Sidewall Tapering in Reactive Ion Etching

Abstract

This paper reports for the first time the existence of a sidewall tapering phenomenon in reactive ion etching (an oxide process in a commercially available hex‐type system) which is akin to that seen in sputter etching or ion milling. A facet forms in the photoresist mask because of an angular dependence of the resist loss rate. The facet angle is about 16° off vertical, and its downward propagation rate is more than twice the vertical etch rate of the resist. If this facet is allowed to reach the etching material during the course of the etch, it will replicate significantly into this material. When an initially vertical unmasked silicon step is exposed to the same oxide etch process, an identical facet is formed. However, when a bare silicon dioxide step is exposed to the process, no faceting is seen.