15 March 2006 Aerial image based lens metrology for wafer steppers
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Abstract
Phase Measurement Interferometers (PMI) are widely used during the manufacturing process of high quality lenses. Although they have an excellent reproducibility and sensitivity, the set-up is expensive and the accuracy of the measurement needs to be checked frequently. This paper discusses an alternative lens metrology method that is based on an aerial image measurement. We discuss the Extended Nijboer-Zernike (ENZ) method and its application to aberration measurement of a high-NA optical system of a wafer stepper. ENZ is based on the observation of the through-focus intensity point-spread function of the projection lens. The advantage of ENZ is a simple set-up that is easy to run and maintain and provides good accuracy. Therefore the method is useful during lens assembly in the factory. The mathematical framework of ENZ is shown and the experimental procedure to extract aberrations for a high-NA lens is demonstrated on a high-NA DUV lithographic lens. PMI data is given as reference data. It is shown that ENZ provides an attractive alternative to the interferometer.
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Peter Dirksen, Joseph J. M. Braat, Augustus J. E. M. Janssen, Ad Leeuwestein, Tomoyuki Matsuyama, Tomoya Noda, "Aerial image based lens metrology for wafer steppers", Proc. SPIE 6154, Optical Microlithography XIX, 61540X (15 March 2006); doi: 10.1117/12.659428; https://doi.org/10.1117/12.659428
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