Titanyl-bis[tetramethylheptanedionate] TiO(thd)2 (M=) is white solid, has some volatility and was proposed as potential precursor for MOCVD of Ti-contaning layers (foe example SrTiO3 or (Ba,Sr)TiO3).
Titanyl-bis[tetramethylheptanedionate] TiO(thd)2
was considered as possible titanium precursors for SrTiO3 deposition and the ab-initio simulations (with the quantum chemistry code DMOL) of the adsorption behaviour of TiO(thd)2 ((and for comparison conventional Ti precursor Ti(OiPr)4). A model system for the adsorption at a 2-D (100) SrO terminated surface was developed (a cluster representation of 3x3 elementary cells); model calculations for TiO2 and CH4 adsorption were used for estimation of the errors introduced
by the use of a finite cluster instead of the infinite surface. The calculation showed that TiO(thd)2 precursor molecule has much lower energy of adsorption, larger distance of the adsorbed state to the surface and lower dissociation energy than Ti(OiPr)4.
These results lead to expectation of lower sticking probability and a higher surface mobility TiO(thd)2 compared to Ti(OiPr)4. This conclusion was confirmed by the experimental results on edge coverage of (Ba,Sr)TiO3 films deposited by the MOCVD using TiO(thd)2
and Ti(OiPr)4).[i]
[i] R. Metzger, Ch. Werner, A. Spitzer, Thin Solid Films 365 (2000) 242-250, Adsorption of precursor molecules in the CVD process of (Ba;Sr)titanate simulated by ab-initio calculations », https://www.researchgate.net/publication/248314325_Adsorption_of_precursor_molecules_in_the_CVD_process_of_BaSrtitanate_simulated_by_ab-initio_calculations
Titanyl bis[2,2,6,6-tetramethyl-3,5-heptanedionate] TiO(thd)2, combined with Ba(thd)2 and Sr(thd)2 precursors, was applied as Ti precursor for the MOCVD deposition of
perfectly conformal (Ba, Sr)TiO3 films under the kinetically limited conditions for their application in three-dimensional capacitors. The Ba/Sr composition ratio was determined by the partial pressure ratio of Ba(thd)2 and Sr(thd)2 (due to the kinetically
limited condition), resulting in the self-matching Ti/(Ba+Sr) stoichiometry (occurred under certain TiO(thd)2 supply range). It was suggested that the possible reactive species were Ba(thd)2-O-Ti(thd)2 and Sr(thd)2-O-Ti(thd)2 dimers.[i]
[i] K. Eguchi, M. Kiyotoshi, Integr. Ferroelec., An International Journal, 1997, Vol.14, Iss. 1-4, p.33-42, « Chemical vapor deposition of (Ba,Sr)TiO3 thin films for application in gigabit scale dynamic random access memories », https://doi.org/10.1080/10584589708019974
The properties of (Ba,Sr)TiO3 [BST] films grown by liquid source CVD on Pt/SiO2/Si substrates using TiO(thd)2 (or [titanyl bis (dipivaloylmethanato) TiO(DPM)2
= TiO(C11 H19O2)2] as Ti precursor (and for comparison Ti(OiPr)2(thd)2 and Ti(OiPr)4) were investigated []. With TiO(DPM)2 precursor, improved electrical properties and step coverage were obtained at substrate temperature TS=420°C and reactor pressure
P=1.5Torr: dielectric constant ε=210, equivalent SiO2 thickness teq=0.51nm, leakage current density JL=6.6×10∼−8A/cm2 at +1.1V, dielectric loss tan δ=0.007,
step coverage 0.8. However, with Ti(OiPr)2(thd)2 in these conditions hillocks were present on the (Ba,Sr)TiO3 film surface whereas using Ti(OiPr)4 the film surface was relatively smooth. The density of the hillocks was correlating to the BST(110) peak intensity
of the XRD pattern.[i]
[i] T. Kawahara, M. Yamamuka, T. Makita, A. Yuuki, MRS Symp. Proc., 1994, Vol.361 (Symp. I2 – Ferroelectric Thin Films IV), 361, « Influence of Ti Sources on Properties of (Ba,Sr)TiO3 Films Prepared by Liquid Source CVD », https://doi.org/10.1557/PROC-361-361, https://www.cambridge.org/core/journals/mrs-online-proceedings-library-archive/article/influence-of-ti-sources-on-properties-of-basrtio3-films-prepared-by-liquid-source-cvd/1E4DFDDD61DCEFB2D11C79627D8D8528