Fabrication of Nb Films on Sapphire Wafers: Influence of Sputtering Power and Temperature

Various dissipation sources in superconducting circuits such as dielectric loss, radiation, and two-level system hinder the achievement of long lifetime in superconducting qubits.

Recent studies have identified two critical factors that can enhance qubit performance: (1) increasing the residual resistivity ratio (RRR) of niobium films and (2) reducing surface roughness[1], which is influenced by grain size and crystallographic orientation.

These film characteristics are strongly dependent on sputtering power and substrate temperature during the deposition. For instance, increasing the deposition temperature leads to a shift in the crystallographic orientation from the (110) to the (111) plane and correlates with reduced grain boundaries. However, the (110) plane offers lower surface roughness. In this study, we aim to investigate the dependence of RRR and surface roughness on sputtering power and deposition temperature, while maintaining film thicknesses similar to that used in typical 2D resonator fabrication. The goal is to identify the conditions that maximize RRR and minimize surface roughness.

[1] M. Drimmer, S. Telkamp, F. L. Fischer, I. C. Rodrigues, C. Todt, F. Krizek, D. Kriegner, C. Müller, W. Wegscheider and Y. Chu, (2024), pp. arXiv:2403.12164.