Gas-Phase N-Si Ion Clusters in Ammonia/Silane Mixtures

Abstract

Ammonidsilane mixtures have been studied by ion trap mass spectrometry, and variations of ion abundances with reaction time in 1 5 , 1:1, and 5 : 1 mixtures have been reported. Mechanisms of ion-molecule reactions have been elucidated by single and multiple isolation steps, and exact mass measurements of isobaric ions have been carried out by Fourier transform mass spectrometry. The SiH,+ (n = 0-3) primary ions give self-condensation processes in which Si,H,+ species are formed. These ions react with NH3 and give Si2-NH,+ (n = 3-6) and Si2N2Hn+ (n = 4-7) ions in successive steps with elimination of H2. In parallel processes, the SiH,+ (n = 0-3) primary ions react with NH3 to give ions belonging to the SiNH,+ (n = 2-4) and SiN2H,+ (n = 4-7) families, which do not react with Si& furtherly. A number of precursors give SiNH6+ and N&+ through different pathways, the last ion being the most abundant one also after short reaction times in all the mixtures examined. The rate constants of the gas-phase reactions of the most important ions have been determined by ion trap mass spectrometry, compared with calculated collision rate constants, and the efficiencies have been determined. Formation of Si2N2H,+ (n = 4-7) and SigN2Hn+ (n = 7, 8) ions, even if with rather low efficiencies, suggests that ionic species in addition to radicals can give a contribution to the deposition of solid silicon nitride from ammonidsilane mixtures by radiolytical methods.

Gas Phase Ion−Molecule Reactions in Phosphine/Silane Mixtures

“…Comparison between the PH 3 /SiH 4 system and the NH 3 /SiH 4 system studied previously 28 indicates some important differences. Primary ions of silane generally react faster with NH 3 than with PH 3 , to give the corresponding SiNH n + (n ) 2-4) and SiPH n + (n ) 1-4) ions, respectively.…”

“…28 Unfortunately, it has been impossible to calculate the ∆H°values for the reactions involving ions containing phosphorus and silicon atoms, as heats of formation of these ionic species are not available in the literature.…”

“…The ITMS experiments were performed at 333 K to obtain data comparable with previous results. 28 The gas inlet system was modified to introduce simultaneously reagents and buffer gases into the ion trap through four different lines. The pressures were measured by a Bayard Alpert ionization gauge.…”

“…26,28 Further experiments were also performed with isolation of every product ion; subsequent reaction of each isolated ion species revealed its contribution to the formation of ionic species common to different precursors. Moreover, in some reactions, a unique ionic precursor yields a unique product ion by reaction with both neutral reactants.…”

Gas‐Phase Ion Chemistry of Silicon‐Containing Molecules†This article is dedicated to Saul Patai.

“…The ion molecule reactions occurring between SiH x C (x D 0 3) cations and neutral ammonia, as well as the reactions between NH x C cations and SiH 4 were studied by FTMS 113,114 . The main channel for the reaction between SiH x C ions and NH 3 was found to correspond to the elimination addition reaction, well-known for silanes (equation 20), which formally corresponds to the transfer of a nitrene-unit (NH) 113 .…”