Resolution enhancement for high-numerical aperture extreme ultraviolet lithography by split pupil exposures: a modeling perspective

BackgroundThe lithographic imaging performance of extreme ultraviolet (EUV) lithography is limited by the efficiency of light diffraction and contrast fading caused by 3D mask effects. The dual monopole concept has been proposed by Joern-Holger Franke to mitigate contrast fading for line-space (L/S) patterns.AimWe employ various modeling techniques to investigate the extendibility of dual monopole or split pupil exposures (SPs) to dense arrays of contacts on dark field and light field masks using different mask absorber options.ApproachFirst, a semi-analytic model is introduced to understand the relevant imaging mechanisms of split pupil exposures for L/S patterns. Next, we apply the split pupil exposure to a regular array of contact holes on a dark field mask. A multi-objective optimization approach helps to identify general trends and specific solutions. Analysis of the near fields of the light reflected from the mask for these particular solutions provides further insights into the imaging mechanisms of split pupil exposures and the different behavior of dark field (DF) and light field (LF) masks. Investigations for several mask absorber materials, tonalities, source fillings, and target sizes demonstrate the application of SP to different use-case scenarios.ResultsOur simulations indicate that split pupil exposures benefit 1D (L/S) and 2D (arrays of contacts/pillars) features. The achievable gain compared with a single exposure (SE) depends on tonality, source filling, absorber material, and target size. The application of SP significantly impacts source mask optimization (SMO). SP affects optical proximity correction (OPC) and optimum source shape and may even modify the optimum absorber thickness. The combination of low-n absorbers, SP, and multi-objective SMO enables the identification of the best imaging solutions and pushes low k1 high-numerical aperture (NA) imaging to its ultimate limits.ConclusionsSplit pupil exposures can provide a promising addition to the toolbox of resolution enhancement techniques for low k1 high-NA lithography and unleash the full potential of low-n/low-k absorber materials.