TITANIUM (IV) ALKYLAMIDES
Fig. Mass deposition rates as a function of reciprocal temperature (1000/T) for the TDMAT(scaled down to 4 sccm)-NH3 and TDEAT(20 sccm) -NH3 chemistry.
Titanium amide-based CVD processes [[i], [ii], [iii], [iv], [v]], are an attractive alternative to titanium halides, if TiN thin films are to be applied on more thermally sensitive substrates such as aluminum-metallized chips, amorphous silicon solar cells, and plastics. The reason is that titanium amides are precursors allowing significantly lower deposition temperatures (<500°C), than TiCl4-TiN-CVD processes.
Transamination mechanism of TiN growth from amides with ammonia
The deposition of TiN films at 200-400 °C occurs via a transamination reaction of [Ti(NR2)4] and ammonia: (R = methyl, ethyl, or butyl), as it is proven that the nitrogen in titanium nitride film comes from ammonia, and not from the dialkylamido ligand. Low carbon content in the films (especially when R = Et) also indicates that the alkylamine ligands leave cleanly, probably by a combination of transamination reactions and β-H elimination, as suggested by Fix et al. [689]. According to R. Gordon [652], the approximate reaction mechanism of TiN growth is following:
1) Ti(NR2)4 + NH3→ Ti(NR2)3(NH2) + R2NH,
2) Ti(NR2)3(NH2)+ NH3→ Ti(NR2)2(NH2)2+ R2NH,
3) Ti(NR2)2(NH2)2 + NH3→ Ti(NR2)(NH2)3 + R2NH,
4) Ti(NR2)(NH2)3 + NH3→ Ti(NH2)4 + R2NH
„Titanium amide“ is not a known compound, it undergoes rapid unimolecular decomposition: 5) Ti(NH2)4→ HN=Ti(NH2)2 + NH3
Further elimination from HN=Ti(NH2)2 is unlikely [[vi]], although R. Gordon [652] considered it as a possible process step: 6) HN=Ti(NH2)2→ HN=Ti=NH + NH3
Another possible mechanism of imido intermediates formation is β-elimination (starting from R = Et): Ti(NEt2)4 → Ti(NEt2)2NEt + Et2NH + C2H4. A theoretical study using thermodinamical and quantummechanical considerations shows that this pathway contributes less to titanium imido formation than the ligand exchange followed by elimination.[[vii]]
Whatever of this formation ways is correct, the experimental evidence clearly shows that imido compounds play a significant role as intermediates in Ti-N film growth.[[viii]] The formation of oligomers from these complexes occurs [[ix]], as an example the calculations show that the formation of a dimer from Ti(NH2)2=NH is a barrierless reaction resulting in a large binding energy [[x]].
Further surface-assisted polymerization of titanium imides leads to formation of hydrogen-containing titanium nitride [652]. The hydrogen content under correctly selected deposition conditions can be very low. Another possible pathway is the abstraction of hydrazine from the imido dimer complex with formation of hydrogen-free TiN. However, calculations show that this reaction is highly endothermic, suggesting that reduction of Ti(IV) to Ti(III) may occur on the surface rather than in the gas phase.
TiN films prepared from less reactive TDEAT (and TEMAT) have a lower resistivity and a negligible level of oxygen
contamination and show excellent stability in resistivity upon air exposure. [699] Optimised hardware (Tricent, AIXTRON SE) and process conditions allowed to achieve good step coverage
and low particle levels, as well as good resistivity: <500 μΩ∙cm of TiN with the TDEAT precursor [[xi]] It has been calculated that a resistivity of less than 600 μΩ∙cm is acceptable for the TiN adhesion or barrier layer.[699]
[i] A. Intermann, H. Koerner, and F. Koch, J. Electrochem. Soc. 140, 3215, (1993).
[ii] A. Weber, R. Nikulski, C.-P. Klages, M. E. Gross, L. W. Brown, E. Dons, R. M. Charatan, J. Electrochem. Soc. 141, 849 (1993).
[iii] Eizenberg, M.; Littau, K.; Ghanayem, S.; Liao, M.; Mosely, R.; Sinha, A. K. J. Vac. Sci. Technol. 1995, A13, 590
[iv] Y. H. Chang, J. C. Chun, J. E. Oh, S. J. Won, S. H. Paek, D. H. Lee, S. I. Lee, J. S. Choi, and J. G. Lee, Appl. Phys. Lett. 68, 2580 ~1996!.
[v] A. Paranjpe and M. IslamRaja, J. Vac. Sci. Technol. B 13, 2105 (1995).
