Deposition of TCO films by reactive magnetron sputtering from metallic Zn:Al alloy targets

The use of aluminum doped zinc oxide (ZAO) as transparent conductive oxide(TCO) has gained importance with the beginning of Cu(In,Ga)Se2 (CIGS)-based thin-film module production. Commonly these layers are deposited from ceramic ZAO targets. However, a high cost reduction is expected if it is possible to use much less expensive metallic alloy targets. A comparison of the results of applying different reactive sputtering techniques is presented. Plasma emission monitoring (PEM) is needed to control the process. A multichannel PEM system is used to obtain homogeneity over long target lengths. A comparison between sputtering from Zn:Al targets and pure Zn targets aids to understand specifics of the sputtering process. Samples deposited by the different techniques are characterized by resistivity and transmittance measurements. It is shown that ZAO films deposited from metallic targets show comparable properties compared with films deposited from ceramic targets. As a first result of applying this reactive sputtering technique with metallic targets, module efficiencies exceeding 10% could be realized on 30×30 cm2 CIGS modules.