Ab initio chemical kinetics for reactions of H atoms with SiH_x (x = 1–3) radicals and related unimolecular decomposition processes

Abstract

Hydrogen atoms and SiHx (x = 1–3) radicals coexist during the chemical vapor deposition (CVD) of hydrogenated amorphous silicon (a‐Si:H) thin films for Si‐solar cell fabrication, a technology necessitated recently by the need for energy and material conservation. The kinetics and mechanisms for H‐atom reactions with SiHx radicals and the thermal decomposition of their intermediates have been investigated by using a high high‐level ab initio molecular‐orbital CCSD (Coupled Cluster with Single and Double)(T)/CBS (complete basis set extrapolation) method. These reactions occurring primarily by association producing excited intermediates, 1SiH2, 3SiH2, SiH3, and SiH4, with no intrinsic barriers were computed to have 75.6, 55.0, 68.5, and 90.2 kcal/mol association energies for x = 1–3, respectively, based on the computed heats of formation of these radicals. The excited intermediates can further fragment by H2 elimination with 62.5, 44.3, 47.5, and 56.7 kcal/mol barriers giving 1Si, 3Si, SiH, and 1SiH2 from the above respective intermediates. The predicted heats of reaction and enthalpies of formation of the radicals at 0 K, including the latter evaluated by the isodesmic reactions, SiHx + CH4 = SiH4 + CHx, are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and unimolecular reactions have been predicted with tunneling corrections using transition state theory (for direct abstraction) and variational Rice–Ramsperger–Kassel–Marcus theory (for association/decomposition) by solving the master equation covering the P,T‐conditions commonly employed used in industrial CVD processes. The predicted results compare well experimental and/or computational data available in the literature. © 2013 Wiley Periodicals, Inc.

Ideal gas thermochemical properties of silicon containing inorganic, organic compounds, radicals, and ions

“…The thermal electron G3B3 result for the SiF 4 ions is 44,45 calculate Δ f H • (0 K) = 369.0 kJ mol −1 . Finally Lin and coworkers report 19 Δ f H • (0 K) = 370.7 to 374.9 ± 5 kJ mol −1 .…”

“…of Δ f H° (0 K) = 374.5 ± 2.9 kJ mol −1 (compared with our value of Δ f H °(0 K) = 375.4 ± 8 kJ mol −1 ), and Jursic and others calculate Δ f H °(0 K) = 369.0 kJ mol −1 . Finally Lin and coworkers report Δ f H °(0 K) = 370.7 to 374.9 ± 5 kJ mol −1 .…”

“…Sukkaew et al 18 calculated some Si-C-H compounds. And finally Lin and coworkers [19][20][21][22][23] published in 2013-2017 articles about SiH x and Si 2 H y family including some cations.…”

Selective Vacuum Evaporation by the Control of the Chemistry of Gas Phase in Vacuum Refining of Si

“…The Si–He and Si–Ar interactions are clearly more attractive at a long range and less repulsive at a short range than the P–He and P–Ar curves, and the Si–H 2 interaction is clearly quite attractive and strongly anisotropic, being most attractive for a 90° angle of approach. This latter behavior can be understood by realizing that the Si–H 2 interaction is reactive. ,, There is a fairly high calculated energy barrier of about 0.94 eV for forming an excited triplet SiH 2 molecule . This triplet SiH 2 can make spin-forbidden transition to the singlet ground-state SiH 2 through a crossing point only 0.10 eV above the triplet SiH 2 minimum .…”

Opening the Pandora's jar of molecule-to-material conversion in chemical vapor deposition: Insights from theory

“…Such a scenario has stimulated the development of multiscale models for the CVD growth, that comprise a set of submodels tailored for dealing with different length scales . On the other hand, the study of the plasma‐activated SiH 3 formation and of its reactivity with other plasma‐generated species requires a very high theory level and should be performed with post‐HF methods …”