Stabilization of amide-based complexes of niobium and tantalum using malonates as chelating ligands: precursor chemistry and thin film deposition

The stabilization of the reactive amide complexes of niobium and tantalum with malonates as chelating ligands leads to stable six-coordinated monomeric complexes ([M(NMe2)4(dbml)]; M ) Nb, Ta), namely tetrakis(dimethylamido)(di-tert-butylmalonato)niobium(V) (1) and tetrakis(dimethylamido)(di-tert-butylmalonato) tantalum(V) (2). Compounds 1 and 2 were characterized by 1H NMR, 13C NMR, EI-mass spectroscopy, elemental analysis, and single-crystal X-ray diffraction studies. The thermal properties of the compounds were studied by thermogravimetric analysis. Both the complexes possess good thermal characteristics, improved resistance to air and moisture, and high solubility and stability in solvents compared to their respective parent alkyl amides. Compound 1 was studied for metalorganic chemical vapor deposition (MOCVD) of Nb2O5 while compound 2 was studied for liquid injection metalorganic chemical vapor deposition (LI-MOCVD) of Ta2O5 thin films. The films were deposited at substrate temperatures from 400 to 800 °C, and for both Nb2O5 and Ta2O5 the maximum growth rate was at 600 °C. The films were characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy for their crystallinity and morphology. Thin film composition was analyzed by X-ray photoelectron spectroscopy, Rutherford backscattering, and depth profiling the composition with secondary neutral mass spectrometry. Electrical properties of the films were studied in terms of the C-V characteristics.