22 June 2013 Interferometric measurement of functional surfaces
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Proceedings Volume 8769, International Conference on Optics in Precision Engineering and Nanotechnology (icOPEN2013); 876904 (2013); doi: 10.1117/12.2021478
Event: International Conference on Optics in Precision Engineering and Nanotechnology (icOPEN2013), 2013, Singapore, Singapore
Increasing capabilities in precision manufacturing and micro technology are accompanied by increasing demands of high precision industrial metrology systems. Especially for measuring functional surfaces, areal optical principles are widely used. If, in addition, nanometer height resolution is needed interferometers seem to be the most promising instruments. First, this contribution focuses on the transfer characteristics of white-light interferometers with microscopic field of view. In general, microscopic instruments suffer from their limited lateral resolution capabilities. Hence, the transfer function of these instruments is typically assumed to show a linear low-pass characteristic. We studied the transfer characteristics of white-light interferometers by theoretical simulations and experimental investigations. Our results show that in most practical cases these instruments behave nonlinear, i.e. the output surface profile cannot be obtained from the input profile by a simple linear filter operation. Although they are well-established, there are some further limitations of white-light interferometers if they are used to measure micro or even sub-microstructures. If edges, steeper slopes or abrupt slope changes are present on a measuring object characteristic errors such as batwings occur. Furthermore, a high effort concerning the correction of chromatic aberration is necessary in order to avoid dispersion effects. Otherwise, there will be systematic discrepancies between profiles obtained from evaluation of the coherence peak and those resulting from the phase of the interference signals. These may lead to 2π phase jumps if the fringe order is obtained from the position of the coherence peak. Finally, measurement artifacts may also result if the measured micro-structure shows discontinuities of the surface slope. This contribution analyses the different phenomena and discusses approaches to overcome existing limitations.
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Peter Lehmann, Weichang Xie, Peter Kühnhold, Jan Niehues, "Interferometric measurement of functional surfaces", Proc. SPIE 8769, International Conference on Optics in Precision Engineering and Nanotechnology (icOPEN2013), 876904 (22 June 2013); doi: 10.1117/12.2021478; https://doi.org/10.1117/12.2021478


Modulation transfer functions


Imaging systems


Image resolution

Linear filtering

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