Impact of Annealing Temperature on Atomic Layer Deposited In-Ga-Zn-O Thin-Film Transistors

Oxide semiconductor thin film transistors (TFTs) are promising materials for adoption in display and memory devices due to their large-area uniformity and low off-current characteristics. Because of the scaling down of devices, a uniform deposition technique is required to fabricate devices of high aspect ratio. Atomic layer deposition (ALD) is based on self-limited reaction, which enables conformal coating of high-aspect-ratio substrates. In this study, highly oriented crystalline indium-gallium-zinc oxide (IGZO) thin films and TFTs incorporating such films are fabricated by using plasma-enhanced ALD (PEALD). The postannealing process is conducted at 400-700 degrees C with 100 degrees C intervals. As the annealing temperature increases, the device performances and reliability gradually degrade. High density and highly ordered crystalline IGZO thin films are obtained at high annealing temperature. However, the device characteristics using such films are degraded due to the dramatically reduced hydrogen content in the oxide semiconductor at high annealing temperature. This study shows that highly ordered IGZO thin films can be deposited by ALD. If the process used to fabricate highly ordered IGZO thin films could retain moderate hydrogen content, it would be possible to manufacture oxide TFTs with excellent electrical performances.