We used our etching simulator [H. Ito et al., J. Phys. Chem. C, 2014, 118, 21580–21588] based on tight-binding quantum chemical molecular dynamics (TB-QCMD) to elucidate SiC etching mechanisms. First, the SiC surface is irradiated with SF₅ radicals, which are the dominant etchant species in experiments, with the irradiation energy of 300 eV. After SF₅ radicals bombard the SiC surface, Si–C bonds dissociate, generating Si–F, C–F, Si–S, and C–S bonds. Then, etching products, such as SiS, CS, SiF_x, and CF_x (x = 1–4) molecules, are generated and evaporated. In particular, SiF_x is the main generated species, and Si atoms are more likely to vaporize than C atoms. The remaining C atoms on SiC generate C–C bonds that may decrease the etching rate. Interestingly, far fewer Si–Si bonds than C–C bonds are generated. We also simulated SiC etching with SF₃ radicals. Although the chemical reaction dynamics are similar to etching with SF₅ radicals, the etching rate is lower. Next, to clarify the effect of O atom addition on the etching mechanism, we also simulated SiC etching with SF₅ and O radicals/atoms. After bombardment with SF₅ radicals, Si–C bonds dissociate in a similar way to the etching without O atoms. In addition, O atoms generate many C–O bonds and CO_y (y = 1–2) molecules, inhibiting the generation of C–C bonds. This indicates that O atom addition improves the removal of C atoms from SiC. However, for a high O concentration, many C–C and Si–Si bonds are generated. When the O atoms dissociate the Si–C bonds and generate dangling bonds, the O atoms terminate only one or two dangling bonds. Moreover, at high O concentrations there are fewer S and F atoms to terminate the dangling bonds than at low O concentration. Therefore, few dangling bonds of dissociated Si and C atoms are terminated, and they form many Si–Si and C–C bonds. Furthermore, we propose that the optimal O concentration is 50–60% because both Si and C atoms generate many etching products producing fewer C–C and Si–Si bonds are generated. Finally, we conclude that our TB-QCMD etching simulator is effective for designing the optimal conditions for etching processes in which chemical reactions play a significant role.