Fabrication effects on Niobium oxidation and surface contamination in Niobium-metal bilayers using X-ray photoelectron spectroscopy

TL;DR

This study uses X-ray photoelectron spectroscopy to evaluate how different fabrication processes and capping layers affect niobium surface oxidation and contamination, impacting superconducting device performance.

Contribution

It introduces a rapid XPS-based method to assess and select effective niobium capping layers and fabrication processes for superconducting devices.

Findings

Identified resilient capping layers that prevent oxygen diffusion.

Evaluated effects of annealing, resist stripping, and acid cleaning on niobium surfaces.

Correlated surface chemistry with microwave resonator performance.

Abstract

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 (XPS) as a rapid characterization tool to study the effectiveness 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.