Characterization of the energy flux toward the substrate during magnetron sputter deposition of ZnO thin films

The characterization of energy influxes from plasma to substrate during sputter deposition of ZnO films is presented and discussed. Measurements were carried out in a triple rf magnetron sputter deposition system using calorimetric probes in various Ar/N₂ and Ar/H₂ mixtures at typical substrate positions. By variation of the probe bias the different contributions originating from the kinetic energy of charge carriers, the recombination of charge carriers (electrons and ions) at the surface as well as the contributions from the impact of neutral sputtered particles and subsequent film growth were determined. Radial scans in the substrate plane were recorded to obtain information about inhomogeneities in the total energy influx. The results show that the crystallinity reaches its optimum at that Ar/N₂ ratio where the influence of the bombarding ions reaches its lowest value, indicating the destructive character of ion impact. Radial measurements indicate the influence of the magnetic field on the homogeneity of the energy influx caused by the superposition of the three (balanced) magnetic configurations. The superposition leads to an 'unbalanced character' resulting in a lowering of the electron trapping. The admixture of H₂ leads to a drastic increase in the energy influx due to molecule formation at the (substrate/probe) surface.