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Modeling for field-to-field overlay error

The tightening of overlay budgets forces us to revisit the characterization and control of exposure tools to eliminate remaining systematic errors. Even though field-to-field overlay has been a known characterization and control technique for quite some time, there is still room to further explore and exploit the technique. In particular, it can be used to characterize systematic errors in a scanner's dynamic exposure behavior. In this paper we investigate the modeling of field-to-field overlay error starting from a scanner point of view. From a set of general equations we show how systematic dynamic differences between up and down scanned fields can be extracted from field-to-field overlay measurements in addition to apparent constant effects. We apply our model to characterize scan speed dependent dynamic behavior and to verify scanner setup.