Product layout induced topography effects on intrafield levelling

Abstract : With continuing dimension shrinkage using the TWINSCAN NXT:1950i scanner on the 28nm node and beyond, the imaging depth of focus (DOF) becomes more critical. Focus budget breakdown studies [Ref 2, 5] show that even though the intrafield component stays the same, it becomes a larger relative percentage of the overall DOF. Process induced topography along with reduced Process Window can lead to yield limitations and defectivity issues on the wafer. In a previous paper, the feasibility of anticipating the scanner levelling measurements (Level Sensor, Agile and Topography) has been shown [1]. This model, built using a multiple variable analysis (PLS: Partial Least Square regression) and GDS densities at different layers showed prediction capabilities of the scanner topography readings up to 0.78 Q² (the equivalent of R² for expected prediction). Using this model, care areas can be defined as parts of the field that cannot be seen nor corrected by the scanner, which can lead to local DOF shrinkage and printing issues. This paper will investigate the link between the care areas and the intrafield focus that can be seen at the wafer level, using offline topography measurements as a reference. Some improvements made on the model are also presented.
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Submitted on : Monday, February 15, 2016 - 9:02:08 AM
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J-G Simiz, T Hasan, F Staals, B Le-Gratiet, Wim Tel, et al.. Product layout induced topography effects on intrafield levelling. EMLC 2015, 31st European Mask and Lithography Conference, Jun 2015, Eindhoven, Netherlands. pp.96610R, ⟨10.1117/12.2194079⟩. ⟨ujm-01272856⟩

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