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4 May 2005 Resist component leaching in 193-nm immersion lithography
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The leaching of ionic PAGs from model resist films into a static water volume is shown to follow first order kinetics. From the saturation concentration and the leaching time constant, the leaching rate at time zero is obtained which is a highly relevant parameter for evaluating lens contamination potential. The levels of leaching seen in the model resists generally exceed both static and rate-based dynamic leaching specifications. The dependence of leaching on anion structure shows that more hydrophobic anions have lower saturation concentration; however, the time constant of leaching increases with anion chain length. Thus in our model system, the initial leaching rates of nonaflate and PFOS anions are identical. Investigation of a water pre-rinse process unexpectedly showed that some PAG can still be leached from the surface although the pre-rinse times greatly exceeded the times required for saturation of the leaching phenomenon, which are expected to correspond to complete depletion of leachable PAG from the surface. A model is proposed to explain this phenomenon through re-organization of the surface as the surface energy changes during the air/water/air contact sequence of the pre-rinse process.
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Ralph R. Dammel, Georg Pawlowski, Andrew Romano, Frank M. Houlihan, Woo-Kyu Kim, Raj Sakamuri, and David Abdallah "Resist component leaching in 193-nm immersion lithography", Proc. SPIE 5753, Advances in Resist Technology and Processing XXII, (4 May 2005);

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