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

Abstract

This paper describes the synthesis of eight novel zirconium and hafnium complexes containing N-alkoxy carboxamidate-type ligands, as potential precursors for metal oxides and atomic layer deposition (ALD) for HfO 2 . A series of ligands, viz., Nethoxy-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 °C), good volatility (1 Torr at 112 °C), high thermal stability, and excellent endurance over 6 weeks at 120 °C. Therefore, an ALD process for the growth of HfO 2 was developed using HfCp(edpa) 3 (8) as a novel precursor. Furthermore, the HfO 2 film exhibited a low capacitance equivalent oxide thickness of ∼1.5 nm, with J g as low as ∼3 × 10 −4 A/cm 2 at V g −1 V in a metal−insulator−semiconductor capacitor (Au/HfO 2 /p-Si).

High Volatile Antimony(III) Precursors for Metal Oxide Thin Film Deposition

“…The OC H 2 CH 3 of the ethoxy group in 4 – 6 shifted downfield relative to those of the relevant starting materials L 4 – L 6 (from 3.93 to 4.08 ppm for 4 , from 3.86 to 4.06 ppm for 5 , and from 3.86 to 4.06 ppm for 6 ), thereby indicating that the oxygen in the electron donor was coordinated to the antimony atom. The imine peak of all complexes in the 13 C NMR spectrum showed peaks in the range of 163.66–168.38; this range is similar to that observed for previously reported homoleptic metal monomer complexes using these types of ligands. , These observations confirmed that the ligand was attached via a desalted oxygen atom to the antimony metal center.…”

Amidoxime-Containing Zr and Hf Atomic Layer Deposition Precursors for Metal Oxide Thin Films

“…Recently, to overcome this, alkoxide ligands with additional functionalized donors have been used as bidentate ligands in ALD processes for metal oxide thin films. The bidentate ligands that have been widely studied for ALD thin films of ZrO 2 and HfO 2 are alkoxyalkoxides, such as 1-methoxy-2-methyl-2-propanolate (mmp), , as well as aminoalkoxides, such as dimethylaminoethoxide (dmae) and 1-dimethylamino-2-methyl-2-propoxide (dmamp). − In the previous study, we discussed new high-κ metal precursors for Zr and Hf oxide containing N -alkoxy carboxamides as bidentate ligands and ALD applications using a novel hafnium precursor …”

“…21−23 In the previous study, we discussed new high-κ metal precursors for Zr and Hf oxide containing Nalkoxy carboxamides as bidentate ligands and ALD applications using a novel hafnium precursor. 24 With this knowledge, we have focused on the synthesis of new zirconium and hafnium precursors containing modified bidentate donor�functionalized alkoxide ligands to coordinatively saturate the metal center and hence improve the volatility and thermal stability of the metal precursor. While searching for new bidentate ligands for zirconium and hafnium oxide precursors, we decided to introduce amidoxime ligands, which are analogues of an oxime with one of the substituents being an amino group, expecting that these ligands would improve the new zirconium and hafnium complexes' thermal stability and volatility.…”

“…28,29 Furthermore, in the previous study, we also confirmed that the melting point decreased when a Cp ligand was introduced into the respective homoleptic solid compound to yield the corresponding heteroleptic. 24 Therefore, it was expected that the mixed ligand systems combining amidoxime and Cp ligand would provide improved physical properties. Herein, we report the synthesis, chemical and crystal structure characterization, and thermal behaviors of new heteroleptic complexes, namely, CpZr(mdao) 3 (5), CpHf(mdao) 3 (6), CpZr(tdao) 3 (7), and CpHf(tdao) 3 (8).…”

“…, ( E )- N ′-hydroxy- N , N -dimethylacetimidamide (mdaoH) and ( Z )- N ′-hydroxy- N , N -dimethylpivalimidamide (tdaoH), along with their Zr and Hf homoleptic complexes, Zr­(mdao) 4 ( 1 ), Hf­(mdao) 4 ( 2 ), Zr­(tdao) 4 ( 3 ), and Hf­(tdao) 4 ( 4 ). It is well-known that the replacement of one ligand with a cyclopentadienyl (Cp) ligand enhances the thermal stability and volatility of the given precursors. , Furthermore, in the previous study, we also confirmed that the melting point decreased when a Cp ligand was introduced into the respective homoleptic solid compound to yield the corresponding heteroleptic . Therefore, it was expected that the mixed ligand systems combining amidoxime and Cp ligand would provide improved physical properties.…”