Absorption coefficient of metal-containing photoresists in the extreme ultraviolet

Roberto Fallica; Jarich Haitjema; Lianjia Wu; Sonia Castellanos Ortega; Albert M. Brouwer; Yasin Ekinci

doi:10.1117/1.JMM.17.2.023505

10 May 2018 Absorption coefficient of metal-containing photoresists in the extreme ultraviolet

Roberto Fallica, Jarich Haitjema, Lianjia Wu, Sonia Castellanos Ortega, Albert M. Brouwer, Yasin Ekinci

Journal of Micro/Nanolithography, MEMS, and MOEMS, Vol. 17, Issue 2, 023505 (May 2018). https://doi.org/10.1117/1.JMM.17.2.023505

Abstract

The amount of absorbed light in thin photoresist films is a key parameter in photolithographic processing, but its experimental measurement is not straightforward. The optical absorption of metal oxide-based thin photoresist films for extreme ultraviolet (EUV) lithography was measured using an established methodology based on synchrotron light. Three types of materials were investigated: tin cage molecules, zirconium oxoclusters, and hafnium oxoclusters. The tin-containing compound was demonstrated to have optical absorption up to three times higher than conventional organic-based photoresists have. The absorptivity of the zirconium oxocluster was comparable to that of organic polymer-based photoresists, owing to the low absorption cross section of zirconium at EUV. The hafnium-containing resist shows about twice as high absorptivity as an organic photoresist, owing to the significantly higher absorbance of hafnium. From the chemical composition and crystal structure, the density of the spin-coated films was determined. Using the density of the films and the tabulated data for atomic cross section at EUV, the expected absorptivity of these resists was calculated and discussed in comparison to the experimental results. The agreement between measured and expected absorption was fairly good with some substantial discrepancies due to differences in the actual film density or to thickness inhomogeneity due to the spin coating. The developed method here enables the accurate measurement of the EUV absorption of the photoresists and can contribute to the further development of EUV resists and more accurate lithographic modeling.

Citation Download Citation

Roberto Fallica, Jarich Haitjema, Lianjia Wu, Sonia Castellanos Ortega, Albert M. Brouwer, and Yasin Ekinci "Absorption coefficient of metal-containing photoresists in the extreme ultraviolet," Journal of Micro/Nanolithography, MEMS, and MOEMS 17(2), 023505 (10 May 2018). https://doi.org/10.1117/1.JMM.17.2.023505

Received: 30 January 2018; Accepted: 12 April 2018; Published: 10 May 2018

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