DIELECTRIC BEHAVIOR OF O2/CF4 PLASMA ETCHED POLYIMIDE EXPOSED TO HUMID ENVIRONMENTS

The influence of moisture on plasma etched polyimide (PI) films is reported. Reactive ion etching plasmas with different CF4/O2 ratios (0%-30% CF4) are used to etch metal-polyimide-metal parallel plate capacitors. Plasma etching leads to a geometrical modification of the capacitor structures studied. This results in a reduction of the device capacitance which is modeled using a three-dimensional Poisson solver (SESES). A Debye type dielectric relaxation is observed in O2/CF4 plasma treated capacitors when measured at 85% relative humidity. The location of the loss peak is found to be dependent on CF4/O2 ratios. Wet capacitors do not exhibit this loss peak prior to etching. The observed relaxation in plasma treated PI capacitors can be removed by reheating to the cure temperature. A Debye model is used to extract a RC equivalent circuit for the etched capacitor structures. In parallel, x-ray photoelectron spectroscopy (electron spectroscopy for chemical analysis) is used to monitor the chemical changes in PI due to plasma treatment, and the observed chemical and dielectric changes are correlated.