Konferenzbeiträge

This paper reports about enhanced compliant mechanisms with flexure hinge based on new analytic and/or FEM models that have been manufactured by state of the art wire EDM technology. Experimental proofs at test benches, equipped with ultra-precise interferometer based length and angular measurement systems, show first time the residual deviation to the intended path of motion with a resolution of nanometers/arc seconds. Theoretically determined and measured data are in good correlation. Repeatability limitations are rather more given by the residual noise of the overall test arrangement and mainly not by the mechanism itself.

By combining classic differential interference contrast (DIC) with the chromatic confocal principle, we show that phaseshifting calibration can be avoided in DIC by using spectral information induced by the investigated sample. The created spectral fringe can be further used to unwrap the phase. This unwrapping is limited by the spectral resolution of the spectrometer. Therefore, the depth-difference around a single measurement point can be determined instantaneously. To reconstruct the depth profile, the integration of a depth-gradient is necessary. By combining the depth information of the chromatic confocal carrier signal with the differential depth information of the carried DIC signal, the accumulation of measurement uncertainty can be reduced. To our best knowledge, the proposed chromatic confocal differential interference contrast (CCDIC) is a novel profile reconstruction principle. To verify the feasibility of the CCDIC, a prototype probe with an adjustable shear and phase has been developed. Preliminary experiments achieve sub-micrometer depth resolution. A current challenge requiring further work is the stable unwrapping of the phase-difference by spectral frequencies. Keywords: chromatic confocal, differential interference contrast, unwrapping, industrial metrology

In principal, optical measurement methods suffer from physical limits related to finite wavelengths and diffraction. In laser focus scanning, vertical resolutions below 1 nm can be achieved while the lateral accuracy is more or less restricted by the diameter of the focused laser beam, i.e. values of half the wavelength can be reached in the best case. We present a model based approach having the potential to show a way out of this limitation. It is based on the rigorous modeling of the complete measurement device including sophisticated ray tracing in combination with Maxwell based modeling of the sample diffraction and scattering providing a simulated signal for an assumed sample profile. Furthermore, the sample profile is parametrized on the basis of a priori information. The simulated signal is then iteratively compared with the measured signal while updating the floating parameters of the model in order to improve the match between the two signals. Eventually, the improved sample profile obtained in this way is considered to represent the real sample profile as soon as a certain goodness of fit is achieved. On the other hand, the profile model has to be changed in case there is no satisfying fit. In this way, the lateral accuracy can be increased considerably. Edge detection errors below a few tens nanometer or even below 10 nm become possible while measuring with visible light. This is demonstrated by first comparisons of modeled and measured signals and validation by alternative metrology techniques.