Hafnium tetrakis-acetylacetonate [Hf(acac)4] can be used for CVD of HfO2, but requires high vaporisation temperatures (~ 200°C) for sufficient evaporation, and the oxide films are often heavily contaminated with carbon [[i]].
[i] M. Pulver, G. Wahl, Electrochem. Soc. Proc., 97-25, 960 (1997)
Hafnium trifluoroacetylacetonate [Hf(tfac)4] is more volatile than acetylacetonate [[i]], but the presence of fluorine is often undesirable in microelectronics applications.
[Hf(tfac)4] was applied as precursor for the growth of HfO2 by CVD as early as 1972
[i] M. Balog, M. Schieber, S. Patai, M. Michman, J. Cryst. Growth, 1972, 17, 298.
Hf(thd)4 for HfO2 by MOCVD
Hafnium 2,2,6,6-tetramethyl-3,5-heptanedionate Hf(thd)4 has been applied as precursor for the growth of HfO2 by MOCVD (“oxygen-assisted depositon”) as early as 1977 by Balog et. al. [[i]] HfO2 layers were grown on Si substrates at 400–550 °C temperatures; the films were characterized by TEM, XRD, electron microprobe analysis and measurements of dielectric and optical properties (refractive index 2.1, optical energy gap 5.68 eV). The grown HfO2 layers were fine-grained (~32.5nm) nearly stoichiometric monoclinic HfO2; the films showed high resistance to most aqueous acids and bases. HfO2 films had dielectric constant 22–25 at 1 MHz, and the dielectric strength of the HfO2 films varied between 2 × 106 and 4.5 × 106 V/cm; The VFB values were between −0.6 and 0 V; effective surface states varied 1-6 × 1011 cmt−2 according to C-V measurements at 1 MHz (for films grown >500 °C or annealed at above 750 °C (deposited at 400–450 °C)).
[i] M. Balog ∗, M. Schieber, M. Michman, S. Patai, Thin Solid Films, Volume 41, Issue 3, 15 March 1977, Pages 247-259, “Chemical vapor deposition and characterization of HfO2 films from organo-hafnium compounds,”
Hafnium tetrakis(2,2,8,8-tetramethyl-4,6-nonanedionate) was synthesized and characterized by elemental analysis, 1H NMR, FT-IR and mass spectrometry.
Hf(tmnd)4 was tested as precursor for the growth of HfO2 films by MOCVD on R- plane sapphire and Si(100). Preferentially (001)/(010)/(100) textured and in-plane oriented monoclinic HfO2 films were deposited by pulsed liquid injection MOCVD. Smooth films were grown, especially on sapphire and at low growth temperature (500 °C), whereas films on Si(100) were polycrystalline and had rougher surface. 3–4 at.% of carbon contamination was detected by XPS. Hf(tmnd)4 leads to significantly higher growth rate of HfO2 films at low temperature than conventional Hf(thd)4 precursors and is therefore attractive precursor for oxide films. [[i]]
[i] S.V. Pasko, A. Abrutis, L.G. Hubert-Pfalzgraf, Materials Letters, Vol.59, Issues 2–3, February 2005, Pages 261-265, “Hafnium and zirconium tetramethylnonanedionates as new MOCVD precursors for oxide films”, http://www.sciencedirect.com/science/article/pii/S0167577X04007074