Anisotropy of Interfacial Bond-Induced Atom Removal Mechanisms of Silicon

Using chemical mechanical polishing (CMP) to flatten the surface of polycrystalline silicon wafers is a crucial step in semiconductor device manufacturing. The pending issue for such a process is the uneven surface removal during CMP of polycrystalline Si wafers. Such a phenomenon leads to the formation of surface microprotrusions on the wafers, while the underlying mechanism is not well understood. This work aims to reveal the mechanisms of anisotropic atomic removal from the perspective of bond formation and breakage by simulating the atomic removal process of crystal silicon by using molecular dynamics simulations. The results indicate that the differences in atomic removal behaviors for various crystal faces of silicon are attributed to their different atomic surface densities and hydrophilicities, which lead to different interfacial bond-forming abilities. However, there is no difference in the abilities to remove the atom by interfacial bonds for these crystal faces. In addition, the removal mechanism of the amorphous structure has also been revealed to represent the grain boundaries. Compared with the (100) crystal face, an amorphous surface has a similar bond formation capability but a higher rate of atomic removal. Such phenomena suggest a lower removal energy barrier for the amorphous face compared with the other three crystal faces, which explains their different atomic removal. In summary, this work unveils the atomic-scale mechanisms behind the uneven removal during the polishing of polycrystalline silicon. This revelation is conducive to the advancement of mechanical chemical polishing technology for polycrystalline silicon.