Atomic layer etching of niobium nitride using sequential exposures of O$_2$ and H$_2$/SF$_6$ plasmas
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| Format: | Preprint |
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2025
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| _version_ | 1866911135297437696 |
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| author | Hossain, Azmain A. Murphy, Sela Catherall, David S. Ardizzi, Anthony J. Minnich, Austin J. |
| author_facet | Hossain, Azmain A. Murphy, Sela Catherall, David S. Ardizzi, Anthony J. Minnich, Austin J. |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2502_17745 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Atomic layer etching of niobium nitride using sequential exposures of O$_2$ and H$_2$/SF$_6$ plasmas Hossain, Azmain A. Murphy, Sela Catherall, David S. Ardizzi, Anthony J. Minnich, Austin J. Materials Science Superconductivity 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. |
| title | Atomic layer etching of niobium nitride using sequential exposures of O$_2$ and H$_2$/SF$_6$ plasmas |
| topic | Materials Science Superconductivity |
| url | https://arxiv.org/abs/2502.17745 |