12 April 2013 Flare management for 40-nm logic devices
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Since flare-related CD variation was observed in some 40-nm test chips, we evaluated the flare level of an ArF immersion scanner by the Kirk method. We found that the tool flare for a 1.3-μm pad was more than 5% and the short-range flare (scattering range < 10 μm) was quite large when the optics were degraded. Optics maintenance reduced the tool flare to about 2%. An evaluation of the impact of short-range flare on the space CDs of 40-nm logic devices revealed it to be quite large. The point spread function for flare was determined from measured flare data, and the flare density was calculated for various patterns. A simulation analysis showed that the measured CD error was closely related to flare density. Since the impact of a change in dose on space CD is nonlinear, the impact of a change in flare is also nonlinear. Simulations using tool flare and flare density can predict most of the CD error. In the active layer of 40-nm logic devices, the flare density is generally in the range of 40-70% for critical space patterns. Varying the dose control pattern from small-area L/S (< 5 μm square) to large-area L/S (50 μm square) should reduce the impact of flare on space CD. Patterns with a medium flare density are preferable for dose control.
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Yuusuke Tanaka, Takao Tamura, Masashi Fujimoto, Kyoichi Tsubata, Naka Onoda, Kiyoshi Fujii, "Flare management for 40-nm logic devices", Proc. SPIE 8683, Optical Microlithography XXVI, 86832E (12 April 2013); doi: 10.1117/12.2010082; https://doi.org/10.1117/12.2010082

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