Tight-binding quantum chemical molecular dynamics simulations for the elucidation of chemical reaction dynamics in SiC etching with SF₆/O₂ plasma

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.