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In this paper, we present an AIMS® EUV study of the impact of mask 3D effects on the through-focus image formation in a three-beam interference regime. Our experiments on a dense vertical 20nm lines and spaces clip using dedicated monopole illumination demonstrate a prominent, focus-dependent line shape deformation for each of the single pole positions. For the center monopole setting, frequency doubling of the aerial image is observed for one particular focus value. To describe the line shapes recorded, we applied an analytical model for three-beam-imaging in the presence of defocus and mask 3D effects. We obtained an excellent agreement between measurements and calculated data that allows us to derive the mutual phase-shifts of the single interference cross-terms involved. We conclude that the aerial image behavior as observed can be traced back to a coupling of the defocus aberration and mask 3D driven effects. |
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3D mask effects
Light sources and illumination
Extreme ultraviolet
Diffraction
3D image processing
3D modeling
Phase shifts
