Editing Immersion lithography (section)

==Defects==
Defect concerns, e.g.,  water left behind (watermarks) and loss of resist-water adhesion (air gap or bubbles), have led to considerations of using a topcoat layer directly on top of the [[photoresist]].<ref>Y. Wei and R. L. Brainard, Advanced Processes for 193-nm Immersion Lithography, (c) SPIE 2009, Ch.6.</ref> This topcoat would serve as a barrier for chemical diffusion between the liquid medium and the photoresist. In addition, the interface between the liquid and the topcoat would be optimized for watermark reduction. At the same time, defects from topcoat use should be avoided.

As of 2005, Topcoats had been tuned for use as [[antireflection]] coatings, especially for hyper-NA (NA>1) cases.<ref>J. C. Jung et al., Proc. SPIE 5753 (2005).</ref>

By 2008, defect counts on wafers printed by immersion lithography had reached zero level capability.<ref>[https://www.researchgate.net/publication/228517572_Image_contrast_contributions_to_immersion_lithography_defect_formation_and_process_yield B. Rathsack et al., Proc. SPIE 6924, 69244W (2008).]</ref>