Electrical Performance and Reliability Enhancement of a-IGZO TFTs via Post-N₂O Plasma Optimization

N2O plasma treatment is widely implemented into the fabrication process of mass-produced amorphous oxide semiconductors for its effectiveness, simplicity, and cost efficiency. However, N2O plasma-treated amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have been reported to exhibit reliability issues due to a nonideal threshold voltage (Vth) shift that occurs under positive bias temperature stress (PBTS). Here, the cause of this abnormal positive bias temperature instability is investigated, and a simple solution applicable to the fabrication process for mass production is proposed. While the supply of N2O plasma in the fabrication chamber is immediately suspended after plasma treatment in mass production, the supply of N2O plasma in the chamber was maintained even during the postprocesses that follow plasma treatment for this study. While plasma-treated a-IGZO TFTs fabricated with the supply of N2O plasma turned off during the postprocesses exhibited nonideal negative Vth shifts under PBTS, the devices fabricated with N2O plasma supplied during the postprocesses exhibited superior electrical performance and reliability under bias stress. The defect and physical analyses demonstrate that the nonideal Vth shift is caused by leakage-current paths generated by the breakage of metal-oxygen bonds and the formation of weak bonds, such as -OH bonds, that occur from plasma damage and bias temperature stress, respectively. This study demonstrates that maintaining the supply of N2O plasma during the postprocesses is a straightforward and effective method for ensuring robust a-IGZO TFTs in mass production.