Methods and apparatus for producing high aspect ratio features in a substrate using reactive ion etching (RIE). In some embodiments, a method comprises flowing a gas mixture of C3H2F4 and a companion gas into a process chamber, forming a plasma from the gas mixture using an RF power source connected to an upper electrode above the substrate and at least one RF bias power source connected to a lower electrode under the substrate, performing an anisotropic etch, via the plasma, of at least one layer of oxide or nitride on the substrate using a pattern mask, reducing power of the at least one RF bias power source to produce deposition of a passivation layer on the at least one layer of oxide or nitride on the substrate, and evacuating the process chamber while interrupting the RF power source to stop plasma formation.