Surface Engineering with Monolayer Precision Using Atomic Layeretching—Application to Superconducting Microwave Resonators

Imperfections associated with the surface of a solid are a fundamental limitation to the performance of various technologies such as superconducting resonators used in qubits and single-photon detectors. Although the role of the surface is well known, experimental approaches to mitigate these imperfections are lacking. Here, we report an atomic layer etching/deposition (ALE/ALD) method to remedy the surface imperfections on aluminum (Al) films. Our approach enables the removal of the surface metal oxide (Al₂O₃) and deposition of an ultrathin layer of AlF₃ with monolayer precision. Atomic force microscopy (AFM) analysis reveals a reduction in surface roughness of around 50% compared to the original samples. Characterization of the etched sample using x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and energy-dispersive spectroscopy confirms the removal of alumina and deposition of ultrathin AlF₃ on the Al layer. We characterize the dielectric loss of the resulting film by measuring the quality factor and resonator noise of Al superconducting microwave resonators with the surface treated with the ALE/ALD process. We anticipate that surface engineering using ALE/ALD may be applicable to other technologies that are limited by surface and interface imperfections.