Low-Pressure Chemical Vapor Deposition of Cu−Pd Films:  Alloy Growth Kinetics

We have examined the formation of copper films alloyed with small quantities of palladium. Independent control studies of palladium and copper deposition from palladium bis(hexafluoroacetylacetonate) [Pd(hfac)2] and (hexafluoroacetylacetonato)copper(I)(vinyltrimethylsilane) [(hfac)Cu(I)(vtms)], both in the presence and absence of H2, were carried out. The growth kinetics for both metals were feed-rate-limited under similar reactor conditions. No significant variation in deposition rate (100 nm/min, Pd; 100−500 nm/min, Cu), morphology, resistivity, and purity of the copper films was observed due to the addition of H2. Simultaneous introduction of both precursors yielded Cu−Pd alloy films. The absence of pure palladium grains was confirmed by X-ray diffraction analysis which showed binary solid solutions (Cu99.5Pd0.5−Cu80Pd20) as the only crystalline phases. Auger electron spectroscopy analysis showed a significant reduction in the palladium content of the films as compared to that expected on the basis of the growth rates obtained during independent palladium deposition. Co-deposition of copper and palladium also resulted in a change of the palladium growth kinetics from a feed-rate-limited to a surface-reaction-limited regime (E a = 16 kcal/mol). The Cu/Pd stoichiometry could be varied by controlling both the Pd(hfac)2 partial pressure and substrate temperature. Experiments to investigate the cause of the change in Pd CVD kinetics showed that vinyltrimethylsilane (vtms) severely inhibits Pd growth during independent Pd deposition. The films were also contaminated with C when vtms was added. This study has shown that alloy CVD kinetics can be drastically different from the independent metal deposition kinetics.