Kudo R, Okuda K, Usuki K, Nakano M, Yamamura K, Endo K
Research Center for Ultra-Precision Science and Technology, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
Department of Precision Science and Technology, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
Rev Sci Instrum. 2014 Apr;85(4):045101. doi: 10.1063/1.4869473.
Processing technology using an extreme ultraviolet light source, e.g., next-generation lithography, requires next-generation high-accuracy mirrors. As it will be difficult to attain the degree of precision required by next-generation high-accuracy mirrors such as aspherical mirrors through conventional processing methods, rapid progress in nanomeasurement technologies will be needed to produce such mirrors. Because the measuring methods used for the surface figure measurement of next-generation mirrors will require high precision, we have developed a novel nanoprofiler that can measure the figures of high-accuracy mirrors without the use of a reference surface. Because the accuracy of the proposed method is not limited by the accuracy of a reference surface, the measurement of free-form mirrors is expected to be realized. By using an algorithm to process normal vectors and their coordinate values at the measurement point obtained by a nanoprofiler, our measurement method can reconstruct three-dimensional shapes. First, we measured the surface of a concave spherical mirror with a 1000-mm radius of curvature using the proposed method, and the measurement repeatability is evaluated as 0.6 nm. Sub-nanometer repeatability is realized, and an increase in the repeatability would be expected by improving the dynamic stiffness of the nanoprofiler. The uncertainty of the measurement using the present apparatus is estimated to be approximately 10 nm by numerical simulation. Further, the uncertainty of a Fizeau interferometer is also approximately 10 nm. The results obtained using the proposed method are compared with those obtained using a Fizeau interferometer. The resulting profiles are consistent within the range of each uncertainty over the middle portions of the mirror.
使用极紫外光源的加工技术，例如下一代光刻技术，需要下一代高精度反射镜。由于通过传统加工方法难以达到诸如非球面镜等下一代高精度反射镜所需的精度程度，因此需要纳米测量技术取得快速进展才能制造出此类反射镜。因为用于下一代反射镜表面形状测量的方法需要高精度，所以我们开发了一种新型纳米轮廓仪，它可以在不使用参考面的情况下测量高精度反射镜的形状。由于所提出方法的精度不受参考面精度的限制，因此有望实现自由曲面镜的测量。通过使用一种算法来处理由纳米轮廓仪获得的测量点处的法向量及其坐标值，我们的测量方法可以重建三维形状。首先，我们使用所提出的方法测量了曲率半径为1000毫米的凹面球面镜的表面，测量重复性评估为0.6纳米。实现了亚纳米级的重复性，并且通过提高纳米轮廓仪的动态刚度有望提高重复性。通过数值模拟估计，使用本装置进行测量的不确定度约为10纳米。此外，斐索干涉仪的不确定度也约为10纳米。将使用所提出方法获得的结果与使用斐索干涉仪获得的结果进行比较。在反射镜中部的每个不确定度范围内，所得轮廓是一致的。
