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)] (<b>1</b>), [(C₅H₅)­Co­(η⁴-CH₂C­(Me)­C­(Me)­CH₂)] (<b>2</b>), and [(C₅H₅)­Co­(η⁴-C₆H₈)] (<b>4</b>) as possible cobalt metal organic chemical vapor deposition (MOCVD) precursors. Atmospheric pressure MOCVD was employed using precursor <b>1</b>, 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