New Tungsten(VI) Guanidinato Complexes:  Synthesis, Characterization, and Application in Metal−Organic Chemical Vapor Deposition of Tungsten Nitride Thin Films

Two new tungsten complexes, [W(NtBu)₂(NMe₂){(iPrN)₂CNMe₂}] (2) and [W(NtBu)₂(H){(iPrN)₂CNMe₂}] (3), as precursors for metal−organic chemical vapor deposition (MOCVD) of tungsten nitride thin films were synthesized from the starting compound [W(NtBu)₂(Cl){(iPrN)₂CNMe₂}] (1) by substitution of the chloro ligand by a dimethylamido and a hydrido group, respectively. Compounds 1−3 were characterized by ¹H NMR, ¹³C NMR, EI-MS, IR, and elemental analysis including single-crystal X-ray diffraction studies on 1 and 3. The thermal properties of the compounds were studied by thermogravimetric and differential thermal analysis. Precursors 2 and 3 were compared for the growth of tungsten nitride thin films by MOCVD. The obtained films were characterized by X-ray diffraction and scanning electron microscopy and by depth-profiling the composition with secondary neutron mass spectroscopy. Films grown without ammonia had surprisingly low nitrogen levels, indicating that 2 and 3 are not suited as single-source precursors for pure WN_x phases. When ammonia was used as a co reactant gas, the carbon content in the films decreased significantly and crystalline β-W₂N was obtained. Interestingly, films grown in the presence of ammonia by amido compound 2 yielded lower carbon contents than films obtained from hydrido compound 3.