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Amplification of the index of refraction of aqueous immersion fluids with crown ethers

[+] Author Affiliations
Juan López-Gejo

Columbia University, Department of Chemistry, New York, New York 10027

Joy T. Kunjappu

Columbia University, Department of Chemistry, New York, New York 10027

Nicholas J. Turro

Columbia University, Department of Chemistry, New York, New York 10027

Will Conley

Freescale Semiconductor, Centre de Recherche, 870 rue Jean Monnet, Crolles, France

J. Micro/Nanolith. MEMS MOEMS. 6(1), 013002 (March 09, 2007). doi:10.1117/1.2435730
History: Received June 03, 2006; Revised September 25, 2006; Accepted October 04, 2006; Published March 09, 2007
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There is a current need for high refractive index (RI) materials that can be used in aqueous systems for improving 193-nm immersion photolithography. Although heavy metal salts such as Ca2+ and Ba2+ have the potential to substantially increase the RI of aqueous solutions, the water solubility of these salts with common anions is often too low to achieve concentrations that significantly increase the RI to the desired values. We therefore investigate the use of crown ethers to enhance the solubility of these cations. Most of crown ethers are soluble in water, are inexpensive materials, and are available commercially. 15-crown-5-ether and 12-crown-4-ether are liquids at room temperature and therefore can be used as neat immersion fluids without dilution in water. Saturation of crown ethers with inorganic salts do not lead to any increase in the refractive index due to their low solubility in such an apolar medium. Thus, the use of inorganic salts as refractive index enhancement agents does not seem to be a desirable proposition in the present case. Instead, the use of crown ethers or their derivatives can be an alternative system, since these compounds have properties such as density, viscosity, and boiling point similar to aqueous media.

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© 2007 Society of Photo-Optical Instrumentation Engineers

Citation

Juan López-Gejo ; Joy T. Kunjappu ; Nicholas J. Turro and Will Conley
"Amplification of the index of refraction of aqueous immersion fluids with crown ethers", J. Micro/Nanolith. MEMS MOEMS. 6(1), 013002 (March 09, 2007). ; http://dx.doi.org/10.1117/1.2435730


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