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

Abstract

We investigated the carrier generation mechanism in the stacked film of fluorinated silicon nitride $(\hbox{SiN}_{x}\hbox{:F})$ on InGaZnO $(\hbox{IGZO/SiN}_{x}\hbox{:F})$ through post-annealing and compared its mechanism to that of the $\hbox{SiO}_{x}$ stack $(\hbox{IGZO/SiO}_{x})$ . The resistivity $(\rho)$ and carrier concentration $(n)$ of two types of the stacked films through post-annealing were measured by the Hall measurement. The as-deposited $\hbox{n}^{+}$ a-IGZO film with the $\hbox{SiN}_{x}\\hbox{:F}$ stack showed $\rho$ of 3.3 $\times\hbox{ 10} ^{-3}~\Omega\cdot\hbox{cm}$ and $n$ of 1.0 $\times \hbox{ 10} ^{20}~\hbox{cm}^{-3}$ , which was approximately one order of magnitude higher than that with the $\hbox{SiO}_{x}$ stack. X-ray photoelectron spectroscopy (XPS) analyses indicated that ${\rm V}_{\rm O}$ defect was the main source of free electrons in both of the as-deposited $\hbox{IGZO/SiO}_{x}$ and $\hbox{IGZO/SiN}_{x}\hbox{:F}$ stacks. After post-annealing at 300 $^{\circ}\hbox{C}$ , the carrier generation mechanism in the $\hbox{IGZO/SiN}_{x}\hbox{:F}$ stack changed from defects related to ${\rm V}_{\rm O}$ to the fluorine doping. XPS depth profile analyses also revealed that fluorine in IGZO film passivated ${\rm V}_{\rm O}$ and substituted metal–oxygen to thermally stable metal–fluorine (M-F) bonds simultaneously. As a consequence, the thermal stability of $n$ in the $\hbox{IGZO/SiN}_{x}\hbox{:F}$ stack drastically improved, as compared with that in the $\hbox{IGZO/SiO}_{x}$ stack. 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.