Target Surface Temperature Measurements in dc Magnetrons

Abstract

New simple method for direct measurements of target surface temperature during DC magnetron sputtering is developed. Along with temperature measurements we measured also the emissivity of targets. It is demonstrated that the surface temperature of the targets (Cu, Mo, Nb discs) may substantially (up to $\sim 3000\mathrm{C})$ exceed the temperature of the volume of the target. The definition of a “target surface temperature” is given. It is supposed that the thickness of the surface layer that appears on a target subjected to the ion bombardment is equal or close to the penetration depth of ions bombarding the target. The physical model explaining the formation of the surface layer is suggested. The main idea of the model is that the Ar ions bombarding the target may effectively transfer their kinetic energy mostly to the ionic subsystem of a metal rather than to its electron subsystem. Due to very low mobility of metal ions within the layer the thermal conductivity of the layer is substantially lower compared to the rest target volume. As a result the temperature of the layer is higher than that of the rest part of the target.