System-level line-edge roughness limits in extreme ultraviolet lithography

As critical dimensions shrink, line-edge roughness (LER) and linewidth roughness become of increasing concern. Traditionally, LER is viewed as a resist-limited effect; however, as critical dimensions shrink and LER requirements become proportionally more stringent, system-level effects begin to play an important role. Recent advanced extreme-ultraviolet resist testing results have demonstrated lower bounds on achievable LER at the level of approximately 2-3 nm. Here, the authors use modeling to demonstrate that a significant portion of this low bound may, in fact, be do to system-level effects and, in particular, the mask. Of concern are both LER on the mask as well as roughness of the multilayer reflector. Modeling also shows roughness (flare) in the projection optics not to be of concern. (c) 2008 American Vacuum Society.