Cobalt(III)
Diazabutadiene Precursors for Metal Deposition:
Nanoparticle and Thin Film Growth
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Abstract
We report the synthesis and characterization
of a family of cobalt(III) metal precursors, based around cyclopentadienyl
and diazabutadiene ligands. The molecular structure of the complexes
cyclopentadienyl-Cobalt(III)(<i>N,N</i>′-dicyclohexyl-diazabutadiene)
(<b>2c</b>) and cyclopentadienyl-Cobalt(III)(<i>N,N</i>′-dimesityl-diazabutadiene) (<b>2d</b>) are described,
as determined by single crystal X-ray diffraction analysis. Thermogravimetric
analysis of the complexes highlighted the isopropyl derivative CpCo(<sup><i>i</i></sup>Pr<sub>2</sub>-dab) (<b>2a</b>) as
a possible cobalt metal chemical vapor deposition (CVD) precursor.
Atmospheric pressure CVD (AP-CVD) was employed using precursor <b>2a</b> to synthesize thin films of metallic cobalt on silicon
substrates under an atmosphere of hydrogen (H<sub>2</sub>). Analysis
of the thin films deposited at substrate temperatures of 250 °C,
275 °C, 300 °C, 325 °C, and 350 °C, respectively,
by scanning electron microscopy (SEM) and atomic force microscopy
(AFM) reveal temperature dependent growth features: films grown at
325 and 350 °C are continuous and pinhole free, whereas those
films grown at substrate temperatures of 250 °C, 275 °C,
and 300 °C consist of crystalline nanoparticles. Powder X-ray
diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all
show the films to be high purity metallic cobalt. Raman spectroscopy
has also been used to prove the absence of cobalt silicides at the
substrate/thin film interface
