Molecular dynamic simulation of orientation-dependent effect on silicon crystalline during sputtering process of focused ion beam

Abstract

In this paper, experiments and molecular dynamic simulation are performed to investigate the crystal orientation-dependent effects in a focused ion beam (FIB) sputtering etching process on silicon crystal planes. The experimental results indicate that different silicon orientation planes have different etched profiles, aspect ratios on microstructures, and sputtering yields under the same process conditions, which brings difficulty in deciding the process parameters for the fabrication of high-resolution nanostructures. Molecular dynamic simulation based on empirical potential is carried out to explain this effect on an atomic scale. The sputtered profiles of different silicon crystal planes after hundreds of impacts by Ga⁺ ions are analyzed. Both the simulation and experimental results show that with the same FIB etching conditions, structures on an Si (111) plane have the maximum opening width and minimum depth. Compared with the etched profile on an Si (100) plane, trenches on Si (110) have a smaller width, but greater depth. The Si (111) plane has the minimum sputtering yield. Furthermore, simulation results on the distribution of Ga⁺ ions remaining inside the substrate, number of ions sputtered out of the surface, and common neighbor analysis (CNA) can explain the orientation-dependent effect during FIB sputtering etching.