TITANIUM (IV) HALIDES
Titanium tetrafluoride TiF4
Titanium tetrafluoride TiF4 was applied as ALD precursor, but actually it was used as fluorinating agent/ F precursor, not as Ti source, for example
during MgF2 layer growth from Mg(thd)2 and TiF4 by ALD. (see Fluorine precursors) [[i]]
[i] T. Pilvi, T. Hatanpää, E. Puukilainen, K. Arstila, M. Bischoff, U. Kaiser, N. Kaiser, M. Leskelä, M. Ritala, J. Mater. Chem., 2007, 17, 5077–5083, Study of a novel ALD process for depositing MgF2 thin films, https://pubs.rsc.org/en/content/articlelanding/2007/jm/b710903b/unauth#!divAbstract
https://www.researchgate.net/profile/Kai_Arstila/publication/230605170_Study_of_a_novel_ALD_process_for_depositing_MgF2_thin_films/links/0f31753073aa01b74d000000.pdf
Titanium tetrachloride TiCl4
Fig. Vapor pressure equation of TiCl4:
logP (Torr) = 7.64 – 1947/T (K)
Titanium tetrachloride TiCl4 (M = 189.68) is colorless moisture sensitive liquid, (reacts very rapidly with H2O to give TiO2 and 4 HCl), melting point -24°C (-25°C), boiling point 137°C (136°C), d = 1.726 g/ml (20°C).
Vapor pressure: 1 Torr/-13.9 °C, 9.0 Torr/20°C, 10 Torr/ 21°C, 100 Torr/71 °C, 400 Torr/112.7 °C, 760Torr/136°C,
Vapor pressure equation logP (Torr) = 7.64 – 1947/T (K)
Synthesis of TiCl4 on industrial scale:
TiO2 + 2 C + 2 Cl2 → TiCl4 + 2 CO + 80.4 kJ
TiCl4 for Ti metal films by thermal ALD
TiCl4 was applied as precursor (with 2-Methyl-1,4-bis(trimethylsilyl)-2,5-cyclohexadiene or 1,4-Bis(trimethylsilyl)-1,4-dihydropyrazine as reducing agents) for the growth
of Ti metal films by thermal ALD. [[i]]
[i] J.P. Klesko, Ch.M. Thrush, Ch.H. Winter, Chem. Mater., 2015, 27 (14), pp 4918–4921, DOI: 10.1021/acs.chemmater.5b01707, « Thermal Atomic Layer Deposition of Titanium Films Using Titanium Tetrachloride and 2-Methyl-1,4-bis(trimethylsilyl)-2,5-cyclohexadiene or 1,4-Bis(trimethylsilyl)-1,4-dihydropyrazine », https://pubs.acs.org/doi/abs/10.1021/acs.chemmater.5b01707?journalCode=cmatex
TiCl4 for TiSi2 (on Si substrates) – CVD- like process
TiCl4 was reported to react with Si substrates (in the absence or presence of H2), what can be used for forming TiSi2 layers on silicon:
TiCl4(g) + 3 Si(s) -> TiSi2(s) + SiCl4(g) (1)
TiCl4(g) + 2 H2(g) + 2 Si(s) -> TiSi2(s) + 4 HCl(g) (2)
In the absence of H2 excessive etching has been observed (see reaction (1)). When TiCl4 and SiH4 as source gases are used then pure TiSi2 is formed.
A further deposition mechanism includes disproportionation. Thermolysis of TiCl4 can result in the formation of TiCl3 and TiCl2, observed as purple (TiCl3) and brown (TiCl2) deposits in the CVD reactor. The formed TiCl3 species can disproportionate to TiCl4 and TiCl2, respectively: 2 TiCl3 -> TiCl4 + TiCl2. Also, partial reduction of TiCl4 by Si is possible:
4 TiCl4(g) + Si(s) -> 4 TiCl3(g) + SiCl4(g) [[i]]
[i] Prof. Dr. Heinrich Lang, « The Chemistry of Metal CVD », International Research Training Group, “Materials and Concepts for Advanced Interconnects”
TiCl4 for TiO2 layers by CVD/ALD
The high decomposition temperature of TiCl4 is attractive in view of the flexible multiprecursor ALD process conditions. However, TiCl4 generates corrosive HCl as a result of a reaction with H2O (if water used as oxygen source in ALD).
