TUNGSTEN (VI) IMIDES-HALIDES

Fig. W(=N-C3H5)Cl4(MeCN) as precursor for CVD

    A series of tungsten imide-halides nitrile adducts W(=NR)Cl4(R’CN) (imido group had various R substituents such as isopropyl, phenyl or allyl; R’CN was acetonitrile or benzonitrile) has been applied as single source CVD precursors for the deposition of tungsten nitride WN and tungsten carbonitride WCN films. Chlorine contamination was not studied although it can be expected from the precursor composition. Due to the low vapour pressure of precursors, the use of aerosol-assisted CVD was required.

      Films deposited from allylamides W(=N-C3H5)Cl4(R’CN)  (R’CN = acetonitrile or benzonitrile) below 550 °C contained amorphous β-WNxCy, while layers grown at higher temperatures were polycrystalline. Film growth rates was 5-10 Å/min over a temperature range of 450−650 °C, and the apparent activation energy for film growth was 0.15 eV.

    The plot of activation energies Ea for CVD deposition from W(NR‘)Cl4(RCN) [R‘ = Ph, iPr, allyl] versus the N−C imido bond strengths for the analogous amines R‘NH2 is linear, indicating that cleavage of the N−C bond is the rate-determining step in film growth. The significance of facile N−C bond cleavage in film growth is supported by the correlation of mass spectral fragmentation patterns for W(NR‘)Cl4(RCN) with film properties such as N content. [i]

[i]  O.J. Bchir, K.M. Green, H.M. Ajmera, E.A. Zapp, T.J. Anderson, B.C. Brooks, L.L. Reitfort, D.H. Powell, Kh.A. Abboud, L. McElwee-White, J. Am. Chem. Soc. 2005, 127, 21, 7825–7833, https://doi.org/10.1021/ja043799d , “Tungsten Allylimido Complexes Cl4(RCN)W(NC3H5) as Single-Source CVD Precursors for WNxCy Thin Films. Correlation of Precursor Fragmentation to Film Properties”

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