In this study, the effect of solvents, HCl and aqua regia at room temperature, on the etching behavior of ITO film was investigated. A higher etching rate was obtained in aqua regia than in HCl. However, via XPS analysis, it was found that there was more surface residual byproduct in aqua regia etchant than in HCl. The surface concentration (ratio of chlorine to indium) was 7.2 and 0.38 in aqua regia and HCl, respectively. It was also observed that the surface residual byproduct reduced the carrier mobility due to the ionized impurity scattering. As seen in the ITO pattern after the etching process, a serious undercut occurred with the aqua regia due to the fast etching rate. Thus, the 9 M HCl solution is more suitable as an etchant for ITO/OLED application. (C) 2003 Elsevier B.V. All rights reserved.