18 March 2016 EUV implementation of assist features in contact patterns
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Abstract
As feature sizes become smaller and smaller, the complexity and the cost of using multiple patterning with 193i becomes a significant issue in lithography. Hence, EUV starts to play an important role for 7nm node and beyond. Industry is now investigating solutions on all major EUV components – source, resist mask technology, as well as resolution enhancement techniques (RET), including sub-resolution assist features (SRAFs). Unlike ArF lithography, the non-telecentricity of the EUV optical system coupled with the relatively thick mask stack causes shadowing effects. This asymmetric imaging may in turn have an impact on assist feature placement, requiring different SRAF rules for different directions at the edges and corners. In this work, simulation studies were conducted using Calibre on 20x20 nm contact patterns through pitch to investigate the impact of assist features. Assist features were varied as a function of horizontal / vertical positions independently and the image quality parameters such as depth of focus (DOF), MEEF, best focus (BF) shift and overlapping process window were monitored with and without SRAFs. Both rules-based and model based assist feature placements were implemented for selected patterns. Results indicate that inclusion of assist features for contact arrays improve individual and overlapping process windows with minimal effect on best focus shift. Wafer data collected from these patterns confirmed the improvement in overlapping process window with the inclusion of assist features.
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Fan Jiang, Fan Jiang, Ananthan Raghunathan, Ananthan Raghunathan, Martin Burkhardt, Martin Burkhardt, Nicole Saulnier, Nicole Saulnier, Alexander Tritchkov, Alexander Tritchkov, Srividya Jayaram, Srividya Jayaram, James Word, James Word, } "EUV implementation of assist features in contact patterns", Proc. SPIE 9776, Extreme Ultraviolet (EUV) Lithography VII, 97761U (18 March 2016); doi: 10.1117/12.2218315; https://doi.org/10.1117/12.2218315
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