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. Increased accuracy requirements and overall complexity in product stacks require a sensor with a higher flexibility. To address this an advanced metrology system is introduced in the fab, providing full flexibility in the selection of measurement wavelengths. On top of the wavelength flexibility, the increased wavelength switching speed enables the use of asymmetry robust recipes by combining multiple wavelength measurements at each overlay target.
In this paper we will introduce a method to select the most accurate multi-wavelength recipe that provides significant improvement in accuracy compared to the best single wavelength recipe. We will introduce KPIs to monitor the health of the multi-wavelength measurement. The KPIs are reported per site indicating the accuracy for every measured point.
Additionally we will show our steps towards the recovery of the points flagged by multi-wavelength KPI by a combination of measuring more wavelengths and an accuracy guided region of interest selection.
In this technical presentation we will review the above developments and remaining gaps in technology (litho and dimensional metrology applications), as well as design and integration. Mitigation of such challenges need a large team effort that is industry-wide and not just limited in litho.
In order to address the signal formation physics, an effort is made towards studying the swing-curve phenomena through wavelength and polarizations on production stacks using simulations as well as experimental technique using DBO. The results provide a wealth of information on target and recipe selection for robustness. Details from simulation and measurements will be reported in this technical publication.
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.
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