Characterization and in-situ monitoring of sub-stoichiometric adjustable superconducting critical temperature titanium nitride growth

• Published in: Thin solid films Vol. 548; pp. 485 - 488
• Main Authors: Vissers, Michael R., Gao, Jiansong, Kline, Jeffrey S., Sandberg, Martin, Weides, Martin P., Wisbey, David S., Pappas, David P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 02.12.2013; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Deposition by sputtering; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Ellipsometry; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Physics; Sputtering; Sub-stoichiometric; Superconductivity; Superconductors; Theory and models of film growth; Titanium nitride; Transition temperature variations; X-ray diffraction; Titanium nitride; X-ray diffraction; Superconductors; Sputtering; Sub-stoichiometric; Ellipsometry; Transition temperature; Spectroscopic ellipsometry; Electrical properties; Superconducting transitions; Process control; XRD; Thin films; Wafers; Growth mechanism; Physical vapor deposition; Reactive sputtering; Critical temperature
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2013.07.046

The structural and electrical properties of Ti–N films deposited by reactive sputtering depend on their growth parameters, in particular the Ar:N2 gas ratio. We show that the nitrogen percentage changes the crystallographic phase of the film progressively from pure α-Ti, through an α-Ti phase with interstitial nitrogen, to stoichiometric Ti2N, and through a substoichiometric TiNx to stoichiometric TiN. These changes also affect the superconducting transition temperature, TC, allowing, the superconducting properties to be tailored for specific applications. After decreasing from a TC of 0.4K for pure Ti down to below 50mK at the Ti2N point, the TC then increases rapidly up to nearly 5K over a narrow range of nitrogen incorporation. This very sharp increase of TC makes it difficult to control the properties of the film from wafer-to-wafer as well as across a given wafer to within acceptable margins for device fabrication. Here we show that the nitrogen composition and hence the superconductive properties are related to, and can be determined by, spectroscopic ellipsometry. Therefore, this technique may be used for process control and wafer screening prior to investing time in processing devices. Contribution of the U.S. government, not subject to copyright. •Properties of reactively sputtered TiNx are controlled by argon:nitrogen process gas ratio.•The superconducting transition temperature, Tc, is reduced for lower nitrogen content.•Lower nitrogen content corresponds to greater (111) TiN and Ti2N texture.•The optical properties of TiNx are related to these compositional changes.•The position dependence of the optical properties predicts the Tc variation.