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Highly sensitive wavefront sensor for visual inspection of bare and patterned silicon wafers

: Lazareva, I.; Nutsch, A.; Schellenberger, M.; Pfitzner, L.; Frey, L.


Gorecki, C. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Micro- and Nanometrology III : 13 - 16 April 2010, Brussels, Belgium
Bellingham, WA: SPIE, 2010 (Proceedings of SPIE 7718)
ISBN: 978-0-8194-8191-7
Paper 77181H
Conference "Optical Micro- and Nanometrology" <3, 2010, Brussels>
Conference Paper
Fraunhofer IISB ()

Wave front sensing allows determination of topography and flatness of reflecting surfaces. As there is no contact to the surface, the method enables a contamination free and non-destructive surface analysis which meets the requirements of semiconductor and optical industries. This paper demonstrates that the sensor is suitable for defect estimation on the studied surface without topography reconstruction, where defect is considered as a dimple or a mound on the wafer surface. Based on the development, it is possible to reduce the evaluation time for the measurements by the reduction of both processing time for topography calculation and the number of acquired images. The method judges whether the surface of the studied sample is defect-free. That is a key for fast and reliable inspection. The Makyoh image shows the light distribution of the beam reflected from the surface. The images of bare wafers show unevenly alternate bright and dark areas. These areas appear due to the focusing and defocusing of the wave front and are caused by the local surface defects. The intensity changes are qualitatively interpreted with the help of the geometrical optics, and the maximum curvature of the defects on the studied surface is roughly estimated. Furthermore, the measurements of the sample rotated underneath the fixed sensor prove that the intensity changes are the result of the surface shape and not due to the aberration in the optical system. According to the results the method is useful for characterization of both micro- and nanometer scale surface flatness deviations.