Resistivity of ALD TiN Thin Films Limited by Oxygen and Carbon Contamination

Titanium nitride (TiN) is a widely used superconducting material for quantum resonators and kinetic-inductance devices, valued for its high kinetic inductance and compatibility with integrated fabrication. We achieve low-resistivity TiN films through atomic layer deposition (ALD), limiting contamination from vacuum integrity issues. Impurities in the film can result in resistivities ranging from 1\,000--2\,000~$\mu\Omega\!\cdot\!\mathrm{cm}$ at 25--30~nm. We examined how oxygen and carbon incorporation under these conditions affect the composition and resistivity of ALD TiN. Films were deposited with varied recipes that adjusted hydrogen gas presence, plasma exposure time (20--50~s), and chamber temperature at 250--300~$^\circ$C. Each film was analyzed by X-ray photoelectron spectroscopy (XPS) depth profiling and four-point resistivity measurements. XPS depth profiles extending to approximately 10~nm reveal a surface layer of adventitious carbon from handling and atmospheric exposure, followed by elevated carbon and oxygen signals that decrease with argon-ion sputtering; carbon falls to nearly zero beyond the surface, while oxygen remains present and does not fall below about four atomic percent. Oxygen impurities are likely forming TiO$_x$ phases that significantly increase resistivity. Carbon contamination disrupts the uniform TiN lattice and may further increase resistivity.