In summary of this subsection, positive taper is often a compromise between the taper, length and pore widening. The 3-step process gives more control over the tapering that the 2-step. Increasing the pressure is also method to eliminate positive tapering, though may affect the integrity of the walls. Negative tapering is rarer in this work, but can result from a too high end pressure or a too short boost step time to etch step time ratio at the end of the etch. Tapering can be controlled by carefully ramping the mentioned parameters to find a balance between length, side wall erosion and tapering. Tapering is the prime example of RIE being a technique of balance and compromise.