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28 June 2005 Investigation of pellicle influence on reticle flatness
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Proceedings Volume 5853, Photomask and Next-Generation Lithography Mask Technology XII; (2005)
Event: Photomask and Next Generation Lithography Mask Technology XII, 2005, Yokohama, Japan
In lithography systems, the need for increased resolution requires larger numerical apertures and shorter illumination wavelengths. Both of these requirements cause a reduction in the system’s depth of focus resulting in the need for flatter photomasks with specifications under 0.5 micron. Currently the mask blank substrates are measured after polishing, and all subsequent process steps are assumed to have little or no impact on the final mask flatness. With today’s ever tightening flatness requirements, this assumption can no longer be taken for granted. This paper investigates the distortions seen at the reticle surface induced by the mounting of a standard optical pellicle frame to the photomask and relates these distortions to the pellicle frame flatness. The experiment involves using a set of mask blanks that are better than 0.5 micron flatness with similar form errors before attaching the pellicle. Two groups of pellicles are used to create two distinct frame flatness populations: one set assumed to be within specification as purchased; and a second set of pellicles that are intentionally distorted. Mask flatness is compared before and after mounting the pellicles, and all frames are measured for flatness. Correlation between the frame flatness and form to the measured distortion on the reticle surface are made and discussed, and a practical guideline for selecting an appropriate blank flatness and pellicle flatness to achieve the desired reticle flatness is suggested.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Christopher Lee, Kenneth Racette, and Monica Barrett "Investigation of pellicle influence on reticle flatness", Proc. SPIE 5853, Photomask and Next-Generation Lithography Mask Technology XII, (28 June 2005);

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