Cyclic C4F8 and O2 plasma etching of TiO2 for high-aspect-ratio three-dimensional devices

Abstract

The present study investigates the cyclic etching of TiO2 with CF polymer deposition and removal. We find that C4F8 plasma treatment forms a CF polymer deposition layer on the TiO2 and a modified TiO2 surface under the CF polymer layer. Subsequent O2 plasma treatment removes the CF polymer and the modified layer at the same time. This sequence is repeated. Accordingly, the TiO2 film is etched at a rate of 0.67 nm per cycle. The CF polymer and modified TiO2 layer also form on the sidewall TiO2 surface of a trench pattern. We realize the isotropic TiO2 etching of a trench pattern having a high aspect ratio exceeding 40 adopting the cyclic C4F8 and O2 plasma process.