Photoassisted Chemical Vapor Deposition Using (η⁴-Diene)Ru(CO)₃ Precursors

Six (η⁴-diene)Ru(CO)₃ (diene = cyclooctatetraene, cyclohexadiene, cyclobutadiene, 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene) complexes that undergo photolytic loss of diene and/or CO ligands at room temperature have been synthesized and prescreened for their utility in Ru photoassisted chemical vapor deposition (PACVD). PACVD onto functionalized alkanethiolate self-assembled monolayers (SAMs) with -COOH, -OH, or -CH₃ terminal groups has identified four of these precursors as suitable candidates for area-selective deposition of Ru. After exposure to 150,000 L of (η⁴-2,3-dimethyl-1,3-butadiene)Ru(CO)₃ under UV irradiation, selective deposition of Ru is observed on -COOH-terminated SAMs. However, after exposure to 500,000 L, deposition selectivity is lost and deposition is observed on all three functionalized SAMs studied. Deposition from (η⁴-1,3-butadiene)Ru(CO)₃ was nonselective, with Ru deposition observed on all three functionalized SAMs. Further, the deposition was less efficient; Ru deposition was observed to begin after 303,000 L, which is approximately twice the dose required for (η⁴-2,3-dimethyl-1,3-butadiene)Ru(CO)₃. After exposure to 76,000 L of (η⁴-isoprene)Ru(CO)₃ under UV light, selective deposition of Ru is also observed on -COOH-terminated SAMs. Using (η⁴-COT)Ru(CO)₃ selective deposition onto -COOH-functionalized SAMs was achieved at 25× lower precursor dose than using (η⁴-2,3-dimethyl-1,3-butadiene)Ru(CO)₃. The deposition results are discussed in the context of precursor design for area-selective deposition by PACVD.