Atmosphere Effect in Post-Annealing Treatments for Amorphous InGaZnO Thin-Film Transistors with SiOx Passivation Layers

We investigated the electrical performance and positive bias stress (PBS) stability of the amorphous InGaZnO thin-film transistors (a-IGZO TFTs) with SiOx passivation layers after the post-annealing treatments in different atmospheres (air, N2, O2 and vacuum). Both the chamber atmospheres and the device passivation layers proved important for the post-annealing effects on a-IGZO TFTs. For the heat treatments in O2 or air, the larger threshold voltage (VTH) and off current (IOFF), smaller field-effect mobility (μFE), and slightly better PBS stability of a-IGZO TFTs were obtained. The X-ray photoemission spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) measurement results indicated that the oxygen atoms from the ambience led to less oxygen vacancies (VO) and more oxygen-related defects in a-IGZO after the heat treatments in O2 or air. For the annealing processes in vacuum or N2, the electrical performance of the a-IGZO TFTs showed nearly no change, but their PBS stability evidently improved. After 4500 seconds’ stressing at 40 V, the VTH shift decreased to nearly 1 V. In this situation, the SiOx passivation layers were assumed to effectively prevent the oxygen diffusion, keep the VO concentration unchanged and refuse the oxygen-related defects into the a-IGZO films.