ZIRCONIUM (IV) TETRAKIS(β-DIKETONATES)

    Zirconium tetrakis(β-diketonates) are conventional precursors for the growth of Zr-contaning layers by MOCVD.

      Homoleptic Zr (β-diketonates) are white sublimable solids.

     However, mixed ligand zirconium β-diketonates Zr(R1,2,3,4CO-CH-CO-R5,6,7,8) were reported to be liquids, which were tested for direct liquid injection MOCVD of ZrO2 layers (with evaporation in N2 at 185°C, oxidation of precursor by O2  resulting in the growth of ZrO2 layer at substrate temperatures 420-460°C). [[i]]

[i] Xinye Liu, PhD Thesis, Harvard University, 1999

Zirconium tetrakis(acetylacetonate) Zr(acac)4

     Zirconium tetrakis(acetylacetonate) Zr(acac)4 is colorless solid with melting point 172 °C, fairly stable.

    Zirconium tetrakis(acetylacetonate) is synthesized by the metathesis reaction between  zirconium tetrachloride and alkaline metal acetylacetonates in the presence of amines:

 ZrCl4 + 4 Li(acac) (HOR / NEt3) → Zr(acac)4 + 4 LiCl (NEt3H+Cl-)

Zr(acac)4 is potentially applicable as precursor for the growth of Zr-containing layers by MOCVD.

Zirconium tetrakis(2,2,6,6-tetramethylheptane-3,5-dionate) Zr(thd)4

Fig. Growth rate with Zr(thd)4 vs. [Zr(OiPr)3(thd)]2 precursor

Among zirconium β-diketonates, zirconium tetrakis(2,2,6,6-tetramethylheptane-3,5-dionate) Zr(thd)4 is one of the most popular precursors for the growth of zirconia thin films by MOCVD.

            Although generally higher temperatures are required for the reasonable growth rates using  Zr(thd)4 , compared to f.e. mixed alkoxides-diketonates like Zr2(OiPr)6(thd)2 (see Fig), the deposition at lower temperatures can be promoted by Pd(hfac)2[[i]]

 [i] Zhang, Y. et al. J. Am. Chem. Soc. 119, 9295, (1997)

Thermal properties of Zr(thd)4

Fig. TGA/DSC curve of Zr(thd)4

Zr(thd)4 was analyzed by the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)

The TGA /DSC curve of Zr(thd)4 is presented in Fig. Two endothermic peaks are observed on the DSC curves : the first is releated to melting (308°C), the second at ~330°C indicates the maximum of the evaporation rate. About 6% of residue is not evaporated.

High purity Zr(DPM)4 (DPM = dipivaloylmethanate = 2,2,6,6-tetramethyl-3,5-heptanedionate) was successfully synthesized from inorganic salts and HDPM in ethanol/aqueous solution, purified by recrystallization from toluene and characterized by elemental analysis, XRD, TGA/DTA, NMR and FTIR spectroscopy (both fresh and aged for 30 days in air), Zr(DPM)4 was applied as precursor of MOCVD of Zr-containing multi-component oxide thin films. [[i]]

[i]H. Song, Y. Jiang, Ch. Xia, G. Meng, D. Peng, https://doi.org/10.1016/S0022-0248(02)02413-2, https://www.sciencedirect.com/science/article/pii/S0022024802024132

“Synthesis and characterization of volatile metal β-diketonate chelates of M(DPM)n (M=Ce, Gd, Y, Zr, n=3,4) used as precursors for MOCVD” 

Zr(thd)4 for ZrO2 deposition by MOCVD

Zirconium tetramethylheptanedionate [Zr(thd)4] was synthesized; the purity of Zr(thd)4 was confirmed by melting point check, C, H elemental analysis and proton NMR.

Zr(thd)4 was applied as precursor for the growth of excellent quality ZrO2 thin films on single-crystal Si wafers by low-pressure MOCVD. At substrate temperature <530 °C, the layer growth rate was very small (<1 nm/min), however, the deposition rate was significantly affected by either source temperature, substrate temperature, or total pressure. Only the tetragonal ZrO2 phase was identified in as-deposited films, the layers were carbon free. The tetragonal phase transformed progressively into the monoclinic upon a high-temperature post-deposition anneal. The optical properties of the ZrO2 layers were studied as a function of wavelength (200 nm - 2000 nm). A simplified theoretical model considering surface reactions during deposition of ZrO2 films was developed; it well predicted the deposition rates using Zr(thd)4 for various conditions in the hot wall reactor.[[i]]

