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High-contrast, high-sensitivity aqueous base-developable polynorbornene dielectric

Authors

  • Mehrsa Raeis-Zadeh,

    Corresponding author
    1. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, Georgia 30332-0100
    • School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, Georgia 30332-0100
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  • Paul A. Kohl

    1. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Dr., Atlanta, Georgia 30332-0100
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Abstract

The impact of multifunctional epoxy-based additives on the crosslinking, photolithographic properties, and adhesion properties of a tetramethyl ammonium hydroxide developable, polynorbornene (PNB)-based dielectric was investigated. Three different multifunctional epoxy additives were investigated: di-functional, tri-functional, and tetra-functional epoxy compounds. The tetra-functional epoxy crosslinker enhanced the UV absorbing properties of the polymer at 365 nm wavelength. It was found that the epoxy photo-catalyst could be efficiently activated without a photosensitizer when the tetra-functional epoxy was used. The polymer mixture with additional (3 wt %) tetra-functional epoxy crosslinker and without a UV sensitizer showed improved sensitivity by a factor of 4.7 as compared to a polymer mixture containing the same number of equivalents of non-UV sensitive epoxy with a UV sensitizer. The contrast improved from 7.4 for the polymer mixture with non-UV absorbing epoxy and a UV sensitizer to 33.4 for the new formulation with 3 wt % tetra-functional epoxy and no UV sensitizer. The addition of the tetra-functional epoxy crosslinker also improved the polymer-to-substrate adhesion, which permitted longer development times, and allowed the fabrication of high-aspect-ratio structures. Hollow-core pillars were fabricated in 96-µm thick polymer films with a depth-to-width aspect-ratio of 14 : 1. The degree of crosslinking in the cured films was studied by nanoindentation and swelling measurements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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