Volatile Hexavalent Oxo-amidinate Complexes: Molybdenum and Tungsten Precursors for Atomic Layer Deposition

New complexes MoO2(tBuAMD)2 (1) and WO2((t)BuAMD)(2) (2) (AMD = acetamidinato) are synthesized and fully characterized as precursors for atomic layer deposition (ALD). They contain metal-oxo functionalities not previously utilized in ALD-type growth processes and are fully characterized by H-1 and C-13 NMR, X-ray diffraction (XRD), Fourier transform infrared, thermogravimetric analysis, single-crystal XRD, and elemental analysis. Guided by quartz crystal microbalance studies, ALD growth methodologies for both complexes have been developed. Remarkably, these isostructural compounds exhibit dramatic differences in ALD properties. Using 1 and O-3, amorphous, ultrathin molybdenum oxynitride (MoON) films are grown on Si(100) wafers. Using 2 and H2O yields amorphous WO3 films on Si(100) wafers that crystallize as WO3 nanowires upon annealing. Although 1/H2O and 2/O-3 growth was attempted, effective ALD growth could only be obtained with 1/O-3 and 2/H2O, underscoring reactivity differences in these precursors. Film thicknesses, compositions, and optical and electrical parameters are characterized by variable angle spectroscopic ellipsometry, X-ray reflectivity, grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and atomic force microscopy techniques. The hitherto unknown ALD chemistry of group VI metal-oxo compounds lays a foundation for their use in the ALD synthesis of heterogeneous catalysts.