[vi] J.B. Cross, H.B. Schlegel, Chem. Mater., 2000, 12, 2466
[vii] J.B. Cross, H.B. Schlegel, Chem. Phys. Lett., 2001, 340, 343-347
[viii] C.H. Winter, P.H. Sheridan, T.S. Lewkebandara, M.J. Heeg, J.W. Proscia, J. Am. Chem. Soc., 1992, 114, 1095
[ix] L.H. Dubois, Polyhedron, 1994, 13, 1329
[x] J.B. Cross, S.M. Smith, H.B. Schlegel, Chem. Mater., 2001, 13, 1095
[xi] M. Lukosius, Ch. Wenger, S. Pasko, H.-J. Müssig, B. Seitzinger, Ch. Lohe, submitted to Chem. Vap. Dep., 2008
Titanium tetrakis(dimethylamide) Ti(NMe2)4
Ti(NMe2)4 for TiN CVD (with NH3)
TiN growth with dialkylamides (especially TDMAT) and ammonia in the early reports revealed poor step coverage, probably due to the highly reactive intermediates produced in the gas phase. In addition, this binary chemistry process also suffers from particle contamination arising from high operating pressure (~50 Torr). The advantage of TDMAT is that produces TiN films with higher growth rate than less reactive TDEAT precursor – Fig. .[699]
The first examples reports of use of simple titanium amides Ti(NMe2)4 and Ti(NEt2)4 were reported by Sugiyama et al.[[i]], produced TiN films at temperatures as low as 300 °C, but the films contained carbon and oxygen as well, what degrades the properties of TiN films by increasing electrical resistance and decreasing hardness.
Titanium dimethylamide [659,[ii],[iii],[iv]], was used as a precursor for the deposition of high-quality titanium nitride (TiN) films at low temperatures (<400 °C) using ammonia.
Because of their relevance to TiN CVD, the gas phase and surface reactions of TDMAT and NH3 have received much attention [[v], [vi], [vii], [viii], [ix]] The following reaction is believed to occur by a combination of transamination exchange and amine elimination reactions: Ti(NMe2)4 + 4/3NH3 → TiN + 4 NHMe2 + 1/6N2 [689]
TiN layers grown from TDMAT at low temperature (200 ° C) by atmospheric pressure chemical vapor deposited (APCVD) were shown to be effective diffusion barriers for the Au/TiN/Si contact scheme for duration up to 40min at 550 ° C, at which point the TiN cracks and peels.. Even thin layers of TiN (200/k thick) can significantly reduce the amount of interdiffusion between the gold and silicon.[[x]]
[i] K. Sugiyama, S. Pac, Y. Takanashi, S. Motojima, J. Electrochem. Soc., 1975, 122, 1545
[ii] S. R. Kurtz, R. G. Gordon, Thin Solid Films 1986, 140, 277.
[iii] (b) Weber, A.; Klages, C.-P.; Gross, M. E.; Charatan, R. M.; Brown, W. L. J. Electrochem. Soc. 1995, 142, L79
(e) Weber, A.; Nikulski, R.; Klages, C.-P. Appl. Phys. Lett. 1993, 63, 325.
(f) Sandhu, G. S.; Meikel, S. G.; Doan, T. T. Appl. Phys. Lett. 1993, 62, 240.
(g) Prybyla, J. A.; Chiang, C.-M.; Dubois, L. H. J. Electrochem. Soc. 1993, 140, 2695
[iv] R. M. Fix, R. G. Gordon and D. M. Hoffman, Chem. Mater., 3, (1991) 1138.
[v] L.H. Dubois, B.R. Zegarski, G.S. Giraoami, J. Electrochem.Soc. 139 (1992) 3603.
[vi] B.H. Weiller, J. Am. Chem. Soc. 118 (1996) 4975.
[vii] A. Katz, A. Feingold, S. Nakahara, S.J. Pearton, E. Lane, M.Geva, F.A. Stevie, K. Jones, J. Appl. Phys. 71 (1992) 993.
[viii] J.S. Corneille, P.J. Chen, C.M. Truong, W.S. Oh, D.W. Goodman, J. Vac. Sci. Tech. A 13 (1995) 1116.
[ix] L.A. Okada, S.M. George, Appl. Surf. Sci. 137 (1999) 113.
