The Bosch process is a well known process that adds a large degree of directionality to RIE. The 2-step Bosch process process consists of a protection step and an etching step. During the protection step a protective layer is deposited onto and inside the sample, notably on the sidewalls of the nanopores. Consequently, the sidewalls are protected from the subsequent ions and radicals. Moreover, the insulating nature of the protective layer decreases the image force that attracts ions to the sidewalls. During the subsequent etch step, the directional flux of ions removes the protective layer at the bottom of the nanopores and the ions and radicals present in the plasma etch the silicon further leading to a deeper nanopore. After each etch step, an protection step is performed to protect the newly formed silicon walls. This cycling of etch and protection steps results in the distinctive scallops characteristic of the Bosch process. The etching of high aspect ratio structures using the Bosch process is an adjustment between multiple factors. The etching process hinges on getting ions and radicals to the bottom of the pore to continue etching, while maintaining the integrity of the walls by reducing lateral etching. Even with a protective coating there are two factors that cause an undesired widening of the pores, namely the image force and the angular distribution of the incident ions. While the angular distribution of the ions can be controlled by varying the etch parameters, the image force is affected by the nature of the structure to be etched. When the ions are closer to the walls of the structure, the electrostatic image force in stronger, hence going from 1-to 2-to 3-dimensional structures, the effect of the image force increases. Therefore nanopores are more affected by image forces than trenches of the same width, and a narrow 500 nm nanopore is more strongly affected than a wide 10 µm micropore. Moreover, as the ions transverse the nanopore, they lose energy, until they have lost so much energy that they are attracted to the walls, thus the longer the nanopore (or trench) becomes, the more ions will be lost due to collisions with the walls due to the image force.