Methyltungsten cyclopentadienyl tris(carbonyl) WMe(η5-C5H5)(CO)3 (or WMe(Cp)(CO)3) is dark yellow, fairly stable solid (18-valence electron species). Monomeric WMe(Cp)(CO)3 can dimerize producing red, stable, volatile [WMe(Cp)(CO)3]2 (complex having W-W bond). On heating less stable [WMe(Cp)(CO)2]2 is formed having a W≡W triple bond is formed, which is highly reactive toward moisture and air).
Vapour pressure measurements showed relatively low volatility of WMe(Cp)(CO)3: 89 mTorr (8.9*10-2 Torr) at 75°C[i]
WMe(Cp)(CO)3 is synthesized by the reaction of tungsten carbonyl with sodium cyclopentadienyl and subsequent addition of excess of iodomethane, resulting in methylation of tungsten cyclopentadienyl tricarbonyl anion:
W(CO)6 + NaCp → [WCp(CO)3]-Na+ + 3 CO
[WCp(CO)3]Na + CH3I(excess) → WMe(Cp)(CO)3 + NaI (40 °C, THF)
[i] C.I.M.A. Spee, F. Verbeek, J.G. Kraaijkamp, J.L. Linden, T. Rutten, H. Delhaye, E.A. van der Zouwen, H.A. Meinema, Mater. Sci. Eng.: B, Vol.17, Iss.1–3, 1993, p.108-111, https://doi.org/10.1016/0921-5107(93)90090-A “Tungsten deposition by organometallic chemical vapour deposition with organotungsten precursors”
WMe(Cp)(CO)3 was applied as precursor for the MOCVD deposition of W coatings on Si(100) substrates at 320–620 °C temperatures, either in vertical hot-wall reactor (background pressure 0.1 – 0.01 Torr, H2/N2=1:1 carrier gas (100 slm)), or a cold-wall reactor (background pressure of 0.001 Torr, H2/N2=1:1 carrier gas (18 slm)). WMe(Cp)(CO)3 precursor was vaporised at 72 – 81 °C temperatures. Growth rate varied with temperature: increased from 0.4 μm/h at 400 °C to 2 μm/h at 620 °C; growth rate dependence vs. reciprocal substrate temperatures indicated kinetically limited deposition (with low growth rates) up to relatively high temperatures (400–500°C). At 400°C, ~0.16 μm/h growth rates were obtained using CpW(CO)3CH3 precursor (much higher compared to ~5 nm/h with Cp2WH2 precursor). According to XRD, mainly β-W films were formed (probably due to O contamination of the layers: the deposited W films contained 5–15 at. % C and 5–10 at. % O. Surface carbon was present as WC, according to XPS. Layer resistivity varied from 40 – 600 μWcm to 15 and 17 μWcm and down to 0.01– 0.1 μWcm . [[i]]
[i] C.I.M.A. Spee, F. Verbeek, J.G. Kraaijkamp, J.L. Linden, T. Rutten, H. Delhaye, E.A. van der Zouwen, H.A. Meinema, Mater. Sci. Eng.: B, 1993, Vol.17, Iss.1–3, p.108-111, “Tungsten deposition by organometallic chemical vapour deposition with organotungsten precursors”, https://doi.org/10.1016/0921-5107(93)90090-A
WMe(Cp)(CO)3 was applied as precursor for the growth of WC films on Si substrates by MOCVD. Growth temperature was 350-700°C, reactor pressure 10-7 Torr, no carrier gas was used. High growth rate was achieved : 40µm/h, WC layers contained 50-70%, however the resistivity was very high.[i]
[i] Prof. Dr. Heinrich Lang, The Chemistry of Metal CVD, International Research Training Group, “Materials and Concepts for Advanced Interconnects”