[x] J. N. Musher, R. G. Gordon, J. Elec. Mater., Vol. 20, No. 12, 1991
Ti(NMe2)4 for TiN CVD (without NH3)
Optimisation of step coverage and particle level on a single-source-based process by using
only a titanium-organic compound, in the absence of ammonia, is described in [[i],[ii],[iii]]. MOCVD of TiN films from single-precursor TDMAT with excellent step coverage has been well characterized. However, unstable air-reactive films with high resistivity and high level of oxygen contamination are produced.
[i] Pintchovski, F.; White, T.; Travis, E.; Tobin, P. J.; Price, J. B. In Tungsten and Other Refractory Metals for VLSI Applications IV; Blewer, R. S., McConica, C. M., Eds.; Materials Research Society: Pittsburgh, PA, 1989; p 275.
[ii] Weber, A.; Klages, C.-P.; Gross, M. E.; Charatan, R. M.; Brown, W. L. J. Electrochem. Soc. 1995, 142, L79
[iii] Kim, J. H.; Lee, J. G.; Park, S. J.; Shin, H. K.; Whang, C. Y. J. Kor. Vac. Soc. 1995, 4 (S1), 28
Ti(NMe2)4 for TiN ALD
The study of surface chemistry of ALD of TiN using TDMAT and ammonia, was studied by in situ FTIR and quartz microbalance techniques by Elam et al. [i] It was
found that TDMAT reacts with NHx* species on the TiN surface, following NH3
exposures deposit new Ti(N(CH3)2)x* species. Subsequent NH3 exposure consumes the dimethylamino species and regenerates the NHx* species. These observations are consistent
with self-limiting transamination exchange reactions during the TDMAT and NH3 exposures. TiN ALD growth rate increases progressively with growth temperature. However,
high-resistivity (≥104 μΩ∙cm) and high porosity (~40%) films have been obtained. High porosity makes the films oxidation-susceptible and impairs their use as diffusion barriers. TiN ALD using TDMAT was reported also in [ii]
[i] J.W. Elam, M. Schuisky, J.D. Ferguson, S.M. George, Thin Solid Films 436 (2003) 145–156
[ii] J.-W. Lim, H.-S. Park, S.-W. Kang, J. Electrochem. Soc. 148 (2001) C403.
Ti(NMe2)4 for TiSiN CVD
TiSiN films were grown by CVD at a substrate temperature ~350°C from TDMAT only (without ammonia). The reduction of carbon contamination in the films was achieved by H+/N+ plasma treatment of thin TiNy(Cx) layers, repeated until the desired film thickness is achieved. The final TiN film thickness is exposed insitu to silane to create the Si-passivated TiN film, or TiSiN:
-Ti[N(CH3)2]4 → TiN(C) + HN(CH3)2 + H2N(CH3) + hydrocarbons (1)
- TiN(C) + SiH4 → TiSiN (2)
According to cross-sectional HRTEM stidies, TiSiN deposits in 130 nm node via as a conformal and continuous films with 100% sidewall and 75% bottom stepcoverage. TiSiN barrier properties allow to replace TaN in the devices.[i]
[i] C. Prindle, B. Brennan, D. Denning, I. Shahvandi, S. Guggilla, L. Chen, Ch.Marcadal, D. Deyo, U. Bhandary, IITC, 2002
Ti(NMe2)4 for TiO2 CVD
Ti(NMe2)4 combined with O2 was applied for the deposition of TiO2 thin films on Si substartes at 250–300 °C by CVD. The obtained TiO2 films
were carbon free and contained no TiN or TiOxNy species. The as-grown TiO2 layers were amorphous before annealing, but crystalline (anatase structure) after annealing at 600 °C in air. The average dielectric
constant (κ) of the annealed films was 50(5), with an average leakage current of 5(3)×10–5 A/cm and breakdown strength of 1.8(0.3) MV/cm.[i]
[i] J. B. Woods, D. B. Beach, C. L. Nygren, Z.-L. Xue, Chem. Vapor Deposition, Vol.11, Iss. 6-7, p.289–291, « CVD of Titanium Oxide Thin Films from the Reaction of Tetrakis(dimethylamido)- titanium with Oxygen »
Tetrakis(diethylamido)titanium Ti(NEt2)4
Fig. Formula of Ti(NEt2)4 molecule
Tetrakis(diethylamido)titanium Ti(NEt2)4 (M = 336.42) is yellow-orange or dark red moisture sensitive viscous liquid (viscosity 8.8 cSt at 34°C) with density d = 0.931 (25°C) (0.95 (20°C?) Alfa), 0.92 (33°C); refractive index n20/D = 1.536 (1.5370 Alfa).
