Stress evolution during growth in direct-current-sputtered zinc oxide films at various oxygen flows

The evolution of stress during the growth of zinc and zinc oxide films deposited from a metallic target using direct-current magnetron sputtering has been analyzed in situ. For this purpose a two-beam wafer curvature setup attached to the sputter chamber was employed. The oxygen flow during the deposition was varied over a wide range to obtain films with stoichiometries between metallic zinc and fully stoichiometric zinc oxide. In good agreement with results from Hinze and Ellmer [J. Appl. Phys. 88, 2443 (2000)] on radio-frequency-sputtered zinc oxide from an oxidic target, the oxidic films analyzed in this work possess high levels of compressive stress. These stresses arise in the early stages of film growth and are constant above a certain film thickness. The level of stress in the films is highly dependent on the deposition pressure, which indicates that the stress originates from bombardment with energetic particles, namely, oxygen ions. In contrast to the oxidic films, metallic zinc films exhibit only very low levels of stress. The stress evolution is similar to that of evaporated high-mobility films and does not change upon variation of deposition pressure. (c) 2005 American Institute of Physics.