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

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