Photoactivated Ru chemical vapor deposition using (η³-allyl)Ru(CO)₃X (X = Cl, Br, I): From molecular adsorption to Ru thin film deposition

We have investigated photoassisted chemical vapor deposition (PACVD) of Ru on functionalized alkanethiolate self-assembled monolayers (SAMs) using (η³-allyl)Ru(CO)₃X (X = Cl, Br, I) precursors. Three SAMs were employed with —CH₃, —OH, or —COOH terminal groups. Our data show that (η³-allyl)Ru(CO)₃Cl molecularly adsorbs on the functionalized SAMs and no Ru(0) is deposited in either the dark or under UV light. Similarly, (η³-allyl)Ru(CO)₃I molecularly adsorbs on all substrates studied. For (η³-allyl)Ru(CO)₃Br at longer deposition times under UV light, Ru(0) and RuO_x are deposited on —CH₃- and —OH-terminated SAMs. In contrast for —COOH-terminated SAMs, little or no Ru is deposited, which is attributed to the formation of Ru-carboxylate complexes that block further deposition. Density Functional Theory calculations show that the different deposition behaviors observed are not due to the primary photoprocess, which is the loss of a carbonyl ligand, but rather can be attributed to the energy required to lose a second carbonyl ligand, a secondary photoprocess. Together, these data suggest that PACVD can be employed for area selective deposition.