Frequency selective illumination for high aperture coherence scanning interferometry

Coherence scanning interferometry is a widely used optical topography measurement technique, which can achieve axial resolutions in the sub-nanometer regime. Nevertheless, in the lateral dimension it is inherently diffraction limited and multiple problems arise when approaching this limit. Especially for challenging surface topographies like steep slopes or small grating periods measurement artifacts start to cause massive deviations in the 3D reconstruction of the surface due to the increased influence of noise on increasingly weak signals. In this study we present an illumination approach for Linnik-type CSI, which highlights oblique incident angles of the illuminating light cone in high numerical aperture (0.95) systems. It is demonstrated, that this approach can significantly improve the signal-to-noise ratio for measurements at steep surface slopes and therefore increase the subsequent surface reconstruction.