5 November 2005 A practical alternating PSM modeling and OPC approach to deal with 3D mask effects for the 65nm node and beyond
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Abstract
Alternating PSM (Alt-PSM) has been recognized as a logical Resolution Enhancement Technique (RET) candidate for the 65nm technology node. One of the key properties this technique has to offer is high Depth of Focus (DOF) and lower Mask Error Enhancement Factor (MEEF). The so-called image imbalance is an Alt-PSM specific property which, if not dealt with correctly, constrains the added DOF. Because of mask topography, intensity differences caused by light scattering become evident between π (180°) and zero degree phase shifters. This causes a line shift that is inversely proportional to the pitch. The traditional solution of applying a fixed trench bias increases the width if the π phase shifter to level out intensities and thus minimize image imbalance. This technique may no longer be sufficient at the 65nm technology node. With the requirement to print even smaller pitches together with a tighter Critical Dimension (CD) budget, intensity imbalance is a larger concern. It may be necessary to apply a pitch dependent or variable trench bias. In this paper, we present a practical OPC modeling approach that accounts for image imbalance. The 2D modeling approach uses boundary layers to represent the 3D effect of light scattering. We demonstrate that with the boundary layer model, it is possible to predict image imbalance caused by mask 3D effects. The model can then be used either to determine the nominal trench bias or can be integrated into the OPC engine to apply a variable trench bias. Results are compared to rigorous Electro Magnetic Field (EMF) simulations and experimental exposures using an ArF scanner, targeting pitches of 130nm and above.
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Martin Drapeau, Paul J. M. van Adrichem, Lieve van Look, Bryan S. Kasprowicz, "A practical alternating PSM modeling and OPC approach to deal with 3D mask effects for the 65nm node and beyond", Proc. SPIE 5992, 25th Annual BACUS Symposium on Photomask Technology, 59921T (5 November 2005); doi: 10.1117/12.632040; https://doi.org/10.1117/12.632040
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