Aluminum remains the central material for superconducting qubits, and considerable effort has been devoted to optimizing its deposition and patterning for quantum devices. However, postprocessing strategies focused on oxide removal of Nb- and Ta-based resonators using buffered oxide etch (BOE), which cannot be used for aluminum (Al). This challenge becomes particularly relevant for industry-scale fabrication with multichip bonding, where delays between sample preparation and cooldown require surface treatments that preserve low dielectric loss during extended exposure to ambient conditions. In this work, we investigate surface modification approaches for Al resonators subjected to a 24-h delay prior to cryogenic measurement. Passivation using self-limiting oxygen and fluorine chemistries was evaluated utilizing different plasma processes. Remote oxygen plasma treatment reduced dielectric losses, in contrast to direct oxygen plasma. A fluorine-based plasma process was developed that passivated the Al surface for subsequent BOE treatment. However, the fluorine content on the surface resulted in higher loss, identifying fluorine as an unsuitable passivation material for Al resonators. Above all, selective oxide removal using HF vapor and phosphoric acid yielded median dielectric losses as low as ${\tilde{\delta }}_{\mathrm{LP}}=5.7\times {10}^{-7}$ ($Q_{\mathrm{LP}}\approx 1.7\mathrm{M}$) with ${\tilde{\delta }}_{\mathrm{TLS}}=3.6\times {10}^{-7}$ ($Q_{\mathrm{TLS}}\approx 2.8\mathrm{M}$) in the single-photon regime. Selective oxide removal provides a promising pathway for robust Al-based qubit fabrication, as it preserves low dielectric losses for a 24-h delay before cooldown.

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• Optoelectronics
• Quantum information with solid state qubits
• Elemental superconductors
• Superconducting devices
• Surfaces
• Focused ion beam
• Microwave techniques
• Plasma etching