Deposition of molybdenum carbonitride thin films from Mo(NBu t ) 2 (NHBu t ) 2
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Mo(NBu') 2 (NHBu t ) 2 is used as a single-source precursor to deposit thin films of cubic phase molybdenum carbonitride, MoQNy (x: 0.2-0.55, y: 0.1-0.47), by chemical vapor deposition on silicon substrates. In general, the C/Mo ratios increased from 0.2 to 0.55 and the N/Mo ratios decreased from 0.47 to 0.1 with increasing the temperature of deposition from 773 to 923 K. Based on the elemental composition and the composition of the gas phase products, it is proposed that the carbon atoms were incorporated through /3-methyl activation of the ligands.
Transition metal carbides and nitrides are interesting materials with many useful physical and chemical properties.1 Many research results of growing thin films of early transition metal carbides, nitrides, and carbonitrides from single-source precursors by chemical vapor deposition (CVD) have been published.2"7 Recently, we have shown that tungsten nitride thin films can be prepared employing a bistertbutylimido complex of tungsten, W(NBu t ) 2 (NHBu t ) 2 . 8 In this communication, we wish to report our preliminary findings applying an analogous molybdenum complex, Mo(NBu t ) 2 (NHBu') 2 , 1, as a single-source precursor of CVD. 1, synthesized according to a literature route with slight modification,9 can be vaporized easily at 323 K in vacuum. Deposition of thin films on silicon and glass substrates was performed in a low-pressure coldwall reactor at 723-923 K and 5-25 Pa depending on the carrier gas flow rate. Initial attempts to grow thin films on silicon substrates were difficult, possibly due to lack of suitable nucleation sites. Thus, we applied hydrogen plasma to etch the substrates before the depositions because our previous experience indicated that this procedure can assist thin film growth, probably by increasing nucleation sites on the surface.10 After this process, grey metallic shining thin films with good adhesion to the substrates (Scotch tape test) were obtained. The surface morphology was smooth with very fine grains as shown by the scanning electron micrograph (SEM) in Fig. 1. Thin films with similar properties were grown on glass substrates without difficulty. X-ray diffraction (XRD) studies, such as the one shown in Fig. 2, showed major CuK a diffraction peaks at angles 20 equal to 36.99-37.35°, 43.19-43.52°, 62.38-63.07°, and 74.74-75.47° for the films. These peaks, characteristic of (111), (200), (220), and (311) reflections of cubic structures, are close to the values of y - M o 2 C (37.77°, 43.69°, 63.39°, and 75.72°) and y - M o 2 N (37.38°, 43.44°, 63.10°, and 75.72°). 1622
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J. Mater. Res., Vol. 9, No. 7, Jul 1994
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FIG. 1. SEM photograph of a thin film deposited at 773 K.
High resolution x-ray photoelectron spectra (XPS) of a typical sample deposited at 773 K showed major signals assignable to the binding energies of the following electrons, Mo3rf5/2 and Mo3rf3/2 (228.4 and 231.6 eV), Mo3/,3/2 and Mo 3p i /2 (394.4 and 412.0 eV), C ls (282.6 eV), N l s (39
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