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11 June 2010 Short-range electron backscattering from EUV masks
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Proceedings Volume 7748, Photomask and Next-Generation Lithography Mask Technology XVII; 774823 (2010)
Event: Photomask and NGL Mask Technology XVII, 2010, Yokohama, Japan
Electron backscattering from Extreme Ultraviolet (EUV) masks during Electron Beam (EB) exposure was studied by simulations and experiments. The film structure of EUV masks is quite different from that of photomasks. The Mo/Si multilayer on the EUV substrate is very thick (280 nm) and heavy metal material such as Ta is used for the absorber. Monte Carlo simulations suggest that the absorbed energy inside the resist caused by the backscattered electrons from these films is non-negligible, about 1/10 of the forward scattering electrons and 1/4 of the backscattered electrons from the substrate. Also the simulations show that the influence range is very short because the backscattering happens near the mask surface. These simulations were verified by conducting EB exposure experiments. Short-range proximity effect was clearly observed by measuring the resist Critical Dimentions (CDs) of short bars laid beside the large exposed area. The data were fitted by assuming a backscattering electron distribution which has an exponential form with 0.4 μm range. The range is very short compared with the conventional proximity range of 10 μm. We conclude that the conventional EB proximity effect correction method needs to be revisited for EUV masks.
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Hiroyoshi Tanabe, Tsukasa Abe, Yuichi Inazuki, and Naoya Hayashi "Short-range electron backscattering from EUV masks", Proc. SPIE 7748, Photomask and Next-Generation Lithography Mask Technology XVII, 774823 (11 June 2010); doi: 10.1117/12.862641;

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