Atomic Layer Deposition of Cobalt Silicide Thin Films Studied by in Situ Infrared Spectroscopy

Abstract

Atomic layer deposition of cobalt silicide (CoSi2) thin films on H-terminated Si(111) surfaces, using the cobalt-based precursor tertiarybutylallylcobalttricarbonyl (tBu-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 tBu-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 CoSi2 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 CoSi2 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 CoSi2 film is stoichiometric with negligible carbon contamination.