Atomic layer deposition of cobalt silicide (CoSi 2 ) thin films on H-terminated Si(111) surfaces, using the cobaltbased precursor tertiarybutylallylcobalttricarbonyl ( t Bu-AllylCo-(CO) 3 ) and trisilane, is investigated by in situ Fourier transform infrared spectroscopy (FTIR) and ex situ X-ray photoelectron spectroscopy (XPS) to uncover the film growth mechanisms. The strong reactivity of t Bu-AllylCo(CO) 3 with H-terminated silicon surfaces and inertness with silicon oxide surfaces, as previously determined by IR spectroscopy [Chem. Mater. 2012, 24, 1025, opens the door for selective deposition. Deposition of CoSi 2 is observed after a brief nucleation period (∼3 cycles), during which the stabilization of the cobalt precursor takes place, as evidenced by a shift of the stretch frequency of the carbonyl groups bonded to the Co center from 2010 to 1980 cm −1 . This shift is evidence for completion of the catalytic reaction and leads to a surface termination and configuration that is favorable for subsequent ligand exchange with trisilane, fostering a classical ligand-exchange ALD growth. In steady state, the CoSi 2 growth rate is 0.15 ± 0.05 Å per cycle, as measured by Rutherford backscattering spectroscopy (RBS). XPS measurements with depth profiling indicate that the CoSi 2 film is stoichiometric with negligible carbon contamination.
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