Cobalt(I) Olefin Complexes: Precursors for Metal–Organic Chemical Vapor Deposition of High Purity Cobalt Metal Thin Films

We report the synthesis and characterization of a family of organometallic cobalt­(I) metal precursors based around cyclopentadienyl and diene ligands. The molecular structures of the complexes cyclopentadienyl–cobalt­(I) diolefin complexes are described, as determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis and thermal stability studies of the complexes highlighted the isoprene, dimethyl butadiene, and cyclohexadiene derivatives [(C5H5)­Co­(η4-CH2CHC­(Me)­CH2)] (1), [(C5H5)­Co­(η4-CH2C­(Me)­C­(Me)­CH2)] (2), and [(C5H5)­Co­(η4-C6H8)] (4) as possible cobalt metal organic chemical vapor deposition (MOCVD) precursors. Atmospheric pressure MOCVD was employed using precursor 1, to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere (760 torr) of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 325, 350, 375, and 400 °C, respectively, by scanning electron microscopy and atomic force microscopy reveal temperature-dependent growth features. Films grown at these temperatures are continuous, pinhole-free, and can be seen to be composed of hexagonal particles clearly visible in the electron micrograph. Powder X-ray diffraction and X-ray photoelectron spectroscopy all show the films to be highly crystalline, high-purity metallic cobalt. Raman spectroscopy was unable to detect the presence of cobalt silicides at the substrate/thin film interface.