Impedance control of reactive sputtering process in mid-frequency mode with dual cathodes to deposit Al-doped ZnO films

Aluminum-doped zinc oxide (AZO) films were deposited on glass substrates at 300degreesC by reactive mid-frequency (mf, 50 kHz) magnetron sputtering using dual magnetron cathodes with aluminum-zinc alloy targets. In order to keep the very high deposition rate stable in the transition region of the reactive sputtering system, the reactive gas (O-2) flow was controlled using the "discharge impedance feedback system", where the discharge current value was used to control the O-2 flow. The highest deposition rate for the transparent conductive AZO films achieved by this dual magnetron sputtering (DMS) system was 242 nm/min, which was higher by one order of magnitude than that achieved by the conventional reactive sputtering system. The lowest resistivity of the AZO film obtained by such a high deposition rate was 4.4 x 10(-4) OmegaCM. The structure and electrical properties of the films varied systematically by controlling the discharge current in the transition region using this system.