Deposition of Ru and RuO₂ thin films employing dicarbonyl bis-diketonate ruthenium complexes as CVD source reagents

Reaction of Ru₃(CO)₁₂ with 6 eq. of β-diketone ligands (hfac)H, (tmhd)H, (acac)H and (tfac)H at 160-170°C in a hydrocarbon solvent (pentane or hexane) affords the diketonate complexes [Ru(CO) ₂(hfac)₂] (1), [Ru(CO)₂(tmhd)₂] (2), [Ru(CO)₂(acac)₂] (3) and [Ru(CO)2(tfac)2] (4) in high yields. These ruthenium complexes were characterized by spectroscopic methods; a single crystal X-ray diffraction study was carried out on one isomer of the tfac complex (4a), revealing an octahedral coordination geometry with two CO ligands located at cis-positions and with the CF₃ groups of the β-diketonate ligands trans to the CO ligands. Thermogravimetric analysis of complex (1) showed an enhanced volatility compared to the parent acac complex (3), attributed to the CF₃ group reducing intermolecular attraction. Employing complexes (1) and (2) as CVD source reagents, ruthenium thin films can be deposited at temperatures of 350°C-450°C under an H₂ atmosphere or at temperatures of 275°C-400°C using a 2% mixture of O₂ in argon as carrier gas. For deposition carried out using complex (1) and under 100% O₂ atmosphere, RuO₂ thin films with a preferred (200) orientation were obtained. The as-deposited thin films were characterized by surface and physical analytical techniques, such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD) and four-point probe measurement.