The moire interference phenomenon caused by the circular diffraction gratings under coherent illumination is studied to utilize it for precise alignment. The phenomenon is investigated by the Fresnel Kirchhoff'S diffraction theory. The characteristics of the moire signals in the diffracted beams are examined as a function of the lateral displacement and the airgap between the gratings. The moire signal obtained in the first order diffracted beam has been employed to the precise short-range alignment. The alignment system consists of a phase shifted pair of circular gratings and a stage driven by piezo-electric actuators. The system is controlled by the micro-computer to keep the alignment position. The alignment has been carried out with the precision of few tens of nm.
|Number of pages
|Proceedings of SPIE - The International Society for Optical Engineering
|Published - 1990
|15th International Optics in Complex Systems 1990 - Garmisch, Germany
Duration: 1990 Aug 5 → …