3D rigorous simulation of EUV defective masks using modal method by Fourier expansion

Simulation is recognized to play a significant role in the optimization of the lithography process. This is especially true for emerging technologies such as EUV. Indeed, the availability of EUV exposure data is still limited and when present these exposures are performed on exposure tools that are still far from the final production equipment. We have already shown (Schiavone, et al., 2001) that electromagnetic simulation based on modal methods (in our case modal method by Fourier expansion also known as RCWA) is an efficient alternative for the modeling of EUV lithography. The main advantage of modal methods is that their convergence decreases relatively slowly when the ratio of the feature size to the wavelength increases. This makes them advantageous for the short wavelength of EUV. In this paper, we recall the basic principle of the modal method by Fourier expansion and its major characteristics and performance when applied to 3D simulation. We also give several results obtained with the code for defective mask topographies. These results emphasize the influence of the oblique illumination on the printed feature size and position depending on the shape and density of the mask features (contact holes, posts, ...). It also analyzes the influence of a defect on the reflected field when it is in the vicinity of the absorber.