<p>Anisotropic high-aspect-ratio silicon oxide etching in the sub-100-nm-diameter domain is a challenge due to lithography and plasma etching difficulties. In this paper, we report oxide-etched holes as narrow as 20&#xa0;nm radius with an aspect ratio of 5 by utilizing electron beam lithography and reactive ion etching with a resist mask and <i>CHF</i>_<i>3</i> and <i>Ar</i> gases. The process parameters were optimized for etching vacant columns in oxide. The results were corroborated through Focused Ion Beam/Scanning Electron Microscope. Moreover, we study the effects of pressure, power, and gas ratios on the etch process. Finally, we present a previously unreported phenomenon in oxide etching in which the resist mask etch rate is dramatically reduced over time under certain process conditions, allowing for controlled etching.</p> Graphical Abstract <p>Fig. (a) Time evolution of resist thickness (T) for a certain process (b) SEM cross section of a sample showing etched oxide</p> <p></p>