Superconducting NbTiN Thin Films with Highly Uniform Properties over a 100 mm diameter Wafer

TL;DR

This study compares the uniformity of NbTiN superconducting thin films produced by different sputtering systems, demonstrating that substrate shuttling in a large-area system significantly improves film uniformity over a 100 mm wafer.

Contribution

It introduces a novel substrate shuttling technique in large-area sputtering to enhance film uniformity in NbTiN superconducting films.

Findings

Shuttling improves thickness uniformity to +/-2% over 100 mm wafer.

Superconducting critical temperature remains high (15.0-15.3 K) with shuttling.

Resistivity increases when shuttling is used, indicating microstructural changes.

Abstract

Uniformity in thickness and electronic properties of superconducting niobium titanium nitride (NbTiN) thin films is a critical issue for upscaling superconducting electronics, such as microwave kinetic inductance detectors for submillimeter wave astronomy. In this article we make an experimental comparison between the uniformity of NbTiN thin films produced by two DC magnetron sputtering systems with vastly different target sizes: the Nordiko 2000 equipped with a circular 100mm diameter target, and the Evatec LLS801 with a rectangular target of 127 mm x 444.5 mm. In addition to the films deposited staticly in both systems, we have also deposited films in the LLS801 while shuttling the substrate in front of the target, with the aim of further enhancing the uniformity. Among these three setups, the LLS801 system with substrate shuttling has yielded the highest uniformity in film thickness (+/-2%), effective resistivity (decreasing by 5% from center to edge), and superconducting critical temperature (T_c = 15.0 K - 15.3 K) over a 100 mm diameter wafer. However, the shuttling appears to increase the resistivity by almost a factor of 2 compared to static deposition. Surface SEM inspections suggest that the shuttling could have induced a different mode of microstructural film growth.