Ti(NEt2)4 has melting point -27-28°C (other data mp. 4 °C[67],).
Vapor pressure of Ti(NEt2)4
Fig. Vapor pressure of Ti(NEt2)4 vs. temperature: Vapor pressure equation: logP (Torr) = 13.67 – 5065/T (K)
Ti(NEt2)4 boiling point 112°C/0.1torr , b.p. 133°C/ 1.2-1.3 torr [39, 4] , other data b.p. 85-90°C/0.1 Torr [244 ], bp. 100°C/0.1 Torr[688]
Vapor pressure of Ti(NEt2)4: 0.05 Torr/60°C, 0.07Torr/80°C, 0.1 Torr/ 85°C (98°C?), 0.5Torr/90°C (Praxair), 1 Torr/ 120°C (other data 0.5 Torr/125°C - Multivalent.co.uk) ,
Vapor pressure equation: logP (Torr) = 13.67 – 5065/T (K)
1H NMR spectroscopy of the Ti(NEt2)4
Fig. 1H NMR spectrum of Ti(NEt2)4
The 1H NMR spectrum of the Ti(NEt2)4 precursor (TDEAT) is presented in Fig. The ligands are magnetically equivalent.
Activation energy for TiN growth for Ti(NEt2)4 was found to be Eact=52kJ/mol [678]
Ti(NEt2)4 for TiN CVD
Titanium diethylamide Ti(NEt2)4 [[i],[ii],[iii],[iv], [v], [vi]], was widely used as a precursor for the deposition of high-quality titanium nitride (TiN) films at low temperatures (<400 °C) using ammonia.[vii]. This process of TiN formation at low temperatures (200-400°C), utilizing Ti(NEt2)4 as precursor,
was reported to be applicable in microelectronics to produce barriers for diffusion of Al and Cu, as well as “glue layers” between
W and SiO2.[viii]
[i] I.J. Raaijmakers, Thin Solid Films, 1994, 247(1), 85
[ii]Raaijmakers, I. J.; Ellwanger, R. C. In Advanced Metallization for ULSI Applications; Cale, T. S., Pintchovski, F. B., Eds.; Mater. Res.Soc.: Pittsburgh, 1993; p 325..
[iii] Kim, J. H.; Lee, J. G.; Park, S. J.; Shin, H. K.; Whang, C. Y. J. Kor. Vac. Soc. 1995, 4 (S1), 28
[iv] S. W. Kim, H. Jimba, A. Sekiguchi, O. Okada, N. Hosokawa, Appl. Surf. Sci. 1996, 100/101, 546.
[v] A. C. Westerheim, J. M. Bulger, C. S. Whelan, T. S. Sriram, L. J. Elliott, J. J. Maziarza, J. Vac. Sci. Technol. B 1998, 16(5), 2729.
[vi] J. M. Bulger, C. S. Whelan, A. Dumont, M. Kuhn, J. Clark, J. Vac. Sci. Technol. B 1999, 17 (2), 410
[vii] J.N. Musher, R.G. Gordon, J. Electrochem. Soc. 1996, vol. 143, iss. 2,736-744, doi: 10.1149/1.1836510 « Atmospheric Pressure Chemical Vapor Deposition of Titanium Nitride from Tetrakis (diethylamido) Titanium and Ammonia », http://jes.ecsdl.org/content/143/2/736.abstract?cited-by=yes&legid=jes;143/2/736
[viii] X. Liu, Y.Z. Lu, R.G. Gordon, MRS. Symp. Proc, Vol. 555, 1998 , 135, « Improved Conformality of CVD Titanium Nitride Films », https://doi.org/10.1557/PROC-555-135
Tetrakis(ethylmethylamido)titanium Ti(NEtMe)4
Fig. Ti(NEtMe)4 molecule
Tetrakis(ethylmethylamido)titanium Ti(NEtMe)4 (TEMAT) (M=280.32) is yellow-orange moisture sensitive liquid (viscosity 3.6 cSt at 30°C), having density d=0.923 (20-25°C), 0.92g/ml(32°C) and melting point mp. <-20°C.
1H NMR spectroscopy (200 MHz, 20 °C, C6D6): δ 1.10 (t, 7 Hz, -CH2CH3, 3H), 3.11 (s, -CH3, 3H), 3.44 (q, 7Hz, CH2CH3, 2H).
