Optimizing CMOS-compatible, superconducting Titanium Nitride Resonators: Deposition Conditions and Structuring Processes

TL;DR

This paper investigates how deposition and structuring processes affect the superconducting properties and dielectric losses of TiN resonators, achieving low TLS losses and high quality factors suitable for scalable quantum devices.

Contribution

It systematically studies the impact of fabrication parameters on TiN resonator performance and demonstrates a scalable process for low-loss, CMOS-compatible superconducting resonators.

Findings

TiN111 orientation exhibits lowest TLS losses and better reoxidation resistance.

Structuring process has a greater impact on TLS loss than crystal orientation.

Buffered oxide etch (BOE) improves TLS losses by removing interfacial oxides.

Abstract

We report on the fabrication and characterization of superconducting coplanar waveguide (CPW) resonators based on titanium nitride (TiN) thin films deposited on 200\,mm diameter high-resistivity Si(100) substrates. We systematically investigate how deposition conditions, dry-etch power and in-situ resist strip temperature affect morphology, superconducting properties and dielectric losses. By tuning reactive sputtering conditions, three distinct preferred crystal orientations - (111), (200), and mixed are achieved. Our results demonstrate that all films exhibiting similar minimal two-level system (TLS) losses, with TiN111 exhibit the lowest median TLS losses $\tilde{\delta}_\mathrm{TLS}$, and greater robustness against reoxidation. The applied structuring process, in contrast, had a far greater influence on the TLS loss than the crystal orientation of the TiN film and, consequently, the intrinsic material properties of the superconducting layer. The lowest TLS losses for all TiN depositons were achieved with a low power etch and low temperature resist strip. An additional buffered oxide etch (BOE) treatment could remove high-loss interfacial oxides at the metal-air (MA) and substrate-air (SA) interface and recover the etch-induced TLS losses. Consequently, TiN resonators exhibiting $\tilde{\delta}_\mathrm{TLS}$ values as low as $9.67 \times 10^{-7}$ were realized. The corresponding median low-power loss, $\tilde{\delta}_\mathrm{LP}$, amounts to $11.04 \times 10^{-7}$, which translates to an internal quality factor approaching one million. These findings highlight the critical role of process induced oxide formation at the MA and SA interfaces in limiting the performance of TiN resonators and provide a scalable, low-loss process compatible with industry-grade 200 mm CMOS qubit fabrication workflows.