Abstract
Interference signals in coherence scanning interferometry at high numerical apertures and narrow bandwidth illumination are spectrally broadened. This enables phase analysis within a spectral range much wider than the spectral distribution of the light emitted by the light source. Consequently, different surface features can be resolved depending on the wavelength used for phase analysis of the interference signals.In addition, the surface topography itself affects the spectral composition of interference signals in different ways. Signals related to tilted surfaces or step height structures show special spectral characteristics. Thus, spectral amplitude and phase analysis enables a better understanding of the underlying physical mechanisms and gives hints how to improve the measurement accuracy.
Highlights
White-light or coherence scanning interferometry (CSI) is one of the most used optical profiling techniques [1,2,3,4,5]
The wavelength dependent spectral composition of CSI signals at steep edges will be demonstrated by use of the RS-N standard manufactured by Simetrics GmbH comprising a rectangular grating of 6 μm period with perpendicular edges and a nominal groove depth of 190 nm [19]
This contribution deals with the analysis of physical phenomena, which affect the spectral distribution of CSI signals and may reduce or enhance the accuracy of CSI measurements
Summary
White-light or coherence scanning interferometry (CSI) is one of the most used optical profiling techniques [1,2,3,4,5]. Proper application of CSI instruments assumes that their transfer characteristics are well-known. This is true only for phase analysis of CSI signals and surface height differences, which are much smaller than a quarter of the wavelength of the illuminating light [6]. A 100x Mirau interferometer with a NA of 0.7 (Nikon CF IC Epi Plan DI) and a Linnik interferometer equipped with objective lenses of NA = 0.9 (Olympus MPLFLN100XBDP) used throughout this study show the well-known NA effect.
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