Aberrations are a big part of OPC for phase-shifting masks

摘要

A prototype CAD system for rapidly determining locations in large layouts that are most impacted by aberrations in projection printing is described. Aberrations are accurately modeled as producing spillover between mask openings with a localized pattern that is the inverse Fourier transform (IFT) of the optical path difference (OPD) function in the pupil. The novel function in the CAD system then quickly rank orders all pattern edges and corners according to the degree of similarity of their surrounding layout to the IFT function. The prototype is based on the Cadence Design Framework II CAD system and adds procedures for evaluating the spillover function, fast pattern matching, and extraction of local layout regions for further user aerial image simulation with SPLAT. Speed and memory limitations prompted the creation of a new C++ binary that incorporates the core data structures and algorithms for pattern matching. A pattern-matching sweep of a mask can now be accomplished in roughly the time it takes to flatten and merge the mask layout in Cadence. Results are presented in current technologies using both binary and phase-shifting masks.