Debris transport analysis at the intermediate focus of an extreme ultraviolet light source

Abstract

As extreme ultraviolet light lithography matures, critical deficits in the technology are being resolved. Research has largely focused on solving the debris issue caused by using warm (Te ∼ 30 eV) and dense (ne ∼ 1020 cm−3) plasma to create 13.5-nm light. This research has been largely focused on the mitigation of the debris between the plasma and the collector optics. The next step of debris mitigation is investigated, namely the effect of debris mitigation on the transport of undesired contaminants to the intermediate focus (IF). In order to investigate emissions from the IF, the Center for Plasma-Material Interactions at the University of Illinois at Urbana-Champaign has developed the Sn intermediate focus flux emission detector. The effects of a secondary RF-plasma, buffer gas flow rate, chamber pressure, and charged plate deflection are investigated. By increasing the chamber pressure to 10 mTorr, flowing 1000 sccm Ar buffer gas, and utilizing charged particle deflection, it is possible to reduce the measured number of post-IF species by greater than 99%. Furthermore, it is shown that typical debris mitigation techniques lead to the development of a plasma near the IF that can be detrimental to post-IF optics.