Leaching Phenomena and their Suppresion in 193 nm Immersion Lithography

• Published in: Journal of Photopolymer Science and Technology Vol. 18; no. 5; pp. 593 - 602
• Main Authors: Dammel, Ralph R., Pawlowski, Georg, Romano, Andrew, Hoolihan, Frank M., Kim, Woo-Kyu, Sakmuri, Raj, Abdallah, David, Padmanaban, Murirathna, Rahman, M. Dalil, McKenzie, Douglas
• Format: Journal Article
• Language: English
• Published: Hiratsuka The Society of Photopolymer Science and Technology(SPST) 01.01.2005; Japan Science and Technology Agency
• Subjects: barrier coat; immersion lithography; kinetics; leaching rate; PAG leaching; photoresist; protective coat; top
• ISSN: 0914-9244; 1349-6336
• DOI: 10.2494/photopolymer.18.593

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. The efficiency of developer-soluble top barrier layers in reducing leaching and their impact on lithography are described as well as the effect of PAG doping into the top layers.