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

摘要

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.