Editing Immersion lithography (section)

==Background==
The ability to resolve features in [[optical lithography]] is directly related to the [[numerical aperture]] of the imaging equipment, the numerical aperture being the sine of the maximum refraction angle multiplied by the [[refractive index]] of the medium through which the light travels. The lenses in the highest resolution "dry" photolithography scanners focus light in a cone whose boundary is nearly parallel to the wafer surface. As it is impossible to increase resolution by further refraction, additional resolution is obtained by inserting an immersion medium with a higher index of refraction between the lens and the wafer. The blurriness is reduced by a factor equal to the refractive index of the medium. For example, for water immersion using [[Ultraviolet|ultraviolet light]] at 193&nbsp;nm wavelength, the index of refraction is 1.44.<ref>{{Cite book |last1=Smith |first1=Bruce W. |last2=Kang |first2=Hoyoung |last3=Bourov |first3=Anatoly |last4=Cropanese |first4=Frank |last5=Fan |first5=Yongfa |title=Optical Microlithography XVI |chapter=Water immersion optical lithography for 45-nm node |editor-first1=Anthony |editor-last1=Yen |date=2003-06-26 |chapter-url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/5040/0000/Water-immersion-optical-lithography-for-the-45-nm-node/10.1117/12.485489.full   |publisher=SPIE |volume=5040 |pages=679–689 |doi=10.1117/12.485489|bibcode=2003SPIE.5040..679S }}</ref>

The resolution enhancement from immersion lithography is about 30–40% depending on materials used. However,{{clarify|date=November 2020|reason="However" implies a contrast, but both sentences describe advantages.}} the depth of focus, or tolerance in wafer topography flatness, is improved compared to the corresponding "dry" tool at the same resolution.<ref>B. J. Lin, J. Microlith Microfab. Microsyst. 1, 7 (2002).</ref>

The idea for immersion lithography was patented in 1984 by Takanashi et al.<ref>A. Takanashi, T. Harada, M. Akeyama, Y. Kondo, T. Karosaki, S. Kuniyoshi, S. Hosaka, and Y. Kawamura, U. S. Patent No. 4,480,910 (1984)</ref> It was also proposed by Taiwanese engineer [[Burn J. Lin]] and realized in the 1980s.<ref>[[Burn J. Lin]] (1987). "The future of subhalf-micrometer optical lithography". ''Microelectronic Engineering'' '''6''', 31&ndash;51</ref> In 2004, [[IBM]]'s director of [[silicon]] technology, [[Ghavam Shahidi]], announced that IBM planned to commercialize lithography based on light filtered through water.<ref name="businessweek">{{Cite web |url=http://www.businessweek.com/technology/content/jan2004/tc20040121_4923_tc139.htm |title=A Whole New World of Chips |website=[[Business Week]] |url-status=dead |archive-url=https://web.archive.org/web/20110221072557/http://www.businessweek.com/technology/content/jan2004/tc20040121_4923_tc139.htm |archive-date=2011-02-21 }}</ref>