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.