High rate reactive magnetron sputter deposition of Al-doped ZnO with unipolar pulsing and impedance control system

Al-doped ZnO (AZO) films were deposited on quartz glass substrates, unheated and heated to 200 °C, using reactive sputtering with a special feedback system of discharge impedance combined with midfrequency pulsing. A planar Zn–Al alloy target was connected to the switching unit, which was operated in a unipolar pulse mode. The oxidation of the target surface was precisely controlled by a feedback system for the entire O2 flow ratio including “the transition region.” The deposition rate was about 10–20 times higher than that for films deposited by conventional sputtering using an oxide target. A deposition rate of AZO films of 390 nm/min with a resistivity of 3.8×10−4 Ω cm and a transmittance in the visible region of 85% was obtained when the films were deposited on glass substrates heated to 200 °C with a discharge power of 4 kW.