Surface modification of SiLK[reg] by graft copolymerization with 4-vinylpyridine for reduction in copper diffusion

Surface modification of Ar plasma-pretreated SiLK[reg] film coating on (1 0 0)-oriented single crystal silicon wafer (the SiLK-Si substrate) via UV-induced graft copolymerization with 4-vinylpyridine (the P4VP-g-SiLK-Si surface) was carried out to enhance the adhesion of the vacuum deposited copper. The composition and morphology of the P4VP-g-SiLK-Si surface were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The 180 deg. -peel adhesion strength of the copper film with the P4VP-g-SiLK-Si surface was about 2.5 N/cm. This adhesion strength was much higher than that of the copper film with the pristine or the Ar plasma-treated SiLK-Si surface. The strong adhesion of evaporated copper with the P4VP-g-SiLK-Si surface was attributed to the strong interaction of the copper atoms with the pyridine groups. The extent of copper diffusion into the P4VP-g-SiLK-Si film at the annealing temperature of 300 deg. C, was investigated by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) and compared to those of copper diffusion into the pristine and Ar plasma-treated SiLK-Si surfaces. The improved resistance of the P4VP-g-SiLK-Si surface to copper diffusion, probably arose from the strong interaction of the copper atoms with the grafted 4VP polymer