Investigation of Carrier Generation Mechanism in Fluorine-Doped n+-In–Ga–Zn-O for Self-Aligned Thin-Film Transistors

We investigated the carrier generation mechanism in the stacked film of fluorinated silicon nitride (SiNx:F) on InGaZnO (IGZO/SiNx:F) through post-annealing and compared its mechanism to that of the SiOxstack (IGZO/SiOx). The resistivity (ρ) and carrier concentration (n) of two types of the stacked films through post-annealing were measured by the Hall measurement. The as-deposited n+a-IGZO film with the SiNxhbox:F stack showed ρ of 3.3 × 10-3Ω·cm and n of 1.0 × 1020cm-3, which was approximately one order of magnitude higher than that with the SiOxstack. X-ray photoelectron spectroscopy (XPS) analyses indicated that VO defect was the main source of free electrons in both of the as-deposited IGZO/SiOxand IGZO/SiNx:F stacks. After post-annealing at 300 °C, the carrier generation mechanism in the IGZO/SiNx:F stack changed from defects related to VO to the fluorine doping. XPS depth profile analyses also revealed that fluorine in IGZO film passivated VO and substituted metal-oxygen to thermally stable metal-fluorine (M-F) bonds simultaneously. As a consequence, the thermal stability of n in the IGZO/SiNx:F stack drastically improved, as compared with that in the IGZO/SiOxstack. Therefore, we consider that this fluorine doping method in IGZO is suitable for achieving self-aligned thin-film transistors to improve operation speed of system-in-display.