Angle-resolved x-ray photoelectron spectroscopy comparison of copper/Teflon AF1600 and aluminum/Kapton metal diffusion

We use angle-resolved x-ray photoelectron spectroscopy to study metal diffusion in the cases of evaporated Cu on Teflon AF1600 and evaporated Al on Kapton polyimide. Although minimal diffusion is essential for long term stability and reliability of microelectronic devices, neither the presently used Al/polyimide nor any new candidates, such as Cu/fluoropolymer, has been sufficiently characterized and compared. Diffusion constants for infinite dilution in both cases were evaluated supposing Fickian diffusion as a first approximation. For the Al/polyimide interface, we found little, if any, diffusion after annealing for 30 min at 150 degrees C. In the case of the Cu/Teflon AF1600 interface, the same annealing induces significantly more copper diffusion. These results are discussed with respect to the diffusion equation, and it is shown that the experimental results indicate a concentration-dependent diffusion coefficient; experimental values, measured at infinite dilution of metal in polymer, are also reported. (C) 1998 American Institute of Physics.