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Rigorous EMF simulation of the impact of photomask line-edge and line-width roughness on lithographic processes

: Rudolph, O.H.; Evanschitzky, P.; Erdmann, A.; Bär, E.; Lorenz, J.


Maurer, W. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Photomask Technology 2011 : 19 September 2011, Monterey, California
Bellingham, WA: SPIE, 2011 (Proceedings of SPIE 8166)
ISBN: 978-0-8194-8791-9
Paper 81663Z
Conference "Photomask Technology" <2011, Monterey/Calif.>
Conference Paper
Fraunhofer IISB ()
phase-shift photomask; rigorous electro-magnetic field (EMF) simulation; waveguide; line-edge roughness (LER); line-width roughness (LWR); CD variation; aerial image contrast; process window

The impact of edge profile roughness of the absorber lines on an optical photomask has been studied by means of rigorous EMF simulation for the mask diffraction spectrum and subsequent imaging. Roughness has been modeled using two different approaches, a sinusoidal description and an algorithm known from literature based on Fourier transformation. The latter one allows one to arbitrarily create rough profiles and surfaces based on the three morphological parameters standard deviation $\sigma$, roughness exponent $\alpha$, and correlation length $\xi$. A software interface for use of the generated profiles with the waveguide EMF solver of the Dr.LiTHO lithography simulation suite has been implemented. It was shown by means of image analysis and study of the resulting process windows that ma sk roughness is partially transferred to the aerial image. Isolated and dense features behave differently, leading i.a. to an iso-dense bias different to that of ideal lines. Process windows shift or even shrink in the presence of roughness, due to a certain smearing of the curves reducing the overall window. Tapered sidewalls can add to these effects in the same order of magnitude.