Rigorous EUV mask simulator using 2D and 3D waveguide methods

Extreme ultraviolet lithography (EUV) lithography at 13-nm wavelengths will require the use of reflective multi-layer mask substrates with a patterned absorbing top layer. The height of the absorber is roughly ten times the wavelength of the exposure radiation. Therefore, scalar Frauenhofer diffraction simulations based on Kirchhoff boundary conditions are not accurate. Rigorous solution of Maxwell's equations within the region of the mask topography is necessary to accurately predict many of the lithographic effects of these masks. Additionally, the interactions of the non-vertical radiation reflectance from the multilayer stack with the absorber causes further non-intuitive lithographic results which need to be understood and optimized. To further the rigorous understanding of EUV mask effects, we have extended existing 2D and 3D rigorous simulators to model diffraction in EUV lithography. These simulators, METRO and METROPOLE-3D respectively, use the waveguide method for fast and accurate computation of electromagnetic field in topographical mask structures. Modifications of these simulators enable an order of magnitude speedup in the calculation of results containing large numbers of EUV multilayers, improve mask dimension modeling accuracy and enable accurate modeling of the non-normal EUV source illumination through a range of pitch values. Rigorous illumination and multilayer defect analysis results will also be shown. Additional comparisons to recently published rigorous EUV simulations results and impressive runtime results on standard desktop workstations are presented. The results show that for EUV lithography the best focus position and the symmetry of the aerial image intensity profile with respect to best focus is affected by the pattern pitch.