On astigmatism of multi-beam optical stress sensor mounted at large incident angle
Abstract:When multi-beam optical stress sensor (MOSS) system is mounted at a large incident angle (α), despite an improvement of the resolution in the measurements, it also induces optical astigmatism in the spot images on a charge coupled device (CCD). During epitaxial growth, as the film stress increases, the astigmatism may result in the spot spacing deflection (δd) changing at different rates in the directions parallel and perpendicular to the incident plane, if the α is large. In this paper, the system error due to the astigmatism is analyzed by the ray tracing method and its predictions are compared with the the experimental results. It is demonstrated here, how the spot spacing deflections along the above mentioned orthogonal directions can be considered separately to minimize the error due to astigmatism in the MOSS measurements at any large α.
Document Type: Research Article
Affiliations: Nanotron Technologies, Inc., Inter-University Semiconductor Research Center, Seoul National University, Seoul 151-742, Korea
Publication date: December 1, 2003