Post-annealing effect of low temperature atomic layer deposited Al₂O₃on the top gate IGZO TFT

Electronical properties of top gate amorphous InGaZnO₄thin film transistors (TFTs) could be controlled by post-annealing treatment, which has a great impact on the Al₂O₃insulator. To investigate the effect of post-annealing on Al₂O₃, Al/Al₂O₃/p-Si MOS capacitoras with Al₂O₃films treated under various post-deposition annealing (PDA) temperature were employed to analysis the change of electrical properties, surface morphology, and chemical components by electrical voltage scanning, atomic force microscope (AFM), and x-ray photoelectron spectroscopy (XPS) technologies. After PDA treatment, the top gate TFTs had a mobility about 7 cm²V^-1s^-1and the minimum subthreshold swing (SS) about 0.11 V/dec, and the threshold voltage (V_th) shifted from positive direction to negative direction as the post-annealing temperature increased. Electrical properties of MOS capacitors revealed the existence of positive fixed charges and the variation of trap state density with increasing PDA temperature, and further explained the change of negative bias stress (NBS) stability in TFT. AFM results clarified the increased leakage current, degraded SS, and NBS stability in MOS capacitors and TFTs, respectively. XPS results not only illuminated the origin of fixed charges and the trap density variation with PDA temperatures of Al₂O₃films, but also showed the O and H diffusion from Al₂O₃into IGZO during post-annealing process, which led to the deviation ofV_th, the change of current density, and the negativeV_thshift after positive bias stress in TFTs.