LI-MOCVD of HfO2 thin films using engineered amide based Hf precursors

Mixed amido–malonato complexes of hafnium were synthesized by protolytic reactions of tetrakis-dialkylamido hafnium {[Hf(NR2)4], where R = Et2 or EtMe} and di-tert-butylmalonate. The introduction of the bidentate malonate ligand stabilized the parent hafnium amide complexes by forming monomeric six coordinated compounds [Hf(NEt2)2(dbml)2] (1) and [Hf(NEtMe)2(dbml)2] (2). The novel complexes were fully characterised by means of single crystal X-Ray analysis, 1H- and 13C-NMR, EI-MS and CHN analysis. Furthermore both the complexes were found to possess suitable thermal properties for CVD application. They are soluble and stable in different organic solvents and hence investigated as precursors for liquid injection metalorganic chemical vapor deposition (LI-MOCVD) of HfO2 thin films. Compound 1 was tested in a multi-wafer planetary MOCVD, whereas compound 2 was tested in a smaller scale, state-of-the-art MOCVD reactor. HfO2 films deposition was achieved over wide temperature range and the films were crystallized in the monoclinic phase at ≥ 500 °C. The low temperature grown HfO2 films were smooth with a very low surface roughness (< 0.4 nm). The electrical properties of metal insulator semiconductor (MIS) capacitor structures were also investigated and the relative dielectric permittivity reached the value of 22. In short, both the precursors are promising for the growth of high quality HfO2 films for high-k gate oxide application.