Crystallisation of indium-tin-oxide (ITO) thin films

The goal of this study has been to investigate the microstructure changes of ITO films and their effects on the physical properties of the material in the amorphous to crystalline transition. ITO films deposited by electron-beam deposition directly onto substrates held at temperature up to 150 degreesC have an amorphous structure. They were highly absorbing and have poor electrical properties. During the thermal crystallisation process, the resistance decreases, and a simultaneous variation in the optical transmission occurs. In particular, as the film resistivity decreases, the visual appearence of the films change optically from very dark brown to transparent. Correspondingly, microstructure changes from amorphous to microcrystalline, and eventually to polycrystalline. It was found that the electron-beam induced crystallization process observed in the microscope can be defined as an initial gradual ordering, followed by a classical nucleation and growth. Before crystals can develop, 'germ nuclei' must be present in the parent phase. These nuclei act as centres for the crystallisation. Because of experimental spatial-resolution limitations, it is difficult to observed the formation of the initial, stable-crystal nuclei. After crystals have ordered, with dimensions of several unit cells, the crystallisation process progresses from these nuclei. The electron-beam crystallised particles are highly ordered and include both cubic and hexagonal phases of In2O3. (C) 2003 Published by Elsevier Ltd.