Study of air bubble induced light scattering effect on the image quality in 193 nm immersion lithography

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dc.contributor.author Fan, Yongfa
dc.contributor.author Lafferty, Neal
dc.contributor.author Bourov, Anatoly
dc.contributor.author Zavyalova, Lena
dc.contributor.author Smith, Bruce
dc.date.accessioned 2010-02-03T21:58:17Z
dc.date.available 2010-02-03T21:58:17Z
dc.date.issued 2004
dc.identifier.citation Proceedings of the SPIE Conference on Optical Microlithography XVII, vol. 5377, pp. 477-486, 2004 en_US
dc.identifier.uri http://hdl.handle.net/1850/11380
dc.description.abstract As an emerging technique, immersion lithography offers the capability of reducing critical dimensions by increasing numerical aperture (NA) due to the higher refractive indices of immersion liquids than that of air. Among the candidates for immersion liquids, water appears to be an excellent choice due to its high transparency at a wavelength of 193 nm, as well as its immediate availability and low processing cost. However, in the process of forming a water fluid layer between the resist and lens surfaces, air bubbles are often created due to the high surface tension of water. The presence of air bubbles in the immersion layer will degrade the image quality because of the inhomogeneity induced light scattering in the optical path. Therefore, it is essential to understand the air bubble induced light scattering effect on image quality. Analysis by geometrical optics indicates that the total reflection of light causes the enhancement of scattering in the region where the scattering angle is less than the critical scattering angle, which is 92 degrees at 193 nm. Based on Mie theory, numerical evaluation of scattering due to air bubbles, polystyrene spheres and PMMA spheres was conducted for TE, TM or unpolarized incident light. Comparison of the scattering patterns shows that the polystyrene spheres and air bubbles resemble each other with respect to scattering properties. Hence polystyrene spheres are used to mimic air bubbles in studies of lithographic imaging of “bubbles” in immersion water. In direct interference lithography, it is found that polystyrene spheres (2 μm in diameter) 0.3 mm away from the resist surface would not image, while for interferometric lithography at 0.5NA, this distance is estimated to be 1.3 mm. Surprisingly, polystyrene spheres in diameter of 0.5 μm (which is 5 times larger than the interferometric line-width) will not image. It is proposed that “bubbles” are repelled from contact with the resist film by surface tension. The scatter of exposure light can be characterized as “flare”. This work shows that microbubbles are not a technical barrier to immersion lithography. en_US
dc.language.iso en_US en_US
dc.publisher SPIE en_US
dc.relation.ispartofseries vol. 5377 en_US
dc.subject Immersion en_US
dc.subject Mie scattering en_US
dc.subject Optical lithography en_US
dc.title Study of air bubble induced light scattering effect on the image quality in 193 nm immersion lithography en_US
dc.type Proceedings en_US

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