Study of fabrication of Cu film on PFA by sputtering

Currently, chemical pretreatment and electroless plating are used to fabricate Cu films on perfluoroalkoxy vinyl ether (PFA) copolymer. In order to reduce the wastage of water during chemical pretreatment and electroless plating, we have investigated the fabrication of Cu films by a dry process as an alternative. In the present report, we have investigated the fabrication of Cu film on the PFA by using a conventional RF sputter deposition apparatus. An Ar ion sputter-etching pretreatment is performed on the PFA prior to sputter deposition; however, it does not significantly influences the peel strength and grain size. The grain size of Cu influences its resistivity in the present experiments. The resistivity increases with decreasing grain size. This result is explained by considering the scattering of conduction electrons at the grain boundaries. Further, substrate temperatures obviously influence the grain size of Cu and the peel strength between Cu and PFA. In particular, for substrate temperatures above 150 °C, the grain size and peel strength increase drastically. We can use the Cu film fabricated on the PFA substrate above 150 °C as a seed layer for CuSO4 electroplating.