Oxidation of Cu in contact with preimidized polyimide

Abstract

We have investigated interface formation and degradation at the junction of preimidized polyimide and Cu by means of scanning Auger and secondary electron microscopies, and x-ray photoelectron spectroscopy. Our approach has been to spin on ultrathin (tens of Å) polyimide overlayers onto Cu substrates, cure the polyimide while in contact with the Cu in an inert atmosphere, and then expose the interface to different environments. We found that only a very small amount of oxidation occurs during the curing process itself. This result is expected on the basis of the preimidization step prior to contact with Cu. The limited amount of oxidation appears to be due to the formation of a Cu–amine complex at the interface. Storage in vacuum leaves the interface abrupt and no further oxidation occurs. However, exposure to room-temperature air or high humidity at 85 °C causes more extensive Cu oxidation to occur. In the case of exposure to high humidity at 85 °C, metal oxidation is accompanied by Cu outdiffusion and polyimide decomposition. The interface degradation process after curing appears to be driven by absorption of water, and the primary degradation reaction product is CuO.