Time resolved spectroscopic investigation of SiD2 + D2: kinetic study

Silylenes (silanediyls) have made an important impact on organosilicon chemistry even if it is of more recent foundation than carbenes in organic chemistry and much less complete. These species are highly reactive intermediates. They play a central role in the chemical vapour deposition (CVD) of various silicon-containing thin films which have a technological importance in microelectronics as well as in the dry etching processes of silicon wafers. Spectroscopic methods have been developed to observe these species, a necessary pre-requisite to their direct monitoring. In this work, deuterated phenylsilane precursor, PhSiD 3 was chosen for SiD 2 because its analogue phenylsilane, PhSiH 3 proved to be a good precursor for SiH 2 and the high quality decay signals observed revealed that SiD 2 be readily detected from PhSiD 3 and that if other decomposition pathways (e.g. PhSiD + D 2 ) are occurring, they do not effect measurements of the rate constants for SiD 2 . The absorption spectrum of SiD 2 formed from the flash photolysis of a mixture of PhSiD 3 and SF 6 at 193nm were found in the region 17384-17391 cm -1 with strong band at 17387.07 cm -1 . This single rotational line of p Q 1 was chosen to monitor SiD 2 removal. Time-resolved studies of SiD 2 have been carried out to obtain rate constants for its bimolecular reactions with D 2 . The reactions were studied over the pressure range 5-100 Torr (in SF 6 bath gas) at four temperatures in the range 298-498K. Single decay from 10 photolysis laser shots were averaged and found to give reasonable first-order kinetics fits. Second order kinetics were obtained by pressure dependence of the pseudo first order decay constants and substance D 2 pressures within experimental error. The reaction was found to be weakly pressure dependent at all temperatures, consistent with a third-body mediated association process. In addition, SiH 2 + H 2 reaction is approximately ca. 60% faster than SiD 2 +D 2 reaction. Theoretical extrapolations (using Lindemann-Hinshelwood model and Rice, Ramsperger, Kassel and Marcus (RRKM) theory) were also carried out and obtained data fitted the Arrhenius equations.