Density functional theory study on the fluorination reactions of silicon and silicon dioxide surfaces using different fluorine-containing molecules

The authors report the reaction mechanism of the initial fluorination process on the H-terminated Si and the OH-terminated SiO₂ surfaces with HF, CF₄, CHF₃, NF₃, and ClF₃. The reaction process in which a fluorine atom in a gas molecule dissociates Si–OH or Si–H surface group to form Si-F bonds is modeled and simulated by density functional theory calculations using a slab surface model. The physisorption and the chemisorption of all gases on the SiO₂ surface are exothermic. However, the activation energy for chemisorption varies depending on the molecule. HF demonstrates the lowest activation energy of 0.18 eV, while CF₄ has the highest value of 6.32 eV. In the case of the Si surface, the physisorption and the chemisorption of all gases are also exothermic reactions. ClF₃ and NF₃ exhibit near zero activation energies of 0.02 and 0.04 eV, whereas CHF₃ has the highest value of 2.33 eV. Their calculation results explain the mechanism of the vapor phase etching of Si and SiO₂.