18 December 2012 Wafer thin film effects in lithographic focus detection
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Typical focus sensors in conventional integrated circuit lithographic equipment have long been known to exhibit errors due to the nature of patterns printed on the wafer. One such error can be characterized as being derived from thin film effects where the derivative of the phase on reflection by the wafer introduces a shift in the beam that is basically identical to a shift that would be generated by a change in wafer height. In this paper we present a theoretical investigation into the nature and magnitude of the focus offset produced by this wafer effect under current typical process parameters.
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Daniel G Smith, Daniel G Smith, } "Wafer thin film effects in lithographic focus detection", Proc. SPIE 8550, Optical Systems Design 2012, 85503L (18 December 2012); doi: 10.1117/12.2002146; https://doi.org/10.1117/12.2002146

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