New CVD Precursors Capable of Depositing Copper Metal under Mixed O₂/Ar Atmosphere

Volatile low-melting Cu^II metal complexes Cu[OC(CF₃)₂CH₂C(Me)NMe]₂ (4) and Cu[OC(CF₃)₂CH₂CHMeNHMe]₂ (5) were synthesized and characterized by spectroscopic methods. A single-crystal X-ray diffraction study on complex 4 shows the anticipated N₂O₂ square-planar geometry with the imino alcoholate ligand arranged in the all-trans orientation. In contrast, a highly distorted N₂O₂ geometry with a dihedral angle of 33° was observed for complex 5, suggesting that the fully saturated amino alcoholate ligand produces a much greater steric congestion around the metal ion. Metal CVD experiments were conducted, showing that both complexes, 4 and 5, are capable of depositing copper metal at temperatures of 275−300 °C using an inert argon carrier gas mixed with low concentrations (2−8%) of O₂. The best copper thin film showed a purity of ∼96 at. % and a resistivity of 2.11 μΩ cm versus that of the bulk standard (1.7 μΩ cm), as revealed by XPS and four-point probe analyses, respectively. We speculate that the low concentration of O₂ promotes partial ligand oxidation, thus releasing the reduced copper on the substrate and affording the high-purity copper deposit.