Group IV Transition Metal (M = Zr, Hf) Precursors for High-kappa Metal Oxide Thin Films

Abstract

This paper describes the synthesis of eight novel zirconium and hafnium complexes containing N-alkoxy carbox-amidate-type ligands, as potential precursors for metal oxides and atomic layer deposition (ALD) for HfO2. A series of ligands, viz., N-ethoxy-2,2-dimethylpropanamide (edpaH), N-ethoxy-2-methylpropanamide (empaH), and N-methoxy-2,2-dimethylpropanamide (mdpaH), were used to afford complexes Zr(edpa)(4) (1), Hf(edpa)(4) (2), Zr(empa)(4) (3), Hf(empa)(4) (4), Zr(mdpa)(4) (5), Hf(mdpa)(4) (6), ZrCp(edpa)(3) (7), and HfCp(edpa)(3) (8). Thermogravimetric analysis curves assessed for the evaporation characteristics of complexes 1-8 revealed single-step weight losses with low residues, except for the mdpa-containing complexes. Single-crystal X-ray diffraction studies of 1, 2, 5, and 6 revealed that all the complexes have monomeric molecular structures, with the central metal ion surrounded by eight oxygen atoms from the four bidentate alkoxyalkoxide ligands. Among the complexes prepared, 8 exhibited a low melting point (64 degrees C), good volatility (1 Torr at 112 degrees C), high thermal stability, and excellent endurance over 6 weeks at 120 degrees C. Therefore, an ALD process for the growth of HfO2 was developed using HfCp(edpa)(3) (8) as a novel precursor. Furthermore, the HfO2 film exhibited a low capacitance equivalent oxide thickness of similar to 1.5 nm, with J(g) as low as similar to 3 X 10(-4) A/cm(2) at V-g-1 V in a metal-insulator-semiconductor capacitor (Au/HfO2/p-Si).