全频段亚纳米精度氟化钙材料加工

摘要

When CaF2 materials are used in projection lenses ,the performance of the projection lenses can be improved greatly .This paper researches the process of CaF 2 crystal fabrication to realize its high precision optical fabrication in all wave bands .Firstly ,the pitch lap and the diamond powder were used to get a relative better figure and surface quality of a CaF 2 element .Then ,the technological parameters of the polishing lap ,such as rotation speed ,movement range and pressure were optimized , and the colloidal silica was used in polishing to reduce the high frequency errors in the CaF 2 element , remove the scratch in machining and to obtain a smaller mid-spatial error and smaller higher frequency roughness .Finally ,the ion beam figuring technique was used to repair finely the surface figure of the element meanwhile maintaining the high frequency error in the CaF 2 element .The Experiments were conduct on a CaF2 crystal plane with a diameter of 100 mm ,and the results indicate that its 37 Zernike fit error and the Zernike residual error reach to 0 .39 nm RMS and 0 .43 nm RMS ,respectively ,and the roughness reaches to 0 .31 nm on average . These results satisfy the nanometer machining requirements of the projection lens ,and lay a basis for development of the high performance projection lenses .%考虑用 CaF2材料制作投影光刻物镜可以明显提高其性能指标，本文研究了 CaF2材料加工工艺的全流程，以实现CaF2材料的全频段高精度加工。首先，利用沥青抛光膜和金刚石微粉使 CaF2元件有较好的面形和表面质量。然后，优化转速、抛光盘移动范围、压力等加工工艺参数，并使用硅溶胶溶液抛光进一步降低 CaF2元件的高频误差，逐渐去除加工中产生的划痕并且获得极小中频误差（Zernike 残差）和高频粗糙度。最后，在不改变 CaF2元件高频误差的同时利用离子束加工精修元件面形。对100 mm 口径氟化钙材料平面进行了加工和测试。结果表明：其 Zernike 37项拟合面形误差 RMS 值可达0．39 nm ，Zernike 残差 RMS 值为0．43 nm ，高频粗糙度均值为0．31 nm ，实现了对 CaF2元件的亚纳米精度加工，为研发高性能深紫外投影光刻物镜奠定了良好基础。