Early stage growth structure of indium tin oxide thin films deposited by reactive thermal evaporation

The initial stage of indium tin oxide (ITO) thin film growth, deposited by reactive thermal evaporation (RTE), was investigated using atomic force microscopy (AFM) measurements. Five ITO thin films were deposited by RTE of an In:Sn alloy in the presence of added oxygen on heated oxide substrates (Ts=440 K), with film thickness as the deposition variable. Surface imaging as well as statistical analysis were applied to obtain information about the structure of the samples from AFM measurements. In the initial stages of the deposition it was possible to distinguish the presence of individual features randomly distributed with characteristic dimensions of up to 100 nm. Subsequently, the ITO films appeared to grow uniformly as a continuous film deposited over the entire surface. As the ITO films were formed under the low-nucleation barrier regime, which involved small critical nucleus with low positive free energy of formation, the films consisted of many small aggregates. The small minimum stable size of the aggregates and the high nucleation frequency gave rise to a fine-grained film. The grain size of the ITO films increased as the film thickness increased until a maximum value of t=80 nm was reached.