Niobium MOCVD/ ALD precursors

  Niobium metal is  used in nuclear fuel particle coatings, superconductors (Nb3Ga, Nb3Ge), NbN diffusion barriers, metal-alloy diffusion barriers, metal-silicide contact barriers

One of potential applications of Nb complexes is growth of conducting and superconducting NbN layers by MOCVD.

Nb precursors for NbN thin films by (MO)CVD and ALD

 

            NbCl5 and NH3 as sources were applied for the ALD growth δ-NbN layers having a very good specific resistivity of 200 μΩ·cm (early report of 1988) [[i]],

    However, using metal-organic complexes as precursors comparable NbN layer properties were initially not achieved.[[ii]], in particular, the control of composition and properties in the early MOCVD-grown NbN films presented a challenge.

    One approach targeting to reduce the impurities incorporation was use of all-N-coordinated Nb complexes as precursors, f.e. the homoleptic Nb(V) compound [Nb(NEt2)5] (the first precursor of this kind tested as single MOCVD sources).[[iii]] Thus, [Nb(NEt2)4] and [Nb(NMe2)5] produced amorphous N-rich phase Nb3N4 films (Nb:N ratio ~0.74), with O and C contaminants <3 at.-% and 103–104 μΩ·cm specific resistivities, by atmospheric pressure MOCVD at 200–400°C temperatures, using NH3 reactive gas [[iv]].

      The mixed amido/imido complexes, such as Tert-butylimido-tris(dimethylamido)-niobium (TBTDMN) [[v]], tert-butylimido-tris-(diethylamido)-niobium (TBTDEN) [[vi]] or [Nb(=N-tert-Amyl)(NMe2)3] [[vii]] were proposed as potential precursors for the growth of NbN layers by MOCVD, however generally the obtained films were contaminated by C and O.

      Volatile mixed ligand all nitrogen-coordinated niobium hydrazide-containing  complexes, such as  1,1-dimethyl-2-(trimethylsilyl)hydrazido (TDMH) imido complex [Nb(=NtBu)(TDMH)2(NMe2)], or even more sophisticated amidinate-containing Nb complexes such as [Nb(NMe2){(N-iPr)2C(NMe2)}2(=N-tBu)] were proposed and preliminary tested as a single source precursors for use in MOCVD of NbN layers.[viii] Metallic, golden-coloured pure δ-NbN phase layers were obtained at 400-600 °C temperatures; the layers had low C impurity (<3 at.-%), but high O contamination (up to 15 at.-%) and specific resistivities ~2000–7700 μΩ·cm. [ix]

 

[i] L. Hitunen, M. Leskelä, M. Mäkelä , L. Ninistö , E. Mykänen, P. Soininen, Thin Solid Films 1988, 166, 149.

[ii] R. A. Fischer, H. Parala, in: Chemical Vapour Deposition: Precursors, Processes and Applications, (Eds: A. C. Jones, M. L. Hitchman), Royal Society of Chemistry, London 2009, Chap. 9, pp. 413–450.

[iii] K. Sugiyama, S. Pac, Y. Takahashi, S. Motojima, J. Electrochem. Soc., 1975, 122, 1545.

[iv] R. Fix, R. G. Gordon, D. M. Hoffman, Chem. Mater. 1993, 5, 614.

[v] A. Baunemann, D. Bekermann, T. Thiede, H. Parala, M. Winter,C. Gemel, R. A. Fischer, J. Chem. Soc, Dalton Trans. 2008, 28, 3715.

[vi] H.-T. Chiu, J.-C. Lin, S.-H. Chuang, G.-H. Lee, S.-M. Peng, J. Chin. Chem. Soc. 1998, 45, 355.

[vii] M. Yasuhara, H. Hidekimi, Jpn. Kokai Tokkyo Koho 2006, JP 2006131606, A20060525.

[viii] D. Gaess, K. Harms, M. Pokoj, W. Stolz, J. Sundermeyer, Inorg. Chem. 2007, 46, 6688.

[ix] A. Baunemann, D. Bekermann, T. Thiede, H. Parala, M. Winter,C. Gemel, R. A. Fischer, J. Chem. Soc, Dalton Trans. 2008, 28, 3715.