Improvement of Flare Modeling and Derivation for Extreme Ultraviolet Optics

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 (TIS) and scatter PSF (PSFSC) derived from the power spectral density (PSD) of the mirror surface. TIS is traditionally obtained by the integration of PSFSC. However, a portion of scatter cannot reach the wafer. Hence, TIS should be defined as the total amount of as-scattered light, while PSFSC should be defined as the amount of light reaching the wafer; i.e., TIS should be derived from PSF different from PSFSC. 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. (C) 2011 The Japan Society of Applied Physics