Dual capacitor technique for measurement of through-plane modulus of thin polymer films

Abstract

Polymer thin films are widely used as coatings and interlevel dielectrics in microelectronic applications. In thin-film structures, stresses are generated due to interaction with adjacent layers and film shrinkage due to solvent evaporation or curing. This causes polymer chain orientation resulting in anisotropic (direction dependent) film properties. The dual capacitor technique has been developed to measure in situ, the through-plane (z) stress-strain behavior of thin polymer films. A parallel plate capacitor device and an interdigitated electrode structure were used as sensors to detect changes in dielectric permittivity and thickness of thin polymer films under compression. The analytical and finite element models used to interpret the capacitance measurements have been presented. The Clausius–Mossotti equation was used to determine the volume change in the film from the permittivity measurements. Results have been reported for 10–14 μm thick, Cyclotene 4026-46 benzocyclobutene films and 10–12 μm thick films of polyimide PI-2611. The Cyclotene 4026-46 films were found to be mechanically isotropic, whereas the PI-2611 films were highly anisotropic. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1634–1644, 2000