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

Abstract

N ₂ O plasma treatment is widely implemented into the fabrication process of mass-produced amorphous oxide semiconductors for its effectiveness, simplicity, and cost efficiency. However, N ₂ O plasma-treated amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have been reported to exhibit reliability issues due to a nonideal threshold voltage ( ${V}_{\text {th}}{)}$ 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 N ₂ O plasma in the fabrication chamber is immediately suspended after plasma treatment in mass production, the supply of N ₂ O 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 N ₂ O plasma turned off during the postprocesses exhibited nonideal negative ${V}_{\text {th}}$ shifts under PBTS, the devices fabricated with N ₂ O plasma supplied during the postprocesses exhibited superior electrical performance and reliability under bias stress. The defect and physical analyses demonstrate that the nonideal ${V}_{\text {th}}$ 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 N ₂ O plasma during the postprocesses is a straightforward and effective method for ensuring robust a-IGZO TFTs in mass production.