Adsorption of silane radicals governing plasma silicon deposition with dilution gases

Abstract

This study offers novel insights into the reaction energetics, pathways, and surface condition dependencies of adsorption phenomena through comprehensive Density Functional Theory calculations and plasma discharge simulations. We focus on SiH4 plasma discharges and investigate the dissociative reactions of SiH3 and Si2H5 radicals on hydride-terminated Si(001) and Si(111) surfaces, aiming to elucidate the mechanisms underlying Si thin-film deposition. Our findings indicate that SiH3 and Si2H5 radicals exhibit minimal differences in surface reactivity, suggesting that surface reactivity is largely independent of the radical species. This observation is attributed to the protonation reaction occurring on the hydride surface, where hydrogen atoms rearrange and bind to gas molecules. Furthermore, we conducted an analysis of the spatial distribution of plasma parameters in capacitively coupled plasmas (CCP) containing SiH4 mixed with either helium (He) or argon (Ar) using a fluid model. Our results showed that, under fixed process conditions, the electron and radical densities were higher in SiH4/Ar CCP compared to SiH4/He CCP. Consequently, the concentration of Si2H5 radicals in the inter-electrode region was approximately five times higher in SiH4/Ar CCP than in SiH4/He CCP. This high concentration of Si2H5 radicals suggests that their contribution to the deposition process using Ar is comparable to that of SiH3 radicals. This comprehensive analysis not only deepens our understanding of the deposition process but also identifies potential pathways for developing more efficient and controllable silicon deposition techniques.