Effect of heat treatment on electrical properties of amorphous oxide semiconductor In-Ga-Zn-O film as a function of oxygen flow rate

The effect of heat treatment on the electrical properties of an amorphous In-Ga-Zn-O (a-IGZO) film deposited by radio frequency (rf) magnetron sputtering at room temperature (RT) was investigated as a function of the oxygen flow rate. All of the films deposited with increasing O₂ concentration in the Ar and Ar + O₂ atmospheres exhibited insulating behavior in terms of their electrical properties, but their carrier concentration and resistivity were markedly affected after annealing at 400 °C in either a vacuum furnace or an rapid thermal annealing (RTA) system. However, the carrier concentration and resistivity of the films annealed in a normal furnace were not changed, compared with those of the as-deposited films annealed in the vacuum furnace. The difference in the electrical properties as a function of the annealing conditions was attributed to the number of oxygen vacancies. From X-ray photoemission spectroscopy (XPS), we confirmed that the formation of an O-rich surface was reduced by heat treatment under vacuum conditions. The output and transfer characteristics of the thin-film transistors (TFTs) exhibited excellent performance as depletion-mode n-channel field-effect TFTs after being annealed irrespective of the annealing system.