Niobium and tantalum derivatives with bidentate nitrogen ligands as potential precursors to nitrides

Early transition metal derivatives with N-donors have attracted interest as precursors of nitrides, the latter being used as diffusion barriers for the ULSI technology. Potential precursors to niobium and tantalum nitrides have been synthesized in good yields and characterized. They are based on bidentate nitrogen donors namely amidinates, benzamidinates and diamido ligands. These have been reacted with niobium or tantalum derivatives namely penta and tetrachlorides, TaCl3(NEt2)2. Disubstituted niobium(IV) and tantalum(V) species such as for instance NbCl2[RNCR'NR2]2 [R = Cy, N(SiMe3)2; R = SiMe3, R' = p-tolyl] have been obtained and structurally characterized. The more rigid o-dimethylphenylene diamido ligand lead to a volatile, air stable disubstituted Nb(V) species NbCl{N2(SiMe3)2C6H3}2. However, π-stacking as shown by X-ray studies are responsible of quite low sublimation rates. Thus, volatility could be reached for some species, their properties, high solubility due to the trimethylsilylligands, their stability in solution is more suited for applications in wet MOCVD than conventional one.