The previous chapter shows that optical lithography has rapidly become an extremely complex process step. Many physical phenomena must be understood when pushing the limits of resolution to achieve feature sizes in the order of or even below the wavelength. Additionally, technology innovations to extend optical lithography introduce different implementation options that must be assessed. Together, the increasing concern for physical effects and the introduction of innovations have greatly augmented the number of parameters whose effects must be characterized and balanced. Modeling offers a solid foundation for efficient characterization and a way to systematically quantify relationships and quickly investigate new innovations. The alternative of a purely experimental approach tends to be empirical, unless simulation is performed to assist in understanding the process and guide the experiments. To turn optical microlithography from a black magic to science is the challenge of theorizing and understanding optical enhancement techniques for projection printing like off-axis illumination, phase-shifting masks, and in-lens filtering as well as a rigorous modeling of the exposure and development of advanced resist systems.
This chapter provides information about modeling and simulation at an introductory level. Firstly, an overview of the modeling phases and the fundamental structure of a typical lithography simulator is given. Then, the role of simulation in practical characterization as well as the modeling of technology innovations is sketched. Finally, a summary of state of the art lithography simulators including their capabilities and limitations is presented, from which the need for new, highly specialized tools becomes clear.