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Proceedings Paper

Overlay target design characterization and optimization for tungsten CMP
Author(s): Stephen Hsu; Mircea V. Dusa; Joost Vlassak; Cameron Harker; Michelle L. Zimmerman
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Paper Abstract

As the semiconductor industry pushes design rules to 0.25 micron and below, tungsten chemical mechanical polishing (WCMP) is emerging as a key process that reduces defect density, increases circuit density and improves yield. However, due to the non-selective nature of the WCMP process, the stepper alignment marks and the overlay metrology target can be seriously damaged during the polishing process. The result of this damage may contribute to the total misregistration error. This paper describes a systematic overlay target optimization on various WCMP layers in order to evaluate and reduce target and measurement noise. Eight different target designs were evaluated on three different metal layers. The quantification of overall measurement counts, measurement precision, modeled residual, and kernel analysis was used as the metric for determining the overall effectiveness of each overlay target design. Short and long term gauge studies were performed to verify the measurement capability of the metrology tool. An experiment was performed in which a known offset was introduced on the stepper to confirm that the overlay measurement responded accordingly. To verify the robustness of the target, oxide thickness, tungsten thickness and polish time were varied on one of the three layers. The measured overlay error was also correlated to cross-section scanning electron microscope (SEM) results.

Paper Details

Date Published: 8 June 1998
PDF: 11 pages
Proc. SPIE 3332, Metrology, Inspection, and Process Control for Microlithography XII, (8 June 1998); doi: 10.1117/12.308744
Show Author Affiliations
Stephen Hsu, National Semiconductor Corp. (United States)
Mircea V. Dusa, National Semiconductor Corp. (United States)
Joost Vlassak, National Semiconductor Corp. (United States)
Cameron Harker, KLA-Tencor Corp. (United States)
Michelle L. Zimmerman, KLA-Tencor Corp. (United States)

Published in SPIE Proceedings Vol. 3332:
Metrology, Inspection, and Process Control for Microlithography XII
Bhanwar Singh, Editor(s)

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