Post-annealing effect of low temperature atomic layer deposited Al 2 O 3 on the top gate IGZO TFT.

Electronical properties of top gate amorphous InGaZnO 4 TFTs could be controlled by post-annealing treatment, which has a great impact on the Al 2 O 3 insulator. To investigate the effect of post-annealing on Al 2 O 3 , Al/Al 2 O 3 /p-Si MOS capacitors with Al 2 O 3 films 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 cm 2 V -1 s -1 and the minimum subthreshold swing (SS) about 0.11V/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 exisitence 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 temperature of Al 2 O 3 , but also showed the O and H diffusion from Al 2 O 3 into IGZO during post-annealing process, which led to the deviation of Vth, the change of current density, and the negative V th shift after positive bias stress in TFTs.