Understanding the Reaction Chemistry of 1,1,3,3-Tetramethyldisilazane as a Precursor Gas in a Catalytic Chemical Vapor Deposition Process.

The reaction chemistry of 1,1,3,3-tetramethyldisilazane (TMDSZ) in catalytic chemical vapor deposition (Cat-CVD), including its primary decomposition on a heated W filament and secondary gas-phase reactions in a Cat-CVD reactor, was studied using 10.5 eV vacuum ultraviolet single-photon ionization and/or laser-induced electron ionization in tandem with time-of-flight mass spectrometry. It has been demonstrated that TMDSZ initially breaks down to form various species, including methyl radical (•CH 3 ), ammonia (NH 3 ), and 1,1-dimethylsilanimine (DMSA). The activation energies ( E a ) for the formation of •CH 3 and NH 3 were determined to be 61.2 ± 1.0 and 42.1 ± 0.9 kJ mol -1 , respectively, in the temperature range of 1400-2000 and 900-2400 °C. It was found that the formation of DMSA may have two different contributing routes, i.e., a concerted one ( E a = 33.6 ± 2.3 kJ mol -1 ) at lower temperatures of 900-1500 °C and a stepwise one ( E a = 155.0 ± 7.8 kJ mol -1 ) at higher temperatures of 2100-2400 °C. The secondary gas-phase reactions occurring in the Cat-CVD reactor environment were found to stem from two competing processes. The first one, free-radical short-chain reactions initiated by •CH 3 formation and propagated by H abstraction reactions, is the dominating chemical process, producing many high-mass stable alkyl-substituted or silyl-substituted disilazane or trisilazane products via radical recombination reactions. Head-to-tail cycloaddition of unstable DMSA is the second contributing chemical process, which forms cyclodisilazane species. In addition, evidence was found for the conversion of NH 3 into H 2 and N 2 in the Cat-CVD reactor.