New Tantalum Amido Complexes with Chelate Ligands as Metalorganic (MO) Precursors for Chemical Vapor Deposition (CVD) of Tantalum Nitride Thin Films

Four new tantalum amido precursors (η²-RN(CH₂)_nNR)Ta(NMe₂)₃ (where R = Me, n = 2, 1; R = Et, n = 2, 2; R = Me, n = 3, 3; R = Et, n = 3, 4) with chelate diamide ligands and one new tantalum amido precursor (η²-^tBuNC(NMe₂)NEt)Ta(NMe₂)₄) (5) with a chelate guanidinate ligand were prepared and characterized. Their thermal behavior, especially (NMe₂)₃Ta(η²-MeN(CH₂)₂NMe) (1), were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) experiments to demonstrate the enhancement of their thermal stability and preservation of the volatility as metalorganic chemical vapor deposition (MOCVD) precursors as compared to Ta(NMe₂)₅ (PDMAT). Introduction of the asymmetric chelate guanidine ligand in complex 5 gave improved volatility as compared with its known isomer [(η²-ⁱPrNC(NMe₂)NⁱPr)Ta(NMe₂)₄ (6). The crystal structures of 5 and 6 were measured to investigate the correlation between the volatility and intermolecular interactions. The MOCVD of tantalum nitride thin films was successfully achieved using 1. The films are based on field emission scanning electron microscopy (FESEM) and show good adhesion properties. Rutherford backscattering spectrometry (RBS) and X-ray photoelectron spectroscopy (XPS) data suggest that the film deposited using 1 at 500 °C under ammonia has a composition of TaN_1.22±0.14 with negligible carbon and oxygen levels. It also shows low resistivity of 1.4 × 10³ μΩ cm on SiO₂/Si and broad X-ray diffraction (XRD) peaks for the stoichiometric cubic refractory TaN, indicating the potential of 1 becoming an alternative MOCVD precursor for barrier applications.