As optical lithography continues to produce ever smaller features on a chip, the industry imposes tighter quality parameters on the optical components used in a lithographic step and scan system. Residual linear birefringence is one such parameter. Currently, optical component suppliers use the Exicor birefringence measurement systems that we have developed to measure photomask blanks and lens blanks to ensure their quality. In this paper, we report a new model of Exicor birefringence measurement system that is specifically designed for measuring lenses. Unlike lens blanks that have flat surfaces, lenses have curved surfaces that refract the measuring light beam to different angles. In this new model of birefringence measurement system, we combine motion control of the light source module, the detector module and the lens under test to achieve accurate measurement of residual birefringence of a lens at different incident angles.
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