Spatial frequency resolved measurement of surface micro-topographies using interference microscopy with wavelength selective pupil illumination at high numerical aperture

白光干涉法已成为表面微观形貌测量的标准工具。测量过程包括干涉仪测量臂中的连续路径长度变化，同时相机等距离地捕获干涉图像。为了获得每个相机像素的高度值，将确定对应的路径长度相关干涉信号的最大干涉对比度的位置。如果另外分析干涉信号的相位，则达到纳米范围内的高度分辨率，因为测量信号的周期等于贡献光的平均有效波长的一半。横向亚微米尺寸的测量需要具有高数值孔径（NA）的干涉显微镜。对于这些，产生的干涉信号显示出额外的低频分量，其与光的倾斜入射角有关。因此，发生了众所周知的NA效应，这导致干涉信号的周期增加，从而导致由增加的NA引起的平均有效波长增加。申请人进行的研究表明，作为该效应的另一个结果，用于相位分析的评估波长的选择系统地影响测量的横向分辨率。本文的目的是通过理论和实验研究来分析其内在机制。因此，在高NA Linnik干涉仪中，将引入不同直径的环形孔径，以提供在被测表面上的光的不同入射角。所产生的干涉信号将相对于其特征参数，特别是其光谱分辨相位进行分析。作为最终的结果，我们期望在实际应用的许多情况下，实现使用WLI的地形测量的精度提高。

White-light interferometry has established as a standard tool for the measurement of surface micro-topography. The measuring process comprises a continuous path-length change in the measurement arm of the interferometer, while a camera captures interference images equidistantly. In order to obtain a height value for each camera pixel the position of maximum interference contrast of the corresponding path-length dependent interference signal will be determined. If the phase of the interference signal is analyzed additionally, a height resolution in the nanometer range is reached, since the period of the measured signal equals half of the mean effective wavelength of the contributing light. The measurement of lateral sub-micrometer dimensions requires interference microscopes with high numerical aperture (NA). For these, the resulting interference signals show additional low-frequency components, which are related to the oblique angles of incidence of the light.Consequently, the well-known NA-effect occurs, which leads to an increasing period of the interference signal and thus an increasing mean effective wavelength caused by the increased NA. Investigations carried out by the applicant turned out that as a further result of this effect, the choice of the evaluation wavelength used for phase analysis systematically influences the lateral resolution of the measurement. The intention of this proposal is to analyze the underlying mechanisms by theoretical and experimental investigations. Therefore, ring-shaped apertures of different diameter providing different angles of incidence of light on the measured surface will be introduced in a high-NA Linnik interferometer. The resulting interference signals are to be analyzed with respect to their characteristic parameters, in particular their spectrally resolved phases. As a final result we expect to achieve an improved accuracy of topography measurement using WLI in many cases of practical application.