Ab Initio Chemical Kinetic Study for Reactions of H Atoms with SiH₄ and Si₂H₆: Comparison of Theory and Experiment

Abstract

The reactions of hydrogen atom with silane and disilane are relevant to the understanding of catalytic chemical vapor deposition (Cat-CVD) and plasma enhanced chemical vapor deposition (PECVD) processes. In the present study, these reactions have been investigated by means of ab initio molecular-orbital and transition-state theory calculations. In both reactions, the most favorable pathway was found to be the H abstraction leading to the formation of SiH(3) and Si(2)H(5) products, with 5.1 and 4.0 kca/mol barriers, respectively. For H + Si(2)H(6), another possible reaction pathway giving SiH(3) + SiH(4) may take place with two different mechanisms with 4.3 and 6.7 kcal/mol barriers for H-atom attacking side-way and end-on, respectively. To validate the calculated energies of the reactions, two isodesmic reactions, SiH(3)+CH(4)-->SiH(4)+CH(3) and Si(2)H(5)+C(2)H(6)-->Si(2)H(6)+C(2)H(5) were employed; the predicted heats of the formation for SiH(3) (49.0 kcal/mol) and Si(2)H(5) (58.6 kcal/mol) were found to agree well with the experimental data. Finally, rate constants for both H-abstraction reactions predicted in the range of 290-2500 K agree well with experimental data. The result also shows that H+Si(2)H(6) producing H(2)+Si(2)H(5) is more favorable than SiH(3)+SiH(4.).

High‐Temperature Rate Constants for H + Tetramethylsilane and H + Silane and Implications about Structure–Activity Relationships for Silanes

“…The present TST calculations tend to underestimate the experimental room temperature data, whereas their high‐temperature predictions (>800 K) are in very good agreement with the theoretical results from Wu et al . The applied composite methods involve geometry optimization and frequency calculation with B3LYP functionals.…”

“…Arrhenius plot of the H + SiH 4 experimental rate constants; orange dotted line: theory (G4), present work; black dashed line: theory (CBS‐QB3), present work; solid blue line: theory, Wu et al ; green dashed line: theory, Qi and Sun ; magenta dashed‐dotted line: theory, Espinosa‐García et al ; circles: experiment, this work; squares: experiment, Arthur et al ; triangles: experiment, Arthur and Miles ; diamonds: experiment, Goumri et al ; star: experiment, Austin and Lampe .…”

“…At room temperature and temperatures below 700 K, numerous experimental data for k 1 have been reported . Also theory studies about reaction have been recently published . Figure contains a comparison between the present rate constant data and available experimental and theoretical results from the literature.…”

“…In contrast, over the whole‐temperature range of 298–2000 K, the TST predictions published by Espinosa‐García et al and Qi and Sun are in excellent agreement with available experimental data, that is with average deviations of less than ±30%, including those reported in this work. These authors applied variational transition state theory (VTST) to calculate rate constants, whereas conventional TST was applied in this work and also by Wu et al Over the temperature range from 300–1600 K, the theoretical rate constants from Espinosa‐García et al and Qi and Sun can be represented by the Arrhenius expression :…”

Ab initiochemical kinetics for the unimolecular decomposition of Si2H5radical and related reverse bimolecular reactions

“…In a typical CVD process, the reactions may include the dissociation of source gases induced by electron collisions in a plasma environment, radicals reactions with silicon compounds, the thermal decomposition of compounds, and so on . For silicon‐based film deposition, silane (SiH 4 ) is often used as the gas source; the disilanyl (Si 2 H 5 ) radical may be generated by H‐atom abstraction by H or other radicals from the disilane (Si 2 H 6 ) formed by the recombination of SiH 3 radicals or the association of SiH 3 with SiH 2 radical, among others . The chemical properties of the transient silicon hydrides, Si 2 H 5 , Si 2 H 4 , Si 2 H 3 , and Si 2 H 2 prepared from fluorine atom reactions with disilane were first investigated and measured with the photoionization mass spectrometry method by Ruscic and Berkowitz .…”