Ab initio analysis of silyl precursor physisorption and hydrogen abstraction during low temperature silicon deposition

Abstract

The energetics of silyl (SiH 3) precursor surface adsorption and hydrogen abstraction on a monohydride terminated silicon surface are described. The abstraction of surface hydrogen by H radicals is more exothermic, and proceeds with a smaller kinetic barrier than H abstraction by silyl. Surface adsorption and abstraction were analyzed using both multi-parent configuration interaction (CI) and several density functional approaches using the Si 4H 10 cluster representing a monohydride terminated silicon (1 1 1) surfaces, and results from the two techniques are critically compared and evaluated. Hydrogen abstraction by H is found to proceed through a kinetic barrier that is between 0 kcal/mol predicted by DFT and 7.2 kcal/mol determined from CI, consistent with experimental values of ∼2 kcal/mol. The barrier height for H abstraction by silyl (without zero point and H tunneling corrections) is determined to be between 4.1 kcal/mol calculated using DFT, and 14.2 kcal/mol determined from the multi-parent CI. These calculations indicate that during typical low temperature silicon deposition processes, H abstraction by impinging hydrogen atoms dominates H abstraction by SiH 3 and plays an important role in creation of surface dangling bonds. None of the Si–H/silyl potential energy surfaces obtained from CI and DFT methods show evidence for stable physisorbed three-center Si–H–(SiH 3) p bond, which is commonly presumed in several models of silicon thin film deposition. We discuss these results in relation to experimental analysis of surface diffusion kinetics in film deposition, and suggest alternate growth models, including H-mediated Si–Si bond breaking and/or direct silyl insertion, to describe activated low temperature silicon-based film deposition.