Controlling the Global and Local CD uniformity (GCDU and LCDU) of Contact Holes (CH) and the associated edge placement errors are important for the implementation of EUV lithography in high-volume production at memory chip manufacturers. The GCDU describes the average CH CD variability within and between the fields on the wafer, while the LCDU comprises the CH-to-CH variation between neighboring CHs. We have experimentally measured these parameters on a representative memory layer to understand the current performance, and suggest possibilities and pathways for future improvement. We report on an extensive experimental imaging study of a 40 nm pitch square CH array use case, using ASML’s NXE:3300 EUV exposure tool at imec. We decompose the GCDU into Intra-Field and Intra-Wafer signatures, and the LCDU into systematic and stochastic components. Through this decomposition, we can assess the contribution of mask, scanner and resist process. A 10-month monitor evaluates the changes over time of these respective components and the relation between GCDU and LCDU. The mask contribution to LCDU was further examined by a CH-to-CH comparison of mask and wafer measurements. LCDU improvements could be obtained by optimizing the source for a better contrast through focus (6% LCDU improvement w.r.t. a Standard Quasar source shape at best focus, up to 30% in defocus) as well as by a resist stack optimization. Optimized resist stacks delivered 15% improvements in a lower LCDU on one hand, or a lower dose-tosize on the other hand. The results of this pitch 40 nm contact hole study lead to a better understanding of the needs for mask and scanner for the memory use case at 0.33 NA EUV lithography.
Lieve Van Look , Joost Bekaert, Andreas Frommhold, Eric Hendrickx, Gijsbert Rispens, and Guido Schiffelers, "Optimization and stability of CD variability in pitch 40 nm contact holes on NXE:3300," Proc. SPIE 10809, International Conference on Extreme Ultraviolet Lithography 2018, 108090M (Presented at SPIE Photomask Technology + Extreme Ultraviolet Lithography: September 19, 2018; Published: 3 October 2018); https://doi.org/10.1117/12.2501797.
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