Etching mechanisms of thin SiO2 exposed to Cl2 plasma

Abstract

Plasma etching is the most standard patterning technology used in micro- and nano-technologies. Chlorine-based plasmas are often used for silicon etching. However, the behavior of thin silicon oxide exposed to such a plasma is still not fully understood. In this paper, we investigate how a thin silicon oxide layer on silicon behaves when it is exposed to a Cl2 plasma. The authors show that chlorine atoms diffuse and/or Cl+ ions are implanted through the thin (<2.5 nm) oxide, leading to the formation of a SiClx interface layer between the two layers of Si and SiO2. Chlorine accumulates at the interface until the SiO2 is thin enough to release volatile SiClx species and the silicon begins to be etched.