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(N t Bu) 2 (NMe 2 ){( i PrN) 2 CNMe 2 }] ( 2 ) and [W(N t Bu) 2 (H){( i PrN) 2 CNMe 2 }] ( 3 ), as precursors for metal−organic chemical vapor deposition (MOCVD) of tungsten nitride thin films were synthesized from the starting compound [W(N t Bu) 2 (Cl){( i PrN) 2 CNMe 2 }] ( 1 ) by substitution of the chloro ligand by a dimethylamido and a hydrido group, respectively. Compounds 1 − 3 were characterized by 1 H NMR, 13 C 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-W 2 N 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 .