Novel technique for measuring through-plane modulus in thin polymer films

Polymer thin films are widely used as coatings and inter-level dielectrics in microelectronic applications. In multi-layer structures, stresses generated in the films due to interaction with adjacent layers and solvent evaporation induced shrinkage, cause the polymer chains to orient in the plane of the film resulting in anisotropic film properties. Characterization of properties in all directions is essential for accurate electrical and mechanical design and modeling. A new 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 constant and thickness of thin polymer films under compression. Results are reported for 8-14 micrometer thick, Dow Chemical Cyclotene 3022 benzocyclobutene (BCB) films. The dielectric constant was found to change linearly with stress. Using this result, the through-plane stress-strain curve was obtained and the modulus estimated.