TITANIUM CYCLOPENTADIENYLS-ALKOXIDES
Several monocyclopentadienyl tris(alkoxide) titanium complexes such as CpTi(OMe)3, (MeCp)Ti(OMe)3, (Me5Cp)Ti(OMe)3, (see below) were tested as precursors for the deposition of TiO2 thin films by ALD. Low growth rates (0.24–0.27 Å/cycle) were observed for these processes. (Me5Cp)Ti(OMe)3 contaning highly substituted Cp ring was much more thermally stable compared to CpTi(OMe)3 and (MeCp)Ti(OMe)3, in disagreement with previous observations about benefits of precursors containing highly substituted Cp ligands.
Titanium cyclopentadienyl tris(methoxide) TiCp(OMe)3
TiCp(OMe)3 was mentioned to be as potential precursor for the deposition of TiO2 layers by ALD (was reported to be less thermally stable than analogous pentamethylcyclopentadienyl
complex Ti(Me5Cp)(OMe)3 ).[i]
[i] J. Niinistö, T. Blanquart, S. Seppälä, M. Ritala, M. Leskelä, 2014, ECS Transactions, 64 (9) 221-232, « Heteroleptic Precursors for Atomic Layer Deposition », http://ecst.ecsdl.org/content/64/9/221.short, http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.850.4157&rep=rep1&type=pdf
Titanium cyclopentadienyl tris(methoxide) Ti(MeCp)(OMe)3
Ti(MeCp)(OMe)3 (“PrimeTi”) for TiO2 films by ALD
Ti(MeCp)(OMe)3 (“PrimeTi™”) was tested as precursor for the deposition of TiO2 layers by ALD. (and compared with conventional Ti(NMe2)4,
Ti(NEt2)4, Ti(NEtMe)4, and novel Ti(Me5Cp)(OMe)3 (StarTi™), (TiCp(NMe2)3 (TyALD™) precursors), using either H2O or O3 as oxygen source. For the TiO2 ALD process using Ti(MeCp)(OMe)3 (as well as other precursor were determined: growth rate per ALD
cycle, process temperature window (range and upper limit), precursor volatility and stability, chemistry with desired oxidizer and other parameters critical for the precursor selection. All titanium alkylamide compounds had narrow process window; the alkylamide
precursor decomposition was occurring at temperatures >225°C, limiting the deposition process at this temperature. On the contrary, with Ti(MeCp)(OMe)3 (PrimeTi™) and Ti(Me5Cp)(OMe)3 (StarTi), TiO2 ALD (self-limited growth) was observed up to
325°C and 400°C, respectively.[i]
[i] R. Katamreddy, V. Omarjee, B. Feist, Ch. Dussarrat, ECS Trans. 2008, vol.16, iss.4, p.113-122, « Ti Source Precursors for Atomic Layer Deposition of TiO2, STO and BST », doi: 10.1149/1.2979986, http://ecst.ecsdl.org/content/16/4/113.short
Ti(MeCp)(OMe)3 (“PrimeTi”) for SrTiO3 films by ALD
Ti(MeCp)(OMe)3 (PrimeTi), and for comparison other novel Ti precursors (Ti(Me5Cp)(OMe)3 (StarTi), TiCp(NMe2)3 (TyALD), Ti(Me5Cp)(NMe2)3 (StarTyALD) was evaluated
as precursor for deposition of SrTiO3 layers by ALD (in combination with several Sr precursors (Sr(iPr3Cp)2 (AbsoluteSr), Sr(iPr3Cp)2·2THF (HyperSr.THF), Sr(iPr3Cp)2.DME (HyperSr.DME), Sr(Me5Cp)2.THF (StarSr.THF), Sr(iPr3Cp)2.DME (StarSr.DME), in which
the effect of stabilizing adducts on the properties of Sr cyclopentadienyl precursors and SrO ALD process was evaluated). The compatibility of Ti(MeCp)(OMe)3 (and (Ti(Me5Cp)(OMe)3) with Sr(iPr3Cp)2·2THF
precursor, as well as composition tunability and material properties of SrTiO3 layers deposited by ALD were studied.[i]
[i] R. Katamreddy, Z. Wang, V. Omarjee, P.V. Rao, Ch. Dussarrat, N. Blasco, ECS Trans. 2009, Vol.19, Iss.2, 525-536, « Advanced Precursor Development for Sr and Ti Based Oxide Thin Film Applications », doi: 10.1149/1.3122114, http://ecst.ecsdl.org/content/19/2/525.short
