Mechanistic study of the atomic layer deposition of cobalt: A combined mass spectrometric and computational approach

Cobaltcarbonyl-tert-butylacetylene (CCTBA) is a conventional precursor for the selective atomic layer deposition of Co onto silica surfaces. However, the limited understanding of the deposition mechanism of such cobalt precursors curbs rational improvements on their design for increased efficiency and tuneable selectivity. The impact of using a less reactive internal alkyne to a terminal alkyne was investigated using experimental and computational methods. Electrospray-ionization mass spectrometry was used to monitor the formation of CCTBA analogs and study their gas phase decomposition pathways. Gas phase analysis show that an internal alkyne dissociates at slightly lower energies than a terminal alkyne, suggesting that an internal alkynyl ligand may be more suited to low temperature ALD. Furthermore, the less reactive internal alkyne will result in fewer carbon impurities embedded in surfaces, in particular due to its reduced reactivity with Si-H bonds on the surface of Si wafers. Computational analysis also predicts increased surface binding in the metal centers of the internal alkynyl complex.