Physical and Spectroscopic Studies of the Nucleation and Growth of Copper Thin Films on Polyimide Surfaces by Chemical Vapor Deposition

The chemical vapor deposition (CVD) of copper from (hexafluoroacetylacetonate)(vinyltrimethylsilane)-copper(I) [Cu^I(hfac)(vtms)] and the thermal evaporation of copper on pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide have been studied with a variety of techniques including reflection absorption infrared spectroscopy (RAIRS), ellipsometry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Our studies reveal that the nucleation and growth of Cu by CVD occurs by the preferential reaction of surface carbonyl groups, (C=O)_a, of PMDA-ODA with the CVD reagent. Preferential trapping of thermally deposited metal atoms also has been seen, although the nucleation processes appear to be less chemically specific than is seen in CVD growth on this substrate. Carbonyl groups at the surface of the polyimide react with the precursor molecules at 300 K, although the reactive sticking probabilities appear to be low (≪10^-3). The facility of nucleation on the polyimide surface depends on both the number and orientation of the carbony groups on the polymer surface which, in turn, depends sensitively on the thickness of the film. The nucleation of Cu growth from Cu^I(hfac)(vtms) is found to proceed from surface reactions mediated by these surface groups. Chemical-vapor deposited thin films grow on the PMDA-ODA surface by the Volmer-Weber mode. The grain size is found to correlate, at least qualitatively, with the number density of the complexes formed between the surface carbonyl groups and Cu^I(hfac)(vtms); these complexes, as inferred from infrared spectroscopic data, are formed by the displacement of vtms to give a Cu^I(hfac)(C=O)₅ adduct.