µ-Analysis. Calculated for C12H32N4Ti: C, 51.40; H, 11.53; N, 19.99. Found: C, 51.31; H, 11.28; N, 20.65
Vapor pressure of Ti(NEtMe)4
Fig. Vapor pressure of Ti(NEtMe)4 vs. temperature
Boiling point: 60°C/10-2 Torr, 80°C/0.1 Torr (other data 85°C/0.05 Torr).
Vapor pressure of Ti(NEtMe)4: 0.2 Torr/50°C, 0.4 Torr/ 60°C, 1 Torr/78°C, 1.2 Torr/80°C, 0.5 Torr/87°C, 1.5Torr/90°C.
Ti(NEtMe)4 is thermally stable 90°C/vac for 7 days (no decomposition), 180°C/ 1h.
Ti(NEtMe)4 (+NH3) for TiN CVD
[i] H.-K. Shin, H.-J. Shin, J.-G. Lee, S-W. Kang, B.-T. Ahn, Chem. Mater. (1997) 9, 76
[ii] D.-H. Kim, G.T. Lim, S.-K. Kim, J.W. Park, J.-G. Lee, J. Vac. Sci. Technol. B, 1999, 17(5), 2197
[iii] S. Panda, J. Kim, B.H. Weiller, D.J. Economou, D.M. Hoffman, Thin Solid Films 357 (1999) 125-131
[iv] J.N. Musher, R.G. Gordon, J. Mater. Res., 1996, 11, 989
[v] J.N. Musher, R.G. Gordon, J. Electrochem. Soc., 1996, 143, 736
Ti(NEtMe)4 (+NH3) for TiN by low temperature MOCVD
Tetrakis (ethylmethylamido) titanium Ti(NEtMe)4 (TEMAT) was applied as precursor for the growth of TiN films by low temperature MOCVD (250–350°C).
Growth rates 7-105 nm/min with excellent bottom coverage of ∼90% over 0.35 μm contacts were obtained. The addition of NH3 during growth process lowered the resistivity of as-deposited TiN film from
3500–6000 μΩ cm to ∼1000 μΩ cm and reduced the change of resistivity in grown TiN layers upon air exposure. The addition of NH3 significantly reduced O and C contents in the films,
according to AES. The deposition process mechanism was studied by the analysis of byproduct gases by quadrupole mass spectrometry (QMS); the transamination reaction (similar to Ti(NMe2)4 reaction with NH3) was proposed to be responsible for TiN deposition.
The reactivity of Ti(NEtMe)4 with NH3 in gas phase is suggested to be less than that of Ti(NMe2)4 with NH3 (due to larger steric interactions in Ti(NEtMe)4 determining the extent of the gas phase reaction), and thus, easier control of the gas phase reaction
is expected using Ti(NEtMe)4 as precursor.[i]
[i] J. Lee, J. Kim, H. Shin, Thin Solid Films, 1998, Vol. 320, Iss.1, p.15-19, « MOCVD of TiN and/or Ti from new precursors », https://doi.org/10.1016/S0040-6090(97)01059-6,
Ti(NEtMe)4 (without NH3) for TiN CVD
TiN films with TEMAT can be grown both without NH3 (with He only) and with NH3. However, higher growth temperature is needed in the absence of NH3: hermal decomposition of TEMAT under He atmosphere produces TiN films starting from 250°C, whereas the reaction with NH3 occurs as low as 100°C. TiN growth rate without NH3 increases with deposition temperature; it is strongly reduced when depositing with NH3, most
probably because of gas-phase pre-reactions. The growth rate without NH3 reaches maximum at 325°C, and further it remains independent of temperature meaning a transition
from reaction-controlled to mass flow-controlled regime. The addition of ammonia and higher growth temperatures produced TiN films of lower resisitivity, while without NH3 smoother
TiN films were obtained. Conformality of the films strongly depended on the deposition temperature and ammonia supply. The performance as Cu barrier was however low even at 550°/1h [[i]]
[i] D.-H. Kim, G.T. Lim, S.-K. Kim, J.W. Park, J.-G. Lee, J. Vac. Sci. Technol. B, 1999, 17(5), 2197
Ti(NEtMe)4 (without NH3) for TiN CVD
TiN films with TEMAT can be grown both without NH3 (with He only) and with NH3. However, higher growth temperature is needed in the absence of NH3: hermal decomposition of TEMAT under He atmosphere produces TiN films starting from 250°C, whereas the reaction with NH3 occurs as low as 100°C. TiN growth rate without NH3 increases with deposition temperature; it is strongly reduced when depositing with NH3, most
probably because of gas-phase pre-reactions. The growth rate without NH3 reaches maximum at 325°C, and further it remains independent of temperature meaning a transition
