ALKOXIDE KETOESTERAT | mocvd-precursor-encyclopedia.de

TITANIUM ALKOXIDES KETOESTERATES

Titanium bis-isopropoxide bis(tert-butyl-2-oxobutanoate) Ti(OiPr)2(tbob)2 (or titanium bis(isopropoxide) bis(tert-butylacetoacetate) [Ti(OPri)2(tbaoac)2] )

Fig. Molecular structure of Ti(OiPr)2(tbaoac)2

Titanium bis-isopropoxide bis(tert-butyl-2-oxobutanoate) Ti(OiPr)2(tbob)2 (or titanium bis(isopropoxide) bis(tert-butylacetocetate) [Ti(OPri)2(tbaoac)2]), was synthesized (from Ti(OiPr)4 and tert-butylacetoacetate tbaoacH) and characterized as pale yellow crystalline solid; the molecular structure of [Ti(OPri)2(tbaoac)2] was determined by single‐crystal XRD. [Ti(OPri)2(tbaoac)2] is a volatile alkoxideβ-ketoesterate precursor having low melting point (58°C) and very good solubility in common organic solvents.[[i]]

[Ti(OPri)2(tbaoac)2] was reported to be potentially useful as MOCVD precursor for Ti-containing layers. Vapour pressure and enthalpy of sublimation of Ti(OiPr)2(tbob)2 was determined by variable temperature thermogravimetric/differential thermogravimetric (TG/DTG) (method based on the Langmuir equation), and Ti(OiPr)2(tbob)2 (and for comparison its titanyl analogue [TiO(tbob)2]2) were evaluated as potential MOCVD precursor for the growth of Ti-contaning layers. The complex Ti(OiPr)2(tbob)2 was found to be a more suitable as titanium MOCVD precursor.[ii]

[i] R. Bhakta, F. Hipler, A. Devi, S. Regnery, P. Ehrhart, R. Waser, Chem. Vapor Dep., 2003, Vol.9, Iss.6, p.295-298, « Mononuclear Mixed β‐Ketoester‐alkoxide Compound of Titanium as a Promising Precursor for Low‐Temperature MOCVD of TiO2 Thin Films »,

https://doi.org/10.1002/cvde.200304151,//onlinelibrary.wiley.com/doi/pdf/10.1002/cvde.200304151

[ii] G.V. Kunte, S.A. Shivashankar, A.M. Umarji, Meas. Sci. Technol., 2008, 19, 025704, doi:10.1088/0957-0233/19/2/025704, « Thermogravimetric evaluation of the suitability of precursors for MOCVD », http://iopscience.iop.org/0957-0233/19/2/025704

Volatility and thermal stability of Ti(OiPr)2(tbaoac)2

Fig. TGA or Ti alkoxides-ketoesterates Ti(OiPr)2(tbaoac)2, Ti(OEt)2(tbaoac)2, Ti(OiPr)2(meaoac)2 (and for comparison of Ti(OiPr)2(thd)2 and Ti(OiPr)4)

The volatility and thermal stability of Ti(OiPr)2(tbaoac)2 (=Ti(OiPr)2(tbob)2) was investigated by thermogravimetry (TGA) and compared to other alkoxides ketoesterates (Ti(OEt)2(tbaoac)2, Ti(OiPr)2(meaoac)2), as well as conventiona Ti precursors Ti(OiPr)2(thd)2 and Ti(Oipr)4 as reference compounds. The new compounds A–C (A=[Ti(OEt)2(tbaoac)2], B=[Ti(OPri)2(tbaoac)2], and C=[Ti(OPri)2(meaoac)2] ) have very similar evaporation temperatures, lower than for [Ti(OPri)2(thd)2]. Small differences were observed: =[Ti(OPri)2(meaoac)2 left highest residue (indication for reactions at the end of the evaporation curve), whereas A=Ti(OPri)2(tbaoac)2] and Ti(OEt)2(tbaoac)2] both had perfect evaporation behavior without indication for decomposition. As the substitution of the (OPri) by the lighter(OEt) did not significantly reduce the evaporation temperature, but slightly increased the residue, [Ti(OPri)2(tbaoac)2] was considered to be slightly better than Ti(OEt)2(tbaoac)2] and was selected for detailed testing as Ti MOCVD precursor.[i]

