Orientation dependent etching of silicon by F₂

Orientation dependent etching of silicon by F₂ gas is used for nano-scale texturing of silicon surface during photovoltaic solar cell manufacturing. For modeling of dry etch chemistry we used several methods, such as transition state theory (TST) and classical molecular dynamics (MD). TST under DFT (density functional theory) approach is powerful method for calculation of rate constants for the elementary steps of plasma-surface interaction. This allows insight into the etching mechanism and perform chemical kinetics modeling to predict the etch rate as a function of gas phase etchants fluxes and surface temperature, predict evolution of the structure and composition of the surface during the etching process. We established that F2 dissociative chemisorption is the rate-limiting step in the etching that determines the overall rate of the whole etching process. Here we present simulation results explaining the orientation dependence of silicon surface etching by F₂ molecules using the TST approach. Namely, we show that the Si etching in the (111) direction is much slower than in the (100) and (110) directions; therefore, F₂ can be used for the anisotropic etching process to produce black silicon.