TiCl4 (+NH3) for TiN by CVD
TiCl4 along with ammonia NH3 is well-known precursor to produce high-quality TiN films, remarkable step coverage even in submicron contacts with an aspect ratio of 7.0, as well as excellent film properties including barrier properties and electrical resistivities, however at quite elevated temperatures (550-600°C) for best 350-390 μΩ·cm films [[i]] , however lower values of 85 μΩ·cm were reported [[ii], [iii]]. Both N2 and NH3 can be used as a nitrogen source (but N2 at high growth temperatures) [652, [iv], [v]]
TiN films were reported to be chemically deposited using TiCl4/NH3 based chemistry [[vi],[vii]], with the partial pressure of reactant being a dominant parameter for process performance and properties of deposited films. The inter-relationship governing the growth kinetics, composition, and properties of TiN films as a function of TiCl4/NH3 flow rate ratio was previously investigated.[[viii]]
The kinetics of TiN-CVD process using TiCl4 and NH3 have not yet been clarified: the effect of partial pressures of TiCl4 (PTiCl4) and NH3 (PNH3) on the growth rate of TiN films is contradictory among different reports.[646, [ix], [x]]
Optimised TiCl4-based CVD processes provide good film quality and excellent step coverage. [xi]However, TiN preparation by CVD using TiCl4 suffers from some serious drawbacks:
- Cl contamination in TiN films leads to serious corrosion in Al/Cu metallization and is a major concern for long-term reliability of the devices. To reduce the chlorine content to a low level (<1 at. % Cl), high substrate temperatures of >600 °C are needed.
- The high-temperature process (>500°C) cannot be applied in modern multilevel metallization schemes.
- An additional drawback of this chemistry is the formation of adducts and NH4Cl salt particles, which brings severe particle generation in the production of microelectronic devices.[xii], [xiii]
[i] S.R. Kurtz, R.G. Gordon, Thin Solid Films, 1986, 140, 277-290
[ii] N. Ramanuja, R. A. Levy, S. N. Dharmadhikari, E. Ramos, C. W. Pearce, S. C. Menasian, P. C. Schamberger, C. C. Collins, Mater. Lett. 2002, 57, 261.
[iii] N. Yokoyama, K. Hinode, Y. Homma , J. Electrochem. Soc. 1991, 138, 190.
[iv] D.M.Hoffman, Polyhedron, 1994, 13, 1169
[v] W. Schintlmeister, O. Pacher, K. Pfaffinger, T. Raine, J. Electrochem. Soc., 1976, 123, 924
[vi] C.-C. Jiang, T. Goto and T. Hirai: J. Mater. Sci. 28 (1993) 6446.
[vii] T. Kaizuka, H. Shinriki, N. Takeyasu and T. Ohta: Jpn. J. Appl. Phys. 33 (1994) 470
[viii] K. Jun, I. T. Im and Y. Shimogaki: Jpn. J. Appl. Phys. 43 (2004) 1619.
[ix] M. J. Buiting, A. F. Otterloo and A. H. Montree: J. Electrochem. Soc. 138 (1991) 500.
[x] L. Imhoff, A. Bouteville and J. C. Remy: J. Electrochem. Soc. 145 (1998) 1672
[xi] M. J. Buiting and A. F. Otterloo, J. Electrochem. Soc. 139, 2580 (1992)
[xii] Sherman, A. J. Electrochem. Soc. 1990, 137, 1892.
[xiii] 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.
