Epitaxial growth of superconducting TiN films by atomic layer deposition

Abstract

Epitaxial titanium nitride (TiN) thin films are attractive for electronic and superconducting devices, as their structural perfection critically influences electrical transport and interfacial properties. Although epitaxial TiN is commonly grown by physical vapor deposition (PVD) at elevated temperatures, low-temperature atomic layer deposition (ALD) is more compatible with back-end-of-line (BEOL) integration and conformal coating of high-aspect-ratio structures. Here, we demonstrate wafer-scale epitaxial TiN growth on 2-in. α-Al2O3(0001) substrates by plasma-enhanced ALD at 270 °C. The 25 nm-thick film exhibits a single (111) out-of-plane orientation and a TiN(111) rocking-curve full width at half maximum of 0.037° (133.2 arc sec), indicating high epitaxial quality. Electrical transport measurements show a superconducting transition temperature (Tc) of 2.53 K. X-ray photoelectron spectroscopy suggests that oxygen incorporation during ALD produces TiOxNy-related bonding, which likely contributes to the higher resistivity and reduced Tc compared with sputtered TiN. These results establish a low-temperature, BEOL-compatible route for scalable epitaxial TiN films for superconducting and electronic applications.