Comparison of rigorous modelling of different structure profiles on photomasks for quantitative linewidth measurements by means of UV- or DUV-optical microscopy

Gerd Ehret; Bernd Bodermann; Martin Woehler

doi:10.1117/12.726340

18 June 2007 Comparison of rigorous modelling of different structure profiles on photomasks for quantitative linewidth measurements by means of UV- or DUV-optical microscopy

Gerd Ehret, Bernd Bodermann, Martin Woehler

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Proceedings Volume 6617, Modeling Aspects in Optical Metrology; 661710 (2007) https://doi.org/10.1117/12.726340
Event: Optical Metrology, 2007, Munich, Germany

Abstract

The optical microscopy is an important instrument for dimensional characterisation or calibration of micro- and nanostructures, e.g. chrome structures on photomasks. In comparison to scanning electron microscopy (possible contamination of the sample) and atomic force microscopy (slow, risk of damage) optical microscopy is a fast and non destructive metrology method. The precise quantitative determination of the linewidth from the microscope image is, however, only possible by knowledge of the geometry of the structures and their consideration in the optical modelling. We compared two different rigorous model approaches, the Rigorous Coupled Wave Analysis (RCWA) and the Finite Elements Method (FEM) for modelling of structures with different edge angles, linewidths, line to space ratios and polarisations. The RCWA method can adapt inclined edges profiles only by a staircase approximation leading to increased modelling errors of the RCWA method. Even today's sophisticated rigorous methods still show problems with TM-polarisation. Therefore both rigorous methods are compared in terms of their convergence for TE and TM- polarisation. Beyond that also the influence of typical illumination wavelengths (365 nm, 248 nm and 193 nm) on the microscope images and their contribution to the measuring uncertainty budget will be discussed.

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Gerd Ehret, Bernd Bodermann, and Martin Woehler "Comparison of rigorous modelling of different structure profiles on photomasks for quantitative linewidth measurements by means of UV- or DUV-optical microscopy", Proc. SPIE 6617, Modeling Aspects in Optical Metrology, 661710 (18 June 2007); https://doi.org/10.1117/12.726340

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