Topographically-selective Atomic Layer Etching of SiO₂ using fluorine-containing plasma

Atomic scale fidelity is continuously sought-after in the minimization of feature sizes in semiconductor device fabrication and among the advantageous process deemed to achieve this goal is plasma-enhanced atomic layer etching (PE-ALE). In this work, a PE-ALE process of silicon dioxide is described based on the sequential exposure of the substrate to sulfur hexafluoride remote plasma and low-energy argon plasma at relatively low substrate temperature (25°C), where the chemical nature of SiO₂ surface fluorination followed by ion bombardment has been studied. In-situ analyses by ATR-FTIR confirmed the surface bonding modification in the plasma-assisted half-reactions, while ellipsometry data revealed the monolayer linear etch per cycle. Furthermore, the etch profile of trenched pattern confirmed the isotropic etch for the two-step process, as well as the feasibility of an anisotropic etch (top and bottom) surfaces if bias is applied in the second half-reaction. Overall, the study highlights the use of an alternative plasma co-reactant at relatively low temperature conditions in the topo-selective PE-ALE process of silicon dioxide.