Understanding of indium-gallium-zinc oxide wet etching in acidic solutions: Reaction mechanism, kinetics, and surface properties

• IGZO etching mechanism and reaction kinetics in acidic solutions are proposed. • IGZO etching occurs through protonation, anion attachment, and metal dissolution. • Etching rate is determined by H + concentration, but changed depending on the anion in etchant. • Cl − on IGZO has a strong affinity with IGZO surface with negative polarity, enhancing etching rate. Integrating indium-gallium-zinc oxide (IGZO) as a channel material in transistors requires precise control of the etching process, necessitating a thorough understanding of the mechanism of IGZO etching using various etchants. This study investigated the etching behavior of IGZO in HCl, H 3 PO 4 , H 2 SO 4 , and H 2 C 2 O 4, and a reaction mechanism is proposed. The rate-determining step of the proposed mechanism is identified, and a rate equation for the etching reaction is derived. The etching rate of IGZO in acidic etchants was found to be governed not only by [H + ], but also by anion attachment and detachment reactions, metal dissolution, and the anion concentration near the IGZO surface. The reaction rate constant and order of IGZO etching are interpreted based on the chemical and physical properties of the anions and anion-bonded IGZO surface, including the nucleophilicity of the anions, bonding strength between the anions and the IGZO surface, surface potential induced by the adsorbed anions, ionic radius, and physicochemical properties of the surface-anion complexes. Furthermore, the etching rate critically depends on the local anion concentration adjacent to the IGZO surface rather than the bulk anion concentration. It is influenced by mass transport through the solution. Additionally, differences in etching behavior of the various metal oxide constituents of IGZO increase the surface roughness of the etched sample and result in spatial variations in the surface potential.