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

Abstract

Controlling the oxygen vacancy (V_O), 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 V_O status, where the deconvoluted O 1s peak with a binding energy (BE) between 531 and 532 eV is considered to represent V_O. However, this work reveals that the In 3d_5/2 peak is a more reliable indicator of the V_O (or carrier) concentration, where a higher In 3d_5/2 peak BE corresponds to a lower V_O concentration and higher TFT threshold voltages. The O 1s peak at 531–532 eV BE did not originate from the oxygen ions near the V_O 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.