Thermal Decomposition of Tungsten Nitrido Precursors for Low Temperature MOCVD of WNxCy
The system design allows the CVD reactor to translate along three-dimensionally, to permit the laser to focus on any spot in the reactor. In-situ Raman experiments were performed using a heater set point temperature of 650 ˚C. Axial centerline temperature profiles in the reactor are measured by analysis of the rotational bands of the diatomic N2 carrier gas. Due to the low volatility of the precursor, it was dissolved in liquid pyridine and delivered to the reactor as an aerosol with N2 carrier gas (6). The 532 nm line of a Nd:YVO4 solid-state laser at 1.5 W was used as the light source to excite the molecules in the sample. Raman spectra were measured at various distances below the heated susceptor surface and thus various temperatures from 159 ˚C to 474 ˚C.
Density Functional Theory (DFT) calculations (using the B3LYP functional and LanL2DZ basis sets) were performed to assess possible pathways of thermal decomposition of WN(NMe2)3 and to assign observed Raman peaks to the decomposition products. The results of this study are consistent with proposed mechanistic steps for the thermal decomposition of the precursor, including dimerization of the precursor and loss of the amine. In addition to gas phase data, liquid phase Raman experiments were performed to better define additional species that are Raman active but not detected in the lower density gas phase experiments and to find vibrational frequencies before the molecule is decomposed.
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