The characterization of the Mask Error Enhancement Factor (MEEF) for a variety of feature types under a variety of processing conditions is presented. Analytic expressions for the aerial image MEEF under simple incoherent and coherent illumination conditions are derived, including the effect of defocus. Errors in processing, such as focus and exposure errors, also affect the value of the MEEF. Thus, another approach to evaluating the impact of mask errors is to look at the reduction in the process window caused by these errors. Using simulation, a study of the impact of mask CD errors on the overlapping process windows is presented and used as the basis for realistic mask CD specifications.
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