Direct-scatterometry-enabled PEC model calibration with two-dimensional layouts

Abstract

Accurate and fast kernel-based proximity effect correction (PEC) models are indispensable to full-chip proximity effect simulation and correction. The attempt to utilize optical scatterometers for PEC model calibration instead of scanning electron microscopes is primarily motivated by the fact that scatterometry can be faster, more stable, and more informative if carefully implemented. Conventional scatterometry measures periodic patterns and retrieves their dimensional parameters by solving inverse problems of optical scattering with predefined libraries of the periodic patterns. PEC model parameters can be subsequently calibrated with the retrieved dimensional parameters. However, measuring only periodic patterns limits the usage of scatterometry, and the dimensional reconstruction is prone to generate estimation errors for patterns with complex three-dimensional geometry. Previously, we have proposed directly utilizing scattering light for PEC model calibration without the need for the intermediate step of retrieving the dimensional parameters. By iteratively comparing scattered light from predefined calibration patterns measured by a scatterometer to that predicted by the corresponding scattering and lithography models, PEC model parameters can be effectively calibrated with standard numerical optimization algorithms and one-dimensional periodic patterns. In this work, two-dimensional periodic circuit layouts are designed and utilized to study the applicability and potential limitations of the proposed method on the lithography of practical circuit designs.