Gas Phase Reactions between SiH₄and B₂H₆:  A Theoretical Study

Abstract

Gas-phase reactions of silane (SiH 4 ) and diborane (B 2 H 6 ) are investigated using ab initio calculations at the MP2/6-311++g** level. Initially SiH 4 and B 2 H 6 are only weakly attracted to each other. Under thermal activation, the two molecules can overcome an energy barrier of 33.87 kcal/mol to associate into a complex SiH 4 -BH 3 -BH 3 with a hydrogen-bridged Si-H-B bond. Upon bonding, one of the two hydrogen-bridged bonds B-H-B in B 2 H 6 is broken and the other becomes polarized. Started from the SiH 4 -BH 3 -BH 3 complex, three comparable fragmentation pathways involving BH 3 and H 2 elimination produce several silaboranes with various silicon-boron-hydrogen ratios. A much higher barrier exists between the initial loosely bonded SiH 4 -B 2 H 6 system and a direct H 2 elimination product SiH 3 -B 2 H 5 with C s symmetry. The bonding nature in the species are further elucidated through topological analysis of electron density using the AIM theory. These intermediate silaboranes are possible precursors for chemical vapor deposition in fabricating boron doped silicon films. Their composition and polarity may determine their tendency of surface adsorption and the properties of the relevant solid. The proposed mechanisms can help to understand and control the initial gas-phase reactions in practice. Calculated IR spectra, dipole moment, and rotational constants of the species are provided to facilitate experimental investigations.

Theoretical Study of the Binding of Silane (SiH4) with Borane (BH3), Diborane (B2H6), and Boron Trichloride (BCl3): The Role of Core–Electron Correlation

“…This exceptionally strong interaction between SiH 4 and BH 3 may be due to the electrondeficient nature of boron, which frequently leads to bridging structures. 7 In contrast, in SiH 4 •••BCl 3 , the electronegative chlorine atoms mitigate this tendency, thereby making the interaction In both cases, the partially frozen core results are used for the extrapolation. The 0 K binding enthalpies are in parentheses.…”

Stability, local structure and electronic properties of borane radicals on the Si(1 0 0) 2 × 1:H surface: A first-principles study

“…First-principles structural optimization and total energy calculations have been performed for Thermodynamic analysis also shows a strong temperature dependence of the chemical reactions 26 with formation of (-)Si-BH 2 or (-)B-SiH 2 becoming more favorable because of the entropy contribution of H 2 gas.…”

“…Recently, Shayeganfar and Rochefort investigated electronic properties of a boron-doped Si(111) surfaces by self-assembling trimeric acid [24]. Using first-principles approaches, Hu and co-workers studied gas-reactions between SiH 4 and B 2 H 6 and revealed the formation of SiH 4 -BH 3 -BH 3 as an intermediate product [26]. However, currently there is still a lack of knowledge about boron/borane radicals/clusters on Si surfaces, which play a crucial role in the PureB preparation process at the initial stage.…”

A multi-nuclear magnetic resonance and density functional theory investigation of epitaxially grown InGaP2

“…Up to now, experimentalists have focused on the structure of the diborane molecule [9] and its decomposition reactions [1][2][3][4][5][11][12][13][14][15]. First-principles approaches have been applied to investigate the geometries of pure Si surfaces [9,10,16], the Si surfaces with hydrogen-termination [10], B doping in Si [17][18][19], and B on the Si surfaces [19][20][21]. We investigated deposition of BHn (n = 0 to 3) radicals on the Si{0 0 1}2×1:H surface [22] which is stable at high temperature (~640°C [15]).…”