ZIRCONIUM (IV) TETRAKIS( ALKOXIDES)
Zirconium alkoxides Zr(OR)4 are synthesized by metathesis reaction of zirconium tetrachloride and lithium alkoxides (or alcohols in the presence of trimethylamine):
ZrCl4 + 4 LiOR (or ROH / Et3N) → Zr(OR)4 + 4 LiCl (or NEt3H+Cl-)
Zirconium alkoxides Zr(OR)4 are widely applied as precursors for the growth of Zr-containing layers by MOCVD or ALD.
Zirconium tert-butoxide Zr(OtBu)4
Zirconium tert-butoxide Zr(OtBu)4 is liquid at room temperature .
The NMR spectrum of Zr(OtBu)4 is presented in Fig. : it reveals the magnetic equivalence of all four tert-butoxide ligands. [244]
The disadvantage of Zr(OtBu)4 is that it is prone to decomposition during storage, and is
very susceptible for catalytic decomposition by traces of moisture [[i]]
[i]Xinye Liu, PhD Theseis, Harvard University, 1999
Zr(OtBu)4 for ZrO2 films by MOCVD
Zr(OtBu)4 is a conventional precursor for MOCVD of ZrO2 films.
Zr(OtBu)4 for ZrSiOx (Zr silicate) films by MOCVD
Zr(OtBu)4 was applied for the CVD growth of Zr silicate containing 27% SiO2 , by using SiH4 as the silicon source, but no subsequent composition control was reported. [[i]]
[i] C.H. Lee, H.F. Luan, W.P. Bai, S.J. Lee, T.S. Jeon, Y. Senzaki, D. Roberts, and D.L. Kwong, Tech. Dig. Int. Electron Devices Meet. (2000), p. 27.
Zr(OtBu)4 for Pb(Zr,Ti)Ox (PZT) films by conventional (bubbling/sublimation) and liquid delivery MOCVD
Zr(OtBu)4 was applied as Zr source for the growth of Pb(Zr,Ti)O 3 (PZT) films by MOCVD, in combination with Pb(thd)2 and Ti(OiPr)4 as Pb, Ti sources and O 2 as oxidant. The effect of solvent ( tetrahydrofurane C 4 H 8 O (THF)
or octane C 8 H 18) on the PZT deposition MOCVD process was investigated by comparing conventional bubbling/ sublimation delivery MOCVD with liquid delivery MOCVD, where the source materials were dissolved in a
solvent and vaporized in separate vaporizers. The deposition rates of all constituent oxides decreased with the liquid-delivery method, and the process window to obtain stoichiometric PZT films [Pb/(Pb+Zr+Ti)=0.5], irrespective of the supply rate of the Pb source, was diminished, suggesting contribution of the solvent on the PZT layer deposition mechanism. These phenomena were observed not only with octane C8H18, but also in case of THF (C
4 H 8 O) used as a solvent.[[i]]
[i] H. Funakubo, G. Asano, T. Ozeki, H. Machida, T. Yoneyama , Y. Takamatsu, J. Electrochem. Soc. 2004, vol. 151, iss.7, C463-C467, doi: 10.1149/1.1751194 , http://jes.ecsdl.org/content/151/7/C463.short, « Effect of Solvent on MOCVD of Pb ( Zr , Ti ) O 3 Films with Liquid-Delivery Source Supply Method »
Zirconium 3-methyl-3-pentoxide, Zr[OC(CH3)(C2H5)2]4, or (Zr(mp)4
Zirconium 3-methyl-3-pentoxide (Zr[OCMeEt2]4,
Zr(mp)4 ) is a liquid at RT, demonstrating an excellent one-step weight loss and a low residual weight (< 3%) by TGA. Zr[OCMeEt2]4 was applied as single source precursor (without additional oxygen source) for the growth of thin ZrO2 films on Si substrates
by MOCVD at the substrate temperature of 300 °C (with the activation energy of 33.5 kJ/mol),; the CVD reaction mechanism was investigated. The growth rate was ∼1.3
nm/min at the moderate (70 °C) precursor evaporation temperature using 50 sccm N2 carrier gas flow. ZrO2 films were growing via β-hydrogen elimination processes of the Zr(mp)4 single precursor, as was determined that the gas chromatography/mass
