Platinum ω-Alkenyl Compounds as Chemical Vapor Deposition Precursors: Synthesis and Characterization of Pt[CH₂CMe₂CH₂CH═CH₂]₂and the Impact of Ligand Design on the Deposition Process

We describe the synthesis and characterization of three platinum(II) ω-alkenyl complexes of stoichiometry Pt[CH2CMe2(CH2)xCH═CH2]2 where x is 0, 1, or 2, as well as some related platinum(II) compounds formed as byproducts during their synthesis. The ω-alkenyl ligands in all three complexes, cis-bis(η1,η2-2,2-dimethylbut-3-en-1-yl)platinum (2), cis-bis(η1,η2-2,2-dimethylpent-4-en-1-yl)platinum (3), and cis-bis(η1,η2-2,2-dimethylhex-5-en-1-yl)platinum (4), bind to Pt by means of a Pt-alkyl sigma bond at one end of the ligand chain and a Pt-olefin pi interaction at the other; the olefins reversibly decomplex from the Pt centers in solution. The good volatility of 3 (10 mTorr at 20 °C), its ability to be stored for long periods without decomposition, and its stability toward air and moisture make it an attractive platinum chemical vapor deposition (CVD) precursor. CVD of thin films from 3 shows no nucleation delay on several different substrates (SiO2/Si, Al2O3, and VN) and gives films that are unusually smooth. At 330 °C in the absence of a reactive gas, the precursor deposits platinum containing 50% carbon, but in the presence of a remote oxygen plasma, the amount of carbon is reduced to below the Rutherford backscattering spectroscopy (RBS) detection limit without affecting the film smoothness. Under hot wall CVD conditions at 250 °C in the absence of a co-reactant, 72% of the carbon atoms in 3 are released as hydrogenated products (largely 4,4-dimethylpentenes), 22% are released as dehydrogenated products (all of which are the result of skeletal rearrangements), and 6% remain in the film. Some conclusions about the CVD mechanism are drawn from this product distribution.