[i] R. Thomas, R. Bhakta, P. Ehrhart, R.A. Fischer, R. Waser, A Devi, Surf. Coat. Technology, 2007, Vol.201, Iss. 22–23, p. 9135-9140, « Liquid injection MOCVD of TiO2 and SrTiO3 thin films from [Ti(OPri)2(tbaoac)2]: Film properties and compatibility with [Sr(thd)2] », https://doi.org/10.1016/j.surfcoat.2007.04.038

https://www.sciencedirect.com/science/article/abs/pii/S0257897207004185

https://www.researchgate.net/profile/Reji_Thomas4/publication/222960270_Liquid_injection_MOCVD_of_TiO2_and_SrTiO3_thin_films_from_TiOPri2tbaoac2_Film_properties_and_compatibility_with_Srthd2/links/5b1520334585150a0a6742db/Liquid-injection-MOCVD-of-TiO2-and-SrTiO3-thin-films-from-TiOPri2tbaoac2-Film-properties-and-compatibility-with-Srthd2.pdf

Thermolysis behaviour of [Ti(OPri)2(tbaoac)2]

Fig. Possible fragmentation pathways of Ti(OiPr)2(tbaoac)2

The thermolysis behaviour of [Ti(OPri)2(tbaoac)2] was studied using matrix-isolation FTIR spectroscopy to understand the mechanism of its thermal decomposition. It was found that the decomposition of [Ti(OPri)2(tbaoac)2] occurs by the formation of ketene intermediates (pathway A) and CO2 and Ti alkoxide (pathway B) (Fig.) [i]

[i] R. Bhakta, R. Thomas, F. Hipler, H. F. Bettinger, J. Müller, P. Ehrhart, A. Devi, J. Mater. Chem., 2004, Iss. 21, 3231-3238, MOCVD of TiO2 thin films and studies on the nature of molecular mechanisms involved in the decomposition of [Ti(OPri)2(tbaoac)2], https://pubs.rsc.org/en/content/articlelanding/2004/jm/b405963h/unauth#!divAbstract, https://www.researchgate.net/profile/Reji_Thomas4/publication/240496736_MOCVD_of_TiO2_Thin_films_and_Studies_on_the_Nature_of_Molecular_Mechanisms_Involved_in_the_Decomposition_of_TiOPri2_tbaoac2/links/0f317539b58f795ae7000000.pdf

[Ti(OPri)2(tbaoac)2)] for TiO2 films by MOCVD

Fig. TiO2 growth rate of Ti(OiPr)2(tbaoac)2 vs Ti(OiPr)2(thd)2)

Bis(isopropoxy)bis(tert-butylacetoacetato)titanium [Ti(OPri)2(tbaoac)2] was developed and tested as precursor for the growth of TiO2 thin films by MOCVD on SiOx/Si and Pt/ZrOx/SiOx/Si substrates. Using [Ti(OPri)2(tbaoac)2] as Ti source, reduced substrate temperatures compared to conventional [Ti(OPri)2(thd)2] were needed for the growth of titania. Uniform TiO2 films with low surface roughness (<2 nm) at high growth rates (∼10 nm/min) were obtained. Electrical properties of the films on Si substrates were studied and lowest equivalent oxide thickness (EOT) was around 2 nm and anatase phase had a dielectric constant around 40.[i]

[Ti(OPri)2(tbaoac)2)] for SrTiO3 and TiO2 by MOCVD

Fig. Stoichiometry of SrTiO3, Sr,Ti efficiency - a) with Ti(OiPr)2(tbaoac)2; b) with Ti(OiPr)2(thd)2

[Ti(OPri)2(tbaoac)2)] was investigated as precursor for the growth SrTiO3 layers (combined with Sr(thd)2 precursor) and TiO2 films by liquid injection MOCVD on Pt/ZrO2/SiO2/Si substrates with emphasis on achieving low deposition temperatures (≤500°C). [Ti(OPri)2(tbaoac)2] and Sr(thd)2 were dissolved in n-butyl acetate (0.05 M solution), O2 gas (200 sccm) was used as oxidant, growth were carried out at deposition temperatures 300–800°C and process pressure 1- 1.5 mbar. At growth temperatures ≤ 450°C the prepared TiO2 layers were amorphous, but at higher temperatures crystallized in the tetragonal anatase structure. Homogeneous on large areas columnar growth was obtained for the crystalline films. Wide temperature range from 450 to 700°C was applicable for the growth of SrTiO3; at T ≥ 600°C high growth rates and (100) textured SrTiO3 films were obtained. However, SrTiO3 stoichiometry was strongly influenced by decrease of Ti incorporation efficiency at lower temperatures (450-500°C). This effect was attributed to the pre-reactions with the Sr precursor, as it could be avoided by long separation times between the Ti and Sr injection pulses.[i]

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