In extreme ultraviolet lithography (EUVL), conventional pellicles are unavailable for protecting the EUVL masks, since they highly absorb the EUV radiation. One of the serious challenges is therefore to prevent particulate contamination of the EUVL masks. In this paper, EUVL mask protection schemes proposed by Asbach et al. were experimentally challenged against horizontal aerosol flow simulating particle transport from the side during mask handling, shipping, and storage at atmospheric pressure. The protection schemes include mounting the critical surface facing down, using a cover plate with particle trap, and applying electrophoresis or thermophoresis. Both electrophoresis and thermophoresis showed very good protection capabilities. Electrophoresis, however, might be counterproductive due to the unknown particle charge polarity in real situations. A particle trap, on which contaminant particles can deposit before they reach the critical surface, could then be used to collect all particles irrespective of their polarity with a sufficiently high electric field but might not work against zero-charged particles. On the other hand, thermophoresis acts on all particles and transports them in the same direction. Therefore, the upside-down mounting and thermophoresis with the cover plate and particle trap are considered the promising protection schemes for the EUVL mask carrier systems.
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Manuscript received November 28, 2006; revised February 13, 2007. This work was supported by the Intel Corporation. S.-J. Yook and D. Y. H. Pui are with the Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455 USA (e-mail: firstname.lastname@example.org). H. Fissan, C. Asbach, T. van der Zwaag, and T. Engelke are with the Institute of Energy and Environmental Technology e.V. (IUTA), 47229 Duisburg, Germany. J. H. Kim is with the Department of Chemical Engineering, University of Seoul, Seoul 130-743, Korea. P.-Y. Yan is with the Technology and Manufacturing Group, Intel Corporation, Santa Clara, CA 95054 USA. Digital Object Identifier 10.1109/TSM.2007.895213 Fig. 1. Schematic diagram of protection schemes for EUVL masks without touching critical surface of mask, proposed in .
- Extreme ultraviolet lithography (EUVL)
- Mask carrier
- Mask protection