Thermal Decomposition of metal alkyls to give metal deposits including titanium alkyls may occur by one of these three decomposition pathways/mechanisms:
1) β-Hydride Elimination
2) α-C-H-Abstraction
3) M-C Bond Homolysis
Synthesis: TiCl4 + 4 LiCH2tBu → Ti(CH2tBu)4 + 4 LiCl
Tetrakis(neopentyl)titanium TiNep4 was reported to be a good precursor for the growth of high-quality TiC thin films by MOCVD at low temperatures (150-250°C) [[i]]
The Ti:C ratio was 1.00:0.95 when the TiC films were grown using TiNep4 under a H2 pressure of 10-2 torr. The as-deposited TiC films are amorphous, and can be induced to crystallize only at temperatures >1100°C. XPS, AES, RBS, SIMS, EXAFS, and electron microscopy were techniques to characterize the grown TiC layers. Deuterium labeling and kinetic studies were used to investigate the mechanism of TiC deposition using TiNep4. It was determined that the primary step in the CVD decomposition pathway involves a-hydrogen elimination forming neopentane and titanium alkylidene intermediates.[[ii], [iii], [iv], [v]]
[i] G. S. Girolami, J. A. Jensen, J. E. Pollina, MRS Symp. Proc., Symp H, spring 1988 (G. S. Girolami, J. A. Jensen, J. E. Gozum, D. M. Pollina, MRS Symp.Proc., 121 (1988), 429-438?)
[ii] G. S. Girolami, J. A. Jensen, D. H. Pollina, C. M. Allocca, A. E. Kaloyeros, W. S. Williams, J. Am. Chem. Soc. 109, 1579 (1987)
[iii] A. E. Kaloyeros, C. M. Allocca, W. S. Williams, D. M. Pollina, G. S. Girolami, Adv. Ceram. Mater. 2, 100 (1987)
[iv] C. M. Allocca, W. S. Williams, A. E. Kaloyeros, J. Electrochem. Soc. 135, 3170 (1987)
[v] A. E. Kaloyeros, W. S. Williams, F. C. Brown, A. E. Greene, J. B. Woodhouse, Phys. Rev. B 37, 771 (1988)
Tetrakis-neopentyltitanium [Ti(CH2CMe3)4] and H2 plasma as the precursor and reactant were applied for the ALD deposition of TiCx films. According to XRD and electron diffraction,
the rock-salt-structured TiCx films were deposited. Rutherford backscattering spectrometry was used for determining the C/Ti ratio (~0.52); layer density was ~4.41 g/cm3; the film resistivity was as low as ~600
μΩ cm. Ca. 90% step coverage was reached over the trench structure with an aspect ratio of ~4.5 (top opening diameter 25 nm).[i]
[i] T.E. Hong, S.‐K. Choi, S.H. Kim, T. Cheon, J. Amer. Ceram. Soc., 2013, Vol.96, Iss.4, p.1060-1062, « Growth of Highly Conformal TiCx Films Using Atomic Layer Deposition Technique « , https://doi.org/10.1111/jace.12289, https://ceramics.onlinelibrary.wiley.com/doi/abs/10.1111/jace.12289
Tetrakis–neopentyl–titanium [Ti(CH2CMe3)4] (TiNep4), combined with direct plasma of H2, was used as Ti source for the growth of TiCx films on thermally grown SiO2 substrates by ALD, at the substrate temperatures 200-400 °C. ALD temperature window was
quite narrow from 275 to 300 °C, in which growth rate 0.054 nm/cycle was obtained. According to XRD and TEM, the ALD-TiCx films had nanocrystalline structure with rock-salt phase. The resistivity of the TiNep4-grown TiCx layers was dependent on the microstructure
features (grain size, crystallinity, density), which could be varied by changing the deposition temperature. At the deposition temperature 300 °C (within ALD window)
after optimization of deposition conditions, the resistivity of ~600 μΩ cm was obtained,. Very thin ALD-TiCx (6 nm) was tested as a diffusion barrier for Cu interconnects; it was demonstrated that Cu (80 nm)/ALD-TiCx (6 nm)/Si structure was stable
after annealing at 600 °C for 30 min. However, at 650 °C ALD-TiCx diffusion barrier failed by the diffusion of Cu through the thin barrier layer into Si without interfacial reactions between the layers, as was found by cross-sectional view TEM combined
with EDX.[i]
[i] S.-K. Choi, H. Kim, J. Kim, T. Cheon, J.H. Seo, S.-H. Kim, Thin Solid Films, 2015, Vol. 590, p.311-317 « Properties of plasma-enhanced atomic layer deposited TiCx films as a diffusion barrier for Cu metallization », https://doi.org/10.1016/j.tsf.2015.05.033, https://www.sciencedirect.com/science/article/pii/S0040609015005672