Fluorocarbon (C4F8) assisted plasma-enhanced atomic layer etching (PEALE) of SiO2 with high repeatability of cycles in industrial ICP reactor. I. experiment

Deep understanding of plasma-surface interaction processes largely determines the progress of modern plasma technologies in microelectronics. Creating reliable ultrasmall nanometer-level devices requires precise low-damage processes. This paper investigates the implementation of fluorocarbon (C4F8) assisted plasma-enhanced atomic layer etching (PEALE) of SiO2 in an industrial 200 mm reactor. The “classical” approach to PEALE of SiO2 is used: (i) deposition of a reactive CxFy nm layer and (ii) activation of reactions at the “CxFy–SiO2” interface by Ar+ ions. We added step (iii), removal of reaction products and reactor cleaning with oxygen atoms. The PEALE dynamics of SiO2 is observed using an in situ laser ellipsometer and a set of plasma diagnostics. The surface state during all steps of the PEALE cycle is analyzed using ex situ x-ray photoelectron spectroscopy. It is shown that the defects in the upper SiO2 layer can be generated by using the energetic (∼130 eV) ions for activation and cleaning. Activation of the ∼1–1.5 nm CxFy layer by low-energy (∼50 eV) Ar+ ions mainly promotes reactions at the “CxFy–SiO2” interface without introducing defects into the underlying SiO2 layers, while the surface is essentially fluorinated. The low-damage PEALE process can be implemented by synchronously optimizing the CxFy thickness and Ar+ energy to release ion energy into the CxFy layer. The use of an additional step using O atoms from the Ar/O2 plasma to remove reaction products and fluorocarbon residues allows us to carefully reproduce both the SiO2 state and the reactor surface state, providing well-controlled PEALE of SiO2 with high repeatability.