A Study on the Development of Chemical Vapor Deposition Precursors. 4. Syntheses and Characterization of New N-Alkoxo-β-ketoiminate Complexes of Niobium and Tantalum

Partial replacement of ethoxide ligands with N -alkoxo-β-ketoiminates in the tantalum or niobium ethoxides resulted in M( N -alkoxo-β-ketoiminate)(OEt) 3 (M = Ta and Nb) complexes. Most of these complexes are liquid and showed enhanced thermal and chemical stability, especially toward moisture. These complexes have octahedral geometry with a meridional N -alkoxo-β-ketoiminate ligand and showed fluxional behaviors. All of these precursors, especially the ones with methyl groups on both the N -alkoxo and β-ketoiminate backbones, demonstrate considerably higher deposition rates than M 2 (OEt) 10 (M = Ta and Nb), one of the most popular precursors for Ta 2 O 5 and Nb 2 O 5 films. Thermogravimetric analysis experiments showed that successive decomposition of ethoxide ligands is followed by decomposition of N -alkoxo-β-ketiminate in the pyrolysis process. Introduction of a methyl group onto the N -hydroxyethyl backbone enhanced the thermal stability at lower temperatures and the pyrolysis rate at higher temperatures. X-ray diffraction patterns indicate that the deposited films are not crystallized until the substrate temperature goes over 650 °C. Well-crystallized longish grains were formed in the Ta 2 O 5 film deposited at 700 °C, but it was found from the depth profile spectra by Auger electron spectroscopy (AES) that the nitrogen and carbon impurities are 2.3% and 4.2%, respectively, for the Ta 2 O 5 film deposited at 550 °C. Heat treatment at 700 °C in oxygen removed the nitrogen impurity in this Ta 2 O 5 completely, and the residual carbon was proved to be negligible from the AES and X-ray photoelectron spectroscopy results.