Thermochemistry of Silicon−Hydrogen Compounds Generalized from Quantum Chemical Calculations

Abstract

Particulate contamination formed by homogeneous clustering reactions of silicon hydrides within silicon chemical vapor deposition processes is an important source of yield loss during semiconductor processing. On the other hand, intentional synthesis of silicon nanoparticles may be of great interest because of the unique optical and electronic properties of nanostructured silicon. Kinetic modeling can play an important role in developing a fundamental understanding of the particle clustering chemistry, and knowledge of the thermochemistry and reactivity of these silicon hydrides is necessary if a mechanistic kinetic model is to be constructed. Experimental measurements of thermochemical properties are usually expensive and difficult, and it is desirable to use computational quantum chemistry as an alternative. In this work, several theoretical methods were used to calculate thermochemical properties of silicon hydrides. Among the methods used, Gaussian-3 theory (G3) using the geometries from B3LYP density functional theory (B3LYP/6-31G(d)), referred to as G3//B3LYP, showed the most promising results with an average absolute deviation of 1.23 kcal/mol from experimental data for standard enthalpies of formation of small (<Si 4 ) silicon hydrides. A series of calculations using G3//B3LYP was carried out on small to medium (<Si 8 ) silicon hydrides to obtain thermochemical properties, and a bond additivity correction was incorporated to obtain more accurate thermochemical properties. A group additivity scheme was fit to these corrected values, allowing accurate estimation of the thermochemical properties of arbitrary silicon-hydrogen clusters. This generalization of the results is essential, since the many thousands of possible isomers of these molecules cannot be treated quantum chemically at even the least expensive levels of theory.

A novel predictive model for formation enthalpies of Si and Ge hydrides with propane‐ and butane‐like structures

“…These enthalpy differences are slightly greater than those found earlier for trisilane and trigermane (25 and 26 kcal/mol, respectively), which are, in turn, even greater than those between disilane and digermane (19 and 20 kcal/mol, respectively). Our values for the heat of formation of Si 4 H 10 can be directly compared with those recently reported by Wong et al 27 who used the G3/B3LYP model. Using a bond-additivity correction scheme, they obtained 37.3 kcal/mol, whereas a homodesmic reaction approach produced estimates between 36.7 and 38.0 kcal/mol for linear and gauche isomers.…”

“…This can be compared with our calculated values of 34.2 and 37.4 kcal/ mol obtained from fit(a) and fit(b), respectively, corroborating that these structures are the most stable structures for most of the foursite compounds. Finally, we note that Wong et al 27 also proposed an atom-based correction to compensate for deficiencies in the G3/B3LYP model, whereas our direct application of the CBS-QB3 and G2 chemistries produced quite reasonable results for the Si hydrides.…”

Kinetics of Substituted Silylene Addition and Elimination in Silicon Nanocluster Growth Captured by Group Additivity

“…Similarly, rate coefficients in the literature [10,76] for silylene addition to monosilane are predicted within a factor of 10 under pyrolysis conditions. In addition, G3//B3LYP was a reasonable choice because the TSGA database is intended to be used in conjunction with an existing G3//B3LYP database developed by our group [52] for the estimation of silicon hydride thermochemical properties.…”

“…An alternative approach for estimating kinetic parameters is transition-state group additivity (TSGA). Inspired by the pioneering group additivity methods developed by Benson for thermochemical property estimation, [51] which have been successfully applied over a wide range of temperatures to silicon hydrides for S, C p , and DH f by Wong et al, [52] Sumathi et al [53][54][55] first applied group additivity to the thermodynamic properties of the transition state for rate coefficient prediction of hydrogen abstraction reactions. Saeys et al [56,57] and Sabbe et al [58] then improved the method for reaction classes governing hydrocarbon chemistry by allowing group additivity to calculate the differences in properties between the transition state and the reactant(s).…”

Review of the potential of silanes as rocket/scramjet fuels

“…E.g., it has been stated above that experimental data on heats of formation of silanes are scarce at best. However, ab initio calculations have been introduced since the 1980s which enable the prediction of thermodynamic data of silanes with high accuracy [72][73][74][75][76][77]. These data are in very good agreement with the experimental data from Gunn and Green, and have therefore been used in the mentioned rocket performance assessments.…”