In a 3-step process the etch step is split into a boost step and an etch step. In addition to reducing the pressure of the etch step, it is also possible to reduce the pressure of the boost step. The pressure is at a set value for both the boost and etch steps, though as the etch step the throttle is controlled by the machine to maintain a pressure value, changing the SF 6 flow does not change the pressure of the etch step, only the boost step. The boost step is at 100% throttle, meaning that the valve to the vacuum pump is fully open though no pressure value is recorded by the machine. This results in as low as possible pressure at a given SF 6 flow rate, giving a low angular ion distribution and high ion energy. The gas flow of the SF 6 can be reduced and as the pressure control remains at 100% throttle, the pressure is effectively reduced during the boost step. The effects of reducing the SF 6 flow from 65 sccm to 50 sccm are shown in Figure . Reducing the SF 6 gas flow to less than 60 sccm results in incomplete removal of the fluorocarbon during the boost step as seen in Figure . The incomplete removal results in a nanopore diameter smaller than that of the mask and a large amount positive tapering early on in the nanopore, giving the nanopores an undesired funnel-shaped appearance. This is a different result than in the 2-step process, where pore splintering was found (Figures and). This suggests that the 3-step process results in an even removal of fluorocarbon, starting at the center of the nanopore, while the 2-step process gives a random removal across the diameter of the nanopore. There is no significant reduction in the size of the scallops when the SF 6 flow is reduced.