Temperature effect on the characteristics of DC magnetron sputtered ITO films

Abstract

The effect of both sputtering temperature and post-annealing on the resistivity and the optical transparency of ITO films was investigated. Transparent conductive ITO films were deposited onto glass substrates using dc magnetron sputtering process with Ar pressure of 5 × 10-3torr, power density of 5.5W/cm2 and temperature ranging from 25°C to 240°C, and the ITO films were then annealed at 250°C in vacuum for 5 minutes. It was found that the sheet resistivity of the as-deposited ITO films decreased with temperature and was dominated by carrier mobility for temperature below 120°C and by the carrier concentration for temperature above 120°C. However after annealing, the lowest sheet resistivity of 1.6 × 10-4 Ω-cm/ and the largest extent of sheet resistivity drop, presented in [ρs(as-grown) - ρs(annealed)]/ρs(as-grown) of 78 percent for the ITO film fabricated at 90°C were observed. The optical transmittance of as-deposited ITO films in visible light region was 76 percent and rapidly increased with temperature to up to T percent equals 88 percent at 120°C, thereafter the optical transmittance varied little with the maximum value of 90.2 percent at 200°C. However after annealing, the transmittance decreased for ITO films deposited at temperature above 120°C and increased for those above 120°C with the maximum transmittance of 89.8 percent at 90°C. This was believed due to the large reduction of defect density in ITO films for low temperature processing and to the appearance of the strong preferred orientation of (222) for high temperature deposited ITO films. The figure of merit, both Ft c (T%/ρs) and Φtc (T%10/ρs, was found to perform the best value of 14.8×10-3 Ω-1 and 5.5×10-3 Ω-1 respectively at substrate temperature of 90°C after annealing. The results suggested the optimized sputter temperature for preparing ITO films could be conducted in the moderate temperature range of 90°C rather than in high temperature if the post-annealing was introduced.