In situ optical analysis of the gas phase during the deposition of silicon carbide from methyltrichlorosilane

Coherent anti-Stokes Raman spectroscopy (CARS) was used for analysis of the gas phase during chemical vapor deposition (CVD) of silicon carbide (SiC) from a methyltrichlorosilane (MTS; CH3SiCl3)-hydrogen (H-2) precursor mixture. CARS experiments were carried out in a low-pressure hot-wall reactor under the selected conditions: temperature T = 1000 to 1300 K, total pressure P-lot = 2 to 5 kPa, H-2 to MTS now rate ratio alpha = 3 to 20, and total gas flow rate Q = 50 to 400 seem. A systematic search for the radical and stable species present in the hot zone of the reactor was first conducted. Then partial pressures of MTS and CH4 were measured at the hot-zone outlet as a function of temperature, initial partial pressures of MTS and H-2, and residence time. Partial pressure of HCl was also measured vs. initial pressure of MTS. A reaction mechanism was tentatively drawn up to describe the decomposition of MTS in the gas phase. Then the experimental results were compared to those of a computer model which calculated concentrations of the gaseous species at the output of the hot zone by numerical integration of reaction rates.