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5 April 2007Non-linear methods for overlay control
Overlay requirements for DRAM devices are decreasing faster than anticipated. With current methods overlay becomes
ever harder to control and therefore novel techniques are needed. This paper will present an alignment based method to
address this issue. The use and impact of several non-linear alignment models will be presented. Issues here include the
number of alignment marks to use and how to distribute them over the wafer in order to minimize the throughput impact
while at the same time providing maximum wafer coverage. Integrating this method into a R2R environment strongly
depends on the stability of the process. Advantages and disadvantages of the method will be presented as well as
experimental results. Finally some comments will be given on the need and feasibility of wafer by wafer corrections.
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Michiel Kupers, Dongsub Choi, Boris Habets, Geert Simons, Erik Wallerbos, "Non-linear methods for overlay control," Proc. SPIE 6518, Metrology, Inspection, and Process Control for Microlithography XXI, 65184S (5 April 2007); https://doi.org/10.1117/12.713092