Titanium pentamethylcyclopentadienyl tris(methoxide) Ti(Me5Cp)(OMe)3 (TiCp*(OMe)3)
Titanium pentamethylcyclopentadienyl tris(methoxide) TiCp*(OMe)3 was tested as precursor for the ALD growth of TiO2 films (with H2O as oxygen source). However, unlike Ti(OMe)4 and H2O giving 0.5 Å/cycle growth rate, the TiCp*(OMe)3 did not show any growth in usualy ALD conditions. This observation is in contradiction with the computed reactivity of the ligands: the energetics of hydrolysis of the gas-phase precursor indicated that TiCp*(OMe)3 was expected to be more reactive to ligand elimination than Ti(OMe)4. This contradiction was explained by another model: a TiO2 slab that is periodic in three dimensions; the calculations according to it revealed that TiCp*(OMe)3 does not chemisorb in the usual way on TiO2 surface because of extreme crowding of the Ti centre by Cp* , what prevents ALD growth of TiO2.
These calculations explain the common finding that titanocene-derived precursors do not yield TiO2 films in ALD with water. [i]
[i] A. Zydor, Aleksandra; S.D. Elliott, J. Nanosci. Nanotechn., Vol.11, No.9, 2011, pp. 8089-8093(5), DOI: https://doi.org/10.1166/jnn.2011.5108, « TiCp*(OMe)3 versus Ti(OMe)4 in Atomic Layer Deposition of TiO2 with Water—Ab Initio Modelling of Atomic Layer Deposition Surface Reactions »,
https://www.ingentaconnect.com/content/asp/jnn/2011/00000011/00000009/art00080
Ti(Me5Cp)(OMe)3 (+O3) for TiO2 by ALD
Fig. QMS study of TiO2 ALD growth using TiCp*(OMe)3 and O3
Successful use of titanium pentamethylcyclopentadienyl tris(methoxide) TiCp*(OMe)3 as precursor for the atomic layer deposition growth of TiO2 films, when O3 was applied as oxidant, was reported.
Thus, TiCp*(OMe)3 was used (with O3 as oxidant) as Ti precursor for the growth of TiO2 films by thermal ALD in a 300 mm wafer reactor, the growth mechanism was studied by quadrupole mass spectrometry (QMS). The deposited TiO2 layers were analyzed by XRR, XPS, grazing incident XRD, and ToF-SIMS. Nearly stoichiometric TiO2
films were grown in a self-limiting growth mode according to XRR and XPS measurements; The growth per cycle increased with temperature: from 0.22 Å at 235 °C to 0.29 Å at 330 °C. Anatase crystal structure TiO2 layers were deposited on TiN,
compared to the rutile phase TiO2 layers grown on Ru substartes. Carbon contamination was reduced to very low levels at 295 °C growth temperature, as was determined by ToF-SIMS analysis. It was demonstrated that QMS studies can be used in a 300 mm reactor
at very low pressures to study the process chemistry. Thus, according to QMS, the release of MeOH during the TiCp*(OMe)3 precursor pulse and release of CO2 and H2O during the O3 pulse was happening at 7 mbar process pressure, whereas at 3 × 10−3
mbar pressure the release of Cp* ligand and the remaining OMe ligands during O3 pulse was observed. [i]
[i] M. Rose, J. Niinistö, P. Michalowski, L. Gerlich, L. Wilde, I. Endler, J.W. Bartha, J. Phys. Chem. C, 2009, 113 (52), pp 21825–21830, « Atomic Layer Deposition of Titanium Dioxide Thin Films from Cp*Ti(OMe)3 and Ozone », DOI: 10.1021/jp907940u, https://pubs.acs.org/doi/abs/10.1021/jp907940u
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