TUNGSTEN (0) HEXACARBONYL W(CO)6

Fig. Octahedral coordination of CO ligands in W(CO)6 molecule

Tungsten hexacarbonyl W(CO)6  (M=351.91) is volatile colorless solid (or white fine crystalline powder) (d=2.650 g/cm3), having melting point 150°C, boiling point 175-180°C (with decomposition).   W(CO)6 is homoleptic complex (having octahedral coordination of carbonyl ligands) (Fig.).

W(CO)6 is insoluble in water and soluble in organic solvents. W(CO)6 is highly toxic and has sufficient vapor pressure at room temperature to create toxic concentrations.

Tungsten hexacarbonyl W(CO)6 is synthesized by the reduction of tugsten hexachloride by triethylaluminium at high pressure of CO (50 °C, 70 bar CO, autoclave)

WCl6 + 2 AlEt3 + 6 CO → W(CO)6 + 2 AlCl3 + 3 C4H10

TUNGSTEN (0) HEXACARBONYL W(CO)6 - VAPOR PRESSURE

Fig. Vapor pressure of W(CO)6 in Arrhenius coordinates

W(CO)6 was reported to have vapor pressure 1.2 Torr ( 67 °C) [[i]] 

Vapor pressure equation of W(CO)6: Log10P(Torr) = 9.046 - 3145/T (K)  (Fig.)

[i] https://www.chemicalbook.com/ChemicalProductProperty_DE_CB6684220.htm

TUNGSTEN (0) HEXACARBONYL W(CO)6 - VAPOR PRESSURE STUDIES

The vapor pressure of solid W(CO)6 was investigated in detail in [i]

[i] R. Chellappa, Dh. Chandra, « Assessment of vapor pressure data of solid metal carbonyls »,

J. Chem. Thermodyn., Vol.37, Iss.4, 2005, p.377–387, http://dx.doi.org/10.1016/j.jct.2004.10.002

TUNGSTEN (0) HEXACARBONYL W(CO)6 - APPLICATION in MOCVD

Tungsten hexacarbonyl, W(CO)6, is widely used  source for (MO)CVD of tungsten-contaning thin films , the use of  W(CO)6 as MOCVD precursor avoids problems arising when using fluorine-contaning tungsten precursors like WF6.  

For instance, W(CO)6 was used as precursor to form by CVD  W gate electrodes on ultra-thin dielectrics needed for high speed/high density MOS and CMOS devices.

  W(CO)6 has also been applied to deposit tungsten nitride, W2N having properties suitable for barriers to diffusion of copper in microelectronics. 

  W(CO)6 vapor combined with O2 produced electrochromic films of tungsten oxide by CVD.

[[i] and refs. therein]

[i] R.G. Gordon, S. Barry, R. N. R. Broomhall-Dillard, V. A. Wagner, Y. Wang, Mat. Res. Soc.Symp. Proc. 2000, Vol. 612,  D9.12.1 « VOLATILE LIQUID PRECURSORS FOR THE CHEMICAL VAPOR DEPOSITION (CVD) OF THIN FILMS CONTAINING TUNGSTEN »,  https://faculty.chemistry.harvard.edu/files/gordon/files/vol_liquid_cvd_tungsten_matressocsympproc612_d9.12.12000.pdf

W(CO)6 for W growth by MOCVD

  In 1947, Lander and Germer applied decomposition of hexacarbonyltungsten W(CO)6 for the preparation of W metal: W(CO)6 →W + 6 CO (300 – 600 °C, carrier gas H2). This was first example of chemical vapor deposition of W from tungsten carbonyls.

 W(CO)6 was later more extensively used  for the growth of W films; in the optimized conditions the obtained layers had good adherence and low impurities content.

W(CO)6 for WS2 growth by MOCVD

The growth of ultra-high optical quality of WS2 thin films from W(CO)6 and ditertirybutylsulfide (tBu)2S was reported in [[i]]. Pulse precursor delivery approach (pulse W precursor, purge with H2O-containing gas, then pulse S precursor was used for reaching larger size of domains.

[i] A. Cohen, A. Patsha, P.K. Mohapatra, M. Kazes, L. Houben, D. Oron, A. Ismach,  « Ultra-High Optical Quality WS2 Atomic-Layers via a Growth-Etch MOCVD Approach », 2020, https://arxiv.org/ftp/arxiv/papers/2008/2008.07150.pdf

W(CO)6 for WNx growth by MOCVD

     W(CO)6 and NH3 have been applied to deposit amorphous WNx films below 275°C [i].

[i] J. E. Kelsey, C. Goldberg, G. Nuesca, G. Peterson, A. E. Kaloyeros, B. Arkles, J. Vac. Sci. Technol. B, 17, 1101 (1999).

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