The double-layered Ti/Si barrier metal is demonstrated for the source/drain Cu interconnections in oxide semiconductor thin-film transistors (TFTs). The transmission electromicroscopy and ion mass spectroscopy analyses revealed that the doublelayered barrier structure suppresses the interfacial reaction and the interdiffusion at the interface after thermal annealing at 350 • C. The underlying Si layer was found to be very useful for the etch stopper during wet etching for the Cu/Ti layers. The oxide TFTs with a double-layered Ti/Si barrier metal possess excellent TFT characteristics. It is concluded that the present barrier structure facilitates the back-channel-etch-type TFT process in the mass production line, where the four-or five-mask process is used.

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