Cyclic C ₄ F ₈ and O ₂ plasma etching of TiO ₂ for high-aspect-ratio three-dimensional devices

The present study investigates the cyclic etching of TiO 2 with CF polymer deposition and removal. We find that C 4 F 8 plasma treatment forms a CF polymer deposition layer on the TiO 2 and a modified TiO 2 surface under the CF polymer layer. Subsequent O 2 plasma treatment removes the CF polymer and the modified layer at the same time. This sequence is repeated. Accordingly, the TiO 2 film is etched at a rate of 0.67 nm per cycle. The CF polymer and modified TiO 2 layer also form on the sidewall TiO 2 surface of a trench pattern. We realize the isotropic TiO 2 etching of a trench pattern having a high aspect ratio exceeding 40 adopting the cyclic C 4 F 8 and O 2 plasma process.