[i] J. Si, Seshu B. Desu, Ch.-Y. Tsai,  J. Mater. Research, 1994, Vol 9, Iss.7  pp. 1721-1727  « Metal-organic chemical vapor deposition of ZrO2 films using Zr(thd)4 as precursors », https://doi.org/10.1557/JMR.1994.1721

https://www.cambridge.org/core/journals/journal-of-materials-research/article/metalorganic-chemical-vapor-deposition-of-zro2-films-using-zrthd4-as-precursors/07C53C6AC95CA5055EE415B70C718BF5

Zr(thd)4 for ZrO2 (Y) (YSZ) deposition by MOCVD

             Zr(thd)4 was applied for the MOCVD growth of yttria-stabilized zirconia (YSZ)  films on silicon and on stainless steel substrates [[i]]

[i] Bourhila, N. et al. Proc. Electrochem. Soc. 97-25, 417, (1997

Zr(thd)4 for PZT deposition by MOCVD

Zr(thd)4 is widely used for the growth of Zr-contaning layers by MOCVD, however it has  rather high decomposition temperature, with optimum deposition temperature being >550°C. Nevertheless, it was successfully applied as Zr source for the growth of Pb-Zr titanate  (PZT) layers by MOCVD, using the precursors listed in the table below.

  Main metal precursors (generally containing b-diketonates) for the MOCVD of PZT layers:      

Zr(thd)4 for PNZT deposition by MOCVD

Zr(thd)4 was demonstrated to be promising zirconium source precursor for the growth good quality PNZT layers by  MOCVD [[i]]

[i] Chen, I-S. et al. Chem. Mater. 11, 209, (1999)

Zirconium tetrakis(methoxyethoxy tetramethylheptanedionate) Zr(methd)4

      Zirconium tetrakis(methoxyethoxytetramethylheptanedionate) Zr(METHD) 4 , in combination with Pb(METHD)2 and Ti(MPD)(METHD)2 ( mixed in a cocktail source dissolved in the ECH (ethylcyclohexane) solvent), was applied as zirconium precursor for the growth of ferroelectric PZT thin films by liquid delivery MOCVD. Zr(METHD) 4  precursors had decomposition temperature around 300°C, close to the Pb and Ti precursors. The cocktail sources in the ECH solvent were perfectly vaporized above 280°C, and were stable at least for 6 months. The deposited films crystallized into perovskite PZT phase with appropriate composition, however undesirable PbPt x alloy admixture formed at the interface between bottom Pt electrodes and PZT layer at substrate temperature 550°C, reactor pressure 3 Torr, vaporizer temperature 280°C/ vaporizer pressure  115 Torr. The polarization properties of the deposited PZT thin films were not sufficient due to the formation of PbPt x layer.[[i], [ii]]

            Zr(METHD)4 , dissolved in a cocktail source together with Pb(METHD)2 and Ti(MPD)(METHD)2 and was examined for the growth of ferroelectric Pb(Zr, Ti)O3 thin films by liquid delivery MOCVD on 6-inch Pt/Ti/SiO2/Si wafers at 550∘C. PbPtx  alloy phase existed in PZT films deposited at 500∘C was disappeared by post-annealing at 600∘C and the annealed film showed hysteresis properties with the 2P r  of 56 μ C/cm2 and the 2E c  of 181 kV/cm.[[iii]]

[i] Y. Otani , N. Abe, Y. Ueda , M. Miyake , S. Okamura  & T. Shiosaki , Integr. Ferroelectrics, An International Journal , Vol. 46, 2002 - Issue 1, p.115-124, https://doi.org/10.1080/10584580215398

[ii] Y. Otani , N. Abe, Y. Ueda , M. Miyake , S. Okamura  & T. Shiosaki , Integrated Ferroelectrics, An International Journal, Vol. 51, 2003 - Issue 1, p.63-72, https://doi.org/10.1080/10584580390229824 , « Fabrication of Pb(Zr,Ti)O 3 Thin Films by Liquid Delivery MOCVD Using a Cocktail Source with Pb(METHD) 2 , Zr(METHD) 4 and Ti(MPD)(METHD) 2 « 

http://www.tandfonline.com/doi/abs/10.1080/10584580390229824

[iii] Y. Otani, S. Okamura, T. Shiosaki, J. Electroceram., 2004, Vol. 13, Iss. 1–3, pp 15–22, “Recent Developments on MOCVD of Ferroelectric Thin Films”, https://link.springer.com/article/10.1007/s10832-004-5069-z

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