The influence of substrate temperature and sputtering gas atmosphere on the electrical properties of reactively sputtered indium tin oxide films

Abstract

Tin-doped indium oxide (ITO) films were prepared by d.c. magnetron sputtering of an In-Sn alloy target, and the influence of the sputtering gas atmosphere and substrate temperature on their electrical properties was studied. The conditions for the deposition of the transparent ITO films were divided into three regions by varying the sputtering gas pressure. The first region was characterized by a high efficiency of oxygen gas consumption for film formation and a high deposition rate. In the second region the as-deposited films contained slightly less than the stoichiometric amount of oxygen. The third region was characterized by a low efficiency of oxygen consumption and a low deposition rate. The ratio of the amount of oxygen consumed to the amount of oxygen admitted to the sputtering chamber was about 15% when films with resistivities as low as 6 × 10 -4Ω cm were prepared at the optimum oxygen partial pressure. In the case of metallic deposited in an oxygen-poor atmosphere the carrier mobility, which mainly depends on the crystal structure, increased and the carrier concentration, which depends on the number of oxygen vacancies and donor centres, decreased with increasing substrate temperature. The opposite results were obtained for films deposited in an oxygen-rich atmosphere. Well-defined grain growth was observed, particularly for metallic films deposited at high substrate temperatures, and this caused the low carrier mobility. Subsequent heat treatment improved the resistivity of films deposited at substrate temperatures below 100°C, mainly because of the increase in carrier mobility, but it had little effect on the resistivity of films deposited at substrate temperatures above 150 °C because the increase in carrier mobility was cancelled by the decrease in carrier concentration.