The effects of CF4 plasma treatment on the performance, gate bias stability, and defect characteristics of low-temperature indium-gallium-tin-oxide thin-film transistors

Abstract

CF₄ plasma treatment, widely recognized for its use in etching processes, has emerged as an effective doping method for amorphous oxide semiconductor (AOS) based thin-film transistors (TFTs). However, a comprehensive understanding of the effects of CF₄ doping on the performance, reliability, and defect characteristics of AOS-based TFTs remains limited. This study investigates the influence of CF₄ plasma treatment on the electrical characteristics, bias stability, film properties, and defect profiles of amorphous In-Ga-Sn-O (a-IGTO) TFTs under varying treatment durations. As treatment time increases, the threshold voltage (V_th) shifts positively, while the subthreshold swing (SS) decreases. The field-effect mobility (μ_FE) initially increases but declines as treatment duration is extended. Notable improvements in V_th stability were observed under positive bias stress (PBS), negative bias stress (NBS), positive bias thermal stress (PBTS), and negative bias illumination stress (NBIS). Defect and physiochemical analyses reveal that these improvements stem from reduced deep-level oxygen vacancies and near-valence band minimum (VBM) hydrogen/oxygen-related defects. Excessive plasma exposure beyond a critical threshold, however, increases deep-level oxygen vacancies, negatively affecting performance and reliability. These findings provide valuable insights into optimizing doping strategies for developing more reliable, high-performance TFTs for advanced applications.