25 March 2010 Reflectivity metrics for optimization of anti-reflection coatings on wafers with topography
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Anti-reflection coatings are commonly used in advanced photolithography in order to minimize CD variability caused by deviations in resist thickness and in the films and structures comprising the substrate. For a planar film stack, reflectivity calculations are a critical tool for optimization of parameters such as coating thicknesses and optical properties of anti-reflection coatings (TARCs and BARCs). However, with the exception of the first lithography layer, all layers on a production wafer have some degree of topography, so that reflectivity calculations for a planar film stack are not strictly correct. In this study, we evaluate three different reflectivity metrics that can be applied to wafers with topography: reflectivity for simplified planar film stacks, standing wave amplitude, and reflected diffraction efficiencies. Each of these metrics has a simple, physical meaning that will be described in detail in the presentation. We then evaluate how well these reflectivity metrics correlate with CD variability for two different example lithography steps: implant layers with STI (where a developable BARC might be used), and Litho-Etch-Litho-Etch style double patterning.
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Mark D. Smith, Mark D. Smith, Trey Graves, Trey Graves, John Biafore, John Biafore, Stewart Robertson, Stewart Robertson, "Reflectivity metrics for optimization of anti-reflection coatings on wafers with topography", Proc. SPIE 7639, Advances in Resist Materials and Processing Technology XXVII, 763935 (25 March 2010); doi: 10.1117/12.846540; https://doi.org/10.1117/12.846540

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