Theoretical and Experimental Studies of the Gas-Phase Decomposition Chemistry of Organosilicon Compounds Containing Silicon-Nitrogen Bonds Via Hot-Wire Chemical Vapor Deposition
Creators: name: Stevenson, James M.
Publisher: name: Science
Year: 2022
Subjects: subject: Silicon Nitride
subject: Silicon Carbonitride
subject: Chemical Vapor Deposition
subject: Gas Phase
subject: Chemistry--Physical

description: The gas phase chemistry of two single-source precursors, bis(dimethylamino)silane (BDMAS) and 1,1,3,3-tetramethyldisilazane (TMDSZ), for silicon nitride (SiNx) and silicon carbonitride (SiCyNz) thin films on hot metal filaments during hot-wire chemical vapor deposition (HWCVD) has been studied. These films are used in microelectronics for their semiconductive properties. Current precursor gases used are SiH4, NH3 and CH4. As SiH4 is pyrophoric, industries search for Si–N-bond-containing single-source precursors. Two molecular groups are studied, a dimethylamino-substituted silane, BDMAS, and disilazanes encompassing TMDSZ and 1,1,1,3,3,3-hexamethyldisilazane (HMDSZ, for comparison). Films deposited via HWCVD from these precursors have been studied. However, the gas-phase chemical processes are yet to be fully understood.Ab initio calculations were carried out to predict how each molecule would behave during gas-phase decomposition. Concerted and stepwise reaction routes of BDMAS, TMDSZ and HMDSZ were mapped using the CCSD(T)/6-311+G(2d,p) (BDMAS) or CCSD(T)/6-311++G(d,p) (TMDSZ, HMDSZ)//B3LYP/6-311++G(d,p) theory level, exploring the cleavage of their main chemical bonds. BDMAS can form methyleneimines and silanimines. By calculating enthalpies, entropies and Gibbs energies, the most kinetically and thermodynamically favorable route of BDMAS was found to be the concerted formation of N-dimethylaminosilyl methyleneimine and methane. Common bond cleavages (Si–N, Si–C, and N–H) require less energy for TMDSZ than HMDSZ, which both create silenes and silanimines. The most kinetically favorable route for TMDSZ is the formation of methane and 1-dimethylsilylaminosilene.BDMAS hydrolyzes, forming dimethylamine, at room temperature and its further study was not pursued. Primary TMDSZ decomposition on hot metal filaments (W and Ta) and secondary gas-phase reactions were studied using respective collision-free and HWCVD reactor setups. Primary formation of methyl radicals had an apparent activation energy (Ea) of 87.5 ± 7.7 kJ mol-1 on W. 1,1-Dimethylsilanimine (DMSA) production showed two Arrhenius trends in the low- and high-temperature region which may correspond to respective concerted (Ea-W = 32.1 ± 4.8 kJ mol-1) and stepwise reactions (Ea-W = 155.0 ± 7.8 kJ mol-1). As the experimental Ea are lower than theoretical values, the creation of •CH3 and DMSA is catalyzed by the metal filaments. Primary ammonia formation has an Ea-W = 22.1 ± 3.5 kJ mol-1. Ammonia forms H2 and N2 in the reactor setup. In the reactor, free-radical chain reactions dominated. Evidence was obtained for silanimine cycloaddition and silylene insertion reactions. Due to its Si–H bonds, TMDSZ is more reactive than HMDSZ and creates promising gas-phase products for SiCyNz film deposition.