Characterization of imaging performance for immersion lithography at NA=0.93

Abstract

We present a systematic analysis of the imaging performance for a 0.93 numerical aperture (NA) state-of-the-art immersion lithography scanner and we compare this performance to its dry NA=0.93 counterpart. The increased depth of focus (DOF) enabled by immersion lithography presents a set of advantages for semiconductor manufacturing which we explore in this article. First, we show that 0.93 NA immersion prevents, for a 65nm gate-level process, the need for imposing pitch restrictions with an attenuated-PSM solution; something not possible with an equivalent "dry" process. Second, we demonstrate the superior critical dimension uniformity (CDU) of an immersion process in the presence of realistic focus variations typically encountered in semiconductor manufacturing. Third, we confirm that the through-pitch behavior of "wet" and "dry" scanners is well matched, enabling the possibility of transferring optical proximity corrections (OPC) between the two types of lithography scanners. The transferability of OPC is key to enabling a fast insertion of immersion lithography into the manufacturing process for the 65nm and 45nm nodes. Finally, we conclude that, from an imaging perspective, immersion is ready for high-volume manufacturing.