Ito Hiroshi, Kuwahara Takuya, Kawaguchi Kentaro, Higuchi Yuji, Ozawa Nobuki, Kubo Momoji
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Phys Chem Chem Phys. 2016 Mar 21;18(11):7808-19. doi: 10.1039/c5cp06515a.
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, SiFx, and CFx (x = 1-4) molecules, are generated and evaporated. In particular, SiFx 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 COy (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.
我们使用基于紧束缚量子化学分子动力学（TB-QCMD）的蚀刻模拟器[H. Ito等人，《物理化学杂志C》，2014年，118卷，21580 - 21588页]来阐明碳化硅（SiC）的蚀刻机制。首先，用实验中主要的蚀刻剂物种SF5自由基以300 eV的辐照能量辐照SiC表面。在SF5自由基轰击SiC表面后，Si - C键解离，生成Si - F、C - F、Si - S和C - S键。然后，生成诸如SiS、CS、SiFx和CFx（x = 1 - 4）分子等蚀刻产物并蒸发。特别地，SiFx是主要生成的物种，并且Si原子比C原子更易汽化。SiC上剩余的C原子生成C - C键，这可能会降低蚀刻速率。有趣的是，生成的Si - Si键比C - C键少得多。我们还用SF3自由基模拟了SiC蚀刻。尽管化学反应动力学与用SF5自由基蚀刻相似，但蚀刻速率较低。接下来，为了阐明添加O原子对蚀刻机制的影响，我们还用SF5和O自由基/原子模拟了SiC蚀刻。在用SF5自由基轰击后，Si - C键的解离方式与不添加O原子的蚀刻相似。此外，O原子生成许多C - O键和COy（y = 1 - 2）分子，抑制了C - C键的生成。这表明添加O原子提高了从SiC中去除C原子的效率。然而，对于高O浓度，会生成许多C - C和Si - Si键。当O原子使Si - C键解离并产生悬空键时，O原子仅终止一两个悬空键。而且，在高O浓度下，与低O浓度相比，用于终止悬空键的S和F原子更少。因此，解离的Si和C原子的悬空键很少被终止，它们形成许多Si - Si和C - C键。此外，我们提出最佳O浓度为50 - 60%，因为Si和C原子都生成许多蚀刻产物，生成的C - C和Si - Si键更少。最后，我们得出结论，我们的TB - QCMD蚀刻模拟器对于设计化学反应起重要作用的蚀刻工艺的最佳条件是有效的。
