Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: Potential precursors for metal nitride MOCVD

The coordination chemistry of the hydrazine derivatives dimethylhydrazine (Hdmh) and N-trimethylsilyl-N′N′-dimethylhydrazine (Htdmh) at Ta, Zr and Hf was investigated aiming at volatile mixed ligand all-nitrogen coordinated compounds. The hydrazido ligands were introduced either by salt metathesis employing the Li salts of the hydrazines and the tetrachlorides MCl₄ (M = Zr, Hf) or by amine substitution using M(NR ₂)₄ (R = Me, Et) and [(t-BuN)Ta(NR₂) ₃]. The new complexes were fully characterised including ¹H/¹³C NMR, mass spectrometry and a study of their thermal behaviour. The crystal structures of [ZrCl(tdmh)₃] and the all-nitrogen coordinated complex [Ta(N-t-Bu)(NMe₂)₂(tdmh)] are discussed as well as the structure of the by-product [Li(tdmh)(py)] ₂. Preliminary MOCVD experiments of the liquid compound [Ta(NEt ₂)₂(N-t-Bu)(tdmh)] were performed and the deposited TaN(Si) films were analysed by RBS and SEM.