Mass spectrometric study of gas-phase chemistry in the hot-wire CVD processes of SiH4/NH3 mixtures

The gas-phase reaction products of SiH4, NH3 and their mixtures from a hot-wire CVD chamber were investigated using laser ionization time-of-flight mass spectrometry. Both vacuum ultraviolet laser single photon ionization and laser-induced electron impact ionization were used. The main products observed from a 50% NH3/He sample were H2 and N2. The study of an NH3/SiH4 mixture (PNH3:PSiH4 = 100:1) has shown that the NH3 dissociation on the filament was suppressed by the presence of SiH4 in the system. Signals from Si(NH2)4 and Si(NH2)3 species were identified as products from the 100:1 NH3/SiH4 mixture. The spectrum for a 1:1 NH3/SiH4 mixture was dominated by mass peaks characteristic of SiH4 chemistry in the reactor, i.e. H2, Si2H6, and Si3H8, at low temperatures. The extent to which the decomposition of NH3 is suppressed is enhanced with more SiH4 molecules in the system.