Isotropic Atomic Layer Etching of TiN by Oxidation to TiO₂ and Selective Etching of TiO₂ by SF₆ and H₂ Plasma

We report isotropic plasma atomic layer etching (ALE) of titanium nitride (TiN) using sequential and self-limiting oxidation and etching steps. TiN is oxidized to TiO₂ via exposure to O₂ gas which is subsequently spontaneously etched by exposure to a H₂ and SF₆ plasma. The process exploits the selectivity of spontaneous etching of TiO₂ over TiN with the plasma. A 4:1 ratio of H₂:SF₆ is shown to be highly selective, etching TiO₂ but exhibiting negligible etching of TiN over 50 cycles. TiN ALE was observed at temperatures between 200°C and 300°C, with a maximum etch rate of 0.8 Å/cycle observed at 300°C, measured using ex-situ ellipsometry. After ALE, the etched surface was characterized using X-ray photoelectron spectroscopy and atomic force microscopy. These findings have relevance for applications of TiN in microwave kinetic inductance detectors and superconducting qubits.