(Georgia Institute of Technology, 2014-12)
Schwartz, Jared M.; Sutlief, Alexandra E.; Kohl, Paul A.; Mueller, Brennen K.
The mechanical properties of an aqueous developed, chemically amplified, polynorbornene-based permanent dielectric have been
investigated. The previously reported hexafluoroisopropanol norbornene and tert-butyl ester norbornene copolymer has been modified
via two routes to improve the mechanical properties of the polymer and enable thick-film deposition. First, a third monomer, butyl
norbornene (ButylNB) was added to the polymer backbone. The inclusion of 24 mol% ButylNB lowered the elastic modulus from
2.64 to 2.35 GPa and raised the dielectric constant from 2.78 to 3.48. The second approach added a lowmolecular weight, plasticizing
additive in the copolymer formulation. Many additives were immiscible with the resin or did not affect the mechanical properties.
Trimethyololpropane ethoxylate (TMPEO) was found to be a miscible additive that improved mechanical properties and could
participate in crosslinking the final dielectric material. TMPEO interacted with the PAG, lowering its decomposition temperature.
An optimal formulation and processing scheme were determined. A formulation with 10 pphr TMPEO was measured to have a
dielectric constant of 2.94, an elastic modulus of 1.95 GPa, a sensitivity at 365 nm of 175 mJ/cm2, and a contrast of 4.36.
(Georgia Institute of Technology, 2014-05)
Mueller, Brennen K.; Schwartz, Jared M.; Sutlief, Alexandra E.; Bell, William K.; Hayes, Colin O.; Elce, Edmund; Willson, C. Grant; Kohl, Paul A.
A low permittivity, positive tone, polynorbornene dielectric has been developed that exhibits excellent lithographic and electrical properties. The polymer resin is a random copolymer of a norbornene hexafluoroalcohol (NBHFA) and a norbornene tert-butyl ester (NBTBE). High optical sensitivity and contrast were achieved using a chemically amplified solubility switching mechanism through the acid-catalyzed deprotection of the tert-butyl ester functionality. After developing in aqueous base, the film was thermally cured through a Fischer esterification reaction, resulting in a cross-linked permanent dielectric. The effect of the photoacid generator (PAG) concentration on the lithographic patterning and curing reactions was studied. Higher PAG loading was favorable for both sensitivity and dielectric constant. The sensitivity of a formulation was measured as low as 8.09 mJ/cm2. The molar ratio of the two monomers composing the polymer was varied. A higher NBHFA content was favorable because it resulted in a lower modulus, lower shrinkage, and lower dielectric constant and loss. A formulation with 70 mol% of the NBHFA had a modulus of 2.60 GPa, a 12.2% volume decrease during cure, and a dielectric constant of 2.23. The direction-dependent coefficient of thermal expansion was measured, and it was found that the anisotropy of the PNB films decreased with higher NBTBE content.