The Impact of EUV Mask Defects on Lithographic Process Performance

摘要

As the options for experimental studies are still limited, a predictive simulation of EUV lithography (extreme ultraviolet lithography) is important for a better understanding of the technology. In particular, the simulation of defective EUV masks is a fundamental task because of the significant impact of certain defects on the lithographic process. The description of such a defective mask is one of the most critical issues for the modeling of EUV lithography. A new model for the simulation of defects inside the multilayer of an EUV reflective mask, developed at Fraunhofer IISB, is used for the presented study. The model consists of a combination of a rigorous electromag-netic field (EMF) computation and an analytical thin film computation. Compared to other methods, such as fully rigorous EMF simulations, this new approach leads to a significant reduction of computation time and memory requirements. The model can be applied to two and three dimensional defects and masks. This paper will present a detailed study of the impact of EUV mask defects on the near fields, the aerial images, and the process windows. Typical mask structures, e. g. 3D contact holes and 2D lines with various defects, are investigated. Defect parameters, such as the defect position with respect to the main feature to be imaged, the defect height, the defect FWHM (full width at half maximum), and the number of compressed layers inside the multilayer are varied. The important defect parameters and their critical ranges are identified using the new simulation method. The impact of these parameters on the image CD and the image position are demonstrated.