Zeitaufgelöste Cavity-Ringdown-Messungen der Druckabhängigkeit der Reaktionen von SiH2-Radikalen mit O2 und den Alkenen C2H4, C3H6, trans-C4H8

The rate constants for the reactions SiH2 + O2 -> products (R1), SiH2 + C2H4 -> products (R2), SiH2 + C3H6 -> products (R3), SiH2 + C4H8 -> products (R4), which play a major role in thermally initiated chemical vapour deposition (CVD) processes were investigated. Time resolved measurements were carried using cavity ring down spectroscopy with a new designed CRD apparatus. SiH2 was generated by photolysis of phenylsilane with an excimer laser at 193 nm. To extract the rate constants from the non-exponential ringdown profiles, the bandwidth effect originating from the overlap of the probe laser and the resonance line was taken into account using the extended simultaneous kinetics and ringdown model. The investigation of the rate constant of the reaction (R1) shows no pressure dependence in the measured pressure range. The rate constant was found to be k1(295 K})=(9.9±1.9) 10^{12} cm^3 mol^{-1} s^{-1}. For the reaction of SiH2 with the alkenes C2H4, C3H6 and trans-C4H8}, the rate constants were found to increase with increasing pressure. The measurements are in the fall-off range of the initial association step. Using the Troe formalism the data allowed us to determine limiting high pressure rate constants.