3. Anisotropic Thermal Conductivity in Polymer Films
Dr. Uma Srinivasan, Dr. Katsuo Kurabayashi, and Deepak Subburam

Organuc films are playing an important role in the development of fast integrated circuits and novel electronic and optoelectronic devices.  Polymer films are targeted for application as low-dielectric constant passivation in multilevel circuit metallization structures.  The lower dielectric constant reduces the electrical signal delay along the interconnect, which is necessary for developing faster logic circuits.  Promising new electronic and optoelectronic devices are using electrically-conducting polymer films as active layers because of their high electroluminescence efficiency and the ease with which they can be processed.  However, the low thermal conductivities of polymer films yield large temperature rises and temperature gradient magnitudes in the metallization and in novel devices, which augment electromigration-induced interconnect failure rates and reduce the lifetime of polymer devices.  The partial orientation of these strands during the spin-on processing of films can cause the thermal conductivity to be strongly anisotropic, but this phenomenon has not been rigorously measured or modeled.

This project develops experiments and theory that determine the thermal conductivity anisotropy.  The vertical conductivity is isolated using Joule heating and electrical-resistance thermometry in the mesa structure shown in Figure 1, which resembles multilevel interconnection in integrated circuits.  The lateral thermal conductivity is measured using harmonic Joule heating in a structure that is made without using the mesa etch.  The lateral conductivity is extracted by comparing the amplitude and phase of the measured temperature fluctuations with finite-difference calculations performed for the two-dimensional geometry with complex imbedding in the frequency domain. Data for BTDA-ODA-MPD polymer films of varying thicknesses are plotted in Figure 2, showing that the anisotropy factor lies between approximately four and eight and favors lateral conduction.  The measurements are supporting the development of a model for the anisotropy that accounts for the average molecular mass, the degree of orientation, and for the mass density distribution within the film, all of which are influenced by the details of the spin-on coating process.  Figure 3 shoes predictions of the anisotropy as functions of the defree of molecular orientation within the film and the anisotropy that could be measured in a material with perfectly ordered strands.  The degree of orientation is quantified by means of the standard deviation of the angle or orientation of melecules with respect to the film plane in-plane direction.

The data, theory, and experimental techniques developed in this project are useful both for the silicon IC industry, which is assessing the potential of organic passivation, and for researchers working on novel organic devices.

Collaboration
Components Research Group, Intel Corporation
IBM Research Laboratory, Almaden

Recent Publications

Kurabayashi, K., Touzelbaev, M.N, Asheghi, M., Ju, Y.S., and Goodson, K. E., 1998, "Measurement of the Anisotropic Thermal Conductivities in Polymer Films," IEEE/ASME Journal of Microelectromechanical Systems, in press.

Kurabayashi, K. and Goodson, K.E., 1999, "Impact of Molecular Orientation on THermal Conduction in Linear-Chain Polymer Films," Proceedings of the 5th ASME/JSME Joint Thermal Engineering Conference, March 15-19, 1999, San Diego, California.  Submitted to the Journal of Applied Physics.

Ju, Y.S., Kurabayashi, K., and Goodson K.E., "Thermal Characterization of Anisotropic Thin Dielectric Films using
Harmonic Joule Heating,"  Thin Solid Films, Vol.339, pp.160-164.

Sponsorship Semiconductor Research Corporation Contract 98-PJ-357