Premium
Ab initio chemical kinetics for the unimolecular decomposition of Si 2 H 5 radical and related reverse bimolecular reactions
Author(s) -
Wu ShangYing,
Lee YunMin,
Wu JongShinn,
Lin MingChang
Publication year - 2013
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.24557
Subject(s) - chemistry , rrkm theory , ab initio , silanes , standard enthalpy of formation , thermal decomposition , isodesmic reaction , computational chemistry , reaction rate constant , decomposition , chemical kinetics , thermochemistry , dissociation (chemistry) , ab initio quantum chemistry methods , kinetics , molecule , silane , organic chemistry , physics , quantum mechanics
For plasma enhanced and catalytic chemical vapor deposition (PECVD and Cat‐CVD) processes using small silanes as precursors, disilanyl radical (Si 2 H 5 ) is a potential reactive intermediate involved in various chemical reactions. For modeling and optimization of homogeneous a‐Si:H film growth on large‐area substrates, we have investigated the kinetics and mechanisms for the thermal decomposition of Si 2 H 5 producing smaller silicon hydrides including SiH, SiH 2 , SiH 3, and Si 2 H 4 , and the related reverse reactions involving these species by using ab initio molecular‐orbital calculations. The results show that the lowest energy path is the production of SiH + SiH 4 that proceeds via a transition state with a barrier of 33.4 kcal/mol relative to Si 2 H 5 . Additionally, the dissociation energies for breaking the SiSi and HSiH 2 bonds were predicted to be 53.4 and 61.4 kcal/mol, respectively. To validate the predicted enthalpies of reaction, we have evaluated the enthalpies of formation for SiH, SiH 2 , HSiSiH 2 , and Si 2 H 4 ( C 2h ) at 0 K by using the isodesmic reactions, such as 2 HSiSiH 2 + 1 C 2 H 6 → 1 Si 2 H 6 + 2 HCCH 2 and 1 Si 2 H 4 ( C 2h ) + 1 C 2 H 6 → 1 Si 2 H 6 + 1 C 2 H 4 . The results of SiH (87.2 kcal/mol), SiH 2 (64.9 kcal/mol), HSiSiH 2 (98.0 kcal/mol), and Si 2 H 4 (68.9 kcal/mol) agree reasonably well previous published data. Furthermore, the rate constants for the decomposition of Si 2 H 5 and the related bimolecular reverse reactions have been predicted and tabulated for different T, P‐conditions with variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory by solving the master equation. The result indicates that the formation of SiH + SiH 4 product pair is most favored in the decomposition as well as in the bimolecular reactions of SiH 2 + SiH 3 , HSiSiH 2 + H 2 , and Si 2 H 4 ( C 2h ) + H under T, P‐conditions typically used in PECVD and Cat‐CVD. © 2013 Wiley Periodicals, Inc.