CW laser-induced fluorescence study of SiH2+SiH4 reaction: Dominance of two-body reaction channel in low-pressure silane plasma

The decay of the SiH2 density in the afterglow of low-pressure SiH4 plasma was studied by laser-induced fluorescence spectroscopy using a cw dye laser . Pressure dependence of the SiH2 loss rate in SiH4/H-2 mixture plasma indi cates that at low pressures (less than or similar to 40 mTorr) the SiH2+SiH 4 reaction mainly occurs at a rate constant of similar to 4 x 10(-11) cm(3) s(-1) via a two-body process, presumably yielding Si2H4+H-2, and not via th e three-body association process yielding Si2H6, which is dominant at high pressures a hydrogen molecule is found to be an inefficient third body prom oting the three-body association process. When SiH4 is diluted with H-2 so that the SiH4 fraction is below similar to 10% with a fixed total SiH4/H-2 pressure of 60 mTorr, the transport to the wall becomes the dominant SiH2 l oss process in the reactor geometry of 3-cm spaced parallel-plate electrode s; the transport loss rate of SiH2 in this condition is close to the free-f all limit because of small momentum transfer in collisions between SiH2 and H-2.