Three dimensional EUV simulations: a new mask near field and imaging simulation system

The integrated European research project "More Moore" is designed to push the limits of lithography to enable and exceed the requirements for the 22 nm node. Within the project the lithography group of Fraunhofer IISB is responsible for the development and evaluation of different simulation approaches for a predictive modeling of EUV (extreme ultraviolet) imaging technology for sub 22 nm features. During the first project year two new three dimensional EUV mask simulation models and a new EUV imaging model were developed. For the three dimensional mask near field simulation the modal method by Fourier expansion, developed by the project partner from Centre National de la Recherche Scientifique (CNRS) France, and the waveguide method (WG), developed by Fraunhofer IISB, are available. Both methods are rigorous electromagnetic field solver operating in the frequency domain. A good agreement with the established finite-difference time-domain (FDTD) method and a significantly higher performance compared to FDTD in case of periodic mask structures with rectangular elements can be observed. Additionally the WG method is able to simulate rigorously EUV masks with defective multilayers and with a full consideration of the defect geometry. The imaging model is characterized by a Jones pupil based representation of the imaging system and by a completely vectorial description of the light propagation, taking into account important polarization dependent effects like source polarization effects, mask topography polarization effects and effects resulting from light propagation in multilayer systems. This paper will present the new three dimensional WG method for the EUV mask near field simulation in combination with the vectorial imaging system and in comparison to our FDTD reference method. Typical 2D and 3D mask structures and new EUV mask concepts like phase shift masks with etched multilayers in combination with defect free and defective multilayers stacks are simulated exemplarily. Additionally aerial images and image CDs resulting from the two different simulation approaches (WG and FDTD) are compared as well as the mask near fields, the computation time, and the convergence.