Optimization of Superconducting Niobium Nitride Thin Films via High-Power Impulse Magnetron Sputtering

TL;DR

This study compares reactive DC and HiPIMS methods for depositing niobium nitride thin films, finding HiPIMS yields higher critical temperatures due to better stoichiometry and crystallinity, with potential enhancements from buffer layers and heating.

Contribution

It provides a systematic comparison of DC and HiPIMS deposition techniques for niobium nitride films, highlighting the advantages of HiPIMS in achieving higher superconducting critical temperatures.

Findings

HiPIMS produces higher critical temperatures than DC sputtering.

Optimal nitrogen concentration is higher in HiPIMS films.

Crystallinity and stoichiometry are improved with HiPIMS.

Abstract

We report a systematic comparison of niobium nitride thin films deposited on oxidized silicon substrates by reactive DC magnetron sputtering and reactive high-power impulse magnetron sputtering (HiPIMS). After determining the nitrogen gas concentration that produces the highest superconducting critical temperature for each process, we characterize the dependence of the critical temperature on film thickness. The optimal nitrogen concentration is higher for HiPIMS than for DC sputtering, and HiPIMS produces higher critical temperatures for all thicknesses studied. We attribute this to the HiPIMS process enabling the films to get closer to optimal stoichiometry before beginning to form a hexagonal crystal phase that reduces the critical temperature, along with the extra kinetic energy in the HiPIMS process improving crystallinity. We also study the ability to increase the critical temperature of the HiPIMS films through the use of an aluminum nitride buffer layer and substrate heating.