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

Juan Lopez Gejo; Joy Kunjappu; Nicholas J. Turro; Willard E. Conley

doi:10.1117/1.2435730

Abstract

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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Juan Lopez Gejo, Juan Lopez Gejo, Joy Kunjappu, Joy Kunjappu, Nicholas J. Turro, Nicholas J. Turro, Willard E. Conley, Willard E. Conley, } "Amplification of the index of refraction of aqueous immersion fluids with crown ethers," Journal of Micro/Nanolithography, MEMS, and MOEMS 6(1), 013002 (1 January 2007). https://doi.org/10.1117/1.2435730 . Submission:

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