Fabrication effects on niobium oxidation and surface contamination in niobium-metal bilayers using x-ray photoelectron spectroscopy

Superconducting resonators and qubits are limited by dielectric losses from surface oxides. Surface oxides are mitigated through various strategies such as the addition of a metal capping layer, surface passivation, and acid processing. In this study, we demonstrate the use of x-ray photoelectron spectroscopy as a rapid characterization tool to study the effectiveness of cap layers for niobium for further device fabrication. We non-destructively evaluate 17 capping layers to characterize their ability to prevent oxygen diffusion and the effects of standard fabrication processes—annealing, resist stripping, and acid cleaning. We downselect for resilient capping layers and test their microwave resonator performance.