from reaction-controlled to mass flow-controlled regime. The addition of ammonia and higher growth temperatures produced TiN films of lower resisitivity, while without NH3 smoother
TiN films were obtained. Conformality of the films strongly depended on the deposition temperature and ammonia supply. The performance as Cu barrier was however low even at 550°/1h [i]
[i] D.-H. Kim, G.T. Lim, S.-K. Kim, J.W. Park, J.-G. Lee, J. Vac. Sci. Technol. B, 1999, 17(5), 2197
Thermolysis of dialkylamides (f.e Ti(NEtMe)4) without ammonia
During thermolysis of alkylamido compounds, the formation of metallacycle dominates during the initial stage of film growth, based on their in situ
XPS studies. [[i]] Higher carbon levels in the films grown without ammonia are consisting of carbidic bonded carbon originating from metallacycle, as well as from residuals of dialkylamine decomposition as a major source of noncarbidic carbon.[688, 690, 710]
The observed film growth rates with TEMAT precursors in the absence of ammonia were between 2 and 60 nm/min and the film growth rate was roughly estimated to about 0.5 order in precursor concentration with an activation energy of 70 kJ/mol for the surface
reaction control regime.[706]
[i] G. Ruhl, R. Rehmet, M. Knizova, R. Merica, and S. Veprek, Chem. Mater. 8, 2712 (1996)
Ti(NEtMe)4 for TiN ALD
Titanium tetrakis-ethylmethylamide (TEMAT) precursor was reported to produce TiN films by ALD with excellent bottom coverage of ~90% over 0.35 μm contacts with an aspect ratio of 2.9 at 250-350 °C. This perfect step coverage is explained by TiN deposition in the surface reaction controlled-region with an activation energy of ~1.0 eV.[705]
TiN ALD depositions were perfromed mainly using TEMAT and NH3 [[i], [ii]] These TiN ALD studies were presented under the assumption that this system displays ideal ALD behavior.
[i] J.-S. Min, Y.-W. Son, W.-G. Kang, S.-S. Chun, S.-W. Kang, Jpn. J. Appl. Phys. 37 (1998) 4999.
[ii] D.-J. Kim, Y.-B. Jung, M.-B. Lee, Y.-H. Lee, J.-H. Lee, Thin Solid Films 372 (2000) 276.
Tetrakis(di-n-propylamido)titanium Ti(NnPr2)4
Titanium tetrakis(di-n-propylamide) Ti(NnPr2)4 is suitable precursor for CVD deposition of TiN films at 300-400°C [652], in contradiction with the older report of Sugiyama who was able to deposit the films only at temperature >500°C with this precursor[685].
Tetrakis(diisopropylamido)titanium Ti(NiPr2)4
Tetrakis(diisopropy1amido)titanium Ti(NiPr2)4 presumably could give cleaner from carbon films, compared to other titanium alkylamides (due to easier leave
of bulky organic radicals). However, Ti(NiPr2)4 was reported to be problematic to synthesize, probably because of excessive steric crowding around the titanium center. [i]
[i] R. M. Fix, R. G. Gordon and D. M. Hoffman, Chem. Mater., 2, (1990) 235.
Tetrakis(di-n-butylamido)titanium Ti(NnBu2)4
Titanium dibutylamide Ti(NnBu2)4, when attempted to use as Ti MOCVD precursor, decomposed at bubbler temperature about 100°C and did not provide adequate transport for growing films at atmospheric pressure. [652] In general, the increase of molecular weight of titanium alkylamide decreases its reactivity [685]
Tetrakis(di-tert-butylamido)titanium Ti(NtBu2)4
Tetrakis(di-tert-butylamido)titanium Ti(NtBu2)4 , similar to its isopropyl analogue, was suggested to could give cleaner from carbon films (due to easier leave of bulky organic
radicals) if using it as MOCVD precursors. However, Ti(NtBu2)4 was reported to be problematic to synthesize, probably because of excessive steric crowding around the titanium center. [i]
[i] R. M. Fix, R. G. Gordon and D. M. Hoffman, Chem. Mater., 2, (1990) 235.
Tetrakis(diallylamido)titanium Ti(N(allyl)2)4
Titanium tetrakis(diallylamide) Ti(N(allyl)2)4 was reported to polymerize upon heating, precluding its purification and excluding use in TiN growth by CVD. [i]
[i] R. M. Fix, R. G. Gordon and D. M. Hoffman, Chem. Mater., 2, (1990) 235.
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