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As introduced previously, all components now exist within the field of Microlithography to accurately measure the aberration content of a projection lens and to apply that information in a lens adjustment optimization procedure. The procedure previously detailed highlighted the use of available in-situ aberration measurement, and utilized the known aberration change response of a given projection lens as a function of lens element movement/adjustment. Various metrics were presented as candidates for inclusion in the optimization function. In any optimization routine, it is this definition of the specific optimization goals that drives the direction of the calculated optimum lens adjustment prescription. This concept has now been applied to several case studies, and tools have been developed to help automate the calculation and subsequent analysis of the optimum solution to a given optimization problem. This paper will discuss examples executed of lens adjustment optimization procedures, including the application of various target optimization functions toward the minimization of various aberration components. Included in the discussion will be the application of Zernike Sensitivity responses of specific patterns and imaging configurations to the optimization sequence. The Zernike Sensitivity treatments serve to bridge the gap between a pure Zernike Coefficient description of a lens and the “imaging performance” that the given lens is capable of. Further, the Zernike Sensitivity calculations can provide a quick overview and comparison of the aberration sensitivity of various patterns, delivering a simultaneously qualitative (e.g. “which aberration impacts the imaging most?”) and quantitative (i.e. “how much change in best focus can I expect from 10 milli-wave of Z9?”) description of the specific case. A summary will be provided of general knowledge gained and lessons learned as they relate to lens adjustment optimization, with an eye towards further progress in this field.
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