Atomic layer deposition of Ru/RuO2Thin 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)2Et) and O2 gas as reactants. The conditions to achieve self-terminated surface reactions (sample temperature, precursor pulse length andprecursor gas pressure) are investigated and the resulting composition, conductivity, and surfacemorphology are determined during/after deposition on hydrogen-terminated silicon (111) surfacesusing in situ FTIR, and ex situ Rutherford back scattering, X-ray photoelectron spectroscopy, andatomic force microscopy. Higher growth rates (∼1.5-3 A˚) are obtained compared to those typical ofALD of metals (∼0.5-1 A˚), under conditions of saturation, i.e., through self-terminated surfacereactions. Infrared absorption measurements reveal that bridged CO formed by the self-reaction ofRu(Cp)(CO)2Et leads to surface passivation, thus terminating the precursor self-reaction. They alsoshow that, under these “saturation” growth conditions, metallic Ru develops during the early stage ofdeposition (1-5 cycles), and RuO2 is observed later in the growth. The deposition rate is linear withcycles 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