β-Ketoiminato-based copper(ii) complexes as CVD precursors for copper and copper oxide layer formation

Abstract

The synthesis of ketoiminato copper(II) complexes [Cu(OCRCHC(CH₃)NCH₂CH₂X)(μ-OAc)]₂ (X = NMe₂: 4a, R = Me; 4b, R = Ph. X = OMe: 5, R = Me) and [Cu(OCRCHCMeNCH₂CH₂NEt₂)(OAc)] (6, R = Me) from RC(O)CHC(CH₃)N(H)CH₂CH₂X (X = NMe₂: 1a, R = Me; 1b, R = Ph. X = NEt₂: 1c, R = Me. X = OMe: 2, R = Me) and [Cu(OAc)₂·H₂O] (3) is reported. The molecular solid-state structures of 4–6 were determined by single crystal X-ray diffraction studies, showing that 4a,b and 5 are dimers which are set up by two [{Cu(μ-OAc)L}] (L = ketoiminato ligand) units featuring a square-planar Cu₂O₂ core with a distorted square-pyramidal geometry at Cu(II). In contrast, 6 is monomeric with a tridentate-coordinated OCMeCHCMeNCH₂CH₂NEt₂ ligand and a σ-bonded acetate group, thus inducing a square-planar environment around Cu(II). The thermal behavior of all complexes was studied by TG (Thermogravimetry) and DSC (Differential Scanning Calorimetry) under an atmosphere of Ar and O₂. Complex 4b shows the highest first onset temperature at 213 °C (under O₂) and 239 °C (Ar). PXRD studies confirmed the formation of CuO under an atmosphere of O₂ and Cu/Cu₂O under Ar. TG-MS studies, exemplarily carried out with 4a, indicate the elimination of the ketoiminato ligands with detectable fragments such as m/z = 15, 28, 43, 44, 45, and 60 at a temperature above 250 °C. Vapor pressure measurements displayed that 5 shows the highest volatility of 3.6 mbar at 70 °C (for comparison, 4a, 1.4; 4b, 1.3; 6, 0.4 mbar) and hence 4a and 5 were used as MOCVD precursors for Cu/Cu₂O deposition on Si/SiO₂ at substrate temperatures of 450 °C and 510 °C. The deposition experiments were carried out under an atmosphere of nitrogen as well as oxygen. The as-obtained layers were characterized by SEM, EDX, XPS, and PXRD, showing that with oxygen as the reactive gas a mixture of metallic copper and copper(I) oxide without carbon impurities was formed, while under N₂ Cu films with 53–68 mol% C contamination were produced. In a deposition experiment using precursor 5 at 510 °C under N₂ a pure copper film was obtained.