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Are pattern and probe aberration monitors ready for prime time?
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Paper Abstract

The first experimental results for interferometric pattern and probe-based aberration monitors designed for use at 193nm wavelength have been obtained using the Zeiss Aerial Image Measurement System (AIMSFab 193TM). Designs developed earlier are being tested on phase-shifting masks in collaboration with Photronics Inc. for use as precision instruments to measure aberrations. Comparison of the results with SEM measurements of the mask and simulations help to characterize second-order effects due to mask topography, high-NA electric-field vector addition, and mask fabrication tolerances in projection printing of advanced process monitors on special phase-shifting test reticles. For this study the aberration targets have been factored into their basic elements, such as probes, rings, lines, and rings surrounding probes. Through-focus studies of well-formed 120nm probes showed peak intensities for actual mask dimensions that were below ideal mask values by a factor of 0.70, 0.49, 0.26, and 0.29 for 0°, 90°, 180°, and 270°, respectively. Measurements for lines and outer rings were consistent with probes and showed intensities of 0.86 and 0.61 of those expected for ideal 0° and 180° 125nm lines in wafer dimensions. The focus sensitivity of the composite mask was clearly larger than that of typical features. However, to leverage the full sensitivity from interference with the probe, the probe must be resized as a function of its phase depth due to electromagnetic effects and the probes must be protected by the use of larger 2D feature biases. Operation at a partial coherence factor of 0.15 or below is recommended to preserve the contribution of the second ring and balance out unwanted proximity effects.

Paper Details

Date Published: 12 May 2005
PDF: 12 pages
Proc. SPIE 5754, Optical Microlithography XVIII, (12 May 2005); doi: 10.1117/12.600611
Show Author Affiliations
Garth C. Robins, Univ. of California/Berkeley (United States)
Andrew R. Neureuther, Univ. of California/Berkeley (United States)

Published in SPIE Proceedings Vol. 5754:
Optical Microlithography XVIII
Bruce W. Smith, Editor(s)

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