Office of President, Nikon Corporation, 2-15-3 Kounan, Minato-ku, Japan.
Research Center for Precision Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, Japan.
Rev Sci Instrum. 2023 Jan 1;94(1):015114. doi: 10.1063/5.0121862.
High-precision free-form surface mirrors are required for synchrotron radiation facilities in the scientific field and semiconductor lithography systems in the industrial field. Previously, we developed a nano-profiler with the goal of achieving a measurement accuracy of 30 nm. The nano-profiler scanned and measured the slope angle of the surface to be measured with laser light and calculated the shape from the angle information. By driving the optical head and surface to be measured with four rotation axes and one translation axis, the surface could be scanned while keeping the optical path length constant. Although the rotation axis was controlled by a high-precision rotary encoder, pitching and yawing errors occurred in the translation axis. In this study, we attempt to eliminate the error of pitching and yawing from the conventional measurement operation of four axes of rotation and one axis of translation to the drive of only four axes of rotation. If the translation drive is eliminated, the optical path length will not be constant, and the sensitivity of the light-receiving element will change. Therefore, we propose a new method to calibrate the sensitivity of the receiving element and perform a comparative measurement with the conventional measurement method. Comparing the measured shapes obtained by both measurement results, it was found that the shapes had a maximum peak to valley difference of 6.2 nm. Thus, the proposed novel measurement method allows a significant reduction in pitching and yawing errors.
高精度自由曲面反射镜在科学领域的同步辐射设施和工业领域的半导体光刻系统中是必需的。此前，我们开发了一种纳米轮廓仪，目标是实现 30nm 的测量精度。纳米轮廓仪使用激光扫描和测量待测量表面的斜率角度，并根据角度信息计算形状。通过驱动光学头和待测量表面的四个旋转轴和一个平移轴，可以在保持光程长度不变的情况下扫描表面。虽然旋转轴由高精度旋转编码器控制，但平移轴会出现俯仰和偏航误差。在这项研究中，我们试图从传统的四轴旋转和一轴平移的测量操作中消除误差，只进行四轴旋转的驱动。如果消除平移驱动，光程长度将不再保持恒定，并且光接收元件的灵敏度将会发生变化。因此，我们提出了一种新的方法来校准接收元件的灵敏度，并与传统的测量方法进行比较测量。通过比较两种测量结果得到的测量形状，发现最大峰谷差值为 6.2nm。因此，所提出的新型测量方法可以显著减少俯仰和偏航误差。
