by only one NC-LWE correcting process.
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