The effect of O2 on reactively sputtered zinc oxide

Abstract

The rf diode sputtering of a ZnO target using an Ar/O2 gas mixture was studied as a function of the O2 content of the sputtering gas. Films sputtered using gas mixtures containing 0-100% O2 were investigated. Glow discharge spectrometry was used to monitor the ionized species present in the various Ar/O2 plasmas. The crystallographic orientation of the films was found to be highly correlated with the ratio of the number of Zn to ZnO ions in the plasma. The most highly ordered films were obtained when the Zn to ZnO ion ratio was at a minimum which occurred when a 75% Ar/25% O2 gas mixture was used. This result can be explained in terms of the relative degree of oxidation of the ZnO target surface and the number of secondary electrons in the plasma for the various Ar/O2 sputtering gas mixtures.