Atomic layer etching of niobium nitride using sequential exposures of O$_2$ and H$_2$/SF$_6$ plasmas

Azmain A. Hossain; Sela Murphy; David S. Catherall; Anthony J. Ardizzi; Austin J. Minnich

doi:10.1116/6.0004548

paper

Atomic layer etching of niobium nitride using sequential exposures of O $_{2}$ and H $_{2}$ /SF $_{6}$ plasmas

arXiv:2502.17745 · doi:10.1116/6.0004548

Abstract

Niobium nitride (NbN) is a metallic superconductor that is widely used for superconducting electronics due to its high transition temperature ( $T_{c}$ ) and kinetic inductance. Processing-induced damage negatively affects the performance of these devices by mechanisms such as microwave surface loss. Atomic layer etching (ALE), with its ability to etch with Angstrom-scale control and low damage, has the potential to address these issues, but no ALE process is known for NbN. Here, we report such a process consisting of sequential exposures of O $_{2}$ plasma and H $_{2}$ /SF $_{6}$ plasma. Exposure to O $_{2}$ plasma rather than O $_{2}$ gas yields a greater fraction of Nb in the +5 oxidation state, which is then volatilized by NbF $_{5}$ formation with exposure to an H $_{2}$ /SF $_{6}$ plasma. The SF $_{6}$ :H $_{2}$ flow rate ratio is chosen to produce selective etching of Nb $_{2}$ O $_{5}$ over NbN, enabling self-limiting etching within a cycle. An etch rate of 1.77 Å/cycle was measured at 125 $^{\circ}$ C using ex-situ ellipsometry. The $T_{c}$ of the ALE-etched film is higher than that of an RIE-etched film of a similar thickness, highlighting the low-damage nature of the process. These findings have relevance for applications of NbN in single-photon detectors and superconducting microresonators.

16 pages, 8 figures

Atomic layer etching of niobium nitride using sequential exposures of O2​ and H2​/SF6​ plasmas

Abstract

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Atomic layer etching of niobium nitride using sequential exposures of O $_{2}$ and H $_{2}$ /SF $_{6}$ plasmas