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Journal of Micro/Nanolithography, MEMS, and MOEMS

Methods for the synthesis and purification of polycycloalkane candidates for photolithography immersion fluids at 193 nm: requirements for removal of oxygen
Author(s): Juan Lopez Gejo; Joy T. Kunjappu; Willard E. Conley; Paul A. Zimmerman; Nicholas J. Turro
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Paper Abstract

Cycloalkanes are candidates for immersion fluids because of their potential for low absorption in the 193-nm region and for a high refractive index (RI). We have developed an empirical correlation between refractive index and density of alkanes, which allows a prediction of the best candidates for immersion fluids based on the alkane structure. In particular, the correlation reveals that polycycloalkanes such as perhydrophenanthrene (PHPh) and perhydrodropyrene (PHPy), which have a higher RI than linear or cyclic alkanes, will be excellent candidates for immersion fluids at 193 nm. Therefore, PHPh and PHPy were synthesized by exhaustive hydrogenation of phenanthrene and pyrene. However, methods for the purification of the synthesized and commercial alkanes such as cyclodecane (CYD), cyclohexane (CYX), pentane (PNT), and decalin (DEC) are required in order to determine the actual absorption of candidates at 193 nm. The presence of an absorbing impurity at 193 nm can cause the premature elimination of otherwise excellent potential candidates. A rather subtle impurity is molecular oxygen, which does not itself absorb at 193 nm, but which forms complexes with alkanes that do absorb at 193 nm. In this case, the "impurity" is readily eliminated by simple purging with nitrogen or argon gas.

Paper Details

Date Published: 1 July 2007
PDF: 7 pages
J. Micro/Nanolith. MEMS MOEMS 6(3) 033003 doi: 10.1117/1.2778641
Published in: Journal of Micro/Nanolithography, MEMS, and MOEMS Volume 6, Issue 3
Show Author Affiliations
Juan Lopez Gejo, Columbia Univ. (United States)
Joy T. Kunjappu, City Univ. of New York/Brooklyn College (United States)
Willard E. Conley, Freescale Semiconductor, Inc. (United States)
Paul A. Zimmerman, SEMATECH, Inc. (United States)
Nicholas J. Turro, Columbia Univ. (United States)

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