Fluorine-passivated In₂O₃ thin film transistors with improved electrical performance via low-temperature CF₄/N₂O plasma

In this Letter, we report the electrical performance improvement of indium oxide (In2O3) thin film transistors (TFTs) via a low-temperature CF4/N2O plasma treatment. It is found that the fluorination via CF4/N2O plasma can reduce the excessive electrons in the In2O3 channel more effectively compared to the oxidative annealing, providing the same low off-currents at a lower temperature of 200 °C, while the hydrogenation could not give rise to the off-current reduction. The fluorinated In2O3 TFTs with a channel thickness of 3.5 nm, a HfO2 dielectric thickness of 3.5 nm, and a channel length ranging from 80 nm to 1 μm demonstrate markedly improved electrical performances, including a high field effect mobility of 72.8 cm2/V s, a more positive threshold voltage, a higher on/off current ratio of ∼106, a smaller subthreshold swing below 200 mV/dec, and a higher stability to both negative and positive gate biases. X-ray photoelectron spectroscopy (XPS) confirms the fluorine incorporation in In2O3/HfO2 heterojunction upon CF4/N2O plasma, speculatively passivating the oxygen vacancies and explaining TFT performance enhancement. This study suggests that the anion doping such as fluorine incorporation could be an effective method to improve the performance of oxide semiconductor TFTs with ultrathin channel and dielectric.