Indium tin oxide (ITO): Sputter deposition processes

Abstract

ITO (or tin-doped indium oxide) coatings have excellent electrical conductivity and optical transparency and are therefore used as transparent electrodes in most display products. Such coatings can be deposited either in a purely reactive sputter process from metallic In-Sn alloy targets or from ceramic ITO targets using a quasi-reactive process. The latter technology implemented as DC magnetron sputtering prevails today in the industry. The formation of nodules on the target surface during the sputtering process over time is associated with the fact that indium oxide exists in three allotropic phases. Such nodules are a source of process instability and of coating pinholes. The usage of rotary cathodes is a way to eliminate or at least strongly reduce this problem. Such cathodes also give rise to considerably reduced coating costs, as will be illustrated with applications taken from the LCD and touch panel industries.