3 May 2016 Two-dimensional low-coherence interferometry for the characterization of nanometer wafer topographies
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Abstract
Within this work a scan-free, low-coherence interferometry approach for surface profilometry with nm-precision is presented. The basic setup consist of a Michelson-type interferometer which is powered by a super-continuum light-source (Δλ= 400-1700 nm). The introduction of an element with known dispersion delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In order to enable scan-free measurements, the interference signal is spectrally decomposed with a grating and imaged onto a two-dimensional detector. One dimension of this detector records spectral, and therefore height information, while the other dimension stores the spatial position of the corresponding height values.

In experiments on a height standard, it could be shown that the setup is capable of recording multiple height steps of 101 nm over a range of 500 m with an accuracy of about 11.5 nm. Further experiments on conductive paths of a micro-electro-mechanical systems (MEMS) pressure sensor demonstrated that the approach is also suitable to precisely characterize nanometer-sized structures on production-relevant components. The main advantage of the proposed measurement approach is the possibility to collect precise height information over a line on a surface without the need for scanning. This feature makes it interesting for a production-accompanying metrology.
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Ch. Taudt, Ch. Taudt, T. Baselt, T. Baselt, B. Nelsen, B. Nelsen, H. Aßmann, H. Aßmann, A. Greiner, A. Greiner, E. Koch, E. Koch, P. Hartmann, P. Hartmann, "Two-dimensional low-coherence interferometry for the characterization of nanometer wafer topographies", Proc. SPIE 9890, Optical Micro- and Nanometrology VI, 98900R (3 May 2016); doi: 10.1117/12.2227887; https://doi.org/10.1117/12.2227887
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