The effect of adding fluorine (F) to an organic passivation is investigated in back channel etched (BCE) amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). The organic passivation consists of propylene glycol monomethyl ether acetate (PGMEA), a polyhydroxy styrene (PHS) resin, a silane coupling agent, and the F additive. From thermogravimetric analysis (TGA), F concentration of 1wt% is found to be the optimum formulation of the organic passivation layer. A-IGZO TFTs fabricated with the fluorinated organic passivation exhibited better stability after thermal annealing at 300°C compared to those without the fluorinated organic passivation. X-ray photoelectron spectroscopy (XPS) depth profiling reveals that components of the organic passivation diffuse into the underlying a-IGZO layer such that traces of C1s and Si2p could be detected at the bottom surface of the a-IGZO. Deconvolution of the O1s spectrum also indicated the reduction of oxygen vacancy (VO) defects. It is assumed that F is responsible for the reduction of VO defects, which in turn leads to better thermal stability.