Identifying the Chemical Structure of Indium–Gallium–Zinc Oxide Thin Films with Oxygen Vacancy Variation

Controlling the oxygen vacancy (VO), or more precisely, the local oxygen deficiency, in amorphous oxide semiconductor InGaZnO (IGZO) thin films during device fabrication is crucial because it affects the transfer characteristics and reliability of thin-film transistor (TFT) devices. Measuring the O 1s peak in X-ray photoelectron spectroscopy (XPS) and performing peak deconvolution have been widely used to identify the VO status, where the deconvoluted O 1s peak with a binding energy (BE) between 531 and 532 eV is considered to represent VO. However, this work reveals that the In 3d5/2 peak is a more reliable indicator of the VO (or carrier) concentration, where a higher In 3d5/2 peak BE corresponds to a lower VO concentration and higher TFT threshold voltages. The O 1s peak at 531–532 eV BE did not originate from the oxygen ions near the VO inside the IGZO film but rather from the oxygen atoms in the acetate molecules on the surface. When the IGZO surface was contaminated by OH and CO2 from the air, more acetate was formed, increasing the peak intensity. Moreover, such adsorption was more prevalent in materials exhibiting weak metal–oxygen bonds. Notably, the O 1s peak at 531–532 eV BE disappeared when the acetate on the IGZO film surface was in situ sputter-cleaned in the XPS chamber.