Tight-binding quantum chemical molecular dynamics simulations of mechanisms of SiO₂ etching processes for CF₂ and CF₃ radicals

The plasma etching of SiO₂ by CF₂ and CF₃ radicals is investigated by using our etching simulator based on tight-binding quantum chemical molecular dynamics method. During etching simulations, C-F and Si-O bonds dissociate and C-O and Si-F bonds are generated. Moreover, CO, CO₂, COF, and COF₂ molecules form, which is consistent with previous experimental studies. We also examine the dependence of the etching mechanism of CF₂ and CF₃ radicals on the kinetic energy of irradiation. At a low kinetic energy of 10 eV, a CF₂ radical dissociates more Si-O bonds than a CF₃ radical does. This is because the high chemical reactivity of the CF₂ diradical accelerates the etching process. At a high kinetic energy of 150 eV, a CF₃ radical dissociates more Si-O bonds than a CF₂ radical does. This is because a CF₃ radical generates a greater number of reactive F atoms than a CF₂ radical does and thus forms more Si-F bonds. Thus, we conclude that our etching simulator modeled the different SiO₂ etching mechanisms of CF₂ and CF₃ radicals, which arose from the different chemical reactivities of radicals and F atoms at different kinetic energies. This is the first quantum chemistry study to model complicated chemical reactions, which are induced by the attack of many radical species, and clarify the different SiO₂ etching mechanisms for CF₂ and CF₃ radicals.