Highly oriented ZnO films obtained by d.c. reactive sputtering of a zinc target

Thin ZnO films were grown by d.c. reactive sputtering of a zinc target in conventional diode and magnetron systems in controlled ArO2 gas mixtures. It was found that in the magnetron system the transition from oxidized to unoxidized target is gradual and it is possible to deposit stoichiometric oxide films at an enhanced rate by sputtering a partially oxidized target. The structure of the films was investigated by X-ray diffraction. For the conventional system when the substrates are situated in front of the cathode the degree of texture was found to depend on the oxygen content Q in the gas mixture, being most pronounced for Q < 20%. On substrates situated outside the intense discharge region highly oriented films are obtained for any value of Q. Magnetron-sputtered films prepared at low pressures possess high compressive stresses caused by energetic oxygen bombardment of the substrates. The transition to higher pressures (4–7 Pa) eliminates this adverse effect. By studying the thickness dependence of the film structure it was found that the preferred orientation in ZnO films is determined in the growth process and that there is a transition region at the interface in which the texture evolves. Post-deposition heat treatment anneals out the stresses in the films and enhances the film texture.

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