KINETICS OF SIO2 DEPOSITION FROM TETRAETHYLORTHOSILICATE

The kinetics of the decomposition of tetraethylorthosilicate (TEOS) vapor to form solid SiO2 in a well-mixed flow reactor at feed pressures from 0.001 to 0.1 Torr have been studied by monitoring reaction rates with a differentially pumped mass spectrometer to determine reactant and product partial pressures. A resistively heated molybdenum foil was used as the deposition substrate to provide surface temperatures up to at least 1300-degrees-C. This technique provides rapid measurement (approximately 10 s) of gas composition in a well-mixed flow reactor so that reaction rates could be examined quantitatively Changes in the partial pressures of TEOS and C2H4 were used to probe SiO2 deposition kinetics. Over a wide range of temperatures and pressures, we observed +1.0 order with respect to TEOS partial pressure and an apparent activation energy of 20.9 +/- 0.5 kcal/mol. The effect of C2H4 partial pressure on the reaction rate was investigated by including C2H, in the reactor feed. Reaction rates were found to decrease as C2H4 partial pressure was increased, with the order with respect to C2H4 varying from 0 to -2.0 as C2H4 pressure was increased. Also, apparent activation energies were found to increase as C2H4 pressures were increased. A Langmuir-Hinshelwood model incorporating product inhibition described the data very well, suggesting that the reaction product C2H4 adsorbs on the growing SiO2 surface, blocking adsorption sites for TEOS. Values for model rate parameters were determined by fitting the LH model to both pressure and temperature dependences.