Atomic Layer Deposition of Ru/RuO₂ Thin Films Studied by In situ Infrared Spectroscopy

The deposition of ruthenium thin films is investigated using a newly synthesized precursor (cyclopentadienyl ethylruthenium dicarbonyl, Ru(Cp)(CO) 2 Et) and O 2 gas as reactants. The conditions to achieve self-terminated surface reactions (sample temperature, precursor pulse length and precursor gas pressure) are investigated and the resulting composition, conductivity, and surface morphology are determined during/after deposition on hydrogen-terminated silicon (111) surfaces using in situ FTIR, and ex situ Rutherford back scattering, X-ray photoelectron spectroscopy, and atomic force microscopy. Higher growth rates (∼1.5−3 Å) are obtained compared to those typical of ALD of metals (∼0.5−1 Å), under conditions of saturation, i.e., through self-terminated surface reactions. Infrared absorption measurements reveal that bridged CO formed by the self-reaction of Ru(Cp)(CO) 2 Et leads to surface passivation, thus terminating the precursor self-reaction. They also show that, under these “saturation” growth conditions, metallic Ru develops during the early stage of deposition (1−5 cycles), and RuO 2 is observed later in the growth. The deposition rate is linear with cycles after an initially slow nucleation stage and the film becomes metallic after ∼22 cycles. Thick films (∼45 nm) grown with short pulses produce metallic polycrystalline ruthenium with hcp structure.