Process optimization using lithography simulation

Lithography simulation has become an indispensable tool for understanding and optimization of lithographic processes and for the development of new processes. A erial image simulations are used to evaluate the imaging of designed photomasks by projection steppers or scanners and to explore the impact of optical parameters such as numerical aperture, spatial coherence, defocus, and wave aberrations on the imaging performance. Other simulation approaches are used to describe the impact of the photoresist thickness, of the post exposure (PEB) temperature, and of the development characteristics of the photoresist on the total process performance. This article reviews the most important modeling approaches which are used in lithography simulation. Several examples demonstrate the application of modern simulation tools for the optimization of lithographic mask and illuminati on geometries. This includes the application of genetic algorithms for global parameter optimization and the rigorous electromagnetic modeling of light diffract ion from advanced lithographic masks.