posted on 2021-09-13, 15:37authored byJames
M. Stevenson, Yujun Shi
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 (H2CN–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 (H2CNMe), whereas
high temperatures promote the formation of N-methylsilanimine
(H2Si = NMe) and 1-dimethylamino-N-methylsilanimine
(Me2NSi = NMe).