TiCl4 (+NH3) for TiN by AP CVD
There are several APCVD routes to TiN films available,[656] but only the method of Gordon and Kurtz gives high quality TiN coatings at high growth rates and temperatures as low as 500°C .[ 652]: 6 TiC14 + 8 NH3 (500-700°C)→ 6 TiN + 24 HCl+ N2. The low temperature range required for reaction 1 is important because it permits depositions to be carried out on thermally sensitive substrates such as silicon chips, solar cells, and glass
The key paramerters to achieve 100% step coverage by TiCl4 - NH3 CVD is to use lower NH3 and relatively higher TiCl4 partial pressures. The sticking probability of Ti-containing species in the 1st-order kinetic regime depended on PNH3 . The growth rate dependence
on PNH3 revealed 2nd-order reaction, the reasons being complicated gas-phase and/or surface reaction chemistries to form TiN. [i]
[i] K.Jun, Y. Egashira, Y. Shimogaki, Jap. J. Appl. Phys., Vol. 43, No. 10, 2004, pp. 7287–7291
TiCl4 (+NH3) for TiN by ALD
A comparison of ALD vs. CVD for TiN growth from TiCl4 as precursor was presented [[i]] Although CVD-grown TiN properties were quite good (180µΩ·cm resistivity, <2% Cl contamination, 95% step coverage for 6:1 aspect ratio trenches), the ALD – grown films were even superior in terms of resistivity and Cl contamination
Preparation of TiN films by ALD using TiCl4 and ammonia as precursors is well established [[ii], [iii], [iv]] Unfortunately, titanium chloride precursors are not optimal for the fabrication of diffusion barriers.The HCl reaction product can combine with the NH3 precursor to form a nonvolatile particle contamination of NH4Cl; it can also etch the metal interconnects. Incomplete reaction of the TiCl4 precursor produces Cl contamination of the TiN film and increases the film resistivity.
100% step coverage in 10:1 aspect ratio trenches have been achieved by
TiN growth by ALD using TiCl4 and NH3 as precursors, with Cl contamination in
the films <1%, good roughness and low resistivity (200 μΩ cm).[v]
[i] B.-Y. Kim, S.-H. Lee, S.-G. Park, K.-Y. Oh, J. Song, D.-H. Kim, MRS Symp. Proc., Spring 2001, p.?
[ii] M. Ritala, M. Leskela, E. Rauhala, P. Haussalo, J. Electrochem.Soc. 142 (1995) 2731.
[iii] M. Ritala, T. Asikainen, M. Leskela, J. Jokinen, R. Lappalainen, M. Utriainen, L. Niinisto, E. Ristolainen, Appl. Surf. Sci. 120 (1997) 199.
[iv] J. Uhm, H. Jeon, Jpn. J. Appl. Phys. 40 (2001) 4657.
[v] J. Kim, H. Hong, K. Oh, C. Lee, Appl. Surf. Sci., vol. 210, Iss. 3-4, 2003, p. 231-239
TiCl4 (+N2) for TiN by CVD
Kuo and Huang reported that the reaction order is influenced by the partial pressure of each reactive species, including TiCl4, N2, and H2 [[i]], and Ohshita et al. reported that the ratio of the amount of TiCl4 adsorbates on the film surface depends on the TiCl4 gas flow rate. This flow rate affects the growth rate, the amount of residual Cl in the grown film, and the step coverage quality [[ii]]. Also, Huang et al. reported that the N/Ti ratio and lattice parameter of TiN films decreased with the N2 volume fraction increasing and the texture coefficient (TC) value of (200) plane of TiN increased with increasing N2 volume fraction.[iii] Thus, the properties of CVD-TiN films are influenced by the partial pressure of reactants.
[i] D. Kuo and K. Huang: Surf. Coat. Technol. 135 (2001) 150.
[ii] Y. Ohshita, W. Fukagawa and A. Kobayashi: J. Cryst. Growth 146 (1995) 188.
