Efficient simulation of EUV pellicles
The paper presents a new simulation model for the efficient simulation of EUV pellicles. Different pellicle stacks, pellicle deformations and particles on the pellicle can be considered. The model is based on properly designed pupil filters representing all pellicle and particle properties to be investigated. The filters are combined with an adapted image simulation. Due to the double transition of the EUV light through the pellicle, two different models for the pupil filter computation have been developed: A model for the forward light propagation from the source to the mask and a model for the backward light propagation from the mask to the entrance pupil of the system. Furthermore, for the accurate representation of particles on the pellicle, a model has been developed, which is able to combine the different size dimensions of particles, of the entrance pupil and of the illumination source. Finally, some specific assumptions on the light propagation make the pellicle model independent from the illumination source and speed up the simulations significantly without introducing an important error. Typically, the consideration of a pellicle increases the overall image simulation time only by a few seconds on a standard personal computer. Furthermore, a simulation study on the printing impact of pellicles on lithographic performance data of a high NA anamorphic EUV system is presented. Typical illumination conditions, a typical mask stack and different mask line features are considered in the study. The general impact of a pellicle as well as the impact of pellicle transmission variations, of pellicle deformations and of particles on the pellicle on typical lithographic performance criteria is investigated.