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10 May 2005 Wavelength dependent mask defects
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For years there has been a mismatch between the photomask inspection wavelength and the usage conditions. While the non-actinic inspection has been a source for concern, there has been essentially no evidence that a defect "escaped" the mask production process due to the inspection mismatch. This paper will describe the discovery of one such defect, as well as the diagnostic and inspection techniques used to identify the location, analyze the composition, and determine the source of the printed wafer defect. Conventional mask inspection techniques revealed no defects, however an actinic Aerial Image Metrology System (AIMS) revealed a 1.5 mm region on the mask with up to 59% transmission reduction at 193 nm. Further diagnostics demonstrated a strong wavelength dependence which accounted for the near invisibility of the defect at I line (365 nm) or even DUV (248 nm) wavelengths, which had 0% and 5% respective transmission reductions. Using some creative imaging techniques via AIMS tool and modeling, the defect was deduced to have a three dimensional Gaussian absorption character, with total width approximately 1.5 mm. Several non-destructive diagnostic techniques were developed to determine the composition and location of the defect within the substrate. These results will be described in addition to identifying methods for ensuring product quality in the absence of actinic inspection.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Karen Badger, Shahid Butt, Jay Burnham, Tom Faure, Michael Hibbs, Jed Rankin, David Thibault, and Andrew Watts "Wavelength dependent mask defects", Proc. SPIE 5752, Metrology, Inspection, and Process Control for Microlithography XIX, (10 May 2005);

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