Reinhard Berger

Measurement errors of mirrorlike, tilted objects in white-light interferometry

White-light interferometry is an absolute 3D-measurement technique, used for the inspection of structured silicon and other materials with high quality surfaces. In this technique, each pixel of the camera detects a separate interference signal, which correlates with the height of the corresponding object point. Different signal processing algorithms are used, which extract the height from the interference signal by using the coherence or the phase information of the signal. However, measurement errors can occur if there are chromatic aberrations in the interferometer system. Then the phase information correlates with the height information in an unexpected manner and there are often disturbing 2&pgr; phase jumps in the numerical evaluation process, although the topography of the object is continuous and a light source with a short coherence length is used. We examined a Mirau type white-light interferometer with chromatic aberrations and explain how mirrorlike, tilted objects cause a correlation of the phase and the height information in each interference signal. We also show that this measurement error depends on both the slope of the object point and its field position. A comparison of measurements and a simulation, which shows the described correlation effect, is given.

Vector simulations of dark beam interaction with nanoscale surface features

In earlier publications, it was shown that scanning of surfaces by dark beams can be exploited for sub-wavelength feature analysis. In this work, we present vector simulations based in Rigorous Coupled-Wave Analysis with the purpose to estimate the expected resolution of the method, both lateral (feature size) and axial (height). The dark beam used in this study has a line singularity generated by a π-phase step positioned in a Gaussian beam. Various combinations of the illumination and detection nuFmerical apertures (from NA=0.2 to NA=0.8) and different surface features were studied. Polarization effects which become significant at high numerical apetures, were considered as an additional source of information for the analysis. In the case of a sub-wavelength feature on an ideal surface, the resolution of the method is limited only by the electronics noise. In particular, under a reasonable assumption of a 105 signal to noise ratio, it is possible to detect a 0.2 nm step.

Interferometrische Messung von Freiform-Schneidkanten auf einer Diamantwerkzeugbearbeitungsmaschine

Zusammenfassung Mit Diamantwerkzeugen lassen sich in einem Bearbeitungsschritt Oberflächen mit optischer Qualität erzeugen. Um insbesondere auch komplexe Oberflächenstrukturen mit einer reduzierten Anzahl an Zerspanungsabläufen fertigen zu können, sollen neue Werkzeuge mit Freiform-Schneidkanten zum Einsatz kommen. Voraussetzung sind jedoch Diamantwerkzeuge mit hoher Maßhaltigkeit, die bei ihrem Herstellungsprozess geprüft werden müssen. Hier werden sowohl das Konzept zur Prüfung dieser Freiform-Diamantwerkzeuge als auch die Ergebnisse eines simulierten messtechnischen Soll-Ist-Vergleichs vorgestellt. Abstract With diamond tools it is possible to achieve high surface qualities with one process step. To produce complex mouldings with a reduced amount of chipping runs new tools with free-form cutting edges will be used. However, this requires a high accuracy of the diamond tools which must be tested consequently and very precisely in real process time. The concept of the used measurement technique for the free-form diamond tools and the simulated results of a set-actual comparison of a cutting edge are presented.