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.
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