8 March 2016 Improving focus performance at litho using diffraction-based focus metrology, novel calibration methods, interface, and control loop
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In advanced optical lithography the requirements of focus control continues to tighten. Usable depth of focus (DoF) is already quite low due to typical sources of focus errors, such as topography, wafer warpage and the thickness of photoresist. And now the usable DoF is further decreased by hotspots (design and imaging hotspots). All these have put extra challenges to improve focus metrology, scanner focus stability calibrations and on-product correction mechanisms.

Asymmetric focus targets are developed to address robustness in focus measurements using diffraction-based focus (DBF and μDBF) metrology. A new layout specific calibration methodology is introduced for baseline focus setup and control in order to improve scanner focus uniformity and stability using the measurements of the above mentioned asymmetric targets. A similar metrology is also used for on product focus measurements. Moreover, a few novel alternative methods are also investigated for on-product focus measurements.

Data shows good correlation between DBF and process on record (POR) method using traditional FEM. The new focus calibration demonstrated robustness, stability and speed. This technical publication will report the data from all the above activities including results from various product layers.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jiarui Hu, Jiarui Hu, Y. L. Chen, Y. L. Chen, K. H. Chen, K. H. Chen, Brian Lee, Brian Lee, Frankie Tsai, Frankie Tsai, C. M. Ke, C. M. Ke, C. H. Liao, C. H. Liao, Desmond Ngo, Desmond Ngo, Benny Gosali, Benny Gosali, Robin Tijssen, Robin Tijssen, Vincent Huang, Vincent Huang, Ward Tu, Ward Tu, Marc Noot, Marc Noot, Maryana Escalante Marun, Maryana Escalante Marun, Christian Leewis, Christian Leewis, Carlo Luijten, Carlo Luijten, Frank Staals, Frank Staals, Martijn Van Veen, Martijn Van Veen, Francois Furthner, Francois Furthner, Stuart Young, Stuart Young, Kaustuve Bhattacharyya, Kaustuve Bhattacharyya, "Improving focus performance at litho using diffraction-based focus metrology, novel calibration methods, interface, and control loop", Proc. SPIE 9778, Metrology, Inspection, and Process Control for Microlithography XXX, 977829 (8 March 2016); doi: 10.1117/12.2220373; https://doi.org/10.1117/12.2220373

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