Morphological Evolution of ZnO Thin Films Deposited by Reactive Sputtering

The morphological evolution of ZnO thin films deposited by magnetron sputtering has been investigated on two types of substrates, (111) textured Pt and (100) Si possessing a native oxide. The films are oriented c-axis [0001] normal to the substrate and possess varying degrees of crystallinity. Images acquired by field emission scanning electron microscopy (FESEM) show that all the films are dense and relatively smooth. These films have a columnar structure with column diameters in the range of 40 nm to 300 nm. The thin film microstructure is strongly dependent on substrate temperature during deposition in the range of near room temperature up to 700 deg C and also on substrate type as observed by FESEM, TEM, and X-ray diffraction. A textured film of platinum promotes nucleation thereby improving crystallinity and texture of sputtered ZnO films. A mechanism for morphological evolution of the films is proposed based on atom mobilities via surface diffusion.