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.