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Kohl, Paul A.

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Author: Elce, Edmund ×

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    Positive Tone, Polynorbornene Dielectric Crosslinking
    (Georgia Institute of Technology, 2014-05) Schwartz, Jared M. ; Mueller, Brennen K. ; Elce, Edmund ; Pritchard, Zachary D. ; Li, Helen W. ; Grillo, Angelica M. ; Lee, Sang Y. ; Kohl, Paul A.
    The processing and properties of a positive-tone, aqueous develop, epoxy crosslinked permanent dielectric based on a polynorbornene (PNB) backbone and bis(diazonaphthoquinone) (DNQ) photosensitive compound were investigated. The developing and cure properties of the films were studied as a function of cure temperature, epoxy crosslinker loading and DNQ loading. Reduced modulus measurements showed that crosslinking of the polymer film occurred via reaction of the polymer with DNQ. The final modulus of the DNQ-crosslinked film was 4.0 GPa. Swelling measurements for a UV exposed film showed material leaching from the film. Residual solvent from swelling measurements was analysed by gel permeation chromatography which showed the indene carboxylic acid form of DNQ leached out of the polymer film. The unexposed film did not exhibit material loss through leaching. When developed, films showed a decline in modulus to 2.6 GPa, likely due to the reaction of DNQ with the aqueous base developer forming nonreactive byproducts that did not contribute to crosslinking. An epoxy crosslinker was added to the formulation which helped crosslink the polymer film by inhibiting uptake of the aqueous base during developing. The epoxy inhibition of the base uptake was confirmed by quartz crystal microbalance, where an increase in epoxy loading led to a decrease in base uptake of the film during developing. 19F-NMR results support the DNQ-PNB crosslinking through esterification. Electrical characterization of the cured PNB films showed a relative dielectric constant of 3.65 for a DNQ and epoxy containing film after curing at 220◦C.
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    Chemically Amplified, Positive Tone, Polynorbornene Dielectric for Microelectronics Packaging
    (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.