Theoretical Study of Decomposition Kinetics and Thermochemistry of Bis(dimethylamino)silane-Formation of Methyleneimine and Silanimine Species.

Abstract

The gas-phase decomposition kinetics and thermochemistry of bis(dimethylamino)silane (BDMAS), a potential precursor in the chemical vapor deposition of silicon nitride and silicon carbonitride thin films, were systematically studied using ab initio calculations at the CCSD(T)/6-311 + G(2d,p)//B3LYP/6-311 + + G(d,p) level of theory. The reaction routes were mapped out, exploring both the concerted and stepwise reactions in three different zones with the initial cleavage of Si-N, N-Me (Me = CH3), and Si-H, respectively. It was found that the energy needed to break N-Me at 80.6 kcal·mol-1 is lower than the ones for Si-N and Si-H, both at 87.4 kcal·mol-1. When compared with tris(dimethylamino)silane (TrDMAS), it has been shown that the three bonds of N-Me, Si-N, and Si-H in BDMAS can be ruptured more easily, suggesting that BDMAS could be a more efficient precursor gas than TrDMAS. Upon decomposition, BDMAS tends to form methyleneimine and silanimine species, where four methyleneimine species and three silanimine species were produced. From the investigation of the effect of temperature on the kinetic and thermodynamic competition of different decomposition pathways, it has been demonstrated that the concerted formation of N-dimethylaminosilyl methyleneimine (H2C═N-SiH2NMe2) by the elimination of CH4 from BDMAS is the most kinetically and thermodynamically favored pathway in the whole temperature range from 0 K (ΔH0‡ = 62.7 kcal·mol-1 and ΔH0 = 7.7 kcal·mol-1) up to 2673 K. In addition, lower temperatures favor the production of N-methyl methyleneimime (H2C═NMe), whereas high temperatures promote the formation of N-methylsilanimine (H2Si = NMe) and 1-dimethylamino-N-methylsilanimine (Me2NSi = NMe).