Influence of the target composition on the discharge voltage during magnetron sputtering

The discharge voltage measured during magnetron sputtering is inversely proportional with the Ion Induced Electron Emission (ISEE) coefficient of the target material. In this way, it is possible to investigate the influence of the target composition on the ISEE coefficient by measuring the discharge voltage at constant current for targets composed of a mixture of metals and/or oxides. Three different targets were investigated. A special designed Al / Cu target built from Cu and Al parts was used to investigate the generally accepted idea that the ISEE coefficient of a target is a linear composition of the ISEE coefficient of its components. This proposition seems to hold as the inverse of the discharge voltage is indeed linearly dependent on the target composition. Also for the second series of targets, oxygen deficient TiO2 targets, a linear relation between the target composition and the inverse of the discharge voltage was found. However, for a third series of targets, mixtures of Zr and Y, a deviation from this linear behaviour was noticed.