FLUOROPOLYMER SURFACE MODIFICATION FOR ENHANCED EVAPORATED METAL ADHESION

Adhesion of evaporated Cu to Teflon PFA (polytetrafluoroethylene-co-perfluoroalkoxy vinyl ether) was greatly enhanced by plasma pretreatment. The efficiency of the treatment decreased in the following order: N-2 > O-2 > (N-2 + H-2) > (O-2 + H-2) > H-2. X-ray photoelectron spectroscopy (XPS) showed the loss of fluorine and the incorporation of oxygen and nitrogen at the polymer surface. Among the gases, H-2 was found to be the most efficient for fluorine elimination, and (N-2 + H-2) for surface functionalization. Based on this investigation, it is proposed that Cu reacts with both oxygen and nitrogen to form, respectively, Cu-O and Cu-N bonds at the interface but no reaction occurs with carbon and fluorine. While greater enhancement in polymer surface wettability and stronger interfacial reactions can account for the higher performance of N-2 over O-2 in improving adhesion, these effects cannot explain the lower efficiency of H-2. Several possibilities are discussed, including surface cleaning, oxygen incorporation and the formation of weak boundary layers.