The formation of high-aspect-ratio trench structures with vertical sidewalls on Si wafers is a key process for preparing advanced MEMS devices, and their anisotropic etching requirements are very strict. The deep silicon etching process is the BOSCH process. During the etching process, the polymer protective layer of the etched part will be completely removed. After removing the bottom protective layer, the silicon material under the protective layer is etched, and the protective layer on the side wall will not be removed due to the directionality of ion etching and the low etching speed. The passivation step is then repeated, resulting in the etching continuing in the vertical direction.