Electrical transport, optical properties, and structure of TiN films synthesized by low-energy ion assisted deposition

Abstract

Thin films of TiN, covering a narrow range around stoichiometric composition, were synthesized by low‐energy ion assisted growth at deposition temperatures T_D=100, 300, 500, and 700 °C. The deposition apparatus consisted of an unbalanced dc magnetron sputter source which allowed high rate deposition from a titanium target with simultaneous bombardment of the growing film by a beam of mixed Ar⁺ and N⁺₂ ion species at an ion‐to‐condensing atom arrival rate ratio of five. For each deposition temperature, films were prepared at various ion energies in the range E_i =2–100 eV. The presence of reactive N⁺₂ ions and the effects of ion bombardment facilitate increased incorporation of nitrogen and decrease the overall defect density in the structure of TiN. Electrical transport properties of films were investigated by measurements of the temperature dependence of resistivity ρ(T) in the range T=4–300 K, and superconducting transition temperature T_c. These measurements were complemented by measurement of optical reflectance, x‐ray diffraction, and scanning electron microscopy investigations to determine the structure and composition of films. Collectively the film properties have a strong dependence on ion energy and deposition temperature. Films deposited at optimum conditions (T_D =500 °C and E_i =30–50 eV) possess a high degree of crystalline perfection with a strong (200) texture and a high optical reflectance (82% at λ=800 nm). These properties correlate with the following optimum electrical properties: room‐temperature resistivity ρ₃₀₀∼26 μΩ cm, resistivity ratio RR=2.13, temperature coefficient of resistivity TCR=2.43×10⁻³ K⁻¹, and T_c =5.35 K. These results represent the best results yet reported for microcrystalline TiN films. The temperature dependence of resistivity has a normal‐metal behavior and it obeys Matthiessen’s rule. The phonon contribution to resistivity at room temperature, ρ_thermal, is about 14 μΩ cm and is in agreement with that of single‐crystal TiN. As the disorder in the structure of TiN increases, TCR is found to decrease and zero TCR is predicted for limiting values of resistivity ρ₃₀₀=300–400 μΩ cm.