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

摘要

Thin films of TiN, covering a narrow range around stoichiometric composition, were synthesized by lowhyphen;energy ion assisted growth at deposition temperaturesTD=100, 300, 500, and 700thinsp;deg;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+2ion species at an ionhyphen;tohyphen;condensing atom arrival rate ratio of five. For each deposition temperature, films were prepared at various ion energies in the rangeEi=2ndash;100 eV. The presence of reactive N+2ionsand 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 rgr;(T) in the rangeT=4ndash;300 K, and superconducting transition temperatureTc. These measurements were complemented by measurement of optical reflectance, xhyphen;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 (TD=500thinsp;deg;C andEi=30ndash;50 eV) possess a high degree of crystalline perfection with a strong (200) texture and a high optical reflectance (82percnt; at lgr;=800 nm). These properties correlate with the following optimum electrical properties: roomhyphen;temperature resistivity rgr;300sim;26 mgr;OHgr; cm, resistivity ratio RR=2.13, temperature coefficient of resistivity TCR=2.43times;10minus;3Kminus;1, andTc=5.35 K. These results represent the best results yet reported for microcrystalline TiN films. The temperature dependence of resistivity has a normalhyphen;metal behavior and it obeys Matthiessenrsquo;s rule. The phonon contribution to resistivity at room temperature, rgr;thermal, is about 14 mgr;OHgr; cm and is in agreement with that of singlehyphen;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 rgr;300=300ndash;400 mgr;OHgr; cm.