Defects, overlay, and focus performance improvements with five generations of immersion exposure systems

This paper discusses the current performance and the evolution of five generations TWINSCAN immersion scanning exposure tools. It is shown that production worthy overlay and focus performance can be achieved at high scan speeds. The more critical part for immersion tools is related to defects, but also here improvements resulted in production worthy defect levels. In order to keep the defect level stable special measures are needed in the application of wafers. Especially Edge Bead Removal (EBR) design and wafer bevel cleanliness are important.