[iii] H. H. Huang, M. H. Hon and M. C. Wang: J. Cryst. Growth 240(2002) 513
TiCl4 for TiCx by CVD
Titanium chloride TiCl4 was used also for the deposition of titanium carbide layers via carbidisation using methane CH4 [1]
TiCl4 (+S2(tBu)2 / StBu2/ S(SiMe3)2) for TiS2, TiS3 by CVD
TiCl4 and a series of sulfur sources (t-butyl disulfide S2(tBu)2, t-butyl sulfide S(tBu)2, and hexamethyldisilthiane S(SiMe3)2, was applied for the growth of thin films of TiS2 and TiS3 by thermal CVD. TiS3 layers were obtained by reacting TiCl4 and S2(tBu)2 (TBDS) at lower (<260°C) growth temperature. As the deposition temperature was increased, TiS2 started to appear in the deposited film, and at >400°C temperatures only TiS2 was formed.
Using other sulfurizing sources (S(tBu)2 and S(SiMe3)2),
only TiS2 layers were obtained in the whole studied temperature range (200–550°C). The morphology of the TiS2 films strongly varied with growth temperature: At low temperatures very dense layers were
formed (with preferential crystallographic “c” axis perpendicular to the substrate, according to XRD), but at >300°C temperatures, a porous honeycomb structure was obtained with “c” axis parallel to the substrate. [[i]]
[i] H.S.W. Chang, D.M. Schleich, J. Solid State Chem., 1992, Vol.100, Iss.1, p. 62-70, « TiS2 and TiS3 thin films prepared by MOCVD », doi.org/10.1016/0022-4596(92)90156-P
https://www.sciencedirect.com/science/article/pii/002245969290156P
TiCl4 for TiP by CVD
Titanium tetrachloride TiCl4 combined with PCl3 as phoshorus source has been applied for the growth of titanium phosphide TiP thin films by CVD at 850-1050°C temperatures under H2 and Ar atmosphere [574]
Titanium tetrabromide TiBr4
Titanium tetrabromide TiBr4 (M =) is orange solid meting at 38.3 °C, boiling at 233.5 °C
TiBr4 for TiSi2 by CVD
Titanium tetrabromide TiBr4 was reported to be useful precursor for the formation of titanium silicide TiSi2 thin films on Si substrates. [i]
[i] Lee, C-.Y. J. Mater. Synth. Process. 1998, 6, 55.
TiBr4 for TiN by CVD
TiBr4 was reported to be tested for the growth of TiN films by CVD, but halogen contamination remains a problem.
Titanium tetraiodide TiI4
Titanium tetraiodide TiI4 (M =) is red-brown solid melting at 155 °C and boiling at 377 °C.
TiI4 for metallic Ti by CVD
Titanium tetraiodide (and for comparison TiBr4 and TiCl4) was applied as CVD precursor for the deposition metallic titanium by CVD. [1]
TiX4 (X = Cl, Br, I) were also used as CVD precursors for metallic titanium on stainless steel substrates (using laser CVD reaction). The purity of obtained TiN films was ca. 90 %
Use of TiX4 (X = Br, I) as CVD Precursors:
2 TiX4 → 2 TiX3 + X2
2 TiX3 → TiX4 + TiX2
2 TiX2 → TiX4 + Ti
High temperatures (900 °C) were needed, which were attainted by laser heating or photochemical reactions to produce titanium films. Obtained films: 90 at. % Ti, 10 at. % O.
TiI4 for TiN by CVD
TiI4 was reported to be tested for the growth of TiN films by CVD, but halogen contamination remains a problem.
TiI4 for TiN by ALD
ALD of TiN using titanium tetraiodide TiI4 has been reported [[i]]
[i] M. Ritala, M. Leskela, E. Rauhala, J. Jokinen, J. Electrochem. Soc. 145 (1998) 2914.
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