spectrometry and NMR analysis of the thermally decomposed vapor phase by-products collected during the deposition of ZrO2 films. Only negligible carbon impurity incorporation in the deposited ZrO2 films was found by XPS indicating that, apart the β-hydrogen
elimination processes, no additional decomposition and/or recombination processes contributed to the ZrO2 films growth. The crystallinity, morphology and electrical properties of the deposited ZrO2 films were investigated by XRD, SEM, and capacitance-voltage
measurements.[[i]]
[i]Cho, Wontae; Jang, Hong Suk; An, Ki-Seok; Lee, Young Kuk; Chung, Taek-Mo; Kim, Chang Gyoun; Kim, Yunsoo; So, Byung-Soo; Hwang, Jin-Ha; Jung, Donggeun; J. Vac. Tech. A: Vacuum, Surf., Films, Jul 2006, Vol.24 Iss:4, p. 1208 -1212
Zirconium tetrakis(methoxymethylpropanolate) Zr (mmp)4
Zirconium tetrakis(methoxymethylpropanolate) Zr(MMP)4, dissolved together with Pb(DMAMP)2 and Ti(MMP)4 in the ethylcyclohexane
(ECH) solvent (a “cocktail” solution), was applied for the growth of ferroelectric PbZrTiOx (PZT) thin films by liquid delivery MOCVD. This cocktail solution is stable at least 3 months and perfectly vaporized above 290°C. Deposited films were
crystallized into perovskite PZT phase with preferred 111-orientation at 400°C substrate temperature.[[i]
[i] Y. Otani, K. Uchiyama, S. Okamura, T. Shosaki, Integrated Ferroelectrics: An International Journal, 2006, Vol. 81, Iss.1, pages 261-270, DOI: 10.1080/10584580600663326 , Low temperature deposition of Pb(Zr,Ti)O3 thon films by liquid delivery MOCVD using a cocktail source with Pb(DMAMP)2, Zr(MMP)4 and Ti(MMP)4
Tetrakis(2-methyl-3-butene-2-oxy)zirconium Zr(O-CMe2-CH=CH2)4
The unsaturated zirconium alkoxide tetrakis(2-methyl-3-butene-2-oxy)zirconium Zr(O-CMe2-CH=CH2)4 was proposed by as potential precursor for the ALD growth of Zr-containing layers. Compared to the best zirconium precursor TEMAZ, it has relatively higher thermal stability, higher cost performance than TEMAZ and higher reactivity with O3, what can significantly increase throughput. [Asahi Denka]
Tetrakis(2-methyl-3-butene-2-oxy)zirconium was synthesized by the reaction:
ZrCl4 + 4 CH2=CH-CNe2-OH + 4 Et2NH (dry hexane, -10°C/ RT (18h)/ +50°C(5h)) -> Zr(O-CMe2-CH=CH2)4 + 4 [Et2NH2]+ Cl-
The diethylammonium chloride precipitate was removed by the filtration, and the filtrate was concentrated and distilled under reduced pressure. Pure Zr(O-CMe2-CH=CH2)4 was obtained with yield: 54.6% as a colorless transparent liquid (the fraction distilled at vapor temperature 83-95° C/ pressure 0.17- 0.18 torr). The compound was characterised by elemental analysis (Zr: 20.8 mass % (metal analysis ICP-AES), theoretical value: 21.13 mass %) and 1 H-NMR (in the C6D6 solvent). Vapor pressure of Zr(O-CMe2-CH=CH2)4 was found to follow the equation Log P (Torr)=6.01−2308/ T ( K ); it was determined by measuring the vapor temperature in the vicinity of the liquid surface at a constant pressure kept during the measurement.
Thermal stability of Zr(O-CMe2-CH=CH2)4 was evaluated and compared to Zr(NEtMe)4, Zr(OtBu)4, by keeping complexes sealed under Ar for 1 hour at 160°C.,180°C, and 200°, and analysing the complexes differential thermal analysis (thermogravimetry) with a temperature elevation rate of 10° C./min from 30° C. in a dry Ar stream (100 sccm). The resulting 400° C. residue in mass % was compared for the different complexes. The measurement results are shown in the Tables 1 and 2.
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