Improvement of Flare Modeling and Derivation for Extreme Ultraviolet Optics

概要

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Flare has a critical impact on extreme ultraviolet (EUV) lithography. Precise estimation and control of flare amount are important for optical proximity correction (OPC). Flare can be calculated by the convolution of a reticle pattern with a flare point spread function (PSF) containing total integrated scatter (\mathit{TIS}) and scatter PSF (\mathit{PSF}^{\text{SC}}) derived from the power spectral density (PSD) of the mirror surface. \mathit{TIS} is traditionally obtained by the integration of \mathit{PSF}^{\text{SC}}. However, a portion of scatter cannot reach the wafer. Hence, \mathit{TIS} should be defined as the total amount of as-scattered light, while \mathit{PSF}^{\text{SC}} should be defined as the amount of light reaching the wafer; i.e., \mathit{TIS} should be derived from PSF different from \mathit{PSF}^{\text{SC}}. We also had other considerations: the termination of linear approximation, the scatter extinction effect of multilayers, and the obscuration effect. With these considerations, we can calculate flare behaviors that agree well with the experiments.
2011-06-25