Capturing H and H-2 by SiHx+ (x <= 4) ions: Comparison between Langevin and quantum statistical models

Abstract

H, H-2, and SiHx+ (x <= 4) ions coexist under plasma-enhanced chemical vapor deposition (PECVD) conditions. We have studied the kinetics of their interactions by high-level quantum chemical and statistical theory calculations, and compared the results with classical Langevin values (similar to 2 x 10(-9)cm(3) molecule(-1) s(-1) independent of temperature). The results indicate that, for H capturing by SiHx+ (x <= 4), both theories agree within a factor of 2-4, whereas for H-2 capturing by SiHx+ (x <= 3), the modern theory gives higher and weakly temperature-dependent values by up to more than one order of magnitude, attributable to reaction path degeneracies and increased entropies of activation. The heats of formation and structural parameters of SiHx+ ions (x <= 5) in this work agree well with available experimental data. For practical applications, we have provided tables of rate constants for modeling various processes of relevance to the PECVD of a-Si: H films. (C) 2017 The Japan Society of Applied Physics