Role of the Oxidizing Co-Reactant in Pt Growth by Atomic Layer Deposition Using MeCpPtMe₃ and O₂/O₃/O₂-Plasma

Atomic layer deposition (ALD) of Pt using MeCpPtMe3 and the O-2/O-3/O-2-plasma (O-2*) at 300 degrees C is investigated with in vacuo X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) to gain a better understanding of the Pt growth mechanism. Most notably, the chemical state of the surface Pt atoms and the role of surface O species in Pt growth are revealed. In the MeCpPtMe3/O-2 process, the surface Pt atoms remain in a metallic Pt-0 state throughout the ALD cycle, and the surface O species generated by the O-2 exposure only exist as unstable adatoms, desorbing in vacuum. As for the O-3/O-2* processes, the surface Pt layer is oxidized to a mixture of Pt-0, Pt2+O and Pt4+O2 upon O-3/O-2* exposure and then fully reduced to Pt-0 during the precursor exposure. Surface Pt oxides are stable in a vacuum but can be reduced by hydrocarbon vapors. Quantification analysis shows that the O-3/O-2* processes have a much higher surface O species content than the O-2 process after the coreactant exposure, favoring precursor ligand combustion over dehydrogenation in the next precursor exposure and leading to lower surface C density after the precursor pulse. DFT reveals differences in the combustion mechanism for Me vs Cp species, during the metal precursor and coreactant pulses. Importantly, the differences in the surface O content do not significantly affect the growth per cycle. Moreover, the MeCpPtMe3/O-2 process with surface O species and a tailored MeCpPtMe3/O-2 process without surface O species, both at 300 degrees C, yield nearly identical growth rates and as-deposited Pt with the same chemical state. This indicates that surface O species present before the precursor exposure have little impact on the overall Pt growth, in contrast to a previous assumption.