Atomic Layer Etching of Silicon Oxide with CF3I and O2 Plasma

Abstract

Perfluorinated compounds (PFCs) such as CF4, C2F6, C3F8, and C4F8 have been widely used in plasma dry etching and in-situ deposition chamber cleaning processes.[1] More recently, the PFCs have been used in atomic layer etching (ALE), which is considered the promising etching technique that can control the etched thickness in atomic scale levels.[2] However, PFCs generally have a high global warming potential (GWP), which is a significant figure of merit concerned with global warming. CF3I has been studied as a dry etching gas to replace PFCs because of its ultra-low GWP (GWP100=0.3). However, most of the results have been required at high plasma power over 1000 W, which made it difficult to commercialize.[3] Therefore, the feasibility of applying CF3I to ALE processed at low plasma power (400 W or less) is an important factor to replace PFCs. In this study, ALE of SiO2 was performed with CF3I as an etchant gas. In the ALE process, one cycle involved two steps: surface modification and removal steps. In the first step, surface modification, CF3I plasma was treated on the SiO2 surface to deposit fluorocarbon polymer. In the second step, removal step, O2 plasma was used to remove the deposited polymer. When fluorocarbon polymer was removed by O2 plasma, SiO2 film was etched by the byproduct of volatile SiFx generated in the interlayer between fluorocarbon polymer and SiO2. The surface change in the respective modification and removal step was confirmed by X-ray photoelectron spectroscopy (XPS), and the etched thickness of SiO2 film during ALE process was measured by using ellipsometry and transmission electron microscopy (TEM). As a result of SiO2 ALE using CF3I, etched thickness per cycle (EPC) saturation with both CF3I plasma treatment time and O2 plasma treatment time shows that etching was proceeding to atomic scale. When the plasma power is 300 W, the EPC is 0.93 nm/cycle. It means the fast etch rate enough to replace other PFCs at a low power condition.[2] References [1] C. J. Mogab, et. al., J. Appl. Phys. 49, 3796 (1978).[2] D. Metzler, et. al., J. Vac. Sci. Technol. A 32, 020603 (2014).[3] A. Misra, et. al., D. Rufin, Mat. Let. 34 415 (1998).