Thin film Indium Tin oxide transparent conductors: Comparing the effects of deposition temperature and annealing

Indium Tin-Oxide (ITO) transparent conducting films were prepared by RF magnetron sputtering on glass substrates. The effects of two different heat treatments – annealing and heating the substrate, both at 300 °C and 500 °C – were examined to determine how they affect the microstructure, optical and electrical properties of the films. Despite extensive work on both heat treatment methods in literature, the two have not been compared in a side-by-side study thus far, and this work aims to address this. Heating the substrate during deposition produced lower resistivity films with higher carrier concentrations and higher transmission over visible wavelengths. Microstructural analysis revealed that both heat treatments produced crystalline ITO films, but the preferred crystal orientations were different. Annealing resulted in a preferred cubic (222) orientation, and high substrate temperatures yielded a mixed phase crystal structure (cubic and rhombohedral) with a preferred cubic (211) orientation. Scanning Transmission Electron Microscopy (STEM) analysis showed that sputtering at room temperature with no added heat produced films with a mostly amorphous structure which were converted into equiaxed grains by annealing. High substrate temperatures resulted in a columnar grain structure. These results have useful implications for the deposition of ITO films for various opto-electronic applications.