Decontamination and Passivation of Superconducting Al Resonators with Supercritical NF₃

Surface contamination encountered during microfabrication and packaging of superconducting devices is known to limit qubit performance. Here, a method and system of abating participation of surface contamination on coplanar waveguide resonators using supercritical NF₃ is introduced. Application of NF₃ in its supercritical form, as opposed to a plasma, is explored as a less-invasive means of device processing, mitigating any further artifact formation and extending greater control over the chemical treatment. Previous efforts with supercritical CO₂ have been shown to reduce the spread of measured internal quality factor (Qi) in Al resonators, with Qi greater than 10⁶ at the single photon level. However, subsequent analysis of processed devices has indicated that carbon is a persistent surface adsorbate that would appear to contribute to losses. With this in mind, the oxidizing behavior of supercritical NF₃ is being explored to both scavenge residual carbon, while also fluorinating the underlying native oxide surfaces. Using observations from x-ray photoelectron spectroscopy and helium ion microscopy, ongoing efforts to evaluate and exploit the cleaning potential of NF₃, and subsequent passivation of Al surfaces will be discussed.