The quality of ultrathin superconducting films is enhanced by ion-energy control during film growth

What is it about?

Atomic layer deposition (ALD) has been a truly enabling method in recent generations of nanoelectronic devices, pushing the limits on feature size, 3D scaling, and device performance. Similarly, ALD is expected to play a key role in realizing large-scale quantum computing, as this area requires major advances in materials and fabrication to come to fruition. Among the main priorities is the growth of high-quality superconducting films, where Ta is garnering much attention due to the record superconducting quantum bit performance achieved with this material. As surface oxidation is a detrimental loss source for quantum devices, the more oxidation-resistant TaCxN1-x holds much promise. Plasma-enhanced ALD (PEALD) uniquely enables preparation of highly-conductive metal-nitride films with atomic level growth control. In addition, tuning material properties through ion-energy control can be achieved by the application of a radiofrequency bias to the substrate. In this article, we demonstrate that ion-energy control in PEALD is not only vital for the growth of highly-conductive, dense material with low impurity contents, but also for achieving superconductivity in ultrathin TaCxN1-x films. By optimizing ion energies, we obtain superconducting TaCxN1-x films with comparatively high critical temperature (Tc) for film thicknesses down to 7 nm.

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Photo by Fractal Hassan on Unsplash

Photo by Fractal Hassan on Unsplash

Why is it important?

This work extends the technique of substrate biasing in PEALD to superconductor applications, producing promising results for future quantum device implementations. Our work helps to tackle the increasingly important challenges with materials and fabrication in quantum technology. Additionally, the findings of this study can be readily applied to other PEALD processes to prepare high-quality superconducting thin films.

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