Investigation of strain and stoichiometry of epitaxial titanium nitride on sapphire

Abstract Titanium nitride (TiN) is a recent material of interest for plasmonics and electrodes due to its high-temperature stability, robustness, and CMOS-compatibility. Previously we found that optical plasmonic quality correlated with the microstructural quality of TiN, and both properties depended on deposition temperature: TiN grown at 550 ˚C resulted in favorable optical properties for plasmonic materials. The present work investigates strain and stoichiometry of TiN films as a result of varying deposition temperature. Six (111)-oriented TiN films were grown on c-sapphire with reactive magnetron sputtering; substrate temperatures ranged from 280 ˚C to 760 ˚C. The TiN films were analyzed with X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy to examine composition, strain, lattice constants, unit cell angles, dislocation defects, mosaicity, and low-angle tilt boundaries. We found that lattice constants only remained a constant 4.242 A at temperatures above 490 ˚C. Above this substrate temperature the deviation from a 90˚ unit cell angle remained at a minimum, indicating less strain. When combined with the previously-found plasmonic material properties of the films, this trend suggests that more relaxed films grow above 490 ˚C and yield lower relative optical loss, and favorable plasmonic material quality factors. Rocking curves suggested fewest dislocation defects and least mosaicity in the optically favorable 550 ˚C film. The results of this work indicate that microstructure, most significantly strain and defects, correlates with optical properties in TiN. This work emphasizes the importance of specific deposition conditions—in this case, substrate temperature—to minimize strain and defect density for achieving optimal plasmonic properties for TiN thin films.