In situ measurement of mechanical stress in polycrystalline zinc-oxide thin films prepared by magnetron sputtering

The generation of stress in magnetron-sputtered undoped and aluminum-doped zinc-oxide (ZnO:Al) films has been measured by an in situ technique. Radio- frequency magnetron sputtering from ceramic targets in an argon atmosphere was used for film deposition. The stress was measured by optically detectin g the deflection of a thinned silicon cantilever on which the films were de posited. This in situ stress measurement setup was tested by investigating the sputtering pressure dependence of stress in molybdenum films. For zinc- oxide films it was found that by increasing the argon-sputtering pressure d uring deposition the intrinsic compressive stress decreased by about a fact or of 2, both for undoped and doped zinc-oxide films. The undoped films exh ibit significantly higher compressive stresses (1-2.5 GPa) compared to the aluminum-doped films (0.7-1.5 GPa). This fact was ascribed to a surfactant- like effect of the dopant aluminum, which improved the crystallinity of the doped films. In contrast to magnetron-sputtered metallic films (like molyb denum) the zinc-oxide films did not show a transition from compressive to t ensile stress when the argon-sputtering pressure was increased. It is assum ed that this behavior of the zinc-oxide films is due to an additional incor poration of oxygen into the films. By adjusting the oxygen partial pressure during the deposition at a fixed argon pressure, a minimum of the compress ive stress in ZnO: Al films was found which coincided with a minimum of the film resistivity. This observation stresses the role of even small changes in deposition parameters on the mechanical and electrical properties of zi nc-oxide films. The possibilities of the in situ stress measurement are dem onstrated during the deposition of zinc-oxide multilayers. (C) 2000 America n Institute of Physics. [S0021-8979(00)02318-5].