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28 May 2004 Calibration of OPC models for multiple focus conditions
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Ability to predict process behavior under defocus has until now relied on explicit calculations, which while accurate, cannot be realistically used in full-chip optical and process correction strategies due to the long run times. In this work, we have applied a vector model for the optics, and a compact model for the resist development process. Simulations with these models are fast enough to be the basis of full-chip OPC. We verify this strategy with an independent set of measurements, and compare it to current lithographic process fitting strategies. The results indicate that by describing optical processes as accurately as possible, the model accuracy improves over a wider range of defocus conditions when compared to the traditional calibration method. As long as the calibration process successfully decouples optical and resist effects, relatively simple resist models deliver excellent accuracy within the noise level of the metrology measurements. Our data are based on one-dimensional and two-dimensional results using a 193nm system using 0.75 NA and off axis illumination with 6% attenuated phase shift mask. In all cases, a wide variety of sub-resolution assist feature rules were used in order to further test the ability of the models to predict various optical and resist environments.
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Jochen Schacht, Klaus Herold, Rainer Zimmermann, J. Andres Torres, Wilhelm Maurer, Yuri Granik, Ching-Hsu Chang, G. Kuei-Chun Hung, and Benjamin Szu-Min Lin "Calibration of OPC models for multiple focus conditions", Proc. SPIE 5377, Optical Microlithography XVII, (28 May 2004);

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