Thermochemistry of silicon-hydrogen compounds generalized from quantum chemical calculations

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 (<Si₄) silicon hydrides. A series of calculations using G3//B3LYP was carried out on small to medium (<Si₈) 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.